COMBINED APPROACH TO BROADLY PROTECTIVE AIDS VACCINES: I

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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. Heterologous "prime-boost" immunization has been shown to elicit protective immunity against multiple primate lentiviruses, including SIVmne, SHIVIIIB and SHIV89.6P. However, there have been relatively few studies comparing the protective efficacy of different prime-boost combinations. The goal of this project is to examine "prime-boost" immunization strategies to identify combinations that induce antibody and CD8+ T cell-mediated immune responses against primate lentiviruses. In the first two stages of this study, we compared recombinant vaccinia virus or DNA vaccine for priming, followed by DNA, protein, or alphavirus boosting, for their ability to protect against mucosal challenge with a CCR5-using SHIVSF162 P4. Twenty-four pig-tailed macaques were primed either with recombinant vaccinia viruses expressing HIV-1 SF162 full length env and SIVmac239 gag/pol (Groups 1-3), or DNA plasmids expressing the same antigens (Groups 5-7). After a resting period, six animals per group were boosted twice (3 mos apart) with one of the following immunogens: Groups 1 and 5, DNA plasmids expressing codon-optimized SF162 env gp140, or SIVmac239 gag-pol, formulated in PBS; Groups 2 and 6, protein immunogens SIVmac239 Gag-Pol particles and SF162 Env gp140 protein formulated in MF59; or recombinant viral vectors expressing the same antigens (Group 3 with alpha virus replicons and Group 7 with vaccinia virus recombinants). Control animals received parental vaccinia virus for prime and empty vector or adjuvant only for boost. After the last immunization, animals in all experimental groups generated SIV- and HIV-specific antibody responses. Compared to animals in other experimental groups, animals boosted with proteins (Groups 2 and 6) had significantly higher SIV-specific and HIV-1-specific gp120 antibody titers, including homologous neutralization titers in a pseudotyped virus assay (p lt 0.001). Four weeks after the last immunization, all animals were challenged with 1,800 50% tissue culture infectious dose of SHIVSF162 P4 by intrarectal inoculation. SHIVSF162 P4 infection in pig-tailed macaques was robust, as shown by mean peak plasma viral of gt 10^7 copies/ml and persistent viremia in gt 1/3 of the animals. Significant reduction of mean plasma viral load was observed in all immunization groups (p lt 0.01 for Groups 2 and 6 vs controls; p lt 0.05 for all other groups). We also observed a significant inverse correlation (Spearman's r = -0.819, p lt 0.0001) between homologous neutralizing antibody (NtAb) titer on day of challenge and peak plasma viral load after challenge, consistent with the role of NtAb to protect against infection. T-cell responses as measured by HIV-specific interferon-gamma and TNF-alpha secreting cells in flow cytometric analysis were weak or undetectable before challenge. Together, these results indicate that protective immunity against mucosal infection with a CCR5-using primate lentivirus can be elicited by systemic prime-boost immunization and that boosting with protein immunogens appears to be superior than DNA or viral vectors in recombinant vaccinia virus or DNA primed animals in the generation of antigen-specific antibody responses.