This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Natural transmission of HIV occurs through mucosal surfaces at low efficiency, but few SIV vaccine studies have examined protective immunity under conditions designed to model these conditions. We investigated the efficacy of a multigenic DNA/MVA prime/boost vaccination regimen to induce mucosal immune responses to SIV and protect against repeated low-dose vaginal SIV challenge. DNA/MVA immunization induced vigorous IFN-gamma ELISPOT responses to Gag, Env and Nef, with Gag-specific spot forming cells (SFC) that exceeded 3500 SFCs/10 to the 6th PBMC 2 weeks after the MVA boost. Gag181-189 tetramer-binding cells in DNA/MVA vaccinees were detected in vaginal and rectal biopsies at similar frequencies to those observed in peripheral blood 2 weeks after the MVA boost. The DNA/MVA prime boost regimen resulted in a significant reduction in viremia after challenge. Control of viremia in DNA/MVA vaccinated animals was associated with significant anamnestic SIV-specific CD8-positive T cell responses, with peak values of A*01/Gag181-189 tetramer-binding CD8-positive T cells ranging from 10.6 percent to 36 percent, compared to 1.8 percent plus or minus 1.2 percent in controls. Improved control of viremia was observed in both A*01-positive and A*01- vaccines with preservation of CD4-positive T cell counts. Our results demonstrate the ability of a multigenic DNA/MVA prime/boost vaccine to induce CD8-positive T cell responses in rectal and vaginal tissues and provide substantial reduction in viremia after repeated low dose vaginal challenge.
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