EFFICACY OF GLYCAN-MODIFIED ENV VACCINES AGAINST HETEROLOGOUS SHIV CHALLENGE

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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. We previously showed that immunization of pig-tailed macaques with the N7 Env, which had a N-linked glycan at amino acid residue 197 removed, resulted in enhanced neutralizing antibody (NAb) response not only against the homologous virus, 89.6, but also HIV-1 SF162 and a standard panel of subtype B primary isolates. In this study, we aimed to extend these studies to evaluate the protective efficacy of N7 Env vaccines against a heterologous CCR5 virus challenge. We immunized three groups of pig-tailed macaques (N=6/group) with a "prime-boost" regimen, consisting of priming with recombinant vaccinia virus and boosting with recombinant proteins. Two of these groups were immunized with either wild-type or mutant N7 Env vaccines. An additional group of animals received both N7 Env and SIV Gag-Pol vaccines. Control animals received parental vaccinia virus and adjuvant only. All animals generated lentivirus-specific antibody responses, including NAb against the heterologous virus SF162, albeit at 5- to10-fold less than what we observed in the first study described above. This prompted us to administer an additional booster immunization. However, no increase in NAb titer was observed, consistent with the notion that the magnitude of response was determined largely by the effectiveness of the primary immunization. After challenge with an intrarectal inoculation of SHIV162P4, all control and immunized animals were infected, consistent with the low titer of Nab titer at the day of challenge. However, animals immunized with the N7 Env showed significant reduction of peak viral load and those received both N7 Env and SIV Gag-Pol vaccines showed reduction of setpoint viral loads. These results indicate that protective immunity against a heterologous virus can be generated by the prime boost immunization regimen. However, the immunogen and immunization regimen, especially the efficacy of the primary immunization, need further improvements.