We hypothesized earlier that an effective vaccination strategy against HIV-induced AIDS should focus on priming cell-mediated immunity (CMI) by employing a cocktail of highly conserved epitopes identified to be reactive with multiple MHC haplotypes. Our long-term goal is to formulate a synthetic peptide-based vaccine against HIV because it offers the advantage of being defined, safe and economical. To achieve this goal, we proposed an innovative approach that included employing autologous dendritic cells (DC) for presenting the peptide cocktail and inducing efficient CMI responses for control of infection and pathology by SHIV in a rhesus monkey model. The vaccine consisted of a mixture of six synthetic peptides corresponding to highly conserved regions in the HIV envelope protein gpl60 that we identified in our previous studies, in a series of animal models (murine, rhesus and chimpanzee) and samples from HIV infected people (including long-term nonprogressors), to be capable of inducing HIV-specific CMI responses. The SHIV-rhesus model is best suited for testing the protective efficacy of the peptide-cocktail because, SHIV, a chimeric virus comprised of HIV envelope and SIV core, induces AIDS-like disease in macaques, and thus provides the best alternative for testing HIV env-based vaccines and therapeutics. Our study design for the innovation HIV vaccine proposal involved immunizing rhesus monkeys initially with the peptides in Freund's adjuvant followed later by infusions of peptide-pulsed autologous DC that resulted in efficient induction of proliferative and CTL responses in the vaccinated animals. Importantly, upon challenge with SHIV KU -2, efficient clearance of virus infected cells in circulation and reduction in plasma infectivity were observed in all the vaccinated animals but not in the controls, despite uniform infection in all the monkeys initially. In one of the control monkeys this coincided with a precipitous drop in CD4+ cells to below 50 in three weeks, and signs of wasting by week 34, typical of AIDS. These results serve as proof of the principle for a peptide-based vaccine against HIV. Now, we propose to use the same six-peptide cocktail as a vaccine in combination with autologous DC, as sole adjuvant, for priming protective immunity in the SHIV-rhesus model. Additionally, we propose to adopt the SHIV-rhesus model to test the immunogenicity and efficacy of the six-conserved HIV env peptide cocktail for mucosal vaccination strategies employing adjuvants based on novel bacterial toxins that are modified to eliminate toxicity but retain adjuvant capacity. We obtained pilot data showing the effectiveness of mutated forms of cholera toxin and a hitherto untested cytotoxic enterotoxin from Aeromonos hydrophila, as model mucosal adjuvants for inducing HIV env-specific Th and CTL responses in mice. Finally, we propose to formulate a DNA vaccine, consisting of a cocktail of plasmids with mini-gene constructs encoding the six conserved HIV env peptides, and test immunogenicity and protective efficacy in the SHIV-rhesus model.
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