Antigenics Begins 120-Patient Phase II Trial of AG-858 Cancer Vaccine in Chronic Myelogenous Leukemia.

Business Editors/Health/Medical Writers

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NEW YORK--(BUSINESS WIRE)--April 9, 2003

Antigenics Inc. (NASDAQ: AGEN):

Trial to Be Conducted at Leading Medical Centers Worldwide

Antigenics Inc. (NASDAQ: AGEN) announced today that it has begun a Phase II study evaluating AG-858 personalized cancer vaccine in combination with Gleevec(TM) (imatinib mesylate, Novartis) for treatment of chronic myelogenous leukemia (CML), a cancer characterized by the proliferation of abnormal white blood cells.

The international clinical trial will evaluate the safety and efficacy of the combination treatment in up to 120 patients with chronic phase CML who are currently receiving Gleevec treatment but have not achieved complete clinical response.

"We are highly encouraged by the responses seen in our earlier clinical trial of CML patients receiving AG-858, and are pleased to be initiating a Phase II development program that can be used in support of a biologicals license application filing," said Jonathan J. Lewis, MD, PhD, chief medical officer of Antigenics. "We feel confident that enrollment for the trial can be completed quickly, given the positive findings from the first study and the enthusiasm expressed by CML patients and leading experts alike."

The launch of the Phase II study is based on earlier clinical data that demonstrated objective clinical responses associated with combination AG-858 and Gleevec treatment in five out of five patients tested, four of whom were unresponsive to treatment with Gleevec alone. Two of the five patients experienced complete molecular responses - a result achieved by fewer than 10 percent of patients treated with Gleevec alone, according to published reports. Updated findings from the earlier study will be announced in an oral presentation at this year's annual meeting of the American Society of Clinical Oncology in June.

Like Antigenics' lead product Oncophage(R) (HSPPC-96), AG-858 is a personalized cancer vaccine based on the company's proprietary heat shock protein technology. Derived from each patient's blood cells, the vaccine is designed to capture the 'antigenic fingerprint' of the patient's particular cancer to reprogram the body's immune system to target and destroy only the cancerous cells bearing this fingerprint.

About Chronic Myelogenous Leukemia

Chronic myelogenous leukemia is a cancer of the blood and bone marrow characterized by overproduction of white blood cells. The disease is caused by a genetic mutation that produces an abnormal enzyme (Bcr-Abl tyrosine kinase). Approved in 2001 for CML, Gleevec specifically blocks the action of this abnormal enzyme.

The American Cancer Society estimates that there will be about 4,400 new cases of chronic myelogenous leukemia in the United States this year. CML mainly affects adults and is slightly more common in men than women.

About Antigenics

Antigenics is developing personalized immunotherapeutics and revolutionary treatments for cancers, infectious diseases and autoimmune disorders. The company's lead product is Oncophage, a late-stage, personalized cancer vaccine being evaluated in several indications, including kidney cancer and metastatic melanoma. Antigenics' portfolio also includes AG-858, a personalized cancer vaccine in Phase II development; Aroplatin and ATRA-IV, two Phase II liposomal chemotherapeutics; and AG-702/AG-70X, a Phase I genital herpes immunotherapeutic. For more information about Antigenics, please visit www.antigenics.com.

This press release contains forward-looking statements, including the statements regarding the sites at which the trial will be conducted; that the Phase II clinical trial of AG-858 for chronic myelogenous leukemia will provide adequate data to support a biologicals licensing application filing; that trial enrollment will be completed quickly; and the number of projected new cases of CML this year. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those projected in these forward-looking statements. These risks and uncertainties include, among others, that we may not be able to initiate the trial at sufficient sites to meet our enrollment expectations and our expectations regarding the numbers, locations and reputations of participating medical centers; that enrollment rates and total enrollment may not meet our expectations; that the trial may not generate safety and efficacy data that supports a biologicals licensing application filing; estimates regarding the incidence of CML may not be accurate; that budget constraints will limit or slow down our development program in this disease; that we may fail to adequately protect our intellectual property or are determined to infringe on the intellectual property of others; and the factors described in the company's periodic filings with the Securities and Exchange Commission. Please see Exhibit 99.1 of our most recent Annual Report on Form 10-K for a discussion of these and other risk factors. We caution investors not to place undue reliance on the forward-looking statements contained in this document. These statements speak only as of the date of this document, and we undertake no obligation to update or revise the statements. All forward-looking statements are expressly qualified in their entirety by this cautionary statement.