UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-Q/A

For the Quarterly Period Ended March 31,September 30, 2008

For the transition period from            to            

Commission File Number: 000-29089

Antigenics Inc.

(Exact name of registrant as specified in its charter)

162 Fifth Avenue, Suite 900, New York, New York 10010

(Address of principal executive offices, including zip code)

(212) 994-8200

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x¨    No  ¨x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer,” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

Number of shares outstanding of the registrant’s Common Stock as of May 1,October 31, 2008: 65,660,79766,270,710 shares.

EXPLANATORY NOTE

The purpose of this amendment on Form 10-Q/A to our Quarterly Report on Form 10-Q for the quarterly period ended March 31,September 30, 2008 is to: (1) properly reference a Certificate of Amendment to file in unredacted form Exhibit 10.1 (Exclusive License Agreement dated September 24, 1986, between Aronex Pharmaceuticals,the Amended and Restated Certificate of Incorporation of Antigenics Inc. (formerly Argus Pharmaceuticals Inc.(the “Company”), The Universityand (2) file the Third Amended and Restated By-laws of Texas System Board of Regents and The University of Texas M.D. Anderson Cancer Center) and Exhibit 10.2 (Exclusive License Agreement dated July 1, 1988, between Aronex Pharmaceuticals, Inc., (formerly Argus Pharmaceuticals Inc.), The University of Texas System Board of Regents and The University of Texas M.D. Anderson Cancer Center), which were originally filed in redacted form pursuant to a request for an extension of confidential treatment. We have withdrawn our request for an extension of confidential treatment.the Company.

PART II –II. OTHER INFORMATION

Item 6 –Exhibits

During the quarter ended September 30, 2008, we failed to file a Form 8-K to disclose the adoption of an amendment to our by-laws. The amendment provides, among other things, that a meeting of stockholders may be conducted by means of remote communication and notices to stockholders and directors may be given in writing or by electronic transmission. The amendment also modifies the advance notice provisions for stockholder proposals.

The exhibitsExhibits listed in the Exhibit Index are included in this amendment on Form 10-Q/A.A to our Quarterly Report on Form 10-Q.

2

ANTIGENICS INC.

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 thereunto duly authorized.

Date: May 28,November 10, 2008

3

EXHIBIT INDEX

4