Edgar Filing: ANTIGENICS INC /DE/

Form 424(b)(5)

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-164481

PROSPECTUS SUPPLEMENT

(To Prospectus Dated February 3, 2010)

Antigenics Inc.

20,000,000 Shares of Common Stock

You should read this prospectus supplement and the accompanying prospectus carefully before you invest. Both documents contain information you should consider carefully before making your investment decision.

This prospectus supplement relates to the issuance and sale of up to 20,000,000 shares of our common stock from time to time through our sales agents, McNicoll, Lewis & Vlak LLC and Wm Smith & Co. These sales, if any, will be made pursuant to the terms of a sales agreement, as entered into, between us and the sales agents, which was filed with the Securities and Exchange Commission as an exhibit to our report on Form 8-K dated March 1, 2010.

Our common stock trades on the NASDAQ Capital Market (NASDAQ) under the symbol “AGEN.” Sales of shares of our common stock under this prospectus supplement, if any, may be made by any method deemed to be an “at the market” offering as defined in Rule 415 under the Securities Act of 1933, as amended, which includes sales made directly on the NASDAQ, the existing trading market for our common stock. Each sales agent will make all sales on a best efforts basis using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between the sales agent and us. On February 25, 2010, the last reported sales price of our common stock on the NASDAQ was $0.81 per share.

The compensation to the sales agents for sales of common stock sold pursuant to the sales agreement will be an aggregate of 3% of the gross proceeds of the sales price of common stock sold. The net proceeds from any sales under this prospectus supplement will be used as described under “Use of Proceeds.” The proceeds that we receive from sales of our common stock will depend on the number of shares actually sold and the offering price of such shares.

In connection with the sale of common stock on our behalf, each sales agent may be deemed to be an “underwriter” within the meaning of the Securities Act of 1933, as amended, and the compensation of such sales agent may be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to the sales agents against certain liabilities, including liabilities under the Securities Act of 1933, as amended.

You should read carefully and consider the “Risk Factors” referenced on page 2 of the accompanying prospectus and the risk factors described in other documents incorporated by reference herein.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined that this prospectus supplement or the accompanying prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

LOGO LOGO

The date of this prospectus supplement is March 1, 2010.

TABLE OF CONTENTS


Prospectus Supplement		Page
About this Prospectus Supplement		S-ii

Summary		S-1

Note Regarding Forward-Looking Statements		S-3

Use of Proceeds		S-5

Plan of Distribution		S-6

Where You Can Find More Information		S-7

Incorporation of Certain Documents by Reference		S-7

Prospectus		Page
Prospectus Summary		1

Risk Factors		2

Note Regarding Forward-Looking Statements		2

Use of Proceeds		4

Plan of Distribution		5

Description of Common Stock		7

Description of Preferred Stock		8

Description of Warrants		10

Description of Debt Securities		11

Legal Matters		18

Experts		18

Where You Can Find More Information		19

Incorporation of Certain Documents by Reference		19

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document consists of two parts. The first part is this prospectus supplement, which describes the specific terms of this offering. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. Generally, when we refer only to the “prospectus,” we are referring to both parts combined. This prospectus supplement may add to, update or change information in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement or the accompanying prospectus.

If information in this prospectus supplement is inconsistent with the accompanying prospectus, you should rely on this prospectus supplement. This prospectus supplement, the accompanying prospectus and the documents incorporated into each by reference include important information about us, the shares being offered and other information you should know before investing in our common shares.

You should rely only on this prospectus supplement, the accompanying prospectus and the information incorporated or deemed to be incorporated by reference in this prospectus supplement and the accompanying prospectus. We have not, and the sales agents have not, authorized anyone to provide you with information that is in addition to or different from that contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the sales agents are not, offering to sell these securities in any jurisdiction where the offer or sale is not permitted. You should not assume that the information contained or incorporated by reference in this prospectus supplement or the accompanying prospectus is accurate as of any date other than as of the date of this prospectus supplement or the accompanying prospectus, as the case may be, or in the case of the documents incorporated by reference, the date of such documents regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or any sale of our common shares. Our business, financial condition, liquidity, results of operations and prospects may have changed since those dates.

All references in this prospectus supplement or the accompanying prospectus to “Antigenics,” the “Company,” “we,” “us,” or “our” mean Antigenics Inc. and its subsidiaries, unless we state otherwise or the context otherwise requires.

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SUMMARY

The following is a summary of selected information contained elsewhere or incorporated by reference in this prospectus supplement and the accompanying prospectus. It does not contain all of the information that you should consider before buying our securities. You should read this prospectus supplement and the accompanying prospectus in their entirety, including the information incorporated by reference.

The Company

Our Business

We are a biotechnology company developing and commercializing technologies to treat cancers and infectious diseases, primarily based on immunological approaches. Our most advanced product, Oncophage^® (vitespen), is a patient-specific therapeutic cancer vaccine registered for use in Russia. As resources allow, we explore potential opportunities to seek product approval in other jurisdictions. Oncophage has been tested in Phase 3 clinical trials for the treatment of renal cell carcinoma, the most common type of kidney cancer, and for the treatment of metastatic melanoma. It has also been tested in Phase 1 and Phase 2 clinical trials in a range of indications and is currently in Phase 2 clinical trials in glioma, a type of brain cancer. Our product candidate portfolio also includes (1) QS-21 Stimulon^® adjuvant, or QS-21, which is used in numerous vaccines in third party clinical trials as advanced as Phase 3 for a variety of diseases, including hepatitis, human immunodeficiency virus, influenza, cancer, Alzheimer’s disease, malaria, and tuberculosis, (2) AG-707, a therapeutic vaccine program tested in a Phase 1 clinical trial for the treatment of genital herpes, and (3) Aroplatin™, a liposomal chemotherapeutic tested in a Phase 1 clinical trial for the treatment of solid malignancies and B-cell lymphomas. Further internal clinical development of AG-707 and Aroplatin is currently on hold due to cost-containment efforts. Our business activities have included product research and development, intellectual property prosecution, manufacturing, regulatory and clinical affairs, corporate finance and development activities, market development, and support of our collaborations.

Risk Factors

Our business is subject to substantial risk. Please carefully consider the “Risk Factors” on page 2 of the accompanying prospectus and other information included and incorporated by reference in this prospectus supplement, for a discussion of the factors you should consider carefully before deciding to purchase these securities. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also impair our business operations. You should be able to bear a complete loss of your investment.

Corporate Information

Our principal executive office is located at 3 Forbes Road, Lexington, MA, 02421, and our telephone number is (781) 674-4400. Our website address is www.antigenics.com. Information contained on our website is not a part of this prospectus supplement.

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The Offering

The following summary contains basic information about our common stock and the offering and is not intended to be complete. It does not contain all the information that may be important to you. For a more complete understanding of our common stock, you should read the section of the accompanying prospectus entitled “Description of Common Stock.”


Issuer		Antigenics Inc.

Common stock offered		Up to 20,000,000 shares

Risk factors		Your investment in our common shares involves substantial risks. You should consider the “Risk Factors” included and incorporated by reference in this prospectus supplement and the accompanying prospectus, including the risk factors incorporated by reference from our filings with the Securities and Exchange Commission, or the SEC.

NASDAQ symbol		AGEN

S-2

NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference contain forward-looking statements. Except for strictly historical information contained herein, matters discussed in this report constitute forward-looking statements. Generally, these statements can be identified by the use of terms like “believe,” “expect,” “anticipate,” “plan,” “may,” “will,” “could,” “estimate,” “potential,” “opportunity,” “future,” “project,” and similar terms.

