Phase 2 HIV Vaccine Trials Using Vical's Technology Produce Encouraging Results

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HIV Vaccine Trials

Results from a series of HIV vaccine Phase 2a clinical trials, using a plasmid DNA (pDNA) vaccine developed by the NIHVaccine Research Center and manufactured by Vical, reinforced previously reported Phase 1 conclusions that a "DNA prime-adenoviral vector boost" vaccine regimen was safe and well-tolerated, and was effective in inducing T-cell immune responses in up to 70% of the vaccine recipients.

"These recent vaccine trials contribute to the growing body of knowledge demonstrating plasmid DNA priming as a key factor in achieving significant immune responses against HIV, a particularly difficult target pathogen, bringing us one step closer to evaluating the effectiveness of a prime-boost HIV vaccine regimen in a prophylactic setting," said Vijay B. Samant, Vical's President and Chief Executive Officer. "The latest International AIDS Vaccine Initiative (IAVI) listing of ongoing preventive HIV vaccine clinical trials shows that more than half use pDNA either alone or in combination with other vaccine modalities. We are very pleased that DNA technology is an integral part of the effort to address this high priority global health problem."

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The trials involved priming an immune response with three doses of a pDNA vaccine over a two month period, based on Vical's proprietary DNA technology, and boosting the response with a single dose of adenoviral vector vaccine at six months. The three trials, collectively known as TRIAD, were conducted by the National Institute of Allergy and Infectious Diseases (NIAID) HIV Trials Vaccine Network (HVTN), the IAVI, and the U.S. Military HIV Research Program (USMHRP). Richard Koup, M.D., Chief of Immunology at the Dale and Betty Bumpers Vaccine Research Center (VRC), NIAID, National Institutes of Health (NIH), highlighted TRIAD summary results and conclusions in an oral presentation, "Update on safety and immunogenicity of VRC products," at the AIDS Vaccine 2007 conference (Seattle - August 20-23).

About the Vaccine

The "prime-boost" strategy uses two vaccine components given at different times. Both contain synthetic versions of genes encoding three HIV proteins: gag, pol and env. The DNA component also includes a gene encoding a fourth protein, nef. The gag, pol and nef genes come from HIV subtype B, the primary virus found in Europe and North America. The env gene encodes an HIV coat protein that allows the virus to recognize and attach to human cells. The vaccine incorporates modified env genes from subtypes A and C, most common in Africa and parts of Asia, as well as subtype B. These three subtypes collectively represent about 85 percent of HIV infections worldwide.

The two vaccine components differ in how the genes are packaged. The pDNA component contains only the specific gene sequences in a pDNA ring, and cannot reconstitute into an infectious virus. The adenoviral vector component uses a replication-defective adenoviral vector to shuttle the same non-infectious gene sequences into the body. The pDNA vaccine used in the trials was developed by VRC scientists and was manufactured by Vical. The adenoviral vector vaccine was developed by VRC in collaboration with GenVec Inc., of Gaithersburg, Md., which also manufactured the adenoviral vector vaccine.

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