Edgar Filing: ANTIGENICS INC /DE/

Prospectus Supplement


PROSPECTUS SUPPLEMENT		Filed Pursuant to Rule 424(b)(5)
(To Prospectus dated April 24, 2007)		Registration No. 333-118175

LOGO

ANTIGENICS INC.

This prospectus supplement relates to the issuance of 1,623,377 shares of our common stock, par value $0.01 per share (“common stock”), together with 10,000 shares of Series B1 Convertible Preferred Stock, par value $0.01 per share (“Series B1 Convertible Preferred Stock”), which will expire one year from the date of issuance, and 5,250 shares of Series B2 Convertible Preferred Stock, par value $0.01 per share (“Series B2 Convertible Preferred Stock” and, together with the Series B1 Convertible Preferred Stock, the “Class B Convertible Preferred Stock”), which will expire seven years from the date of issuance. This prospectus supplement also relates to the shares of common stock issuable upon conversion of the Series B1 Convertible Preferred Stock and the Series B2 Convertible Preferred Stock. Pursuant to our issuance of common stock, the Series B1 Convertible Preferred Stock and the Series B2 Convertible Preferred Stock, we will receive total proceeds of $5,000,000, less offering costs.

Our common stock is traded on the NASDAQ Global Market under the symbol “AGEN.” The last reported sale price of our common stock on August 31, 2007 was $2.48 per share. There is no public market for the Class B Convertible Preferred Stock and we do not intend to list the Class B Convertible Preferred Stock for trading on any national securities exchange or for inclusion on any automated quotation system.

Investing in our common stock and the Class B Convertible Preferred Stock involves a high degree of risk. Before buying any of these shares of our common stock you should carefully consider the risk factors described in “ Risk Factors” beginning on page S-1 of this prospectus supplement.

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 supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.


	Per Share		Total
Offering price	$	3.08	$	5,000,000
Placement agent fees	$	0.1232	$	200,000
Proceeds, before offering costs, to us	$	2.9568	$	4,800,000

The placement agent is offering the shares of our common stock, Series B1 Convertible Preferred Stock and Series B2 Convertible Preferred Stock on a best efforts basis, as described in “Plan of Distribution.” Delivery of the shares will be made on or about September 10, 2007.

We maintain our principal operations in Lexington, Massachusetts and our executive offices in New York, New York. The address for our executive offices is 162 Fifth Avenue, Suite 900, New York, New York 10010. Our telephone number there is (212) 994-8200.

Wm Smith Securities, Incorporated

The date of this prospectus supplement is August 31, 2007

You should rely only on the information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus. We have not and the placement agent has not authorized anyone to provide you with information that is different from that contained in or referred to 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 offering to sell, and seeking offers to buy, shares of common stock, Series B1 Convertible Preferred Stock and Series B2 Convertible Preferred Stock only in jurisdictions where offers and sales are permitted. The information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus is accurate only as of the date of this prospectus supplement, regardless of the time of delivery of this prospectus supplement or of any sale of our common stock.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT


		Page
Risk Factors		S-1
Forward-Looking Statements		S-20
Use of Proceeds		S-21
Dividend Policy		S-21
Dilution		S-21
Description of the Class B Convertible Preferred Stock		S-22
Plan of Distribution		S-25

PROSPECTUS

About This Prospectus		3
Antigenics Inc.		3
Risk Factors		4
Note Regarding Forward-Looking Statements		4
Use of Proceeds		5
Ratio of Earnings to Fixed Charges and Preferred Stock Dividends		5
Description of Common Stock		6
Description of Preferred Stock		7
Description of Debt Securities		9
Anti-Takeover Effects of Delaware Law and of Our Charter and By-Laws		16
Plan of Distribution		17
Validity of Securities		19
Experts		19
Incorporation of Certain Documents by Reference		19
Where You Can Find More Information		19

This document is in two parts. The first part is the prospectus supplement, which describes the specific terms of this offering. The second part, the accompanying prospectus, provides more general information. If the description of the offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information in this prospectus supplement.

Oncophage^® and Aroplatin™ are trademarks of Antigenics Inc. Other trademarks included herein are the property of their respective owners.

RISK FACTORS

You should carefully consider each of the risks described below and all other information in this prospectus supplement and the accompanying prospectus before making a decision to invest in our common stock, Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock. If any of the following risks actually occur, our business, financial condition, operating results or cash flows could be harmed. This could cause the trading price of our common stock to decline, and you may lose all or part of your investment.

Risks Related to our Business

If we incur operating losses for longer than we expect, or we are not able to raise additional capital, we may become insolvent and be unable to continue our operations.

From our inception through June 30, 2007, we have generated net losses totaling $480.4 million. Our net losses for the six months ended June 30, 2007 and for the year ended December 31, 2006 were $18.5 million and $51.9 million, respectively. We expect to incur significant losses over the next several years as we continue our clinical trials, apply for regulatory approvals, continue development of our technologies, and pursue commercialization efforts and related activities. Furthermore, our ability to generate cash from operations is dependent on if and when we will be able to enter into strategic licensing and partnering relationships and/or commercialize our product candidates. If we incur operating losses for longer than we expect, and/or we are unable to raise additional capital, we may become insolvent and be unable to continue our operations.

If we fail to obtain the capital necessary to fund our operations, we will be unable to advance our development programs and complete our clinical trials.

On June 30, 2007, we had $25.4 million in cash, cash equivalents, and short-term investments. We believe that, based on our current plans and activities, our working capital resources at June 30, 2007, along with the estimated proceeds from our license, supply, and collaborative agreements, will be sufficient to satisfy our liquidity requirements into 2008. However, we plan to attempt to raise additional funds prior to that time. For the six months ended June 30, 2007, the sum of our average monthly cash used in operating activities plus our average monthly capital expenditures was $2.6 million. Total capital expenditures for the six months ended June 30, 2007 were $19,000. We do not anticipate significant capital expenditures during the remainder of 2007. Since our inception, we have financed our operations principally by sales of equity and convertible debt instruments. In order to finance future operations, we will be required to raise additional funds in the capital markets, through arrangements with collaborative partners, or from other sources. Additional financing, however, may not be available on favorable terms or at all. If we are unable to raise additional funds when we need them, we will be required to delay, reduce, or eliminate some or all of our development programs and some or all of our clinical trials, including the development programs and clinical trials supporting our most advanced product candidate, Oncophage. We also may be forced to license technologies to others under agreements that allocate to third parties substantial portions of the potential value of these technologies.

We have significant long-term debt, and we may not be able to make interest or principal payments when due.

As of June 30, 2007, our total long-term debt, excluding the current portion, was $76.3 million. Our 5.25% convertible senior notes due 2025 do not restrict our ability or the ability of our subsidiaries to incur additional indebtedness, including debt that effectively ranks senior to the notes. On each of February 1, 2012, February 1, 2015 and February 1, 2020, holders may require us to purchase their notes for cash equal to 100% of the principal amount of the notes, plus any accrued and unpaid interest. Holders may also require us to repurchase their notes upon a fundamental change, as defined, at a repurchase price, in cash, equal to 100% of the principal amount of the notes to be repurchased, plus any accrued and unpaid interest, and in some cases, an additional “make-whole” premium.

Our senior secured convertible notes (the “2006 Notes”) mature on August 30, 2011, at which point we may elect to repay the outstanding balance in cash or in common stock, subject to certain limitations. In no event will any of the noteholders be obligated to accept equity that would result in them owning in excess of 9.99% of our outstanding common stock at any given time in connection with any conversion, redemption, or repayment of these notes. The note agreements include material restrictions on our incurrence of debt and liens while these notes are outstanding, as well as other customary covenants.

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Our ability to satisfy our obligations will depend upon our future performance, which is subject to many factors, including the factors identified in this “Risk Factors” section and other factors beyond our control. If we are not able to generate sufficient cash flow from operations in the future to service our indebtedness, we may be required, among other things:

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to seek additional financing in the debt or equity markets;

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to refinance or restructure all or a portion of our indebtedness;

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to sell, out-license, or otherwise dispose of assets; and/or

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to reduce or delay planned expenditures on research and development and/or commercialization activities.

Such measures might not be sufficient to enable us to make principal and interest payments. In addition, any such financing, refinancing, or sale of assets might not be available on economically favorable terms.

To date, we have had negative cash flow from operations. For the six months ended June 30, 2007 and for the year ended December 31, 2006, net cash used in operating activities was $15.7 million and $44.9 million, respectively. Excluding our 2006 Notes, which mature in 2011 and for which we may elect to pay the interest in cash or additional notes, at our option, and for which the outstanding balance at maturity may be paid in cash or in common stock, subject to certain limitations, and assuming no additional interest-bearing debt is incurred and none of our notes are converted, redeemed, repurchased, or exchanged, our interest payments will be $1.3 million during the remainder of 2007 and $2.6 million annually during 2008 and thereafter until maturity.

Because part I of our Phase 3 trial in renal cell carcinoma did not achieve its primary endpoint, this trial would generally not be sufficient to support a marketing application for product approval, and we would generally not expect to generate product revenue from sales of Oncophage until after the achievement of regulatory approval, which may require the completion of additional clinical studies that demonstrate the efficacy and safety of Oncophage.

On March 24, 2006, we announced top-line results from part I of our Phase 3 study of Oncophage in renal cell carcinoma patients who are at high risk of recurrence after surgery, indicating that the trial did not meet its primary endpoint.

Guidance received from past discussions with the United States Food and Drug Administration (“FDA”) indicates that further clinical studies must be conducted to demonstrate the efficacy and safety of Oncophage. We intend to seek a meeting with the FDA to discuss the results of the updated analyses utilizing data through March 2007 to determine whether there is an opportunity to file a biologics license application (“BLA”) on the basis of these results with appropriate commitments to conduct further clinical investigations to support the efficacy of Oncophage in renal cell carcinoma. Because evidence of clinically significant improvement has been observed in a subgroup analysis and was not demonstrated in the pre-specified analysis of the primary and secondary endpoints of the Phase 3 study of Oncophage in renal cell carcinoma, this trial may not be sufficient to support a BLA for product approval. Furthermore, this trial may not be sufficient to support approval outside of the U.S.

We may not be able to secure additional financing to continue our clinical studies. If we cannot secure additional financing, we may become insolvent.

The FDA has previously told us that part I of our Phase 3 trial in renal cell carcinoma, by itself, will not be sufficient to support a BLA for product approval in this indication. Unless the FDA changes its position, we do not expect that part I alone will support approval of a future BLA that we ultimately may file with the FDA in this indication. In addition, the timing of launch is uncertain in any indication.

On September 2, 2003, the FDA placed our Phase 3 Oncophage clinical trials in renal cell carcinoma and in melanoma on partial clinical hold. The FDA’s written correspondence instituting the partial clinical hold indicated that Oncophage was not sufficiently characterized. On October 22, 2003, we submitted to the FDA additional

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specifications for purity, identity, potency, and pH, which represent product characterization data, and on November 21, 2003, the FDA lifted the partial clinical hold. Even though the FDA lifted the partial clinical hold, the FDA informed us that, for purposes of part I of our Phase 3 trial in renal cell carcinoma and our Phase 3 trial in melanoma, Oncophage has been insufficiently characterized and that the results obtained with an insufficiently characterized product could not be used to provide efficacy data in support of a BLA. The FDA deemed the Oncophage provided to patients before December 2003 to be insufficiently characterized because it had not prospectively undergone the full battery of tests required for drugs used in pivotal trials. Some of these tests, such as potency assays, were not fully developed until after September 2003. The imposition of the partial clinical hold prevented us from enrolling new patients in our Phase 3 clinical trials between September 3, 2003 and November 21, 2003. We believe that we addressed the comments the FDA raised in connection with the partial clinical hold. After the clinical hold was lifted, the FDA asked us to implement the use of potency assays to release vaccine lots for all trials of Oncophage, including our Phase 3 trials. Subsequently, we submitted, during 2004, our validation package to the FDA for the potency assays, and in May 2005 we successfully concluded discussions with the FDA on this matter. Validation of the assays refers, in general terms, to establishing the robustness and reproducibility of the assays on an ongoing basis and under various different conditions to demonstrate that the potency assays work consistently. The potency assays have been used to test product administered since December 2003, and we have performed tests on frozen stored portions of product administered to patients prior to December 2003. This data will be submitted to the FDA as part of any BLA filing for Oncophage. We believe we have addressed all product characterization issues raised by the FDA to date.