Forward-looking statements include, but are not limited to, statements about generating sales from Oncophage in Russia, generating royalty revenue from QS-21 in 2011 or thereafter, our or our partners’ or licensees’ intentions for executing plans or timelines for performing and completing research, preclinical studies and clinical trials, and releasing data, plans or timelines for initiating new clinical trials, expectations regarding research, preclinical studies, clinical trials, and regulatory processes (including additional clinical studies for Oncophage in renal cell carcinoma), expectations regarding test results, future product research and development activities, the expected effectiveness and safety profile of therapeutic drugs, vaccines, and combinations in treating diseases, statements regarding the potential benefit of Oncophage in kidney cancer based on a subgroup analysis, as well as other potential benefits of Oncophage based on preliminary clinical data, applicability of our heat shock protein technology to multiple cancers and infectious diseases, competitive position, regulatory plans and actions, including with respect to regulatory filings and meetings and communications with regulatory authorities (including potential requests for meetings with the U.S. Food and Drug Administration regarding Oncophage clinical studies and strategies for responding to the Committee for Medicinal Products for Human Use’s decision regarding the conditional authorization of Oncophage in Europe and for making Oncophage available in other territories), the sufficiency of our clinical trials in renal cell carcinoma and melanoma, or subgroup analyses of data from these trials, to support a biologics license application or foreign marketing application for product approval, possible receipt of future regulatory approvals, the performance of collaborative partners in, and revenue expectations from, our strategic license and partnering collaborations, expected liquidity and cash needs, plans to commence, accelerate, decelerate, postpone, discontinue, or resume clinical programs, the rate of our net cash burn (defined as cash used in operating activities plus capital expenditures, debt repayments, and dividend payments), plans for commercial launch, and sales and marketing activities in Russia, implementation of corporate strategy, increased foreign currency exposure when we commercialize in Russia, and future financial performance.

These forward-looking statements involve a number of risks and uncertainties that could cause actual results to differ materially from those suggested by the forward-looking statements. These risks and uncertainties include, among others, that clinical trials may not demonstrate that our products are safe and more effective than current standards of care; that the subgroup analyses of our Oncophage clinical trials do not predict survival or efficacy of the product in future studies or use of Oncophage; that we may be unable to obtain sufficient funding or the regulatory authorization necessary to conduct additional clinical trials; that we may not be able to enroll sufficient numbers of patients in our clinical trials; that we may be unable to obtain the regulatory review or approval necessary to commercialize our product candidates because regulatory agencies are not satisfied with our trial protocols or the results of our trials; that we may fail to adequately protect our intellectual property or that it is determined that we infringe on the intellectual property of others; our strategic licenses and partnering collaborations may not meet expectations; that we or our business partners may fail to take all steps necessary for the successful commercial launch of Oncophage in Russia; that we may not be able to secure adequate reimbursement mechanisms and/or private-pay for Oncophage in Russia; that we may not continue to pursue a marketing authorization application for Oncophage with the European Medicines Agency (“EMEA”), and that even if we do continue such pursuit, Oncophage may not achieve conditional approval in Europe, because we may not successfully address issues associated with post-hoc analysis, subgroup analysis, lack of immunological data in renal cell carcinoma, product characterization, or other issues that may be of concern to the EMEA; that named patient programs may not be launched in the near-term, if ever, and if launched may not generate significant revenue, if any; that manufacturing problems may cause product development and launch delays and unanticipated costs; our ability to raise additional capital; our ability to attract and retain

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key employees; changes in financial markets, regulatory requirements, and geopolitical developments; the solvency of counterparties under material agreements, including subleases; and general real estate risks.

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USE OF PROCEEDS

We intend to use the net proceeds from this offering for general corporate purposes, which may include working capital, capital expenditures, research and development expenditures, clinical trial expenditures, acquisitions of new technologies, and investments.

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PLAN OF DISTRIBUTION

We have entered into a sales agreement, dated as of February 26, 2010, with McNicoll, Lewis & Vlak LLC and Wm Smith & Co. (collectively, the “sales agents”), under which we may sell an aggregate of 20,000,000 shares of our common stock from time to time through the sales agents. The sales agents may sell the common stock by any method that is deemed to be an “at the market” offering as defined in Rule 415 of the Securities Act of 1933, as amended (the “Securities Act”), including sales made directly on the NASDAQ Capital Market or on any other existing trading market for the common stock. The sales agents may also sell the common stock in privately negotiated transactions, subject to our prior approval.

Each time that we wish to issue and sell common stock under the sales agreement, we will agree with the sales agents on the number of shares to be issued, the dates on which such sales are anticipated to be made and any minimum price below which sales may not be made. Once we have so instructed the sales agents, the sales agents have agreed to use their commercially reasonable efforts consistent with their normal trading and sales practices to sell such shares up to the amount specified on such terms. The settlement between us and the sales agents of our common stock is generally anticipated to occur on the third trading day following the date on which the sale was made. The obligation of the sales agents under the sales agreement to sell our common stock is subject to a number of conditions that we must meet.

We will pay the sales agents a total commission equal to an aggregate of 3% of the gross proceeds we receive from the sales of our common stock. Because there is no minimum offering amount required as a condition to closing this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time.

In connection with the sale of our common stock contemplated in this prospectus supplement, the sales agents may be deemed to be “underwriters” within the meaning of the Securities Act, and the compensation paid to the sales agents may be deemed to be underwriting commissions or discounts. We have agreed to indemnify the sales agents against certain civil liabilities, including liabilities under the Securities Act.

Sales of our common stock as contemplated in this prospectus supplement will be settled through the facilities of The Depository Trust Company or by such other means as we and the sales agents may agree upon.

The offering of our common stock pursuant to the sales agreement will terminate on the earliest of (1) the sale of all of our common stock subject to the sales agreement, or (2) termination of the sales agreement by us or either sales agent. Each sales agent may terminate the sales agreement at any time in certain circumstances, including the occurrence of a material adverse change that, in such sales agent’s reasonable judgment, may impair its ability to sell the common stock, our failure to satisfy any condition under the sales agreement or a suspension or limitation of trading of our common stock on the NASDAQ Capital Market. We and the sales agents may each terminate the sales agreement at any time upon 10 days prior notice.

This summary of the material provisions of the sales agreement does not purport to be a complete statement of its terms and conditions. A copy of the sales agreement is filed with the SEC and incorporated by reference into the registration statement of which this prospectus supplement forms a part. See “Where You Can Find More Information” below.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly, and special reports, proxy statements, and other information with the SEC. These documents are on file with the SEC under file number 000-29089. You may read and copy any document we file at the SEC’s public reference room at 100 F Street, N.E., Washington, D.C., 20549. You can request copies of these documents by contacting the SEC and paying a fee for the copying cost. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. Our SEC filings are also available to the public from the SEC’s website at www.sec.gov.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

This prospectus supplement and the accompany prospectus are part of a registration statement on Form S-3 filed by us with the SEC. This prospectus supplement and the accompanying prospectus do not contain all of the information set forth in the registration statement, certain parts of which are omitted in accordance with the rules and regulations of the SEC. Statements contained in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference into this prospectus supplement or the accompanying prospectus as to the contents of any contract or other document referred to are not necessarily complete and in each instance reference is made to the copy of that contract or other document filed with the SEC. For further information about us and the securities offered by this prospectus supplement, we refer you to the registration statement and its exhibits and schedules which may be obtained as described herein.

The SEC allows us to “incorporate by reference” the information contained in documents that we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus, and information in documents that we file later with the SEC will automatically update and supersede information in this prospectus supplement and the accompanying prospectus. We incorporate by reference the documents listed below into this prospectus supplement, and any future filings made by us with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act until the offering of all the securities by this prospectus supplement is completed, including all filings made after the date of this prospectus supplement. We hereby incorporate by reference the documents listed below (File No. 000-29089).

