8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

October 31, 2006

Date of Report (Date of earliest event reported)

ANTIGENICS INC.

(Exact name of registrant as specified in its charter)

DELAWARE	000-29089	06-1562417
(State or other jurisdiction of incorporation)	(Commission File Number)	(IRS Employer Identification No.)

630 Fifth Avenue, Suite 2100 New York, NY 10111	10111
(Address of principal executive offices)	(Zip Code)

212-994-8200

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01 Entry into a Material Definitive Agreement

Antigenics Inc. (the “Company”) entered into a Securities Purchase Agreement dated as of October 30, 2006 (the “Purchase Agreement”) with various investors (the “Purchasers”) to issue senior secured convertible notes (the “Notes”) in the aggregate principal amount of $25 million subject to customary closing conditions.

The Notes are convertible at the option of the holders into the Company’s common stock at $3.50 per share. Alternatively, the Notes may be converted into a thirty percent (30%) interest in Antigenics Inc., a Massachusetts corporation (“Antigenics MA”), a wholly owned subsidiary of the Company. Notes arising from accrued interest (see below) would convert into an incremental interest in such subsidiary. The maturity date for the Notes is August 30, 2011, at which point the Company may repay the outstanding balance in cash or in common stock of the Company.

If the Company elects to satisfy the outstanding balance with common shares at maturity, the number of shares issued will be determined by dividing the cash obligation by ninety percent (90%) of the average closing price of the common shares for the twenty (20) trading days preceding the maturity date of the Notes. This right is subject to the market capitalization of the Company exceeding $300 million at such time.

The Notes will bear interest at a rate of 8% per annum, payable in cash or in additional Notes, at the Company’s option. Interest is to be paid semiannually on December 30 and June 30. At any time after October 30, 2009, the Company may call the Notes and accrued interest at face value for cash if its shares have a minimum average trading price during the prior thirty (30) day period of $7.00 or higher. Such redemption shall not be effective until the twentieth (20th) business day following notice from the Company, during which period the Purchasers may exercise their conversion rights. If the Purchasers choose at any time to convert into ownership of Antigenics MA shares, the Company will have thirty (30) days to redeem the Notes, including accrued interest, at a thirty percent (30%) internal rate of return to the Purchasers. Each Purchaser has the option to convert into a combination of equity in Antigenics MA and in the Company. The Notes are secured by the Company’s equity ownership of Antigenics MA.

In no event will the Purchasers be obligated to accept equity that would result in a Purchaser owning in excess of 9.99 percent of the Company’s outstanding common stock at any given time.

The transaction documents include material restrictions on the Company’s incurrence of debt and liens while the Note is outstanding, as well as other customary covenants. The documents also include (i) a change of control put right by the holders of the Note at 101% of the principal amount then outstanding and (ii) and rights of first refusal for holders of the Note.

The foregoing summary of the proposed transaction is subject to, and qualified in its entirety by, the documents attached as Exhibits 4.1 through 4.6, and incorporated herein by reference.

Item 8.01. OTHER EVENTS.

On October 31, 2006, the Company issued a press release announcing the completion of the $25 million financing described in item 1.01.

ITEM 9.01. FINANCIAL STATEMENTS AND EXHIBITS.

(d) Exhibits

4.1 Form of Note under the Securities Purchase Agreement dated as of October 30, 2006 by among Antigenics Inc., a Delaware corporation and the investors listed on the Schedule of Buyers thereto.

4.2 Form of PIK Note under the Securities Purchase Agreement dated as of October 30, 2006 by among Antigenics Inc., a Delaware corporation and the investors listed on the Schedule of Buyers thereto.

4.3 Pledge and Security Agreement dated as of October 30, 2006 by and among Antigenics Inc., a Delaware corporation and Ingalls & Snyder LLC, as Collateral Agent for the Buyers.

4.4 Guaranty dated as of October 30, 2006 by and between Antigenics Inc., a Massachusetts corporation and Ingalls & Snyder LLC, as Collateral Agent for the Buyers.

4.5 Guaranty dated as of October 30, 2006 by and between Aronex Pharmaceuticals, Inc. and Ingalls & Snyder LLC, as Collateral Agent for the Buyers.

4.6 Securities Purchase Agreement dated as of October 30, 2006 by and among Antigenics Inc., a Delaware corporation and the investors listed on the Schedule of Buyers thereto.

99.1 Press Release issued by Antigenics Inc. on October 31, 2006.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	ANTIGENICS INC.
Date: October 31, 2006
	By:	/s/ Garo H. Armen
		Garo H. Armen, Ph.D.
		Chairman and Chief Executive Officer

EX-4.1

Exhibit 4.1

EXHIBIT A

TO SECURITIES PURCHASE AGREEMENT

SENIOR SECURED CONVERTIBLE NOTE

NEITHER THIS NOTE NOR THE SECURITIES INTO WHICH THIS NOTE IS CONVERTIBLE HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF (A) AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND APPLICABLE STATE SECURITIES LAWS, OR (B) THE TRANSFEROR PROVIDES THE COMPANY WITH REASONABLE ASSURANCES AND CUSTOMARY REPRESENTATIONS THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAWS. THIS NOTE IS ISSUED SUBJECT TO THE TERMS OF A SECURITIES PURCHASE AGREEMENT, DATED AS OF OCTOBER 30, 2006 (“SECURITIES PURCHASE AGREEMENT”), BY AND AMONG ANTIGENICS INC. AND THE HOLDER OF THIS NOTE.

ANTIGENICS INC.

SENIOR SECURED CONVERTIBLE NOTE

Issuance Date: October     , 2006 Principal: U.S. $            

FOR VALUE RECEIVED, ANTIGENICS INC., a Delaware corporation (the “Company”), hereby promises to pay to the order of [                                                 ] or its registered assigns (“Holder”) the amount set out above as the Principal (as reduced pursuant to the terms hereof pursuant to redemption, conversion or otherwise, the “Principal”) when due, whether upon the Maturity Date (as defined below), acceleration, redemption or otherwise (in each case, in accordance with the terms hereof) and to pay interest (“Interest”) on any outstanding Principal at the Interest Rate, from the date set out above as the Issuance Date (the “Issuance Date”) until the same becomes due and payable, whether upon an Interest Date (as defined below) or the Maturity Date, acceleration, conversion, redemption or otherwise (in each case in accordance with the terms hereof). This Senior Secured Convertible Note (including all Senior Secured Convertible Notes issued in exchange, transfer or replacement hereof, this “Note”) is one of an issue of Senior Secured Convertible Notes issued pursuant to the Securities Purchase Agreement (as defined below) (collectively, the “Notes” and such other Senior Secured Convertible Notes, the “Other Notes”). Certain capitalized terms used herein are defined in Section 29.

(1) INTEREST; INTEREST RATE. Interest on this Note shall commence accruing on the Issuance Date and shall be computed on the basis of a 360-day year of twelve 30-day months from the actual number of days elapsed and shall be payable in arrears for each Interest Period on the last day of the applicable Interest Period during the period beginning on the Issuance Date and ending, subject to earlier acceleration, redemption or conversion, on, and

including, the Maturity Date (even if the Maturity Date is not the last day of an Interest Period) (each, an “Interest Date”) with the first Interest Date being December 30, 2006. Interest shall be payable on each Interest Date to the record holder of this Note on the applicable Interest Date in cash (“Cash Interest”) or, at the option of the Company may be paid in kind notes in the form of Exhibit B to the Securities Purchase Agreement (“PIK Notes”) or a combination thereof, provided that the Interest which accrued during any period will be payable in PIK Notes unless the Company delivers written notice (each a “Cash Election Notice”) of such election to each holder of the Notes on or prior to the twentieth (20^th) Company Trading Day prior to the Interest Date (each, an “Interest Election Date”). Each Cash Election Notice must specify the amount of Interest that shall be paid as Cash Interest, if any, and the amount of Interest that shall be paid in PIK Notes. If the Company elects to pay in PIK Notes, such PIK Notes shall be issued to the record holder of the Note within twenty (20) days after the Interest Date. Prior to the payment of Interest on an Interest Date, Interest on this Note shall accrue at the Interest Rate and be payable by way of inclusion of the Interest in the Conversion Amount (as defined below) in accordance with Section 2(b)(i).

(2) CONVERSION OF NOTES. This Note shall be convertible into (i) shares of the Company’s common stock, par value $.01 per share (the “Company Common Stock”) or (ii) Antigenics MA Stock, on the terms and conditions set forth in this Section 2.

(a) Conversion Right. Subject to the provisions of Section 2(g), at any time or times on or after the Issuance Date, the Holder shall be entitled to convert any portion of the outstanding and unpaid Conversion Amount in multiples of $10,000 (or, if less, any remaining Conversion Amount) into (i) fully paid and nonassessable shares of Company Common Stock in accordance with Section 2(e), at the Conversion Rate (as defined below) or (ii) Antigenics MA Stock, at the Antigenics MA Conversion Rate (as defined below). The Company shall not issue any fraction of a share of Company Common Stock or Antigenics MA Stock upon any conversion. If the issuance would result in the issuance of a fraction of a share of Company Common Stock or Antigenics MA Stock, the Company shall round such fraction of a share of Company Common Stock or Antigenics MA Stock, respectively, up to the nearest whole share. The Company shall pay any and all taxes that may be payable with respect to the issuance and delivery of Company Common Stock or Antigenics MA Stock upon conversion of any Conversion Amount; provided that the Company shall not be required to pay any tax that may be payable in respect of any transfer involved in the issue and delivery of Company Common Stock or Antigenics MA Stock to any Person other than the Holder or with respect to any income tax due by the Holder with respect to such Company Common Stock or Antigenics MA Stock issued upon conversion.

(b) Company Common Stock Conversion Rate. The number of shares of Company Common Stock issuable upon conversion of any Conversion Amount pursuant to Section 2(a)(i) shall be determined by dividing (x) such Conversion Amount by (y) the Conversion Price (as defined below) (the “Conversion Rate”).

(i) “Conversion Price” means as of any Conversion Date (as defined below) during the period beginning on the Issuance Date and ending on and including the Maturity Date, the Fixed Conversion Price.

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(ii) “Fixed Conversion Price” means $3.50 (also referred to as the “Initial Fixed Conversion Price”), subject to adjustment as provided herein.

(c) Antigenics MA Stock Conversion Rate. The percentage of shares of Antigenics MA Stock issuable upon conversion of any Conversion Amount pursuant to Section 2(a)(ii) (the “Antigenics MA Conversion”) shall be determined by multiplying (x) the quotient of the Conversion Amount divided by $25,000,000 by (y) thirty percent (30%). To convert any Conversion Amount into shares of Antigenics MA Stock on any date (a “Antigenics MA Conversion Date”), the Holder shall give the Company ninety (90) days’ prior written notice (the “Antigenics MA Stock Conversion Notice”) transmitted by facsimile (or otherwise deliver).

(d) Company Buyout Right. Notwithstanding anything in this Section 2 to the contrary, upon receipt of a Antigenics MA Stock Conversion Notice, the Company shall have the right to redeem the Notes subject to the Antigenics MA Stock Conversion Notice (the “Company Buyout Right”) at a price equal to the value of the Conversion Amount plus an amount, when taken together with any Cash Interest payments made prior to the exercise of the Company Buyout Right, that would generate an annual internal rate of return to the Holder of thirty percent (30%) in respect of the Principal. The Company shall have sixty (60) days, following receipt of the Antigenics MA Stock Conversion Notice to give notice of its decision to exercise the Company Buyout Right.

(e) Mechanics of Stock Conversion.

(i) Optional Conversion. To convert any Conversion Amount into shares of Company Common Stock on any date (a “Conversion Date”), the Holder shall (A) transmit by facsimile (or otherwise deliver), for receipt on or prior to 11:59 p.m., New York Time, on such date, a copy of an executed notice of conversion in the form attached hereto as Exhibit I (the “Conversion Notice”) to the Company and (B) if required by Section 2(e)(iii), surrender this Note to a common carrier for delivery to the Company as soon as practicable on or following such date (or an indemnification undertaking with respect to this Note in the case of its loss, theft or destruction). On or before the second (2^nd) Business Day following the date of receipt of a Conversion Notice, the Company shall transmit by facsimile a confirmation of receipt of such Conversion Notice to the Holder and the Transfer Agent (as defined below). On or before the third (3^rd) Business Day following the date of receipt of a Conversion Notice (the “Share Delivery Date”), the Company shall issue and deliver to the address as specified in the Conversion Notice, a certificate, registered in the name of the Holder or its designee, for the number of shares of Company Common Stock to which the Holder shall be entitled. If this Note is physically surrendered for conversion as required by Section 2(e)(iii) and the outstanding Principal of this Note is greater than the Principal portion of the Conversion Amount being converted, then the Company shall as soon as practicable and in no event later than three (3) Business Days after receipt of this Note (the “Note Delivery Date”) and at its own expense, issue and deliver to the holder a new Note (in accordance with Section 17(d)) representing the outstanding Principal not converted. The Person or Persons entitled to receive the shares of Company Common Stock issuable upon a

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conversion of this Note shall be treated for all purposes as the record holder or holders of such shares of Company Common Stock on the Conversion Date to the extent permitted by applicable law.

(ii) Company’s Failure to Timely Convert. If the Company shall fail to issue a certificate to the Holder or credit the Holder’s balance account with Depository Trust Company for the number of shares of Company Common Stock to which the Holder is entitled upon conversion of any Conversion Amount on or prior to the date which is five (5) Business Days after the Conversion Date (a “Conversion Failure”), then (A) the Company shall pay damages in cash to the Holder for each day of such Conversion Failure in an amount equal to 0.25% of the product of (I) the sum of the number of shares of Company Common Stock not issued to the Holder on or prior to the Share Delivery Date and to which the Holder is entitled, and (II) the Closing Sale Price of the Company Common Stock on the Share Delivery Date and (B) the Holder, upon written notice to the Company, may void its Conversion Notice with respect to, and retain or have returned, as the case may be, any portion of this Note that has not been converted pursuant to such Conversion Notice.

(iii) Book-Entry. Notwithstanding anything to the contrary set forth herein, upon conversion of any portion of this Note in accordance with the terms hereof, the Holder shall not be required to physically surrender this Note to the Company unless (A) the full Conversion Amount represented by this Note is being converted or (B) the Holder has provided the Company with prior written notice (which notice may be included in the Conversion Notice or Antigenics MA Stock Conversion Notice) requesting reissuance of this Note upon physical surrender of this Note. The Holder and the Company shall maintain records showing the Principal and Interest converted and the dates of such conversions or shall use such other method, reasonably satisfactory to the Holder and the Company, so as not to require physical surrender of this Note upon conversion.

(iv) Pro Rata Conversion; Disputes. In the event that the Company receives a Conversion Notice from more than one holder of Notes for the same Conversion Date and the Company can convert some, but not all, of such portions of the Notes submitted for conversion, the Company, subject to Section 2(g), shall convert from each holder of Notes electing to have Notes converted on such date a pro rata amount of such holder’s portion of its Notes submitted for conversion based on the principal amount of Notes submitted for conversion on such date by such holder relative to the aggregate principal amount of all Notes submitted for conversion on such date. In the event of a dispute as to the number of shares of Company Common Stock issuable to the Holder in connection with a conversion of this Note, the Company shall issue to the Holder the number of shares of Company Common Stock not in dispute and resolve such dispute in accordance with Section 22.

(f) Payment of Principal at Maturity; Company Election. On the Maturity Date, the Company shall pay to the Holder the sum of the Principal and accrued and unpaid Interest (“Unpaid Principal Amount”) in same day funds; provided, however, that if the

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Company has satisfied the Company Election Conversion Condition (as defined below), the Company may elect to pay such Unpaid Principal Amount by converting such Unpaid Principal Amount into the number of Company Common Stock equal to the amount of such Unpaid Principal Amount divided by the ninety percent (90%) of the Weighted Average Price of Company Common Stock during the prior twenty (20) Company Trading Days preceding the Company Election Date (a “Company Election Conversion”). If a Company Election Conversion occurs, the Company and the Holder shall follow the procedures for Conversion set forth in this Section 2; provided, however, the Holder shall not be required to send the Conversion Notice contemplated by paragraph 2(e)(i) above. The “Company Election Conversion Condition” means that the average equity market capitalization for the Company calculated based on the closing prices for the shares of Company Common Stock during the twenty (20) Company Trading Days preceding the Maturity Date , shall be greater than $300,000,000 on a fully diluted basis.

(g) Limitations on Conversions.

(i) Beneficial Ownership. The Company shall not effect any conversion of this Note, and the Holder of this Note shall not have the right to convert any portion of this Note, pursuant to this Section 2 or otherwise, to the extent that after giving effect to such conversion, the Holder (together with the Holder’s affiliates), would beneficially own in excess of 9.99% (the “Maximum Percentage”) of the number of shares of Company Common Stock outstanding immediately after giving effect to such conversion. For purposes of the foregoing sentence, the number of shares of Company Common Stock beneficially owned by the Holder and its affiliates shall include the number of shares of Company Common Stock issuable upon conversion of this Note with respect to which the determination of such sentence is being made, but shall exclude the number of shares of Company Common Stock which would be issuable upon (A) conversion of the remaining, nonconverted portion of this Note beneficially owned by the Holder or any of its affiliates and (B) exercise or conversion of the unexercised or nonconverted portion of any other securities of the Company (including, without limitation, any Other Notes or warrants) subject to a limitation on conversion or exercise analogous to the limitation contained herein beneficially owned by the Holder or any of its affiliates. Except as set forth in the preceding sentence, for purposes of this Section 2(g)(i), beneficial ownership shall be calculated in accordance with Section 13(d) of the Securities Exchange Act of 1934, as amended (the “1934 Act”). For purposes of this Section 2(g)(i), in determining the number of outstanding shares of Company Common Stock, the Holder may rely on the number of outstanding shares of Company Common Stock as reflected in (x) the Company’s most recent Form 10-Q or Form 10-K, as the case may be, (y) a more recent public announcement by the Company or (z) any other more recent notice from the Company or the Transfer Agent setting forth the number of shares of Company Common Stock outstanding. For any reason at any time, upon the written or oral request of the Holder, the Company shall within three (3) Business Days confirm orally and in writing to the Holder the number of shares of Company Common Stock then outstanding. In any case, the number of outstanding shares of Company Common Stock shall be determined after giving effect to the conversion or exercise of securities of the Company, including this Note, by the Holder or its affiliates since the date as of which such number of outstanding shares of Company Common Stock was reported.

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(ii) Principal Market Regulation. The Company shall not be obligated to issue any shares of Company Common Stock upon conversion of this Note, whether pursuant to this Section 2 or otherwise, if the issuance of such shares of Company Common Stock would exceed the aggregate number of shares of Company Common Stock which the Company may issue upon conversion or exercise of the Notes without breaching the Company’s obligations under the rules or regulations of the Principal Market (the “Exchange Cap”), except that such limitation shall not apply in the event that the Company (A) obtains the approval of its stockholders as required by the applicable rules of the Principal Market for issuances of Company Common Stock in excess of such amount, regardless of whether or not the shares of Company Common Stock are then listed on the applicable market or (B) obtains a written opinion from outside counsel to the Company that such approval is not required, which opinion shall be reasonably satisfactory to the Required Holders. In the event the Company is unable to obtain a written opinion pursuant to Section g(ii)(A), the Company shall use its reasonable best efforts to obtain stockholder approval. Until such approval or written opinion is obtained, no purchaser of the Notes pursuant to the Securities Purchase Agreement (the “Purchasers”) shall be issued in the aggregate, upon conversion of Notes, shares of Company Common Stock in an amount greater than the product of the Exchange Cap multiplied by a fraction, the numerator of which is the principal amount of Notes issued to such Purchaser pursuant to the Securities Purchase Agreement on the Closing Date and the denominator of which is the aggregate principal amount of all Notes issued to the Purchasers pursuant to the Securities Purchase Agreement on the Closing Date (with respect to each Purchaser, the “Exchange Cap Allocation”). In the event that any Purchaser shall sell or otherwise transfer any of such Purchaser’s Notes, the transferee shall be allocated a pro rata portion of such Purchaser’s Exchange Cap Allocation, and the restrictions of the prior sentence shall apply to such transferee with respect to the portion of the Exchange Cap Allocation allocated to such transferee. In the event that any holder of Notes shall convert all of such holder’s Notes into a number of shares of Company Common Stock which, in the aggregate, is less than such holder’s Exchange Cap Allocation, then the difference between such holder’s Exchange Cap Allocation and the number of shares of Company Common Stock actually issued to such holder shall be allocated to the respective Exchange Cap Allocations of the remaining holders of Notes on a pro rata basis in proportion to the aggregate principal amount of the Notes then held by each such holder.

(h) Notwithstanding anything in the above provisions to the contrary, if the Holder exercises any of its rights under the Pledge and Security Agreement in Article 9 of the Uniform Commercial Code then it shall no longer have the right to convert its shares into Antigenics MA Stock.

(3) COMPANY CALL OPTION. After October 30, 2009, the Company shall have the option, at any time when the Weighted Average Price of the Company Common Stock

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during the prior thirty (30) day period is $7.00 (appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction) or higher, to redeem the Note for cash at (100%) of the Conversion Amount, provided that (i) such redemption shall occur on the date that is twenty (20) Company Trading Days (the “Call Date”) following the date of the Company notice and (ii) prior to the Call Date, the provisions in Section 2 shall remain in effect.

(4) RIGHTS UPON EVENT OF DEFAULT.

(a) Event of Default. Each of the following events (so long as its continuing) shall constitute an “Event of Default”:

(i) the Company’s failure to pay to the Holder any amount of Principal or Interest except, in the case of a failure to pay Interest only if such failure continues for a period of at least five (5) Business Days;

(ii) any default under, redemption of or acceleration prior to maturity of any Indebtedness (as defined in the Securities Purchase Agreement) of the Company aggregating in excess of $1,000,000;

(iii) the Company pursuant to or within the meaning of Title 11, U.S. Code, or any similar Federal, foreign or state law for the relief of debtors (collectively, “Bankruptcy Law”), (A) commences a voluntary case, (B) has an involuntary case filed against it and such case is not dismissed within thirty (30) days, (C) consents to the appointment of a receiver, trustee, assignee, liquidator or similar official, or (D) makes a general assignment for the benefit of its creditors;

(iv) a final judgment or judgments for the payment of money aggregating in excess of $1,000,000 are rendered against the Company and which judgment or judgments are not, within sixty (60) days after the entry thereof, bonded, discharged or stayed pending appeal, or are not discharged within sixty (60) days after the expiration of such stay; provided, however, that any judgment which is covered by insurance or an indemnity from a credit worthy party shall not be included in calculating the $1,000,000 amount set forth above;

(v) the Company breaches any representation or warranty in this Note or makes a misleading representation or warranty which results in a material adverse effect on the financial condition of the Company;

(vi) the Company breaches, in any material respect, a covenant or agreement in this Note which remains uncured after notice for a period of at least thirty (30) consecutive days.; or

(vii) the Company ceases to operate.

(b) Redemption Right. Promptly after the occurrence of an Event of Default, the Company shall deliver written notice thereof via facsimile and overnight courier (an “Event of Default Notice”) to the Holder. At any time after the earlier of the Holder’s receipt of an Event of Default Notice and the Holder becoming aware of an Event of Default and prior to 90 days after written notice from the Company to the Holder that such Event of Default is cured (which

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written notice shall provide reasonably satisfactory evidence that such Event of Default has actually been cured), the Holder may require the Company to redeem all or any portion of this Note by delivering written notice thereof (the “Event of Default Redemption Notice”) to the Company, which Event of Default Redemption Notice shall indicate the portion of this Note that the Holder is electing to redeem. Each portion of this Note subject to redemption by the Company pursuant to this Section 4(b) shall be redeemed by the Company at a price equal to the Conversion Amount to be redeemed (the “Event of Default Redemption Price”). Redemptions required by this Section 4(b) shall be made in accordance with the provisions of Section 10.

(5) RIGHTS UPON FUNDAMENTAL TRANSACTION AND CHANGE OF CONTROL.

(a) Assumption. Without limiting any rights of the Holder pursuant to paragraph (b) below, the Company shall not enter into or be party to a Fundamental Transaction unless (i) the Successor Entity assumes in writing all of the obligations of the Company under this Note in accordance with the provisions of this Section 5(a) pursuant to a written agreement prior to such Fundamental Transaction, including an undertaking to deliver to the Holder in exchange for this Note a security of the Successor Entity evidenced by a written instrument substantially similar in form and substance to the Notes, including, without limitation, having a principal amount and interest rate equal to the principal amounts and the interest rate of this Note and (ii) the Successor Entity (including its Parent Entity) is a publicly traded corporation whose common stock is quoted on or listed for trading on an Eligible Market. Upon the occurrence of any Fundamental Transaction, the Successor Entity shall succeed to, and be substituted for (so that from and after the date of such Fundamental Transaction, the provisions of this Note referring to the “Company” shall refer instead to the Successor Entity), and may exercise every right and power of the Company and shall assume all of the obligations of the Company under this Note with the same effect as if such Successor Entity had been named as the Company herein. Upon consummation of the Fundamental Transaction, the Successor Entity shall deliver to the Holder confirmation that there shall be issued upon conversion or redemption of this Note at any time after the consummation of the Fundamental Transaction, in lieu of the shares of the Company Common Stock (or other securities, cash, assets or other property) purchasable upon the conversion or redemption of the Notes prior to such Fundamental Transaction, such shares of stock, securities, cash, assets or any other property whatsoever (including warrants or other purchase or subscription rights) which the Holder would have been entitled to receive upon the happening of such Fundamental Transaction had this Note been converted immediately prior to such Fundamental Transaction, as adjusted in accordance with the provisions of this Note. The provisions of this Section shall apply similarly and equally to successive Fundamental Transactions and shall be applied without regard to any limitations on the conversion or redemption of this Note.

(b) Holder Redemption Right. No sooner than fifteen (15) Business Days nor later than ten (10) Business Days prior to the consummation of a Change of Control, but not prior to the public announcement of such Change of Control, the Company shall deliver written notice thereof via facsimile and overnight courier to the Holder (a “Change of Control Notice”). At any time during the period beginning after the Holder’s receipt of a Change of Control Notice and ending on the date of the consummation of such Change of Control (or, in the event a Change of Control Notice is not delivered at least ten (10) Business Days prior to consummation of such Change of Control, at any time on or after the date which is ten (10) Business Days prior

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to a Change of Control and ending ten (10) Business Days after the consummation of such Change of Control), the Holder may require the Company to redeem all or any portion of this Note by delivering written notice thereof (“Holder Change of Control Redemption Notice”) to the Company, which Holder Change of Control Redemption Notice shall indicate the Conversion Amount the Holder is electing to redeem. The portion of this Note subject to redemption pursuant to this Section 5 shall be redeemed by the Company at a price equal to 101% of the Conversion Amount being redeemed (the “Holder Change of Control Redemption Price”). Redemptions required by this Section 5(b) shall be made in accordance with the provisions of Section 10 and shall have priority to payments to stockholders in connection with a Change of Control. Notwithstanding anything to the contrary in this Section 5(b), but subject to Sections 2(g), until the Holder Change of Control Redemption Price (together with any interest thereon) is paid in full, the Conversion Amount submitted for redemption under this Section 5(b) (together with any interest thereon) may be converted, in whole or in part, by the Holder into Company Common Stock pursuant to Section 2.

(6) RIGHT OF FIRST REFUSAL.

(a) Equity Offering. If the Company sells, at any time up to the Maturity Date, an equity interest in Antigenics MA (“Equity Offering”), the Holder shall have a right of first refusal (which shall be transferable to affiliates of the Holder and to a purchaser of this Note and automatically transferred with this Note while this Note is outstanding) to purchase Holder’s pro rata share (in proportion to the principal amount this Note represents to the aggregate principal amount of all the Notes) of up to 50% of such Equity Offering on the same terms as the third party purchaser, including without limitation any preemptive rights in connection with any subsequent offering or sales. In the event that this Note is redeemed prior to the Maturity Date (the “Redemption Date”), this right of first refusal shall survive for the benefit of the entity holding this Note at the time of redemption until the Maturity Date, and after the Redemption Date, such right shall be assignable, in whole or in part, other than to a competitor of GSK, based on the pro rata ownership of the Notes at the time of redemption; provided, however, that no such transfer shall be effected unless the transferee would have the right to purchase at least 10% of the transferor’s right to participate in such Equity Offering.

(b) Offer. The Company shall deliver to the Holder written notice of an Equity Offering, specifying the price and terms and conditions of a proposed Equity Offering. Unless the Company determines not to consummate such Equity Offering, the Holder shall have a period of ten (10) Business Days from the date of the notice from the Company (the “10-Day Period”) to irrevocable determine whether to exercise this right.

(c) Notice of Acceptance. Holder shall evidence its intention to accept the Offer by delivering a written notice setting forth the equity interest, subject to Section 6(a) above, that it elects to purchase (the “Notice of Acceptance”). The Notice of Acceptance must be delivered to the Company prior to the end of the 10-day Period.

(d) Purchase of Shares. If the Holder tenders its Notice of Acceptance prior to the end of the 10-day Period indicating its intention to purchase its pro rata share of the Equity Offering, the Company shall schedule a closing. Upon the closing of the sale of the Equity Offering to be purchased by the holders, the Holder shall (i) purchase from the Company that portion of the Equity Offering for which it tendered a Notice of Acceptance upon the terms

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specified in the Offer, and (ii) execute and deliver an agreement further restricting transfer of such Equity Offering. The obligation of any Holder to purchase such Equity Offering is further conditioned upon the preparation of a purchase agreement embodying the terms of the Equity Offering, which shall be reasonably satisfactory in form and substance to the participating Holders.

(7) RIGHTS UPON ISSUANCE OF OTHER SECURITIES.

(a) Adjustment of Fixed Conversion Price upon Issuance of Company Common Stock. If and whenever on or after the Issuance Date, the Company issues or sells, or in accordance with this Section 7(a) is deemed to have issued or sold, any shares of Company Common Stock (including the issuance or sale of shares of Company Common Stock owned or held by or for the account of the Company, but excluding shares of Company Common Stock comprising Excluded Securities) for a consideration per share (the “New Issuance Price”) less than $3.00 (the “Applicable Price”) (the foregoing a “Dilutive Issuance”), then immediately after such Dilutive Issuance, the Fixed Conversion Price then in effect shall be reduced to an amount equal to a 16.66% premium to the New Issuance Price. For purposes of determining the adjusted Fixed Conversion Price under this Section 7(a), the following shall be applicable:

(i) Issuance of Options. If the Company in any manner grants or sells any Options and the lowest price per share for which one share of Company Common Stock is issuable upon the exercise of any such Option or upon conversion or exchange or exercise of any Convertible Securities issuable upon exercise of such Option is less than the Applicable Price, then such share of Company Common Stock shall be deemed to be outstanding and to have been issued and sold by the Company at the time of the granting or sale of such Option for such price per share. For purposes of this Section 7(a)(i), the “lowest price per share for which one share of Company Common Stock is issuable upon the exercise of any such Option or upon conversion or exchange or exercise of any Convertible Securities issuable upon exercise of such Option” shall be equal to the sum of the lowest amounts of consideration (if any) received or receivable by the Company with respect to any one share of Company Common Stock upon granting or sale of the Option, upon exercise of the Option and upon conversion or exchange or exercise of any Convertible Security issuable upon exercise of such Option. No further adjustment of the Fixed Conversion Price shall be made upon the actual issuance of such Company Common Stock or of such Convertible Securities upon the exercise of such Options or upon the actual issuance of such Company Common Stock upon conversion or exchange or exercise of such Convertible Securities.

(ii) Issuance of Convertible Securities. If the Company in any manner issues or sells any Convertible Securities and the lowest price per share for which one share of Company Common Stock is issuable upon such conversion or exchange or exercise thereof is less than the Applicable Price, then such share of Company Common Stock shall be deemed to be outstanding and to have been issued and sold by the Company at the time of the issuance of sale of such Convertible Securities for such price per share. For the purposes of this Section 7(a)(ii), the “price per share for which one share of Company Common Stock is issuable upon such conversion or exchange or exercise” shall be equal to the sum of the lowest

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amounts of consideration (if any) received or receivable by the Company with respect to any one share of Company Common Stock upon the issuance or sale of the Convertible Security and upon the conversion or exchange or exercise of such Convertible Security. No further adjustment of the Fixed Conversion Price shall be made upon the actual issuance of such Company Common Stock upon conversion or exchange or exercise of such Convertible Securities, and if any such issue or sale of such Convertible Securities is made upon exercise of any Options for which adjustment of the Fixed Conversion Price had been or are to be made pursuant to other provisions of this Section 7(a), no further adjustment of the Fixed Conversion Price shall be made by reason of such issue or sale.

(iii) Change in Option Price or Rate of Conversion. If the purchase price provided for in any Options, the additional consideration, if any, payable upon the issue, conversion, exchange or exercise of any Convertible Securities, or the rate at which any Convertible Securities are convertible into or exchangeable or exercisable for Company Common Stock changes at any time, the Fixed Conversion Price in effect at the time of such change shall be adjusted to the Fixed Conversion Price which would have been in effect at such time had such Options or Convertible Securities provided for such changed purchase price, additional consideration or changed conversion rate, as the case may be, at the time initially granted, issued or sold. For purposes of this Section 7(a)(iii), if the terms of any Option or Convertible Security that was outstanding as of the Issuance Date are changed in the manner described in the immediately preceding sentence, then such Option or Convertible Security and the Company Common Stock deemed issuable upon exercise, conversion or exchange thereof shall be deemed to have been issued as of the date of such change. No adjustment shall be made if such adjustment would result in an increase of the Fixed Conversion Price then in effect.

(iv) Calculation of Consideration Received. In case any Option is issued in connection with the issue or sale of other securities of the Company, together comprising one integrated transaction in which no specific consideration is allocated to such Options by the parties thereto, the Options will be deemed to have been issued for a consideration of $.01. If any Company Common Stock, Options or Convertible Securities are issued or sold or deemed to have been issued or sold for cash, the consideration received therefor will be deemed to be the net amount received by the Company therefor. If any Company Common Stock, Options or Convertible Securities are issued or sold for a consideration other than cash, the amount of the consideration other than cash received by the Company will be the fair value of such consideration, except where such consideration consists of securities, in which case the amount of consideration received by the Company will be the Closing Sale Price of such securities on the date of receipt. If any Company Common Stock, Options or Convertible Securities are issued to the owners of the non-surviving entity in connection with any merger in which the Company is the surviving entity, the amount of consideration therefor will be deemed to be the fair value of such portion of the net assets and business of the non-surviving entity as is attributable to such Company Common Stock, Options or Convertible Securities, as the case may be.

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The fair value of any consideration other than cash or securities will be determined jointly by the Company and the Required Holders. If such parties are unable to reach agreement within ten (10) Business Days after the occurrence of an event requiring valuation (the “Valuation Event”), the fair value of such consideration will be determined within five (5) Business Days after the tenth (10^th) Business Day following the Valuation Event by an independent, reputable appraiser jointly selected by the Company and the Required Holders. The determination of such appraiser shall be deemed binding upon all parties absent manifest error and the fees and expenses of such appraiser shall be borne by the Company.