Because the FDA indicated that, by itself, part I of our Phase 3 clinical trial in renal cell carcinoma was not sufficient to support a BLA filing, we expanded our clinical development plan by initiating a part II to this Phase 3 trial in a similar patient population. The FDA agreed with this registration plan, which was comprised of two components — part I and part II.

Guidance received from past discussions with the FDA indicates that further clinical studies must be conducted to demonstrate the efficacy and safety of Oncophage. We intend to seek a meeting with the FDA to discuss the results of the updated analyses utilizing data through March 2007 to determine whether there is an opportunity to file a BLA on the basis of these results with appropriate commitments to conduct further clinical investigations to support the efficacy of Oncophage in renal cell carcinoma. Because evidence of clinically significant improvement has been observed in a subgroup analysis and was not demonstrated in the pre-specified analysis of the primary and secondary endpoints of the Phase 3 study of Oncophage in renal cell carcinoma, this trial may not be sufficient to support a BLA for product approval. Furthermore, this trial may not be sufficient to support approval outside of the U.S.

Because we expect additional Phase 3 clinical trials of Oncophage in the treatment of melanoma will be required prior to submitting a BLA for this indication, we may not commercialize Oncophage in this indication for several years, if ever.

During the quarter ended September 30, 2004, we completed enrollment of our Phase 3 trial in metastatic melanoma. Our overall manufacturing success rate for this trial was approximately 70%, and as a result during 2004 we indicated that we did not believe this trial would qualify as registrational. In October 2005, we announced preliminary survival data from this trial, and updated findings were presented on June 5, 2006 at the meeting of the American Society of Clinical Oncology (“ASCO”). Overall, patients in the intent-to-treat Oncophage arm (M1a, b, and c combined categories as defined by the American Joint Committee on Cancer (“AJCC”)) fared similarly to those in the physician’s choice arm in terms of survival, the primary endpoint. In a subgroup of patients who received at least 10 injections of Oncophage, overall median survival increased by approximately 29% in the Oncophage-treated arm as compared with those in the physician’s choice treatment arm (16.5 months versus 12.8 months). These findings also noted that in a subgroup of randomized stage IV M1a and M1b combined patients, who received at least 10 doses of Oncophage vaccine, median survival increased by approximately 143% in the Oncophage-treated arm compared with those in the physician’s choice treatment arm (31.2 months versus 12.8 months; nominal, one-sided p value of 0.017 and hazard ratio of 0.452). This analysis was not pre-specified. The physician’s choice treatment arm included the current array of therapies such as chemotherapeutics, biological agents, and/or surgery. This OS analysis of the primary endpoint on an intent-to-treat basis was not statistically significant.

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Due to a relatively high failure rate in vaccine manufacturing, this study would not, by itself, be expected to support a BLA filing. Even if we had not experienced the high manufacturing failure rate, the FDA has indicated that this study, like part I of our Phase 3 renal cell carcinoma study, could not, by itself, support a BLA filing, because the FDA views the Oncophage administered to patients in this study prior to December 2003 as insufficiently characterized. We have not yet had any specific discussions with the FDA regarding our clinical development plan for melanoma. Accordingly, we do not know the types of studies that the FDA will require to support a BLA filing. Even if the FDA were to indicate agreement with our clinical development plan, that plan may fail to support a BLA filing for many reasons, including failure of the trials to demonstrate that Oncophage is safe and effective in this indication, failure to conduct the studies in compliance with the clinical trial protocols, or a change in the FDA’s views.

Analysis of subgroups in clinical trials is generally hypothesis-generating, supportive of future clinical trials, and not generally supportive, alone, of registration or approval of a product.

The signals and trends observed in the Phase 3 renal cell carcinoma and melanoma trials of Oncophage are based on data analysis of subgroups of patients that were not pre-specified in these studies. While the data might be suggestive of treatment effect, the results cannot be expected, alone, to support registration or approval of Oncophage. While the data provide important evidence that is useful for physicians in designing and conducting future clinical trials, additional evidence may be required to recruit physicians for future clinical research.

The drug development and approval process is uncertain, time-consuming, and expensive.

The process of obtaining and maintaining regulatory approvals for new therapeutic products is lengthy, expensive, and uncertain. It also can vary substantially based on the type, complexity, and novelty of the product. We must provide regulatory authorities with preclinical and clinical data demonstrating that our product candidates are safe and effective before they can be approved for commercial sale. Clinical development, including preclinical testing, is also a long, expensive, and uncertain process. It may take us several years to complete our testing, and failure can occur at any stage of testing. Interim results of preclinical studies or clinical trials do not necessarily predict their final results, and acceptable results in early studies might not be seen in later studies. Any preclinical or clinical test may fail to produce results satisfactory to regulatory authorities. Preclinical and clinical data can be interpreted in different ways, which could delay, limit, or prevent regulatory approval. Negative or inconclusive results from a preclinical study or clinical trial, adverse medical events during a clinical trial, or safety issues resulting from products of the same class of drug could require a preclinical study or clinical trial to be repeated or cause a program to be terminated, even if other studies or trials relating to the program are successful.

Oncophage is a novel therapeutic cancer vaccine that is patient-specific, meaning it is derived from the patient’s own tumor. To date, the FDA has not approved any therapeutic cancer vaccines for commercial sale, and foreign regulatory agencies have approved only a limited number. Both the FDA and foreign regulatory agencies, including the European Medicines Agency, which is responsible for product approvals in Europe, and Health Canada, which is responsible for product approvals in Canada, have relatively little experience in reviewing patient-specific oncology therapies. The partial clinical hold that the FDA had placed, and subsequently lifted, on our Phase 3 Oncophage clinical trials primarily related to product characterization issues. Oncophage may experience a long regulatory review process and high development costs, either of which could delay or prevent our commercialization efforts. We have also initiated communications with regulatory health authorities in other jurisdictions to discuss requirements for the approval of Oncophage in renal cell carcinoma. As of June 30, 2007, we have spent approximately 13 years and $232.8 million on our research and development program in heat shock proteins for cancer.

To obtain regulatory approvals, we must, among other requirements, complete carefully controlled and well designed preclinical studies and clinical trials demonstrating that a particular product candidate is safe and effective for the applicable disease. Data collection and analysis are uncertain, and may negatively affect or not affect the acceptability of the overall results of a trial, and even if clinically meaningful, may not meet the requirements of the FDA or other regulatory authorities for submission and approval of a marketing application or similar ex-U.S.

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applications for product approval. Several biotechnology companies have failed to obtain regulatory approvals because regulatory agencies were not satisfied with the structure or conduct of the preclinical studies and clinical trials, or the ability to collect data or interpret the data from the trials. In addition, data from clinical trials are subject to varying interpretations and the data may not demonstrate the desired safety and efficacy. Similar problems could delay or prevent us from obtaining approvals.

We may not complete our planned preclinical studies or clinical trials on schedule or at all. We may not be able to confirm the safety and efficacy of our potential drugs in long-term clinical trials, which may result in a delay or failure to commercialize our product candidates. The timing and success of a clinical trial is dependent on enrolling sufficient patients in a timely manner, avoiding serious or significant adverse patient reactions, and demonstrating efficacy of the product candidate in order to support a favorable risk versus benefit profile, among other considerations. Because we rely on third-party clinical investigators and contract research organizations to conduct our clinical trials, we may encounter delays outside our control, particularly if our relationships with any third-party clinical investigators or contract research organizations are adversarial. The timing and success of our clinical trials, in particular, are also dependent on regulatory authorities accepting each trial’s protocol, statistical analysis plan, product characterization tests, and clinical data. If we are unable to satisfy regulatory authorities with such matters, including the specific matters noted above, or our clinical trials yield inconclusive or negative results, we will be required to modify or expand the scope of our clinical studies or conduct additional studies to support marketing approvals. In addition, regulatory authorities may request additional information or data that is not readily available. Delays in our ability to respond to such requests would delay, and failure to adequately address all concerns would prevent, our commercialization efforts.

Also, we, or regulatory authorities, might further delay or halt our clinical trials for various reasons, including but not limited to:

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we may fail to comply with extensive regulations;

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a product candidate may not appear to be more effective than current therapies;

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a product candidate may have unforeseen, undesirable, or significant adverse side effects, toxicities, or other characteristics;

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we may fail to prospectively identify the most appropriate patient populations and/or statistical analyses for inclusion in our clinical trials;

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the time required to determine whether a product candidate is effective may be longer than expected;

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we may be unable to adequately follow or evaluate patients after treatment with a product candidate;

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patients may die during a clinical trial because their disease is too advanced or because they experience medical problems that may not be related to the product candidate;

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sufficient numbers of patients may not meet our eligibility criteria and/or enroll in our clinical trials and may withdraw from our clinical trials after they have enrolled; or

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we may be unable to produce sufficient quantities of a product candidate to complete the trial.

Furthermore, regulatory authorities, including the FDA, may have varying interpretations of our preclinical study and clinical trial data, which could delay, limit, or prevent regulatory approval or clearance. Any delays or difficulties in obtaining regulatory approvals or clearances for our product candidates may:

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adversely affect the marketing of any products we or our collaborators develop;

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impose significant additional costs on us or our collaborators;

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diminish any competitive advantages that we or our collaborators may attain;

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limit our ability to receive royalties and generate revenue and profits; and

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adversely affect our business prospects and ability to obtain financing.

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If we are delayed in these activities or do not receive regulatory approval for our product candidates in a timely manner, we will have to incur additional development expense, and subject to securing additional financing, we will not be able to commercialize them in the timeframe anticipated, and therefore our business will suffer.

We typically require separate regulatory approvals for each of our product candidates for each type of disease indication before we can market and sell them in the United States or internationally.

We and our collaborators generally cannot sell any drug or vaccine until we receive regulatory approval from governmental authorities in the United States and from similar agencies in other jurisdictions. Oncophage and any other drug candidate could take a significantly longer time to gain regulatory approval than we expect, or may never gain approval, or may gain approval for only limited indications.

Even if we do receive regulatory approval for our product candidates, the FDA or international regulatory authorities will generally impose limitations on the indicated uses for which our products may be marketed, or subsequently withdraw approval, or may take other actions against us or our products adverse to our business.

The FDA and international regulatory authorities generally approve products for particular indications. If an approval is for a limited indication, this limitation reduces the size of the potential market for that product. Product approvals, once granted, may be withdrawn if problems occur after initial marketing. Failure to comply with applicable FDA and other regulatory requirements can result in, among other things, warning letters, fines, injunctions, civil penalties, recall or seizure of products, total or partial suspension of production, refusal of the government to renew marketing applications, and/or criminal prosecution.

Challenges in identifying sufficient numbers of patients that meet our eligibility criteria, enrolling patients in our studies, or retaining patients in our studies after they have enrolled will slow or prevent completion of clinical trials.

We have encountered in the past, and may encounter in the future, delays in initiating trial sites and in enrolling patients into our clinical trials. Future enrollment delays will postpone the dates by which we expect to complete the impacted trials and the potential receipt of regulatory approvals. If we fail to enroll a sufficient number of patients in clinical trials, the trials may fail to demonstrate the efficacy of a product candidate at a statistically significant level.

While such trials may help support our efforts to obtain marketing approval, they generally would not, by themselves, be sufficient for obtaining approval. In our cancer trials, enrollment difficulties may arise due to many factors, including the novel nature of our product candidates such as Oncophage, the identification of patients meeting the specific criteria for inclusion in our trials, the speed by which participating clinical trial sites review our protocol and allow enrollment, and any delay in contract negotiations between us and the participating clinical trial sites. In addition, we may encounter problems in our clinical trials due to increased pharmaceutical industry demand for clinical trial patients, as well as limited patient availability due to the advanced disease state of the target patient population. Even if our patient enrollment is adequate, patients may die during a clinical trial if their disease is too advanced or because they experience problems that may be unrelated to the product candidate. A high dropout rate in a trial may undermine the ability to gain statistically significant data from the study.

If new data from our research and development activities continues to modify our strategy, then we expect to continually adjust our projections of timelines and costs of programs; this uncertainty may depress the market price of our stock and increase our expenses.

Because we are focused on novel technologies, our research and development activities, including our preclinical studies and clinical trials, involve the ongoing discovery of new facts and the generation of new data, based on which we determine next steps for a relevant program. These developments are sometimes a daily occurrence and constitute the basis on which our business is conducted. We need to make determinations on an ongoing basis as to which of these facts or data will influence timelines and costs of programs. We may not always be able to make such judgments accurately, which may increase the costs we incur attempting to commercialize our product candidates. These issues are pronounced in our efforts to commercialize Oncophage, which represents an unprecedented approach to the treatment of cancer.