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our Annual Report on Form 10-K for the fiscal year ended December 31, 2008 as filed on March 16, 2009;

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our Current Reports on Form 8-K filed on January 21, 2009, February 4, 2009, March 30, 2009, April 17, 2009, April 22, 2009, May 4, 2009, May 11, 2009, May 27, 2009, June 4, 2009, June 5, 2009, June 9, 2009, June 11, 2009, June 15, 2009, July 7, 2009, July 15, 2009, August 3, 2009 (other than with respect to Item 2.02), August 5, 2009, September 11, 2009, September 18, 2009, December 31, 2009, and March 1, 2010;

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our Proxy Statement on Schedule 14A filed with the SEC on April 27, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended March 31, 2009 as filed on May 11, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended June 30, 2009 as filed on August 10, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended September 30, 2009 as filed on November 9, 2009; and

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the description of our common stock contained in our registration statement on Form 8-A filed under the Securities Exchange Act on January 24, 2000, including any amendment or reports filed for the purpose of updating such descriptions.

We will provide each person to whom this prospectus supplement is delivered a copy of all of the information that has been incorporated by reference in this prospectus supplement or the accompanying prospectus but not delivered with this prospectus supplement and the accompanying prospectus. You may

S-7

obtain copies of these filings, at no cost, through the “Investor Relations” section of our website (www.antigenics.com), and you may request copies of these filings, at no cost, by writing or telephoning us at:

Antigenics Inc.

Attention: Secretary

3 Forbes Road

Lexington, MA 02421

Telephone: (781) 674-4400

The information contained on our website is not a part of this prospectus.

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PROSPECTUS

$100,000,000

LOGO

Common Stock

Preferred Stock

Warrants

Debt Securities

We may offer to the public from time to time in one or more series or issuances:

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shares of our common stock;

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shares of our preferred stock;

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warrants to purchase shares of our common stock, preferred stock, and/or debt securities; or

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debt securities consisting of debentures, notes, or other evidences of indebtedness.

Our common stock is traded on The NASDAQ Capital Market under the symbol “AGEN.” On January 20, 2010, the reported closing price per share of our common stock was $0.84.

This prospectus provides a general description of the securities we may offer. Each time we sell securities, we will provide specific terms of the securities offered in a supplement to this prospectus. The prospectus supplement may also add, update, or change information contained in this prospectus. This prospectus may not be used to consummate a sale of securities unless accompanied by the applicable prospectus supplement. You should read both this prospectus and any prospectus supplement together with additional information described under the heading “Where You Can Find More Information” before you make your investment decision.

We will sell these securities directly to our stockholders or to purchasers or through agents on our behalf or through underwriters or dealers as designated from time to time. If any agents or underwriters are involved in the sale of any of these securities, the applicable prospectus supplement will provide the names of the agents or underwriters and any applicable fees, commissions, or discounts.

As of January 20, 2010, the aggregate market value of our outstanding common stock held by non-affiliates was approximately $63,998,000 based on approximately 90,921,000 shares of outstanding common stock, of which approximately 76,188,000 shares are held by non-affiliates, and a per share price of $0.84, based on the closing sale price of our common stock on January 20, 2010. As of the date hereof, we have not offered any securities pursuant to General Instruction I.B.6 of Form S-3 during the prior 12 calendar month period that ends on and includes the date hereof.

Investing in these securities involves certain risks. Please carefully consider the “Risk Factors” on page 2 and other information included and incorporated by reference in this prospectus, and in any applicable prospectus supplement, for a discussion of the factors you should consider carefully before deciding to purchase these securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is February 3, 2010.

TABLE OF CONTENTS


		Page

Prospectus Summary		1

Risk Factors		2

Note Regarding Forward-Looking Statements		2

Use of Proceeds		4

Plan of Distribution		5

Description of Common Stock		7

Description of Preferred Stock		8

Description of Warrants		10

Description of Debt Securities		11

Legal Matters		18

Experts		18

Where You Can Find More Information		19

Incorporation of Certain Documents by Reference		19

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission (the “SEC”) utilizing a “shelf” registration process. Under this shelf process, we may sell different types of securities described in this prospectus in one or more offerings. This prospectus provides you with a general description of the securities we may offer. Each time we offer securities, we will provide a prospectus supplement and attach it to this prospectus. The prospectus supplement will contain specific information about the nature of the persons offering securities and the terms of the securities being offered at that time. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement, together with additional information under the headings “Where You Can Find More Information” and “Incorporation of Certain Documents By Reference” and any other information that you may need to make your investment decision.

This prospectus does not contain all of the information that is in the registration statement. We omitted certain parts of the registration statement from this prospectus as permitted by the SEC. We refer you to the registration statement and its exhibits for additional information about us and the securities that may be sold under this prospectus.

All references in this prospectus to “Antigenics,” the “Company,” “we,” “us,” or “our” mean Antigenics Inc., unless we state otherwise or the context otherwise requires.

You should rely only on the information contained or incorporated by reference in this prospectus. We have not authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer is not permitted. The information contained in this prospectus is accurate only as of the date of this prospectus, regardless of the time of delivery of this prospectus or the time of any sale of our securities. Our business, financial condition, results of operations, and prospects may have changed since such date.

PROSPECTUS SUMMARY

The following is a summary of selected information contained elsewhere or incorporated by reference in this prospectus. It does not contain all of the information that you should consider before buying our securities. You should read this entire prospectus carefully, especially the section entitled “Risk Factors” and the consolidated financial statements and the notes to the consolidated financial statements incorporated by reference.

The Company

Our Business

We are a biotechnology company developing and commercializing technologies to treat cancers and infectious diseases, primarily based on immunological approaches. Our most advanced product, Oncophage^® (vitespen), is a patient-specific therapeutic cancer vaccine registered for use in Russia. As resources allow, we explore potential opportunities to seek product approval in other jurisdictions. Oncophage has been tested in Phase 3 clinical trials for the treatment of renal cell carcinoma, the most common type of kidney cancer, and for metastatic melanoma, and it has also been tested in Phase 1 and Phase 2 clinical trials in a range of indications. It is currently in Phase 2 clinical trials in glioma, a type of brain cancer. Our product candidate portfolio includes (1) QS-21 Stimulon^® adjuvant, or QS-21, which is used in numerous vaccines in clinical trials as advanced as Phase 3 for a variety of diseases, including hepatitis, human immunodeficiency virus, influenza, cancer, Alzheimer’s disease, malaria, and tuberculosis, (2) AG-707, a therapeutic vaccine program tested in a Phase 1 clinical trial for the treatment of genital herpes, and (3) Aroplatin™, a liposomal chemotherapeutic tested in a Phase 1 clinical trial for the treatment of solid malignancies and B-cell lymphomas. Further internal clinical development of AG-707 and Aroplatin is currently on hold due to cost-containment efforts. Our related business activities include product research and development, intellectual property prosecution, manufacturing therapeutic vaccines, regulatory and clinical affairs, corporate finance and development activities, market development, and support of our collaborations.

Risk Factors

Our business is subject to substantial risk. Please carefully consider the “Risk Factors” on page 2 and other information included and incorporated by reference in this prospectus, and in any applicable prospectus supplement, for a discussion of the factors you should consider carefully before deciding to purchase these securities. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also impair our business operations. You should be able to bear a complete loss of your investment.

Corporate Information

Our principal executive office is located at 3 Forbes Road, Lexington, MA, 02421, and our telephone number is (781) 674-4400. Our website address is www.antigenics.com. Information contained on our website is not a part of this prospectus.

Ratios of Earnings to Fixed Charges and Earnings to Combined Fixed Charges and Preferred Stock Dividends

The following table sets forth our dollar coverage deficiency because our earnings in each of the periods shown below were insufficient to cover fixed charges (in thousands).