(v) Record Date. If the Company takes a record of the holders of Company Common Stock for the purpose of entitling them (A) to receive a dividend or other distribution payable in Company Common Stock, Options or in Convertible Securities or (B) to subscribe for or purchase Company Common Stock, Options or Convertible Securities, then such record date will be deemed to be the date of the issue or sale of the Company Common Stock deemed to have been issued or sold upon the declaration of such dividend or the making of such other distribution or the date of the granting of such right of subscription or purchase, as the case may be.

(b) Adjustment of Fixed Conversion Price upon Subdivision or Combination of Company Common Stock. If the Company at any time on or after the Issuance Date subdivides (by any stock split, stock dividend, recapitalization or otherwise) one or more classes of its outstanding shares of Company Common Stock into a greater number of shares, the Fixed Conversion Price in effect immediately prior to such subdivision will be proportionately reduced. If the Company at any time on or after the Issuance Date combines (by combination, reverse stock split or otherwise) one or more classes of its outstanding shares of Company Common Stock into a smaller number of shares, the Fixed Conversion Price in effect immediately prior to such combination will be proportionately increased.

(c) Other Events. If any event occurs of the type contemplated by the provisions of this Section 7 but not expressly provided for by such provisions (including, without limitation, the granting of stock appreciation rights, phantom stock rights or other rights with equity features), then the Company’s Board of Directors will make an appropriate adjustment in the Fixed Conversion Price so as to protect the rights of the Holder under this Note; provided that no such adjustment will increase the Fixed Conversion Price as otherwise determined pursuant to this Section 7.

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(8) NONCIRCUMVENTION. The Company hereby covenants and agrees that the Company will not, by amendment of its Certificate of Incorporation, Bylaws or through any reorganization, transfer of assets, consolidation, merger, scheme of arrangement, dissolution, issue or sale of securities, or any other voluntary action, avoid or seek to avoid the observance or performance of any of the terms of this Note, and will at all times in good faith carry out all of the provisions of this Note and take all action as may be required to protect the rights of the Holder of this Note.

(9) RESERVATION OF AUTHORIZED SHARES.

(a) Reservation. The Company shall initially reserve out of its authorized and unissued Company Common Stock a number of shares of Company Common Stock for each of the Notes equal to the number of shares of Company Common Stock as shall be necessary to effect the conversion of all of the Notes. So long as any of the Notes are outstanding, the Company shall take all action necessary to reserve and keep available out of its authorized and unissued Company Common Stock, solely for the purpose of effecting the conversion of the Notes, the number of shares of Company Common Stock as shall from time to time be necessary to effect the conversion of all of the Notes then outstanding at the Company Conversion Price (the “Required Reserve Amount”). The initial number of shares of Company Common Stock reserved for conversions of the Notes and each increase in the number of shares so reserved shall be allocated pro rata among the holders of the Notes based on the principal amount of the Notes held by each holder at the Closing (as defined in the Securities Purchase Agreement) or increase in the number of reserved shares, as the case may be (the “Authorized Share Allocation”). In the event that a holder shall sell or otherwise transfer any of such holder’s Notes, each transferee shall be allocated a pro rata portion of such holder’s Authorized Share Allocation. Any shares of Company Common Stock reserved and allocated to any Person which ceases to hold any Notes shall be allocated to the remaining holders of Notes, pro rata based on the principal amount of the Notes then held by such holders.

(b) Insufficient Authorized Shares. If at any time while any of the Notes remain outstanding the Company does not have a sufficient number of authorized and unreserved shares of Company Common Stock to satisfy its obligation to reserve for issuance upon conversion of the Notes at least a number of shares of Company Common Stock equal to the Required Reserve Amount (an “Authorized Share Failure”), then the Company shall use its reasonable best efforts to immediately take all action necessary to increase the Company’s authorized shares of Company Common Stock to an amount sufficient to allow the Company to reserve the Required Reserve Amount for the Notes then outstanding. Without limiting the generality of the foregoing sentence, as soon as practicable after the date of the occurrence of an Authorized Share Failure, but in no event later than ninety (90) days after the occurrence of such Authorized Share Failure, the Company shall hold a meeting of its stockholders for the approval of an increase in the number of authorized shares of Company Common Stock (the earlier of the date of such meeting and such ninetieth day, the “Authorized Share Failure Stockholder Meeting Deadline”).

(10) HOLDER’S REDEMPTIONS.

(a) Mechanics. The Company shall deliver the applicable Event of Default Redemption Price to the Holder within five (5) Business Days after the Company’s receipt of the Holder’s valid Event of Default Redemption Notice. If the Holder has submitted a Holder

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Change of Control Redemption Notice in accordance with Section 5(b), the Company shall deliver the Holder Change of Control Redemption Price to the Holder, concurrently with the consummation of such Change of Control if such notice is received by the Company prior to the consummation of such Change of Control and within five (5) Business Days after the Company’s receipt of such notice otherwise. In the event of a redemption of less than all of the Conversion Amount of this Note, the Company shall promptly cause to be issued and delivered to the Holder (after such original Note has been delivered to the Company) a new Note (in accordance with Section 17(d)) representing the outstanding Principal which has not been redeemed. In the event that the Company does not pay the applicable Redemption Price to the Holder within the time period required, at any time thereafter and until the Company pays such unpaid Redemption Price in full, the Holder shall have the option, in lieu of redemption, to require the Company to promptly return to the Holder all or any portion of this Note representing the Conversion Amount that was submitted for redemption and for which the applicable Redemption Price has not been paid. Upon the Company’s receipt of such notice, (x) the Redemption Notice shall be null and void with respect to such Conversion Amount and (y) the Company shall immediately return this Note, or issue a new Note (in accordance with Section 17(d)) to the Holder representing such Conversion Amount.

(b) Redemption by Other Holders. Upon the Company’s receipt of notice from any of the holders of the Other Notes for redemption or repayment as a result of an event or occurrence substantially similar to the events or occurrences described in Section 4(b) or Section 5(b) (each, an “Other Redemption Notice”), the Company shall immediately forward to the Holder by facsimile a copy of such notice. If the Company receives a Redemption Notice and one or more Other Redemption Notices during the seven (7) Business Day period beginning on and including the date which is three (3) Business Days prior to the Company’s receipt of the Holder’s Redemption Notice and ending on and including the date which is three (3) Business Days after the Company’s receipt of the Holder’s Redemption Notice and the Company is unable to redeem all principal, interest and other amounts designated in such Redemption Notice and such Other Redemption Notices received during such seven (7) Business Day period, then the Company shall redeem a pro rata amount from each holder of the Notes (including the Holder) based on the principal amount of the Notes submitted for redemption pursuant to such Redemption Notice and such Other Redemption Notices received by the Company during such seven Business Day period.

(11) RESTRICTION ON REDEMPTION AND CASH DIVIDENDS. Other than (x) in connection with employee stock repurchases pursuant to an Approved Stock Plan existing as of the date hereof and (y) cash payments in lieu of fractional shares of Company Common Stock, until all of the Notes have been converted, redeemed or otherwise satisfied in accordance with their terms, the Company shall not, directly or indirectly, redeem, repurchase or declare or pay any cash dividend or distribution on shares of Company Common Stock without the prior express written consent of the holders of Notes representing at least a majority of the aggregate principal amount of the Notes then outstanding.

(12) RIGHTS. Except as otherwise provided for herein, the Holder shall have no rights as a holder of Company Common Stock as a result of being a holder of this Note, except as required by law, including, but not limited to, the General Corporation Law of the State of Delaware, and as expressly provided in this Note.

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(13) AFFIRMATIVE COVENANTS.

(a) Corporate Existence. The Company shall, and shall cause Antigenics MA to, so long as any holder of the Notes or any affiliate of such holder beneficially owns a Note or Notes (or any interest therein), maintain its corporate existence in good standing and pay its taxes when due except for disputed taxes which could not reasonably be expected to have a Material Adverse Effect on its consolidated business or financial condition. The Company shall notify the Holder of any change of name, jurisdiction of incorporation, principal place of business or any similar change with respect to the Company or Antigenics MA.

(b) Maintenance of Properties. The Company shall, and shall cause Antigenics MA to, (i) keep its properties in such repair, working order and condition, and shall from time to time make such repairs, replacements, additions and improvements thereto, as are necessary for the efficient operation of its business and (ii) take all reasonable actions to possess and maintain all Intellectual Property Rights (as defined in the Securities Purchase Agreement) material to the conduct of their respective business and all right, title and interest in and to (subject to Permitted Liens), or have a valid license for, all such Intellectual Property Rights.

(c) Compliance with Material Agreements. The Company shall, and shall cause Antigenics MA to comply with all material agreements to which it is a party.

(d) Financial Statements. To the extent not available electronically with the SEC, the Company shall deliver to the Holder on a consolidated basis (including any Subsidiaries) (i) as soon as practicable, but no later than 120 days following the end of each fiscal year, annual audited financial statements (including balance sheets, income statements and statements of cash flow) of the Company and its consolidated Subsidiaries on a consolidated basis; and (ii) commencing with the third fiscal quarter of 2006, as soon as practicable, but no later than 45 days following the end of each fiscal quarter, quarterly unaudited financial statements (including balance sheets, income statements, statements of cash flow and store profitability figures) of the Company and its consolidated Subsidiaries on a consolidated basis. In addition, if at any time Antigenics MA is not a wholly owned subsidiary of the Company, then the Company shall cause Antigenics MA to deliver to the Holder audited financial statements (including balance sheets, income statements and statements of cash flow). All such financial statements shall be prepared in accordance with the GAAP, applied on a consistent basis.

(e) Other Reports. To the extent not available electronically with the SEC or on the Company’s website, the Company shall promptly furnish to the Holder all press releases, budgets, statements of operations and other documents or reports furnished to stockholders of the Company and, if applicable, Antigenics MA.

(f) Insurance. The Company shall, and shall cause Antigenics MA to, be insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as management of the Company believes to be prudent and customary in the businesses in which the Company is engaged.

(g) Payment of Taxes and Claims. The Company shall, and shall cause Antigenics MA to, to pay and discharge when due all obligations and liabilities, including tax liabilities, except for disputed obligations and/or liabilities, including taxes, which could not reasonably be expected to have a Material Adverse Effect on its consolidated business or financial condition.

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(h) Access to Company and Employees. The Company shall, and shall cause Antigenics MA to, permit representatives of the Holder to visit and inspect any of its respective properties and to discuss its affairs, finances and accounts with its respective officers, employees and independent public accounts as often as may reasonably be desired, but in no event more than twice in any fiscal year.

(i) Notices of Litigation, Defaults, etc. The Company shall, and shall cause Antigenics MA to, promptly furnish to the Holder notice of (i) any material litigation or any administrative or arbitration proceeding in an aggregate amount in excess of $200,000, (ii) any labor dispute or other work stoppage, and (iii) any default or breach of Environmental Laws (as defined in the Securities Purchase Agreement).

(j) Environmental Law. The Company shall and shall cause Antigenics MA to comply with all Environmental Laws other than violations which will not result in a Material Adverse Effect on the financial condition of the Company.

(k) Intellectual Property. The Company shall, or shall cause Antigenics MA, to at all times own all right, title and interest in all Intellectual Property Rights, which the Company or Antigencis MA own as of the Issuance Date, relating to QS-21 and AG-707. Notwithstanding anything in this Section 14(k) to the contrary, the Company may consummate a Spin-off (as such term is defined the Pledge and Security Agreement), enter into partnership, license and collaboration agreements and other similar arrangements.

(14) NEGATIVE COVENANTS.

Except as disclosed on Company filings with the SEC prior to the date hereof:

(a) Incurrence of Indebtedness. So long as this Note is outstanding, the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, incur or guarantee, assume or suffer to exist any Indebtedness (as defined in Section 3(r) of the Securities Purchase Agreement), other than (i) the Indebtedness evidenced by this Note and the Other Notes and (ii) Permitted Indebtedness.

(b) Existence of Liens. So long as this Note is outstanding, the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, allow or suffer to exist any mortgage, lien, pledge, charge, security interest or other similar encumbrance in an aggregate amount in excess of $5,000,000, upon or in any property or assets (including accounts and contract rights) owned by the Company or Antigenics MA (collectively “Liens”), other than (i) pursuant to the Pledge and Security Agreement and (ii) Permitted Liens.

(c) Restricted Payments. Except as set forth on Schedule 14(c), the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, redeem, defease, repurchase, repay or make any payments in respect of, by the payment of cash or cash equivalents (in whole or in part, whether by way of open market purchases, tender offers, private transactions or otherwise), all or any portion of any Permitted Indebtedness whether by way of payment in respect of principal of (or premium, if any) or interest on such Indebtedness if at the

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time such payment is due or is otherwise made or, after giving effect to such payment, an event constituting, or that with the passage of time and without being cured would constitute, an Event of Default has occurred and is continuing.

(d) Investment, Loan and Advances. Except as listed on Schedule 14(d), the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, lend money or credit (by way of guarantee or otherwise) or make advances to any Person, or purchase or acquire stock, bonds, debentures or other obligations or securities of, or any other interest in, or make any capital contribution to, any other Person (collectively “Investments”) other than Permitted Investments.

(e) Mergers, Asset Dispositions and Acquisitions. The Company shall not, and shall not permit Antigenics MA to, merge or consolidate with any other Person or acquire (in any way whatsoever, in one or a series of transactions) shares or assets of any other Person, or sell all or otherwise dispose of any of its shares or assets or the shares or assets of any of its Subsidiaries, or acquire (in any way whatsoever, in one or a series of transactions) any of the shares or assets of a Person, business or line of business, unless (a) the Company is the surviving entity in such merger, consolidation, transfer, sale or acquisition, or (b) the Person acquiring the shares or assets of the Company or its Subsidiaries shall be solvent (both before and after giving effect to such transaction) and shall have executed and delivered to the Holder an assumption of the due and punctual performance and observance of each covenant and agreement of the Company under the Transaction Documents.

(f) Related Party Transactions. Except in the ordinary course of business, the Company shall not, and shall not permit Antigenics MA to, enter into transactions of the type discussed under Item 404(a) of Regulation S-X (including with respect to monetary limitations).

(g) Asset Sales. The Company shall not, and shall not permit Antigenics MA to, sell or dispose of any of its assets other than (i) sales of obsolete assets in the ordinary course of business, (ii) sales of inventory in the ordinary course of business in a manner consistent with past practice, or (iii) as not prohibited under Section 14(e).

(h) Business Activities. The Company shall not, and shall not permit Antigenics MA to, exit the life sciences business.

(15) VOTE TO ISSUE, OR CHANGE THE TERMS OF, NOTES. The affirmative vote at a meeting duly called for such purpose or the written consent without a meeting of the Required Holders shall be required for any change or amendment to this Note or the Other Notes.

(16) TRANSFER. This Note and any shares of Company Common Stock issued upon conversion of this Note may be offered, sold, assigned or transferred by the Holder without the consent of the Company, subject only to the provisions of Sections 2(g) and 2(h) of the Securities Purchase Agreement.

(17) REISSUANCE OF THIS NOTE.

(a) Transfer. If this Note is to be transferred, the Holder shall surrender this Note to the Company, whereupon the Company will forthwith issue and deliver upon the order of the

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Holder a new Note (in accordance with Section 17(d)), registered as the Holder may request, representing the outstanding Principal being transferred by the Holder and, if less then the entire outstanding Principal is being transferred, a new Note (in accordance with Section 17(d)) to the Holder representing the outstanding Principal not being transferred. The Holder and any assignee, by acceptance of this Note, acknowledge and agree that, by reason of the provisions of Section 2(e)(iii), following conversion or redemption of any portion of this Note, the outstanding Principal represented by this Note may be less than the Principal stated on the face of this Note.

(b) Lost, Stolen or Mutilated Note. Upon receipt by the Company of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Note, and, in the case of loss, theft or destruction, of an indemnification undertaking by the Holder to the Company, in customary form and, in the case of mutilation, upon surrender and cancellation of this Note, the Company shall execute and deliver to the Holder a new Note (in accordance with Section 17(d)) representing the outstanding Principal.

(c) Note Exchangeable for Different Denominations. This Note is exchangeable, upon the surrender hereof by the Holder at the principal office of the Company, for a new Note or Notes (in accordance with Section 17(d) and in principal amounts of at least $100,000) representing in the aggregate the outstanding Principal of this Note, and each such new Note will represent such portion of such outstanding Principal as is designated by the Holder at the time of such surrender.

(d) Issuance of New Notes. Whenever the Company is required to issue a new Note pursuant to the terms of this Note, such new Note (i) shall be of like tenor with this Note, (ii) shall represent, as indicated on the face of such new Note, the Principal remaining outstanding (or in the case of a new Note being issued pursuant to Section 17(a) or Section 17(c), the Principal designated by the Holder which, when added to the principal represented by the other new Notes issued in connection with such issuance, does not exceed the Principal remaining outstanding under this Note immediately prior to such issuance of new Notes), (iii) shall have an issuance date, as indicated on the face of such new Note which is the same as the Issuance Date of this Note, (iv) shall have the same rights and conditions as this Note, and (v) shall represent accrued and unpaid Interest of this Note from the Issuance Date.

(18) REMEDIES, CHARACTERIZATIONS, OTHER OBLIGATIONS, BREACHES AND INJUNCTIVE RELIEF. The remedies provided in this Note shall be cumulative and in addition to all other remedies available under this Note and any of the other Transaction Documents, at law or in equity (including a decree of specific performance and/or other injunctive relief), and nothing herein shall limit the Holder’s right to pursue actual and consequential damages for any failure by the Company to comply with the terms of this Note. Amounts set forth or provided for herein with respect to payments, conversion and the like (and the computation thereof) shall be the amounts to be received by the Holder and shall not, except as expressly provided herein, be subject to any other obligation of the Company (or the performance thereof). The Company acknowledges that a breach by it of its obligations hereunder will cause irreparable harm to the Holder and that the remedy at law for any such breach may be inadequate. The Company therefore agrees that, in the event of any such breach or threatened breach, the Holder shall be entitled, in addition to all other available remedies, to an injunction restraining any breach, without the necessity of showing economic loss and without any bond or other security being required.

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(19) PAYMENT OF COLLECTION, ENFORCEMENT AND OTHER COSTS. If (a) this Note is placed in the hands of an attorney for collection or enforcement or is collected or enforced through any legal proceeding or the Holder otherwise takes action to collect amounts due under this Note or to enforce the provisions of this Note or (b) there occurs any bankruptcy, reorganization, receivership of the Company or other proceedings affecting Company creditors’ rights and involving a claim under this Note, then the Company shall pay the costs incurred by the Holder for such collection, enforcement or action or in connection with such bankruptcy, reorganization, receivership or other proceeding, including, but not limited to, attorneys’ fees and disbursements.

(20) CONSTRUCTION; HEADINGS. This Note shall be deemed to be jointly drafted by the Company and all the Purchasers and shall not be construed against any person as the drafter hereof. The headings of this Note are for convenience of reference and shall not form part of, or affect the interpretation of, this Note.

(21) FAILURE OR INDULGENCE NOT WAIVER. No failure or delay on the part of the Holder in the exercise of any power, right or privilege hereunder shall operate as a waiver thereof, nor shall any single or partial exercise of any such power, right or privilege preclude other or further exercise thereof or of any other right, power or privilege.

(22) DISPUTE RESOLUTION. In the case of a dispute as to the determination of the Closing Bid Price, the Closing Sale Price, the Weighted Average Price, the Redemption Price or the arithmetic calculation of the Conversion Rate, Antigenics MA Conversion Rate or the Redemption Price, the Company shall submit the disputed determinations or arithmetic calculations via facsimile within one (1) Business Day of receipt, or deemed receipt, of the Conversion Notice or the Redemption Notice or other event giving rise to such dispute, as the case may be, to the Holder. If the Holder and the Company are unable to agree upon such determination or calculation of the Redemption Price or the Conversion Rate, as applicable, within one (1) Business Day of such disputed determination or arithmetic calculation being submitted to the Holder, then the Company shall, within one (1) Business Day submit via facsimile (a) the disputed determination of the Closing Bid Price, the Closing Sale Price or the Weighted Average Price to an independent, reputable investment bank selected by the Company and approved by the Holder or (b) the disputed arithmetic calculation of the Conversion Rate or the Redemption Price to the Company’s independent, outside accountant. The Company, at the Company’s expense, shall cause the investment bank or the accountant, as the case may be, to perform the determinations or calculations and notify the Company and the Holder of the results no later than five (5) Business Days from the time it receives the disputed determinations or calculations. Such investment bank’s or accountant’s determination or calculation, as the case may be, shall be binding upon all parties absent demonstrable error. To the extent of a good faith dispute by the Company, any related penalty payments due hereunder shall not be made until such dispute is resolved.

(23) NOTICES; PAYMENTS.

(a) Notices. Whenever notice is required to be given under this Note, unless otherwise provided herein, such notice shall be given in accordance with Section 9(f) of the Securities Purchase Agreement. The Company shall provide the Holder with prompt written notice of all actions taken pursuant to this Note, including in reasonable detail a description of

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such action and the reason therefore. Without limiting the generality of the foregoing, the Company will give written notice to the Holder (i) immediately upon any adjustment of the Conversion Price or Antigenics MA Conversion Rate, setting forth in reasonable detail, and certifying, the calculation of such adjustment and (ii) at least fifteen (15) days prior to the date on which the Company closes its books or takes a record (A) with respect to any dividend or distribution upon the Company Common Stock, (B) with respect to any pro rata subscription offer to holders of Company Common Stock or (C) for determining rights to vote with respect to any Fundamental Transaction, dissolution or liquidation, provided in each case that such information shall be made known to the public prior to or in conjunction with such notice being provided to the Holder.

(b) Payments. Whenever any payment of cash is to be made by the Company to any Person pursuant to this Note, such payment shall be made in lawful money of the United States of America by a check drawn on the account of the Company and sent via overnight courier service to such Person at such address as previously provided to the Company in writing (which address, in the case of each of the Purchasers shall initially be as set forth on the Schedule of Buyers attached to the Securities Purchase Agreement); provided that the Holder may elect to receive a payment of cash via wire transfer of immediately available funds by providing the Company with prior written notice setting out such request and the Holder’s wire transfer instructions. Whenever any amount expressed to be due by the terms of this Note is due on any day which is not a Business Day, the same shall instead be due on the next succeeding day which is a Business Day and, in the case of any Interest Date which is not the date on which this Note is paid in full, the extension of the due date thereof shall not be taken into account for purposes of determining the amount of Interest due on such date.

(24) CANCELLATION. After all Principal, accrued Interest and other amounts at any time owed on this Note have been paid in full, this Note shall automatically be deemed canceled, shall be surrendered to the Company for cancellation and shall not be reissued.

(25) WAIVER OF NOTICE. To the extent permitted by law, the Company hereby waives demand, notice, protest and all other demands and notices in connection with the delivery, acceptance, performance, default or enforcement of this Note and the Securities Purchase Agreement.

(26) NO PERSONAL LIABILITY. None of the Company’s past, present or future directors, officers, employees or stockholders, as such, shall have any liability for any of the Company’s obligations under this Note or for any claim based on, or in respect or by reason of, such obligations or their creation. Except as otherwise provided by applicable law, by accepting this Note, the Holder waives and releases all such liability and such waiver and release is part of the consideration for the issue of this Note.

(27) CONFIDENTIALITY. At no time will a party, without the prior written consent of any other party, make any press releases or public announcements concerning this Note; provided, however, that any party may make any public disclosure required by applicable law or any listing or trading agreement concerning its publicly traded securities (in which case the disclosing party will use its best efforts to advise the other parties prior to making the disclosure). Each party shall keep confidential any and all information obtained in connection with this Note and shall not disclose any such information to any other Person except: (a) with

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the prior written consent of the other party; (b) as required by law, regulation, or court order, but only after notice has been provided to such other party; or (c) for such information as shall have been publicly disclosed other than in violation of this Note or of any other obligation of confidentiality to such other party.

(28) GOVERNING LAW. This Note shall be construed and enforced in accordance with, and all questions concerning the construction, validity, interpretation and performance of this Note shall be governed by, the internal laws of the State of New York, without giving effect to any choice of law or conflict of law provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York.

(29) CERTAIN DEFINITIONS. For purposes of this Note, the following terms shall have the following meanings:

(a) “AG-707” means an investigational therapeutic vaccine for the treatment of genital herpes consisting of recombinant heat shock proteins complexed with multiple peptides derived from herpes simplex 2 virus.

(b) “Antigenics MA” means Antigenics Inc., a Massachusetts corporation.

(c) “Antigenics MA Stock” means up to a thirty percent (30%) interest in Antigenics MA.

(d) “Approved Stock Plan” means any employee benefit plan, contract or arrangement which has been, or is in the future, approved by the Company Board of Directors, including a committee thereof, pursuant to which the Company’s securities may be issued to employees, consultants, officers or directors.

(e) “Bloomberg” means Bloomberg Financial Markets.

(f) “Business Day” means any day other than Saturday, Sunday or other day on which commercial banks in The City of New York are authorized or required by law to remain closed.

(g) “Change of Control” means any (i) Fundamental Transaction other than (A) a Fundamental Transaction in which holders of the Company’s voting power immediately prior to the Fundamental Transaction continue after the Fundamental Transaction to hold publicly traded securities and, directly or indirectly, the voting power of the surviving entity or entities necessary to elect a majority of the members of the board of directors (or their equivalent if other than a corporation) of such entity or entities, (B) pursuant to a migratory merger effected solely for the purpose of changing the jurisdiction of incorporation of the Company or (C) the majority of the Company Board of Directors in place prior to a Fundamental Transaction remains the majority of the Company Board of Directors following such Fundamental Transaction,(ii) a change within any 12-month period of a majority of the Company Board of Directors of the Company in connection with the acquisition by a Person (or Persons acting in concert) of 30% or more of the Company Common Stock; or (iii) an amalgamation or arrangement whereby Company Common Stock ceases to exist and a Person (or Persons acting jointly or in concert) acquire control of the Company.

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(h) “Closing Bid Price” and “Closing Sale Price” means, for any security as of any date, the last closing bid price and last closing trade price, respectively, for such security on the Principal Market, as reported by Bloomberg, or, if the Principal Market begins to operate on an extended hours basis and does not designate the closing bid price or the closing trade price, as the case may be, then the last bid price or last trade price, respectively, of such security prior to 4:00 p.m., New York Time, as reported by Bloomberg, or, if the Principal Market is not the principal securities exchange or trading market for such security, the last closing bid price or last trade price, respectively, of such security on the principal securities exchange or trading market where such security is listed or traded as reported by Bloomberg, or if the foregoing do not apply, the last closing bid price or last trade price, respectively, of such security in the over-the-counter market on the electronic bulletin board for such security as reported by Bloomberg, or, if no closing bid price or last trade price, respectively, is reported for such security by Bloomberg, the average of the bid prices, or the ask prices, respectively, of any market makers for such security as reported in the “pink sheets” by Pink Sheets LLC (formerly the National Quotation Bureau, Inc.). If the Closing Bid Price or the Closing Sale Price cannot be calculated for a security on a particular date on any of the foregoing bases, the Closing Bid Price or the Closing Sale Price, as the case may be, of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved pursuant to Section 22. All such determinations to be appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction during the applicable calculation period.

(i) “Closing Date” shall have the meaning set forth in the Securities Purchase Agreement, which date is the date the Company initially issued Notes pursuant to the terms of the Securities Purchase Agreement.

(j) “Company Board of Directors” means the board of directors of the Company or any authorized committee of the board of directors.

(k) “Company Election Date” means three Company Trading Days prior to the Maturity Date.

(l) “Company Trading Day” means any day on which the Company Common Stock is traded on the Principal Market, or, if the Principal Market is not the principal trading market for the Company Common Stock, then on the principal securities exchange or securities market on which the Company Common Stock is then traded; provided that “Company Trading Day” shall not include any day on which the Company Common Stock is scheduled to trade on such exchange or market for less than 4.5 hours or any day that the Company Common Stock is suspended from trading during the final hour of trading on such exchange or market (or if such exchange or market does not designate in advance the closing time of trading on such exchange or market, then during the hour ending at 4:00 p.m., New York Time).

(m) “Conversion Amount” means the amount of (A) the portion of the Principal to be converted, redeemed or otherwise with respect to which this determination is made, and (B) accrued and unpaid Interest with respect to such Principal.

(n) “Conversion Date” means the date on which any Conversion Amount is converted into shares of Company Common Stock.

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(o) “Convertible Securities” means with respect to any issuer, any stock or securities (other than Options) directly or indirectly convertible into or exercisable or exchangeable for such issuer’s common stock.

(p) “Eligible Market” means the Principal Market, The New York Stock Exchange, Inc. or The Nasdaq SmallCap Market.

(q) “Excluded Securities” means any Company Common Stock issued or issuable: (i) in connection with any Approved Stock Plan; (ii) upon conversion of the Notes; (iii) pursuant to a bona fide firm commitment underwritten public offering with an institution that regularly underwrites as a principal part of its business public offerings on a firm commitment basis which generates gross proceeds to the Company in excess of $15,000,000 (other than an “at-the-market offering” as defined in Rule 415(a)(4) under the 1933 Act and “equity lines”); (iv) securities issued in connection with corporate partnering transactions on terms approved by the Board of Directors of the Company and the primary purpose of which is not to raise equity capital; (v) in connection with a strategic licensing arrangement, corporate partnering transaction or similar collaboration and (vi) upon conversion of any Options or Convertible Securities which are outstanding on the day immediately preceding the Issuable Date, provided that the terms of such Options or Convertible Securities are not amended, modified or changed on or after the Issuable Date to decrease the price, increase the number of shares issuable thereunder or extend the term of such Options or Convertible Securities; issued or issuable upon conversion of the Notes.

(r) “Fundamental Transaction” means that the Company shall, directly or indirectly, in one or more related transactions, (i) consolidate or merge with or into (whether or not the Company is the surviving corporation) another Person, or (ii) sell, assign, transfer, convey or otherwise dispose of all or substantially all of the properties or assets of the Company to another Person, or (iii) allow another Person to make a purchase, tender or exchange offer that is accepted by the holders of more than the 50% of the outstanding shares of Company Common Stock (not including any shares of Company Common Stock held by the Person or Persons making or party to, or associated or affiliated with the Persons making or party to, such purchase, tender or exchange offer), or (iv) consummate a stock purchase agreement or other business combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) with another Person whereby such other Person acquires up to 50% of the outstanding shares of Company Common Stock not including any shares of Company Common Stock held by the other Person or other Persons making or party to, or associated or affiliated with the other Persons making or party to, such stock purchase agreement or other business combination), or (v) reorganize, recapitalize or reclassify its Company Common Stock.

(s) “GSK” means GlaxoSmithKline Biologicals SA, a Belgian company, having an address at 89 rue de l’Institut, 1330 Rixensart Belgium.

(t) “Interest Period” means, initially, the period beginning on and including the Issuance Date and ending on and including December 30, 2006 and each successive period as follows: the period beginning on and including December 31 and ending on and including June 30; the period beginning on and including July 31 and ending on and including December 30.

(u) “Interest Rate” means eight percent (8.0%) per annum.

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(v) “Issuance Date” means October 30, 2006.

(w) “Maturity Date” means August 30, 2011, as extended at the option of the Holder.

(x) “Options” means with respect to any issuer, any rights, warrants or options to subscribe for or purchase such issuer’s common stock or such issuer’s Convertible Securities.

(y) “Parent Entity” of a Person means an entity that, directly or indirectly, controls the applicable Person and whose common stock or equivalent equity security is quoted or listed on an Eligible Market, or, if there is more than one such Person or Parent Entity, the Person or Parent Entity with the largest public market capitalization as of the date of consummation of the Fundamental Transaction.

(z) “Permitted Indebtedness” means (A) Indebtedness incurred by the Company that is made expressly subordinate in right of payment to the Indebtedness evidenced by this Note, as reflected in a written agreement acceptable to the Holder and approved by the Holder in writing, and which Indebtedness does not provide at any time for (1) the payment, prepayment, repayment, repurchase or defeasance, directly or indirectly, of any principal or premium, if any, thereon until ninety-one (91) days after the Maturity Date or later and (2) total interest and fees at a rate in excess of six percent (6%) per annum, (B) up to $5 million of aggregate Indebtedness, (C) up to $12,000,000 in Indebtedness for the sole purpose of financing an exclusive manufacturing facility for QS-21, (D) Indebtedness secured by Permitted Liens, (E) Indebtedness to trade creditors incurred in the ordinary course of business, (F) Permitted Non-Recourse Indebtedness, (G) any Indebtedness listed on Schedule 3(p) of the Securities Purchase Agreement and (H) extensions, refinancings and renewals of any items of Permitted Indebtedness, provided that the principal amount is not increased or the terms modified to impose more burdensome terms upon the Company or its Subsidiary, as the case may be.

(aa) “Permitted Investments” means (A) investments outstanding on the Closing Date and identified on Schedule 14(d), (B) accounts receivables owing to either the Company or Antigenics MA, (C) investment in cash or Cash Equivalents, (D) negotiable instruments held for collection in the ordinary course of business, (E) loans and advances, in the ordinary course of business, to directors, employees and officers of the Company, (F) intercompany loans between the Company and any Subsidiary, (G) investments in securities of trade creditors or customers in the ordinary course of business, and (H) other Investments in an aggregate amount not to exceed $7,500,000 at any time outstanding.

(bb) “Permitted Liens” means (i) any Lien for taxes not yet due or delinquent or being contested in good faith by appropriate proceedings for which adequate reserves have been established in accordance with GAAP, (ii) any statutory Lien arising in the ordinary course of business by operation of law with respect to a liability that is not yet due or delinquent, (iii) any Lien created by operation of law, such as materialmen’s liens, mechanics’ liens and other similar liens, arising in the ordinary course of business with respect to a liability that is not yet due or delinquent or that are being contested in good faith by appropriate proceedings, (iv) Liens securing the Company’s obligations under the Notes, (v) Liens (A) upon or in any equipment acquired or held by the Company or any of its Subsidiaries to secure the purchase price of such equipment or indebtedness incurred solely for the purpose of financing the acquisition or lease of

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such equipment, or (B) existing on such equipment at the time of its acquisition, provided that the Lien is confined solely to the property so acquired and improvements thereon, and the proceeds of such equipment, (vi) Liens incurred in connection with the extension, renewal or refinancing of the indebtedness secured by Liens of the type described in clauses (i) and (v) above, provided that any extension, renewal or replacement Lien shall be limited to the property encumbered by the existing Lien and the principal amount of the Indebtedness being extended, renewed or refinanced does not increase, (vii) leases or subleases and licenses and sublicenses granted to others in the ordinary course of the Company’s business, not interfering in any material respect with the business of the Company and its Subsidiaries taken as a whole, (viii) Liens in favor of customs and revenue authorities arising as a matter of law to secure payments of custom duties in connection with the importation of goods, (ix) Lien securing Permitted Indebtedness, and (x) Liens arising from judgments, decrees or attachments in circumstances not constituting an Event of Default under Section 4(a)(iv).

