Cambridge, MA, July 14, 1997 - The United States Patent and Trademark Office has issued Therion Biologics Corporation two patents broadly protecting the Company's recombinant viral vector technologies for producing AIDS vaccines that incorporate multiple human immunodeficiency virus (HIV) proteins, the Company announced today. The patents cover recombinant viral vectors that express at least two proteins from HIV or related viruses, and are capable of producing virus-like particles resulting from the aggregation of the expressed proteins.

"Research suggests that the pathway to an effective preventive AIDS vaccine involves broadly arming the immune system by presenting it with multiple HIV proteins, or antigens," said Dennis Panicali, Ph.D., President and Chief Executive Officer of Therion Biologics. "The newly issued patents cover this multi-antigen approach using our recombinant pox virus vector technology to generate and present the HIV antigens in a natural form."

Dr. Panicali noted that Therion's first multi-antigen preventive AIDS vaccine, TBC-3B, is currently in Phase I clinical development in collaboration with the National Institute of Allergy and Infectious Diseases (NIAID). TBC-3B is a live recombinant vaccinia virus expressing the major structural and non-structural proteins of HIV, including the matrix, core, nucleocapsid, envelope, reverse transcriptase, integrase, and protease antigens. Therion is actively developing additional multi-antigen AIDS vaccines using its recombinant pox virus vector technology.

The issued patents, U.S. patent numbers 5,614,404 and 5,631,154, cover recombinant viral vectors expressing at least two different proteins from the lentivirus family, which includes HIV and other immunodeficiency viruses. The non-self-propagating virus-like particles produced by aggregation of the expressed proteins are also protected under the patents. Both the recombinant vectors and the HIV-like particles can be used as AIDS vaccines.

To complement the vaccine strategies covered by the issued patents, Therion is also investigating live attenuated HIV vaccines. The Company is pursing this technology in collaboration with its inventor, Dr. Ronald Desrosiers, Professor of Microbiology and Medical Genetics, Harvard Medical School and Director, AIDS Unit, New England Regional Primate Research Center. All of Therion's preventive AIDS vaccines are being developed with the support of the National Institutes of Health.

Therion is also applying its recombinant pox virus vector technology to the development of therapeutic vaccines for cancer immunotherapy. The Company is currently conducting Phase I clinical trials of products for the treatment of colorectal and lung cancers, melanoma and prostate cancer.

Therion Biologics Corporation is engaged in the development of immunotherapeutic products and vaccines for the treatment of major cancers and the prevention of AIDS. Therion is headquartered in Cambridge, Massachusetts.