	Nine Months Ended September 30, 2009			Years Ended December 31,
	Nine Months Ended September 30, 2009			2008			2007			2006			2005			2004
Ratio of Earnings to Fixed Charges		—			—			—			—			—			—
Deficiency of Earnings to Cover Fixed Charges	$	(32,177	)	$	(28,698	)	$	(36,795	)	$	(51,881	)	$	(74,104	)	$	(68,751	)
Ratio of Earnings to Combined Fixed Charges and Preferred Stock Dividends		—			—			—			—			—			—
Deficiency of Earnings to Cover Combined Fixed Charges and Preferred Stock Dividends	$	(32,770	)	$	(29,488	)	$	(37,585	)	$	(52,671	)	$	(74,894	)	$	(69,541	)

For purposes of the ratio of earnings to fixed charges and the ratio of combined fixed charges and preferred stock dividends to earnings, “earnings” consist of income before income taxes, interest and the portions of rentals representative of the interest factor. “Fixed charges” consist of interest expense and the portions of rentals representative of the interest factor.

RISK FACTORS

You should consider the “Risk Factors” included and incorporated by reference in this prospectus and any applicable prospectus supplement, including the risk factors incorporated by reference from our most recent Annual Report on Form 10-K for the fiscal year ended December 31, 2008, filed with the SEC on March 16, 2009, as updated by our Quarterly Reports on Form 10-Q and our other filings with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) filed after such annual report. The risks and uncertainties we describe are not the only ones facing us. Additional risks not presently known to us, or that we currently deem immaterial, may also impair our business operations. If any of these risks were to occur, our business, financial condition, or results of operations would likely suffer. In that event, the trading price of our common stock could decline, and you could lose all or part of your investment.

Our stock may be delisted from The NASDAQ Capital Market, which could affect its market price and liquidity.

Our common stock is currently listed on The NASDAQ Capital Market under the symbol “AGEN.” In the event that we fail to satisfy any of the listing requirements, our common stock may be put under review or removed from the listing on The NASDAQ Capital Market.

On December 30, 2009, we were notified by the Listing Qualifications Staff of NASDAQ (the “Staff”) indicating that we are not in compliance with Nasdaq Marketplace Rule 5550(a)(2) (the “Bid Price Requirement”) because the bid price for our common stock has closed below the minimum $1.00 per share requirement for 30 consecutive business days. In accordance with Nasdaq Marketplace Rule 5810(c)(3)(A), we have been provided 180 calendar days, or until June 28, 2010, to regain compliance with the Bid Price Requirement. After the initial 180 calendar day period, we may be eligible for an additional 180 day compliance period to regain compliance with the Bid Price Requirement, assuming we continue to meet The NASDAQ Capital Market initial listing criteria set forth in Nasdaq Marketplace Rule 5505, excluding the Bid Price Requirement. To regain compliance with the minimum bid price continued listing requirement, the bid price of our common stock must close at $1.00 per share or more for a minimum of ten consecutive business days. The Staff may, in its discretion, require our common stock to maintain a bid price of at least $1.00 per share for a period in excess of ten consecutive business days before determining that we have demonstrated an ability to maintain long-term compliance.

If compliance is not demonstrated within the applicable compliance period, the Staff will notify us that our securities will be delisted from The NASDAQ Capital Market. However, we may appeal the Staff’s determination to delist our securities to a Hearings Panel. During any appeal process, shares of our common stock would continue to trade on The NASDAQ Capital Market. There can be no assurance that we will meet the requirements for continued listing on The NASDAQ Capital Market or whether any appeal would be granted by the Hearings Panel.

NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference contain forward-looking statements. Except for strictly historical information contained herein, matters discussed in this report constitute forward-looking statements. Generally, these statements can be identified by the use of terms like “believe,” “expect,” “anticipate,” “plan,” “may,” “will,” “could,” “estimate,” “potential,” “opportunity,” “future,” “project,” and similar terms.

Forward-looking statements include, but are not limited to, statements about generating sales from Oncophage in Russia, generating royalty revenue from QS-21 in 2011 or thereafter, our or our partners’ or licensees’ intentions for performing plans or timelines for performing and completing research, preclinical studies and clinical trials, and releasing data, plans or timelines for initiating new clinical trials, expectations regarding research, preclinical studies, clinical trials, and regulatory processes (including additional clinical studies for Oncophage in renal cell carcinoma), expectations regarding test results, future product research and development activities, the expected effectiveness and safety profile of therapeutic drugs, vaccines, and combinations in treating diseases, statements regarding the potential benefit of Oncophage in kidney cancer based on a subgroup of interim analysis, as well as other potential benefits of Oncophage based on preliminary data, applicability of our heat shock protein technology to multiple cancers and infectious diseases, competitive position, regulatory plans and actions, including with respect to regulatory filings and meetings with regulatory authorities (including potential requests for meetings with the U.S. Food and Drug Administration regarding Oncophage clinical studies and strategies for responding to the Committee for Medicinal Products for Human Use’s decision regarding the conditional authorization of Oncophage in Europe and for making Oncophage available in other territories), the sufficiency of our clinical trials in renal cell carcinoma and melanoma, or subgroup analyses of data from these trials, to support a biologics license application or foreign marketing application for product approval, possible receipt of future regulatory approvals, the performance of collaborative partners in, and revenue expectations from, our strategic license and partnering collaborations, expected liquidity and cash needs, plans to commence, accelerate, decelerate, postpone, discontinue, or resume clinical programs, the rate of our net cash burn (defined as cash used in operating activities plus capital expenditures, debt repayments, and dividend payments), plans for commercial launch, and sales and marketing activities in Russia, implementation of corporate strategy, increased foreign currency exposure when we commercialize in Russia, and future financial performance.

These forward-looking statements involve a number of risks and uncertainties that could cause actual results to differ materially from those suggested by the forward-looking statements. These risks and uncertainties include, among others, that clinical trials may not demonstrate that our products are safe and more effective than current standards of care; that the subgroup analyses of our Oncophage clinical trials do not predict survival or efficacy of the product in future studies or use of Oncophage; that we may be unable to obtain sufficient funding or the regulatory authorization necessary to conduct additional clinical trials; that we may not be able to enroll sufficient numbers of patients in our clinical trials; that we may be unable to obtain the regulatory review or approval necessary to commercialize our product candidates because regulatory agencies are not satisfied with our trial protocols or the results of our trials; that we may fail to adequately protect our intellectual property or that it is determined that we infringe on the intellectual property of others; our strategic licenses and partnering collaborations may not meet expectations; that we or our business partners may fail to take all steps necessary for the successful commercial launch of Oncophage in Russia; that we may not be able to secure adequate reimbursement mechanisms and/or private-pay for Oncophage in Russia; that Oncophage may not achieve conditional approval in Europe because we may not successfully address issues associated with post-hoc analysis, subgroup analysis, lack of immunological data, product characterization, or other issues that may be of concern to the European Medicines Agency; that named patient programs may not be launched in the near-term, if ever, and if launched may not generate significant revenue, if any; that manufacturing problems may cause product development and launch delays and unanticipated costs; our ability to raise additional capital; our ability to attract and retain key employees; changes in financial markets, regulatory requirements, and geopolitical developments; the solvency of counterparties under material agreements, including subleases; general real estate risks; and the matters described under the heading “Risk Factors.”

We have included more detailed descriptions of these risks and uncertainties and other risks and uncertainties applicable to our business in Part II-Item 1A. “Risk Factors” of our most recent Quarterly Report on Form 10-Q. We encourage you to read those descriptions carefully. We caution investors not to place significant reliance on forward-looking statements contained in this document; such statements need to be evaluated in light of all the information contained in this document. Furthermore, the statements speak only as of the date they are made, and we undertake no obligation to update or revise these statements.