(cc) “Person” means an individual, a limited liability company, a partnership, a joint venture, a corporation, a trust, an unincorporated organization, any other entity and a government or any department or agency thereof.

(dd) “Pledge and Security Agreement” means that certain Pledge and Security Agreement, dated as of the Issuance Date, made by the Company in favor of the Holder.

(ee) “Pledged Collateral” has the meaning ascribed to such term in the Pledge and Security Agreement.

(ff) “Principal Market” means the Nasdaq National Market.

(gg) “QS-21” means a substantially pure saponin adjuvant isolated from crude Quillaja saponaria tree extract and referred to as QS-21, a Stimulonâ adjuvant.

(hh) “Redemption Notice” means any of an Event of Default Redemption Notice or Holder Change of Control Redemption Notice .

(ii) “Redemption Price” means any of an Event of Default Redemption Price or Holder Change of Control Redemption Price.

(jj) “Required Holders” means the holders of Notes representing at least a majority of the aggregate principal amount of the Notes then outstanding.

(kk) “SEC” means the United States Securities and Exchange Commission.

(ll) “Securities Purchase Agreement” means that certain securities purchase agreement, dated as of the date hereof, by and among the Company and the initial holders of the Notes pursuant to which the Company issued the Notes.

(mm) “Subsidiary” means any Person of which the Company (or other specified Person) shall at the time, directly or indirectly through one or more of its Subsidiaries, (a) own at least 50% of the outstanding capital stock (or other shares of beneficial interest) entitled to vote generally, (b) hold at least 50% of the partnership, joint venture or similar interests or (c) be general partner or joint venturer.

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(nn) “Successor Entity” means the Person, which may be the Company, formed by, resulting from or surviving any Fundamental Transaction or the Person with which such Fundamental Transaction shall have been made, provided that if such Person is not a publicly traded entity whose common stock or equivalent equity security is quoted or listed for trading on an Eligible Market, Successor Entity shall mean such Person’s Parent Entity.

(oo) “Transaction Documents” has the meaning ascribed to such term in the Securities Purchase Agreement.

(pp) “Transfer Agent” means the Company’s transfer agent.

(qq) “Weighted Average Price” means, for any security as of any date, the dollar volume-weighted average price for such security on the Principal Market during the period beginning at 9:30:01 a.m., New York Time (or such other time as the Principal Market publicly announces is the official open of trading), and ending at 4:00:00 p.m., New York Time (or such other time as the Principal Market publicly announces is the official close of trading) as reported by Bloomberg through its “Volume at Price” functions, or, if the foregoing does not apply, the dollar volume-weighted average price of such security in the over-the-counter market on the electronic bulletin board for such security during the period beginning at 9:30:01 a.m., New York Time (or such other time as such market publicly announces is the official open of trading), and ending at 4:00:00 p.m., New York Time (or such other time as such market publicly announces is the official close of trading) as reported by Bloomberg, or, if no dollar volume-weighted average price is reported for such security by Bloomberg for such hours, the average of the highest closing bid price and the lowest closing ask price of any of the market makers for such security as reported in the “pink sheets” by Pink Sheets LLC (formerly the National Quotation Bureau, Inc.). If the Weighted Average Price cannot be calculated for a security on a particular date on any of the foregoing bases, the Weighted Average Price of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved pursuant to Section 22. All such determinations to be appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction during the applicable calculation period.

(30) SECURITY. The Notes shall be secured by and to the extent provided in the Pledge and Security Agreement.

[Signature Page Follows]

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IN WITNESS WHEREOF, the Company has caused this Note to be duly executed as of the Issuance Date set out above.

ANTIGENICS INC.

By:

Name:

Title:

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EXHIBIT I

ANTIGENICS INC.

CONVERSION NOTICE

TO BE EXECUTED BY THE REGISTERED HOLDER TO CONVERT THIS NOTE INTO COMMON STOCK

Reference is made to the Senior Secured Convertible Note (the “Note”) issued to the undersigned by Antigenics Inc. (the “Company”). In accordance with and pursuant to the Note, the undersigned hereby elects to convert the Conversion Amount (as defined in the Note) of the Note indicated below into shares of Company Common Stock, par value $.01 per share (the “Company Common Stock”), of the Company as of the date specified below.

Date of Conversion:

Aggregate Conversion Amount to be converted:

Notwithstanding anything to the contrary contained herein, this Conversion Notice shall constitute a representation by the holder of the Note submitting this Conversion Notice that, after giving effect to the conversion provided for in this Conversion Notice, such holder (together with its affiliates) will not have beneficial ownership (together with the beneficial ownership of such Person’s affiliates) of a number of shares of Company Common Stock which exceeds the maximum percentage of the total outstanding shares of Company Common Stock as determined pursuant to the provisions of Section 2(g)(i) of the Note.

Please confirm the following information:

Conversion Price:

Number of shares of Company Common Stock to be issued:

Please issue the Company Common Stock into which the Note is being converted in the following name and to the following address:

Issue to:

Facsimile Number:
Authorization:
By:
	Title: ________________

Dated:

Account Number:

  (if electronic book entry transfer)

Transaction Code Number:

  (if electronic book entry transfer)

ACKNOWLEDGMENT

The Company hereby acknowledges this Conversion Notice and hereby directs [INSERT TRANSFER AGENT NAME] to issue the above indicated number of shares of Company Common Stock in accordance with the Transfer Agent Instructions dated October     , 2006 from the Company and acknowledged and agreed to by [INSERT TRANSFER AGENT NAME].

ANTIGENICS INC.

By:

Name:

Title:

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Schedule 14(c)

Restricted Payments

1. The Company owes $1,065,800 as debt to General Electric Corporation.

2. The Company may owe a capital call of $375,000 to Applied Genomic Technology Capital Fund.

3. Antigenics MA owes $146,061 in the form of subordinated debentures plus accrued interest of $51,590.

Schedule 14(d)

Permitted Investments

1. The Company may owe a capital call of $375,000 to Applied Genomic Technology Capital Fund.

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EX-4.2

Exhibit 4.2

EXHIBIT B

TO SECURITIES PURCHASE AGREEMENT

SENIOR SECURED CONVERTIBLE NOTE

NEITHER THIS NOTE NOR THE SECURITIES INTO WHICH THIS NOTE IS CONVERTIBLE HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF (A) AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND APPLICABLE STATE SECURITIES LAWS, OR (B) THE TRANSFEROR PROVIDES THE COMPANY WITH REASONABLE ASSURANCES AND CUSTOMARY REPRESENTATIONS THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAWS. THIS NOTE IS ISSUED SUBJECT TO THE TERMS OF A SECURITIES PURCHASE AGREEMENT, DATED AS OF OCTOBER 30, 2006 (“SECURITIES PURCHASE AGREEMENT”), BY AND AMONG ANTIGENICS INC. AND THE HOLDER OF THIS NOTE.

ANTIGENICS INC.

SENIOR SECURED CONVERTIBLE NOTE

Issuance Date: [    ]     , 200   Principal: U.S. $

FOR VALUE RECEIVED, ANTIGENICS INC., a Delaware corporation (the “Company”), hereby promises to pay to the order of [                                ] or its registered assigns (“Holder”) the amount set out above as the Principal (as reduced pursuant to the terms hereof pursuant to redemption, conversion or otherwise, the “Principal”) when due, whether upon the Maturity Date (as defined below), acceleration, redemption or otherwise (in each case, in accordance with the terms hereof) and to pay interest (“Interest”) on any outstanding Principal at the Interest Rate, from the date set out above as the Issuance Date (the “Issuance Date”) until the same becomes due and payable, whether upon an Interest Date (as defined below) or the Maturity Date, acceleration, conversion, redemption or otherwise (in each case in accordance with the terms hereof). This Senior Secured Convertible Note (including all Senior Secured Convertible Notes issued in exchange, transfer or replacement hereof, this “Note”) is one of an issue of Senior Secured Convertible Notes issued pursuant to the Securities Purchase Agreement (as defined below) (collectively, the “Notes” and such other Senior Secured Convertible Notes, the “Other Notes”). Certain capitalized terms used herein are defined in Section 29.

(1) INTEREST; INTEREST RATE. Interest on this Note shall commence accruing on the Issuance Date and shall be computed on the basis of a 360-day year of twelve 30-day months from the actual number of days elapsed and shall be payable in arrears for each Interest Period on the last day of the applicable Interest Period during the period beginning on the Issuance Date and ending, subject to earlier acceleration, redemption or conversion, on, and including, the Maturity Date (even if the Maturity Date is not the last day of an Interest Period)

(each, an “Interest Date”) with the first Interest Date being [June/December]     , 200  . Interest shall be payable on each Interest Date to the record holder of this Note on the applicable Interest Date in cash (“Cash Interest”) or, at the option of the Company may be paid in kind notes in the form of Exhibit B to the Securities Purchase Agreement (“PIK Notes”) or a combination thereof, provided that the Interest which accrued during any period will be payable in PIK Notes unless the Company delivers written notice (each a “Cash Election Notice”) of such election to each holder of the Notes on or prior to the twentieth (20^th) Company Trading Day prior to the Interest Date (each, an “Interest Election Date”). Each Cash Election Notice must specify the amount of Interest that shall be paid as Cash Interest, if any, and the amount of Interest that shall be paid in PIK Notes. If the Company elects to pay in PIK Notes, such PIK Notes shall be issued to the record holder of the Note within twenty (20) days after the Interest Date. Prior to the payment of Interest on an Interest Date, Interest on this Note shall accrue at the Interest Rate and be payable by way of inclusion of the Interest in the Conversion Amount (as defined below) in accordance with Section 2(b)(i).

(2) CONVERSION OF NOTES. This Note shall be convertible into (i) shares of the Company’s common stock, par value $.01 per share (the “Company Common Stock”) or (ii) Antigenics MA Stock, on the terms and conditions set forth in this Section 2.

(a) Conversion Right. Subject to the provisions of Section 2(g), at any time or times on or after the Issuance Date, the Holder shall be entitled to convert any portion of the outstanding and unpaid Conversion Amount in multiples of $10,000 (or, if less, any remaining Conversion Amount) into (i) fully paid and nonassessable shares of Company Common Stock in accordance with Section 2(e), at the Conversion Rate (as defined below) or (ii) Antigenics MA Stock, at the Antigenics MA Conversion Rate (as defined below). The Company shall not issue any fraction of a share of Company Common Stock or Antigenics MA Stock upon any conversion. If the issuance would result in the issuance of a fraction of a share of Company Common Stock or Antigenics MA Stock, the Company shall round such fraction of a share of Company Common Stock or Antigenics MA Stock, respectively, up to the nearest whole share. The Company shall pay any and all taxes that may be payable with respect to the issuance and delivery of Company Common Stock or Antigenics MA Stock upon conversion of any Conversion Amount; provided that the Company shall not be required to pay any tax that may be payable in respect of any transfer involved in the issue and delivery of Company Common Stock or Antigenics MA Stock to any Person other than the Holder or with respect to any income tax due by the Holder with respect to such Company Common Stock or Antigenics MA Stock issued upon conversion.

(b) Company Common Stock Conversion Rate. The number of shares of Company Common Stock issuable upon conversion of any Conversion Amount pursuant to Section 2(a)(i) shall be determined by dividing (x) such Conversion Amount by (y) the Conversion Price (as defined below) (the “Conversion Rate”).

(i) “Conversion Price” means as of any Conversion Date (as defined below) during the period beginning on the Issuance Date and ending on and including the Maturity Date, the Fixed Conversion Price.

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(ii) “Fixed Conversion Price” means [$3.50]¹ (also referred to as the “Initial Fixed Conversion Price”), subject to adjustment as provided herein.

(c) Antigenics MA Stock Conversion Rate. The number shares of Antigenics MA Stock issuable upon conversion of any Conversion Amount pursuant to Section 2(a)(ii) (“the Antigenics MA Conversion”) shall be equal to the number of shares constituting x% of the total shares of Antigenics MA stock, where x is calculated by dividing the Conversion Amount by $833,333.00. To convert any Conversion Amount into shares of Antigenics MA Stock on any date (an “Antigenics MA Conversion Date”), the Holder shall give the Company ninety (90) days’ prior written notice (the “Antigenics MA Stock Conversion Notice”) transmitted by facsimile (or otherwise deliver).

(d) Company Buyout Right. Notwithstanding anything in this Section 2 to the contrary, upon receipt of a Antigenics MA Stock Conversion Notice, the Company shall have the right to redeem the Notes subject to the Antigenics MA Stock Conversion Notice (the “Company Buyout Right”) at a price equal to the value of the Conversion Amount plus an amount, when taken together with any Cash Interest payments made prior to the exercise of the Company Buyout Right, that would generate an annual internal rate of return to the Holder of thirty percent (30%) in respect of the Principal. The Company shall have sixty (60) days, following receipt of the Antigenics MA Stock Conversion Notice to give notice of its decision to exercise the Company Buyout Right.

(e) Mechanics of Stock Conversion.

(i) Optional Conversion. To convert any Conversion Amount into shares of Company Common Stock on any date (a “Conversion Date”), the Holder shall (A) transmit by facsimile (or otherwise deliver), for receipt on or prior to 11:59 p.m., New York Time, on such date, a copy of an executed notice of conversion in the form attached hereto as Exhibit I (the “Conversion Notice”) to the Company and (B) if required by Section 2(e)(iii), surrender this Note to a common carrier for delivery to the Company as soon as practicable on or following such date (or an indemnification undertaking with respect to this Note in the case of its loss, theft or destruction). On or before the second (2^nd) Business Day following the date of receipt of a Conversion Notice, the Company shall transmit by facsimile a confirmation of receipt of such Conversion Notice to the Holder and the Transfer Agent (as defined below). On or before the third (3^rd) Business Day following the date of receipt of a Conversion Notice (the “Share Delivery Date”), the Company shall issue and deliver to the address as specified in the Conversion Notice, a certificate, registered in the name of the Holder or its designee, for the number of shares of Company Common Stock to which the Holder shall be entitled. If this Note is physically surrendered for conversion as required by Section 2(e)(iii) and the outstanding Principal of this Note is greater than the Principal portion of the Conversion Amount being converted, then the Company shall as soon as practicable and in no event later than three (3) Business Days after receipt of this Note (the “Note Delivery Date”) and at its own expense,

¹ The Initial Fixed Conversion Price may be adjusted at any time on or after October 27, 2006 pursuant to section 7(b).

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issue and deliver to the holder a new Note (in accordance with Section 17(d)) representing the outstanding Principal not converted. The Person or Persons entitled to receive the shares of Company Common Stock issuable upon a conversion of this Note shall be treated for all purposes as the record holder or holders of such shares of Company Common Stock on the Conversion Date to the extent permitted by applicable law.

(ii) Company’s Failure to Timely Convert. If the Company shall fail to issue a certificate to the Holder or credit the Holder’s balance account with Depository Trust Company for the number of shares of Company Common Stock to which the Holder is entitled upon conversion of any Conversion Amount on or prior to the date which is five (5) Business Days after the Conversion Date (a “Conversion Failure”), then (A) the Company shall pay damages in cash to the Holder for each day of such Conversion Failure in an amount equal to 0.25% of the product of (I) the sum of the number of shares of Company Common Stock not issued to the Holder on or prior to the Share Delivery Date and to which the Holder is entitled, and (II) the Closing Sale Price of the Company Common Stock on the Share Delivery Date and (B) the Holder, upon written notice to the Company, may void its Conversion Notice with respect to, and retain or have returned, as the case may be, any portion of this Note that has not been converted pursuant to such Conversion Notice.

(iii) Book-Entry. Notwithstanding anything to the contrary set forth herein, upon conversion of any portion of this Note in accordance with the terms hereof, the Holder shall not be required to physically surrender this Note to the Company unless (A) the full Conversion Amount represented by this Note is being converted or (B) the Holder has provided the Company with prior written notice (which notice may be included in the Conversion Notice or Antigenics MA Stock Conversion Notice) requesting reissuance of this Note upon physical surrender of this Note. The Holder and the Company shall maintain records showing the Principal and Interest converted and the dates of such conversions or shall use such other method, reasonably satisfactory to the Holder and the Company, so as not to require physical surrender of this Note upon conversion.

(iv) Pro Rata Conversion; Disputes. In the event that the Company receives a Conversion Notice from more than one holder of Notes for the same Conversion Date and the Company can convert some, but not all, of such portions of the Notes submitted for conversion, the Company, subject to Section 2(g), shall convert from each holder of Notes electing to have Notes converted on such date a pro rata amount of such holder’s portion of its Notes submitted for conversion based on the principal amount of Notes submitted for conversion on such date by such holder relative to the aggregate principal amount of all Notes submitted for conversion on such date. In the event of a dispute as to the number of shares of Company Common Stock issuable to the Holder in connection with a conversion of this Note, the Company shall issue to the Holder the number of shares of Company Common Stock not in dispute and resolve such dispute in accordance with Section 22.

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(f) Payment of Principal at Maturity; Company Election. On the Maturity Date, the Company shall pay to the Holder the sum of the Principal and accrued and unpaid Interest (“Unpaid Principal Amount”) in same day funds; provided, however, that if the Company has satisfied the Company Election Conversion Condition (as defined below), the Company may elect to pay such Unpaid Principal Amount by converting such Unpaid Principal Amount into the number of Company Common Stock equal to the amount of such Unpaid Principal Amount divided by the ninety percent (90%) of the Weighted Average Price of Company Common Stock during the prior twenty (20) Company Trading Days preceding the Company Election Date (a “Company Election Conversion”). If a Company Election Conversion occurs, the Company and the Holder shall follow the procedures for Conversion set forth in this Section 2; provided, however, the Holder shall not be required to send the Conversion Notice contemplated by paragraph 2(e)(i) above. The “Company Election Conversion Condition” means that the average equity market capitalization for the Company calculated based on the closing prices for the shares of Company Common Stock during the twenty (20) Company Trading Days preceding the Maturity Date , shall be greater than $300,000,000 on a fully diluted basis.

(g) Limitations on Conversions.

(i) Beneficial Ownership. The Company shall not effect any conversion of this Note, and the Holder of this Note shall not have the right to convert any portion of this Note, pursuant to this Section 2 or otherwise, to the extent that after giving effect to such conversion, the Holder (together with the Holder’s affiliates), would beneficially own in excess of 9.99% (the “Maximum Percentage”) of the number of shares of Company Common Stock outstanding immediately after giving effect to such conversion. For purposes of the foregoing sentence, the number of shares of Company Common Stock beneficially owned by the Holder and its affiliates shall include the number of shares of Company Common Stock issuable upon conversion of this Note with respect to which the determination of such sentence is being made, but shall exclude the number of shares of Company Common Stock which would be issuable upon (A) conversion of the remaining, nonconverted portion of this Note beneficially owned by the Holder or any of its affiliates and (B) exercise or conversion of the unexercised or nonconverted portion of any other securities of the Company (including, without limitation, any Other Notes or warrants) subject to a limitation on conversion or exercise analogous to the limitation contained herein beneficially owned by the Holder or any of its affiliates. Except as set forth in the preceding sentence, for purposes of this Section 2(g)(i), beneficial ownership shall be calculated in accordance with Section 13(d) of the Securities Exchange Act of 1934, as amended (the “1934 Act”). For purposes of this Section 2(g)(i), in determining the number of outstanding shares of Company Common Stock, the Holder may rely on the number of outstanding shares of Company Common Stock as reflected in (x) the Company’s most recent Form 10-Q or Form 10-K, as the case may be, (y) a more recent public announcement by the Company or (z) any other more recent notice from the Company or the Transfer Agent setting forth the number of shares of

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Company Common Stock outstanding. For any reason at any time, upon the written or oral request of the Holder, the Company shall within three (3) Business Days confirm orally and in writing to the Holder the number of shares of Company Common Stock then outstanding. In any case, the number of outstanding shares of Company Common Stock shall be determined after giving effect to the conversion or exercise of securities of the Company, including this Note, by the Holder or its affiliates since the date as of which such number of outstanding shares of Company Common Stock was reported.

(ii) Principal Market Regulation. The Company shall not be obligated to issue any shares of Company Common Stock upon conversion of this Note, whether pursuant to this Section 2 or otherwise, if the issuance of such shares of Company Common Stock would exceed the aggregate number of shares of Company Common Stock which the Company may issue upon conversion or exercise of the Notes without breaching the Company’s obligations under the rules or regulations of the Principal Market (the “Exchange Cap”), except that such limitation shall not apply in the event that the Company (A) obtains the approval of its stockholders as required by the applicable rules of the Principal Market for issuances of Company Common Stock in excess of such amount, regardless of whether or not the shares of Company Common Stock are then listed on the applicable market or (B) obtains a written opinion from outside counsel to the Company that such approval is not required, which opinion shall be reasonably satisfactory to the Required Holders. In the event the Company is unable to obtain a written opinion pursuant to Section g(ii)(A), the Company shall use its reasonable best efforts to obtain stockholder approval. Until such approval or written opinion is obtained, no purchaser of the Notes pursuant to the Securities Purchase Agreement (the “Purchasers”) shall be issued in the aggregate, upon conversion of Notes, shares of Company Common Stock in an amount greater than the product of the Exchange Cap multiplied by a fraction, the numerator of which is the principal amount of Notes issued to such Purchaser pursuant to the Securities Purchase Agreement on the Closing Date and the denominator of which is the aggregate principal amount of all Notes issued to the Purchasers pursuant to the Securities Purchase Agreement on the Closing Date (with respect to each Purchaser, the “Exchange Cap Allocation”). In the event that any Purchaser shall sell or otherwise transfer any of such Purchaser’s Notes, the transferee shall be allocated a pro rata portion of such Purchaser’s Exchange Cap Allocation, and the restrictions of the prior sentence shall apply to such transferee with respect to the portion of the Exchange Cap Allocation allocated to such transferee. In the event that any holder of Notes shall convert all of such holder’s Notes into a number of shares of Company Common Stock which, in the aggregate, is less than such holder’s Exchange Cap Allocation, then the difference between such holder’s Exchange Cap Allocation and the number of shares of Company Common Stock actually issued to such holder shall be allocated to the respective Exchange Cap Allocations of the remaining holders of Notes on a pro rata basis in proportion to the aggregate principal amount of the Notes then held by each such holder.

(h) Notwithstanding anything in the above provisions to the contrary, if the Holder exercises any of its rights under the Pledge and Security Agreement in Article 9 of the Uniform Commercial Code then it shall no longer have the right to convert its shares into Antigenics MA Stock.

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(3) COMPANY CALL OPTION. After October 30, 2009, the Company shall have the option, at any time when the Weighted Average Price of the Company Common Stock during the prior thirty (30) day period is $7.00 (appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction) or higher, to redeem the Note for cash at (100%) of the Conversion Amount, provided that (i) such redemption shall occur on the date that is twenty (20) Company Trading Days (the “Call Date”) following the date of the Company notice and (ii) prior to the Call Date, the provisions in Section 2 shall remain in effect.

(4) RIGHTS UPON EVENT OF DEFAULT.

(a) Event of Default. Each of the following events (so long as its continuing) shall constitute an “Event of Default”:

(i) the Company’s failure to pay to the Holder any amount of Principal or Interest except, in the case of a failure to pay Interest only if such failure continues for a period of at least five (5) Business Days;

(ii) any default under, redemption of or acceleration prior to maturity of any Indebtedness (as defined in the Securities Purchase Agreement) of the Company aggregating in excess of $1,000,000;

(iii) the Company pursuant to or within the meaning of Title 11, U.S. Code, or any similar Federal, foreign or state law for the relief of debtors (collectively, “Bankruptcy Law”), (A) commences a voluntary case, (B) has an involuntary case filed against it and such case is not dismissed within thirty (30) days, (C) consents to the appointment of a receiver, trustee, assignee, liquidator or similar official, or (D) makes a general assignment for the benefit of its creditors;

(iv) a final judgment or judgments for the payment of money aggregating in excess of $1,000,000 are rendered against the Company and which judgment or judgments are not, within sixty (60) days after the entry thereof, bonded, discharged or stayed pending appeal, or are not discharged within sixty (60) days after the expiration of such stay; provided, however, that any judgment which is covered by insurance or an indemnity from a credit worthy party shall not be included in calculating the $1,000,000 amount set forth above;

(v) the Company breaches any representation or warranty in this Note or makes a misleading representation or warranty which results in a material adverse effect on the financial condition of the Company;

(vi) the Company breaches, in any material respect, a covenant or agreement in this Note which remains uncured after notice for a period of at least thirty (30) consecutive days.; or

(vii) the Company ceases to operate.

(b) Redemption Right. Promptly after the occurrence of an Event of Default, the Company shall deliver written notice thereof via facsimile and overnight courier (an “Event of Default Notice”) to the Holder. At any time after the earlier of the Holder’s receipt of an Event

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of Default Notice and the Holder becoming aware of an Event of Default and prior to 90 days after written notice from the Company to the Holder that such Event of Default is cured (which written notice shall provide reasonably satisfactory evidence that such Event of Default has actually been cured), the Holder may require the Company to redeem all or any portion of this Note by delivering written notice thereof (the “Event of Default Redemption Notice”) to the Company, which Event of Default Redemption Notice shall indicate the portion of this Note that the Holder is electing to redeem. Each portion of this Note subject to redemption by the Company pursuant to this Section 4(b) shall be redeemed by the Company at a price equal to the Conversion Amount to be redeemed (the “Event of Default Redemption Price”). Redemptions required by this Section 4(b) shall be made in accordance with the provisions of Section 10.

(5) RIGHTS UPON FUNDAMENTAL TRANSACTION AND CHANGE OF CONTROL.

(a) Assumption. Without limiting any rights of the Holder pursuant to paragraph (b) below, the Company shall not enter into or be party to a Fundamental Transaction unless (i) the Successor Entity assumes in writing all of the obligations of the Company under this Note in accordance with the provisions of this Section 5(a) pursuant to a written agreement prior to such Fundamental Transaction, including an undertaking to deliver to the Holder in exchange for this Note a security of the Successor Entity evidenced by a written instrument substantially similar in form and substance to the Notes, including, without limitation, having a principal amount and interest rate equal to the principal amounts and the interest rate of this Note and (ii) the Successor Entity (including its Parent Entity) is a publicly traded corporation whose common stock is quoted on or listed for trading on an Eligible Market. Upon the occurrence of any Fundamental Transaction, the Successor Entity shall succeed to, and be substituted for (so that from and after the date of such Fundamental Transaction, the provisions of this Note referring to the “Company” shall refer instead to the Successor Entity), and may exercise every right and power of the Company and shall assume all of the obligations of the Company under this Note with the same effect as if such Successor Entity had been named as the Company herein. Upon consummation of the Fundamental Transaction, the Successor Entity shall deliver to the Holder confirmation that there shall be issued upon conversion or redemption of this Note at any time after the consummation of the Fundamental Transaction, in lieu of the shares of the Company Common Stock (or other securities, cash, assets or other property) purchasable upon the conversion or redemption of the Notes prior to such Fundamental Transaction, such shares of stock, securities, cash, assets or any other property whatsoever (including warrants or other purchase or subscription rights) which the Holder would have been entitled to receive upon the happening of such Fundamental Transaction had this Note been converted immediately prior to such Fundamental Transaction, as adjusted in accordance with the provisions of this Note. The provisions of this Section shall apply similarly and equally to successive Fundamental Transactions and shall be applied without regard to any limitations on the conversion or redemption of this Note.

(b) Holder Redemption Right. No sooner than fifteen (15) Business Days nor later than ten (10) Business Days prior to the consummation of a Change of Control, but not prior to the public announcement of such Change of Control, the Company shall deliver written notice thereof via facsimile and overnight courier to the Holder (a “Change of Control Notice”). At any time during the period beginning after the Holder’s receipt of a Change of Control Notice and ending on the date of the consummation of such Change of Control (or, in the event a

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Change of Control Notice is not delivered at least ten (10) Business Days prior to consummation of such Change of Control, at any time on or after the date which is ten (10) Business Days prior to a Change of Control and ending ten (10) Business Days after the consummation of such Change of Control), the Holder may require the Company to redeem all or any portion of this Note by delivering written notice thereof (“Holder Change of Control Redemption Notice”) to the Company, which Holder Change of Control Redemption Notice shall indicate the Conversion Amount the Holder is electing to redeem. The portion of this Note subject to redemption pursuant to this Section 5 shall be redeemed by the Company at a price equal to 101% of the Conversion Amount being redeemed (the “Holder Change of Control Redemption Price”). Redemptions required by this Section 5(b) shall be made in accordance with the provisions of Section 10 and shall have priority to payments to stockholders in connection with a Change of Control. Notwithstanding anything to the contrary in this Section 5(b), but subject to Sections 2(g), until the Holder Change of Control Redemption Price (together with any interest thereon) is paid in full, the Conversion Amount submitted for redemption under this Section 5(b) (together with any interest thereon) may be converted, in whole or in part, by the Holder into Company Common Stock pursuant to Section 2.

(6) RIGHT OF FIRST REFUSAL.

(a) Equity Offering. If the Company sells, at any time up to the Maturity Date, an equity interest in Antigenics MA (“Equity Offering”), the Holder shall have a right of first refusal (which shall be transferable to affiliates of the Holder and to a purchaser of this Note and automatically transferred with this Note while this Note is outstanding) to purchase Holder’s pro rata share (in proportion to the principal amount this Note represents to the aggregate principal amount of all the Notes) of up to 50% of such Equity Offering on the same terms as the third party purchaser, including without limitation any preemptive rights in connection with any subsequent offering or sales. In the event that this Note is redeemed prior to the Maturity Date (the “Redemption Date”), this right of first refusal shall survive for the benefit of the entity holding this Note at the time of redemption until the Maturity Date, and after the Redemption Date, such right shall be assignable, in whole or in part, other than to a competitor of GSK, based on the pro rata ownership of the Notes at the time of redemption; provided, however, that no such transfer shall be effected unless the transferee would have the right to purchase at least 10% of the transferor’s right to participate in such Equity Offering.

(b) Offer. The Company shall deliver to the Holder written notice of an Equity Offering, specifying the price and terms and conditions of a proposed Equity Offering. Unless the Company determines not to consummate such Equity Offering, the Holder shall have a period of ten (10) Business Days from the date of the notice from the Company (the “10-Day Period”) to irrevocable determine whether to exercise this right.

(c) Notice of Acceptance. Holder shall evidence its intention to accept the Offer by delivering a written notice setting forth the equity interest, subject to Section 6(a) above, that it elects to purchase (the “Notice of Acceptance”). The Notice of Acceptance must be delivered to the Company prior to the end of the 10-day Period.

(d) Purchase of Shares. If the Holder tenders its Notice of Acceptance prior to the end of the 10-day Period indicating its intention to purchase its pro rata share of the Equity Offering, the Company shall schedule a closing. Upon the closing of the sale of the Equity

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Offering to be purchased by the holders, the Holder shall (i) purchase from the Company that portion of the Equity Offering for which it tendered a Notice of Acceptance upon the terms specified in the Offer, and (ii) execute and deliver an agreement further restricting transfer of such Equity Offering. The obligation of any Holder to purchase such Equity Offering is further conditioned upon the preparation of a purchase agreement embodying the terms of the Equity Offering, which shall be reasonably satisfactory in form and substance to the participating Holders.

(7) RIGHTS UPON ISSUANCE OF OTHER SECURITIES.

(a) Adjustment of Fixed Conversion Price upon Issuance of Company Common Stock. If and whenever on or after the Issuance Date, the Company issues or sells, or in accordance with this Section 7(a) is deemed to have issued or sold, any shares of Company Common Stock (including the issuance or sale of shares of Company Common Stock owned or held by or for the account of the Company, but excluding shares of Company Common Stock comprising Excluded Securities) for a consideration per share (the “New Issuance Price”) less than $3.00 (the “Applicable Price”) (the foregoing a “Dilutive Issuance”), then immediately after such Dilutive Issuance, the Fixed Conversion Price then in effect shall be reduced to an amount equal to a 16.66% premium to the New Issuance Price. For purposes of determining the adjusted Fixed Conversion Price under this Section 7(a), the following shall be applicable:

(i) Issuance of Options. If the Company in any manner grants or sells any Options and the lowest price per share for which one share of Company Common Stock is issuable upon the exercise of any such Option or upon conversion or exchange or exercise of any Convertible Securities issuable upon exercise of such Option is less than the Applicable Price, then such share of Company Common Stock shall be deemed to be outstanding and to have been issued and sold by the Company at the time of the granting or sale of such Option for such price per share. For purposes of this Section 7(a)(i), the “lowest price per share for which one share of Company Common Stock is issuable upon the exercise of any such Option or upon conversion or exchange or exercise of any Convertible Securities issuable upon exercise of such Option” shall be equal to the sum of the lowest amounts of consideration (if any) received or receivable by the Company with respect to any one share of Company Common Stock upon granting or sale of the Option, upon exercise of the Option and upon conversion or exchange or exercise of any Convertible Security issuable upon exercise of such Option. No further adjustment of the Fixed Conversion Price shall be made upon the actual issuance of such Company Common Stock or of such Convertible Securities upon the exercise of such Options or upon the actual issuance of such Company Common Stock upon conversion or exchange or exercise of such Convertible Securities.

(ii) Issuance of Convertible Securities. If the Company in any manner issues or sells any Convertible Securities and the lowest price per share for which one share of Company Common Stock is issuable upon such conversion or exchange or exercise thereof is less than the Applicable Price, then such share of Company Common Stock shall be deemed to be outstanding and to have been issued and sold by the Company at the time of the issuance of sale of such Convertible Securities for such price per share. For the purposes of this Section 7(a)(ii), the

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“price per share for which one share of Company Common Stock is issuable upon such conversion or exchange or exercise” shall be equal to the sum of the lowest amounts of consideration (if any) received or receivable by the Company with respect to any one share of Company Common Stock upon the issuance or sale of the Convertible Security and upon the conversion or exchange or exercise of such Convertible Security. No further adjustment of the Fixed Conversion Price shall be made upon the actual issuance of such Company Common Stock upon conversion or exchange or exercise of such Convertible Securities, and if any such issue or sale of such Convertible Securities is made upon exercise of any Options for which adjustment of the Fixed Conversion Price had been or are to be made pursuant to other provisions of this Section 7(a), no further adjustment of the Fixed Conversion Price shall be made by reason of such issue or sale.