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We may need to successfully address a number of technological challenges in order to complete development of our product candidates. Moreover, these product candidates may not be effective in treating any disease or may prove to have undesirable or unintended side effects, toxicities or other characteristics that may preclude our obtaining regulatory approval or prevent or limit commercial use.

Failure to enter into significant collaboration agreements may hinder our efforts to develop and commercialize our product candidates and will increase our need to rely on other financing mechanisms, such as sales of securities to fund our operations.

We have been engaged in efforts to enter into collaborative agreements with a pharmaceutical or larger biotechnology company to assist us with development and/or commercialization of our product candidates.

While we have been pursuing these business development efforts for several years, we have not negotiated a definitive agreement relating to the potential commercialization of Oncophage. Following the announcement in March 2006 that part I of our Phase 3 trial in renal cell carcinoma did not achieve its primary endpoint, many larger companies may be unwilling to commit to a substantial agreement prior to receipt of additional clinical data. In the absence of such data, potential collaborative partners may demand economic terms that are unfavorable to us. Even if Oncophage generates favorable clinical data over the next several years, we may not be able to negotiate a transaction that provides us with favorable economic terms.

We plan on pursuing business development efforts to partner each of Aroplatin and AG-707. These products are at an early stage, and collaborative partners or licensees may defer discussions until results from early clinical trials become available.

While some other biotechnology companies have negotiated large collaborations, we may not be able to negotiate any agreements with terms that replicate the terms negotiated by those other companies. We may not, for example, obtain significant up-front payments or substantial royalty rates. Some larger companies are skeptical of the commercial potential and profitability of a patient-specific product candidate like Oncophage or early-stage products like Aroplatin and AG-707. If we fail to enter into such collaboration agreements, our efforts to develop and/or commercialize Oncophage, Aroplatin, or AG-707 may be undermined. In addition, if we do not raise funds through collaboration agreements, we will need to rely on other financing mechanisms, such as sales of securities to fund our operations. Sales of certain securities may substantially dilute the ownership of existing stockholders.

We may not receive significant royalty, milestone, or manufacturing revenue payments from collaborators or licensees due to unsuccessful results in existing collaborations and licenses, failure to enter into future collaborations or license agreements, or our inability to manufacture product supply requirements for our collaborators and licensees.

Part of our strategy is to develop and commercialize some of our product candidates by continuing our existing arrangements with academic and corporate collaborators and licensees and by entering into new collaborations. Our success depends on our ability to negotiate such agreements and on the success of the other parties in performing research and preclinical and clinical testing. Our collaborations involving QS-21, for example, depend on our collaborative partners or licensees successfully completing clinical trials, our entering into a successful contract manufacturing relationship to meet collaborative partner or licensee demand, and our collaborative partners or licensees obtaining regulatory approvals.

These development activities frequently fail to produce marketable products. For example, in August 2006, Pharmexa A/S announced a decision to cease dosing patients in their Phase 2 clinical trial of their HER-2 Protein AutoVac™ breast cancer vaccine containing our QS-21 adjuvant, after it was determined that the trial was unlikely to meet its primary endpoint. Several of our agreements also require us to transfer important rights and regulatory compliance responsibilities to our collaborators and licensees. As a result of collaborative agreements, we will not control the nature, timing, or cost of bringing these product candidates to market. Our collaborators and licensees could choose not to devote resources to these arrangements or, under certain circumstances, may terminate these arrangements early. They may cease pursuing the programs or elect to collaborate with different companies. In addition, these collaborators and licensees, outside of their arrangements with us, may develop technologies or products that are competitive with those that we are developing. From time to time we may also become involved in disputes with our collaborators. Such disputes could result in the incurrence of significant expense. As a result of

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these factors, our strategic collaborations may not yield revenue. Furthermore, we may be unable to enter into new collaborations or enter into new collaborations on favorable terms. Failure to generate significant revenue from collaborations would increase our need to fund our operations through sales of securities and could limit financial resources available for investment in manufacturing capacity expansion.

If we are unable to purify heat shock proteins from some cancer types, we may have difficulty successfully initiating clinical trials in new indications or completing our clinical trials, and even if we do successfully complete our clinical trials, the size of our potential market could decrease.

Our ability to successfully develop and commercialize Oncophage for a particular cancer type depends on our ability to purify heat shock proteins from that type of cancer. If we experience difficulties in purifying heat shock proteins for a sufficiently large number of patients in our clinical trials, it may lower the probability of a successful analysis of the data from these trials and, ultimately, the ability to obtain FDA approval. Our overall manufacturing success rate for part I of our Phase 3 trial in renal cell carcinoma was 92%; for our Phase 3 trial in metastatic melanoma, it was 70%. Our inability to manufacture adequate amounts of Oncophage for approximately 30% of the patients randomized in the Oncophage treatment arm of the metastatic melanoma trial undermined the potential for the trial to meet its pre-specified clinical endpoints. To address this lower success rate for melanoma, we instituted an inhibitor process to avoid the breakdown of proteins. Subsequent to the implementation of this change, we successfully produced Oncophage for 18 of 23 patients, a success rate of approximately 78%, whereas previously we had produced Oncophage for 123 of 179 patients, a success rate of approximately 69%. The small sample size used subsequent to our process change may make the reported improvement in our manufacturing success unreliable as a predictor of future success.

We have successfully manufactured product for 100%, 10 of 10, of the patients randomized to treatment in our Phase 2 lung cancer trial and 95%, 21 of 22, of the patients randomized to treatment in our Phase 2 metastatic renal cell carcinoma trial. Based on our clinical trials to date, we have been able to manufacture Oncophage from 87% of the tumors delivered to our manufacturing facility; for non-metastatic renal cell carcinoma, 92%; for melanoma, 70%; for colorectal cancer, 98%; for gastric cancer, 81%; for lymphoma, 89%; and for pancreatic cancer, 46%. The relatively low rate for pancreatic cancer is due to the abundance of proteases in pancreatic tissue. Proteases are enzymes that break down proteins. These proteases may degrade the heat shock proteins during the purification process. We have made process development advances that have improved the manufacture of Oncophage from pancreatic tissue. In an expanded Phase 1 pancreatic cancer study, Oncophage was manufactured from five of five tumor samples (100%), bringing the aggregate success rate for this cancer type, which was previously 30%, to 46%.

We may encounter problems with other types of cancer as we expand our research. If we cannot overcome these problems, the number of cancer types that our heat shock protein product candidates could treat would be limited. In addition, if we commercialize our heat shock protein product candidates, we may face claims from patients for whom we are unable to produce a vaccine.

Manufacturing problems may cause product launch delays and unanticipated costs.

If one of our product candidates or our licensees’ product candidates for which we maintain exclusive or primary manufacturing rights nears marketing approval or is approved for sale, we expect we would be required to manufacture substantially more than we have been required to manufacture for preclinical studies and clinical trials. We have no experience manufacturing products in commercial quantities, and we can provide no assurance that we will be able to do so successfully. We may experience higher manufacturing failure rates than we have in the past if and when we attempt to substantially increase production volume.

Currently, we manufacture Oncophage and AG-707 in our own manufacturing facility. Because Oncophage is a patient-specific biologic, it requires product characterization steps that are more onerous than those required for most chemical pharmaceuticals. Accordingly, we employ multiple steps to attempt to control the manufacturing processes. Minor deviations in these manufacturing processes could result in unacceptable changes in the vaccine and result in production failures. AG-707 is also a complex product requiring Good Manufacturing Practices (“GMP”) for the manufacture and release of a recombinant protein and a large number of peptides. In order to prepare additional AG-707 to support future clinical trials, Antigenics will have to manufacture or have manufactured both of these critical raw materials.

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We have the right to elect to manufacture QS-21 and Aroplatin in our own manufacturing facility as well. If we choose to do so, the investment of substantial funds and the recruitment of qualified personnel would be required in order to build or lease and operate new manufacturing facilities. In order to continue to support QS-21 programs and Aroplatin development, apply for regulatory approvals, and commercialize these product candidates, we or our licensees or collaborators will need to develop, contract for, or otherwise arrange for the necessary manufacturing capabilities. We currently rely and expect to continue to rely upon third parties, potentially including our collaborators, to produce materials required for preclinical studies and clinical trials and for these product candidates. A number of factors could cause production interruptions at our manufacturing facility or our contract manufacturers, including equipment malfunctions, labor or employment retention problems, natural disasters, power outages, terrorist activities, or disruptions in the operations of our suppliers. Alternatively, there is the possibility we may have excess manufacturing capacity if programs do not progress as planned.

There are a limited number of contract manufacturers that operate under the FDA’s GMP regulations that are capable of manufacturing our product candidates. If we are unable to do so ourselves or arrange for third-party manufacturing of these product candidates, or to do so on commercially reasonable terms, we may not be able to complete development of these product candidates or commercialize them ourselves or through our collaborative partners or licensees. Reliance on third-party manufacturers entails risks to which we would not be subject if we manufactured products ourselves, including reliance on the third party for regulatory compliance, the possibility of breach of the manufacturing agreement by the third party because of factors beyond our control and the possibility of termination or non-renewal of the agreement by the third party, based on its own business priorities, at a time that is costly or inconvenient for us.

Manufacturing is also subject to extensive government regulation. Regulatory authorities must approve the facilities in which human healthcare products are produced. In addition, facilities are subject to ongoing inspections and minor changes in manufacturing processes may require additional regulatory approvals, either of which could cause us to incur significant additional costs and lose revenue.

If we fail to sustain and further build our intellectual property rights, competitors will be able to take advantage of our research and development efforts to develop competing products.

If we are not able to protect our proprietary technology, trade secrets, and know-how, our competitors may use our inventions to develop competing products. We currently have exclusive rights to 78 issued U.S. patents and 114 foreign patents. We also have rights to 27 pending U.S. patent applications and 118 pending foreign patent applications. However, we may not have patent coverage in all territories where we may pursue regulatory approval. In addition, our patents may not protect us against our competitors. Our patent positions, and those of other pharmaceutical and biotechnology companies, are generally uncertain and involve complex legal, scientific, and factual questions. The standards which the United States Patent and Trademark Office uses to grant patents, and the standards which courts use to interpret patents, are not always applied predictably or uniformly and can change, particularly as new technologies develop. Consequently, the level of protection, if any, that will be provided by our patents if we attempt to enforce them, and they are challenged, is uncertain. In addition, the type and extent of patent claims that will be issued to us in the future is uncertain. Any patents that are issued may not contain claims that permit us to stop competitors from using similar technology.

In addition to our patented technology, we also rely on unpatented technology, trade secrets, and confidential information. We may not be able to effectively protect our rights to this technology or information. Other parties may independently develop substantially equivalent information and techniques or otherwise gain access to or disclose our technology. We generally require each of our employees, consultants, collaborators, and certain contractors to execute a confidentiality agreement at the commencement of an employment, consulting, collaborative, or contractual relationship with us. However, these agreements may not provide effective protection of our technology or information, or in the event of unauthorized use or disclosure, they may not provide adequate remedies.

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We may incur substantial costs as a result of litigation or other proceedings relating to patent and other intellectual property rights, and we may be unable to protect our rights to, or use, our technology.

If we choose to go to court to stop someone else from using the inventions claimed in our patents, that individual or company has the right to ask a court to rule that our patents are invalid and should not be enforced against that third party. These lawsuits are expensive and would consume time and other resources even if we were successful in stopping the infringement of our patents. In addition, there is a risk that the court will decide that our patents are not valid and that we do not have the right to stop the other party from using the inventions. There is also the risk that, even if the validity of our patents is upheld, the court will refuse to stop the other party on the grounds that such other party’s activities do not infringe our patents.

We may not have rights under some patents or patent applications related to some of our existing and proposed products or processes. Third parties may own or control these patents and patent applications in the United States and abroad. Therefore, in some cases, such as those described below, in order to develop, use, manufacture, sell, or import some of our existing or proposed products, or develop or use some of our existing or proposed processes, we or our collaborators may choose to seek, or be required to seek, licenses under third-party patents issued in the United States and abroad, or those that might issue from United States and foreign patent applications. In such an event, we likely would be required to pay license fees or royalties or both to the licensor. If licenses are not available to us on acceptable terms, we or our collaborators may not be able to exploit these products or processes.