USE OF PROCEEDS

Except as otherwise provided in the applicable prospectus supplement, we intend to use the net proceeds from the sale of the securities covered by this prospectus for general corporate purposes, which may include working capital, capital expenditures, research and development expenditures, clinical trial expenditures, acquisitions of new technologies, and investments. Additional information on the use of net proceeds from the sale of securities covered by this prospectus may be set forth in the prospectus supplement relating to the specific offering.

PLAN OF DISTRIBUTION

We may sell securities in any of the ways described below, including any combination thereof:

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to or through underwriters or dealers;

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through one or more agents; or

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directly to purchasers or to a single purchaser.

The distribution of the securities may be effected from time to time in one or more transactions:

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at a fixed price, or prices, which may be changed from time to time;

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at market prices prevailing at the time of sale;

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at prices related to such prevailing market prices; or

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at negotiated prices.

Each prospectus supplement will describe the method of distribution of the securities and any applicable restrictions.

The prospectus supplement with respect to the securities of a particular series will describe the terms of the offering of the securities, including the following:

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the name or names of any underwriters, dealers or agents, and the amounts of securities underwritten or purchased by each of them;

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the initial public offering price of the securities and the proceeds to us and any discounts, commissions, or concessions allowed or reallowed or paid to dealers; and

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any securities exchanges on which the securities may be listed.

Any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time. In no event will any underwriter or dealer receive fees, commissions, and markups which, in the aggregate, would exceed eight percent of the price of the securities being registered.

Only the agents or underwriters named in the prospectus supplement are agents or underwriters in connection with the securities being offered.

We may authorize underwriters, dealers, or other persons acting as our agents to solicit offers by certain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on the date stated in the prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions, and other institutions, but shall in all cases be subject to our approval. Delayed delivery contracts will be subject only to those conditions set forth in the prospectus supplement, and the prospectus supplement will set forth any commissions we pay for solicitation of these contracts.

Agents, underwriters, and other third parties described above may be entitled to indemnification by us against certain civil liabilities, including liabilities under the Securities Act, or to contribution with respect to payments which the agents or underwriters may be required to make in respect thereof. Agents, underwriters, and such other third parties may be customers of, engage in transactions with, or perform services for us in the ordinary course of business.

One or more firms, referred to as “remarketing firms,” may also offer or sell the securities, if the prospectus supplement so indicates, in connection with a remarketing arrangement upon their purchase. Remarketing firms will act as principals for their own accounts or as our agents. These remarketing firms will offer or sell the securities in accordance with the terms of the securities. The prospectus supplement will identify any remarketing firm and describe the terms of its agreement, if any, with us and the remarketing firm’s compensation. Remarketing firms may be deemed to be underwriters in connection with the securities they remarket. Remarketing firms may be entitled under agreements that may be entered into with us to indemnification by us against certain civil liabilities, including liabilities under the Securities Act, and may be customers of, engage in transactions with, or perform services for us in the ordinary course of business.

Certain of the underwriters may use this prospectus and the accompanying prospectus supplement for offers and sales related to market-making transactions in the securities. These underwriters may act as principal or agent in these transactions, and the sales will be made at prices related to prevailing market prices at the time of sale.

The securities may be new issues of securities and may have no established trading market. The securities may or may not be listed on a national securities exchange. Underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We can make no assurance as to the liquidity of or the existence of trading markets for any of the securities.

Certain persons participating in this offering may engage in overallotment, stabilizing transactions, short covering transactions, and penalty bids in accordance with rules and regulations under the Exchange Act. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

DESCRIPTION OF COMMON STOCK

The following summary of the terms of our common stock is subject to and qualified in its entirety by reference to our charter and by-laws, copies of which are on file with the SEC as exhibits to previous SEC filings. Please refer to “Where You Can Find More Information” below for directions on obtaining these documents.

We have authority to issue 250,000,000 shares of common stock. As of January 15, 2010, we had 89,821,671 shares of common stock outstanding.

General

Subject to preferences that may apply to shares of preferred stock outstanding at the time, the holders of outstanding shares of common stock are entitled to receive dividends out of assets legally available for payment of dividends, as the board may from time to time determine. Each stockholder is entitled to one vote for each share of common stock held on all matters submitted to a vote of stockholders. Our certificate of incorporation does not provide for cumulative voting for the election of directors, which means that the holders of a majority of the shares voted can elect all of the directors then standing for election. The common stock is not entitled to preemptive rights and is not subject to conversion or redemption. Each outstanding share of common stock offered by this prospectus will, when issued, be fully paid and nonassessable.

Our common stock is traded on The NASDAQ Capital Market under the symbol “AGEN.”

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is American Stock Transfer and Trust Company. Its telephone number is (800) 937-5449.

DESCRIPTION OF PREFERRED STOCK

We currently have authorized 25,000,000 shares of preferred stock, of which 31,620 shares have been designated as series A convertible preferred stock, 10,000 shares have been designated as series B1 convertible preferred stock, and 5,250 have been designated as series B2 convertible preferred stock. As of the date of this prospectus, the series A convertible preferred stock is issued and outstanding in the amount described in the preceding sentence and we have 3,105 shares of our series B2 convertible preferred stock outstanding although no further shares can be converted into shares of common stock. In April 2009, we issued 5,929,212 shares of our common stock upon conversion of 2,145 shares of our series B2 convertible preferred stock via cashless conversions. In April 2008, all of the series B1 convertible preferred stock was converted into 1,585,197 shares of our common stock via a cashless conversion. The remaining 24,953,130 authorized shares of preferred stock are undesignated and not issued or outstanding as of the date of this prospectus. As of the date of this prospectus, we do not have any equity securities that would be senior to, or on par with, our authorized preferred stock.

Series A Preferred Stock

On September 24, 2003, we sold 31,620 shares of series A convertible preferred stock, par value $.01 per share, which we refer to as “series A preferred stock,” to Brad M. Kelley. Under the terms and conditions of the Certificate of Designation creating the series A preferred stock, the stock is convertible by the holder at any time into shares of our common stock, is non-voting, carries a 2.5 percent annual dividend yield, has an initial conversion price of $15.81, and is redeemable by us at its face amount on or after September 24, 2013. The liquidation value of the series A preferred stock is equal to $1,000 per share outstanding plus any accrued unpaid dividends. The Certificate of Designation does not restrict the repurchase or redemption of shares by us while there is an arrearage in the payment of dividends. The Certificate of Designation does not contemplate a sinking fund. This description of the series A preferred stock is qualified in its entirety by reference to the Certificate of Designation.

Series B Preferred Stock

On September 10, 2007, we issued 10,000 shares of our series B1 convertible preferred stock and 5,250 shares of our series B2 convertible preferred stock (the series B1 convertible preferred stock and the series B2 convertible preferred stock are referred to collectively as the class B convertible preferred stock) to a single institutional investor. In April 2008, all of the series B1 convertible preferred stock was converted into 1,585,197 shares of our common stock via a cashless conversion. Shares of the series B2 convertible preferred stock permit the investor to purchase common shares for consideration of up to 35 percent of the total dollar amount previously invested pursuant to the agreement with the investor, including conversions of the series B1 convertible preferred stock, at a purchase price equal to the lesser of $4.16 per common share or a price calculated based on the then-prevailing price of our common stock, and expire seven years from the date of issuance. The total number of shares of common stock issued or issuable to the holder of the class B convertible preferred stock cannot exceed 19.9% of our outstanding common stock. In April 2009, we issued 5,929,212 shares of our common stock upon conversion of 2,145 shares of our series B2 convertible preferred stock via cashless conversions. No dividends are paid on the class B convertible preferred stock and there are no liquidation preferences. This description of the class B convertible preferred stock is qualified in its entirety by reference to the Certificate of Designations.