(iii) Change in Option Price or Rate of Conversion. If the purchase price provided for in any Options, the additional consideration, if any, payable upon the issue, conversion, exchange or exercise of any Convertible Securities, or the rate at which any Convertible Securities are convertible into or exchangeable or exercisable for Company Common Stock changes at any time, the Fixed Conversion Price in effect at the time of such change shall be adjusted to the Fixed Conversion Price which would have been in effect at such time had such Options or Convertible Securities provided for such changed purchase price, additional consideration or changed conversion rate, as the case may be, at the time initially granted, issued or sold. For purposes of this Section 7(a)(iii), if the terms of any Option or Convertible Security that was outstanding as of the Issuance Date are changed in the manner described in the immediately preceding sentence, then such Option or Convertible Security and the Company Common Stock deemed issuable upon exercise, conversion or exchange thereof shall be deemed to have been issued as of the date of such change. No adjustment shall be made if such adjustment would result in an increase of the Fixed Conversion Price then in effect.

(iv) Calculation of Consideration Received. In case any Option is issued in connection with the issue or sale of other securities of the Company, together comprising one integrated transaction in which no specific consideration is allocated to such Options by the parties thereto, the Options will be deemed to have been issued for a consideration of $.01. If any Company Common Stock, Options or Convertible Securities are issued or sold or deemed to have been issued or sold for cash, the consideration received therefor will be deemed to be the net amount received by the Company therefor. If any Company Common Stock, Options or Convertible Securities are issued or sold for a consideration other than cash, the amount of the consideration other than cash received by the Company will be the fair value of such consideration, except where such consideration consists of securities, in which case the amount of consideration received by the Company will be the Closing Sale Price of such securities on the date of receipt. If any Company Common Stock, Options or Convertible Securities are issued to the owners of the non-surviving entity in connection with any merger in which the Company is the surviving entity, the amount of consideration therefor will be deemed to be the fair value of such portion of the

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net assets and business of the non-surviving entity as is attributable to such Company Common Stock, Options or Convertible Securities, as the case may be. The fair value of any consideration other than cash or securities will be determined jointly by the Company and the Required Holders. If such parties are unable to reach agreement within ten (10) Business Days after the occurrence of an event requiring valuation (the “Valuation Event”), the fair value of such consideration will be determined within five (5) Business Days after the tenth (10^th) Business Day following the Valuation Event by an independent, reputable appraiser jointly selected by the Company and the Required Holders. The determination of such appraiser shall be deemed binding upon all parties absent manifest error and the fees and expenses of such appraiser shall be borne by the Company.

(v) Record Date. If the Company takes a record of the holders of Company Common Stock for the purpose of entitling them (A) to receive a dividend or other distribution payable in Company Common Stock, Options or in Convertible Securities or (B) to subscribe for or purchase Company Common Stock, Options or Convertible Securities, then such record date will be deemed to be the date of the issue or sale of the Company Common Stock deemed to have been issued or sold upon the declaration of such dividend or the making of such other distribution or the date of the granting of such right of subscription or purchase, as the case may be.

(b) Adjustment of Fixed Conversion Price upon Subdivision or Combination of Company Common Stock. If the Company at any time on or after the Issuance Date subdivides (by any stock split, stock dividend, recapitalization or otherwise) one or more classes of its outstanding shares of Company Common Stock into a greater number of shares, the Fixed Conversion Price in effect immediately prior to such subdivision will be proportionately reduced. If the Company at any time on or after the Issuance Date combines (by combination, reverse stock split or otherwise) one or more classes of its outstanding shares of Company Common Stock into a smaller number of shares, the Fixed Conversion Price in effect immediately prior to such combination will be proportionately increased.

(c) Other Events. If any event occurs of the type contemplated by the provisions of this Section 7 but not expressly provided for by such provisions (including, without limitation, the granting of stock appreciation rights, phantom stock rights or other rights with equity features), then the Company’s Board of Directors will make an appropriate adjustment in the Fixed Conversion Price so as to protect the rights of the Holder under this Note; provided that no such adjustment will increase the Fixed Conversion Price as otherwise determined pursuant to this Section 7.

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(8) NONCIRCUMVENTION. The Company hereby covenants and agrees that the Company will not, by amendment of its Certificate of Incorporation, Bylaws or through any reorganization, transfer of assets, consolidation, merger, scheme of arrangement, dissolution, issue or sale of securities, or any other voluntary action, avoid or seek to avoid the observance or performance of any of the terms of this Note, and will at all times in good faith carry out all of the provisions of this Note and take all action as may be required to protect the rights of the Holder of this Note.

(9) RESERVATION OF AUTHORIZED SHARES.

(a) Reservation. The Company shall initially reserve out of its authorized and unissued Company Common Stock a number of shares of Company Common Stock for each of the Notes equal to the number of shares of Company Common Stock as shall be necessary to effect the conversion of all of the Notes. So long as any of the Notes are outstanding, the Company shall take all action necessary to reserve and keep available out of its authorized and unissued Company Common Stock, solely for the purpose of effecting the conversion of the Notes, the number of shares of Company Common Stock as shall from time to time be necessary to effect the conversion of all of the Notes then outstanding at the Company Conversion Price (the “Required Reserve Amount”). The initial number of shares of Company Common Stock reserved for conversions of the Notes and each increase in the number of shares so reserved shall be allocated pro rata among the holders of the Notes based on the principal amount of the Notes held by each holder at the Closing (as defined in the Securities Purchase Agreement) or increase in the number of reserved shares, as the case may be (the “Authorized Share Allocation”). In the event that a holder shall sell or otherwise transfer any of such holder’s Notes, each transferee shall be allocated a pro rata portion of such holder’s Authorized Share Allocation. Any shares of Company Common Stock reserved and allocated to any Person which ceases to hold any Notes shall be allocated to the remaining holders of Notes, pro rata based on the principal amount of the Notes then held by such holders.

(b) Insufficient Authorized Shares. If at any time while any of the Notes remain outstanding the Company does not have a sufficient number of authorized and unreserved shares of Company Common Stock to satisfy its obligation to reserve for issuance upon conversion of the Notes at least a number of shares of Company Common Stock equal to the Required Reserve Amount (an “Authorized Share Failure”), then the Company shall use its reasonable best efforts to immediately take all action necessary to increase the Company’s authorized shares of Company Common Stock to an amount sufficient to allow the Company to reserve the Required Reserve Amount for the Notes then outstanding. Without limiting the generality of the foregoing sentence, as soon as practicable after the date of the occurrence of an Authorized Share Failure, but in no event later than ninety (90) days after the occurrence of such Authorized Share Failure, the Company shall hold a meeting of its stockholders for the approval of an increase in the number of authorized shares of Company Common Stock (the earlier of the date of such meeting and such ninetieth day, the “Authorized Share Failure Stockholder Meeting Deadline”).

(10) HOLDER’S REDEMPTIONS.

(a) Mechanics. The Company shall deliver the applicable Event of Default Redemption Price to the Holder within five (5) Business Days after the Company’s receipt of the Holder’s valid Event of Default Redemption Notice. If the Holder has submitted a Holder

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Change of Control Redemption Notice in accordance with Section 5(b), the Company shall deliver the Holder Change of Control Redemption Price to the Holder, concurrently with the consummation of such Change of Control if such notice is received by the Company prior to the consummation of such Change of Control and within five (5) Business Days after the Company’s receipt of such notice otherwise. In the event of a redemption of less than all of the Conversion Amount of this Note, the Company shall promptly cause to be issued and delivered to the Holder (after such original Note has been delivered to the Company) a new Note (in accordance with Section 17(d)) representing the outstanding Principal which has not been redeemed. In the event that the Company does not pay the applicable Redemption Price to the Holder within the time period required, at any time thereafter and until the Company pays such unpaid Redemption Price in full, the Holder shall have the option, in lieu of redemption, to require the Company to promptly return to the Holder all or any portion of this Note representing the Conversion Amount that was submitted for redemption and for which the applicable Redemption Price has not been paid. Upon the Company’s receipt of such notice, (x) the Redemption Notice shall be null and void with respect to such Conversion Amount and (y) the Company shall immediately return this Note, or issue a new Note (in accordance with Section 17(d)) to the Holder representing such Conversion Amount.

(b) Redemption by Other Holders. Upon the Company’s receipt of notice from any of the holders of the Other Notes for redemption or repayment as a result of an event or occurrence substantially similar to the events or occurrences described in Section 4(b) or Section 5(b) (each, an “Other Redemption Notice”), the Company shall immediately forward to the Holder by facsimile a copy of such notice. If the Company receives a Redemption Notice and one or more Other Redemption Notices during the seven (7) Business Day period beginning on and including the date which is three (3) Business Days prior to the Company’s receipt of the Holder’s Redemption Notice and ending on and including the date which is three (3) Business Days after the Company’s receipt of the Holder’s Redemption Notice and the Company is unable to redeem all principal, interest and other amounts designated in such Redemption Notice and such Other Redemption Notices received during such seven (7) Business Day period, then the Company shall redeem a pro rata amount from each holder of the Notes (including the Holder) based on the principal amount of the Notes submitted for redemption pursuant to such Redemption Notice and such Other Redemption Notices received by the Company during such seven Business Day period.

(11) RESTRICTION ON REDEMPTION AND CASH DIVIDENDS. Other than (x) in connection with employee stock repurchases pursuant to an Approved Stock Plan existing as of the date hereof and (y) cash payments in lieu of fractional shares of Company Common Stock, until all of the Notes have been converted, redeemed or otherwise satisfied in accordance with their terms, the Company shall not, directly or indirectly, redeem, repurchase or declare or pay any cash dividend or distribution on shares of Company Common Stock without the prior express written consent of the holders of Notes representing at least a majority of the aggregate principal amount of the Notes then outstanding.

(12) RIGHTS. Except as otherwise provided for herein, the Holder shall have no rights as a holder of Company Common Stock as a result of being a holder of this Note, except as required by law, including, but not limited to, the General Corporation Law of the State of Delaware, and as expressly provided in this Note.

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(13) AFFIRMATIVE COVENANTS.

(a) Corporate Existence. The Company shall, and shall cause Antigenics MA to, so long as any holder of the Notes or any affiliate of such holder beneficially owns a Note or Notes (or any interest therein), maintain its corporate existence in good standing and pay its taxes when due except for disputed taxes which could not reasonably be expected to have a Material Adverse Effect on its consolidated business or financial condition. The Company shall notify the Holder of any change of name, jurisdiction of incorporation, principal place of business or any similar change with respect to the Company or Antigenics MA.

(b) Maintenance of Properties. The Company shall, and shall cause Antigenics MA to, (i) keep its properties in such repair, working order and condition, and shall from time to time make such repairs, replacements, additions and improvements thereto, as are necessary for the efficient operation of its business and (ii) take all reasonable actions to possess and maintain all Intellectual Property Rights (as defined in the Securities Purchase Agreement) material to the conduct of their respective business and all right, title and interest in and to (subject to Permitted Liens), or have a valid license for, all such Intellectual Property Rights.

(c) Compliance with Material Agreements. The Company shall, and shall cause Antigenics MA to comply with all material agreements to which it is a party.

(d) Financial Statements. To the extent not available electronically with the SEC, the Company shall deliver to the Holder on a consolidated basis (including any Subsidiaries) (i) as soon as practicable, but no later than 120 days following the end of each fiscal year, annual audited financial statements (including balance sheets, income statements and statements of cash flow) of the Company and its consolidated Subsidiaries on a consolidated basis; and (ii) commencing with the third fiscal quarter of 2006, as soon as practicable, but no later than 45 days following the end of each fiscal quarter, quarterly unaudited financial statements (including balance sheets, income statements, statements of cash flow and store profitability figures) of the Company and its consolidated Subsidiaries on a consolidated basis. In addition, if at any time Antigenics MA is not a wholly owned subsidiary of the Company, then the Company shall cause Antigenics MA to deliver to the Holder audited financial statements (including balance sheets, income statements and statements of cash flow). All such financial statements shall be prepared in accordance with the GAAP, applied on a consistent basis.

(e) Other Reports. To the extent not available electronically with the SEC or on the Company’s website, the Company shall promptly furnish to the Holder all press releases, budgets, statements of operations and other documents or reports furnished to stockholders of the Company and, if applicable, Antigenics MA.

(f) Insurance. The Company shall, and shall cause Antigenics MA to, be insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as management of the Company believes to be prudent and customary in the businesses in which the Company is engaged.

(g) Payment of Taxes and Claims. The Company shall, and shall cause Antigenics MA to, to pay and discharge when due all obligations and liabilities, including tax liabilities, except for disputed obligations and/or liabilities, including taxes, which could not reasonably be expected to have a Material Adverse Effect on its consolidated business or financial condition.

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(h) Access to Company and Employees. The Company shall, and shall cause Antigenics MA to, permit representatives of the Holder to visit and inspect any of its respective properties and to discuss its affairs, finances and accounts with its respective officers, employees and independent public accounts as often as may reasonably be desired, but in no event more than twice in any fiscal year.

(i) Notices of Litigation, Defaults, etc. The Company shall, and shall cause Antigenics MA to, promptly furnish to the Holder notice of (i) any material litigation or any administrative or arbitration proceeding in an aggregate amount in excess of $200,000, (ii) any labor dispute or other work stoppage, and (iii) any default or breach of Environmental Laws (as defined in the Securities Purchase Agreement).

(j) Environmental Law. The Company shall and shall cause Antigenics MA to comply with all Environmental Laws other than violations which will not result in a Material Adverse Effect on the financial condition of the Company.

(k) Intellectual Property. The Company shall, or shall cause Antigenics MA, to at all times own all right, title and interest in all Intellectual Property Rights, which the Company or Antigencis MA own as of the Issuance Date, relating to QS-21 and AG-707. Notwithstanding anything in this Section 14(k) to the contrary, the Company may consummate a Spin-off (as such term is defined the Pledge and Security Agreement), enter into partnership, license and collaboration agreements and other similar arrangements.

(14) NEGATIVE COVENANTS.

Except as disclosed on Company filings with the SEC prior to the date hereof:

(a) Incurrence of Indebtedness. So long as this Note is outstanding, the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, incur or guarantee, assume or suffer to exist any Indebtedness (as defined in Section 3(r) of the Securities Purchase Agreement), other than (i) the Indebtedness evidenced by this Note and the Other Notes and (ii) Permitted Indebtedness.

(b) Existence of Liens. So long as this Note is outstanding, the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, allow or suffer to exist any mortgage, lien, pledge, charge, security interest or other similar encumbrance in an aggregate amount in excess of $5,000,000, upon or in any property or assets (including accounts and contract rights) owned by the Company or Antigenics MA (collectively “Liens”), other than (i) pursuant to the Pledge and Security Agreement and (ii) Permitted Liens.

(c) Restricted Payments. Except as set forth on Schedule 14(c), the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, redeem, defease, repurchase, repay or make any payments in respect of, by the payment of cash or cash equivalents (in whole or in part, whether by way of open market purchases, tender offers, private transactions or otherwise), all or any portion of any Permitted Indebtedness whether by way of payment in respect of principal of (or premium, if any) or interest on such Indebtedness if at the

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time such payment is due or is otherwise made or, after giving effect to such payment, an event constituting, or that with the passage of time and without being cured would constitute, an Event of Default has occurred and is continuing.

(d) Investment, Loan and Advances. Except as listed on Schedule 14(d), the Company shall not, and shall not permit Antigenics MA to, directly or indirectly, lend money or credit (by way of guarantee or otherwise) or make advances to any Person, or purchase or acquire stock, bonds, debentures or other obligations or securities of, or any other interest in, or make any capital contribution to, any other Person (collectively “Investments”) other than Permitted Investments.

(e) Mergers, Asset Dispositions and Acquisitions. The Company shall not, and shall not permit Antigenics MA to, merge or consolidate with any other Person or acquire (in any way whatsoever, in one or a series of transactions) shares or assets of any other Person, or sell all or otherwise dispose of any of its shares or assets or the shares or assets of any of its Subsidiaries, or acquire (in any way whatsoever, in one or a series of transactions) any of the shares or assets of a Person, business or line of business, unless (a) the Company is the surviving entity in such merger, consolidation, transfer, sale or acquisition, or (b) the Person acquiring the shares or assets of the Company or its Subsidiaries shall be solvent (both before and after giving effect to such transaction) and shall have executed and delivered to the Holder an assumption of the due and punctual performance and observance of each covenant and agreement of the Company under the Transaction Documents.

(f) Related Party Transactions. Except in the ordinary course of business, the Company shall not, and shall not permit Antigenics MA to, enter into transactions of the type discussed under Item 404(a) of Regulation S-X (including with respect to monetary limitations).

(g) Asset Sales. The Company shall not, and shall not permit Antigenics MA to, sell or dispose of any of its assets other than (i) sales of obsolete assets in the ordinary course of business, (ii) sales of inventory in the ordinary course of business in a manner consistent with past practice, or (iii) as not prohibited under Section 14(e).

(h) Business Activities. The Company shall not, and shall not permit Antigenics MA to, exit the life sciences business.

(15) VOTE TO ISSUE, OR CHANGE THE TERMS OF, NOTES. The affirmative vote at a meeting duly called for such purpose or the written consent without a meeting of the Required Holders shall be required for any change or amendment to this Note or the Other Notes.

(16) TRANSFER. This Note and any shares of Company Common Stock issued upon conversion of this Note may be offered, sold, assigned or transferred by the Holder without the consent of the Company, subject only to the provisions of Sections 2(g) and 2(h) of the Securities Purchase Agreement.

(17) REISSUANCE OF THIS NOTE.

(a) Transfer. If this Note is to be transferred, the Holder shall surrender this Note to the Company, whereupon the Company will forthwith issue and deliver upon the order of the

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Holder a new Note (in accordance with Section 17(d)), registered as the Holder may request, representing the outstanding Principal being transferred by the Holder and, if less then the entire outstanding Principal is being transferred, a new Note (in accordance with Section 17(d)) to the Holder representing the outstanding Principal not being transferred. The Holder and any assignee, by acceptance of this Note, acknowledge and agree that, by reason of the provisions of Section 2(e)(iii), following conversion or redemption of any portion of this Note, the outstanding Principal represented by this Note may be less than the Principal stated on the face of this Note.

(b) Lost, Stolen or Mutilated Note. Upon receipt by the Company of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Note, and, in the case of loss, theft or destruction, of an indemnification undertaking by the Holder to the Company, in customary form and, in the case of mutilation, upon surrender and cancellation of this Note, the Company shall execute and deliver to the Holder a new Note (in accordance with Section 17(d)) representing the outstanding Principal.

(c) Note Exchangeable for Different Denominations. This Note is exchangeable, upon the surrender hereof by the Holder at the principal office of the Company, for a new Note or Notes (in accordance with Section 17(d) and in principal amounts of at least $100,000) representing in the aggregate the outstanding Principal of this Note, and each such new Note will represent such portion of such outstanding Principal as is designated by the Holder at the time of such surrender.

(d) Issuance of New Notes. Whenever the Company is required to issue a new Note pursuant to the terms of this Note, such new Note (i) shall be of like tenor with this Note, (ii) shall represent, as indicated on the face of such new Note, the Principal remaining outstanding (or in the case of a new Note being issued pursuant to Section 17(a) or Section 17(c), the Principal designated by the Holder which, when added to the principal represented by the other new Notes issued in connection with such issuance, does not exceed the Principal remaining outstanding under this Note immediately prior to such issuance of new Notes), (iii) shall have an issuance date, as indicated on the face of such new Note which is the same as the Issuance Date of this Note, (iv) shall have the same rights and conditions as this Note, and (v) shall represent accrued and unpaid Interest of this Note from the Issuance Date.

(18) REMEDIES, CHARACTERIZATIONS, OTHER OBLIGATIONS, BREACHES AND INJUNCTIVE RELIEF. The remedies provided in this Note shall be cumulative and in addition to all other remedies available under this Note and any of the other Transaction Documents, at law or in equity (including a decree of specific performance and/or other injunctive relief), and nothing herein shall limit the Holder’s right to pursue actual and consequential damages for any failure by the Company to comply with the terms of this Note. Amounts set forth or provided for herein with respect to payments, conversion and the like (and the computation thereof) shall be the amounts to be received by the Holder and shall not, except as expressly provided herein, be subject to any other obligation of the Company (or the performance thereof). The Company acknowledges that a breach by it of its obligations hereunder will cause irreparable harm to the Holder and that the remedy at law for any such breach may be inadequate. The Company therefore agrees that, in the event of any such breach or threatened breach, the Holder shall be entitled, in addition to all other available remedies, to an injunction restraining any breach, without the necessity of showing economic loss and without any bond or other security being required.

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(19) PAYMENT OF COLLECTION, ENFORCEMENT AND OTHER COSTS. If (a) this Note is placed in the hands of an attorney for collection or enforcement or is collected or enforced through any legal proceeding or the Holder otherwise takes action to collect amounts due under this Note or to enforce the provisions of this Note or (b) there occurs any bankruptcy, reorganization, receivership of the Company or other proceedings affecting Company creditors’ rights and involving a claim under this Note, then the Company shall pay the costs incurred by the Holder for such collection, enforcement or action or in connection with such bankruptcy, reorganization, receivership or other proceeding, including, but not limited to, attorneys’ fees and disbursements.

(20) CONSTRUCTION; HEADINGS. This Note shall be deemed to be jointly drafted by the Company and all the Purchasers and shall not be construed against any person as the drafter hereof. The headings of this Note are for convenience of reference and shall not form part of, or affect the interpretation of, this Note.

(21) FAILURE OR INDULGENCE NOT WAIVER. No failure or delay on the part of the Holder in the exercise of any power, right or privilege hereunder shall operate as a waiver thereof, nor shall any single or partial exercise of any such power, right or privilege preclude other or further exercise thereof or of any other right, power or privilege.

(22) DISPUTE RESOLUTION. In the case of a dispute as to the determination of the Closing Bid Price, the Closing Sale Price, the Weighted Average Price, the Redemption Price or the arithmetic calculation of the Conversion Rate, Antigenics MA Conversion Rate or the Redemption Price, the Company shall submit the disputed determinations or arithmetic calculations via facsimile within one (1) Business Day of receipt, or deemed receipt, of the Conversion Notice or the Redemption Notice or other event giving rise to such dispute, as the case may be, to the Holder. If the Holder and the Company are unable to agree upon such determination or calculation of the Redemption Price or the Conversion Rate, as applicable, within one (1) Business Day of such disputed determination or arithmetic calculation being submitted to the Holder, then the Company shall, within one (1) Business Day submit via facsimile (a) the disputed determination of the Closing Bid Price, the Closing Sale Price or the Weighted Average Price to an independent, reputable investment bank selected by the Company and approved by the Holder or (b) the disputed arithmetic calculation of the Conversion Rate or the Redemption Price to the Company’s independent, outside accountant. The Company, at the Company’s expense, shall cause the investment bank or the accountant, as the case may be, to perform the determinations or calculations and notify the Company and the Holder of the results no later than five (5) Business Days from the time it receives the disputed determinations or calculations. Such investment bank’s or accountant’s determination or calculation, as the case may be, shall be binding upon all parties absent demonstrable error. To the extent of a good faith dispute by the Company, any related penalty payments due hereunder shall not be made until such dispute is resolved.

(23) NOTICES; PAYMENTS.

(a) Notices. Whenever notice is required to be given under this Note, unless otherwise provided herein, such notice shall be given in accordance with Section 9(f) of the Securities Purchase Agreement. The Company shall provide the Holder with prompt written notice of all actions taken pursuant to this Note, including in reasonable detail a description of

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such action and the reason therefore. Without limiting the generality of the foregoing, the Company will give written notice to the Holder (i) immediately upon any adjustment of the Conversion Price or Antigenics MA Conversion Rate, setting forth in reasonable detail, and certifying, the calculation of such adjustment and (ii) at least fifteen (15) days prior to the date on which the Company closes its books or takes a record (A) with respect to any dividend or distribution upon the Company Common Stock, (B) with respect to any pro rata subscription offer to holders of Company Common Stock or (C) for determining rights to vote with respect to any Fundamental Transaction, dissolution or liquidation, provided in each case that such information shall be made known to the public prior to or in conjunction with such notice being provided to the Holder.

(b) Payments. Whenever any payment of cash is to be made by the Company to any Person pursuant to this Note, such payment shall be made in lawful money of the United States of America by a check drawn on the account of the Company and sent via overnight courier service to such Person at such address as previously provided to the Company in writing (which address, in the case of each of the Purchasers shall initially be as set forth on the Schedule of Buyers attached to the Securities Purchase Agreement); provided that the Holder may elect to receive a payment of cash via wire transfer of immediately available funds by providing the Company with prior written notice setting out such request and the Holder’s wire transfer instructions. Whenever any amount expressed to be due by the terms of this Note is due on any day which is not a Business Day, the same shall instead be due on the next succeeding day which is a Business Day and, in the case of any Interest Date which is not the date on which this Note is paid in full, the extension of the due date thereof shall not be taken into account for purposes of determining the amount of Interest due on such date.

(24) CANCELLATION. After all Principal, accrued Interest and other amounts at any time owed on this Note have been paid in full, this Note shall automatically be deemed canceled, shall be surrendered to the Company for cancellation and shall not be reissued.

(25) WAIVER OF NOTICE. To the extent permitted by law, the Company hereby waives demand, notice, protest and all other demands and notices in connection with the delivery, acceptance, performance, default or enforcement of this Note and the Securities Purchase Agreement.

(26) NO PERSONAL LIABILITY. None of the Company’s past, present or future directors, officers, employees or stockholders, as such, shall have any liability for any of the Company’s obligations under this Note or for any claim based on, or in respect or by reason of, such obligations or their creation. Except as otherwise provided by applicable law, by accepting this Note, the Holder waives and releases all such liability and such waiver and release is part of the consideration for the issue of this Note.

(27) CONFIDENTIALITY. At no time will a party, without the prior written consent of any other party, make any press releases or public announcements concerning this Note; provided, however, that any party may make any public disclosure required by applicable law or any listing or trading agreement concerning its publicly traded securities (in which case the disclosing party will use its best efforts to advise the other parties prior to making the disclosure). Each party shall keep confidential any and all information obtained in connection with this Note and shall not disclose any such information to any other Person except: (a) with

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the prior written consent of the other party; (b) as required by law, regulation, or court order, but only after notice has been provided to such other party; or (c) for such information as shall have been publicly disclosed other than in violation of this Note or of any other obligation of confidentiality to such other party.

(28) GOVERNING LAW. This Note shall be construed and enforced in accordance with, and all questions concerning the construction, validity, interpretation and performance of this Note shall be governed by, the internal laws of the State of New York, without giving effect to any choice of law or conflict of law provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York.

(29) CERTAIN DEFINITIONS. For purposes of this Note, the following terms shall have the following meanings:

(a) “AG-707” means an investigational therapeutic vaccine for the treatment of genital herpes consisting of recombinant heat shock proteins complexed with multiple peptides derived from herpes simplex 2 virus.

(b) “Antigenics MA” means Antigenics Inc., a Massachusetts corporation.

(c) “Antigenics MA Stock” means up to a thirty percent (30%) interest in Antigenics MA.

(d) “Approved Stock Plan” means any employee benefit plan, contract or arrangement which has been, or is in the future, approved by the Company Board of Directors, including a committee thereof, pursuant to which the Company’s securities may be issued to employees, consultants, officers or directors.

(e) “Bloomberg” means Bloomberg Financial Markets.

(f) “Business Day” means any day other than Saturday, Sunday or other day on which commercial banks in The City of New York are authorized or required by law to remain closed.

(g) “Change of Control” means any (i) Fundamental Transaction other than (A) a Fundamental Transaction in which holders of the Company’s voting power immediately prior to the Fundamental Transaction continue after the Fundamental Transaction to hold publicly traded securities and, directly or indirectly, the voting power of the surviving entity or entities necessary to elect a majority of the members of the board of directors (or their equivalent if other than a corporation) of such entity or entities, (B) pursuant to a migratory merger effected solely for the purpose of changing the jurisdiction of incorporation of the Company or (C) the majority of the Company Board of Directors in place prior to a Fundamental Transaction remains the majority of the Company Board of Directors following such Fundamental Transaction, (ii) a change within any 12-month period of a majority of the Company Board of Directors of the Company in connection with the acquisition by a Person (or Persons acting in concert) of 30% or more of the Company Common Stock; or (iii) an amalgamation or arrangement whereby Company Common Stock ceases to exist and a Person (or Persons acting jointly or in concert) acquire control of the Company.

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(h) “Closing Bid Price” and “Closing Sale Price” means, for any security as of any date, the last closing bid price and last closing trade price, respectively, for such security on the Principal Market, as reported by Bloomberg, or, if the Principal Market begins to operate on an extended hours basis and does not designate the closing bid price or the closing trade price, as the case may be, then the last bid price or last trade price, respectively, of such security prior to 4:00 p.m., New York Time, as reported by Bloomberg, or, if the Principal Market is not the principal securities exchange or trading market for such security, the last closing bid price or last trade price, respectively, of such security on the principal securities exchange or trading market where such security is listed or traded as reported by Bloomberg, or if the foregoing do not apply, the last closing bid price or last trade price, respectively, of such security in the over-the-counter market on the electronic bulletin board for such security as reported by Bloomberg, or, if no closing bid price or last trade price, respectively, is reported for such security by Bloomberg, the average of the bid prices, or the ask prices, respectively, of any market makers for such security as reported in the “pink sheets” by Pink Sheets LLC (formerly the National Quotation Bureau, Inc.). If the Closing Bid Price or the Closing Sale Price cannot be calculated for a security on a particular date on any of the foregoing bases, the Closing Bid Price or the Closing Sale Price, as the case may be, of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved pursuant to Section 22. All such determinations to be appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction during the applicable calculation period.

(i) “Closing Date” shall have the meaning set forth in the Securities Purchase Agreement, which date is the date the Company initially issued Notes pursuant to the terms of the Securities Purchase Agreement.

(j) “Company Board of Directors” means the board of directors of the Company or any authorized committee of the board of directors.

(k) “Company Election Date” means three Company Trading Days prior to the Maturity Date.

(l) “Company Trading Day” means any day on which the Company Common Stock is traded on the Principal Market, or, if the Principal Market is not the principal trading market for the Company Common Stock, then on the principal securities exchange or securities market on which the Company Common Stock is then traded; provided that “Company Trading Day” shall not include any day on which the Company Common Stock is scheduled to trade on such exchange or market for less than 4.5 hours or any day that the Company Common Stock is suspended from trading during the final hour of trading on such exchange or market (or if such exchange or market does not designate in advance the closing time of trading on such exchange or market, then during the hour ending at 4:00 p.m., New York Time).

(m) “Conversion Amount” means the amount of (A) the portion of the Principal to be converted, redeemed or otherwise with respect to which this determination is made, and (B) accrued and unpaid Interest with respect to such Principal.

(n) “Conversion Date” means the date on which any Conversion Amount is converted into shares of Company Common Stock.

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(o) “Convertible Securities” means with respect to any issuer, any stock or securities (other than Options) directly or indirectly convertible into or exercisable or exchangeable for such issuer’s common stock.

(p) “Eligible Market” means the Principal Market, The New York Stock Exchange, Inc. or The Nasdaq SmallCap Market.

(q) “Excluded Securities” means any Company Common Stock issued or issuable: (i) in connection with any Approved Stock Plan; (ii) upon conversion of the Notes; (iii) pursuant to a bona fide firm commitment underwritten public offering with an institution that regularly underwrites as a principal part of its business public offerings on a firm commitment basis which generates gross proceeds to the Company in excess of $15,000,000 (other than an “at-the-market offering” as defined in Rule 415(a)(4) under the 1933 Act and “equity lines”); (iv) securities issued in connection with corporate partnering transactions on terms approved by the Board of Directors of the Company and the primary purpose of which is not to raise equity capital; (v) in connection with a strategic licensing arrangement, corporate partnering transaction or similar collaboration and (vi) upon conversion of any Options or Convertible Securities which are outstanding on the day immediately preceding the Issuable Date, provided that the terms of such Options or Convertible Securities are not amended, modified or changed on or after the Issuable Date to decrease the price, increase the number of shares issuable thereunder or extend the term of such Options or Convertible Securities; issued or issuable upon conversion of the Notes.

(r) “Fundamental Transaction” means that the Company shall, directly or indirectly, in one or more related transactions, (i) consolidate or merge with or into (whether or not the Company is the surviving corporation) another Person, or (ii) sell, assign, transfer, convey or otherwise dispose of all or substantially all of the properties or assets of the Company to another Person, or (iii) allow another Person to make a purchase, tender or exchange offer that is accepted by the holders of more than the 50% of the outstanding shares of Company Common Stock (not including any shares of Company Common Stock held by the Person or Persons making or party to, or associated or affiliated with the Persons making or party to, such purchase, tender or exchange offer), or (iv) consummate a stock purchase agreement or other business combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) with another Person whereby such other Person acquires up to 50% of the outstanding shares of Company Common Stock not including any shares of Company Common Stock held by the other Person or other Persons making or party to, or associated or affiliated with the other Persons making or party to, such stock purchase agreement or other business combination), or (v) reorganize, recapitalize or reclassify its Company Common Stock.

(s) “GSK” means GlaxoSmithKline Biologicals SA, a Belgian company, having an address at 89 rue de l’Institut, 1330 Rixensart Belgium.

(t) “Interest Rate” means eight percent (8.0%) per annum.

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(u) “Issuance Date” means [            ]     , 200  .

(v) “Maturity Date” means August 30, 2011, as extended at the option of the Holder.

(w) “Options” means with respect to any issuer, any rights, warrants or options to subscribe for or purchase such issuer’s common stock or such issuer’s Convertible Securities.

(x) “Parent Entity” of a Person means an entity that, directly or indirectly, controls the applicable Person and whose common stock or equivalent equity security is quoted or listed on an Eligible Market, or, if there is more than one such Person or Parent Entity, the Person or Parent Entity with the largest public market capitalization as of the date of consummation of the Fundamental Transaction.

(y) “Permitted Indebtedness” means (A) Indebtedness incurred by the Company that is made expressly subordinate in right of payment to the Indebtedness evidenced by this Note, as reflected in a written agreement acceptable to the Holder and approved by the Holder in writing, and which Indebtedness does not provide at any time for (1) the payment, prepayment, repayment, repurchase or defeasance, directly or indirectly, of any principal or premium, if any, thereon until ninety-one (91) days after the Maturity Date or later and (2) total interest and fees at a rate in excess of six percent (6%) per annum, (B) up to $5 million of aggregate Indebtedness, (C) up to $12,000,000 in Indebtedness for the sole purpose of financing an exclusive manufacturing facility for QS-21, (D) Indebtedness secured by Permitted Liens, (E) Indebtedness to trade creditors incurred in the ordinary course of business, (F) Permitted Non-Recourse Indebtedness, (G) any Indebtedness listed on Schedule 3(p) of the Securities Purchase Agreement and (H) extensions, refinancings and renewals of any items of Permitted Indebtedness, provided that the principal amount is not increased or the terms modified to impose more burdensome terms upon the Company or its Subsidiary, as the case may be.