Furthermore, a third party may claim that we are using inventions covered by such third party’s patents or other intellectual property rights and may go to court to stop us from engaging in our normal operations and activities. These lawsuits are expensive and would consume time and other resources. There is a risk that a court would decide that we are infringing the third party’s patents and would order us to stop the activities covered by the patents. In addition, there is a risk that a court will order us to pay the other party substantial damages for having violated the other party’s patents. The biotechnology industry has produced a proliferation of patents, and it is not always clear to industry participants, including us, which patents cover various types of products. The coverage of patents is subject to interpretation by the courts, and the interpretation is not always uniform. We know of patents issued to third parties relating to heat shock proteins and alleviation of symptoms of cancer. We have reviewed these patents, and we believe, as to each claim in those patents, that we either do not infringe the claim, or that the claim is invalid. Moreover, patent holders sometimes send communications to a number of companies in related fields suggesting possible infringement, and we, like a number of biotechnology companies, have received this type of communication, including with respect to the third-party patents mentioned above, as well as a communication alleging infringement of a patent relating to certain gel-fiberglass structures. If we are sued for patent infringement, we would need to demonstrate that our products either do not infringe the patent claims of the relevant patent and/or that the patent claims are invalid, which we may not be able to do. Proving invalidity, in particular, is difficult, since it requires a showing of clear and convincing evidence to overcome the presumption of validity enjoyed by issued patents. Additionally, two of the patent applications licensed to us contain claims that are substantially the same as claims in a third-party patent relating to heat shock proteins. At our request, the United States Patent and Trademark Office declared an interference with this third-party patent, U.S. Patent No. 6,713,608 which we believe is owned by the Science & Technology Corporation @ UNM (University of New Mexico). The patentee failed to participate in the interference proceedings and the United States Patent and Trademark Office cancelled all of the claims of U.S. Patent No. 6,713,608. The patentee has the options of requesting reconsideration of this decision by the United States Patent and Trademark Office and filing a civil action requesting reversal of that decision. Although we believe that we should prevail against this third-party patent in either circumstance, there is no guarantee that that will be the outcome.

On October 12, 2005, a third party filed a notice of opposition in the European Patent Office to European patent EP 0750513 B1 which has claims relating to AG-702/707 and to which we hold the exclusive license. We have filed a response to this opposition. The opposition division of the European Patent Office has subsequently issued a summons to oral proceedings to be held on January 24, 2008, and has issued a preliminary nonbinding opinion that at least claim 1 of the patent is invalid. We believe this patent claims valid subject matter. However, there is no guarantee that we will continue to defend the opposition, that this patent will not be revoked, or that we may not have to amend the claims.

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We may become involved in expensive patent litigation or other proceedings, which could result in our incurring substantial costs and expenses or substantial liability for damages, or require us to stop our development and commercialization efforts.

There has been substantial litigation and other proceedings regarding patent and other intellectual property rights in the pharmaceutical and biotechnology industries. We may become a party to patent litigation or other proceedings regarding intellectual property rights. Interference proceedings before the United States Patent and Trademark Office may be necessary to establish which party was the first to invent a particular invention.

The cost to us of any patent litigation or other proceeding, even if resolved in our favor, could be substantial. Some of our competitors may be able to sustain the cost of such litigation or proceedings more effectively than we can because of their substantially greater financial resources. If a patent litigation or other proceeding is resolved against us, we or our collaborators may be enjoined from using, manufacturing, selling, or importing our products or processes without a license from the other party, and we may be held liable for significant damages. We may not be able to obtain any required licenses on commercially acceptable terms or at all.

Uncertainties resulting from the initiation and continuation of patent litigation or other proceedings could have a material adverse effect on our ability to enter into collaborations with other entities, obtain financing, or compete in the marketplace. Patent litigation and other proceedings may also absorb significant management time.

Our patent protection for any compound or product that we seek to develop may be limited to a particular method of use or indication such that, if a third party were to obtain approval of the compound or product for use in another indication, we could be subject to competition arising from off-label use.

Although we generally seek the broadest patent protection available for our proprietary compounds, we may not be able to obtain patent protection for the actual composition of matter of any particular compound and may be limited to protecting a new method of use for the compound or otherwise restricted in our ability to prevent others from exploiting the compound. If we are unable to obtain patent protection for the actual composition of matter of any compound that we seek to develop and commercialize and must rely on method of use patent coverage, we would likely be unable to prevent others from manufacturing or marketing that compound for any use that is not protected by our patent rights. If a third party were to receive marketing approval for the compound for another use, physicians might nevertheless prescribe it for indications that are not described in the product’s labeling or approved by the FDA or other regulatory authorities. Even if we have patent protection of the prescribed indication, as a practical matter, we likely would have little recourse as a result of this off-label use. In that event, our revenues from the commercialization of the compound would likely be adversely affected.

If we fail to comply with our obligations in our intellectual property licenses with third parties, we could lose license rights that are important to our business.

We are a party to various license agreements under which we receive the right to practice and use important third-party patent rights. We may enter into additional licenses in the future. Our existing licenses impose, and we expect future licenses will impose, various diligence, milestone payment, royalty, insurance, and other obligations on us. If we fail to comply with these obligations, the licensor may have the right to terminate the license, in which event we might not be able to market any product that is covered by the licensed patents.

If we fail to retain the services of key individuals and our employees, we may be unable to successfully develop our product candidates, conduct clinical trials, and obtain financing.

Garo H. Armen, Ph.D., the Chairman of our Board of Directors and our Chief Executive Officer, and Pramod K. Srivastava, Ph.D., a former member of our Board of Directors and a consultant to us, who together founded Antigenics in 1994, have been integral to building the company and developing our technology. If either of these individuals severs their relationship with the company, our business may be adversely impacted.

Effective December 1, 2005, the company entered into an employment agreement (the “Agreement”) with Dr. Armen. Subject to the earlier termination as provided in the Agreement, the Agreement shall have an original term of one year and shall be automatically extended thereafter for successive terms of one year each, unless either party provides notice to the other at least ninety days prior to the expiration of the original or any extension term. Dr. Armen plays an important role in the day to day activities of the Company. We do not carry key employee insurance policies for Dr. Armen or any other employee.

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Dr. Srivastava currently has a consulting agreement with Antigenics pursuant to which he provides advice and services to the Company from time to time. This agreement has an initial term ending March 31, 2010. Although this agreement includes financial incentives for Dr. Srivastava to remain associated with us, the parties have recently been in discussions regarding a potential early termination of the agreement. Even if the parties do not terminate the agreement prior to March 31, 2010, it is likely that the parties will not continue the agreement beyond that time.

We also rely greatly on employing and retaining other highly trained and experienced senior management and scientific and operations personnel. The competition for these and other qualified personnel in the biotechnology field is intense. In order to reduce our expenses, we have restructured the company and reduced staffing levels. This has in many cases eliminated any redundancy in skills and capabilities in key areas. If we are not able to attract and retain qualified personnel, we may not be able to achieve our strategic and operational objectives.

We may face litigation that could result in substantial damages and may divert management’s time and attention from our business.

Antigenics, our Chairman and Chief Executive Officer, Garo H. Armen, Ph.D., and two investment banking firms that served as underwriters in our initial public offering have been named as defendants in a federal civil class action lawsuit. The suit alleges that the brokerage arms of the investment banking firms charged secret excessive commissions to certain of their customers in return for allocations of our stock in the offering. The suit also alleges that shares of our stock were allocated to certain of the investment banking firms’ customers based upon agreements by such customers to purchase additional shares of our stock in the secondary market. We submitted settlement papers with the Federal District Court for the Southern District of New York, which the court preliminarily approved in August 2005. The settlement remained subject to a number of conditions, including final court approval. In December 2006, the appellate court overturned the certification of classes in the six test cases that were selected by the underwriter defendants and plaintiffs in the coordinated proceedings. Class certification was one of the conditions of the settlement. Accordingly, on June 25, 2007, the court entered an order terminating the proposed settlement based on a stipulation among the parties to the settlement. It is uncertain whether there will be any revised or future settlement. To date, the plaintiffs have not asserted a specific amount of damages and, at this time, we cannot make a reliable estimate of possible loss, if any, related to this litigation. Regardless of the outcome, participation in this lawsuit diverts our management’s time and attention from our business and may result in our paying damages.

Antigenics and our Chairman and Chief Executive Officer were named as defendants in a purported shareholder class action complaint filed on June 16, 2006 in Federal District Court in New Mexico by Steven J. Tuckfelt on behalf of himself and all others similarly situated (the “Plaintiffs”). The complaint alleged that certain of our disclosures in connection with the conduct of the Oncophage Phase 3 renal cell carcinoma trial violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended (the “Securities Exchange Act”). The complaint also included purported claims for breach of fiduciary duty. On March 14, 2007, the court dismissed the action without prejudice due to the Plaintiffs’ failure to prosecute the action. However, there is the possibility the case could be re-filed.

In addition, we are involved in other litigation and may become involved in additional litigation. Any such litigation could be expensive in terms of out-of-pocket costs and management time, and the outcome of any such litigation is uncertain.

Our Directors and Officers insurance policies provide $25.0 million annual aggregate coverage and $25.0 million per occurrence coverage. This limited insurance coverage may not be sufficient to cover us for future claims.

If we fail to obtain adequate levels of reimbursement for our product candidates, the commercial potential of our product candidates will be significantly limited.

In many of the markets where we or our collaborative partners would commercialize a product following regulatory approval, the prices of pharmaceutical products are subject to direct price controls by law and to drug reimbursement programs with varying price control mechanisms. Public and private health care payers control costs and influence drug pricing through a variety of mechanisms, including through negotiating discounts with the manufacturers and through the use of tiered formularies and other mechanisms that provide preferential access to certain drugs over others within a therapeutic class. Payers also set other criteria to govern the uses of a drug that

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will be deemed medically appropriate and therefore reimbursed or otherwise covered. In particular, in the U.S., many public and private health care payers limit reimbursement and coverage to the uses of a drug that are either approved by the FDA or that are supported by other appropriate evidence, such as published medical literature, and appear in a recognized drug compendium.

In the U.S. and elsewhere, sales of therapeutic and other pharmaceutical products are dependent in part on the availability of reimbursement to the physician or consumer from third-party payers, such as the government or private insurance plans. Our profitability will depend on the extent to which government authorities, private health insurance providers, and other organizations provide reimbursement for the cost of our product candidates. Government and private third-party payers are increasingly challenging the prices charged for medical products and services, through class action litigation and otherwise, and increasingly attempt to limit and/or regulate the reimbursement for medical products, including branded prescription drugs. Many patients will not be capable of paying for our product candidates by themselves. A primary trend in the United States health care industry is toward cost containment. Large private payers, managed care organizations, group purchasing organizations, and similar organizations are exerting increasing influence on decisions regarding the use of particular treatments. Furthermore, many third-party payers limit reimbursement for newly approved health care products. Cost containment measures may prevent us from becoming profitable.

It is not clear that public and private insurance programs will determine that Oncophage or our other product candidates come within a category of items and services covered by their insurance plans. The application of existing Medicare regulations, and interpretive coverage and payment determinations to newly approved products, especially novel products such as Oncophage, is uncertain, and those regulations and interpretive determinations are subject to change. For example, although the federal Medicare program covers drugs and biological products, the Medicare program takes the position that the FDA’s treatment of a product as a drug or biologic does not require the Medicare program to treat the product in the same manner. Accordingly, it is possible that the Medicare program will not cover Oncophage or our other product candidates if they are approved for commercialization. It is also possible that there will be substantial delays in obtaining coverage of Oncophage or our other product candidates and that, if coverage is obtained, there may be significant restrictions on the circumstances in which there would be reimbursement. Where insurance coverage is available, there may be limits on the payment amount. Congress and the Medicare program periodically propose significant reductions in the Medicare reimbursement amounts for drugs and biologics. Such reductions could have a material adverse effect on sales of any of our product candidates that receive marketing approval. In December 2003, the President of the United States signed the Medicare Prescription Drug, Improvement, and Modernization Act of 2003, which provides for a change in reimbursement methodology that reduces the Medicare reimbursement rates for many drugs, including oncology therapeutics, which may adversely affect reimbursement for Oncophage if it is approved for sale, or our other product candidates. If we are unable to obtain or retain adequate levels of reimbursement from Medicare or from private health plans, our ability to sell Oncophage and our other potential products will be adversely affected The future impact of this legislation on our product candidates is uncertain. Effective January 1, 2004, Medicare payments for many drugs administered in physicians’ offices were reduced significantly. This provision impacts many drugs used in cancer treatment by oncologists and urologists. The payment methodology changes in future years, and it is unclear how the payment methodology will impact reimbursement for Oncophage, if it receives regulatory approval, and incentives for physicians to recommend Oncophage relative to alternative therapies.

