CHICAGO, June 1, 2003 - Georgetown University researchers presented clinical data confirming the safety and the first evidence of clinical activity of Therion Biologics' TRICOM� therapeutic vaccines. Proprietary to Therion, TRICOM consists of three co-stimulatory molecules designed to optimize the immune response necessary for tumor destruction when delivered as part of the company's pox virus-based vaccines. This innovative approach, delivered in a "prime-boost" dosing regimen, induced tumor-specific immune responses and significant clinical benefit in some patients with CEA- expressing cancers (in this study, predominantly gastrointestinal cancers). Specifically, disease stabilization was achieved in 40 percent of study participants with one patient exhibiting a complete response.

Dr. John Marshall, Associate Professor of Medicine at Georgetown University and Lead Investigator of the study, presented results from Abstract #662 today at 9:15 am at the 39th Annual Meeting of the American Society of Clinical Oncologists (ASCO). Dr. Marshall will also be featured as part of ASCO's press briefing today at 2:30 pm.

This Phase I trial was conducted at the Lombardi Cancer Center in Washington, D.C. as part of Therion's existing Cooperative Research and Development Agreement (CRADA) with the National Cancer Institute (NCI) and supported by ROI number CA88972.

"Previous trials have demonstrated that Therion's prototype vaccines were able to motivate the immune system to attack cancer cells. This trial illustrates that this response can be amplified with the addition of multiple co-stimulatory molecules to the vaccines, as shown through encouraging clinical responses and immunologic evidence of activity," said Dr. Marshall. "Prior to the trial, these patients had failed to respond to multiple therapies, essentially running out of treatment options. That 40 percent showed a positive response to these vaccines, without any serious side effects, underscores the potential role of these vaccines in the fight against cancer and supports further clinical evaluation."

"These encouraging results build on our earlier studies reported at the last two ASCO meetings, first demonstrating the benefit of prime boost dosing in 2001, followed by the safety of TRICOM in 2002, and provide strong confirmation of our stepwise approach to vaccine development," said Mark Leuchtenberger, President and Chief Executive Officer of Therion. "Together, these findings set the stage to evaluate, in advanced clinical trials, our optimized commercial vaccine candidates. Three product candidates, PROSTVAC^�-VF, PANVAC-VF and VF-TRICOM, entered the clinic this year for the treatment of prostate cancer, pancreatic cancer and melanoma, respectively, and will move to Phase II in the next 12 months. We anticipate beginning Phase II evaluation of our CEA-based vaccine for pancreatic cancer, PANVAC-VF, in early 2004."

About the Study
The trial, which has been underway for 29 months, enrolled 58 patients with advanced Carcinoembryonic Antigen (CEA)-bearing cancers, an antigen that is present on more than 90 percent of colorectal and pancreatic tumors. Patients were assigned to one of three therapeutic regimens of Therion's prototype vaccines, Vaccinia-CEA/TRICOM (V) and Fowlpox-CEA/TRICOM (F). Patients received sequential doses of FFFF, VFFF or VFFF plus GM-CSF (a cytokine that enhances the induction of T-cell responses), respectively. Vaccines were administered monthly for the first six months, followed by dosing every three months. If disease progressed on the three-month schedule, treatment reverted to a monthly dosing schedule. Measures of immune response included induction of CEA specific T-cells stimulated by vaccination, reduction of circulating CEA levels in the blood and assessment of tumor progression.

Significant CEA-specific T-cell responses were observed in all measurable patients (n=17). Specifically, this measure increased 2.5 to 7.3 fold in those patients also receiving GM-CSF. Of 58 patients, disease was stabilized in 23 (40%), five exhibited decreasing CEA levels and one patient achieved a pathologic complete response. Stable disease was defined as neither sufficient tumor shrinkage to qualify for partial response (i.e., shrinkage of <30%) nor progressive disease, for a period of at least four months. No significant toxicity was observed; mild side effects included mild fever, skin reactions and swollen glands.

"We have pursued a deliberate strategy to clinically evaluate target antigens, prime-boost dosing regimens, and most recently, the combination of TRICOM with target antigens," said Dennis Panicali, Ph.D., Chief Scientific Officer at Therion. "This clinical experience has yielded an optimized vaccine configuration that comprises recombinant vaccinia and fowlpox viruses that simultaneously express TRICOM with a target antigen, administered sequentially in a prime-boost regimen which uses vaccinia to stimulate an initial immune response, followed by multiple immunizations with fowlpox, to sustain the response."

In addition to Dr. Marshall, study authors included Loretta Odogwu, M.D.; Jimmy Hwang, M.D.; Evelyn Fox, N.P.; Susie Park, R.N., M.S.N. from the Lombardi Cancer Center and Philip Arlen, M.D.; James Gulley, M.D.; Kwong Tsang, Ph.D. and Jeffrey Schlom, Ph.D. from the Laboratory of Tumor Immunology and Biology at the NCI.

About TRICOM
TRICOM, which stands for a TRIad of CO-stimulatory Molecules, is designed to enhance antigen presentation and activation of immune responses critical for tumor destruction. Therion is using the co-stimulatory molecules ICAM-1, B7.1 and LFA-3, TRICOM, as part of its pox virus vector-based approach to cancer immunotherapy for prostate cancer, pancreatic cancer and melanoma.

About Therion Biologics Corporation
Therion Biologics Corporation develops therapeutic vaccines for cancer and preventive vaccines for AIDS. The Company has three lead programs involving multiple clinical trials: PROSTVAC^�-VF for prostate cancer; PANVAC-VF for pancreatic cancer; and VF-TRICOM� for melanoma. Therion is also applying its technology platform to develop vaccines to treat breast cancer and other solid tumors. The Company's strategic partners include the National Cancer Institute, 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.