(z) “Permitted Investments” means (A) investments outstanding on the Closing Date and identified on Schedule 14(d), (B) accounts receivables owing to either the Company or Antigenics MA, (C) investment in cash or Cash Equivalents, (D) negotiable instruments held for collection in the ordinary course of business, (E) loans and advances, in the ordinary course of business, to directors, employees and officers of the Company, (F) intercompany loans between the Company and any Subsidiary, (G) investments in securities of trade creditors or customers in the ordinary course of business, and (H) other Investments in an aggregate amount not to exceed $7,500,000 at any time outstanding.

(aa) “Permitted Liens” means (i) any Lien for taxes not yet due or delinquent or being contested in good faith by appropriate proceedings for which adequate reserves have been established in accordance with GAAP, (ii) any statutory Lien arising in the ordinary course of business by operation of law with respect to a liability that is not yet due or delinquent, (iii) any Lien created by operation of law, such as materialmen’s liens, mechanics’ liens and other similar liens, arising in the ordinary course of business with respect to a liability that is not yet due or delinquent or that are being contested in good faith by appropriate proceedings, (iv) Liens securing the Company’s obligations under the Notes, (v) Liens (A) upon or in any equipment acquired or held by the Company or any of its Subsidiaries to secure the purchase price of such equipment or indebtedness incurred solely for the purpose of financing the acquisition or lease of

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such equipment, or (B) existing on such equipment at the time of its acquisition, provided that the Lien is confined solely to the property so acquired and improvements thereon, and the proceeds of such equipment, (vi) Liens incurred in connection with the extension, renewal or refinancing of the indebtedness secured by Liens of the type described in clauses (i) and (v) above, provided that any extension, renewal or replacement Lien shall be limited to the property encumbered by the existing Lien and the principal amount of the Indebtedness being extended, renewed or refinanced does not increase, (vii) leases or subleases and licenses and sublicenses granted to others in the ordinary course of the Company’s business, not interfering in any material respect with the business of the Company and its Subsidiaries taken as a whole, (viii) Liens in favor of customs and revenue authorities arising as a matter of law to secure payments of custom duties in connection with the importation of goods, (ix) Lien securing Permitted Indebtedness, and (x) Liens arising from judgments, decrees or attachments in circumstances not constituting an Event of Default under Section 4(a)(iv).

(bb) “Person” means an individual, a limited liability company, a partnership, a joint venture, a corporation, a trust, an unincorporated organization, any other entity and a government or any department or agency thereof.

(cc) “Pledge and Security Agreement” means that certain Pledge and Security Agreement, dated as of the Issuance Date, made by the Company in favor of the Holder.

(dd) “Pledged Collateral” has the meaning ascribed to such term in the Pledge and Security Agreement.

(ee) “Principal Market” means the Nasdaq National Market.

(ff) “QS-21” means [a substantially pure saponin adjuvant isolated from crude Quillaja saponaria tree extract and referred to as QS-21, a Stimulonâ adjuvant.

(gg) “Redemption Notice” means any of an Event of Default Redemption Notice or Holder Change of Control Redemption Notice .

(hh) “Redemption Price” means any of an Event of Default Redemption Price or Holder Change of Control Redemption Price.

(ii) “Required Holders” means the holders of Notes representing at least a majority of the aggregate principal amount of the Notes then outstanding.

(jj) “SEC” means the United States Securities and Exchange Commission.

(kk) “Securities Purchase Agreement” means that certain securities purchase agreement, dated as of the date hereof, by and among the Company and the initial holders of the Notes pursuant to which the Company issued the Notes.

(ll) “Subsidiary” means any Person of which the Company (or other specified Person) shall at the time, directly or indirectly through one or more of its Subsidiaries, (a) own at least 50% of the outstanding capital stock (or other shares of beneficial interest) entitled to vote generally, (b) hold at least 50% of the partnership, joint venture or similar interests or (c) be general partner or joint venturer.

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(mm) “Successor Entity” means the Person, which may be the Company, formed by, resulting from or surviving any Fundamental Transaction or the Person with which such Fundamental Transaction shall have been made, provided that if such Person is not a publicly traded entity whose common stock or equivalent equity security is quoted or listed for trading on an Eligible Market, Successor Entity shall mean such Person’s Parent Entity.

(nn) “Transaction Documents” has the meaning ascribed to such term in the Securities Purchase Agreement.

(oo) “Transfer Agent” means the Company’s transfer agent.

(pp) “Weighted Average Price” means, for any security as of any date, the dollar volume-weighted average price for such security on the Principal Market during the period beginning at 9:30:01 a.m., New York Time (or such other time as the Principal Market publicly announces is the official open of trading), and ending at 4:00:00 p.m., New York Time (or such other time as the Principal Market publicly announces is the official close of trading) as reported by Bloomberg through its “Volume at Price” functions, or, if the foregoing does not apply, the dollar volume-weighted average price of such security in the over-the-counter market on the electronic bulletin board for such security during the period beginning at 9:30:01 a.m., New York Time (or such other time as such market publicly announces is the official open of trading), and ending at 4:00:00 p.m., New York Time (or such other time as such market publicly announces is the official close of trading) as reported by Bloomberg, or, if no dollar volume-weighted average price is reported for such security by Bloomberg for such hours, the average of the highest closing bid price and the lowest closing ask price of any of the market makers for such security as reported in the “pink sheets” by Pink Sheets LLC (formerly the National Quotation Bureau, Inc.). If the Weighted Average Price cannot be calculated for a security on a particular date on any of the foregoing bases, the Weighted Average Price of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved pursuant to Section 22. All such determinations to be appropriately adjusted for any stock dividend, stock split, stock combination or other similar transaction during the applicable calculation period.

(qq) “Interest Period” means, initially, the period beginning on and including the Issuance Date and ending on and including [June 30/December 30], 200_ and each successive period as follows: the period beginning on and including [December 31/July 1] and ending on and including [June 30/December 30]; the period beginning on and including [December 31/July 1] and ending on and including [June 30/December 30].

(30) SECURITY. The Notes shall be secured by and to the extent provided in the Pledge and Security Agreement.

[Signature Page Follows]

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IN WITNESS WHEREOF, the Company has caused this Note to be duly executed as of the Issuance Date set out above.

ANTIGENICS INC.

By:

Name:

Title:

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EXHIBIT I

ANTIGENICS INC.

CONVERSION NOTICE

TO BE EXECUTED BY THE REGISTERED HOLDER TO CONVERT THIS NOTE

INTO COMMON STOCK

Reference is made to the Senior Secured Convertible Note (the “Note”) issued to the undersigned by Antigenics Inc. (the “Company”). In accordance with and pursuant to the Note, the undersigned hereby elects to convert the Conversion Amount (as defined in the Note) of the Note indicated below into shares of Company Common Stock, par value $.01 per share (the “Company Common Stock”), of the Company as of the date specified below.

            Date of Conversion:

            Aggregate Conversion Amount to be converted:

Notwithstanding anything to the contrary contained herein, this Conversion Notice shall constitute a representation by the holder of the Note submitting this Conversion Notice that, after giving effect to the conversion provided for in this Conversion Notice, such holder (together with its affiliates) will not have beneficial ownership (together with the beneficial ownership of such Person’s affiliates) of a number of shares of Company Common Stock which exceeds the maximum percentage of the total outstanding shares of Company Common Stock as determined pursuant to the provisions of Section 2(g)(i) of the Note.

Please confirm the following information:

            Conversion Price:

            Number of shares of Company Common Stock to be issued:

Please issue the Company Common Stock into which the Note is being converted in the following name and to the following address:

            Issue to:

            Facsimile Number:

            Authorization:

                    By:

                    Title:

Dated:

Account Number:

  (if electronic book entry transfer)

Transaction Code Number:

  (if electronic book entry transfer)

ACKNOWLEDGMENT

The Company hereby acknowledges this Conversion Notice and hereby directs [INSERT TRANSFER AGENT NAME] to issue the above indicated number of shares of Company Common Stock in accordance with the Transfer Agent Instructions dated October             , 2006 from the Company and acknowledged and agreed to by [INSERT TRANSFER AGENT NAME].

ANTIGENICS INC.

By:

Name:

Title:

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Schedule 14(c)

Restricted Payments

1. The Company owes $1,065,800 as debt to General Electric Corporation.

2. The Company may owe a capital call of $375,000 to Applied Genomic Technology Capital Fund.

3. Antigenics MA owes $146,061 in the form of subordinated debentures plus accrued interest of $51,590.

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Schedule 14(d)

Permitted Investments

1. The Company may owe a capital call of $375,000 to Applied Genomic Technology Capital Fund.

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EX-4.3

Exhibit 4.3

EXECUTION COPY

PLEDGE AND SECURITY AGREEMENT

This Agreement, dated as of October 30, 2006 is between Antigenics Inc., a Delaware corporation (the “Pledgor”), and Ingalls & Snyder LLC, as agent (the “Agent”) for itself and the other Buyers under the Securities Purchase Agreement (as defined below). The parties agree as follows:

1. Securities Purchase Agreement; Certain Rules of Construction; Definitions. The Agent and the Buyers are purchasing senior secured convertible notes of the Pledgor (the “Notes”) pursuant to a Securities Purchase Agreement dated as of the date hereof, as from time to time in effect (the “Securities Purchase Agreement”), among the Pledgor, the Buyers and the Agent. As a condition to purchasing the Notes, the Buyers are requiring the Pledgor to pledge the stock and indebtedness contemplated hereby to secure the payment of the Credit Obligations. Capitalized terms defined in the Securities Purchase Agreement and not otherwise defined herein are used herein with the meanings so defined. Certain other capitalized terms are used in this Agreement as specifically defined below in this Section 1. Except as the context otherwise explicitly requires, (a) the capitalized term “Section” refers to sections of this Agreement, (b) the capitalized term “Exhibit” refers to exhibits to this Agreement, (c) references to a particular Section shall include all subsections thereof, (d) the word “including” shall be construed as “including without limitation”, (e) terms defined in the UCC and not otherwise defined herein have the meaning provided under the UCC, (f) references to a particular statute or regulation include all rules and regulations thereunder and any successor statute, regulation or rules, in each case as from time to time in effect and (g) references to a particular Person include such Person’s successors and assigns to the extent not prohibited by this Agreement and the other Transaction Documents. References to “the date hereof” mean the date first set forth above.

“AG-707” means an investigational therapeutic vaccine for the treatment of genital herpes consisting of recombinant heat shock proteins complexed with multiple peptides derived from herpes simplex 2 virus.

“Agreement” means this Pledge and Security Agreement as amended, modified and from time to time in effect.

“Antigenics MA” refers to Antigenics Inc., a Massachusetts corporation.

“Credit Obligations” means all present and future liabilities, obligations and Indebtedness of the Pledgor, any of its Subsidiaries owing to the Agent or any Buyer under or in connection with this Agreement or any other Transaction Document, including obligations in respect of principal and interest and other fees, charges, indemnities and expenses from time to time owing hereunder or under any other Transaction Document.

“Credit Security” is defined in Section 2.1.

“Event of Default” is defined in Section 4(a) of the Note.

“Foreign Subsidiary” means each Subsidiary that is organized under the laws of, and conducting its business primarily in a jurisdiction outside of, the United States of America and that is not domesticated or dually incorporated under the laws of the United States of America or the states thereof.

“Lien” mean shall mean any mortgage, deed of trust, pledge, hypothecation, assignment, security interest, lien (whether statutory or otherwise), charge, claim or encumbrance, or preference, priority or other security agreement or preferential arrangement held or asserted in respect of any asset of any kind or nature whatsoever including, without limitation, any conditional sale or other title retention agreement, any lease having substantially the same economic effect as any of the foregoing, and the filing of, or agreement to give, any financing statement under the UCC.

“Margin Stock” means “margin stock” within the meaning of Regulations T, U or X of the Board of Governors of the Federal Reserve System.

“Pledged Indebtedness” is defined in Section 2.1.3.

“Pledged Rights” is defined in Section 2.1.2.

“Pledged Securities” means all Pledged Stock, all Pledged Rights, all Pledged Indebtedness and the investment property described in Section 2.1.4.

“Pledged Stock” is defined in Section 2.1.1.

“QS-21” is defined in Section 29 (ee) of the Note.

“Securities Act” means the federal Securities Act of 1933.

“Subsidiary” means any Person of which Antigenics MA (or other specified Person) shall at the time, directly or indirectly through one or more of its Subsidiaries, (a) own at least 50% of the outstanding capital stock (or other shares of beneficial interest) entitled to vote generally, (b) hold at least 50% of the partnership, joint venture or similar interests or (c) be a general partner or joint venturer.

“UCC” means the Uniform Commercial Code as in effect in Massachusetts on the date hereof; provided, however, that with respect to the perfection of the Agent’s Lien on the Credit Security and the effect of nonperfection thereof, the term “UCC” means the Uniform Commercial Code as in effect in any jurisdiction the laws of which are made applicable by section 9-301 of the Uniform Commercial Code as in effect in Massachusetts.

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2. Security.

2.1. Credit Security. As security for the payment and performance of the Credit Obligations, the Pledgor mortgages, pledges and collaterally grants and assigns to the Agent for the benefit of the Buyers and the holders from time to time of any Credit Obligation, and creates a security interest in favor of the Agent for the benefit of the Buyers and such holders in all of the Pledgor’s right, title and interest in and to (but none of its obligations or liabilities with respect to) the items and types of present and future property described in Sections 2.1.1 through 2.1.5 (subject, however, to Section 2.1.6), whether now owned or hereafter acquired, all of which shall be included in the term “Credit Security”:

2.1.1. Pledged Stock. (a) All shares of capital stock, limited partnership interests, general partnership interests, member interests or other evidence of beneficial interest in Antigenics MA and (b) all options, warrants and similar rights to acquire such capital stock or such interests. All such capital stock, interests, options, warrants and other rights are collectively referred to as the “Pledged Stock”.

2.1.2. Pledged Rights. All rights to receive profits or surplus of, or other distributions (including income, return of capital and liquidating distributions) from any partnership, joint venture or limited liability company that constitutes a Subsidiary of Antigenics MA, including any distributions by any such Person to partners, joint venturers or members. All such rights are collectively referred to as the “Pledged Rights”.

2.1.3. Pledged Indebtedness. All Indebtedness from time to time owing to the Pledgor from Antigenics MA. All such Indebtedness is referred to as the “Pledged Indebtedness”.

2.1.4. Investment Property. All other investment property issued by Antigenics MA.

2.1.5. Proceeds and Products. All proceeds and products of the items of Credit Security described or referred to in Section 2.1.1 through 2.1.4 and, to the extent not included in the foregoing, all distributions with respect to the Pledged Securities.

2.1.6. Excluded Property. Notwithstanding Sections 2.1.1 through 2.1.5, the payment and performance of the Credit Obligations shall not be secured by:

(a) any rights or property to the extent that any valid and enforceable law or regulation applicable to such rights or property prohibits the creation of a security interest therein; provided, however, that the provisions of this Section 2.1.6 shall not prohibit the security interests created by this Agreement from extending to the proceeds of such rights or property or to the monetary value of the good will and other general intangibles of the Pledgor relating thereto; or

(b) Margin Stock unless the applicable requirements of Regulations T, U and X of the Board of Governors of the Federal Reserve System have been satisfied.

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2.2. Covenants with Respect to Credit Security. The Pledgor covenants that:

2.2.1. Pledged Stock. All shares of capital stock, limited partnership interests, membership interests and similar securities included in the Pledged Stock shall be at all times duly authorized, validly issued, fully paid and (in the case of capital stock and limited partnership interests) nonassessable. The Pledgor will deliver to the Agent certificates representing any Pledged Stock held by the Pledgor from time to time, accompanied by a stock transfer power executed in blank and, if the Agent so requests, with the signature guaranteed, all in form and manner reasonably satisfactory to the Agent. Pledged Stock that is not evidenced by a certificate held by the Pledgor will be described in appropriate control statements and UCC financing statements provided to the Agent, all in form and substance reasonably satisfactory to the Agent. In the event the Pledged Stock includes uncertificated equity interests in a limited liability company, limited partnership, general partnership or other entity, except with the prior written consent of the Agent, which consent may not be unreasonably withheld, the Pledgors shall take all action within their power to prevent such limited liability company, limited partnership, general partnership or other entity from (a) opting to have such uncertificated equity interests treated as “securities” for purposes of Article 8 of the UCC or (b) issuing certificates for such uncertificated equity interests. Upon the occurrence and during the continuance of an Event of Default, the Agent may transfer into its name or the name of its nominee any Pledged Stock. In the event the Pledged Stock includes any Margin Stock, the Pledgor will furnish to the Buyers Federal Reserve Form U-1 and take such other action as the Agent may request to ensure compliance with applicable laws.

2.2.2. Pledged Indebtedness. The Pledgor will, immediately upon the receipt thereof, deliver to the Agent any promissory note or similar instrument representing any Pledged Indebtedness from time to time, after having endorsed such promissory note or instrument in blank.

2.2.3. No Liens or Restrictions on Transfer or Change of Control. All Credit Security shall be free and clear of any Liens and restrictions on the transfer thereof, except for restrictions on transfer permitted by this Section 2.2.3. None of the Pledged Stock shall be subject to any option to purchase or similar rights of any Person. Except with the written consent of the Agent, the Pledgor will in good faith attempt to exclude from any agreement, instrument, deed or lease provisions that would restrict (a) the change of control or ownership of Antigenics MA or (b) the creation of a security interest in the ownership of Antigenics MA.

2.2.4. Issuance of Stock by Antigenics MA. The Pledgor shall cause Antigenics MA not to issue or sell any shares of its capital stock or other evidence of beneficial ownership to any Person other than the Pledgor, who shall take all steps reasonably necessary to perfect the Agent’s security interest therein as provided hereunder.

2.2.5. No Sale of Credit Security. The Pledgor will not sell, transfer or otherwise dispose of all or any portion of its interests in the Credit Security (except to the Agent as contemplated hereby).

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2.2.6. Perfection of Credit Security. This Agreement shall create in favor of the Agent, for the benefit of the Buyers, a legal, valid and enforceable first priority security interest in the Credit Security described herein. In the case of the Pledged Stock, when stock certificates representing such Pledged Stock and stock powers related thereto duly executed in blank by the Pledgor are delivered to the Agent, and in the case of the other Credit Security described in this Agreement, when financing statements in appropriate form are filed in Delaware, this Agreement shall provide a fully perfected, first priority Lien on, and security interest in, all right, title and interest of the Pledgor in such Credit Security, in each case prior and superior in right to any other Person. Upon the Agent’s reasonable request from time to time, the Pledgor will execute and deliver, and file and record in the proper filing and recording places, all such documents, and will take all such other action, as the Agent deems reasonably necessary for confirming to it the Credit Security or to carry out any other purpose of this Agreement or any other Transaction Document. The Agent may at any time and from time to time file UCC financing statements, continuation statements and amendments thereto that describe the Credit Security and contain any information required by the UCC or the applicable filing office with respect to any such UCC financing statement, continuation statement or amendment thereof.

2.2.7. Spin-off Exception. Notwithstanding Sections 2.2.1 through 2.2.6., the Pledgor may consummate a stock purchase agreement or other business combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) with another Person or Persons whereby such other Person or Persons acquire up to 49.99% of the outstanding shares of Antigenics MA (“Spin-off”) and such shares shall thereafter be free of any pledge obligations to Buyers under this Agreement; provided, however, the first ten million dollars ($10,000,000) of the proceeds from any such Spin-off will fund the development and commercialization activities related to QS-21 and AG-707 and/or general corporate purposes.

2.3. Administration of Credit Security. The Credit Security shall be administered as follows, and if an Event of Default shall have occurred and be continuing, Section 2.4 shall also apply.

2.3.1. Segregated Proceeds. To the extent specified by prior written notice from the Agent, whether prior to or after the occurrence and continuance of an Event of Default, all sums collected or received and all property recovered or possessed by the Pledgor in connection with any Credit Security shall be received and held by the Pledgor in trust for and on the Buyers’ behalf, shall be segregated from the assets and funds of the Pledgor, and shall be delivered to the Agent for the benefit of the Buyers.

2.3.2. Distributions.

(a) Until an Event of Default shall occur and be continuing, the Pledgor shall be entitled to receive all distributions on or with respect to the Pledged Stock (other than distributions constituting additional Pledged Stock and liquidating distributions). All distributions constituting additional Pledged Stock or liquidating distributions will be

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retained by the Agent (or if received by the Pledgor shall be held by the Pledgor in trust and shall be immediately delivered by the Pledgor to the Agent in the original form received, endorsed in blank) and held by the Agent as part of the Credit Security.

(b) If an Event of Default shall have occurred and be continuing, all distributions on or with respect to the Pledged Stock shall be retained by the Agent (or if received by the Pledgor shall be held by such Person in trust and shall be immediately delivered by it to the Agent in the original form received, endorsed in blank) and held by the Agent as part of the Credit Security or applied by the Agent to the payment of the Credit Obligations in accordance with Section 2.4.5.

2.3.3. Voting.

(a) Until an Event of Default shall occur and be continuing, the Pledgor shall be entitled to vote or consent with respect to the Pledged Stock in any manner not inconsistent with the terms of any Transaction Document, and the Agent will, if so requested, execute appropriate revocable proxies therefor.

(b) If an Event of Default shall have occurred and be continuing, if and to the extent that the Agent shall so notify the Pledgor in writing, only the Agent shall be entitled to vote or consent or take any other action with respect to the Pledged Stock (and the Pledgor will, if so requested, execute or cause to be executed appropriate proxies therefor).

2.4. Right to Realize upon Credit Security. Except to the extent prohibited by applicable law that cannot be waived, this Section 2.4 shall govern the Buyers’ right to realize upon the Credit Security if any Event of Default shall have occurred and be continuing. The provisions of this Section 2.4 are in addition to any rights and remedies available at law or in equity and in addition to the provisions of any other Transaction Document. In the case of a conflict between this Section 2.4 and any other Transaction Document, this Section 2.4 shall govern.

2.4.1. General Authority. To the extent specified in written notice from the Agent to the Pledgor, the Pledgor grants the Agent full and exclusive power and authority, subject to the other terms hereof and applicable law, to take any of the following actions (for the sole benefit of the Agent on behalf of the Buyers and the holders from time to time of any Credit Obligations, but at the Pledgor’s expense):

(a) To ask for, demand, take, collect, sue for and receive all payments in respect of any Pledged Securities which the Pledgor could otherwise ask for, demand, take, collect, sue for and receive for its own use.

(b) To extend the time of payment of any Pledged Securities and to make any allowance or other adjustment with respect thereto.

(c) To settle, compromise, prosecute or defend any action or proceeding with respect to any Pledged Securities and to enforce all rights and remedies thereunder which the Pledgor could otherwise enforce.

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(d) To enforce the payment of any Pledged Securities, either in the name of the Pledgor or in its own name, and to endorse the name of the Pledgor on all checks, drafts, money orders and other instruments tendered to or received in payment of any Pledged Securities.

(e) To notify the issuer with respect to any Pledged Securities of the existence of the security interest created hereby and to cause all payments in respect thereof thereafter to be made directly to the Agent; provided, however, that whether or not the Agent shall have so notified such issuer, the Pledgor will at its expense render all reasonable assistance to the Agent in collecting such items and in enforcing claims thereon.

(f) To sell, transfer, assign or otherwise deal in or with any Credit Security or the proceeds thereof, as fully as the Pledgor otherwise could do.

2.4.2. Marshaling, etc. Neither the Agent nor the Buyers shall be required to make any demand upon, or pursue or exhaust any of their rights or remedies against, the Pledgor or any other guarantor, pledgor or any other Person with respect to the payment of the Credit Obligations or to pursue or exhaust any of their rights or remedies with respect to any collateral therefor or any direct or indirect guarantee thereof. Neither the Agent nor the Buyers shall be required to marshal the Credit Security or any guarantee of the Credit Obligations or to resort to the Credit Security or any such guarantee in any particular order, and all of its and their rights hereunder or under any other Transaction Document shall be cumulative. To the extent it may lawfully do so, the Pledgor absolutely and irrevocably waives and relinquishes the benefit and advantage of, and covenants not to assert against the Agent or the Buyers, any valuation, stay, appraisement, extension, redemption or similar laws now or hereafter existing which, but for this provision, might be applicable to the sale of any Credit Security made under the judgment, order or decree of any court, or privately under the power of sale conferred by this Agreement, or otherwise. Without limiting the generality of the foregoing, the Pledgor (a) agrees that it will not invoke or utilize any law which might prevent, cause a delay in or otherwise impede the enforcement of the rights of the Agent or any Buyer in the Credit Security, (b) waives its rights under all such laws, and (c) agrees that it will not invoke or raise as a defense to any enforcement by the Agent or any Buyer of any rights and remedies relating to the Credit Security or the Credit Obligations any legal or contractual requirement with which the Agent or any Buyer may have in good faith failed to comply. In addition, the Pledgor waives any right to prior notice (except to the extent expressly required by this Agreement) or judicial hearing in connection with foreclosure on or disposition of any Credit Security, including any such right which the Pledgor would otherwise have under the Constitution of the United States of America, any state or territory thereof or any other jurisdiction.

2.4.3. Sales of Credit Security. All or any part of the Credit Security may be sold for cash or other value in any number of lots at public or private sale, without demand, advertisement or notice; provided, however, that unless the Credit Security to be sold threatens to decline speedily in value or is of a type customarily sold on a recognized market, the Agent shall give the Pledgor 10 days prior written notice of the time and

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place of any public sale, or the time after which a private sale may be made, which notice the Pledgor and the Buyers hereby agree to be reasonable. At any sale or sales of Credit Security, any Buyer or any of its respective officers acting on its behalf, or such Buyer’s assigns, may bid for and purchase all or any part of the property and rights so sold, may use all or any portion of the Credit Obligations owed to such Buyer as payment for the property or rights so purchased, and upon compliance with the terms of such sale may hold and dispose of such property and rights without further accountability to the Pledgor, except for the proceeds of such sale or sales pursuant to Section 2.4.5. The Pledgor acknowledges that any such sale will be made by the Agent on an “as is” basis with disclaimers of all warranties, whether express or implied. The Pledgor will execute and deliver or cause to be executed and delivered such instruments, documents, assignments, waivers, certificates and affidavits, will supply or cause to be supplied such further information and will take such further action as the Agent shall reasonably request in connection with any such sale.

2.4.4. Sale without Registration. If, at any time when the Agent shall determine to exercise its rights hereunder to sell all or part of the securities included in the Credit Security, the securities in question shall not be effectively registered under the Securities Act (or other applicable law), the Agent may, in its sole discretion, sell such securities by private or other sale not requiring such registration in such manner and in such circumstances as the Agent may deem necessary or advisable in order that such sale may be effected in accordance with applicable securities laws without such registration and the related delays, uncertainty and expense. Without limiting the generality of the foregoing, in any event the Agent may, in its sole discretion, (a) approach and negotiate with a single purchaser or one or more possible purchasers to effect such sale, (b) restrict such sale to one or more purchasers each of whom will represent and agree that such purchaser is purchasing for its own account, for investment and not with a view to the distribution or sale of such securities and (c) cause to be placed on certificates representing the securities in question a legend to the effect that such securities have not been registered under the Securities Act (or other applicable law) and may not be disposed of in violation of the provisions thereof. The Pledgor agrees that such manner of disposition is commercially reasonable, that it will upon the Agent’s request give any such purchaser access to such information regarding the issuer of the securities in question as the Agent may reasonably request and that the Agent and the Buyers shall not incur any responsibility for selling all or part of the securities included in the Credit Security at any private or other sale not requiring such registration, notwithstanding the possibility that a substantially higher price might be realized if the sale were deferred until after registration under the Securities Act (or other applicable law) or until made in compliance with certain other rules or exemptions from the registration provisions under the Securities Act (or other applicable law). The Pledgor acknowledges that no adequate remedy at law exists for breach by it of this Section 2.4.4 and that such breach would not be adequately compensable in damages and therefore agrees that this Section 2.4.4 may be specifically enforced.

2.4.5. Application of Proceeds. The proceeds of all sales and collections in respect of any Credit Security or other assets of the Pledgor, all funds collected from the

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Pledgor and any cash contained in the Credit Security, the application of which is not otherwise specifically provided for herein, shall be applied as follows:

(a) First, to the payment of the costs and expenses of such sales and collections, the reasonable expenses of the Agent and the reasonable fees and expenses of its special counsel;

(b) Second, any surplus then remaining to the payment of the Credit Obligations in such order and manner as the Agent may in its reasonable discretion determine; provided, however, that any such payment shall be distributed to the Buyers in accordance with the Securities Purchase Agreement and the other Transaction Documents; and

(c) Third, any surplus then remaining shall be paid to the Pledgor, subject, however, to the rights of the holder of any then existing Lien of which the Agent has actual notice.

2.5. Custody of Credit Security. Except as provided by applicable law that cannot be waived, the Agent will have no duty as to the custody and protection of the Credit Security, the collection of any part thereof or of any income thereon or the preservation or exercise of any rights pertaining thereto, including rights against prior parties, except for the use of reasonable care in the custody and physical preservation of any Credit Security in its possession. The Buyers will not be liable or responsible for any loss or damage to any Credit Security, or for any diminution in the value thereof, by reason of the act or omission of any agent selected by the Agent acting in good faith.

3. Representations and Warranties. In order to induce the Buyers to purchase the Notes under the Securities Purchase Agreement, the Pledgor represents and warrants that:

3.1. Organization and Business. The Pledgor is a duly organized and validly existing corporation, in good standing under the laws of the State of Delaware, with all power and authority, corporate or otherwise, necessary (a) to enter into and perform this Agreement and each other Transaction Document to which it is a party and (b) to own its properties and carry on the business now conducted or proposed to be conducted by it. Certified copies of the Certificate of Incorporation and bylaws of the Pledgor have been previously delivered to the Agent and are correct and complete.

3.2. Authorization and Enforceability. The Pledgor has taken all corporate action required to execute, deliver and perform this Agreement and each other Transaction Document to which it is a party. Each of this Agreement and each other Transaction Document to which the Pledgor is party constitutes the legal, valid and binding obligation of the Pledgor, enforceable against the Pledgor in accordance with its terms.

3.3. No Legal Obstacle to Agreements. Neither the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party, nor the consummation

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of any transaction referred to in or contemplated by this Agreement or any other Transaction Document, has constituted or resulted, or will constitute or result, in:

(a) Any breach or termination of the provisions of any agreement, instrument, deed or lease to which the Pledgor is a party or by which it is bound, or of the Certificate of Incorporation or Bylaws of the Pledgor; or

(b) The violation of any law, statute, judgment, decree or governmental order, rule or regulation applicable to the Pledgor.

No approval, authorization or other action by, or declaration to or filing with, any governmental or administrative authority or any other Person is required to be obtained or made by the Pledgor in connection with the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party or the transactions contemplated hereby or thereby.

4. Defeasance. When all Credit Obligations have been paid, performed and reasonably determined by the Buyers to have been indefeasibly discharged in full, and if at the time no Buyer continues to be committed to extend any credit to the Pledgor under the Securities Purchase Agreement or any other Transaction Document, this Agreement shall terminate and, at the Pledgor’s written request, accompanied by such certificates and other items as the Agent shall reasonably deem necessary, the Credit Security shall revert to the Pledgor and the right, title and interest of the Buyers therein shall terminate. Thereupon, on the Pledgor’s demand and at its cost and expense, the Agent shall execute proper instruments, acknowledging satisfaction of and discharging this Agreement, and shall redeliver to the Pledgor any Credit Security then in its possession.

5. Successors and Assigns. The provisions of this Agreement shall inure to the benefit of the Buyers and their successors and assigns and shall be binding upon the Pledgor and its respective successors and assigns. The Pledgor may not assign its rights or obligations under this Agreement without the written consent of the Agent.

6. Notices. Any notice or other communication in connection with this Agreement shall be deemed to be given if and only if given in accordance with the notice requirements set forth in Section 9(f) of the Securities Purchase Agreement dated as of the date hereof.

7. Reimbursement of Expenses. The Pledgor shall pay at closing the reasonable, direct professional fees, not to exceed a total payment of one hundred thousand dollars ($100,000), of the Agent and Buyers in the connection with the preparation of this Agreement and the other Transaction Documents.

8. Venue; Service of Process. Each of the Pledgor and the Agent:

(a) Irrevocably submits to the nonexclusive jurisdiction of the any New York State or Federal court sitting in the Borough of Manhattan in The City of New York for the purpose of any suit, action or other proceeding arising out of or based upon this Agreement or any other Transaction Document or the subject matter hereof or thereof;

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(b) Waives to the extent not prohibited by applicable law, and agrees not to assert, by way of motion, as a defense or otherwise, in any such proceeding brought in any of the above-named courts, any claim that it is not subject personally to the jurisdiction of such court, that its property is exempt or immune from attachment or execution, that such proceeding is brought in an inconvenient forum, that the venue of any such proceeding is improper, or that this Agreement or any other Transaction Document, or the subject matter hereof or thereof, may not be enforced in or by such court;

(c) Consents to service of process in any action or proceeding by registered or certified mail, return receipt requested, at its address specified in or pursuant to Section 6; and

(d) Waives to the extent not prohibited by applicable law that cannot be waived any right it may have to claim or recover in any such proceeding any special, exemplary, punitive or consequential damages.

9. WAIVER OF JURY TRIAL. TO THE EXTENT NOT PROHIBITED BY APPLICABLE LAW WHICH CANNOT BE WAIVED, EACH OF THE AGENT AND THE PLEDGOR WAIVES, AND COVENANTS THAT IT WILL NOT ASSERT (WHETHER AS PLAINTIFF, DEFENDANT OR OTHERWISE), ANY RIGHT TO TRIAL BY JURY IN ANY FORUM IN RESPECT OF ANY ISSUE, CLAIM, DEMAND OR ACTION ARISING OUT OF OR BASED UPON THIS AGREEMENT, THE SECURITIES PURCHASE AGREEMENT OR ANY OTHER TRANSACTION DOCUMENT OR THE SUBJECT MATTER HEREOF OR THEREOF OR ANY CREDIT OBLIGATION OR IN ANY WAY CONNECTED WITH THE DEALINGS OF THE AGENT OR THE PLEDGOR IN CONNECTION WITH ANY OF THE ABOVE, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING AND WHETHER IN CONTRACT OR TORT OR OTHERWISE. The Pledgor acknowledges that it has been informed by the Agent that the provisions of this Section constitute a material inducement upon which each of the Buyers has relied, is relying and will rely in entering into the Securities Purchase Agreement and any other Transaction Document, and that it has reviewed the provisions of this Section with its counsel. The Agent or the Pledgor may file an original counterpart or a copy of this Section with any court as written evidence of the consent of the Agent and the Pledgor to the waiver of the right to trial by jury.

