Cambridge, MA, September 7, 2000 - To advance ongoing clinical studies of a promising new prostate cancer treatment, Therion Biologics Corporation and the National Cancer Institute (NCI) have initiated two additional Phase II trials for PROSTVAC VF. PROSTVAC VF, a novel vaccine designed to stimulate and strengthen the body's natural immune response against prostate tumor cells, has demonstrated strong Phase I clinical results and may also have potential utility as a complement to standard radiotherapy and anti-androgen hormone therapies. Through the new studies, over one hundred patients with localized prostate cancer will receive Therion's PROSTVAC VF product. Prostate cancer is the second leading cause of cancer death in men, with an estimated 180,000 new cases and 37,000 deaths in the U.S. annually. The trials are part of a broader Collaborative Research and Development Agreement (CRADA) between Therion and the NCI's Laboratory of Tumor Immunology and Biology under the direction of Dr. Jeffrey Schlom.

"Through our successful partnership with NCI, Therion continues to build on promising early clinical data supporting the safety and potential utility of our lead product, PROSTVAC VF," said Dennis Panicali, Ph.D., President and Chief Executive Officer of Therion Biologics Corporation. "In addition to other ongoing Phase II trials, these new studies will provide human clinical data in a broader range of patients, including those with early-stage disease and those receiving complementary therapies. Positive Phase II clinical data will form the foundation for moving our PROSTVAC VF product into Phase III trials." Dr. Panicali noted that Therion and its collaborators, NCI and Dana Farber Cancer Institute, recently published results from a Phase I study of PROSTVAC in the May issue of Clinical Cancer Research.

PROSTVAC VF is a recombinant vaccine that targets prostate-specific antigen (PSA), a protein produced by prostate tumor cells. Circulating PSA levels serve as a marker of disease progression. Therion's PROSTVAC VF product consists of two components, rV-PSA, which is designed to "prime" or generate an initial immune response against cells displaying PSA, and rF-PSA, which is administered subsequently as a booster to enhance and sustain the immune response. Additionally, initial dosings in the NCI Phase II trials will include vaccination with rV-B7.1 which acts to further strengthen cellular immune responses against cancer cells.

Study Designs

The first Phase II study will assess the safety and immunologic effects of PROSTVAC VF in 30 patients who have localized prostate cancer and are receiving standard radiotherapy. Patients will be randomized to receive PROSTVAC VF before, during and after primary radiotherapy with an initial dose of rV-PSA + rV-B7.1 followed by subsequent rF-PSA vaccinations. The primary measure of immune response will be the level of PSA specific T-cells stimulated by vaccination, with serum PSA levels used as secondary measures of treatment effects. Principal investigator Bill Dahut, M.D., of the National Naval Medical Center will lead this study.

The second Phase II study will also test the safety and immunologic effects of PROSTVAC VF, and will additionally compare the efficacy of PROSTVAC VF to anti-androgen hormone therapy with Nilutamide. Anti-androgen therapy is a standard first course of treatment for patients diagnosed with localized prostate cancer. Nilutamide is an established second line treatment for patients with cancer that has progressed. The study will involve 78 patients with localized hormone refractory prostate cancer, and will evaluate comparative evidence of disease progression as measured by serum PSA levels as well as effect on immune response. Principal investigator Philip M. Arlen, M.D., of the National Institutes of Health (NIH) will lead this study.

Therion Biologics Corporation is engaged in the development of therapeutic vaccines for cancer and preventive vaccines for AIDS. Currently, Therion has nine products in Phase I and Phase II clinical development for the treatment of major cancers, including prostate, colorectal and breast cancer and melanoma. The Company also has a major corporate alliance with Aventis Pasteur for the development of therapeutic vaccines for colorectal and lung cancers and melanoma. Therion is headquartered in Cambridge, Massachusetts.