Power of Attorney
For Executing Reports under Section 16(a)

The undersigned hereby constitutes and appoints each of Susan
P. Cogswell, Jodie Vasily-Cioffi and Peter Wirth, each acting
singly, his true and lawful attorney-in-fact, from the date
hereof until this Power of Attorney is revoked, to:

(1) execute, for and on behalf of the undersigned, Forms 3, 4 and
5 in accordance with Section 16(a) of the Securities Exchange Act
of 1934 and the rules thereunder, as amended (the "1934 Act"), it
being understood that the documents executed by such
attorney-in-fact on behalf of the undersigned pursuant to this
Power of Attorney shall be in such form and shall contain such
terms and conditions as such attorney-in-fact may approve in his
or her discretion; and

(2) do and perform any and all acts, for and on behalf of the
undersigned, that may be necessary or desirable to complete the
execution of any such Form 3, 4 or 5 and the timely filing of
such form with the United States Securities and Exchange
Commission and any other authority.

The undersigned hereby grants to each such attorney-in-fact full
power and authority to do and preform all and every act and
thing whatsoever requisite, necessary and proper to be done in
the exercise of any of the rights and powers herein granted, as
fully for all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution
or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or his or her substitute or substitutes, shall
lawfully do or cause to be done by virture of this power of
attorney and the rights and powers herein granted.  The
undersigned acknowledges that the foregoing attorneys-in-fact,
in serving in such capacity at the request of the undersigned,
are not assuming any of the undersigned's responsibilites to
comply with Section 16 of the Act.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed this 18th day of August 2003.

/S/Georges Gemayem