10. General. All covenants, agreements, representations and warranties made in this Agreement or any other Transaction Document or in certificates delivered pursuant hereto or thereto shall be deemed to have been relied on by each Buyer, notwithstanding any investigation made by the Agent on its behalf, and shall survive the execution and delivery to the Buyers hereof and thereof. The invalidity or unenforceability of any provision hereof shall not affect the validity or enforceability of any other provision hereof, and any invalid or unenforceable provision shall be modified so as to be enforced to the maximum extent of its validity or enforceability. The headings in this Agreement are for convenience of reference only and shall not limit, alter or otherwise affect the meaning hereof. This Agreement and the other Transaction Documents constitute the entire understanding of the parties with respect to the subject matter hereof and thereof and supersede all prior and current understandings and agreements, whether written or

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oral. This Agreement is a Transaction Document and may be executed in any number of counterparts, which together shall constitute one instrument. This Agreement and all action taken in connection herewith shall be governed by and construed in accordance with the laws (other than the conflict of laws rules) of the State of New York.

[the rest of this page is intentionally blank]

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Each of the undersigned has caused this Agreement to be executed and delivered by its duly authorized officer as an agreement under seal as of the date first written above.

ANTIGENICS INC.
By	/s/ Garo H. Armen
Title:	Chairman & Chief Executive Officer
INGALLS AND SNYDER LLC as Agent under the Securities Purchase Agreement
By	/s/ Thomas O. Boucher, Jr.
Title:	Manager

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EX-4.4

Exhibit 4.4

EXECUTION COPY

ANTIGENICS INC.

GUARANTEE

Dated as of October 30, 2006

Ingalls & Snyder LLC, as Agent

TABLE OF CONTENTS

1.	Reference to Securities Purchase Agreement; Definitions; Certain Rules of Construction		1
	1.1.	“Agreement”	1
	1.2.	“Bankruptcy Code”	1
	1.3.	“Credit Obligations”	1
	1.4.	“Credit Security”	1
	1.5.	“Default”	1
	1.6.	“Event of Default”.	1
	1.7.	“Guarantee”	1
	1.8.	“Pledge Agreement”	2
	1.9.	“Obligors”	2
	1.10.	“Subsidiary”	2
2.	Guarantee.		2
	2.1.	Guarantee of Credit Obligations	2
	2.2.	Continuing Obligation	2
	2.3.	Spin-off, Termination	3
	2.4.	Waivers with Respect to Credit Obligations	3
	2.5.	Buyers’ Power to Waive, etc	4
	2.6.	Information Regarding the Borrower, etc	5
	2.7.	Certain Guarantor Representations	5
	2.8.	Subrogation	6
	2.9.	Subordination	6
3.	Representations and Warranties		6
	3.1.	Organization and Business	6
	3.2.	Authorization and Enforceability	7
	3.3.	No Legal Obstacle to Agreements	7
	3.4.	Litigation	7
4.	Successors and Assigns		7
5.	Notices		7

i

6.	Reimbursement of Expenses	8
7.	Venue; Service of Process	8
8.	WAIVER OF JURY TRIAL	8
9.	General	9

ii

ANTIGENICS INC.

GUARANTEE

This Agreement, dated as of October 30, 2006, is among Antigenics Inc., a Massachusetts corporation (the “Guarantor”), and Ingalls & Snyder LLC, as agent (the “Agent”) for itself and the other Buyers under the Securities Purchase Agreement (as defined below). The parties agree as follows:

1. Reference to Securities Purchase Agreement; Definitions; Certain Rules of Construction. Reference is made to the Securities Purchase Agreement dated as of the date hereof, as from time to time in effect (the “Securities Purchase Agreement”), among Antigenics Inc., a Delaware corporation (the “Borrower”), the Buyers and the Agent. Capitalized terms defined in the Securities Purchase Agreement and not otherwise defined herein are used herein with the meanings so defined. Certain other capitalized terms are used in this Agreement as specifically defined below in this Section 1. Except as the context otherwise explicitly requires, (a) the capitalized term “Section” refers to sections of this Agreement, (b) the capitalized term “Exhibit” refers to exhibits to this Agreement, (c) references to a particular Section shall include all subsections thereof, (d) the word “including” shall be construed as “including without limitation”, (e) references to a particular statute or regulation include all rules and regulations thereunder and any successor statute, regulation or rules, in each case as from time to time in effect and (f) references to a particular Person include such Person’s successors and assigns to the extent not prohibited by this Agreement and the other Transaction Documents. References to “the date hereof” mean the date first set forth above.

1.1. “Agreement” means this Guarantee as from time to time in effect.

1.2. “Bankruptcy Code” means Title 11 of the United States Code.

1.3. “Credit Obligations” means all present and future liabilities, obligations and Indebtedness of the Company, any of its Subsidiaries or any other Obligor owing to the Agent or any Buyer (or any Affiliate of a Buyer) under or in connection with this Agreement or any other Transaction Document.

1.4. “Credit Security” is defined in section 2.1 of the Pledge Agreement.

1.5. “Default” means any Event of Default and any event or condition which with the passage of time or giving of notice, or both, would become an Event of Default, including the filing against the Company, any of its Subsidiaries or any other Obligor of a petition commencing an involuntary case under the Bankruptcy Code

1.6. “Event of Default” is defined in section 4(a) of the Note.

1.7. “Guarantee” is defined in section 2.1 of this Agreement.

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1.8. “Pledge Agreement” means the Pledge and Security Agreement, dated as of the date hereof, between the Borrower and the Agent.

1.9. “Obligors” means the Borrower, the Guarantor and the Subsidiaries of the Borrower party hereto from time to time.

1.10. “Subsidiary” means any person of which the Borrower (or other specified Person) shall at the time, directly or indirectly through one or more of its subsidiaries, (a) own at least 50% of the outstanding capital stock (or other shares of beneficial interest) entitled to vote generally, (b) hold at lest 50% of the partnership, joint venture or similar interests or (c) be a general partner or joint venturer.

2. Guarantee.

2.1. Guarantee of Credit Obligations. The Guarantor unconditionally guarantees (the “Guarantee”) that the Credit Obligations will be performed and paid in full in cash when due and payable, whether at the stated or accelerated maturity thereof or otherwise, this guarantee being a guarantee of payment and not of collectability and being absolute and in no way conditional or contingent. In the event any part of the Credit Obligations shall not have been so paid in full when due and payable, the Guarantor will, immediately upon notice by the Agent pay or cause to be paid to the Agent for the account of each Buyer in accordance with the Buyers’ respective percentage interests therein the amount of such Credit Obligations which are then due and payable and unpaid. The obligations of the Guarantor hereunder shall not be affected by the invalidity, unenforceability or irrecoverability of any of the Credit Obligations as against the Borrower, any other Obligor, any other guarantor thereof or any other Person. For purposes hereof, the Credit Obligations shall be due and payable when and as the same shall be due and payable under the terms of the Securities Purchase Agreement or any other Transaction Document notwithstanding the fact that the collection or enforcement thereof may be stayed or enjoined under Bankruptcy Code or other applicable law.

2.2. Continuing Obligation. The Guarantor acknowledges that the Buyers have entered into the Securities Purchase Agreement (and, to the extent that the Buyers or the Agent may enter into any future Transaction Document, will have entered into such agreement) in reliance on this Section 2 being a continuing irrevocable agreement, and the Guarantor agrees that its guarantee may not be revoked in whole or in part. The obligations of the Guarantor hereunder shall terminate when all of the Credit Obligations have been indefeasibly paid in full in cash and discharged; provided, however, that:

(a) if a claim is made upon the Buyers at any time for repayment or recovery of any amounts or any property received by the Buyers from any source on account of any of the Credit Obligations and the Buyers repay or return any amounts or property so received (including interest thereon to the extent required to be paid by the Buyers) or

(b) if the Buyers become liable for any part of such claim by reason of (i) any judgment or order of any court or administrative authority having competent jurisdiction, or (ii) any settlement or compromise of any such claim,

2

then the Guarantor shall remain liable under this Agreement for the amounts so repaid or property so returned or the amounts for which the Buyers become liable (such amounts being deemed part of the Credit Obligations) to the same extent as if such amounts or property had never been received by the Buyers, notwithstanding any termination hereof or the cancellation of any instrument or agreement evidencing any of the Credit Obligations. Not later than five days after receipt of notice from the Agent, the Guarantor shall pay to the Agent an amount equal to the amount of such repayment or return for which the Buyers have so become liable. Payments hereunder by the Guarantor may be required by the Agent on any number of occasions.

2.3. Spin-off, Termination. Notwithstanding anything else in this Agreement to the contrary, the obligations of the Guarantor hereunder shall terminate upon the consummation of a stock purchase agreement or other business combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) pursuant to which at least 10% of the outstanding shares of the Guarantor are acquired at a pre-money valuation amount of at least $60,000,000.

2.4. Waivers with Respect to Credit Obligations. Except to the extent expressly required by the Securities Purchase Agreement or any other Transaction Document, the Guarantor waives, to the fullest extent permitted by the provisions of applicable law, all of the following (including all defenses, counterclaims and other rights of any nature based upon any of the following):

(a) presentment, demand for payment and protest of nonpayment of any of the Credit Obligations, and notice of protest, dishonor or nonperformance;

(b) notice of acceptance of this guarantee and notice that credit has been extended in reliance on the Guarantor’s guarantee of the Credit Obligations;

(c) notice of any Default or of any inability to enforce performance of the obligations of the Borrower or any other Person with respect to any Transaction Document or notice of any acceleration of maturity of any Credit Obligations;

(d) demand for performance or observance of, and any enforcement of any provision of the Securities Purchase Agreement, the Credit Obligations or any other Transaction Document or any pursuit or exhaustion of rights or remedies with respect to any Credit Security or against the Borrower or any other Person in respect of the Credit Obligations or any requirement of diligence or promptness on the part of the Agent or the Buyers in connection with any of the foregoing;

(e) any act or omission on the part of the Agent or the Buyers which may impair or prejudice the rights of the Guarantor, including rights to obtain subrogation, exoneration, contribution, indemnification or any other reimbursement from the Borrower or any other Person, or otherwise operate as a deemed release or discharge;

(f) failure or delay to perfect or continue the perfection of any security interest in any Credit Security or any other action which harms or impairs the value of, or any failure to preserve or protect the value of, any Credit Security;

3

(g) any statute of limitations or any statute or rule of law which provides that the obligation of a surety must be neither larger in amount nor in other respects more burdensome than the obligation of the principal;

(h) any “single action” or “anti deficiency” law which would otherwise prevent the Buyers from bringing any action, including any claim for a deficiency, against the Guarantor before or after the Agent’s or the Buyers’ commencement or completion of any foreclosure action, whether judicially, by exercise of power of sale or otherwise, or any other law which would otherwise require any election of remedies by the Agent or the Buyers;

(i) all demands and notices of every kind with respect to the foregoing; and

(j) to the extent not referred to above, all defenses (other than payment) which the Borrower may now or hereafter have to the payment of the Credit Obligations, together with all suretyship defenses, which could otherwise be asserted by the Guarantor.

The Guarantor represents that it has obtained the advice of counsel as to the extent to which suretyship and other defenses may be available to it with respect to its obligations hereunder in the absence of the waivers contained in this Section 2.3.

No delay or omission on the part of the Agent or the Buyers in exercising any right under any other Transaction Document or under any other guarantee of the Credit Obligations or with respect to the Credit Security shall operate as a waiver or relinquishment of such right. No action which the Agent or the Buyers or the Borrower or any other Obligor may take or refrain from taking with respect to the Credit Obligations shall affect the provisions of this Agreement or the obligations of the Guarantor hereunder. None of the Buyers’ or the Agent’s rights shall at any time in any way be prejudiced or impaired by any act or failure to act on the part of the Borrower or any other Obligor, or by any noncompliance by the Borrower or any other Obligor with any Transaction Document, regardless of any knowledge thereof which the Agent or the Buyers may have or otherwise be charged with.

2.5. Buyers’ Power to Waive, etc. The Guarantor grants to the Agent and the Buyers full power in their discretion, without notice to or consent of such Guarantor, such notice and consent being expressly waived to the fullest extent permitted by applicable law, and without in any way affecting the liability of the Guarantor under its guarantee hereunder:

(a) To waive compliance with, and any Default under, and to consent to any amendment to or modification or termination of any provision of, or to give any waiver in respect of, the Securities Purchase Agreement, any other Transaction Document, the Credit Security, the Credit Obligations or any guarantee thereof (each as from time to time in effect);

(b) To grant any extensions of the Credit Obligations (for any duration), and any other indulgence with respect thereto, and to effect any total or partial release (by operation of law or otherwise), discharge, compromise or settlement with respect to the obligations of the Obligors or any other Person in respect of the Credit Obligations, whether or not rights against the Guarantor under this Agreement are reserved in connection therewith;

4

(c) To take security in any form for the Credit Obligations, and to consent to the addition to or the substitution, exchange, release or other disposition of, or to deal in any other manner with, any part of any property contained in the Credit Security whether or not the property, if any, received upon the exercise of such power shall be of a character or value the same as or different from the character or value of any property disposed of, and to obtain, modify or release any present or future guarantees of the Credit Obligations and to proceed against any of the Credit Security or such guarantees in any order;

(d) To collect or liquidate or realize upon any of the Credit Obligations or the Credit Security in any manner or to refrain from collecting or liquidating or realizing upon any of the Credit Obligations or the Credit Security; and

(e) To extend credit under the Securities Purchase Agreement, any other Transaction Document or otherwise in such amount as the Buyers may determine, including increasing the amount of credit and the interest rate and fees with respect thereto, even though the condition of the Obligors (financial or otherwise, on an individual or consolidated basis) may have deteriorated since the date hereof.

2.6. Information Regarding the Borrower, etc. The Guarantor has made such investigation as it deems desirable of the risks undertaken by it in entering into this Agreement and is fully satisfied that it understands all such risks. The Guarantor waives any obligation which may now or hereafter exist on the part of the Agent or the Buyers to inform it of the risks being undertaken by entering into this Agreement or of any changes in such risks and, from and after the date hereof, the Guarantor undertakes to keep itself informed of such risks and any changes therein. The Guarantor expressly waives any duty which may now or hereafter exist on the part of the Agent or the Buyers to disclose to such Guarantor any matter related to the business, operations, character, collateral, credit, condition (financial or otherwise), income or prospects of the Borrower and its Affiliates or their properties or management, whether now or hereafter known by the Agent or the Buyers. The Guarantor represents, warrants and agrees that it assumes sole responsibility for obtaining from the Borrower all information concerning the Securities Purchase Agreement and all other Transaction Documents and all other information as to the Borrower and its affiliates or their properties or management as the Guarantor deems necessary or desirable.

2.7. Certain Guarantor Representations. The Guarantor represents that:

(a) it is in its best interest and in pursuit of the purposes for which it was organized as an integral part of the business conducted and proposed to be conducted by the Borrower and its Subsidiaries, and reasonably necessary and convenient in connection with the conduct of the business conducted and proposed to be conducted by them, to induce the Buyers to enter into the Securities Purchase Agreement and to extend credit to the Guarantor by making the Guarantee contemplated by this Section 2;

5

(b) the credit available under the Securities Purchase Agreement will directly or indirectly inure to its benefit;

(c) by virtue of the foregoing it is receiving at least reasonably equivalent value from the Buyers for its Guarantee;

(d) it will not be rendered insolvent as a result of entering into this Agreement;

(e) after giving effect to the transactions contemplated by this Agreement, it will have assets having a fair saleable value in excess of the amount required to pay its probable liability on its existing debts as such debts become absolute and matured;

(f) it has, and will have, access to adequate capital for the conduct of its business;

(g) it has the ability to pay its debts from time to time incurred in connection therewith as such debts mature; and

(h) it has been advised by the Agent that the Buyers are unwilling to enter into the Securities Purchase Agreement unless the Guarantee contemplated by this Section 2 is given by it.

2.8. Subrogation. The Guarantor agrees that, until the Credit Obligations are indefeasibly paid in full, it will not exercise any right of reimbursement, subrogation, contribution, offset or other claims against the Borrower or any other Obligor arising by contract or operation of law in connection with any payment made or required to be made by the Guarantor under this Agreement. After the payment in full of the Credit Obligations, the Guarantor shall be entitled to exercise against the Borrower and the other Obligors all such rights of reimbursement, subrogation, contribution and offset, and all such other claims, to the fullest extent permitted by law.

2.9. Subordination. The Guarantor covenants and agrees that all Indebtedness, claims and liabilities now or hereafter owing by the Borrower or any other Obligor to the Guarantor whether arising hereunder or otherwise are subordinated to the prior payment in full of the Credit Obligations and are so subordinated as a claim against such Obligor or any of its assets, whether such claim be in the ordinary course of business or in the event of voluntary or involuntary liquidation, dissolution, insolvency or bankruptcy, so that no payment with respect to any such Indebtedness, claim or liability will be made or received while any Event of Default exists and is continuing.

3. Representations and Warranties. In order to induce the Buyers to extend credit under the Securities Purchase Agreement, the Guarantor represents and warrants that:

3.1. Organization and Business. The Guarantor is a duly organized and validly existing corporation, in good standing under the laws of the Commonwealth of Massachusetts, with all power and authority, corporate or otherwise, necessary (a) to enter into and perform this Agreement and each other Transaction Document to which it is a party and (b) to own its

6

properties and carry on the business now conducted or proposed to be conducted by it. Certified copies of the charter and by-laws of the Guarantor have been previously delivered to the Agent and are correct and complete.

3.2. Authorization and Enforceability. The Guarantor has taken all corporate action required to execute, deliver and perform this Agreement and each other Transaction Document to which it is a party. Each of this Agreement and each other Transaction Document to which the Guarantor is party constitutes the legal, valid and binding obligation of the Guarantor, enforceable against the Guarantor in accordance with its terms.

3.3. No Legal Obstacle to Agreements. Neither the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party, nor the consummation of any transaction referred to in or contemplated by this Agreement or any other Transaction Document, has constituted or resulted, or will constitute or result, in:

(a) Any breach or termination of the provisions of any agreement, instrument, deed or lease to which the Guarantor is a party or by which it is bound, or of the charter or by-laws of the Guarantor; or

(b) The violation of any law, statute, judgment, decree or governmental order, rule or regulation applicable to the Guarantor.

No approval, authorization or other action by, or declaration to or filing with, any governmental or administrative authority or any other Person is required to be obtained or made by the Guarantor in connection with the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party or the transactions contemplated hereby or thereby.

3.4. Litigation. No litigation, at law or in equity, or any proceeding before any court, board or other governmental or administrative agency or any arbitrator is pending or, to the knowledge of the Guarantor, threatened which may involve any material risk of any final judgment, order or liability which, after giving effect to any applicable insurance, has resulted, or creates a material risk of resulting, in any material adverse change in the Guarantor’s business, assets, financial condition, income or prospects or which seeks to enjoin the consummation, or which questions the validity, of any of the transactions contemplated by this Agreement or any other Transaction Document. No judgment, decree or order of any court, board or other governmental or administrative agency or any arbitrator has been issued against or binds the Guarantor which has resulted, or creates a material risk of resulting, in any material adverse change in the Guarantor’s business, assets, financial condition, income or prospects.

4. Successors and Assigns. The provisions of this Agreement shall inure to the benefit of the Buyers and their successors and assigns and shall be binding upon the Guarantor and its respective successors and assigns. The Guarantor may not assign its rights or obligations under this Agreement without the written consent of the Agent.

5. Notices. Any notice or other communication in connection with this Agreement shall be deemed to be given if and only if given in accordance with the notice requirements set forth in Section 9(f) of the Securities Purchase Agreement.

7

6. Reimbursement of Expenses. The Guarantor shall pay at closing the reasonable, direct professional fees, not to exceed a total payment of one hundred thousand dollars ($100,000), of the Agent and Buyers in the connection with the preparation of this Agreement and the other Transaction Documents.

7. Venue; Service of Process. The Guarantor:

(a) Irrevocably submits to the nonexclusive jurisdiction of the any New York State or Federal court sitting in the Borough of Manhattan in The City of New York for the purpose of any suit, action or other proceeding arising out of or based upon this Agreement or any other Transaction Document or the subject matter hereof or thereof;

(b) Waives to the extent not prohibited by applicable law, and agrees not to assert, by way of motion, as a defense or otherwise, in any such proceeding brought in any of the above-named courts, any claim that it is not subject personally to the jurisdiction of such court, that its property is exempt or immune from attachment or execution, that such proceeding is brought in an inconvenient forum, that the venue of any such proceeding is improper, or that this Agreement or any other Transaction Document, or the subject matter hereof or thereof, may not be enforced in or by such court;

(c) Consents to service of process in any action or proceeding by registered or certified mail, return receipt requested, at its address specified in or pursuant to section 5; and

(d) Waives to the extent not prohibited by applicable law that cannot be waived any right it may have to claim or recover in any such proceeding any special, exemplary, punitive or consequential damages.

8. WAIVER OF JURY TRIAL. TO THE EXTENT NOT PROHIBITED BY APPLICABLE LAW WHICH CANNOT BE WAIVED, EACH OF THE AGENT AND THE GUARANTOR WAIVES, AND COVENANTS THAT IT WILL NOT ASSERT (WHETHER AS PLAINTIFF, DEFENDANT OR OTHERWISE), ANY RIGHT TO TRIAL BY JURY IN ANY FORUM IN RESPECT OF ANY ISSUE, CLAIM, DEMAND OR ACTION ARISING OUT OF OR BASED UPON THIS AGREEMENT, THE SECURITIES PURCHASE AGREEMENT OR ANY OTHER TRANSACTION DOCUMENT OR THE SUBJECT MATTER HEREOF OR THEREOF OR ANY CREDIT OBLIGATION OR IN ANY WAY CONNECTED WITH THE DEALINGS OF THE AGENT OR THE GUARANTOR IN CONNECTION WITH ANY OF THE ABOVE, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING AND WHETHER IN CONTRACT OR TORT OR OTHERWISE. The Guarantor acknowledges that it has been informed by the Agent that the provisions of this Section constitute a material inducement upon which each of the Buyers has relied, is relying and will rely in entering into the Securities Purchase Agreement and any other Transaction Document, and that it has reviewed the provisions of this Section with its counsel. The Agent or the Guarantor may file an original counterpart or a copy of this Section with any court as written evidence of the consent of the Agent and the Guarantor to the waiver of the right to trial by jury.

8

9. General. All covenants, agreements, representations and warranties made in this Agreement or any other Transaction Document or in certificates delivered pursuant hereto or thereto shall be deemed to have been relied on by each Buyer, notwithstanding any investigation made by the Agent on its behalf, and shall survive the execution and delivery to the Buyers hereof and thereof. The invalidity or unenforceability of any provision hereof shall not affect the validity or enforceability of any other provision hereof, and any invalid or unenforceable provision shall be modified so as to be enforced to the maximum extent of its validity or enforceability. The headings in this Agreement are for convenience of reference only and shall not limit, alter or otherwise affect the meaning hereof. This Agreement and the other Transaction Documents constitute the entire understanding of the parties with respect to the subject matter hereof and thereof and supersede all prior and current understandings and agreements, whether written or oral. This Agreement is a Transaction Document and may be executed in any number of counterparts, which together shall constitute one instrument. This Agreement and all action taken in connection herewith shall be governed by and construed in accordance with the laws (other than the conflict of laws rules) of the State of New York.

9

Each of the undersigned has caused this Agreement to be executed and delivered by its duly authorized officer as an agreement under seal as of the date first written above.

ANTIGENICS INC
By	/s/ Garo H. Armen
Title:	Chairman & Chief Executive Officer
INGALLS AND SNYDER LLC, as Agent under the Securities Purchase Agreement
By	/s/ Thomas O. Boucher, Jr.
Title:	Manager

10

EX-4.5

Exhibit 4.5

EXECUTION COPY

ARONEX PHARMACEUTICALS, INC.

GUARANTEE

Dated as of October 30, 2006

Ingalls & Snyder, as Agent

TABLE OF CONTENTS

1.	REFERENCE TO SECURITIES PURCHASE AGREEMENT; DEFINITIONS; CERTAIN RULES OF CONSTRUCTION		4
	1.1.	“Agreement”	4
	1.2.	“Bankruptcy Code”	4
	1.3.	“Credit Obligations”	4
	1.4.	“Credit Security”	4
	1.5.	“Default”	4
	1.6.	“Event of Default”	4
	1.7.	“Guarantee”	4
	1.8.	“Pledge Agreement”	5
	1.9.	“Obligors”	5
	1.10.	“Subsidiary”	5
2.	GUARANTEE.		5
	2.1.	Guarantee of Credit Obligations	5
	2.2.	Continuing Obligation	5
	2.3.	Waivers with Respect to Credit Obligations	6
	2.4.	Buyers’ Power to Waive, etc	7
	2.5.	Information Regarding the Borrower, etc	8
	2.6.	Certain Guarantor Representations	8
	2.7.	Subrogation	9
	2.8.	Subordination	9
3.	REPRESENTATIONS AND WARRANTIES		9
	3.1.	Organization and Business	9
	3.2.	Authorization and Enforceability	9
	3.3.	No Legal Obstacle to Agreements	10
	3.4.	Litigation	10
4.	SUCCESSORS AND ASSIGNS		10
5.	NOTICES		10
6.	REIMBURSEMENT OF EXPENSES		10

7.	VENUE; SERVICE OF PROCESS	10
8.	WAIVER OF JURY TRIAL	11
9.	GENERAL	11

-3-

ARONEX PHARMACEUTICALS, INC.

GUARANTEE

This Agreement, dated as of October 30, 2006, is among Aronex Pharmaceuticals, Inc., a Delaware corporation (the “Guarantor”), and Ingalls & Snyder LLC, as agent (the “Agent”) for itself and the other Buyers under the Securities Purchase Agreement (as defined below). The parties agree as follows:

1. Reference to Securities Purchase Agreement; Definitions; Certain Rules of Construction. Reference is made to the Securities Purchase Agreement dated as of the date hereof, as from time to time in effect (the “Securities Purchase Agreement”), among Antigenics Inc., a Delaware corporation (the “Borrower”), the Buyers and the Agent. Capitalized terms defined in the Securities Purchase Agreement and not otherwise defined herein are used herein with the meanings so defined. Certain other capitalized terms are used in this Agreement as specifically defined below in this Section 1. Except as the context otherwise explicitly requires, (a) the capitalized term “Section” refers to sections of this Agreement, (b) the capitalized term “Exhibit” refers to exhibits to this Agreement, (c) references to a particular Section shall include all subsections thereof, (d) the word “including” shall be construed as “including without limitation”, (e) references to a particular statute or regulation include all rules and regulations thereunder and any successor statute, regulation or rules, in each case as from time to time in effect and (f) references to a particular Person include such Person’s successors and assigns to the extent not prohibited by this Agreement and the other Transaction Documents. References to “the date hereof” mean the date first set forth above.

1.1. “Agreement” means this Guarantee as from time to time in effect.

1.2. “Bankruptcy Code” means Title 11 of the United States Code.

1.3. “Credit Obligations” means all present and future liabilities, obligations and Indebtedness of the Company, any of its Subsidiaries or any other Obligor owing to the Agent or any Buyer (or any Affiliate of a Buyer) under or in connection with this Agreement or any other Transaction Document.

1.4. “Credit Security” is defined in section 2.1 of the Pledge Agreement.

1.5. “Default” means any Event of Default and any event or condition which with the passage of time or giving of notice, or both, would become an Event of Default, including the filing against the Company, any of its Subsidiaries or any other Obligor of a petition commencing an involuntary case under the Bankruptcy Code.

1.6. “Event of Default” is defined in section 4(a) of the Note.

1.7. “Guarantee” is defined in section 2.1 of this Agreement.

1.8. “Pledge Agreement” means the Pledge and Security Agreement, dated as of the date hereof, between the Borrower and the Agent.

1.9. “Obligors” means the Borrower, the Guarantor and the Subsidiaries of the Borrower party hereto from time to time.

1.10. “Subsidiary” means any person of which the Borrower (or other specified Person) shall at the time, directly or indirectly through one or more of its subsidiaries, (a) own at least 50% of the outstanding capital stock (or other shares of beneficial interest) entitled to vote generally, (b) hold at lest 50% of the partnership, joint venture or similar interests or (c) be a general partner or joint venturer.

2. Guarantee.

2.1. Guarantee of Credit Obligations. The Guarantor unconditionally guarantees (the “Guarantee”) that the Credit Obligations will be performed and paid in full in cash when due and payable, whether at the stated or accelerated maturity thereof or otherwise, this guarantee being a guarantee of payment and not of collectability and being absolute and in no way conditional or contingent. In the event any part of the Credit Obligations shall not have been so paid in full when due and payable, the Guarantor will, immediately upon notice by the Agent pay or cause to be paid to the Agent for the account of each Buyer in accordance with the Buyers’ respective percentage interests therein the amount of such Credit Obligations which are then due and payable and unpaid. The obligations of the Guarantor hereunder shall not be affected by the invalidity, unenforceability or irrecoverability of any of the Credit Obligations as against the Borrower, any other Obligor, any other guarantor thereof or any other Person. For purposes hereof, the Credit Obligations shall be due and payable when and as the same shall be due and payable under the terms of the Securities Purchase Agreement or any other Transaction Document notwithstanding the fact that the collection or enforcement thereof may be stayed or enjoined under Bankruptcy Code or other applicable law.

2.2. Continuing Obligation. The Guarantor acknowledges that the Buyers have entered into the Securities Purchase Agreement (and, to the extent that the Buyers or the Agent may enter into any future Transaction Document, will have entered into such agreement) in reliance on this Section 2 being a continuing irrevocable agreement, and the Guarantor agrees that its guarantee may not be revoked in whole or in part. The obligations of the Guarantor hereunder shall terminate when all of the Credit Obligations have been indefeasibly paid in full in cash and discharged; provided, however, that:

(a) if a claim is made upon the Buyers at any time for repayment or recovery of any amounts or any property received by the Buyers from any source on account of any of the Credit Obligations and the Buyers repay or return any amounts or property so received (including interest thereon to the extent required to be paid by the Buyers) or

(b) if the Buyers become liable for any part of such claim by reason of (i) any judgment or order of any court or administrative authority having competent jurisdiction, or (ii) any settlement or compromise of any such claim,

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then the Guarantor shall remain liable under this Agreement for the amounts so repaid or property so returned or the amounts for which the Buyers become liable (such amounts being deemed part of the Credit Obligations) to the same extent as if such amounts or property had never been received by the Buyers, notwithstanding any termination hereof or the cancellation of any instrument or agreement evidencing any of the Credit Obligations. Not later than five days after receipt of notice from the Agent, the Guarantor shall pay to the Agent an amount equal to the amount of such repayment or return for which the Buyers have so become liable. Payments hereunder by the Guarantor may be required by the Agent on any number of occasions.

2.3. Waivers with Respect to Credit Obligations. Except to the extent expressly required by the Securities Purchase Agreement or any other Transaction Document, the Guarantor waives, to the fullest extent permitted by the provisions of applicable law, all of the following (including all defenses, counterclaims and other rights of any nature based upon any of the following):

(a) presentment, demand for payment and protest of nonpayment of any of the Credit Obligations, and notice of protest, dishonor or nonperformance;

(b) notice of acceptance of this guarantee and notice that credit has been extended in reliance on the Guarantor’s guarantee of the Credit Obligations;

(c) notice of any Default or of any inability to enforce performance of the obligations of the Borrower or any other Person with respect to any Transaction Document or notice of any acceleration of maturity of any Credit Obligations;

(d) demand for performance or observance of, and any enforcement of any provision of the Securities Purchase Agreement, the Credit Obligations or any other Transaction Document or any pursuit or exhaustion of rights or remedies with respect to any Credit Security or against the Borrower or any other Person in respect of the Credit Obligations or any requirement of diligence or promptness on the part of the Agent or the Buyers in connection with any of the foregoing;

(e) any act or omission on the part of the Agent or the Buyers which may impair or prejudice the rights of the Guarantor, including rights to obtain subrogation, exoneration, contribution, indemnification or any other reimbursement from the Borrower or any other Person, or otherwise operate as a deemed release or discharge;

(f) failure or delay to perfect or continue the perfection of any security interest in any Credit Security or any other action which harms or impairs the value of, or any failure to preserve or protect the value of, any Credit Security;

(g) any statute of limitations or any statute or rule of law which provides that the obligation of a surety must be neither larger in amount nor in other respects more burdensome than the obligation of the principal;

(h) any “single action” or “anti deficiency” law which would otherwise prevent the Buyers from bringing any action, including any claim for a deficiency, against the Guarantor before or after the Agent’s or the Buyers’ commencement or

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completion of any foreclosure action, whether judicially, by exercise of power of sale or otherwise, or any other law which would otherwise require any election of remedies by the Agent or the Buyers;

(i) all demands and notices of every kind with respect to the foregoing; and

(j) to the extent not referred to above, all defenses (other than payment) which the Borrower may now or hereafter have to the payment of the Credit Obligations, together with all suretyship defenses, which could otherwise be asserted by the Guarantor.

The Guarantor represents that it has obtained the advice of counsel as to the extent to which suretyship and other defenses may be available to it with respect to its obligations hereunder in the absence of the waivers contained in this Section 2.3.

No delay or omission on the part of the Agent or the Buyers in exercising any right under any other Transaction Document or under any other guarantee of the Credit Obligations or with respect to the Credit Security shall operate as a waiver or relinquishment of such right. No action which the Agent or the Buyers or the Borrower or any other Obligor may take or refrain from taking with respect to the Credit Obligations shall affect the provisions of this Agreement or the obligations of the Guarantor hereunder. None of the Buyers’ or the Agent’s rights shall at any time in any way be prejudiced or impaired by any act or failure to act on the part of the Borrower or any other Obligor, or by any noncompliance by the Borrower or any other Obligor with any Transaction Document, regardless of any knowledge thereof which the Agent or the Buyers may have or otherwise be charged with.

2.4. Buyers’ Power to Waive, etc. The Guarantor grants to the Agent and the Buyers full power in their discretion, without notice to or consent of such Guarantor, such notice and consent being expressly waived to the fullest extent permitted by applicable law, and without in any way affecting the liability of the Guarantor under its guarantee hereunder:

(a) To waive compliance with, and any Default under, and to consent to any amendment to or modification or termination of any provision of, or to give any waiver in respect of, the Securities Purchase Agreement, any other Transaction Document, the Credit Security, the Credit Obligations or any guarantee thereof (each as from time to time in effect);

(b) To grant any extensions of the Credit Obligations (for any duration), and any other indulgence with respect thereto, and to effect any total or partial release (by operation of law or otherwise), discharge, compromise or settlement with respect to the obligations of the Obligors or any other Person in respect of the Credit Obligations, whether or not rights against the Guarantor under this Agreement are reserved in connection therewith;

(c) To take security in any form for the Credit Obligations, and to consent to the addition to or the substitution, exchange, release or other disposition of, or to deal in any other manner with, any part of any property contained in the Credit Security whether or not the property, if any, received upon the exercise of such power shall be of a

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character or value the same as or different from the character or value of any property disposed of, and to obtain, modify or release any present or future guarantees of the Credit Obligations and to proceed against any of the Credit Security or such guarantees in any order;

(d) To collect or liquidate or realize upon any of the Credit Obligations or the Credit Security in any manner or to refrain from collecting or liquidating or realizing upon any of the Credit Obligations or the Credit Security; and

(e) To extend credit under the Securities Purchase Agreement, any other Transaction Document or otherwise in such amount as the Buyers may determine, including increasing the amount of credit and the interest rate and fees with respect thereto, even though the condition of the Obligors (financial or otherwise, on an individual or consolidated basis) may have deteriorated since the date hereof.

