Cambridge, MA, August 2003 � Using a prototype vaccine developed by Therion Biologics Corporation administered in combination with interleukin-2 (IL-2), researchers at the National Cancer Institute (NCI) under the direction of Steven A. Rosenberg, M.D., Ph.D., NCI Chief of Surgery, generated objective tumor response in six of 12 (50 percent) treated patients with metastatic melanoma, including three complete regressions. The results of the Phase II clinical study appear in the August issue of Clinical Cancer Research.

One arm of the study evaluated a fowlpox-based vaccine encoding a modified peptide of the gp100 melanoma-melanocyte antigen. The vaccine was administered to 23 patients with metastatic melanoma. Patients were prospectively randomized to receive the vaccine either intravenously (IV, n=11) or by intramuscular (IM) injection (n=12) every four weeks for up to four doses or until disease progressed. Eligible patients with progressive disease (n=12) then received vaccine plus high-dose IL-2 (720,000IU/kg) every four weeks for up to four doses. Although no tumor regression was seen in patients treated with vaccine alone, six of 12 patients who received the combination treatment exhibited objective tumor regressions, three of whom remained free of disease at 16, 18 and 26 months, respectively. Although this appears to be higher than the 15% clinical response rate seen with IL-2 alone, the number of patients is small and additional patients are currently being treated to test that observation. Treatment results were similar in both the IV and IM groups. Observed side effects included fever, chills, nausea and headache, with no serious adverse events reported.

�The exciting clinical responses to immunotherapy described in this study provide further evidence of the versatility of Therion�s pox virus vectors and our ability to tailor vaccine candidates to address multiple disease indications,� stated Mark Leuchtenberger, President and Chief Executive Officer of Therion Biologics Corporation. �Our long-standing and ongoing clinical partnership with the NCI helps fuel our early stage vaccine pipeline. Through our collaborations with the NCI, we have evaluated multiple vaccine candidates, Therion Melanoma Vaccine Improves Efficacy of Existing Immunotherapy resulting in the development of our two lead product candidates, PANVAC-VF and PROSTVAC^�-VF, both of which will soon enter Phase II clinical investigation in pancreatic cancer and prostate cancer, respectively.�

About Therion Biologics Corporation
Therion Biologics Corporation develops therapeutic vaccines for cancer and preventive vaccines for AIDS. The Company has two lead programs involving multiple clinical trials: PANVAC-VF for pancreatic cancer and PROSTVAC^�-VF for prostate cancer. Therion is also applying its technology platform to develop vaccines to treat melanoma, breast cancer and other solid tumors. In addition to studies conducted under a collaboration agreement with the National Cancer Institute, the Company�s strategic partners include a global network of leading clinical institutions, and Aventis Pasteur, Ltd., which is developing ALVAC-CEA/B7.1, a clinical candidate for colon cancer. Therion is headquartered in Cambridge, Massachusetts.