Federal, state, and foreign governments continue to propose legislation designed to contain or reduce health care costs. Legislation and regulations affecting the pricing of our potential products may change further or be adopted before Oncophage or any of our potential products are approved for marketing. Cost control initiatives by governments or third-party payers could decrease the price that we receive for any one or all of our potential products or increase patient coinsurance to a level that makes Oncophage and our other products under development unaffordable. In addition, government and private health plans persistently challenge the price and cost-effectiveness of therapeutic products. Accordingly, these third parties may ultimately not consider Oncophage or any or all of our products under development to be cost-effective, which could result in products not being covered under their health plans or covered only at a lower price. Any of these initiatives or developments could prevent us from successfully marketing and selling any of our potential products. We are unable to predict what impact any future regulation or third-party payer initiatives relating to reimbursement for Oncophage or any of our other potential products will have on sales, if any of them are approved for sale.

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Our sales, marketing, and commercial operations experience is limited and needs to be developed or acquired.

We have very limited experience in marketing and selling pharmaceutical products or in running commercial operations. In addition, for our patient-specific heat shock protein product candidates, we will need to develop specialized commercial operations to manage patient-specific ordering, tracking, and control. There are few companies that have developed this expertise. We must either develop commercial operations and marketing capabilities and a sales force or enter into arrangements with third parties to perform such operations and/or market and sell any of our product candidates that are approved by regulatory authorities. We do not know whether we will be able to enter into commercial operations or marketing and sales agreements with others on acceptable terms, if at all. We may not be able to successfully develop our own commercial operations capabilities or sales and marketing force for drug candidates for which we have retained or elect to retain marketing or co-promotion rights. As we develop our own commercial operations or marketing and sales capability, we may be competing with other companies that currently have experienced and well funded operations. Where we have licensed our products to third-party collaborators or licensees, we will be dependent on their commercial operations, sales and marketing expertise and resources, and any revenues we receive from those products will depend primarily on the sales and marketing efforts of others.

Product liability and other claims against us may reduce demand for our products and/or result in substantial damages.

We face an inherent risk of product liability exposure related to testing our product candidates in human clinical trials and will face even greater risks if we sell our product candidates commercially. An individual may bring a product liability claim against us if one of our product candidates causes, or merely appears to have caused, an injury. Product liability claims may result in:

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decreased demand for our product candidates;

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injury to our reputation;

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withdrawal of clinical trial volunteers;

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costs of related litigation; and

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substantial monetary awards to plaintiffs.

We manufacture Oncophage from a patient’s cancer cells, and a medical professional must inject Oncophage into the patient from which it was manufactured. A patient may sue us if we, a hospital, or a shipping company fails to deliver the removed cancer tissue or that patient’s Oncophage. We anticipate that the logistics of shipping will become more complex if the number of patients we treat increases, and it is possible that all shipments will not be made without incident. In addition, administration of Oncophage at a hospital poses risk of delivery to the wrong patient. Currently, we do not have insurance that covers loss of or damage to Oncophage, and we do not know whether insurance will be available to us at a reasonable price or at all. We have limited product liability coverage for clinical research use of product candidates. Our product liability policy provides $10.0 million aggregate coverage and $10.0 million per occurrence coverage. This limited insurance coverage may be insufficient to fully cover us for future claims.

If we do not comply with environmental laws and regulations, we may incur significant costs and potential disruption to our business.

We use hazardous, infectious, and radioactive materials, and recombinant DNA in our operations, which have the potential of being harmful to human health and safety or the environment. We store these hazardous (flammable, corrosive, toxic), infectious, and radioactive materials, and various wastes resulting from their use, at our facilities pending use and ultimate disposal. We are subject to a variety of federal, state, and local laws and regulations governing use, generation, storage, handling, and disposal of these materials. We may incur significant costs complying with both current and future environmental health and safety laws and regulations. In particular, we are subject to regulation by the Occupational Safety and Health Administration, the Environmental Protection Agency, the Drug Enforcement Agency, the Department of Transportation, the Centers for Disease Control and Prevention, the National Institutes of Health, the International Air Transportation Association, and various state and local agencies. At any time, one or more of the aforementioned agencies could adopt regulations that may affect our operations. We are also subject to regulation under the Toxic Substances Control Act and the Resource Conservation Development programs.

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Although we believe that our current procedures and programs for handling, storage, and disposal of these materials comply with federal, state, and local laws and regulations, we cannot eliminate the risk of accidents involving contamination from these materials. Although we have limited pollution liability coverage ($2 million) and a workers’ compensation liability policy, in the event of an accident or accidental release, we could be held liable for resulting damages, which could be substantially in excess of any available insurance coverage and could substantially disrupt our business.

Our competitors in the biotechnology and pharmaceutical industries may have superior products, manufacturing capability, and/or marketing expertise.

Our business may fail because we face intense competition from major pharmaceutical companies and specialized biotechnology companies engaged in the development of product candidates directed at cancer and infectious diseases. Several of these companies have products that utilize similar technologies and/or patient-specific medicine techniques, such as Dendreon’s Sipuleucel-T, for which Dendreon announced in March 2007 that the FDA’s Office of Cellular, Tissue and Gene Therapies Advisory Committee recommended to the FDA that there is substantial evidence of efficacy and safety of Provenge for the treatment of patients with prostate cancer (on May 8, 2007, the FDA issued a Complete Response Letter requesting additional data from Dendreon), Dendreon’s Lapuleucel-T in Phase 1 trials for ovarian, colorectal, and breast cancer, Northwest Biotherapeutics’ DCVax-Brain in a Phase 2 trial for brain cancer, Nventa’s (formerly Stressgen) HspE7, which is currently in or has completed Phase 2 trials in HPV-related diseases, such as internal genital warts, recurrent respiratory papillomatosis, and cervical dysplasia, AVAX’s AC Vaccine therapeutic platform vaccines in clinical trials for melanoma and non-small cell lung cancer and approved for sale in Switzerland for melanoma, Intracel’s OncoVax, currently approved for administration in the Netherlands, Switzerland, and Israel and in a Phase 3 trial in the U.S. for colon cancer, Liponova’s Reniale, which completed a Phase 3 trial in Germany for non-metastatic renal cell carcinoma, Oxford BioMedica and its partner Sanofi-Aventis’ Trovax, which is in a Phase 3 trial for metastatic renal cell carcinoma, Vical’s Allovectin-7 with a special protocol assessment for a Phase 3 trial for metastatic melanoma, Favrille’s FavID currently in a Phase 3 trial for NHL, Accentia’s BiovaxID currently in a Phase 3 trial for NHL, Genitope’s MyVax currently in a Phase 3 trial for NHL, and Cell Genesys’ GVAX vaccines currently in trials for prostate cancer (Phase 3), AML (Phase 1), pancreatic cancer (Phase 2), lung cancer (Phase 2), and myeloma (Phase 1). Patents have been issued in both the U.S. and Europe related to Nventa’s heat shock protein technology.

More specifically, if we receive regulatory approvals, some of our product candidates will compete with FDA-approved therapies such as interleukin-2 and interferon-alpha for renal cell carcinoma and melanoma, which have generated substantial sales over a number of years. In addition, the FDA recently approved sorafenib and sunitinib for the treatment of patients with advanced renal cell carcinoma, or kidney cancer. Sorafenib and sunitinib are also being developed for non-metastatic renal cell carcinoma. Other companies’ product candidates, including Wilex AG’s Rencarex (WX-G250), are also being developed for non-metastatic renal cell carcinoma, including in Phase 3 clinical trials. Our product candidates, such as Aroplatin, may compete with existing approved chemotherapies or other chemotherapies that are in development. Several other platinum therapies are in development for a variety of diseases. The most advanced candidate is GPC Biotech’s satraplatin for second-line hormone-refractory prostate cancer, for which the FDA has accepted for filing the new drug application based on the completed Phase 3 trial and granted the application priority review. Additionally, Poniard Pharmaceuticals’ picoplatin is in Phase 2 clinical trials. In addition, prior to regulatory approval, we may compete for access to patients with other products in clinical development, with products approved for use in the indications we are studying, or with off-label use of products in the indications we are studying. We anticipate that we will face increased competition in the future as new companies enter markets we seek to address and scientific developments surrounding immunotherapy and other traditional cancer therapies continue to accelerate.

Several other vaccine adjuvants are in development and could compete with QS-21 for inclusion in vaccines in development. These adjuvants include, but are not limited to, oligonucleotides, under development by Coley, Idera, Juvaris, and Dynavax, anti-CTLA-4 antibody, under development by Medarex, MF59 and SAF, under development by Novartis, and MPL, under development by GlaxoSmithKline. In addition, several companies, such as CSL Limited and Galenica, are developing saponin adjuvants, including synthetic formulations.

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Additionally, many of our competitors, including large pharmaceutical companies, have greater financial and human resources and more experience than we do. Our competitors may:

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commercialize their product candidates sooner than we commercialize our own;

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develop safer or more effective therapeutic drugs or preventive vaccines and other therapeutic products;

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implement more effective approaches to sales and marketing and capture some of our potential market share;

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establish superior intellectual property positions;

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discover technologies that may result in medical insights or breakthroughs, which render our drugs or vaccines obsolete, possibly before they generate any revenue; or

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adversely affect our ability to recruit patients for our clinical trials.

Risks Related to our Common Stock

Our officers and directors may be able to block proposals for a change in control.

Antigenics Holdings L.L.C. is a holding company that owns shares of our common stock, and as of June 30, 2007, Antigenics Holdings L.L.C. controlled approximately 24% of our outstanding common stock. Due to this concentration of ownership, Antigenics Holdings L.L.C. may be able to prevail on all matters requiring a stockholder vote, including:

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the election of directors;

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the amendment of our organizational documents; or

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the approval of a merger, sale of assets, or other major corporate transaction.

Certain of our directors and officers, including our Chief Executive Officer, directly and indirectly own approximately 48% of Antigenics Holdings L.L.C. In addition, several of our directors and officers directly and indirectly own approximately 1% of our outstanding common stock.

A single, otherwise unaffiliated, stockholder holds a substantial percentage of our outstanding common stock and all of our outstanding preferred stock, and another single, unaffiliated holder of our 2006 Notes issued in October 2006 has the right to convert such notes into a substantial percentage of our outstanding capital stock.

According to publicly filed documents, Mr. Brad M. Kelley beneficially owns 5,546,240 shares of our outstanding common stock and 31,620 shares of our series A convertible preferred stock. The shares of preferred stock are currently convertible at any time into 2,000,000 shares of common stock at an initial conversion price of $15.81, are non-voting, and carry a 2.5% annual dividend yield. If Mr. Kelley had converted all of the shares of preferred stock on June 30, 2007, he would have held approximately 16% of our outstanding common stock. We currently have a right of first refusal agreement with Mr. Kelley that provides us with limited rights to purchase certain of Mr. Kelley’s shares if he proposes to sell them to a third party.

Mr. Kelley’s substantial ownership position provides him with the ability to substantially influence the outcome of matters submitted to our stockholders for approval. Furthermore, collectively, Mr. Kelley and Antigenics Holdings L.L.C. control approximately 36% of our outstanding common stock as of June 30, 2007, providing substantial ability, if they vote in the same manner, to determine the outcome of matters submitted to a stockholder vote. If Mr. Kelley were to convert all of his preferred stock into common stock, the combined percentage would increase to 39%. Additional purchases of our common stock by Mr. Kelley also would increase both his own percentage of outstanding voting rights and the percentage combined with Antigenics Holdings L.L.C. While Mr. Kelley’s shares of preferred stock do not carry voting rights, the shares of common stock issuable upon conversion carry the same voting rights as other shares of common stock.

S-16

On October 30, 2006, we sold $25.0 million of our 2006 Notes to a group of accredited investors. These 2006 Notes, together with any interest paid in the form of additional 2006 Notes, are convertible into our common stock at an initial fixed conversion price of $3.50 per share at the option of the investors. While the 2006 Notes do not carry any voting rights, the common stock issuable upon conversion of the 2006 Notes do carry the same voting rights as other shares of common stock. On June 30, 2007, one holder of the 2006 Notes had holdings, which if totally converted into shares of our common stock, would result in this holder owning 6,022,095 shares. If such holder had exercised such conversion right on June 30, 2007, such holder would have owned approximately 12% of our outstanding common stock. However, the holder is limited to a 9.99% maximum percentage of ownership, in accordance with the terms of the 2006 Notes. Such ownership position following any such conversion along with any open market purchases by such holder could provide the holder with the ability to substantially influence the outcome of matters submitted to our stockholders for approval.

