Antigenics Reports Significant Data from Pilot Study Combining Personalized Cancer Vaccine with Gleevec in Leukemia; Clinical Findings Lead to Phase II Trial.

Business Editors & Health/Medical Writers

BIOWIRE2K

NEW YORK--(BUSINESS WIRE)--Dec. 17, 2002

Antigenics Inc. (NASDAQ: AGEN) today reported interim results from an ongoing pilot study of AG-858, its personalized heat shock protein 70 (HSP70) product, in combination with Gleevec(TM) (imatinib mesylate, Novartis) for treatment of chronic myeloid leukemia (CML), a cancer characterized by the proliferation of abnormal white blood cells.

Marking the first clinical experience with AG-858, five out of five evaluable patients showed objective clinical responses in the trial, including two patients who had complete molecular responses. Based on these encouraging data, Antigenics plans to initiate a Phase II study to further assess the efficacy of this combination therapy.

"We have now seen objective responses using our personalized HSP products in patients with CML, melanoma and kidney cancer who had little or no other treatment options available," said Garo H. Armen, PhD, chairman and CEO of Antigenics. "Clearly, the cumulative data give us much confidence going forward."

In the pilot study, Zihai Li, MD, PhD, and colleagues at the University of Connecticut School of Medicine found that the combined treatment was associated with the complete elimination of leukemia cells in two of the five chronic phase CML patients evaluated, as determined by polymerase chain reaction (PCR), the most sensitive measure available to detect the presence of leukemia cells. Based on previous reports, only 10 percent of patients treated with Gleevec alone achieve responses using these same criteria. The three remaining patients evaluated were determined to be responders using other measures - including two who showed cytogenetic response, one of the criteria used in the approval of Gleevec. Four of the five patients in the study were determined to be unresponsive to treatment with Gleevec alone.

"Gleevec controls blood counts in most CML patients but fewer than 10 percent are PCR-negative. By eliminating all of the CML cells, combination treatment with Gleevec and HSP70 vaccine opens up the possibility of a cure," said Jonathan J. Lewis, MD, PhD, chief medical officer of Antigenics.

Like Antigenics' lead product Oncophage(R) (HSPPC-96), AG-858 is a personalized cancer vaccine based on Antigenics' proprietary heat shock protein technology. Derived from each patient's blood, 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 cells bearing this fingerprint.

About Chronic Myeloid Leukemia

Chronic myeloid 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 myeloid leukemia in the United States this year. CML mainly affects adults and is slightly more common in men than women.

About Antigenics

Antigenics' mission is to enhance and extend lives through the development of superior health care products for a wide range of cancers, infectious diseases, and autoimmune and degenerative disorders. The company's lead product is Oncophage, a personalized cancer vaccine in Phase III trials and granted fast track and orphan drug designations by the US Food and Drug Administration for kidney cancer and melanoma. Antigenics' cancer portfolio also includes AG-858, a personalized cancer vaccine in Phase I development for chronic myeloid leukemia, and two Phase II liposomal products: Aroplatin(TM), a third-generation platinum chemotherapeutic, and ATRA-IV, a form of vitamin A. Other products in development include QS-21, an immunomodulator being tested in several advanced clinical vaccine programs in partnership with leading pharmaceutical companies, and AG-702, a genital herpes immunotherapeutic agent in Phase I testing. For more information about Antigenics, please visit www.antigenics.com.

This press release contains forward-looking statements, including the statements regarding the timing for initiating an expanded study and the potential that the combination treatment will prove effective in a larger study, and development of HSP70 for chronic myeloid leukemia. 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 enroll sufficient numbers of patients in clinical trials to demonstrate statistically significant results; that we may be unable to obtain the regulatory approvals necessary to conduct additional clinical trials or to market HSP70 alone or in combination with Gleevec for the treatment of chronic myeloid leukemia; 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 Quarterly Report on Form 10-Q 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.