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VIRXSYS PUBLISHES RESULTS OF GENE THERAPY STUDY

November 8, 2006

VIRxSYS has announced the publication of results from its Phase I, open-label, non-randomized clinical trial evaluating VRX496, a gene-based immunotherapy for the treatment of HIV. Results of the trial, conducted at the University of Pennsylvania School of Medicine, were published in the Proceedings of the National Academy of Sciences. The trial evaluated the safety and tolerability of VRX496, enrolling five subjects with chronic HIV infection who had failed to respond to at least two antiretroviral (ARV) drug regimens. Each of the five patients who tolerated the gene therapy treatment experienced decreases in viral load and stable or increased CD4 T-cell counts.

VRX496 is the first application of VIRxSYS' lentiviral vector platform. It is the first, and continues to be the only, lentiviral vector currently in human clinical trials approved by the FDA. The backbone of VRX496 is an HIV-based lentiviral vector from which the disease-causing aspects of the virus have been removed, leaving behind an efficient gene-delivery vehicle. VIRxSYS then equips the vector with a long antisense sequence against the HIV envelope protein to create VRX496. Preclinical studies indicated that HIV is unable to mutate around the antisense therapy, so the virus is unable to form resistant strains in treated patients. VRX496 is transduced into a patient's own CD4 T-cells to block HIV replication.

The Phase I trial demonstrated that a single intravenous infusion of autologous CD4 T-cells genetically modified with VRX496 was safe and well-tolerated. All patients had stable or decreased viral load, with three of the five patients exhibiting clinically significant reductions in viral load without changes in their ARV treatment at six months after the infusion. Four of the five patients had stable or increased CD4 T-cell counts. In addition, all five patients had stable or increased immune response to HIV antigens and other pathogens. Patients will have follow-up safety visits every year for 15 years.