P41.18
Background: HIV-1 protease mediates the cleavage of Gag, Gag-Pol and Nef precursor polyproteins in a highly specific and temporally regulated manner. Because a total of 12 cleavage reactions are required to generate a mature virion, generating focused immune response targeting the sequences surrounding the protease cleavage sites (PCS) could drive viral mutations to its disadvantage. We have conducted a pilot study to investigate the feasibility and effectiveness of a vaccine targeting the sequences around the 12 PCS using Cynomolgus macaques and pathogenic SIVmac239 as a model.
Methods: Twelve recombinant VSVpcs were used to immunize 12 Cynomolgus macaques and nanopackaged PCS peptides were used as a boost. The immunized macaques and 6 controls were repeatedly challenged intrarectally with an increased dosage of SIVmac239. Antibody and T cell responses to the PCS peptides, CD4+ and CD8+ T cell counts and challenge dosage were monitored. 454 Pyrosequencing was conducted to analyze break-through viruses and the amino acid mutations surrounding the PCS sites were correlated with viral load.
Results: Antibody and T cell responses to the 12 PCS protected macaques against higher dosage of SIVmac239 intrarectal challenge (p=0.005, R=0.42). The vaccine group maintained higher CD4+ counts (p=0.0002) than the controls weeks after being infected. Analysis of viral mutations around 12 PCS of 276 samples (14 to 20 sampling points/monkey) detected extensive mutations. These mutations, both conserved and non-conserved amino substitutions around PCS, are correlated with lower viral load (p<0.0001).
Conclusions: Our study with nonhuman primates and pathogenic SIVmac239 as a model showed that a vaccine targeting the sequences surrounding the 12 protease cleavage sites is promising at prevention of HIV-1 infection and disease progression. It demonstrated that the pathogenic SIVmac239 is extremely vulnerable to any amino acid alternations around PCS. Targeting PCS of HIV-1 could be an effective vaccine approach.
