Phase 3 Demographic Data on Antigenics’ Oncophage Cancer Vaccine in Kidney Cancer Published at ASCO Meeting

Immunological Data on Oncophage in Combination Treatment of Melanoma Presented

NEW ORLEANS — June 7, 2004 — Antigenics Inc. (NASDAQ: AGEN) today announced findings from two clinical trials of the company’s investigational cancer vaccine Oncophage^® (HSPPC-96). Demographic data from the company’s Phase 3 trial of Oncophage in renal cell carcinoma (the most common type of kidney cancer), being conducted by The Antigenics Renal Cell Carcinoma Study Group, were published at the 40^th annual meeting of the American Society of Clinical Oncology (ASCO).

“This Phase 3 study represents the largest randomized study to date in the adjuvant treatment setting of renal cell carcinoma,” said Christopher G. Wood, MD, of the M. D. Anderson Cancer Center, and lead author of the abstract. “With such a high unmet medical need faced by this patient community, we are proud to contribute towards a better understanding of the epidemiology of this disease.”

Oncophage, Antigenics’ lead product in development, is a personalized cancer vaccine based on the company’s proprietary heat shock protein technology. Derived from each patient’s cancerous tissue or cells, the vaccine is designed to capture the ‘antigenic fingerprint’ of the patient’s particular cancer. This is designed to reprogram the body’s immune system to target and destroy only cells bearing this fingerprint, leaving healthy tissue unaffected and minimizing debilitating side effects.

First Phase 3 Demographic Data on Oncophage

Antigenics announced demographic findings from the company’s Phase 3 trial evaluating Oncophage as an adjuvant treatment of nonmetastatic renal cell carcinoma (abstract #2618). The study will assess the effect of addition of Oncophage vaccination to the current standard of care (nephrectomy, or surgical removal of the diseased kidney) in patients whose renal cell cancer is at high risk of recurrence after nephrectomy. In the trial, half of the patients undergo nephrectomy alone, and half undergo nephrectomy plus Oncophage vaccination. After nephrectomy, patients randomized to the Oncophage treatment arm receive their personalized vaccines once a week for four weeks, then every other week until depletion of their vaccine supply. All patients are followed for recurrence-free survival and overall survival.

At the meeting, researchers reported that patients were accrued at 132 medical centers in North America, and Western and Eastern Europe at a randomization rate of 20–50 patients per month, and that as of September 2003, 644 patients had been randomized. Vaccine could be produced for most patients (92 percent) in the Oncophage treatment arm; these patients received a median number of 10 vaccinations. Investigators from The Antigenics Renal Cell Carcinoma Study Group concluded that patient accrual has been rapid and the vaccine production rate is high.

“The publication of our first Phase 3 demographic data is a significant step in the clinical development of our lead product candidate, and an important milestone for the company,” said Renu Gupta, MD, senior vice president of development.

Oncophage Combination Treatment in Melanoma

In a poster session, investigators from the Istituto Nazionale Tumori in Milan, Italy, presented findings from a Phase 2 trial of Oncophage as part of combination treatment for metastatic melanoma (abstract #7510). Based on an earlier Phase 2 study published in the Journal of Clinical Oncology (2002;20:4169) that found that Oncophage vaccination was associated with clinical and immunological response in patients with metastatic melanoma, researchers investigated how immune response to Oncophage vaccination could be modulated by concurrent administration of cytokines (immune-regulating hormones).

The study involved 18 evaluable patients with stage IV melanoma, the majority of whom had received prior chemotherapy and/or biological therapy. All patients underwent surgery, then received a course of treatment that consisted of their personalized Oncophage vaccines in combination with the cytokines GM-CSF (granulocyte macrophage colony-stimulating factor) and interferon a (IFN-a).

The investigators reported that one of two patients rendered disease-free by surgery remained free of disease for 419 days. Of 16 patients with residual melanoma post-surgery, 10 experienced disease stabilization, lasting from 97 to 372 days. In addition, of 16 patients evaluated for immunological response, six of them — all exhibiting stabilized disease — had a demonstrable increase in anti-melanoma immune response. Researchers concluded that the immunological and clinical responses induced by Oncophage given in combination with GM-CSF and IFN-a did not appear to be significantly superior to those mediated by vaccination with Oncophage alone.

About Antigenics 

Antigenics is working to develop personalized immunotherapeutics and revolutionary treatments for cancers, infectious diseases and autoimmune disorders. The company’s lead product in development is Oncophage, a late-stage, personalized cancer vaccine being evaluated in several indications, including renal cell carcinoma and metastatic melanoma. Antigenics’ portfolio of investigational products also includes AG-858, a personalized cancer vaccine in Phase 2 development; two Phase 2 liposomal cancer treatments, Aroplatin™ and ATRA-IV; and AG-702/AG-707, a Phase 1 genital herpes program.

This press release contains forward-looking statements, including statements regarding the significance of the publication of demographic data from the Phase 3 of Oncophage in renal cell carcinoma. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those projected in these forward-looking statements. Risks and uncertainties relating to commercialization of Oncophage and our other product candidates include, among others, the ability to satisfy the FDA and other regulatory authorities regarding product characterization; the results of clinical trials; the ability to successfully prepare Oncophage; and the factors described in the company’s periodic filings with the Securities and Exchange Commission. Please see the disclosure under the heading “Factors That May Impact Future Results” in the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of the Antigenics Quarterly Report on Form 10-Q for the fiscal quarter ending March 31, 2004, for a more complete discussion of these and other risk factors. Antigenics cautions investors not to place considerable reliance on the forward-looking statements contained in this press release. These statements speak only as of the date of this document, and Antigenics undertakes no obligation to update or revise the statements. All forward-looking statements are expressly qualified in their entirety by this cautionary statement. Antigenics’ business is subject to substantial risks and uncertainties, including those identified above. When evaluating Antigenics’ business and securities, investors should give careful consideration to these risks and uncertainties.