Undesignated Shares

Under Delaware law and our charter, our board of directors is authorized, without stockholder approval, to issue shares of preferred stock from time to time in one or more series. Subject to limitations prescribed by Delaware law and our charter and by-laws, the board of directors can determine the number of shares constituting each series of preferred stock and the designation, preferences, voting powers, qualifications, and special or relative rights or privileges of that series. These may include provisions concerning voting, redemption, dividends, dissolution or the distribution of assets, conversion or exchange, and other subjects or matters as may be fixed by resolution of the board or an authorized committee of the board.

Our board of directors could authorize the issuance of shares of preferred stock with terms and conditions which could have the effect of discouraging a takeover or other transaction which holders of some, or a majority, of our common stock might believe to be in their best interests or in which holders of some, or a majority, of our common stock might receive a premium for their shares over the then market price of those shares.

If we offer a specific series of preferred stock under this prospectus, we will describe the terms of the preferred stock in the prospectus supplement for such offering and will file a copy of the certificate establishing the terms of the preferred stock with the SEC. To the extent required, this description will include:

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the title and stated value;

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the number of shares offered, the liquidation preference per share, and the purchase price;

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the dividend rate(s), period(s), and/or payment date(s), or method(s) of calculation for such dividends;

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whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

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the procedures for any auction and remarketing, if any;

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the provisions for a sinking fund, if any;

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any listing of the preferred stock on any securities exchange or market;

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whether the preferred stock will be convertible into Antigenics common stock, and, if applicable, the conversion price (or how it will be calculated) and conversion period;

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whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange price (or how it will be calculated) and exchange period;

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voting rights, if any, of the preferred stock;

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a discussion of any material and/or special U.S. federal income tax considerations applicable to the preferred stock;

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the relative ranking and preferences of the preferred stock as to dividend rights and rights upon liquidation, dissolution, or winding up of the affairs of Antigenics; and

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any material limitations on issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights upon liquidation, dissolution, or winding up of Antigenics.

The preferred stock offered by this prospectus will, when issued, be fully paid and nonassessable and will not have, or be subject to, any preemptive or similar rights.

Transfer Agent and Registrar

The transfer agent and registrar for any series or class of preferred stock will be set forth in the applicable prospectus supplement.

DESCRIPTION OF WARRANTS

We may issue warrants to purchase shares of our common stock, preferred stock, and/or debt securities in one or more series together with other securities or separately, as described in the applicable prospectus supplement. Below is a description of certain general terms and provisions of the warrants that we may offer. Particular terms of the warrants will be described in the warrant agreements and the prospectus supplement for the warrants.

The applicable prospectus supplement will contain, where applicable, the following terms of and other information relating to the warrants:

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the specific designation and aggregate number of, and the price at which we will issue, the warrants;

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the currency or currency units in which the offering price, if any, and the exercise price are payable;

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the designation, amount, and terms of the securities purchasable upon exercise of the warrants;

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if applicable, the exercise price for shares of our common stock and the number of shares of common stock to be received upon exercise of the warrants;

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if applicable, the exercise price for shares of our preferred stock, the number of shares of preferred stock to be received upon exercise, and a description of that series of our preferred stock;

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if applicable, the exercise price for our debt securities, the amount of debt securities to be received upon exercise, and a description of that series of debt securities;

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the date on which the right to exercise the warrants will begin and the date on which that right will expire or, if you may not continuously exercise the warrants throughout that period, the specific date or dates on which you may exercise the warrants;

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whether the warrants will be issued in fully registered form or bearer form, in definitive or global form, or in any combination of these forms, although, in any case, the form of a warrant included in a unit will correspond to the form of the unit and of any security included in that unit;

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any applicable material U.S. federal income tax consequences;

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the identity of the warrant agent for the warrants and of any other depositaries, execution or paying agents, transfer agents, registrars, or other agents;

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the proposed listing, if any, of the warrants or any securities purchasable upon exercise of the warrants on any securities exchange;

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if applicable, the date from and after which the warrants and the common stock, preferred stock, and/or debt securities will be separately transferable;

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if applicable, the minimum or maximum amount of the warrants that may be exercised at any one time;

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information with respect to book-entry procedures, if any;

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the anti-dilution provisions of the warrants, if any;

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any redemption or call provisions;

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whether the warrants are to be sold separately or with other securities as parts of units; and

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any additional terms of the warrants, including terms, procedures, and limitations relating to the exchange and exercise of the warrants.

DESCRIPTION OF DEBT SECURITIES

We will issue the debt securities offered by this prospectus and any accompanying prospectus supplement under an indenture to be entered into between Antigenics and the trustee identified in the applicable prospectus supplement. The terms of the debt securities will include those stated in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as in effect on the date of the indenture. We have filed a copy of the form of indenture as an exhibit to the registration statement in which this prospectus is included. The indenture will be subject to and governed by the terms of the Trust Indenture Act of 1939.

We may offer under this prospectus up to an aggregate principal amount of $100,000,000 in debt securities; or if debt securities are issued at a discount, or in a foreign currency, foreign currency units or composite currency, the principal amount as may be sold for an initial public offering price of up to $100,000,000. Unless otherwise specified in the applicable prospectus supplement, the debt securities will represent direct, unsecured obligations of Antigenics and will rank equally with all of our other unsecured indebtedness.

The following statements relating to the debt securities and the indenture are summaries, qualified in their entirety to the detailed provisions of the indenture.

General

We may issue the debt securities in one or more series with the same or various maturities, at par, at a premium, or at a discount. We will describe the particular terms of each series of debt securities in a prospectus supplement relating to that series, which we will file with the SEC.

The prospectus supplement will set forth, to the extent required, the following terms of the debt securities in respect of which the prospectus supplement is delivered:

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the title of the series;

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the aggregate principal amount;

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the issue price or prices, expressed as a percentage of the aggregate principal amount of the debt securities;

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any limit on the aggregate principal amount;

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the date or dates on which principal is payable;

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the interest rate or rates (which may be fixed or variable) or, if applicable, the method used to determine such rate or rates;

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the date or dates from which interest, if any, will be payable and any regular record date for the interest payable;

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the place or places where principal and, if applicable, premium and interest, is payable;

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the terms and conditions upon which we may, or the holders may require us to, redeem or repurchase the debt securities;

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the denominations in which such debt securities may be issuable, if other than denominations of $1,000, or any integral multiple of that number;

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whether the debt securities are to be issuable in the form of certificated debt securities (as described below) or global debt securities (as described below);

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the portion of principal amount that will be payable upon declaration of acceleration of the maturity date if other than the principal amount of the debt securities;

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the currency of denomination;

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the designation of the currency, currencies or currency units in which payment of principal and, if applicable, premium and interest, will be made;

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if payments of principal and, if applicable, premium or interest, on the debt securities are to be made in one or more currencies or currency units other than the currency of denomination, the manner in which the exchange rate with respect to such payments will be determined;

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if amounts of principal and, if applicable, premium and interest may be determined by reference to an index based on a currency or currencies, or by reference to a commodity, commodity index, stock exchange index, or financial index, then the manner in which such amounts will be determined;

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the provisions, if any, relating to any collateral provided for such debt securities;

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any addition to or change in the covenants and/or the acceleration provisions described in this prospectus or in the indenture;

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any events of default, if not otherwise described below under “Events of Default”;

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the terms and conditions, if any, for conversion into or exchange for shares of common stock or preferred stock;

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any depositaries, interest rate calculation agents, exchange rate calculation agents, or other agents; and

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the terms and conditions, if any, upon which the debt securities shall be subordinated in right of payment to other indebtedness of Antigenics.

