San Francisco, CA, May 14, 2001 - Demonstrating new success in cancer immunotherapy, researchers today reported that they have increased the survival time of cancer patients using novel therapeutic vaccines. Data show, for the first time, that human T cell immune responses induced by therapeutic vaccines result in increased survival of patients with late-stage metastatic cancers. The Phase I/II trial conducted at Georgetown University's Lombardi Cancer Center tested two cancer vaccines developed by Therion Biologics of Cambridge, MA in collaboration with National Cancer Institute (NCI) and Aventis Pasteur.

These vaccines, vaccinia-CEA (V) and ALVAC-CEA (A), were used in a combination regimen known as a "prime-boost" protocol in late-stage cancer patients. Five of nine patients treated with sequential vaccinations of vaccinia-CEA and ALVAC-CEA (VAAA) not only showed increased immune responses, but also remained alive two years out compared to zero long-term survivors in other treatment groups. The study's principal investigator, John Marshall, M.D., of Georgetown University Medical Center will present this data at the 2001 American Society of Clinical Oncology (ASCO) meeting today.

"Therapeutic cancer vaccines have long been believed to hold great promise. Our data today demonstrate the first link between the ability of vaccines to elicit a strong, specific T cell response against advanced metastatic cancers and subsequently increase patient survival," said John Marshall, M.D., Associate Professor of Medicine at Georgetown University. "The current life expectancy for these late-stage cancer patients is less than one year, so to see more than 50 percent of the patients treated with CEA vaccines alive two years later is striking, even in this small study population."

"These findings strongly support the utility and future studies of Therion's therapeutic vaccines in late-stage cancer patients, the most difficult patient population to treat," said Dennis Panicali, Ph.D., President and Chief Executive Officer of Therion Biologics. "They also validate the ability of our prime-boost products to trigger and sustain powerful anti-cancer immune responses. Based on these encouraging results, the trial has progressed into Phase II development, using the VAAA vaccine regimen in combination with the immune modulator GM-CSF to further enhance immune responses. Preliminary results continue to show promise for this immunotherapeutic regimen."

CEA Vaccine Study Design
The randomized Phase I portion of the trial was conducted in 18 patients with a variety of advanced metastatic cancers (colorectal, stomach, pancreatic, esophageal, cervical and breast) expressing the CEA tumor antigen. All enrolled patients were expected to progress or relapse within one year. The study was designed to compare immune responses and survival following treatment with two different prime-boost vaccination regimens. In the first regimen, patients received vaccinia-CEA followed by three vaccinations with ALVAC-CEA (VAAA); in the second regimen, patients received three doses of ALVAC-CEA followed by vaccinia-CEA (AAAV). Primary endpoints for the study included safety and immune responses. Subsequent analysis of the study data was performed to assess increases in patient survival time.

Trial Results
Study results indicate that pox virus-based CEA vaccines induced an increase in CEA-specific T cell responses and a correlating increase in patient survival (p= 0.03). The Georgetown study found VAAA to be the more effective prime-boost treatment protocol, based primarily on higher CEA-specific T cell responses observed in this treatment group as well as higher survival rates. After two years, five of the nine patients receiving the VAAA regimen were still alive, compared to zero of the nine patients in the AAAV treatment arm. Survival duration was unrelated to disease status at study entry. Based on these findings, Therion and Georgetown will conduct additional Phase II trials designed to replicate this data in a larger patient population.

Background on CEA Vaccines
Vaccinia-CEA and ALVAC-CEA are recombinant, pox virus-based vaccines that target carcinoembryonic antigen (CEA), a protein found on the surface of colorectal, pancreatic, breast and lung cancer cells. Used in a prime-boost treatment protocol, the two products are designed to generate and sustain a therapeutic level of cytotoxic T cell activity critical for destruction of cancer cells. In addition to these products, Therion and the Laboratory of Tumor Immunology and Biology of the NCI have a next-generation vaccine called CEA-TRICOM currently in early clinical trials at Georgetown University. The TRICOM component of this vaccine consists of three co-stimulatory molecules known to elicit even stronger cellular immune responses necessary for complete tumor eradication.

Dr. Panicali also noted that Therion is developing a separate product, ALVAC-CEA/B7.1, in collaboration with worldwide vaccine leader Aventis Pasteur Limited. Currently in Phase II clinical studies, Therion and Aventis expect ALVAC-CEA/B7.1 to enter Phase III trials in 2002. Therion is also conducting ongoing studies of its colorectal, prostate, and breast cancer vaccines with the NCI under its existing Cooperative Research and Development Agreement (CRADA) with the NCI's Laboratory of Tumor Immunology and Biology (LTIB). This agreement was renewed in February 2000, extending Therion's relationship with NCI researcher and LTIB Chief Dr. Jeffrey Schlom for an additional five years.

About Therion
Therion Biologics Corporation is engaged in the development of therapeutic vaccines for cancer and preventive vaccines for AIDS. Currently, Therion has two lead products for colorectal and prostate cancer, ALVAC-CEA/B7.1 and PROSTVAC-VF, respectively, moving into pivotal clinical trials in the next two years. The company also has a broad pipeline of vaccines in early clinical development for treatment of major cancers, including breast cancer, melanoma and other solid tumors. Therion's partners include Aventis Pasteur, the National Cancer Institute and a network of leading clinical institutions around the world. Therion is headquartered in Cambridge, Massachusetts.