2.5. Information Regarding the Borrower, etc. The Guarantor has made such investigation as it deems desirable of the risks undertaken by it in entering into this Agreement and is fully satisfied that it understands all such risks. The Guarantor waives any obligation which may now or hereafter exist on the part of the Agent or the Buyers to inform it of the risks being undertaken by entering into this Agreement or of any changes in such risks and, from and after the date hereof, the Guarantor undertakes to keep itself informed of such risks and any changes therein. The Guarantor expressly waives any duty which may now or hereafter exist on the part of the Agent or the Buyers to disclose to such Guarantor any matter related to the business, operations, character, collateral, credit, condition (financial or otherwise), income or prospects of the Borrower and its Affiliates or their properties or management, whether now or hereafter known by the Agent or the Buyers. The Guarantor represents, warrants and agrees that it assumes sole responsibility for obtaining from the Borrower all information concerning the Securities Purchase Agreement and all other Transaction Documents and all other information as to the Borrower and its affiliates or their properties or management as the Guarantor deems necessary or desirable.

2.6. Certain Guarantor Representations. The Guarantor represents that:

(a) it is in its best interest and in pursuit of the purposes for which it was organized as an integral part of the business conducted and proposed to be conducted by the Borrower and its Subsidiaries, and reasonably necessary and convenient in connection with the conduct of the business conducted and proposed to be conducted by them, to induce the Buyers to enter into the Securities Purchase Agreement and to extend credit to the Guarantor by making the Guarantee contemplated by this Section 2;

(b) the credit available under the Securities Purchase Agreement will directly or indirectly inure to its benefit;

(c) by virtue of the foregoing it is receiving at least reasonably equivalent value from the Buyers for its Guarantee;

(d) it will not be rendered insolvent as a result of entering into this Agreement;

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(e) after giving effect to the transactions contemplated by this Agreement, it will have assets having a fair saleable value in excess of the amount required to pay its probable liability on its existing debts as such debts become absolute and matured;

(f) it has, and will have, access to adequate capital for the conduct of its business;

(g) it has the ability to pay its debts from time to time incurred in connection therewith as such debts mature; and

(h) it has been advised by the Agent that the Buyers are unwilling to enter into the Securities Purchase Agreement unless the Guarantee contemplated by this Section 2 is given by it.

2.7. Subrogation. The Guarantor agrees that, until the Credit Obligations are indefeasibly paid in full, it will not exercise any right of reimbursement, subrogation, contribution, offset or other claims against the Borrower or any other Obligor arising by contract or operation of law in connection with any payment made or required to be made by the Guarantor under this Agreement. After the payment in full of the Credit Obligations, the Guarantor shall be entitled to exercise against the Borrower and the other Obligors all such rights of reimbursement, subrogation, contribution and offset, and all such other claims, to the fullest extent permitted by law.

2.8. Subordination. The Guarantor covenants and agrees that all Indebtedness, claims and liabilities now or hereafter owing by the Borrower or any other Obligor to the Guarantor whether arising hereunder or otherwise are subordinated to the prior payment in full of the Credit Obligations and are so subordinated as a claim against such Obligor or any of its assets, whether such claim be in the ordinary course of business or in the event of voluntary or involuntary liquidation, dissolution, insolvency or bankruptcy, so that no payment with respect to any such Indebtedness, claim or liability will be made or received while any Event of Default exists and is continuing.

3. Representations and Warranties. In order to induce the Buyers to extend credit under the Securities Purchase Agreement, the Guarantor represents and warrants that:

3.1. Organization and Business. The Guarantor is a duly organized and validly existing corporation, in good standing under the laws of the State of Delaware, with all power and authority, corporate or otherwise, necessary (a) to enter into and perform this Agreement and each other Transaction Document to which it is a party and (b) to own its properties and carry on the business now conducted or proposed to be conducted by it. Certified copies of the charter and by-laws of the Guarantor have been previously delivered to the Agent and are correct and complete.

3.2. Authorization and Enforceability. The Guarantor has taken all corporate action required to execute, deliver and perform this Agreement and each other Transaction Document to which it is a party. Each of this Agreement and each other Transaction Document to which the Guarantor is party constitutes the legal, valid and binding obligation of the Guarantor, enforceable against the Guarantor in accordance with its terms.

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3.3. No Legal Obstacle to Agreements. Neither the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party, nor the consummation of any transaction referred to in or contemplated by this Agreement or any other Transaction Document, has constituted or resulted, or will constitute or result, in:

(a) Any breach or termination of the provisions of any agreement, instrument, deed or lease to which the Guarantor is a party or by which it is bound, or of the charter or by-laws of the Guarantor; or

(b) The violation of any law, statute, judgment, decree or governmental order, rule or regulation applicable to the Guarantor.

No approval, authorization or other action by, or declaration to or filing with, any governmental or administrative authority or any other Person is required to be obtained or made by the Guarantor in connection with the execution, delivery and performance of this Agreement or any other Transaction Document to which it is party or the transactions contemplated hereby or thereby.

3.4. Litigation. No litigation, at law or in equity, or any proceeding before any court, board or other governmental or administrative agency or any arbitrator is pending or, to the knowledge of the Guarantor, threatened which may involve any material risk of any final judgment, order or liability which, after giving effect to any applicable insurance, has resulted, or creates a material risk of resulting, in any material adverse change in the Guarantor’s business, assets, financial condition, income or prospects or which seeks to enjoin the consummation, or which questions the validity, of any of the transactions contemplated by this Agreement or any other Transaction Document. No judgment, decree or order of any court, board or other governmental or administrative agency or any arbitrator has been issued against or binds the Guarantor which has resulted, or creates a material risk of resulting, in any material adverse change in the Guarantor’s business, assets, financial condition, income or prospects.

4. Successors and Assigns. The provisions of this Agreement shall inure to the benefit of the Buyers and their successors and assigns and shall be binding upon the Guarantor and its respective successors and assigns. The Guarantor may not assign its rights or obligations under this Agreement without the written consent of the Agent.

5. Notices. Any notice or other communication in connection with this Agreement shall be deemed to be given if and only if given in accordance with the notice requirements set forth in Section 9(f) of the Securities Purchase Agreement.

6. Reimbursement of Expenses. The Guarantor shall pay at closing the reasonable, direct professional fees, not to exceed a total payment of one hundred thousand dollars ($100,000), of the Agent and Buyers in the connection with the preparation of this Agreement and the other Transaction Documents.

7. Venue; Service of Process. The Guarantor:

(a) Irrevocably submits to the nonexclusive jurisdiction of the any New York State or Federal court sitting in the Borough of Manhattan in The City of New York for the purpose of any suit, action or other proceeding arising out of or based upon this Agreement or any other Transaction Document or the subject matter hereof or thereof;

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(b) Waives to the extent not prohibited by applicable law, and agrees not to assert, by way of motion, as a defense or otherwise, in any such proceeding brought in any of the above-named courts, any claim that it is not subject personally to the jurisdiction of such court, that its property is exempt or immune from attachment or execution, that such proceeding is brought in an inconvenient forum, that the venue of any such proceeding is improper, or that this Agreement or any other Transaction Document, or the subject matter hereof or thereof, may not be enforced in or by such court;

(c) Consents to service of process in any action or proceeding by registered or certified mail, return receipt requested, at its address specified in or pursuant to section 5; and

(d) Waives to the extent not prohibited by applicable law that cannot be waived any right it may have to claim or recover in any such proceeding any special, exemplary, punitive or consequential damages.

8. WAIVER OF JURY TRIAL. TO THE EXTENT NOT PROHIBITED BY APPLICABLE LAW WHICH CANNOT BE WAIVED, EACH OF THE AGENT AND THE GUARANTOR WAIVES, AND COVENANTS THAT IT WILL NOT ASSERT (WHETHER AS PLAINTIFF, DEFENDANT OR OTHERWISE), ANY RIGHT TO TRIAL BY JURY IN ANY FORUM IN RESPECT OF ANY ISSUE, CLAIM, DEMAND OR ACTION ARISING OUT OF OR BASED UPON THIS AGREEMENT, THE SECURITIES PURCHASE AGREEMENT OR ANY OTHER TRANSACTION DOCUMENT OR THE SUBJECT MATTER HEREOF OR THEREOF OR ANY CREDIT OBLIGATION OR IN ANY WAY CONNECTED WITH THE DEALINGS OF THE AGENT OR THE GUARANTOR IN CONNECTION WITH ANY OF THE ABOVE, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING AND WHETHER IN CONTRACT OR TORT OR OTHERWISE. The Guarantor acknowledges that it has been informed by the Agent that the provisions of this Section constitute a material inducement upon which each of the Buyers has relied, is relying and will rely in entering into the Securities Purchase Agreement and any other Transaction Document, and that it has reviewed the provisions of this Section with its counsel. The Agent or the Guarantor may file an original counterpart or a copy of this Section with any court as written evidence of the consent of the Agent and the Guarantor to the waiver of the right to trial by jury.

9. General. All covenants, agreements, representations and warranties made in this Agreement or any other Transaction Document or in certificates delivered pursuant hereto or thereto shall be deemed to have been relied on by each Buyer, notwithstanding any investigation made by the Agent on its behalf, and shall survive the execution and delivery to the Buyers hereof and thereof. The invalidity or unenforceability of any provision hereof shall not affect the validity or enforceability of any other provision hereof, and any invalid or unenforceable provision shall be modified so as to be enforced to the maximum extent of its validity or enforceability. The headings in this Agreement are for convenience of reference only and shall

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not limit, alter or otherwise affect the meaning hereof. This Agreement and the other Transaction Documents constitute the entire understanding of the parties with respect to the subject matter hereof and thereof and supersede all prior and current understandings and agreements, whether written or oral. This Agreement is a Transaction Document and may be executed in any number of counterparts, which together shall constitute one instrument. This Agreement and all action taken in connection herewith shall be governed by and construed in accordance with the laws (other than the conflict of laws rules) of the State of New York.

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Each of the undersigned has caused this Agreement to be executed and delivered by its duly authorized officer as an agreement under seal as of the date first written above.

ARONEX PHARMACEUTICALS, INC.
By	/s/ Garo H. Armen
Title:	Chairman & Chief Executive Officer
INGALLS AND SNYDER LLC, as Agent under the Securities Purchase Agreement
By	/s/ Thomas O. Boucher, Jr.
Title:	Manager

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EX-4.6

Exhibit 4.6

EXECUTION COPY

SECURITIES PURCHASE AGREEMENT

SECURITIES PURCHASE AGREEMENT (the “Agreement”), dated as of October 30, 2006 by and among Antigenics Inc., a Delaware corporation (the “Company”), and the investors listed on the Schedule of Buyers attached hereto (individually, a “Buyer” and collectively, the “Buyers”).

A. The Company and each Buyer is executing and delivering this Agreement in reliance upon the exemption from registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the “1933 Act”), and Rule 506 of Regulation D (“Regulation D”) as promulgated by the United States Securities and Exchange Commission (the “SEC”) under the 1933 Act.

B. The Company has authorized the issuance and sale of (i) $25,000,000 in principal amount of senior secured convertible notes of the Company in the form attached hereto as Exhibit A (together with any senior secured convertible notes issued in replacement or exchange thereof in accordance with the terms thereof and any senior secured convertible notes issued to pay interest in the form attached hereto as Exhibit B (“PIK Notes”), the “Notes”), which Notes shall be, in accordance with the terms of the Notes, convertible into shares (as converted, the “Conversion Shares”) of the Company’s common stock, par value $.01 per share (“Company Common Stock”) or into Antigenics MA Shares (as defined below).

C. The Notes bear interest, which at the option of the Company, subject to certain conditions, may be paid in kind through the issuance of additional Notes.

D. Each Buyer wishes to purchase, severally but not jointly, and the Company wishes to sell, upon the terms and conditions stated in this Agreement, that aggregate principal amount of Notes set forth opposite such Buyer’s name in the Schedule of Buyers (which aggregate principal amount for all Buyers shall be $25,000,000).

E. The Company is agreeing to pledge all its shares (“Antigenics MA Shares”) in Antigenics Inc., a Massachusetts corporation (“Antigenics MA”), to secure its obligations to pay interest on and principal of the Notes and, as evidenced by the Pledge and Security Agreement, dated as of the date hereof, by and among the company and the Buyers, substantially in the form attached thereto as Exhibit C (the “Pledge and Security Agreement”) and in connection therewith the Company shall deliver the number of Antigenics MA Shares.

F. The Notes and the Conversion Shares collectively are referred to herein as the “Securities.”

1. PURCHASE AND SALE OF NOTES.

(a) Amount. Subject to the satisfaction (or waiver) of the conditions set forth in Sections 6 and 7 below, the Company shall issue and sell to each Buyer, and each Buyer severally, but not jointly, shall purchase from the Company on the Closing Date (as defined below), the principal amount of Notes set forth opposite such Buyer’s name in the Schedule of Buyers.

(b) Closing. The closing (the “Closing”) of the purchase of the Notes by the Buyers shall occur at the offices of Ropes & Gray, LLP, One International Place, Boston, Massachusetts 02110. The date and time of the Closing (the “Closing Date”) shall be 9:00 a.m., Boston City Time, on October 30, 2006, subject to notification of satisfaction (or waiver) of the conditions to the Closing set forth in Sections 6 and 7 below (or such later date as is mutually agreed to by the Company and each Buyer).

(c) Purchase Price. The purchase price for each Buyer (the “Purchase Price”) of the Notes at the Closing shall be equal to the principal amount set forth opposite such Buyer’s name on the Schedule of Buyers.

(d) Form of Payment. On the Closing Date, (i) each Buyer shall pay its aggregate applicable Purchase Price to the Company for the Notes to be issued and sold to such Buyer at the Closing, by wire transfer of immediately available funds in accordance with the Company’s written wire instructions, and (ii) the Company shall deliver to each Buyer the Notes which such Buyer is then purchasing, duly executed on behalf of the Company and registered in the name of such Buyer or its designee.

2. BUYER’S REPRESENTATIONS AND WARRANTIES.

Each Buyer represents and warrants with respect to only itself that:

(a) No Public Sale or Distribution. Such Buyer is acquiring the Notes, and, upon conversion of the Notes, will acquire the Conversion Shares, for its own account and not with a view towards, or for resale in connection with, the public sale or distribution thereof, except pursuant to sales registered or exempted under the 1933 Act; provided, however, that by making the representations herein, such Buyer does not agree to hold any of the Securities for any minimum or other specific term and reserves the right to dispose of the Securities at any time in accordance with or pursuant to a registration statement or an exemption under the 1933 Act. Such Buyer is acquiring the Securities hereunder in the ordinary course of its business. Such Buyer does not presently have any agreement or understanding, directly or indirectly, with any Person to distribute any of the Securities.

(b) Accredited Investor Status. Such Buyer is an “accredited investor” as that term is defined in Rule 501(a) of Regulation D.

(c) Reliance on Exemptions. Such Buyer understands that the Securities are being offered and sold to it in reliance on specific exemptions from the registration requirements of United States federal and state securities laws and that the Company is relying in part upon the truth and accuracy of, and such Buyer’s compliance with, the representations, warranties, agreements, acknowledgments and understandings of such Buyer set forth herein in order to determine the availability of such exemptions and the eligibility of such Buyer to acquire the Securities.

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(d) Information. Such Buyer and its advisors, if any, have been furnished with all materials relating to the business, finances and operations of the Company and materials relating to the offer and sale of the Securities which have been requested by such Buyer. Such Buyer and its advisors, if any, have been afforded the opportunity to ask questions of the Company.

(e) Experience of Such Buyer. Such Buyer understands that its investment in the Securities involves a high degree of risk. Such Buyer, either alone or together with its representatives, has such knowledge, sophistication and experience in business and financial matters so as to be capable of evaluating the merits and risks of the prospective investment in the Securities, and has so evaluated the merits and risks of such investment. Such Buyer is able to bear the economic risk of an investment in the Securities and is able to afford a complete loss of such investment.

(f) No Governmental Review. Such Buyer understands that no United States federal or state agency or any other government or governmental agency has passed on or made any recommendation or endorsement of the Securities or the fairness or suitability of the investment in the Securities nor have such authorities passed upon or endorsed the merits of the offering of the Securities.

(g) Transfer or Resale. Such Buyer will not sell, offer to sell, assign, pledge, hypothecate or otherwise transfer any of the Securities unless (i) pursuant to an effective registration statement under the 1933 Act, (ii) such Buyer provides the Company with reasonable assurances and customary representations, that such Securities can be sold pursuant to Rule 144 under the 1933 Act. Notwithstanding anything to the contrary contained in the Agreement, such Buyer may transfer (without restriction) the Securities to its affiliates provided that such affiliate is an “accredited investor” under Regulation D and such affiliate agrees to be bound by the terms and conditions of the Agreement.

(h) Legends. Such Buyer understands that the certificates or other instruments representing the Notes and, until such time as the resale of the Conversion Shares have been registered under the 1933 Act, the stock certificates representing the Conversion Shares, except as set forth below, shall bear any legend as required by the “blue sky” laws of any state and a restrictive legend in substantially the following form (and a stop-transfer order may be placed against transfer of such certificates and instruments):

NEITHER THIS NOTE NOR THE SECURITIES INTO WHICH THIS NOTE IS CONVERTIBLE HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF (A) AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND APPLICABLE STATE SECURITIES LAWS, OR (B) THE TRANSFEROR PROVIDES THE COMPANY WITH REASONABLE ASSURANCES AND CUSTOMARY REPRESENTATIONS THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAWS.

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The legend set forth above shall be removed and the Company shall issue a certificate or instrument without such legend to the holder of the Securities upon which it is stamped, if, unless otherwise required by state securities laws, (i) such Securities are registered for resale under the 1933 Act; provided, that each Buyer has complied with or covenants and agrees that it will comply with the prospectus delivery requirements of the 1933 Act as applicable to it in connection with sales of such Securities pursuant to a registration statement or (ii) in connection with a sale, assignment or other transfer, such holder provides the Company with reasonable assurances and customary representations to the effect that such legend is not required under applicable requirements of the 1933 Act.

(i) Validity; Enforcement. This Agreement and Pledge and Security Agreement have been duly and validly authorized, executed and delivered on behalf of such Buyer and shall constitute the legal, valid and binding obligations of such Buyer, enforceable against such Buyer in accordance with their respective terms, except as such enforceability may be limited by general principles of equity or to applicable bankruptcy, insolvency, reorganization, moratorium, liquidation and other similar laws relating to, or affecting generally, the enforcement of applicable creditors’ rights and remedies.

(j) No Conflicts. The execution, delivery and performance by such Buyer of this Agreement and the Pledge and Security Agreement to which such Buyer is a party and the consummation by such Buyer of the transactions contemplated hereby and thereby will not (i) result in a violation of the organizational documents of such Buyer or (ii) conflict with, or constitute a default (or an event which with notice or lapse of time or both would become a default) under, or give to others any rights of termination, amendment, acceleration or cancellation of, any agreement, indenture or instrument to which such Buyer is a party, or (iii) result in a violation of any law, rule, regulation, order, judgment or decree (including federal and state securities laws) applicable to such Buyer, except in the case of clauses (ii) and (iii), for such conflicts, defaults, rights or violations which would not, individually or in the aggregate, reasonably be expected to have a material adverse effect on the ability of such Buyer to perform its obligations hereunder.

(k) Residency. Such Buyer is a resident of that jurisdiction specified in its address on the Schedule of Buyers.

3. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

The Company represents and warrants to each of the Buyers that:

(a) Organization and Qualification. Each of the Company and each Subsidiary is a corporation duly organized, validly existing and in good standing under the laws of the jurisdiction in which it is organized and has all requisite corporate power and authority to carry on its business as now conducted. Each of the Company and each Subsidiary is duly qualified to transact business and is in good standing in each jurisdiction in which the failure so to qualify would have a Material Adverse Effect. As used in this Agreement, “Material Adverse Effect” means any material adverse effect on the business, properties, assets, operations, results of operations, or financial condition of the Company and its subsidiaries taken as a whole.

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(b) Authorization; Enforcement; Validity. The Company has the requisite power and authority to enter into and perform its obligations under this Agreement, the Notes, the Pledge and Security Agreements and the Guaranty Agreement (collectively, the “Transaction Documents”) and to issue the Securities in accordance with the terms hereof and thereof. The execution and delivery of the Transaction Documents by the Company and the consummation by the Company of the transactions contemplated hereby and thereby, including, without limitation, the issuance of the Notes, the reservation for issuance and the issuance of the Conversion Shares issuable upon conversion of the Notes, and the pledging of the Antigenics MA Shares have been duly authorized by the Company’s Board of Directors and no further corporate action is required by the Company. This Agreement and the other Transaction Documents have been duly executed and delivered by the Company, and constitute the legal, valid and binding obligations of the Company, enforceable against the Company in accordance with their respective terms, except as such enforceability may be limited by general principles of equity or applicable bankruptcy, insolvency, reorganization, moratorium, liquidation or similar laws relating to, or affecting generally, the enforcement of applicable creditors’ rights and remedies.

(c) Issuance of Securities. The issuance of the Notes and the pledging of the Antigenics MA Shares have been duly authorized by the Company. As of the Closing, a number of shares of Company Common Stock shall have been duly authorized and reserved for issuance which equals the sum of 100% of the maximum number of shares of Company Common Stock issuable upon conversion of the Notes on the Closing Date. Upon issuance or conversion in accordance with the Notes, the Conversion Shares will be validly issued, fully paid and nonassessable. Assuming the accuracy of the Buyers’ representations and warranties contained herein, the offer and issuance by the Company of the Notes will be exempt from registration under the 1933 Act.

(d) No Conflicts. The execution, delivery and performance of the Transaction Documents by the Company and the consummation by the Company of the transactions contemplated hereby and thereby (including, without limitation, the issuance of the Notes, the pledging of the Antigenics MA Shares and reservation for issuance and issuance of the Conversion Shares) will not (i) result in a violation of the Certificate of Incorporation (as defined in Section 3(o)) or Bylaws (as defined in Section 3(o)) or (ii) conflict with, or constitute a default (or an event which with notice or lapse of time or both would become a default) under, or give to others any rights of termination, amendment, acceleration or cancellation of, any agreement, indenture or instrument to which the Company is a party, or (iii) result in a violation of any law, rule, regulation, order, judgment or decree (including federal and state securities laws and regulations and the rules and regulations of the Nasdaq Stock Market (the “Principal Market”)) applicable to the Company or by which any property or asset of the Company is bound or affected, except in the case of clauses (ii) and (iii), for such conflicts, defaults, rights or violations which would have a Material Adverse Effect.

(e) Consents. Except as disclosed in Schedule 3(e) and except for those failure of which to obtain or make would not have a Material Adverse Effect, and any filings required pursuant to Section 4(b) hereof, the Company is not required to obtain any consent, authorization

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or order of, or make any filing or registration with, any court, governmental agency or any regulatory or any other Person in order for it to execute, deliver or perform any of its obligations under or contemplated by the Transaction Documents, in each case in accordance with the terms hereof or thereof. All consents, authorizations, orders, filings and registrations which the Company is required to obtain pursuant to the preceding sentence have been obtained or effected on or prior to the Closing Date.

(f) Acknowledgment Regarding Buyer’s Purchase of Securities. The Company acknowledges that no Buyer is acting as a financial advisor or fiduciary of the Company (or in any similar capacity) with respect to the Transaction Documents and the transactions contemplated hereby and thereby, and any advice given by a Buyer or any of its representatives or agents in connection with the Transaction Documents and the transactions contemplated hereby and thereby is merely incidental to such Buyer’s purchase of the Securities. The Company further represents to each Buyer that the Company’s decision to enter into the Transaction Documents has been based solely on the independent evaluation by the Company and its representatives.

(g) No General Solicitation; Placement Agent’s Fees. Neither the Company, nor any Person acting on its behalf, has engaged in any form of general solicitation or general advertising (within the meaning of Regulation D) in connection with the offer or sale of the Notes. No broker has acted on behalf of the Company in connection with this Agreement, and there are no brokerage commissions, finders’ fees or similar fees or commissions payable in connection therewith based on any agreement, arrangement or understanding with the Company or any action taken by the Company.

(h) No Integrated Offering. Neither the Company, nor any Person acting on its behalf, has, directly or indirectly, made any offers or sales of any security or solicited any offers to buy any security, under circumstances that would require registration of the Notes to the Buyers under the 1933 Act or cause this offering of the Notes to be integrated with prior offerings by the Company for purposes of the 1933 Act.

(i) SEC Documents; Financial Statements. Since December 31, 2005, the Company has filed all reports, schedules, forms, statements and other documents required to be filed by it with the SEC pursuant to the reporting requirements of the Securities Exchange Act of 1934 (the “1934 Act”) (all of the foregoing and all exhibits included therein and financial statements, notes and schedules thereto and documents incorporated by reference therein being hereinafter referred to as the “SEC Documents”). As of their respective dates, the SEC Documents complied in all material respects with the requirements of the 1934 Act and the rules and regulations of the SEC promulgated thereunder and applicable thereto, and none of the SEC Documents, at the time they were filed with the SEC, contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. As of their respective dates, the financial statements of the Company included in the SEC Documents complied as to form in all material respects with applicable accounting requirements and the published rules and regulations of the SEC with respect thereto. Such financial statements have been prepared in accordance with generally accepted accounting principles, consistently applied, during the periods involved (except (i) as may be otherwise indicated in such financial

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statements or the notes thereto, or (ii) in the case of unaudited interim statements, to the extent they may exclude footnotes or may be condensed or summary statements) and fairly present in all material respects the financial position of the Company as of the dates thereof and the results of its operations and cash flows for the periods then ended (subject, in the case of unaudited statements, to normal year-end audit adjustments).

(j) Absence of Certain Changes. Except as disclosed in the SEC Documents since December 31, 2005, there has been no material adverse change and no material adverse development in the business, properties, assets, operations, results of operations, or financial condition of the Company or any Subsidiary.

(k) Regulatory Permits. Each of the Company and each Subsidiary possesses all certificates, authorizations and permits issued by the appropriate federal, state or foreign regulatory authorities necessary to conduct its business, except where the failure to possess such certificates, authorizations or permits would not have a Material Adverse Effect. Each of the Company and each Subsidiary is not in violation of any judgment, decree or order or any statute, ordinance, rule or regulation applicable to it, except for violations which would not have a Material Adverse Effect.

(l) Foreign Corrupt Practices. Neither the Company or Subsidiary, nor any director, officer, agent, employee or other Person acting on behalf of the Company or Subsidiary has, in the course of its actions for, or on behalf of, the Company or the Subsidiary (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expenses relating to political activity; (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds; (iii) violated or is in violation of any provision of the U.S. Foreign Corrupt Practices Act of 1977, as amended; or (iv) made any unlawful bribe, rebate, payoff, influence payment, kickback or other unlawful payment to any foreign or domestic government official or employee.

(m) Sarbanes-Oxley Act. The Company is in compliance with any and all applicable requirements of the Sarbanes-Oxley Act of 2002 that are effective as of the date hereof, and any and all applicable rules and regulations promulgated by the SEC thereunder that are effective as of the date hereof, except where such noncompliance would not have a Material Adverse Effect.

(n) Transactions With Affiliates. Except as disclosed in Schedule 3(n) and except as set forth in the SEC Documents, and other than the grant of stock options and restricted and non-restricted stock grants disclosed that are required to be publicly disclosed, none of the officers, directors or employees of the Company is presently a party to any transaction with the Company (other than for ordinary course services as employees, officers or directors) required to be disclosed pursuant to Regulation S-K Item 404, including any contract, agreement or other arrangement providing for the furnishing of services to or by, providing for rental of real or personal property to or from, or otherwise requiring payments to or from any such officer, director or employee or, to the knowledge of the Company, any corporation, partnership, trust or other entity in which any such officer, director, or employee has a substantial interest or is an officer, director, trustee or partner, which such transaction would be required to be disclosed.

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(o) Equity Capitalization. The capitalization of the Company as of September 30, 2006 is as set forth on Schedule 3(o) hereto. All the outstanding shares of Company capital stock have been validly issued and are fully paid and nonassessable. Except as disclosed in Schedule 3(o): (i) none of the Company’s share capital is subject to preemptive rights that would be triggered upon issuance of the Securities; (ii) except as disclosed in the Form 10-K of the Company filed in March 2006 with the SEC or subsequently filed Forms 10-Q or Forms 8-K, there are no outstanding options, warrants, scrip, rights to subscribe for, calls or other rights convertible into, or exercisable or exchangeable for, any share capital of the Company by which the Company is bound to issue additional share capital of the Company, and (iii) there are no outstanding debt securities, notes, credit agreements, credit facilities or other agreements, documents or instruments evidencing Indebtedness (as defined in Section 3(p)) by which the Company is bound. The Company has made available to each Buyer true, correct and complete copies of the Company’s Certificate of Incorporation, as amended and as in effect on the date hereof (the “Certificate of Incorporation”), and the Company’s Bylaws, as amended and as in effect on the date hereof (the “Bylaws”).

(p) Indebtedness and Other Contracts. Except as disclosed in Schedule 3(p) or in the SEC Documents, each of the Company and each Subsidiary (i) has no outstanding Indebtedness (as defined below) other than Permitted Indebtedness (as defined in the Note), including Indebtedness secured by Permitted Liens, and (ii) is not in violation of any term of or in default under any contract, agreement or instrument relating to any Indebtedness, except where such violations and defaults would not result in a Material Adverse Effect. For purposes of this Agreement: (x) “Indebtedness” of any Person means, without duplication (A) all indebtedness for borrowed money, (B) all obligations issued, undertaken or assumed as the deferred purchase price of property or services (including, without limitation, “capital leases” in accordance with generally accepted accounting principals) (other than trade payables entered into in the ordinary course of business), (C) all reimbursement or payment obligations with respect to letters of credit, and surety bonds, (D) all obligations evidenced by notes, bonds, or debentures, (E) all indebtedness created or arising under any conditional sale or other title retention agreement, or incurred as financing, in either case with respect to any property or assets acquired with the proceeds of such indebtedness (even though the rights and remedies of the seller or bank under such agreement in the event of default are limited to repossession or sale of such property), (F) all monetary obligations under any leasing or similar arrangement which, in connection with generally accepted accounting principles, consistently applied for the periods covered thereby, is classified as a capital lease, (G) all indebtedness referred to in clauses (A) through (F) above secured by any mortgage, lien, pledge, charge, or security interest upon or in any property or assets (including accounts and contract rights) owned by any Person, even though the Person which owns such assets or property has not assumed or become liable for the payment of such indebtedness, and (H) all Contingent Obligations in respect of indebtedness or obligations of others of the kinds referred to in clauses (A) through (G) above; (y) “Contingent Obligation” means, as to any Person, any direct or indirect liability, contingent or otherwise, of that Person with respect to any indebtedness, lease, or other monetary obligation of another Person if the primary purpose or intent of the Person incurring such liability is to provide assurance to the obligee of such liability that such liability will be paid or discharged; and (z) “Person” means an individual, a limited liability company, a partnership, a joint venture, a corporation, a trust, an unincorporated organization and a government or any department or agency thereof.

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(q) Litigation. Except as set forth in Schedule 3(q) or in the SEC Reports, there is no action, suit, proceeding, inquiry or investigation before any court, public board, government agency, self-regulatory organization or body pending other than those which would not have a Material Adverse Effect. Each of the Company and Antigenics MA, has, in all material respects, complied with all laws, regulations and orders applicable to its business, including Pharmaceutical Laws (as defined below), and has all material permits and licenses required thereby. For purposes of this Agreement, “Pharmaceutical Law” shall mean any federal, state, local or foreign law, statute, rule or regulation relating to the development, commercialization and sale of pharmaceutical and biotechnology products and devices, including all applicable regulations of the U.S. Food and Drug Administration and comparable applicable foreign regulatory authorities.

(r) Insurance. Each of the Company and each Subsidiary is insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are prudent and customary in the businesses in which either the Company or Subsidiary is engaged.

(s) Employee Relations. The Company is not a party to any collective bargaining agreement. The Company is in compliance with all federal, state, local and foreign laws and regulations respecting labor, employment and employment practices and benefits, terms and conditions of employment and wages and hours, except where failure to be in compliance would not reasonably be expected to result in a Material Adverse Effect.

(t) Intellectual Property Rights. Except as disclosed with the Securities and Exchange Commissions or as set forth on Schedule 3(t): (a) the Company and each of its subsidiaries owns or possesses adequate rights or licenses to use all trademarks, trade names, service marks, service mark registrations, service names, patents, patent rights, copyrights, trade secrets and other intellectual property rights (“Intellectual Property Rights”) necessary to conduct their respective businesses as now conducted; (b) the Company does not have any knowledge of any infringement by the Company of Intellectual Property Rights of others, nor does the Company have reason to believe that the Company has, or would infringe on the Intellectual Property Rights of others, the enforcement of which would result in a Materially Adverse Effect on financial conditions; (c) there is no claim, action or proceeding against the Company regarding its Intellectual Property Rights; (d) the Company has no knowledge of any infringement or improper use by any third party of any of the Company’s Intellectual Property Rights; (e) the Company has taken reasonable security measures to protect the secrecy, confidentiality and value of all of its Intellectual Property Rights; (f) the Company shall own, or shall cause Antigenics MA to at all times own all right, title and interest in all Intellectual Property Rights, which the Company or Antigenics MA, respectively own as of the Issuance Date and which may exist in the future, relating to QS-21 and AG-707. Such rights held by Antigenics MA shall include without limitation all rights, royalties or licensing revenues from the sale thereof relating to QS-21 and AG-707. Notwithstanding anything in this Section 3(t) to the contrary, the Company may consummate a Spin-off (as such term is defined the Pledge and Security Agreement), enter into partnership, license and collaboration agreements and other similar arrangements.

(u) Environmental Laws. Each of the Company and each Subsidiary (i) is in compliance with any and all Environmental Laws (as hereinafter defined), (ii) has received all

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permits, licenses or other approvals required of them under applicable Environmental Laws to conduct their respective businesses and (iii) is in compliance with all terms and conditions of any such permit, license or approval where, in each of the foregoing clauses (i), (ii) and (iii), the failure to so comply could be reasonably expected to have, individually or in the aggregate, a Material Adverse Effect. The term “Environmental Laws” means all federal, state, local or foreign laws relating to pollution or protection of human health or the environment (including, without limitation, ambient air, surface water, groundwater, land surface or subsurface strata), including, without limitation, laws relating to emissions, discharges, releases or threatened releases of chemicals, pollutants, contaminants, or toxic or hazardous substances or wastes (collectively, “Hazardous Materials”) into the environment, or otherwise relating to the manufacture, processing, distribution, use, treatment, storage, disposal, transport or handling of Hazardous Materials, as well as all authorizations, codes, decrees, demands or demand letters, injunctions, judgments, licenses, notices or notice letters, orders, permits, plans or regulations issued, entered, promulgated or approved thereunder.

