Characterization of viral envelopes and cytokine responses among rhesus macaques immunized with vesicular stomatitis virus-based simian immunodeficiency virus (SIV) vaccines and challenged with pathogenic SIV

Precise identification of the transmitted/founder virus envelope sequences responsible for infection is critical for understanding the viral transmission and designing effective vaccines. Single Genome Amplification (SGA) was utilized to identify unambiguously the transmitted viruses. In the SGA technique, viral RNA is isolated from plasma; cDNA is made and amplified by nested PCR. The amplicons showing <30% of the total number of reactions (representing single virus particle as per Poisson distribution) were sequenced and further analyzed using phylogenetic tools. In the current study, vaccinated and immunized macaques were challenged intra-rectally (IR) with 4000 TCID50 of SIVsmE660. The macaques were primed and boosted with VSV (vesicular stomatitis virus) expressing SIVsmE660 Gag, Env proteins (Group I), VSV expressing SIVsmE660 Gag, Env proteins and GM-CSF (Group II) or with VSV expressing an influenza HA (hemagglutinin) protein (Group III) as the control group. After priming with the VSV vaccine vectors, the macaques were boosted with VSV/SFV (Semiliki Forest virus) replicon particles expressing SIVsm E660 Env and Gag proteins. Four of the six animals in the VSV-Gag-Env immunized group were protected from infection while 2 had a transient viral load. Only1/6 was protected from infection among VSV-GM-CSF-Gag-Env immunized animals suggesting that GM-CSF abrogated protection. All animals from the irrelevant antigen vaccinated group showed high viral loads. We first characterized the challenge SIVsmE660 stock virus. In total, 58 full-length Env clones were analyzed and the diversity of the stock was calculated as 1.4%. We obtained full-length envelope sequences from each animal that belongs to Group I (2/2) Group II (4/6) and Group III (6/6). Our preliminary data suggests that few founder viruses (1 founder lineage) were found in the protected animals from Group I as compared to 1 or more founder lineages in Group II / III animals. We also analyzed the cytokines from the plasma of the above vaccinated and challenged macaques pre and post-challenge using non-human primate 23-plex cytokine assay kit. Among the animals that were infected and had high viral loads exhibited elevated levels of IFN-gamma, TNF-alpha, MCP-1 and IL-18.