Because HIV is primarily a sexually transmitted disease, any vaccine intended to halt the dissemination of HIV must prevent transmission following sexual contact with an infected individual. The rhesus macaque/SIV animal model has been used to demonstrate vaccine mediated protection against intravenous challenge with SIV. An animal model of heterosexual transmission of HIV has been developed in this animal model system. The objective of this project is to characterize the mucosal immune response in rhesus macaques immunized mucosally and systemically with SIV and SIV subunits combined with the mucosal adjuvants and replicating vectors. If any of the specific strategies produces a strong genital immune response the animals will be vaginally challenged with virulent SIV. The challenge will consist of a single vaginal inoculation with a 100% infectious dose of cell-free SIVmac251. It is important to emphasize that we are the only group that has defined a 100% vaginal infectious dose of cell-free SIVmac. The initial experiments will combine mucosal immunization and systemic boosting with a whole-killed SIV vaccine (in one group of animals) or SIV gp130 subunit preparation (in another group of animals) and the mucosal adjuvants CT or CT-B. This experiment is designed to determine if CT or CTB produces stronger anti-SIV genital immunity and to determine if these adjuvants improve the local immune response to whole-inactivated virus and subunits. Both cellular and humoral immune responses to the vaccine protocols will be assessed in a variety of anatomic sites including: 1) vaginal mucosa and vaginal secretions, 2) genital lymph nodes, 3) mesenteric lymph nodes, 4) peripheral lymph nodes and 5) blood. The immune parameters to be assessed include SIV specific antibody (IgA and IgG), isotype of SIV specific antibody forming cells (ELISPOT), SIV neutralizing activity, presence of SIV-specific CTL and antigen specific T cell proliferation. Samples of cells from all the tissues will be sent to Drs. McGhee and Kiyono at the University of Alabama at Birmingham to determine which T helper cell subsets (Th1 or Th2) the immunization protocols stimulate. If these analyses reveal strong local anti-SIV immunity, vaginal challenge experiments will be undertaken. In subsequent studies, we will test the ability of a number of mucosal vectors and adjuvants to elicit SIV-specific genital immunity. Our group will have live bacterial vectors (Vibrio cholerae and Salmonella expressing SIVenv and gag), recombinant polio virus and SIV antigen (gp130) incorporated into aqueous microspheres available for testing in rhesus macaques. The collaborative immunology group established in this CMIG will provide an efficient mechanism in which to assess the immune response to these vaccines. If successful these studies will provide the basis for vaccine trials designed to prevent the heterosexual transmission of HIV in humans.
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