Cambridge, MA, and Miami, FL, October 31, 2001 - Therion Biologics Corporation today announced that the AACR-NCI-EORTC International Conference is featuring the company's CEA/TRICOM vaccine as a next generation therapeutic for improved treatment of tumors found in a majority of colorectal cancer patients. CEA/TRICOM, a novel product designed to enhance the body's immune response against cancers expressing the CEA tumor antigen, is currently in Phase I trials at Georgetown University's Lombardi Cancer Center. John Marshall, M.D., principal investigator of the study, will present preliminary findings from the CEA/TRICOM trial at the meeting today. The results reflect progress under an existing Cooperative Research and Development Agreement (CRADA) between Therion and Jeffrey Schlom, Ph.D. of the National Cancer Institute's Laboratory of Tumor Immunology and Biology.

CEA/TRICOM is a next generation vaccine designed to build on clinical results presented in May 2001 at the American Society of Clinical Oncology (ASCO) meeting. The ASCO data demonstrated, for the first time, a significant increase in patient survival using a Therion cancer vaccine to generate an immune response that targets specific tumor cells. Like its predecessors, the CEA/TRICOM product utilizes pox virus vectors bearing the CEA tumor antigen to stimulate and sustain (prime and boost) an immune response against tumor cells. Yet CEA/TRICOM also incorporates, in addition to the CEA tumor antigen, three co-stimulatory molecules to further strengthen the immune system's defenses against colorectal, lung and other CEA-bearing cancers.

"There is a growing appreciation for the promise of cancer vaccines to safely and significantly enhance patient survival," stated Dr. John Marshall, Associate Professor of Medicine at Georgetown University. "Our previous clinical studies have already shown that by combining the CEA antigen with a vaccine vector, we can generate a strong anti-tumor immune response and, most importantly, increase patient survival. We're now taking this approach one step further with the addition of three key co-stimulatory molecules. This change, we believe, will even more dramatically increase the anti-cancer immune response."

Dr. Marshall added, "Even though we just recently began this Phase I trial of CEA/TRICOM, the strong safety profiles and early encouraging response that we've seen to date give us reason to continue evaluating this product. Our next steps will include collection and assessment of immunological data and clinical effects of the CEA/TRICOM vaccine."

"We believe TRICOM to be a powerful and exciting tool to optimize antigen presentation and activation of the immune system," said Dennis Panicali, Ph.D., President and Chief Executive Officer of Therion Biologics. "We therefore are exploring ways to incorporate TRICOM as a key component of Therion's product development programs including prostate, colorectal, and breast cancer and melanoma." Dr. Panicali added, "We look forward to our continued work with Dr. Marshall and the NCI in additional clinical studies designed to evaluate CEA/TRICOM's ability to combat the recurrence of colorectal cancer in early-stage patients. We will also continue our studies in late-stage cancer patients to ensure consistent therapeutic effects of CEA/TRICOM in this population."

CEA/TRICOM Study Design and Preliminary Clinical Data
The Phase I trial is a multi-stage, dose escalation study that will assess the safety and immunologic effect of CEA/TRICOM in up to 42 patients who have advanced metastatic colorectal cancer or CEA-bearing tumors. Subjects will receive rF-CEA/TRICOM alone, rV-CEA/TRICOM followed by booster vaccinations with rF-CEA/TRICOM, or rV-CEA/TRICOM followed by rF-CEA/TRICOM. A subset of patients in the last group will also receive GM-CSF adjuvant. The primary measure of immune response will be the level of CEA-specific T-cells stimulated by vaccination, with effect on levels of CEA-expressing tumor cells in the blood used as a potential secondary measure of response.

Preliminary human clinical results show CEA/TRICOM to be safe and well tolerated in all patients tested to date. In addition, Georgetown researchers have observed clinical activity in at least one patient. The patient's PET scan showed complete clearance of metastatic tumors previously found throughout the upper chest; furthermore, the patient has remained stable for over nine months. The Phase I trial of CEA/TRICOM is nearing 50% enrollment. Georgetown researchers are looking ahead to more advanced studies evaluating the vaccine's efficacy and impact on patient survival.

Background on Colorectal Cancer
According to the American Cancer Society, colorectal cancer is the third most common cause of cancer death in the U.S., with an estimated 130,000 new cases and 60,000 deaths each year. Although 40 percent of colorectal cancer patients can be effectively treated with surgery and radiation when tumors are detected early, nearly 60 percent of those afflicted will be diagnosed with or progress to develop metastatic cancer. In patients with colorectal cancers that have spread regionally to involve adjacent organs or lymph nodes, the five-year relative survival rate is around 65 percent. Current standard treatments for colorectal cancer include surgery, chemotherapy and radiation.

Therion Biologics
Therion Biologics Corporation is focused on the development of therapeutic vaccines for cancer and preventive vaccines for AIDS. Therion's most advanced product, PROSTVAC-VF, is currently in Phase II studies for prostate cancer. Under the terms of a strategic collaboration with Aventis Pasteur, a second product, ALVAC-CEA/B7.1, will move into pivotal clinical trials in the next two years for colorectal cancer. The company also has a broad pipeline of vaccines in early clinical development for treatment of major cancers, including breast cancer, melanoma and other solid tumors. In addition to Aventis, Therion's partners include the National Cancer Institute and a network of leading clinical institutions around the world. Therion is headquartered in Cambridge, Massachusetts.