Pox virus vectors Therion believes that success with active immunotherapy is most likely to be achieved using recombinant viral vectors � viruses genetically engineered to express one or more antigens or co-stimulatory molecules. A number of viral vectors have been developed, including adenovirus, retrovirus, herpes virus and pox virus vectors. Pox viruses are relatively large in size, providing capacity to insert multiple genes, associated with specific cancers, as well as other molecules that stimulate components of the immune system. Advantages of pox virus vectors include: Established safety profile and well tolerated in patients Applicable for broad patient population Capable of eliciting strong cellular immune responses Capable of simultaneously expressing several tumor antigens and co-stimulatory molecules Flexible engineering, responsive to new discoveries Therion's Approach Page Technology Platform Pox Virus Vectors Tumor Specific Antigens Therion optimizes its immunotherapies by employing elements of traditional vaccine strategies and modern genetic engineering techniques designed to create viral vectors that are highly recognizable to the immune system. Specifically, the Company�s products utilize priming and boosting components to stimulate and sustain a strong, cancer-targeted immune response. A proprietary, attenuated strain of vaccinia (similar to the viral vaccine used to eradicate small pox) is administered as the priming dose to establish strong immune recognition and targeting of the tumor. The priming dose is followed by a series of booster vaccines that utilize a fowl pox vector to maintain the strength and specificity of the immune response against the targeted cancer. Based on extensive preclinical and clinical results, Therion believes that pox virus vectors are best suited for use in an active immunotherapy strategy. Therion�s Phase II prime/boost trial data was presented at the 2002 American Society of Clinical Oncology (ASCO) conference, demonstrating that PROSTVAC-VF�, one of Therion�s most advanced clinical candidates, stabilized clinical progression as measured by PSA levels in prostate cancer patients. Click here to read the abstract, "Prime/boost vaccination using poxviruses expressing PSA in D0 prostate cancer: preliminary results of ECOG 7897, a randomized phase II clinical trial." Copyright © Therion Biologics Corporation.