(v) Investment Company. The Company is not, and is not an affiliate of, an “investment company” within the meaning of the Investment Company Act of 1940, as amended.

(w) Tax Status. Except as would not have a Material Adverse Effect, the Company (i) has made or filed all foreign, federal and state income and all other tax returns, reports and declarations required by any jurisdiction to which it is subject, (ii) has paid all taxes and other governmental assessments and charges that are material in amount, shown or determined to be due on such returns, reports and declarations, except those being contested in good faith and (iii) has set aside on its books provision reasonably adequate for the payment of all taxes for periods subsequent to the periods to which such returns, reports or declarations apply.

(x) Internal Accounting and Disclosure Controls. The Company maintains a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations, (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset and liability accountability, (iii) access to assets or incurrence of liabilities is permitted only in accordance with management’s general or specific authorization and (iv) the recorded accountability for assets and liabilities is compared with the existing assets and liabilities at reasonable intervals and appropriate action is taken with respect to any difference. The Company maintains disclosure controls and procedures (as such term is defined in Rule 13a-14 under the 1934 Act) that are effective in ensuring that information required to be disclosed by the Company in the reports that it files or submits under the 1934 Act is recorded, processed, summarized and reported, within the time periods specified in the rules and forms of the SEC, including, without limitation, controls and procedures designed to ensure that information required to be disclosed by the Company in the reports that it files or submits under the 1934 Act is accumulated and communicated to the Company’s management, including its principal executive officer or officers and its principal financial officer or officers, as appropriate, to allow timely decisions regarding required disclosure.

(y) Off Balance Sheet Arrangements. There is no transaction, arrangement, or other relationship between the Company and an unconsolidated or other off balance sheet entity that is required to be disclosed by the Company in its Exchange Act filings and is not so disclosed or that otherwise would have a Material Adverse Effect.

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(z) Ranking of Notes. Except as disclosed on Schedule 3(p) or the SEC Documents, no Indebtedness (other than Permitted Indebtedness (as defined in the Note), including Indebtedness secured by Permitted Liens) of the Company is senior to or ranks pari passu with the Notes in right of payment, whether with respect of payment of redemptions, interest, damages or upon liquidation or dissolution or otherwise.

(aa) Antigenics MA Shares.

i. The Company is the beneficial and record owner of all of the Antigenics MA Shares, free and clear of any Liens, and upon transfer in accordance with the applicable Transaction Documents, the Company will transfer to the Buyers good and marketable title to such Antigenics MA Shares, free and clear of any Liens imposed by or through the Company.

ii. The Company has no legal obligation, absolute or contingent, to any other Person to transfer or sell any of the Antigenics MA Shares. There is no action, claim, suit, investigation or proceeding pending or, to the knowledge of the Company, threatened by or against or affecting the Company or the Company’s ownership of the Antigenics MA Shares before any court or governmental or regulatory authority or body, that could materially impact the ability of the Company to pledge and transfer to the Buyers any Antigenics MA Shares. There are no writs, decrees, injunctions or orders of any court or governmental or regulatory agency, authority or body outstanding against the Company with respect to the Antigenics MA Shares.

(bb) Transfer Taxes. On the Closing Date, all stock transfer or other taxes (other than income or similar taxes) which are required to be paid in connection with the sale and transfer of the Notes to be sold to each Buyer hereunder will be, or will have been, fully paid or provided for by the Company, and all laws imposing such taxes will be or will have been complied with.

(cc) Manipulation of Price. The Company has not, and to its knowledge no one acting on its behalf has, (i) taken, directly or indirectly, any action designed to cause or to result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale of the Notes or (ii) sold, bid for, purchased, or paid any compensation for soliciting purchases in the marketplace of, any of the Notes.

(dd) Seniority. As of the Closing Date, no Indebtedness of the Company will be senior to the Notes in right of payment, whether with respect to interest or upon liquidation or dissolution, except as disclosed on Schedule 3(p).

(ee) Subsidiaries. As of the Closing Date, each of the Company and Antigenics MA have no directly held Subsidiary other than those listed on Schedule 3 (ee). The Company is the beneficial owner (and the Company or the Company’s Subsidiary listed on Schedule 3(ee) is the record owner) of all of the equity interests in the Company’s Subsidiaries and holds such equity interests free and clear of all encumbrances except as are imposed by applicable securities laws.

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4. COVENANTS.

(a) Efforts. Each party shall use its reasonable commercial efforts timely to satisfy each of the conditions to be satisfied by it as provided in Sections 6 and 7 of this Agreement.

(b) Form D and Blue Sky. The Company agrees to file a Form D with respect to the Notes and to provide a copy thereof to each Buyer promptly after such filing. The Company shall, on or before the Closing Date, take such action as the Company shall reasonably determine is necessary to be taken on or before the Closing Date in order to obtain an exemption for or to qualify the Notes for sale to the Buyers at the Closing pursuant to this Agreement under applicable securities or “Blue Sky” laws of the states of the United States (or to obtain an exemption from such qualification). The Company shall make all filings and reports relating to the offer and sale of the Notes required under applicable securities or “Blue Sky” laws of the states of the United States following the Closing Date.

(c) Use of Proceeds. The Company will use the proceeds from the sale of the Notes for working capital and other general corporate purposes.

5. REGISTER; TRANSFER AGENT INSTRUCTIONS.

(a) Register. The Company shall maintain at its principal executive offices (or such other office or agency of the Company as it may designate by notice to each holder of Notes), a register for the Notes, in which the Company shall record the name and address of the Person in whose name the Notes have been issued (including the name and address of each transferee) the principal amount of the Notes held by such Person. The Company shall keep the register open and available during business hours for inspection by any Buyer or its legal representatives upon prior written notice.

(b) Transfer Agent Instructions. The Company shall issue irrevocable instructions to its transfer agent, and any subsequent transfer agent, to issue certificates or credit shares to the applicable balance accounts at The Depository Trust Company, registered in the name of each Buyer or its respective nominee(s), for the Conversion Shares, if any, in such amounts as specified from time to time by each Buyer to the Company upon conversion of the Notes. The Company warrants that no instruction other than the Irrevocable Transfer Agent Instructions referred to in this Section 5(b), and stop transfer instructions to give effect to Section 2(g) hereof, will be given by the Company to its transfer agent with respect to the Securities, and that the Securities shall otherwise be freely transferable on the books and records of the Company, as applicable, and to the extent provided in this Agreement and the other Transaction Documents.

6. CONDITIONS TO THE COMPANY’S OBLIGATION TO SELL.

The obligation of the Company hereunder to issue and sell the Notes to each Buyer at the Closing is subject to the satisfaction, at or before the Closing Date, of each of the following conditions, provided that these conditions are for the Company’s sole benefit and may be waived by the Company at any time in its sole discretion by providing each Buyer with prior written notice thereof:

(a) All of the Buyers shall have executed each of the Transaction Documents to which it is a party and delivered the same to the Company.

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(b) All of the Buyers shall have delivered to the Company the Purchase Price for the Notes being purchased by such Buyer at the Closing by wire transfer of immediately available funds pursuant to the wire instructions provided by the Company.

(c) The representations and warranties of each Buyer shall be true and correct as of the date when made and as of the Closing Date as though made at that time (except for representations and warranties that speak as of a specific date), and each Buyer shall have performed, satisfied and complied in all material respects with the covenants, agreements and conditions required by this Agreement to be performed, satisfied or complied with by such Buyer at or prior to the Closing Date.

7. CONDITIONS TO EACH BUYER’S OBLIGATION TO PURCHASE.

The obligation of each Buyer hereunder to purchase the Notes at the Closing is subject to the satisfaction, at or before the Closing Date, of each of the following conditions, provided that these conditions are for each Buyer’s sole benefit and may be waived by such Buyer at any time in its sole discretion by providing the Company with prior written notice thereof:

(a) The Company shall have executed and delivered to such Buyer (A) each of the Transaction Documents and (B) the Notes being purchased by such Buyer at the Closing pursuant to this Agreement.

(b) Such Buyer shall have received the opinion of internal or external counsel to the Company in form, scope and substance reasonably satisfactory to such Buyer.

(c) The Company shall have delivered to such Buyer a certificate evidencing the incorporation and good standing of the Company and each of its Subsidiaries.

(d) The Company shall have delivered to such Buyer a certificate evidencing the Company’s qualification as a foreign corporation issued by the Secretary of State of Massachusetts as of a date within five (5) days of the Closing Date.

(e) The Company shall have delivered to such Buyer a certified copy of the Certificate of Incorporation as certified by the Secretary of State of the State of Delaware within five (5) days of the Closing Date.

(f) The Company shall have delivered to such Buyer a certificate, executed by the Secretary of the Company and dated as of the Closing Date, as to (i) the resolutions adopted by the Company’s Board of Directors or a committee thereof in connection herewith, (ii) the Bylaws, and (iii) and the incumbency of the officers executing documents on behalf of the Company in connection herewith.

(g) The representations and warranties of the Company shall be true and correct in all material respects (except for those representations and warranties that are qualified by materiality or Material Adverse Effect, which shall be true and correct in all respects) as of the date of this

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Agreement and as of the Closing Date as though made at that time (except for representations and warranties that speak as of a specific date) and the Company shall have performed, satisfied and complied in all material respects with the covenants, agreements and conditions required by the Transaction Documents to be performed, satisfied or complied with by the Company at or prior to the Closing Date. Such Buyer shall have received a certificate, executed by the Chief Executive Officer of the Company, dated as of the Closing Date, as to the foregoing.

8. TERMINATION.

In the event that the Closing shall not have occurred with respect to a Buyer on or before ten (10) Business Days from the date hereof due to the Company’s or such Buyer’s failure to satisfy the conditions set forth in Sections 6 and 7 above (and the nonbreaching party’s failure to waive such unsatisfied condition(s)), the nonbreaching party shall have the option to terminate this Agreement with respect to such breaching party at the close of business on such date without liability of any party to any other party.

9. COLLATERAL AGENT

(a) Collateral Agent’s Authority to Act, etc. Each of the Buyers appoints and authorizes Ingalls & Snyder LLC to act for Buyers as collateral agent (the “Collateral Agent”) in connection with the granting of a security interest in the Pledged Securities as contemplated by this Agreement and the Pledge and Security Agreement. All action in connection with the enforcement of, or the exercise of any remedies under this Agreement and the Pledge and Security Agreement shall be taken in the manner set forth therein.

(b) Collateral Agent’s Resignation. The Collateral Agent may resign at any time by giving at least 30 days’ prior written notice of its intention to do so to each of the Buyers and the Company and upon the appointment by the holders of at least 60% in principal amount of the outstanding Notes (the “Majority Noteholders”) of a successor Collateral Agent reasonably satisfactory to the Company. If no successor Collateral Agent shall have been so appointed and shall have accepted such appointment within 15 days after the retiring Collateral Agent’s giving of such notice of resignation, then the retiring Collateral Agent may appoint a successor Collateral Agent which shall be a bank or a trust company organized under the laws of the United States of America or any state thereof and having a combined capital, surplus and undivided profit of at least $500,000,000 (so long as no Event of Default exists) with the consent of the Company, which shall not be unreasonably withheld; provided, however, that any successor Collateral Agent appointed under this sentence may be removed upon the written request of the Majority Noteholders, which request shall also appoint a successor Collateral Agent (so long as no Event of Default exists) reasonably satisfactory to the Company. Upon the appointment of a new Collateral Agent hereunder, the term “Collateral Agent”, shall for all purposes of this Agreement and the Pledge & Security Agreement thereafter mean such successor. After any retiring Collateral Agent’s resignation hereunder as Collateral Agent, or the removal hereunder of any successor Collateral Agent, the provisions of this Agreement and the Pledge & Security Agreement shall continue to inure to the benefit of such retiring or removed Collateral Agent as to any actions taken or omitted to be taken by it while it was Collateral Agent under this Agreement and the Pledge & Security Agreement.

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(c) Concerning the Collateral Agent

i. Action in Good Faith, etc. The Collateral Agent and its officers, directors, employees and agents shall have no liability to any of the Buyers or to any future holder of any Notes for any action or failure to act taken or suffered in good faith, and any action or failure to act in accordance with an opinion of its counsel shall conclusively be deemed to be in good faith. The Collateral Agent shall in all cases be entitled to rely, and shall be fully protected in relying, on instructions given to the Collateral Agent by the Majority Noteholders. The Collateral Agent may execute releases and other collateral termination documents with respect to assets disposed of by the Company as permitted by this Agreement.

ii. No Implied Duties, etc. The Collateral Agent shall have and may exercise such powers as are specifically delegated to the Collateral Agent under this Agreement or the Pledge & Security Agreement together with all other powers incidental thereto. The Collateral Agent shall have no implied duties to any Person or any obligation to take any action under this Agreement or the Pledge & Security Agreement except for action specifically provided for in this Agreement or the Pledge & Security Agreement to be taken by the Collateral Agent.

iii. Validity, etc. The Collateral Agent shall not be responsible to any Buyer or any future holder of any Notes (a) for the legality, validity, enforceability or effectiveness of this Agreement or the Pledge & Security Agreement, (b) for any recitals, reports, representations, warranties or statements contained in or made in connection with this Agreement or the Pledge & Security Agreement, (c) for the existence or value of any assets included in any security for the Credit Obligations (as defined in the Pledge & Security Agreement), (d) for the effectiveness of any lien purported to be included in the Pledged Securities, (e) for the specification or failure to specify any particular assets to be included in the Pledged Securities, or (f) unless the Collateral Agent shall have failed to comply with Section 9(c)(i), for the perfection of the security interests.

iv. Compliance. The Collateral Agent shall not be obligated to ascertain or inquire as to the performance or observance of any of the terms of this Agreement or the Pledge & Security Agreement.

v. Employment of Agents and Counsel. The Collateral Agent may execute any of its duties as Collateral Agent under this Agreement or the Pledge & Security Agreement by or through employees, agents and attorneys-in-fact and shall not be responsible to any of the Buyers, any future holder of any Notes, or the Company for the default or misconduct of any such agents or attorneys-in-fact selected by the Collateral Agent acting in good faith. The Collateral Agent shall be entitled to advice of counsel concerning all matters pertaining to the agency hereby created and its duties hereunder or under the Pledge & Security Agreement.

vi. Reliance on Documents and Counsel. The Collateral Agent shall be entitled to rely, and shall be fully protected in relying, upon any affidavit, certificate, cablegram, consent, instrument, letter, notice, order, document, statement, facsimile, telegram, telex or teletype message or writing reasonably believed in good faith by the Collateral Agent to be genuine and correct and to have been signed, sent or made by the Person in question, including any telephonic or oral statement made by such Person, and, with respect to legal matters, upon an opinion or the advice of counsel selected by the Collateral Agent.

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vii. Collateral Agent’s Reimbursement. Each of the Buyers, and each future holder of Notes as successor to a Buyer severally agrees to reimburse the Collateral Agent, pro rata in accordance with such Buyer’s percentage interest (determined based on the ratio of the aggregate principal amount of the Notes held by such Buyer or holder of Notes to the aggregate amount of all outstanding Notes), for any reasonable expenses not reimbursed by the Company (without limiting the obligation of the Company to make such reimbursement): (a) for which the Collateral Agent is entitled to reimbursement by the Company under this Agreement or the Pledge & Security Agreement and (b) after the occurrence and during the continuance of an Event of Default, for any other reasonable expenses incurred by the Collateral Agent on the Buyers’ behalf in connection with the enforcement of the Buyers’ rights under this Agreement or the Pledge & Security Agreement; provided, however, that the Collateral Agent shall not be reimbursed for any such expenses arising as a result of its gross negligence or willful misconduct. Such reimbursement shall be provided within 30 days of a written notice by the Collateral Agent , providing proof of expenses and amounts due from each Buyer (calculated in the manner set forth in this Section 9(c)(vii))).

(d) Indemnification. The Buyers shall severally indemnify the Collateral Agent and its officers, directors, employees, agents, attorneys, accountants, consultants and controlling Persons (to the extent not reimbursed by the Buyers and without limiting the obligation of the Buyers to do so), pro rata in accordance with their respective percentage interests (as determined in accordance with Section 9(a)(vii)), from and against any and all liabilities, obligations, damages, penalties, actions, judgments, suits, losses (including accrued and unpaid Collateral Agent’s fees), costs, expenses or disbursements of any kind whatsoever which may at any time be imposed on, incurred by or asserted against a Collateral Agent or such Persons relating to or arising out of this Agreement, the Pledge & Security Agreement, the transactions contemplated hereby or thereby, or any action taken or omitted by the Collateral Agent in connection with any of the foregoing; provided, however, that the foregoing shall not extend to actions or omissions which are determined in a final, nonappealable judgment by a court of competent jurisdiction to have been taken by the Collateral Agent with gross negligence or willful misconduct. Such indemnification shall, in all cases, be provided within 30 days of a written notice by Collateral Agent, providing proof of expenses and amounts due from each Buyer (calculated in the manner set forth in Section 9(c)(vii)).

(e) Assumption of Agent’s Rights. Notwithstanding anything herein or in this Agreement or the Pledge & Security Agreement to the contrary, if at any time no Person constitutes a Collateral Agent hereunder or a Collateral Agent fails to act upon written directions from the Majority Noteholders, the Majority Noteholders shall be entitled to exercise any power, right or privilege granted to the Collateral Agent under this Agreement or the Pledge & Security Agreement and in so acting the Majority Noteholders shall have the same rights, privileges, indemnities and protections provided to the Collateral Agent under this Agreement or the Pledge & Security Agreement.

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10. MISCELLANEOUS.

(a) Governing Law; Jurisdiction; Jury Trial. All questions concerning the construction, validity, enforcement and interpretation of this Agreement shall be governed by the internal laws of the State of New York, without giving effect to any choice of law or conflict of law provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York. Each party hereby irrevocably submits to the exclusive jurisdiction of the state and federal courts sitting in The City of New York, Borough of Manhattan, for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or discussed herein, and hereby irrevocably waives, and agrees not to assert in any suit, action or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action or proceeding is brought in an inconvenient forum or that the venue of such suit, action or proceeding is improper. Each party hereby irrevocably waives personal service of process and consents to process being served in any such suit, action or proceeding by mailing a copy thereof to such party at the address for such notices to it under this Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof. Nothing contained herein shall be deemed to limit in any way any right to serve process in any manner permitted by law.

(b) Counterparts. This Agreement may be executed in two or more identical counterparts, all of which shall be considered one and the same agreement and shall become effective when counterparts have been signed by each party and delivered to the other party; provided that a facsimile signature shall be considered due execution and shall be binding upon the signatory thereto with the same force and effect as if the signature were an original, not a facsimile signature.

(c) Headings. The headings of this Agreement are for convenience of reference and shall not form part of, or affect the interpretation of, this Agreement.

(d) Severability. If any provision of this Agreement shall be invalid or unenforceable in any jurisdiction, such invalidity or unenforceability shall not affect the validity or enforceability of the remainder of this Agreement in that jurisdiction or the validity or enforceability of any provision of this Agreement in any other jurisdiction.

(e) Entire Agreement; Amendments. This Agreement supersedes all other prior oral or written agreements between the Buyers, the Company, their affiliates and Persons acting on their behalf with respect to the matters discussed herein, and this Agreement and the instruments referenced herein contain the entire understanding of the parties with respect to the matters covered herein and therein and, except as specifically set forth herein or therein, neither the Company nor any Buyer makes any representation, warranty, covenant or undertaking with respect to such matters. No provision of this Agreement may be amended other than by an instrument in writing signed by the Company and the holders of Notes representing at least a majority of the aggregate principal amount of the Notes, or, if prior to the Closing Date, the Company and the Buyers listed on the Schedule of Buyers as being obligated to purchase at least a majority of the aggregate principal amount of the Notes, and any amendment to this Agreement made in conformity with the provisions of this Section 9(e) shall be binding on all Buyers and holders of Notes, as applicable. No provision hereof may be waived other than by an instrument in writing signed by the party against whom enforcement is sought. No such amendment shall

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be effective to the extent that it applies to less than all of the holders of the Notes then outstanding. No consideration shall be offered or paid to any Person to amend or consent to a waiver or modification of any provision of any of the Transaction Documents unless the same consideration also is offered to all of the parties to the Transaction Documents. The Company has not, directly or indirectly, made any agreements with any Buyers relating to the terms or conditions of the transactions contemplated by the Transaction Documents except as set forth in the Transaction Documents.

(f) Notices. Any notices, consents, waivers or other communications required or permitted to be given under the terms of this Agreement must be in writing and will be deemed to have been delivered: (i) upon receipt, when delivered personally; (ii) upon receipt, when sent by facsimile (provided confirmation of transmission is mechanically or electronically generated and kept on file by the sending party); or (iii) one Business Day after deposit with an overnight courier service, in each case properly addressed to the party to receive the same. The addresses and facsimile numbers for such communications shall be:

If to the Company:

Antigenics Inc.
630 Fifth Avenue
Suite 2100
New York, NY 10111
Telephone:	(212) 994-8200
Facsimile:	(212) 994-8299
Attention:	Garo H. Armen

with a copy to:

Ropes & Gray LLP
One International Place
Boston, Massachusetts 02110
Telephone:	(617) 951-7000
Facsimile:	(617) 951-7050
Attention:	Paul M. Kinsella

If to a Buyer, to its address and facsimile number set forth on the Schedule of Buyers, with copies to such Buyer’s representatives as set forth on the Schedule of Buyers,

with a copy (for informational purposes only) to:

Cohen & Gresser LLP
100 Park Avenue
New York, New York 10017
Telephone:	(212) 957-7600
Facsimile:	(212) 957-4514
Attention:	Lawrence T. Gresser

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or to such other address and/or facsimile number and/or to the attention of such other Person as the recipient party has specified by written notice given to each other party five (5) days prior to the effectiveness of such change. Written confirmation of receipt (A) given by the recipient of such notice, consent, waiver or other communication, (B) mechanically or electronically generated by the sender’s facsimile machine containing the time, date, recipient facsimile number and an image of the first page of such transmission or (C) provided by an overnight courier service shall be rebuttable evidence of personal service, receipt by facsimile or receipt from an overnight courier service in accordance with clause (i), (ii) or (iii) above, respectively.

(g) Successors and Assigns. This Agreement shall be binding upon and inure to the benefit of the parties and their respective successors and assigns, including any purchasers of the Notes. The Company shall not assign this Agreement or any rights or obligations hereunder without the prior written consent of the holders of at least a majority of the Notes hereunder.

(h) No Third Party Beneficiaries. This Agreement is intended for the benefit of the parties hereto and their respective permitted successors and assigns, and is not for the benefit of, nor may any provision hereof be enforced by, any other Person.

(i) Replacement of Securities. If any certificate or instrument evidencing any Securities is mutilated, lost, stolen or destroyed, the Company shall issue or cause to be issued in exchange and substitution for and upon cancellation thereof, or in lieu of and substitution therefor, a new certificate or instrument, but only upon receipt of evidence reasonably satisfactory to the Company of such loss, theft or destruction and customary and reasonable indemnity, if requested. The applicants for a new certificate or instrument under such circumstances shall also pay any reasonable third-party costs associated with the issuance of such replacement Securities.

(j) Fees and expenses. Each party shall pay all costs and expenses that it incurs with respect to the negotiation, execution, delivery and performance of this Agreement; provided, however, that at the Closing, the Company shall reimburse the Buyers for their reasonable legal and other professional fees and out of pocket expenses up to $100,000 in the aggregate.

(k) Confidentiality. At no time will a party, without the prior written consent of any other party, make any press releases or public announcements concerning this Agreement or the other ancillary agreements; provided, however, that any party may make any public disclosure required by applicable law or any listing or trading agreement concerning its publicly traded securities (in which case the disclosing party will use its best efforts to advise the other parties prior to making the disclosure). Each party shall keep confidential any and all information obtained in connection with this Agreement and shall not disclose any such information to any other Person except: (a) with the prior written consent of the other party; (b) as required by law, regulation, or court order, but only after notice has been provided to such other party; or (c) for such information as shall have been publicly disclosed other than in violation of this Agreement or of any other obligation of confidentiality to such other party.

[Signature Page Follows]

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IN WITNESS WHEREOF, each Buyer and the Company have caused their respective signature page to this Securities Purchase Agreement to be duly executed as of the date first written above.

COMPANY:
ANTIGENICS INC.
By:	/s/ Garo H. Armen
Name:	Garo H. Armen
Title:	Chairman & Chief Executive Officer

Signature Page to Securities Purchase Agreement

IN WITNESS WHEREOF, each Buyer and the Company have caused their respective signature page to this Securities Purchase Agreement to be duly executed as of the date first written above.

COLLATERAL AGENT:
INGALLS & SNYDER LLC
By:	/s/ Thomas O. Boucher, Jr.
Name:	Thomas O. Boucher, Jr.
Title:	Manager

Signature Page to Securities Purchase Agreement

IN WITNESS WHEREOF, each Buyer and the Company have caused their respective signature page to this Securities Purchase Agreement to be duly executed as of the date first written above.

BUYERS:
Ingalls & Snyder Value Partners L.P.
By:	/s/ Thomas O. Boucher, Jr.
Name:	Thomas O. Boucher, Jr.
Title:	General Partner
Penrith LTD
By:	/s/ Yvonne Koenig
Name:
Title:	President + C.E.O.

SCHEDULE OF BUYERS

Buyer	Address and Facsimile Number	Aggregate Principal Amount of Notes
Ingalls & Snyder Value Partners L.P.	c/o Ingalls & Snyder LLC Attn: Tom Boucher 61 Broadway New York, NY 10006 Facsimile: (212) 269-7893	$	20,000,000
Penrith LTD	c/o Ingalls & Snyder LLC Attn: Tom Boucher 61 Broadway New York, NY 10006 Facsimile: (212) 269-7893	$	5,000,000

EXHIBITS

Exhibit A	Form of Notes
Exhibit B	Form of PIK Notes
Exhibit C	Form of Pledge and Security Agreement
Exhibit D	Form of Irrevocable Transfer Agent Instructions

SCHEDULES

Schedule 3(e)	Consents
Schedule 3(n)	Transaction with Affiliates
Schedule 3(o)	Capitalization
Schedule 3(p)	Indebtedness and Other Contracts/Seniority
Schedule 3(q)	Litigation
Schedule 3(t)	Intellectual Property Rights
Schedule3(ee)	Subsidiaries

Schedule 3(e)

Consents

None.

Schedule 3(n)

Transaction with Affiliates

None.

Schedule 3(o)

Capitalization

The following table sets forth our cash, cash equivalents and short-term investments and capitalization as of June 30, 2006:

• on an actual basis; and

• on an adjusted basis to give effect to the sale of $25,000,000 aggregate principal amount of our 8.0% convertible senior notes due 2011, after deducting discounts and commissions and estimated offering expenses to be paid by us.

(in thousands, except per share data)	As of June 30, 2006
	Actual			As adjusted
	(unaudited)
Cash, cash equivalents and short-term investments	$	31,867		$	56,867
Current portion, long-term debt		1,204			1,204
Long-term debt, less current portion		—			—
Convertible senior notes due 2025		50,000			50,000
Convertible senior secured notes due 2011		—			25,000
Total		51,204			76,204
Stockholders’ equity:
Preferred Stock, par value $0.01 per share; 25,000,000 shares authorized; Series A Convertible Preferred Stock, par value $0.01 per share; 31,620 shares designated, issued and outstanding, actual and as adjusted		—			—
Common stock, $0.01 par value per share; 100,000,000 shares authorized; 45,810,870 shares issued and outstanding, actual and as adjusted		458			458
Additional paid in capital		441,926			441,926
Deferred compensation		—			—
Accumulated other comprehensive (loss) income		(52	)		(52	)
Accumulated deficit		(439,286	)		(439,286	)
Total stockholders’ equity		3,046			3,046
Total capitalization	$	54,250		$	79,250

The table above should be read in conjunction with our consolidated financial statements and related notes. The number of actual and as adjusted shares of our common stock outstanding excludes the following:

• 6,246,692 shares of our common stock issuable upon exercise of options outstanding as of June 30, 2006, at a weighted average exercise price of $8.31 per share, of which options to purchase 2,978,702 shares were exercisable as of that date;

• 8,910 shares of our common stock issuable upon exercise of warrants outstanding as of June 30, 2006, at a weighted average exercise price of $54.71 per share, all of which were exercisable as of that date;

• 79,203 shares outstanding under our Directors’ Deferred Compensation plan;

• 2,432,910 shares of our common stock available for future grant under our equity incentive plans as of June 30, 2006;

• 2,000,000 shares of our common stock issuable upon conversion of outstanding Series A Convertible Preferred Stock;

• 4,645,115 shares of our common stock initially issuable upon conversion of $50,000,000 aggregate principal amount of our 5.25% convertible senior notes due 2025; and

• 7,142,857 shares of our common stick initially issuable upon conversion of $25,000,000 aggregate principal amount of our 8.0% convertible senior secured notes due 2011.

Schedule 3(p)

Indebtedness and Other Contracts/Seniority

1. The Company owes $1,065,800 as debt to General Electric Corporation.

2. The Company may owe a capital call of $375,000 to Applied Genomic Technology Capital Fund.

3. Letters of Credit in connection with security deposits in Lexington, Massachusetts, Framingham, Massachusetts and New York, New York.

4. Antigenics MA owes $146,061 in the form of subordinated debentures plus accrued interested of $51,490.

Schedule 3(q)

Litigation

None.

Schedule 3(t)

Intellectual Property Rights

1. Antigenics MA has asserted a claim against Progenics Pharmaceuticals Inc. for possible infringement of Antigenics MA QS-21 patent rights and/or for misuse or misappropriation of QS-21 under its License and Supply Agreement and Material Transfer Agreement with the Antigenics MA. Progenics disputes the claim and the parties are discussing and negotiating a settlement.

2. The Company and its Subsidiaries from time to time in-licenses technology and patent rights that may related to the practice of the QS-21 and AG-707 Intellectual Property rights, and generally only holds non-exclusive license rights under such agreements.

3. The only agreements with third parties under which royalties are payable to third parties are the license agreements pertaining to AG-707 filed with the Securities and Exchange Commission.

4. Antigenics MA in the ordinary course of business enters into collaboration agreements, license agreements, and supply agreements with third parties seeking to develop and use QS-21 as a vaccine adjuvant under which Antigenics MA grants exclusive and non-exclusive license and supply rights under the Intellectual Property Rights to such third parties.

5. The Company and Antigenics MA have entered into a royalty-free cross license that provides Antigenics MA with exclusive license rights to all Intellectual Property Rights owned or controlled by the Company that are necessary to make, use, sell and import AG-707 and QS-21, and that provides the Company with exclusive license rights to all Intellectual Property Rights owned or controlled by Antigenics MA that are necessary to make, use, sell and import any products other than AG-707 and QS-21.

6. Antigenics MA and GlaxoSmithKline each hold an undivided joint ownership interest in 2 patent families covering the combined use of QS-21 and the combined use of saponins with an aminoalkyl glucosminide phosphase. Antigenics MA’s co-ownership interest was assigned to Antigenics by Corixa under an agreement between Corixa and Antigenics MA. Corixa’s joint ownership interest was subsequently transferred to GlaxoSmithKline in connection with its acquisition by GlaxoSmithKline.

Schedule 3(ee)

Subsidiaries

EX-99.1

Exhibit 99.1

FOR IMMEDIATE RELEASE

Robert Anstey

Investor Relations

800.962.2436

ir@antigenics.com

Sunny Uberoi

Corporate Communications

212.994.8206 or 917.443.3325

suberoi@antigenics.com

ANTIGENICS SELLS $25 MILLION

OF CONVERTIBLE SENIOR SECURED NOTES

New York – October 31, 2006 – Antigenics Inc. (NASDAQ: AGEN) announced today that it has executed a definitive agreement for the sale of $25 million of convertible senior notes (“Notes”) to a group of accredited investors (“Investors”). No brokerage or sales commission is associated with the transaction. At the Investors’ option, the Notes are convertible into Antigenics’ common stock at $3.50 per share, representing a 74-percent premium to yesterday’s closing price. Alternatively, the Notes can be converted into a 30-percent interest in a wholly owned subsidiary of Antigenics holding the QS-21 and AG-707 programs. Notes arising from accrued interest (see below) would convert into an incremental interest in such subsidiary. Investors may convert into a combination of equity in this subsidiary and in Antigenics. The Notes reach maturity on August 30, 2011, at which point Antigenics may repay the outstanding balance in cash or in common stock of Antigenics, subject to certain limitations.

The Notes will bear interest at 8 percent, payable in cash or in additional Notes, at Antigenics’ option. Interest is to be paid semiannually on December 30 and June 30. At any time after October 30, 2009, Antigenics may call the Notes and accrued interest at face value for cash if its shares have a minimum average trading price during the prior 30-day period of $7.00 or higher. Such redemption shall not be effective until the 20^th business day following notice from Antigenics, during which period Investors may exercise their conversion rights. If Investors choose at any time to convert into ownership of the subsidiary holding QS-21 and AG-707, Antigenics will have 30 days to redeem the Notes, including accrued interest, at a 30-percent internal rate of return to the Investors. The Notes are secured upon Antigenics’ equity ownership in this subsidiary.

If Antigenics elects to satisfy the outstanding balance with common shares at maturity, the number of shares issued will be determined by dividing the cash obligation by 90 percent of the average closing price of the common shares for the 20 trading days preceding the maturity date of the Notes. This right is subject to the market capitalization of Antigenics exceeding $300 million at such time.

In no event will Investors be obligated to accept equity that would result in any Investor owning in excess of 9.99 percent of Antigenics’ outstanding common stock at any given time.

For further details, please see Antigenics’ 8-K to be filed on or before October 31, 2006.

About Antigenics

Antigenics is a biotechnology company working to develop treatments for cancers, infectious diseases and autoimmune disorders.

This press release contains forward-looking statements, including statements regarding a financing of the company and the potential repayment or conversion of the Notes issued in the financing into common stock of the company or its subsidiary. The ultimate repayment of these Notes, and the form such repayment will take, is dependent on risks and uncertainties, including, among others, the market capitalization of the company, the development and commercialization of the company’s products; decisions by collaborative partners and licensees; decisions by regulatory agencies; timing and results of clinical and preclinical studies; and the factors described under Factors That May Impact Future Results in the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of Antigenics’ Form 10-Q as filed with the Securities and Exchange Commission on August 9, 2006. Antigenics cautions investors not to place considerable reliance on the forward-looking statements contained in this press release. These statements speak only as of the date of this document, and Antigenics undertakes no obligation to update or revise the statements. All forward-looking statements are expressly qualified in their entirety by this cautionary statement. Antigenics’ business is subject to substantial risks and uncertainties, including those identified above. When evaluating Antigenics’ business and securities, investors should give careful consideration to these risks and uncertainties.

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