Exhibit 99.1

    Antigenics Announces Expansion of Its License and Supply Agreement With
 GlaxoSmithKline Biologicals for QS-21 Stimulon(R) Adjuvant; Conference Call to
                         be Held Today at 9:30 a.m. ET

    NEW YORK--(BUSINESS WIRE)--July 10, 2006--Antigenics Inc. (NASDAQ:
AGEN) today announced that the company has signed expanded license and
supply agreements for the use of QS-21 Stimulon(R) adjuvant with
GlaxoSmithKline Biologicals, a vaccine division of GlaxoSmithKline
(GSK). QS-21 is a key component included in several of GSK's
proprietary adjuvant systems. A number of GSK's vaccine candidates
currently under development are formulated with GSK's proprietary
adjuvant systems containing QS-21.
    Under the terms of the agreements, GSK will purchase a percentage
of its QS-21 supply requirements from Antigenics through 2014.
Antigenics will also transfer manufacturing technologies to GSK under
the supply agreement. GSK will make payments contingent upon
successful milestone achievements, and will pay royalties to
Antigenics on net sales for a period of at least 10 years after first
commercial sale under the supply agreement.
    "We are delighted to announce this transaction with
GlaxoSmithKline," said Garo H. Armen, Ph.D., chairman and CEO of
Antigenics. "GSK is the world's leading developer of preventive
vaccines and novel cancer immunotherapeutics and Antigenics' QS-21
offers GSK one of the most potent and widely used immunostimulants in
development. These agreements represent an important strategic
collaboration for both companies."

    About QS-21

    QS-21 is the leading member of the Stimulon family of adjuvants
developed by Antigenics, and has been shown to stimulate both antibody
(humoral) as well as cellular immune responses. Published clinical
studies have shown QS-21 to be significantly more effective in
stimulating antibody responses than aluminum adjuvants, the only
adjuvants used in approved vaccines in the United States today. QS-21
has not only become a critical component in the development of
preventative vaccine formulations across a wide variety of infectious
diseases, but may also be essential in enabling a new generation of
therapeutic vaccines to treat cancer and degenerative disorders.
    QS-21-based vaccines are being evaluated in more than 50 different
indications through commercial partnerships with pharmaceutical
companies, academic institutions and Antigenics' internal programs. A
number of pharmaceutical and biotechnology companies have licensed
QS-21, including GlaxoSmithKline plc, Elan Corporation, plc, Wyeth,
Pharmexa A/S and Advanced BioScience Laboratories, Inc.

    Conference Call Information

    Antigenics executives will host a conference call at 9:30 a.m. ET
today. To access the live call, dial 888.271.9082 (domestic) or
706.679.7741 (international); the access code is 2778694. The call
will also be webcast and will be accessible from the company's website
at www.antigenics.com/webcast/. A replay will be available
approximately two hours after the call through midnight ET on July 24,
2006. The replay number is 800.642.1687 (domestic) or 706.645.9291
(international), and the access code is 2778694. The replay will also
be available on the company's website approximately two hours after
the live call.

    About Antigenics

    Antigenics is working to develop treatments for cancers,
infectious diseases and autoimmune disorders. The company's
investigational product portfolio includes Oncophage(R) (vitespen), a
patient-specific therapeutic cancer vaccine being evaluated in several
indications; Aroplatin(TM), a liposomal, third-generation platinum
chemotherapeutic; ATRA-IV, a liposomal retinoic acid; AG-707, a
therapeutic vaccine for the treatment of genital herpes; AU-801, a
preclinical program targeting autoimmune disorders; and QS-21, an
adjuvant being evaluated by Antigenics' corporate partners in several
late-stage clinical trials. For more information, please visit
www.antigenics.com.

    This press release contains forward-looking statements based on
current management expectations, including statements about the
development of products using QS-21 and its importance to the
development of vaccine formulations, the future purchase by GSK of its
QS-21 requirements, the future transfer of manufacturing technology to
GSK by Antigenics, and the future payment of milestone payments and
royalties in connection with the development and commercialization of
QS-21. These forward-looking statements are subject to risks and
uncertainties that could cause actual results to differ materially.
These risks and uncertainties include, among others, Antigenics'
dependence on its collaborative partners such as GSK to successfully
develop and commercialize products containing QS-21, the scientific
risk associated with the development of vaccines, the competitive risk
that other sources of competitive adjuvants could become available,
and difficulties or delays in manufacturing QS-21 and/or the transfer
to or utilization of QS-21 manufacturing technology by GSK. 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.

    CONTACT: Antigenics Inc.
             Media Relations:
             Sunny Uberoi, 212-994-8206
             suberoi@antigenics.com
             or
             Investor Relations:
             Shalini Sharp, 800-962-2436
             ir@antigenics.com