Provisions in our organizational documents could prevent or frustrate attempts by stockholders to replace our current management.

Our certificate of incorporation and bylaws contain provisions that could make it more difficult for a third party to acquire us without consent of our Board of Directors. Our certificate of incorporation provides for a staggered board and removal of directors only for cause. Accordingly, stockholders may elect only a minority of our board at any annual meeting, which may have the effect of delaying or preventing changes in management. In addition, under our certificate of incorporation, our Board of Directors may issue additional shares of preferred stock and determine the terms of those shares of stock without any further action by our stockholders. Our issuance of additional preferred stock could make it more difficult for a third party to acquire a majority of our outstanding voting stock and thereby effect a change in the composition of our Board of Directors. Our certificate of incorporation also provides that our stockholders may not take action by written consent. Our bylaws require advance notice of stockholder proposals and director nominations and permit only our President or a majority of the Board of Directors to call a special stockholder meeting. These provisions may have the effect of preventing or hindering attempts by our stockholders to replace our current management. In addition, Delaware law prohibits a corporation from engaging in a business combination with any holder of 15% or more of its capital stock until the holder has held the stock for three years unless, among other possibilities, the Board of Directors approves the transaction. Our Board of Directors may use this provision to prevent changes in our management. Also, under applicable Delaware law, our Board of Directors may adopt additional anti-takeover measures in the future.

Our stock has generally had low trading volume, and its public trading price has been volatile.

Between our initial public offering on February 4, 2000 and June 30, 2007, and for the twelve months ended June 30, 2007, the closing price of our common stock has fluctuated between $1.54 and $52.63 per share and $1.54 and $4.43 per share, respectively, with an average daily trading volume for the twelve months ended June 30, 2007 of approximately 421,000 shares. The market may experience significant price and volume fluctuations that are often unrelated to the operating performance of individual companies. In addition to general market volatility, many factors may have a significant adverse effect on the market price of our stock, including:

•

continuing operating losses, which we expect over the next several years as we continue our clinical trials;

•

announcements of decisions made by public officials;

•

results of our preclinical studies and clinical trials;

•

announcements of technological innovations, new commercial products, or progress toward commercialization by our competitors or peers;

•

developments concerning proprietary rights, including patent and litigation matters;

•

publicity regarding actual or potential results with respect to product candidates under development by us or by our competitors;

•

regulatory developments; and

•

quarterly fluctuations in our financial results.

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The sale of a significant number of shares could cause the market price of our stock to decline.

The sale by us or the resale by stockholders of a significant number of shares of our common stock could cause the market price of our common stock to decline. As of June 30, 2007, we had approximately 45,889,000 shares of common stock outstanding. All of these shares are eligible for sale on the NASDAQ Global Market, although certain of the shares are subject to sales volume and other limitations. In addition, we have filed registration statements to permit the sale of 10,436,831 shares of common stock under our equity incentive plan and certain equity plans that we assumed in the acquisitions of Aquila Biopharmaceuticals, Inc. and Aronex Pharmaceuticals, Inc. We have also filed registration statements to permit the sale of 450,000 shares of common stock under our employee stock purchase plan and to permit the sale of 250,000 shares of common stock under our directors’ deferred compensation plan. The market price of our common stock may decrease based on the expectation of such sales.

As of June 30, 2007, options to purchase 5,792,259 shares of our common stock with a weighted average exercise price per share of $6.88 were outstanding. Many of these options are subject to vesting that generally occurs over a period of up to four years following the date of grant. As of June 30, 2007, we have 383,812 nonvested shares outstanding.

Because we are a relatively small public company, we have been disproportionately negatively impacted by the Sarbanes-Oxley Act of 2002 and related regulations, which have increased our costs and required additional management resources.

The Sarbanes-Oxley Act of 2002, which became law in July 2002, has required changes in some of our corporate governance, securities disclosure, and compliance practices. In response to the requirements of that Act, the Securities and Exchange Commission and the NASDAQ have promulgated new rules and listing standards covering a variety of subjects. Compliance with these new rules and listing standards significantly increased our legal, financial, and accounting costs, which we expect to increase as we expand our operations. In addition, the requirements have taxed a significant amount of management’s and the Board of Directors’ time and resources. Likewise, these developments have made it more difficult for us to attract and retain qualified members of our Board of Directors, particularly independent directors, or qualified executive officers. Because we are a relatively small public company, we have been disproportionately negatively impacted by these changes in securities laws and regulations, which have increased our costs and required additional management resources.

Our internal control over financial reporting (as defined in Rules 13a-15 of the Securities Exchange Act) is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of our financial statements for external purposes in accordance with generally accepted accounting principles. Because of its inherent limitations, internal control over financial reporting may not prevent or detect all deficiencies or weaknesses in our financial reporting. While our management has concluded in our Annual Report on Form 10-K for the year ended December 31, 2006 that there were no material weaknesses in our internal control over financial reporting as of December 31, 2006, our procedures are subject to the risk that our controls may become inadequate because of changes in conditions or as a result of a deterioration in compliance with such procedures. No assurance is given that our procedures and processes for detecting weaknesses in our internal control over financial reporting will be effective.

Risks Related to the Offering

There is no public market for the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock sold in this offering.

There is no established trading market for the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock being offered in this offering, and we do not expect a market to develop. In addition, we do not intend to apply for listing of the convertible preferred stock on any securities exchange. Without an active market, the liquidity of the convertible preferred stock will be limited.

S-18

Since we have broad discretion in how we use the proceeds from this offering, we may use the proceeds in ways in which you disagree.

We have not allocated specific amounts of the net proceeds from this offering for any specific purpose. Accordingly, our management will have significant flexibility in applying the net proceeds of this offering. You will be relying on the judgment of our management with regard to the use of these net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. It is possible that the net proceeds will be invested in a way that does not yield a favorable, or any, return for our Company. The failure of our management to use such funds effectively could have a material adverse effect on our business, financial condition, operating results and cash flow.

Purchasers of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock who convert their shares into common stock may incur immediate dilution.

If you convert your shares of Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock into shares of common stock, you may experience immediate and substantial dilution because the per share conversion price of your shares of convertible preferred stock may be higher than the net tangible book value per share of the outstanding common stock immediately after this offering. In addition, you may experience dilution if we issue additional shares of common stock that we are permitted or required to issue under options, warrants, our stock option plan or other employee or director compensations plans.

Holders of our Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock will have no rights as common stockholders until they acquire our common stock.

Until you acquire shares of our common stock upon conversion of the Class B Convertible Preferred Stock, you will have no rights with respect to our common stock, including rights to respond to tender offers and rights to receive any dividends or other distributions on our common stock, and will have only limited rights to vote, separately or with all or any series, class or group of stockholders, with respect to any matter on which holders of our common stock are entitled to vote. Upon conversion of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock, you will be entitled to exercise the rights of a common stockholder only as to matters for which the record date occurs after the conversion date.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the incorporated documents contain 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 may include statements about time lines for completing clinical trials, time lines for releasing data from clinical trials, time lines for initiating new clinical trials, our collaboration efforts, future licensing and acquisition activity, future product research and development activities, the expected effectiveness of our product candidates in treating diseases, applicability of our heat shock protein technology to multiple cancers, infectious diseases and autoimmune disorders, our competitive position, plans for regulatory filings, receipt of future regulatory approvals, our expected cash needs, plans for sales and marketing, implementation of corporate strategy, the use of proceeds from this offering 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 product candidates are both safe and more effective than current standards of care; that we may be unable to obtain the regulatory approvals 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 approvals necessary to commercialize our products because the FDA or other regulatory agencies are not satisfied with our product characterization, our trial protocols or the results of our trials; that we may fail to adequately protect our intellectual property or that we are determined to infringe on the intellectual property of others; that we are affected by changes in financial markets and geopolitical developments; that we are affected by the solvency of counter parties under subleases and general real estate risks; and the information set forth under the heading “Risk Factors” beginning on page S-1. Forward-looking statements, therefore, should be considered in light of all of the information included or referred to in this prospectus supplement and the accompanying prospectus, including the risk factors.

You are cautioned not to place significant reliance on these forward-looking statements, which speak only as of the date of this prospectus supplement, the accompanying prospectus or the dates of incorporated documents, as applicable. We undertake no obligation to update or revise these forward-looking statements.

S-20

USE OF PROCEEDS

We expect to receive net proceeds of approximately $4.7 million from the sale of the 1,623,377 shares of common stock, the 10,000 shares of the Series B1 Convertible Preferred Stock and the 5,250 shares of the Series B2 Convertible Preferred Stock, and after deducting the placement agent fees and estimated offering expenses payable by us, and excluding the proceeds, if any, from the conversion of the Class B Convertible Preferred Stock issued in this offering.

We intend to use the net proceeds of this offering to fund the filing for approval of Oncophage in Russia and potentially other geographical territories including Europe and Canada. In addition, we may use the net proceeds to fund additional clinical trials of our other lead product candidates and for clinical trials and preclinical studies for our other product candidates; for capital expenditures; for potential licenses and other acquisitions of complementary technologies and products; and for working capital and other general corporate purposes. Pending such uses, we intend to invest the net proceeds in accordance with our investment policy, which includes making investments in interest bearing investment grade U.S. government, municipal, corporate or money market securities.

DIVIDEND POLICY

No cash dividends have ever been paid or declared on shares of our common stock. We do not anticipate paying cash dividends on our common stock in the foreseeable future. Our present intention is to retain our future earnings, if any, for the future operation and expansion of our business. Any future payment of dividends on our common stock will be at the discretion of our Board of Directors and will depend upon, among other things, our earnings, financial condition, capital requirements, level of indebtedness and other factors that our Board of Directors deems relevant.

DILUTION

Our net tangible book value on June 30, 2007 was ($41,166,614), or approximately ($0.90) per share. “Net tangible book value” is total assets minus the sum of liabilities and intangible assets. “Net tangible book value per share” is net tangible book value divided by the total number of shares of common stock outstanding.

Dilution per share to new investors represents the difference between the amount per share paid by purchasers of shares of common stock in this offering and the net tangible book value per share of our common stock immediately after completion of this offering. After giving effect to the sale of 1,623,377 shares of our common stock in this offering and after deducting the placement agent fees and our estimated offering costs, our net tangible book value as of June 30, 2007 would have been ($36,437,808), or approximately ($0.77) per share. This amount represents an immediate increase in net tangible book value of approximately $0.13 per share to existing stockholders and an immediate dilution in net tangible book value of approximately $3.85 per share to purchasers of common stock in this offering, as illustrated in the following table:


Public offering price per share				$	3.08
Net tangible book value per share as of June 30, 2007	$	(0.90	)
Increase in net tangible book value per share attributable to this offering		0.13
Pro forma net tangible book value per share as of June 30, 2007 after giving effect to this offering					(0.77	)

Dilution per share to new investors in this offering				$	3.85

This table:

•

assumes no exercise of options to purchase approximately 5,792,259 shares of common stock at a weighted average exercise price of $6.88 per share;

•

excludes 383,812 shares of our common stock issuable upon vesting of unvested stock grants;

•

excludes 99,869 shares of our common stock outstanding under our Directors’ Deferred Compensation plan;

S-21

•

assumes no conversion of the outstanding shares of Series A convertible preferred stock into 2,000,000 shares of common stock;

•

assumes no conversion of the $50,000,000 principal amount of our 5.25% senior convertible notes due 2025 into 4,645,115 shares of our common stock;

•

assumes no conversion of the $26,346,667 principal amount of our 8.0% senior secured convertible notes due 2011 into 7,527,619 shares of our common stock; and

•

assumes no conversion of the Class B Convertible Preferred Stock issued hereunder into 7,514,409 shares of our common stock.

To the extent that options and warrants are exercised, or preferred stock is converted, at an exercise/conversion price less than the offering price, there will be further dilution to new investors.

