Cambridge, MA, June 21, 2004 � Therion Biologics Corporation today announced the initiation of the company�s first pivotal clinical trial. PANVAC-VF, Therion�s lead vaccine candidate, entered a Phase III clinical trial for the treatment of metastatic pancreatic cancer in patients who have not responded to treatment with gemcitabine. The Phase III study will enroll 250 patients at 50 to 60 participating treatment centers across the United States. The study�s primary endpoint will be overall survival compared with palliative chemotherapy or best supportive care.

The study is being conducted under the guidance of a Special Protocol Assessment (SPA) provided by the U.S. Food and Drug Administration (FDA). The SPA indicates that if the trial successfully meets its primary endpoint, the data will provide the basis for an efficacy claim in a marketing application to the FDA. The Phase III trial design is based on encouraging data presented this month at the Annual Meeting of the American Society of Clinical Oncology (ASCO). Specifically, data from two separate Phase I studies of Therion�s investigational vaccines demonstrated a median overall survival of 7.9 months and at least 5.3 months, respectively, in patients with advanced pancreatic cancer, compared to an anticipated median overall survival of approximately three months, based on historical controls.

�Metastatic pancreatic cancer is a devastating disease that brings an especially poor prognosis with few treatment options,� said John Marshall, M.D., Associate Professor of Medicine at Georgetown University Medical Center, who will serve as the lead investigator for the study. �Early studies of Therion�s vaccines suggested improved median overall survival in this challenging patient population. This study will allow us to assess PANVAC-VF�s impact on patient survival in a large, randomized trial.�

PANVAC-VF is designed to stimulate the immune system to target and destroy cancer cells expressing two proteins (or antigens), carcinoembryonic antigen (CEA) and mucin-1 (MUC-1), found on over 90 percent of pancreatic tumor cells. The vaccine also incorporates TRICOM�, Therion�s proprietary triad of costimulatory molecules (B7.1, ICAM-1 and LFA-3), designed to enhance and sustain a targeted immune response against tumor cells.

Study Design
The multicenter, randomized, controlled trial will enroll 250 patients with advanced pancreatic cancer in whom gemcitabine is ineffective. Patients will be randomized 1:1 to receive either PANVAC-VF or control treatment. Patients in the treatment arm will receive an initial �priming� dose of PANVAC-VF plus GM-CSF to initiate an anti-cancer immune response, followed by a series of �booster� vaccinations to sustain the response. Control treatment will consist of either best supportive care or palliative chemotherapy (capcitabine, irinotecan or 5-fluorouracil). Secondary study endpoints include safety, quality of life parameters, change in serum tumor antigen levels, response rate and disease stabilization.

�The commencement of this Phase III trial for PANVAC-VF comes less than one year after the company filed the Investigational New Drug Application, but is actually the culmination of more than 10 years of focused clinical testing with prototypes,� said Mark Leuchtenberger, President and Chief Executive Officer of Therion Biologics Corporation. �In addition to PANVAC-VF, Therion is also evaluating PROSTVAC^�-VF in a Phase II trial in prostate cancer. Together, these two advanced clinical trials place Therion on an accelerated path towards product commercialization.�

About Pancreatic Cancer
Pancreatic cancer remains one of the deadliest forms of cancer, affecting over 30,000 Americans each year. More than 95 percent of patients with pancreatic cancer ultimately die from the disease. Current treatments include surgery, chemotherapy and radiation. There is currently no FDA-approved treatment for patients who do not respond to chemotherapy.

Additional Clinical Studies
In addition to pancreatic cancer, Therion vaccines targeting CEA and MUC-1 have been tested in patients with other tumors that are known to over-express the CEA and MUC-1 antigens, including breast, lung and colorectal cancers. Therion and the NCI are currently planning up to 18 additional trials with PANVAC-VF in these indications.

About Therion Biologics Corporation
Therion Biologics Corporation develops therapeutic vaccines that aim to extend and improve the lives of cancer patients. The company has two lead product candidates: PANVAC-VF, currently in a Phase III clinical trial for pancreatic cancer; and PROSTVAC^�-VF currently in a Phase II clinical trial for prostate cancer. The company is applying its technology to develop its vaccine pipeline, including treatments for breast cancer, lung cancer, and the prevention of AIDS. Therion is also developing a vaccine for colon cancer with its strategic partner, Aventis Pasteur, Ltd. Through Therion�s longstanding partnerships with the National Cancer Institute (NCI) and a network of renowned clinical institutions, over 700 patients in more than 30 clinical trials have been treated with Therion�s vaccine candidates. For more information, please visit www.therionbio.com.