1 AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 3, 2000 REGISTRATION NO. 333- - -------------------------------------------------------------------------------- - -------------------------------------------------------------------------------- SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ------------------------ FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 ANTIGENICS INC. (Exact name of registrant as specified in its charter) DELAWARE 2836 06-1562417 (State or other jurisdiction (Primary Standard Industrial (I.R.S. Employer of incorporation or organization) Classification Code Number) Identification Number) 630 FIFTH AVENUE, SUITE 2100 NEW YORK, NEW YORK 10111 (212) 332-4774 (Address, including zip code, and telephone number, including area code, of registrant's principal executive offices) GARO H. ARMEN, PH.D. Chief Executive Officer Antigenics Inc. 630 Fifth Avenue, Suite 2100 New York, New York (212) 332-477 (Name, address, including zip code, and telephone number, including area code, of agent for service) COPIES TO: MICHAEL LYTTON, ESQ. DANIELLE CARBONE, ESQ. PAUL KINSELLA, ESQ. Shearman & Sterling Palmer & Dodge LLP 599 Lexington Avenue One Beacon Street New York, New York 10022 Boston, Massachusetts 02108 (212) 848-4000 (617) 573-0100 Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this Registration Statement. If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. [ ] If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering.[x] 333-91747 If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering. [ ] If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering. [ ] If delivery of the prospectus is expected to be made pursuant to Rule 434, check the following box. [ ] ------------------------ CALCULATION OF REGISTRATION FEE - -------------------------------------------------------------------------------- - --------------------------------------------------------------------------------------------------------------------------- PROPOSED PROPOSED MAXIMUM MAXIMUM TITLE OF EACH CLASS OF AMOUNT TO BE OFFERING PRICE AGGREGATE AMOUNT OF SECURITIES TO BE REGISTERED REGISTERED(1) PER SHARE(2) OFFERING PRICE(1) REGISTRATION FEE(2) - --------------------------------------------------------------------------------------------------------------------------- Common Stock, $.01 par value per share................................ 575,000 shares $18 $10,350,000 $2,733 - --------------------------------------------------------------------------------------------------------------------------- - --------------------------------------------------------------------------------------------------------------------------- (1) Includes shares which the Underwriters may purchase to cover over-allotments, if any. (2) The registration fee is calculated pursuant to Rule 457(d) under the Securities Act of 1933 based on the initial public offering price of $18 per share. THIS REGISTRATION STATEMENT SHALL BECOME EFFECTIVE UPON FILING WITH THE COMMISSION IN ACCORDANCE WITH RULE 462(B) UNDER THE SECURITIES ACT OF 1933. - -------------------------------------------------------------------------------- - --------------------------------------------------------------------------------

2 EXPLANATORY NOTE AND INCORPORATION OF CERTAIN INFORMATION BY REFERENCE This registration statement is being filed with respect to the registration of additional shares of common stock, $.01 par value per share, of Antigenics Inc., a Delaware corporation, pursuant to Rule 462(b) under the Securities Act of 1933, as amended. The contents of the registrant's effective registration statement on Form S-1 (File No. 333-91747) are incorporated into this registration statement by reference. The required opinions and consents are listed on an Exhibit Index and filed herewith. 1

3 SIGNATURES Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in City of New York, State of New York, on February 3, 2000. ANTIGENICS INC. By: /s/ GARO ARMEN ------------------------------------ Garo H. Armen, Ph.D. Chief Executive Officer and Chairman of the Board of Directors Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities and on the dates indicated. SIGNATURE TITLE DATE --------- ----- ---- /s/ GARO ARMEN Chief Executive Officer and Chairman February 3, 2000 - --------------------------------------------------- of the Board of Directors (Principal Garo Armen, Ph.D. Executive Officer and Principal Financial and Accounting Officer) * Director February 3, 2000 - --------------------------------------------------- Pramod Srivastava, Ph.D. * Director February 3, 2000 - --------------------------------------------------- Noubar Afeyan, Ph.D. * Director February 3, 2000 - --------------------------------------------------- Edward Brodsky * Director February 3, 2000 - --------------------------------------------------- Gamil de Chadarevian * Director February 3, 2000 - --------------------------------------------------- Tom Dechaene * Director February 3, 2000 - --------------------------------------------------- Donald Panoz * Director February 3, 2000 - --------------------------------------------------- Martin Taylor *By: /s/ GARO ARMEN ---------------------------- As Attorney-in-fact 2

4 EXHIBIT INDEX EXHIBIT NO. TITLE - ----------- ----- 5.1 Opinion of Palmer & Dodge LLP 23.1 Consent of Palmer & Dodge LLP (included in the opinion filed as Exhibit 5.1.) 23.2 Consent of KPMG LLP 24.1* Power of Attorney - --------------- * Filed with the registrant's Registration Statement on Form S-1 (Registration No. 333-91747). 3

1 EXHIBIT 5.1 [PALMER & DODGE LLP LETTERHEAD] TELEPHONE: (617) 573-0100 FACSIMILE: (617) 227-4420 February 3, 2000 Antigenics Inc. 630 Fifth Avenue, Suite 2100 New York, New York 10111 We are rendering this opinion in connection with the Registration Statement on Form S-1 (the "Registration Statement") filed by Antigenics Inc. (the "Company") with the Securities and Exchange Commission under the Securities Act of 1933, as amended, on or about the date hereof. The Registration Statement relates to up to 575,000 shares of the Company's Common Stock, $0.01 par value per share (the "Shares"). We understand that the Shares are to be offered and sold in the manner described in the Registration Statement. We have acted as your counsel in connection with the preparation of the Registration Statement. We are familiar with the proceedings of the Board of Directors in connection with the authorization, issuance and sale of the Shares (the "Resolutions"). We have examined such other documents as we consider necessary to render this opinion. Based upon the foregoing, we are of the opinion that the Shares have been duly authorized and, when issued and delivered by the Company against payment therefor at the price to be determined pursuant to the Resolutions, will be validly issued, fully paid and non-assessable. The foregoing opinion is limited to Delaware General Corporation Law and the federal laws of the United States. We hereby consent to the filing of this opinion as a part of the Registration Statement and to the reference to our firm under the caption "Legal Matters" in the Prospectus filed as part thereof. Very truly yours, /s/ Palmer & Dodge LLP PALMER & DODGE LLP 6

1 EXHIBIT 23.2 INDEPENDENT AUDITORS' CONSENT The Members and Board of Managers of Antigenics L.L.C.: We consent to the use of our report incorporated by reference herein, and to the references to our firm under the headings "Selected Consolidated Financial Data" and "Experts" in the Prospectus and Registration Statement. /s/ KPMG LLP Short Hills, New Jersey January 31, 2000 7