DESCRIPTION OF THE CLASS B CONVERTIBLE PREFERRED STOCK

The following description of the material terms of the Class B Convertible Preferred Stock is only a summary and is qualified in its entirety by reference to our certificate of incorporation and the certificate of designations creating the Class B Convertible Preferred Stock. We urge you to read the certificate of incorporation and the certificate of designations, which we have filed with the Securities and Exchange Commission as an exhibit to a Current Report on Form 8-K, because they, and not this description, define your rights as holders of the Class B Convertible Preferred Stock.

General

Our certificate of incorporation authorizes our Board of Directors to issue up to 25,000,000 shares of our preferred stock, par value $0.01 per share. Subject to the limitations prescribed by our certificate of incorporation, our Board of Directors is authorized to establish the number of shares constituting each series of preferred stock and to fix the designations, powers, preferences and rights of the shares of each of those series and the qualifications, limitations and restrictions of each of those series, all without any further vote or action by our stockholders.

On August 30, 2007, the Board of Directors designated 15,250 shares of the undesignated preferred stock as the Class B Convertible Preferred Stock. The Class B Convertible Preferred Stock consists of two series, the Series B1 Convertible Preferred Stock and the Series B2 Convertible Preferred Stock. When issued, the shares of Series B1 Convertible Preferred Stock and the Series B2 Convertible Preferred Stock will be validly issued, fully paid and non-assessable and will not have, or be subject to, any preemptive or similar rights.

Conversion

Series B1 Convertible Preferred Stock

Series B1 Convertible Preferred Stock is convertible in amounts of 1,500 or more shares (or such lesser number as shall constitute all shares of Series B1 Convertible Preferred Stock not yet converted). The conversion price for each share of Series B1 Convertible Preferred Stock will equal an amount, as designated by the holder, not to exceed $1,000. The holder will be entitled to receive upon conversion the number of shares of our common stock equal to (A) the conversion price determined by the holder, divided by (B) the “Conversion Stock Price.”

For the Series B1 Convertible Preferred Stock, “Conversion Stock Price” means the lesser of (i) $3.08 (less any dividends declared or paid on our common stock) and (ii) the “Prevailing Stock Price” less $0.30, where “Prevailing Stock Price” means the lesser of the average of the daily volume-weighted average prices of our common stock during (i) the 30 consecutive business day period ending on the third business day immediately preceding, and excluding, the date on which conversion notice is delivered by the holder, (ii) the first three of such 30 consecutive business days or (iii) the last three of such 30 consecutive business days.

S-22

The aggregate consideration we may receive pursuant to conversions of all converted shares of Series B1 Convertible Preferred Stock is $10,000,000. In addition, if the aggregate consideration we receive on conversions of the Series B1 Convertible Preferred Stock is less than $5,000,000 as of June 30, 2008, then the aggregate consideration we may receive pursuant to conversions of all converted shares of Series B1 Convertible Preferred Stock will be $5,000,000.

Series B2 Convertible Preferred Stock

Series B2 Convertible Preferred Stock is convertible in amounts of 500 or more shares (or such lesser number as shall constitute all shares of Series B2 Convertible Preferred Stock not yet converted). The conversion price for each share of Series B2 Convertible Preferred Stock will equal an amount, as designated by the holder, not to exceed $1,000. The holder will be entitled to receive upon conversion the number of shares of our common stock equal to (A) the conversion price determined by the holder, divided by (B) the “Conversion Stock Price.”

For the Series B2 Convertible Preferred Stock, the “Conversion Stock Price” means the lesser of $4.158 (less dividends declared or paid on our common stock) and the Prevailing Stock Price.

The aggregate consideration we may receive pursuant to conversions of all converted shares of Series B2 Convertible Preferred Stock is 35% of $5,000,000 plus the aggregate proceeds from any conversions of Series B1 Convertible Preferred Stock.

Cashless Conversion

Holders of Class B Convertible Preferred Stock may elect to effect “cashless conversions” in which the holder would receive a number of shares of our common stock (the “Settlement Stock”) equal to “X” where:

X = [(N x D) – C]/P

N = the gross number of shares of our common stock that would have been issuable on conversion if the holder had not elected to effect a cashless conversion

D = the volume-weighted average price of our common stock on the third business day before, and excluding, the date on which conversion notice is delivered by the holder

C = the amount designated by the holder in its conversion notice that would have been payable if the holder had not elected cashless conversion

P = the Conversion Stock Price

In a cashless conversion, the holder will be issued the Settlement Stock and will not be required to pay consideration in connection with the conversion. Cashless conversions of Series B1 Convertible Preferred Stock will not be permitted unless either (i) the total number of shares of common stock we have issued pursuant to this offering and issuable upon future conversions of Series B1 Convertible Preferred Stock exceeds 6,887,778 shares or (ii) the registration statement of which this prospectus supplement forms a part (or any successor registration statement) is not available to issue shares of our common stock for purposes of such conversions.

Adjustments to Conversion Prices and Common Stock Issuable Upon Conversion

Adjustments for Merger, Consolidation and Sale of Assets

If we are acquired by means of merger, consolidation, share exchange or otherwise are involved in a transaction in which 50% or more of our outstanding common stock is exchanged for cash, securities or other assets, or if we sell all or substantially all of our assets (each a “Business Combination”), each holder of our Class B Convertible Preferred Stock will be permitted to convert all or part of its unconverted Class B Convertible Preferred Stock in connection with the Business Combination. This conversion right will be conditioned upon the effectiveness of the Business Combination, may be withdrawn by the holder and will entitle the holder to receive, upon payment of the consideration designated in the conversion notice, the same per share consideration received by holders of our common stock in connection with the Business Combination. If the consideration received by holders of our common stock in the Business Combination is in the form of cash, however, the holder will not be required to tender the relevant conversion consideration to convert its Class B Convertible Preferred Stock, but will receive an amount

S-23

in connection with such Business Combination equal to the consideration received in the Business Combination by holders of our common stock applicable to such holder based on the number of shares of common stock into which such holder’s Class B Convertible Preferred Stock would be convertible if the holder had converted each Class B Convertible Preferred Stock that it owns on the business day immediately preceding the date on which such Business Combination occurs, less such conversion consideration.

Assumption by Acquiror

In the case of any Business Combination, we have agreed not to enter into an agreement resulting in a Business Combination unless the agreement expressly obligates the acquiror to assume all of our obligations under any unconverted shares of Class B Convertible Preferred Stock (a “Stock Assumption Agreement”). In the event that any Class B Convertible Preferred Stock remains unconverted upon consummation of the Business Combination, the holder is entitled to certain adjustments, and will then automatically have equivalent rights with respect to the acquiror.

Transfer

Other than transfers by the initial purchaser to its investors or limited partners, shares of Series B1 Convertible Preferred Stock are transferable only in increments of 2,500 shares, and shares of Series B2 Convertible Preferred Stock are transferable only in increments of 1,750 shares.

Voting Rights

The Class B Convertible Preferred Stock is non-voting on all matters, except that we may not, without the consent of the holders of a majority of the outstanding and unconverted shares of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock, as the case may be: (i) alter or change the rights, powers or limitations of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock, as the case may be; (ii) authorize or issue additional shares of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock, as the case may be; or (iii) effect any split or combination of the shares of the Series B1 Convertible Preferred Stock or Series B2 Convertible Preferred Stock, as the case may be.

Distributions

The Class B Convertible Preferred Stock is not entitled to receive any distributions, whether regular, special, liquidating or otherwise, of cash, or other assets or securities, but is entitled to certain adjustments in the event of a subdivision or combination of our common stock or as described above with respect to Business Combinations.

Expiration

Each share of Series B1 Convertible Preferred Stock that is not converted on or before the first anniversary of the date of issuance of the Series B1 Convertible Preferred Stock shall be cancelled and extinguished and have no further force or effect. This term will be extended by two business days for each business day that (i) the registration statement of which this prospectus supplement forms a part (or any successor registration statement) is not available to issue shares of our common stock for purposes of such conversions or (ii) in the event of a potential restatement of our consolidated financial statements, from the date of such announcement until the date on which we file such a restatement. In addition, if one of these events occurs within 65 business days of the first anniversary of the date of issuance of the Series B1 Convertible Preferred Stock, the Series B1 Convertible Preferred Stock’s expiration date will be extended until a date that is at least 65 business days after the later of when we file the restatement or remediate our failure to provide an effective registration statement.

Each share of Series B2 Convertible Preferred Stock that is not converted on or before the seventh anniversary of the date of issuance of the Series B2 Convertible Preferred Stock shall be cancelled and extinguished and have no further force or effect.

Transfer Agent

We will initially act as the transfer agent for the Class B Convertible Preferred Stock, although we may at any time appoint another person to serve as the transfer agent.

S-24

PLAN OF DISTRIBUTION

We are offering the shares of our common stock and the Class B Convertible Preferred Stock described in this prospectus supplement through Wm Smith Securities, Incorporated. We expect Fletcher International, Ltd. will purchase all of the common stock and Class B Convertible Preferred Stock we initially sell.

Pursuant to a placement agency agreement between us and Wm Smith Securities, Incorporated, we have engaged Wm Smith Securities, Incorporated as our exclusive placement agent in connection with the issuance and sale, on a best efforts basis, of the shares to Fletcher International, Ltd. The placement agent is not purchasing or selling any of the shares we are offering, and it is not required to arrange the purchase or sale of any specific number or dollar amount of common stock, but it has agreed to use reasonable efforts to arrange for the sale of the shares.

We will pay the placement agent a placement agent fee equal to 4.0% of the gross proceeds of this offering. The following table shows the per share and total placement agent fees we will pay to the placement agent in connection with the sale of the shares.


Per share	$	0.1232
Total	$	200,000

We estimate the total expenses of this offering which will be payable by us, excluding the placement agent fees, will be approximately $70,000.

Wm Smith Securities, Incorporated, in its capacity as placement agent, may be deemed to be an underwriter for purposes of the Securities Act of 1933.

We have agreed to indemnify the placement agent and its controlling persons against certain liabilities, including liabilities under the Securities Act of 1933.

It is expected that delivery of the securities offered hereby will be made against payment therefor on or about the date specified on the cover page of this prospectus supplement, which is the 5th business day following the date of this prospectus supplement. Under Rule 15c6-1 under the Securities Exchange Act, trades in the secondary market generally are required to settle in three business days, unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the securities offered hereby on any date prior to the third business day before delivery will be required, by virtue of the fact that the securities offered hereby initially will settle on the fifth business day following the day of pricing (“T + 5”), to specify an alternate settlement cycle at the time of any such trade to prevent a failed settlement and should consult their own advisor.

Our common stock is quoted on the NASDAQ Global Market under the symbol “AGEN.” There is no public market for the Class B Convertible Preferred Stock and we do not intend to list the Class B Convertible Preferred Stock for trading on any national securities exchange or for inclusion on any automated quotation system.

S-25

PROSPECTUS

$100,000,000

ANTIGENICS INC.

Common Stock, Preferred Stock and Debt Securities

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

•

shares of our common stock;

•

shares of our preferred stock; or

•

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

Our common stock trades on the Nasdaq Global Market under the symbol “AGEN.”

This prospectus provides you with a general description of the securities that we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. 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 described under the heading “Where You Can Find More Information” before you make your investment decision. We will reflect any fundamental change to the terms of the offering in a post-effective amendment to the registration statement which includes this prospectus.

Investing in our securities involves a high degree of risk. Before buying any of our securities, you should carefully consider the risk factors identified under “ Risk Factors” beginning on page 4.

We will sell the securities to underwriters or dealers, through agents, or directly to investors.

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

This prospectus may not be used to sell securities unless it is accompanied by a prospectus supplement.

The date of this prospectus is April 24, 2007.

TABLE OF CONTENTS


		Page
About This Prospectus		3
Antigenics Inc.		3
Risk Factors		4
Note Regarding Forward-Looking Statements		4
Use of Proceeds		5
Ratio of Earnings to Fixed Charges and Preferred Stock Dividends		5
Description of Common Stock		6
Description of Preferred Stock		7
Description of Debt Securities		9
Anti-Takeover Effects of Delaware Law and of Our Charter and By-Laws		16
Plan of Distribution		17
Validity of Securities		19
Experts		19
Incorporation of Certain Documents by Reference		19
Where You Can Find More Information		19

Oncophage^® is a registered trademark of Antigenics Inc. and Aroplatin™ is a trademark of Antigenics Inc. Other trademarks included in this prospectus are the property of their owners.

ABOUT THIS PROSPECTUS

This prospectus is part of registration statements that we filed with the Securities and Exchange Commission (“SEC”) using a “shelf” registration process. Under the shelf process, we may, from time to time, issue and sell to the public any combination of the securities described in the registration statement in one or more offerings.

