Cambridge, MA, November 29, 1999 - Therion Biologics Corporation has been awarded three contracts totaling $1.5 million from the NIH's National Institute of Allergy and Infectious Disease (NIAID) for the development and manufacture of novel AIDS vaccines and related research reagents, the company announced today. The two principal agreements cover generation of AIDS vaccines based on MVA, a non-replicating pox virus vector that may offer an improved safety profile for use in healthy individuals. The third contract relates to the production of research reagents for evaluation of specific cell-mediated immune responses in individuals infected with HIV (human immunodeficiency virus) or immunized with candidate HIV vaccines.

"These new NIH contracts reinforce the value of Therion's innovative technology and capitalize on our significant expertise in generating vaccines based on pox virus vectors," said Dennis L. Panicali, Ph.D., President and Chief Executive Officer of Therion. "The agreements also build on the strength of our long-standing relationship with the NIAID. Over the past decade, Therion and our academic collaborators have benefited from strong NIH support for our ongoing AIDS vaccine programs. This latest collaboration demonstrates our continued commitment to advancing the field of AIDS research."

Separate from these agreements, but supported by significant NIAID research funding, Therion is advancing an AIDS vaccine development program that includes TBC-3B, its first multi-antigen vaccine to complete Phase I clinical studies. TBC-3B is a live recombinant vaccinia virus expressing the major structural and non-structural proteins of HIV. Therion is also advancing three additional AIDS vaccine candidates.

Under terms of the NIAID contracts, Therion will develop and manufacture novel, clinical-grade recombinant AIDS vaccines based on the MVA pox virus vector. The Company will generate recombinant MVA-based vaccines that express multiple HIV antigens, manufacture and test sufficient quantities of the vaccines for human Phase I and II clinical trials, and deliver these products to the NIAID for clinical evaluation. In addition, Therion will generate research reagents for use in the evaluation of HIV-infected patients or HIV-vaccinated individuals. These reagents, which will contain recombinant vaccinia viruses expressing individual or multiple proteins from various HIV subtypes, will serve as tools to measure specific immune responses to the expressed HIV antigens.

MVA (Modified Vaccinia Ankara) is one of several pox virus vectors used by Therion for the development of its prophylactic and immunotherapeutic vaccines. Like other pox virus vectors, MVA can simultaneously express multiple foreign antigens and elicit broad immune responses to those antigens, thereby helping the native immune system to fight or prevent disease. MVA is a potent but non-replicating virus that may offer improved safety over replicating viruses currently used in prophylactic vaccine products. The parent MVA vector has already demonstrated a strong safety profile in European studies involving over 120,000 individuals.

Therion Biologics Corporation is engaged in the development of therapeutic vaccines for cancer and preventive vaccines for AIDS. Currently, Therion, in collaboration with the National Cancer Institute, has seven 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 Pasteur M�rieux Connaught for the development of therapeutic colorectal cancer and melanoma vaccines. Therion is headquartered in Cambridge, Massachusetts.