Cambridge, MA, December 15, 2003 � Therion Biologics Corporation today announced it has licensed from Biogen Idec Inc. (NASDAQ/BIIB) patent rights relating to Lymphocyte Function Associated Antigen-3 (LFA-3). LFA-3 is a component of TRICOM�, Therion�s co-stimulatory system for optimizing immune response against tumor cells. TRICOM is an integral component of Therion�s proprietary lead cancer vaccine candidates, PROSTVAC-VF^� and PANVAC-VF, currently in clinical investigation for the treatment of metastatic prostate cancer and pancreatic cancer, respectively.

"The addition of the LFA-3 patent rights to our intellectual property portfolio strengthens our proprietary position as we advance our lead product candidates, both of which incorporate TRICOM, towards product commercialization," said Mark Leuchtenberger, President and Chief Executive Officer of Therion Biologics. "Therion is delivering on its commercialization strategy, having recently begun a Phase II clinical trial with PROSTVAC-VF in prostate cancer and planning to begin a Phase II trial with PANVAC-VF in pancreatic cancer in early 2004. "Under the terms of this agreement, Therion gains a non-exclusive license under the LFA-3 patent rights to develop, manufacture and commercialize oncology product candidates incorporating the LFA-3 co-stimulatory molecule. In return, Therion will pay Biogen Idec Inc. an upfront licensing fee, as well as milestone payments and royalties based on potential product sales." Financial terms of the agreement were not disclosed.

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

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 collaboration 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 the treatment of colon cancer. Therion is headquartered in Cambridge, Massachusetts.

About Biogen Idec
Biogen Idec creates new standards of care in oncology and immunology. As a global leader in the development, manufacturing, and commercialization of novel therapies, Biogen Idec transforms scientific discoveries into advances in human healthcare. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.