ANTIGENICS INC.

We are a biotechnology company developing technologies and products to treat cancers and infectious diseases, primarily based on immunological approaches. Our most advanced product candidate is Oncophage^® (vitespen; formerly HSPPC-96), a personalized therapeutic cancer vaccine candidate that has been tested, or is currently being tested, in several cancer indications, including in Phase 3 clinical trials for the treatment of renal cell carcinoma, the most common type of kidney cancer, and for metastatic melanoma. Oncophage is also being tested in Phase 2 and Phase 1 clinical trials in a range of indications. Our product candidate portfolio also includes (1) QS-21, an adjuvant used in numerous vaccines including, but not limited to, hepatitis, lyme disease, human immunodeficiency virus, influenza, cancer, Alzheimer’s disease, and malaria, (2) AG-707, a therapeutic vaccine program in a Phase 1 clinical trial for the treatment of genital herpes, and (3) Aroplatin™, a liposomal chemotherapeutic in a Phase 1 clinical trial for the treatment of solid tumors and non-Hodgkin’s lymphoma. Our related business activities include research and development, regulatory and clinical affairs, clinical manufacturing, business development, marketing, and administrative functions that support these activities.

RISK FACTORS

You should consider the “Risk Factors” referred to under Item 1A. of our Annual Report on Form 10-K for the fiscal year ended December 31, 2006, filed with the SEC on March 16, 2007, which is incorporated by reference in this prospectus. 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.

NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus contains 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 may include statements about generating royalty revenue from QS-21 in the 2010 timeframe, our timelines for performing and completing research, preclinical studies and clinical trials, timelines for releasing data from clinical trials, timelines for initiating new clinical trials, expectations regarding research, preclinical studies, clinical trials and regulatory processes, expectations regarding test results, future product research and development activities, the expected effectiveness of therapeutic drugs, vaccines, and combinations in treating diseases, applicability of our heat shock protein technology to multiple cancers and infectious diseases, competitive position, plans for regulatory filings, 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 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 for restructuring and reduction of our net cash burn (cash used in operating activities plus cash from investing activities less debt repayments and dividend payments), plans for sales and marketing, implementation of corporate strategy, 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 both 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 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 the United States Food and Drug Administration (“FDA”) or other 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; 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; and the solvency of counter parties under material agreements, subleases, and general real estate risks. Forward-looking statements, therefore, should be considered in light of all of the information included or referred to in this prospectus, including the information referenced under the heading “RISK FACTORS” above.

We caution investors not to place significant reliance on forward-looking statements contained in this prospectus; such statements need to be evaluated in light of all the information contained in this prospectus. Furthermore, the statements speak only as of the date of this prospectus, 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.

RATIO OF EARNINGS TO FIXED CHARGES AND PREFERRED STOCK DIVIDENDS

The following table sets forth our dollar coverage deficiency. The ratio of earnings to fixed charges is not disclosed since it is a negative number in each year shown below. Any time we offer debt securities pursuant to this prospectus, we will provide an updated table setting forth our ratio of earnings to fixed charges on a historical basis in the applicable prospectus supplement, if required. Any time we offer shares of preferred stock pursuant to this prospectus, we will provide a table setting forth our ratio of combined fixed charges and preferred stock dividends to earnings, if required.


	For The Year Ended December 31
	2002			2003			2004			2005			2006
	(in thousands)
Ratio of Earnings to Fixed Charges		—			—			—			—			—
Coverage Deficiency	$	(56,142	)	$	(66,266	)	$	(69,541	)	$	(74,894	)	$	(52,671	)

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” on page 19 for directions on obtaining these documents.

We have authority to issue 100,000,000 shares of common stock. As of April 17, 2007, we had 45,889,327 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.

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, 31,620 shares of which have been designated Series A Convertible Preferred Stock and were issued and outstanding as of the date of this prospectus. The remaining 24,968,380 authorized shares of preferred stock are undesignated and not issued and 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 this Series A Convertible 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.

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:

•

the title and stated value;

•

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

•

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

•

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

•

the procedures for any auction and remarketing, if any;

•

the provisions for a sinking fund, if any;

•

the provisions for redemption, if applicable;

•

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

•

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;

•

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;

•

voting rights, if any, of the preferred stock;

•

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

•

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

•

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 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;

•

the aggregate principal amount;

•

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;

•

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;

•

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;

•

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

•

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;

•

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

•

if payments of principal and, if applicable, premium and 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;

•

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 term 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:

•

“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

•

“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 our 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:

•

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

•

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:

•

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

•

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

•

we fail to observe or perform 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

•

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:

•

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

•

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

•

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:

•

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:

•

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;

•

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

•

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

•

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:

•

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

•

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

•

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;

•

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

•

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:

•

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

•

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:

•

money;

•

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

•

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:

•

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;

•

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;

•

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

•

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.

ANTI-TAKEOVER EFFECTS OF DELAWARE LAW AND OF OUR CHARTER AND BY-LAWS

The following paragraphs summarize certain provisions of the Delaware General Corporation Law and our charter and by-laws. The summary is subject to and qualified in its entirety by reference to the Delaware General Corporation Law and to our charter and by-laws, copies of which are on file with the SEC. Please refer to “Where You Can Find More Information” on page 19 for directions on obtaining these documents.

Delaware Law

Section 203 of the Delaware General Corporation Law is applicable to corporate takeovers of Delaware corporations. Subject to exceptions enumerated in Section 203, Section 203 provides that a corporation shall not engage in any business combination with any “interested stockholder” for a three-year period following the date that the stockholder becomes an interested stockholder unless:

•

prior to that date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

•

upon consummation of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, though some shares may be excluded from the calculation; and

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on or subsequent to that date, the business combination is approved by the board of directors of the corporation and by the affirmative votes of holders of at least two-thirds of the outstanding voting stock that is not owned by the interested stockholder.

Except as specified in Section 203, an interested stockholder is generally defined to include any person who, together with any affiliates or associates of that person, beneficially owns, directly or indirectly, 15% or more of the outstanding voting stock of the corporation, or is an affiliate or associate of the corporation and was the owner of 15% or more of the outstanding voting stock of the corporation, any time within three years immediately prior to the relevant date. Under some circumstances, Section 203 makes it more difficult for an interested stockholder to effect various business combinations with a corporation for a three-year period. Our certificate of incorporation and by-laws do not exclude the company from the restrictions imposed under Section 203. We expect that the provisions of Section 203 may encourage companies interested in acquiring us to negotiate in advance with our board of directors. These provisions may have the effect of deterring hostile takeovers or delaying changes in control of Antigenics, which could depress the market price of our stock and which could deprive stockholders of opportunities to realize a premium on shares of our stock held by them.

Charter and By-Law Provisions

Our certificate of incorporation and by-laws contain provisions that could discourage potential takeover attempts and make more difficult attempts by stockholders to change management. Our certificate of incorporation provides that stockholders may not take action by written consent but may only act at a stockholders’ meeting, and that only our president or a majority of our board of directors may call special meetings of the stockholders. Our by-laws also require that stockholders provide advance notice of business to be brought by a stockholder before the annual meeting. Our certificate of incorporation includes provisions classifying the board of directors into three classes with staggered three-year terms. In addition, our directors may only be removed from office for cause. Under our certificate of incorporation and by-laws, the board of directors determines the size of the board and may fill vacancies on the board. The by-laws provide that stockholders may not make nominations for directors at any annual or special meeting unless the stockholder intending to make a nomination notifies Antigenics of the stockholder’s intention a specified period in advance and furnishes certain information.

PLAN OF DISTRIBUTION

We may sell the securities being offered by us in this prospectus:

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directly to purchasers;

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through agents;

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through dealers;

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through underwriters; or

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through a combination of any of these methods of sale.

We and our agents and underwriters may sell the securities being offered by us in this prospectus from time to time in one or more transactions:

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

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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.

We may solicit directly offers to purchase securities. We may also designate agents from time to time to solicit offers to purchase securities. Any agent that we designate, who may be deemed to be an “underwriter” as that term is defined in the Securities Act of 1933, may then resell such securities to the public at varying prices to be determined by such agent at the time of resale. Additional details of our arrangement with the underwriter, including commissions or fees paid by us and whether the underwriter is acting as principal or agent, would be described in the related prospectus supplement.

If we use underwriters to sell securities, we would enter into an underwriting agreement with the underwriters at the time of the sale to them. The names of the underwriters would be set forth in the prospectus supplement which would be used by them together with this prospectus to make resales of the securities to the public. In connection with the sale of the securities offered, the underwriters may be deemed to have received compensation from us in the form of underwriting discounts or commissions. Underwriters may also receive commissions from purchasers of the securities.

Underwriters may also use dealers to sell securities. If this happens, the dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for whom they may act as agents.

Underwriting compensation paid by us to underwriters in connection with the offering of the securities offered in this prospectus, and discounts, concessions or commissions allowed by underwriters to participating dealers, would be set forth in the applicable prospectus supplement.

Underwriters, dealers, agents and other persons 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 of 1933, or to contribution with respect to payments which they may be required to make in respect of such liabilities.

Underwriters and agents may engage in transactions with, or perform services for, us in the ordinary course of business. If so indicated in the applicable prospectus supplement, we will authorize underwriters, dealers, or other persons to solicit offers by certain institutions to purchase securities pursuant to contracts providing for payment and

delivery on a future date or dates. The obligations of any purchaser under these contracts would be subject only to those conditions described in the applicable prospectus supplement, and the prospectus supplement would set forth the price to be paid for securities pursuant to those contracts and the commissions payable for solicitation of the contracts.

Any underwriter may engage in over-allotment, stabilizing and syndicate short covering transactions and penalty bids in accordance with Regulation M of the Securities Exchange Act of 1934. Over-allotment involves sales in excess of the offering size, which creates a short position. Stabilizing transactions involve bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Syndicate short covering transactions involve purchases of securities in the open market after the distribution has been completed in order to cover syndicate short positions. Penalty bids permit the underwriters to reclaim selling concessions from dealers when the securities originally sold by such dealers are purchased in covering transactions to cover syndicate short positions. These transactions may cause the price of the securities sold in an offering to be higher than it would otherwise be. These transactions, if commenced, may be discontinued by the underwriters at any time.

Each series of securities offered under this prospectus would be a new issue with no established trading market, other than our common stock, which is listed on the Nasdaq Global Market. Any shares of our common stock sold pursuant to a prospectus supplement will be listed on the Nasdaq Global Market or on an exchange on which the common stock offered is then listed, subject (if applicable) to official notice of issuance. Any underwriters to whom we sell securities for public offering and sale may make a market in the securities that they purchase, but the underwriters will not be obligated to do so and may discontinue any market making at any time without notice. We may elect to list any of the securities we may offer from time to time for trading on an exchange or on the Nasdaq Global Market, but we are not obligated to do so.

The anticipated date of delivery of the securities offered hereby will be set forth in the applicable prospectus supplement relating to each offering.

VALIDITY OF SECURITIES

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. and subsidiaries as of December 31, 2006 and 2005, and for each of the years in the three-year period ended December 31, 2006, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2006, 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.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with them, which means that we can disclose important information by referring to those documents. The information incorporated by reference is considered to be part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 prior to the sale of all the securities covered by this prospectus:

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our Annual Report on Form 10-K for the fiscal year ended December 31, 2006 filed with the SEC on March 16, 2007 (File No. 000-29089);

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our Current Reports on Form 8-K filed with the SEC on February 26, 2007 (File No. 000-29089) and March 14, 2007 (File No. 000-29089); and

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the description of our common stock contained in our Registration Statement on Form 8-A, filed on January 24, 2000 (File No. 000-29089), including any amendment or reports filed for the purpose of updating such description.

We will provide to you, without charge, upon your written or oral request, a copy of any or all of the documents that we incorporate by reference, including exhibits. Please direct requests to: Investor Relations at Antigenics Inc., 162 Fifth Avenue, Suite 900, New York, New York 10010, where the phone number is (212) 994-8200.

WHERE YOU CAN FIND MORE INFORMATION

You should rely only on the information contained in this prospectus. We have not authorized any person to provide you different information. You should not assume that the information in this prospectus is accurate as of any date other than the date on the cover.

We file annual, quarterly, and special reports and proxy statements and other information with the SEC. You may read and copy any document that we file at the SEC’s Public Reference Room at 100 F Street, N.E. Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room. Our SEC filings are also available on the SEC’s web site at http://www.sec.gov.