We may issue discount debt securities that provide for an amount less than the stated principal amount to be due and payable upon acceleration of the maturity of such debt securities in accordance with the terms of the indenture. We may also issue debt securities in bearer form, with or without coupons. If we issue discount debt securities or debt securities in bearer form, we will describe material U.S. federal income tax considerations and other material special considerations which apply to these debt securities in the applicable prospectus supplement.

We may issue debt securities denominated in or payable in a foreign currency or currencies or a foreign currency unit or units. If we do, we will describe the restrictions, elections, and general tax considerations relating to the debt securities and the foreign currency or currencies or foreign currency unit or units in the applicable prospectus supplement.

Exchange and/or Conversion Rights

We may issue debt securities which can be exchanged for or converted into shares of common stock or preferred stock. If we do, we will describe the terms of exchange or conversion in the prospectus supplement relating to these debt securities.

Transfer and Exchange

We may issue debt securities that will be represented by either:

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“book-entry securities,” which means that there will be one or more global securities registered in the name of a depositary or a nominee of a depositary; or

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“certificated securities,” which means that they will be represented by a certificate issued in definitive registered form.

We will specify in the prospectus supplement applicable to a particular offering whether the debt securities offered will be book-entry or certificated securities.

Certificated Debt Securities

If you hold certificated debt securities, you may transfer or exchange such debt securities at the trustee’s office or at the paying agent’s office or agency in accordance with the terms of the indenture. You will not be charged a service charge for any transfer or exchange of certificated debt securities but may be required to pay an amount sufficient to cover any tax or other governmental charge payable in connection with such transfer or exchange.

You may effect the transfer of certificated debt securities and of the right to receive the principal of, premium, and/or interest, if any, on the certificated debt securities only by surrendering the certificate representing the certificated debt securities and having us or the trustee issue a new certificate to the new holder.

Global Securities

If we decide to issue debt securities in the form of one or more global securities, then we will register the global securities in the name of the depositary for the global securities or the nominee of the depositary, and the global securities will be delivered by the trustee to the depositary for credit to the accounts of the holders of beneficial interests in the debt securities.

The prospectus supplement will describe the specific terms of the depositary arrangement for debt securities of a series that are issued in global form. None of the Company, the trustee, any payment agent, or the security registrar will have any responsibility or liability for any aspect of the records relating to or payments made on account of beneficial ownership interests in a global debt security or for maintaining, supervising, or reviewing any records relating to these beneficial ownership interests.

No Protection in the Event of Change of Control

The indenture does not have any covenants or other provisions providing for a put or increased interest or otherwise that would afford holders of debt securities additional protection in the event of a recapitalization transaction, a change of control of Antigenics, or a highly leveraged transaction. If we offer any covenants or provisions of this type with respect to any debt securities covered by this prospectus, we will describe them in the applicable prospectus supplement.

Covenants

Unless otherwise indicated in this prospectus or a prospectus supplement, the debt securities will not have the benefit of any covenants that limit or restrict our business or operations, the pledging of our assets, or the incurrence by us of indebtedness. We will describe in the applicable prospectus supplement any material covenants in respect of a series of debt securities.

Consolidation, Merger, and Sale of Assets

We have agreed in the indenture that we will not consolidate with or merge into any other person, or convey, transfer, sell, or lease our properties and assets substantially as an entirety to any person, unless:

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the person formed by the consolidation or into or with which we are merged or the person to which our properties and assets are conveyed, transferred, sold, or leased, is a corporation organized and existing under the laws of the U.S., any state or the District of Columbia, or a corporation or comparable legal entity organized under the laws of a foreign jurisdiction and, if we are not the surviving person, the surviving person has expressly assumed all of our obligations, including the payment of the principal of, and premium, if any, and interest on the debt securities and the performance of the other covenants under the indenture; and

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immediately after giving effect to the transaction, no event of default, and no event which, after notice or lapse of time or both, would become an event of default, has occurred and is continuing under the indenture.

Events of Default

Unless otherwise specified in the applicable prospectus supplement, the following events will be events of default under the indenture with respect to debt securities of any series:

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we fail to pay any principal or premium, if any, when it becomes due;

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we fail to pay any interest within 30 days after it becomes due;

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we fail to comply with any other covenant in the debt securities or the indenture for 60 days after written notice specifying the failure from the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of that series; and

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certain events involving bankruptcy, insolvency, or reorganization of Antigenics or any of our significant subsidiaries.

The trustee may withhold notice to the holders of the debt securities of any series of any default, except in payment of principal of, or premium, if any, or interest on the debt securities of a series, if the trustee considers it to be in the best interest of the holders of the debt securities of that series to do so.

If an event of default (other than an event of default resulting from certain events of bankruptcy, insolvency, or reorganization) occurs, and is continuing, then the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of any series may accelerate the maturity of the debt securities. If this happens, the entire principal amount, plus the premium, if any, of all the outstanding debt securities of the affected series plus accrued interest to the date of acceleration will be immediately due and payable. At any time after the acceleration, but before a judgment or decree based on such acceleration is obtained by the trustee, the holders of a majority in aggregate principal amount of outstanding debt securities of such series may rescind and annul such acceleration if:

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all events of default (other than nonpayment of accelerated principal, premium, or interest) have been cured or waived;

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all lawful interest on overdue interest and overdue principal has been paid; and

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the rescission would not conflict with any judgment or decree.

In addition, if the acceleration occurs at any time when Antigenics has outstanding indebtedness which is senior to the debt securities, the payment of the principal amount of outstanding debt securities may be subordinated in right of payment to the prior payment of any amounts due under the senior indebtedness, in which case the holders of debt securities will be entitled to payment under the terms prescribed in the instruments evidencing the senior indebtedness and the indenture.

If an event of default resulting from certain events of bankruptcy, insolvency, or reorganization occurs, the principal, premium, and interest amount with respect to all of the debt securities of any series will be due and payable immediately without any declaration or other act on the part of the trustee or the holders of the debt securities of that series.

The holders of a majority in principal amount of the outstanding debt securities of a series will have the right to waive any existing default or compliance with any provision of the indenture or the debt securities of that series and to direct the time, method, and place of conducting any proceeding for any remedy available to the trustee, subject to certain limitations specified in the indenture.

No holder of any debt security of a series will have any right to institute any proceeding with respect to the indenture or for any remedy under the indenture, unless:

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the holder gives to the trustee written notice of a continuing event of default;

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the holders of at least 25% in aggregate principal amount of the outstanding debt securities of the affected series make a written request and offer reasonable indemnity to the trustee to institute a proceeding as trustee;

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the trustee fails to institute a proceeding within 60 days after such request; and

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the holders of a majority in aggregate principal amount of the outstanding debt securities of the affected series do not give the trustee a direction inconsistent with such request during such 60-day period.

These limitations do not, however, apply to a suit instituted for payment on debt securities of any series on or after the due dates expressed in the debt securities.

Modification and Waiver

From time to time, we and the trustee may, without the consent of holders of the debt securities of one or more series, amend the indenture or the debt securities of one or more series, or supplement the indenture, for certain specified purposes, including:

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to provide that the surviving entity following a change of control of Antigenics permitted under the indenture will assume all of our obligations under the indenture and debt securities;

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to provide for certificated debt securities in addition to uncertificated debt securities;

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to comply with any requirements of the SEC under the Trust Indenture Act of 1939;

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to cure any ambiguity, defect, or inconsistency, or make any other change that does not materially and adversely affect the rights of any holder; and

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to appoint a successor trustee under the indenture with respect to one or more series.

From time to time, we and the trustee may, with the consent of holders of at least a majority in principal amount of the outstanding debt securities, amend or supplement the indenture or the debt securities, or waive compliance in a particular instance by us with any provision of the indenture or the debt securities. We may not, however, without the consent of each holder affected by such action, modify or supplement the indenture or the debt securities, or waive compliance with any provision of the indenture or the debt securities in order to:

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reduce the amount of debt securities whose holders must consent to an amendment, supplement, or waiver to the indenture or such debt security;

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reduce the rate of or change the time for payment of interest;

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reduce the principal of or change the stated maturity of the debt securities;

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make any debt security payable in money other than that stated in the debt security;

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change the amount or time of any payment required, or reduce the premium payable upon any redemption, or change the time before which no such redemption may be made;

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waive a default in the payment of the principal of, premium, if any, or interest on the debt securities or a redemption payment; or

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take any other action otherwise prohibited by the indenture to be taken without the consent of each holder affected by the action.

Defeasance of Debt Securities and Certain Covenants in Certain Circumstances

The indenture permits us, at any time, to elect to discharge our obligations with respect to one or more series of debt securities by following certain procedures described in the indenture. These procedures will allow us either:

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to defease and be discharged from any and all of our obligations with respect to any debt securities except for the following obligations (which discharge is referred to as “legal defeasance”):

(1)

to register the transfer or exchange of such debt securities;

(2)

to replace temporary or mutilated, destroyed, lost, or stolen debt securities;

(3)

to compensate and indemnify the trustee; or

(4)

to maintain an office or agency in respect of the debt securities and to hold monies for payment in trust; or

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to be released from our obligations with respect to the debt securities under certain covenants contained in the indenture, as well as any additional covenants which may be contained in the applicable supplemental indenture (which release is referred to as “covenant defeasance”).

In order to exercise either defeasance option, we must deposit with the trustee or other qualifying trustee, in trust for that purpose:

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money;

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U.S. Government Obligations (as described below) or Foreign Government Obligations (as described below) which through the scheduled payment of principal and interest in accordance with their terms will provide money; or

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a combination of money and/or U.S. Government Obligations and/or Foreign Government Obligations sufficient in the written opinion of a nationally-recognized firm of independent accountants to provide money;

which in each case specified above, provides a sufficient amount to pay the principal of, premium, if any, and interest, if any, on the debt securities of the series, on the scheduled due dates or on a selected date of redemption in accordance with the terms of the indenture.

In addition, defeasance may be effected only if, among other things:

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in the case of either legal or covenant defeasance, we deliver to the trustee an opinion of counsel, as specified in the indenture, stating that as a result of the defeasance neither the trust nor the trustee will be required to register as an investment company under the Investment Company Act of 1940;

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in the case of legal defeasance, we deliver to the trustee an opinion of counsel stating that we have received from, or there has been published by, the Internal Revenue Service a ruling to the effect that, or there has been a change in any applicable federal income tax law with the effect that (and the opinion shall confirm that), the holders of outstanding debt securities will not recognize income, gain, or loss for U.S. federal income tax purposes solely as a result of such legal defeasance and will be subject to U.S. federal income tax on the same amounts, in the same manner, including as a result of prepayment, and at the same times as would have been the case if legal defeasance had not occurred;

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in the case of covenant defeasance, we deliver to the trustee an opinion of counsel to the effect that the holders of the outstanding debt securities will not recognize income, gain, or loss for U.S. federal income tax purposes as a result of covenant defeasance and will be subject to U.S. federal income tax on the same amounts, in the same manner, and at the same times as would have been the case if covenant defeasance had not occurred; and

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certain other conditions described in the indenture are satisfied.

If we fail to comply with our remaining obligations under the indenture and applicable supplemental indenture after a covenant defeasance of the indenture and applicable supplemental indenture, and the debt securities are declared due and payable because of the occurrence of any undefeased event of default, the amount of money and/or U.S. Government Obligations and/or Foreign Government Obligations on deposit with the trustee could be insufficient to pay amounts due under the debt securities of the affected series at the time of acceleration. We will, however, remain liable in respect of these payments.

The term “U.S. Government Obligations” as used in the above discussion means securities which are direct obligations of or non-callable obligations guaranteed by the United States of America for the payment of which obligation or guarantee the full faith and credit of the United States of America is pledged.

The term “Foreign Government Obligations” as used in the above discussion means, with respect to debt securities of any series that are denominated in a currency other than U.S. dollars (1) direct obligations of the government that issued or caused to be issued such currency for the payment of which obligations its full faith and credit is pledged or (2) obligations of a person controlled or supervised by or acting as an agent or instrumentality of such government the timely payment of which is unconditionally guaranteed as a full faith and credit obligation by that government, which in either case under clauses (1) or (2), are not callable or redeemable at the option of the issuer.

Regarding the Trustee

We will identify the trustee with respect to any series of debt securities in the prospectus supplement relating to the applicable debt securities. You should note that if the trustee becomes a creditor of Antigenics, the indenture and the Trust Indenture Act of 1939 limit the rights of the trustee to obtain payment of claims in certain cases, or to realize on certain property received in respect of any such claim, as security or otherwise. The trustee and its affiliates may engage in, and will be permitted to continue to engage in, other transactions with us and our affiliates. If, however, the trustee acquires any “conflicting interest” within the meaning of the Trust Indenture Act of 1939, it must eliminate such conflict or resign.

The holders of a majority in principal amount of the then outstanding debt securities of any series may direct the time, method, and place of conducting any proceeding for exercising any remedy available to the trustee. If an event of default occurs and is continuing, the trustee, in the exercise of its rights and powers, must use the degree of care and skill of a prudent person in the conduct of his or her own affairs. Subject to that provision, the trustee will be under no obligation to exercise any of its rights or powers under the indenture at the request of any of the holders of the debt securities, unless they have offered to the trustee reasonable indemnity or security.

LEGAL MATTERS

Our counsel, Ropes & Gray LLP, Boston, Massachusetts, will pass on the validity of the securities offered by this prospectus and any accompanying prospectus supplement.

EXPERTS

The consolidated financial statements of Antigenics Inc. as of December 31, 2008 and 2007, and for each of the years in the three-year period ended December 31, 2008, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2008 have been incorporated by reference herein and in the registration statement in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

This prospectus is part of a registration statement on Form S-3 filed by us with the SEC. This prospectus does not contain all of the information set forth in the registration statement, certain parts of which are omitted in accordance with the rules and regulations of the SEC. Statements contained in this prospectus as to the contents of any contract or other document referred to are not necessarily complete and in each instance reference is made to the copy of that contract or other document filed as an exhibit to the registration statement. For further information about us and the securities offered by this prospectus, we refer you to the registration statement and its exhibits and schedules which may be obtained as described herein.

The SEC allows us to “incorporate by reference” the information contained in documents that we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus, and information in documents that we file later with the SEC will automatically update and supersede information in this prospectus. We incorporate by reference the documents listed below into this prospectus, and any future filings made by us with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act until the offering of all the securities by this prospectus is completed, including all filings made after the date of this initial registration statement and prior to its effectiveness. We hereby incorporate by reference the documents listed below (File No. 000-29089).

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our Annual Report on Form 10-K for the fiscal year ended December 31, 2008 as filed on March 16, 2009;

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our Proxy Statement on Schedule 14A filed with the SEC on April 27, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended March 31, 2009 as filed on May 11, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended June 30, 2009 as filed on August 10, 2009;

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our Quarterly Report on Form 10-Q for the quarter ended September 30, 2009 as filed on November 9, 2009; and

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We will provide each person to whom a prospectus is delivered a copy of all of the information that has been incorporated by reference in this prospectus but not delivered with the prospectus. You may obtain copies of these filings, at no cost, through the “Investor Relations” section of our website (www.antigenics.com), and you may request copies of these filings, at no cost, by writing or telephoning us at:

Antigenics Inc.

Attention: Secretary

3 Forbes Road

Lexington, MA 02421

Telephone: (781) 674-4400

The information contained on our website is not a part of this prospectus.

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