CD8+ T Cells From HLA-B*57 Elite Suppressors Inhibit Replication of HIV-1 Escape Mutants

Background: Elite Controllers or Suppressors (ES) are individuals who maintain undetectable plasma viral loads by standard clinical assays in the absence of antiretroviral therapy. Multiple lines of evidence suggest that the control of viral replication in these patients is due to a strong and specific cytotoxic T lymphocyte (CTL) response. Escape mutations are believed to impair the ability of CD8+ T cells to control HIV-1 replication. Interestingly, viruses isolated from the plasma of ES have been shown to contain several escape mutations; it is not clear how immunologic control is maintained despite this virologic escape. Methodology: Using site-directed mutagenesis, we constructed six NL4-3 based viruses with canonical escape mutations in one to three HLA*B-5703 Gag p24 epitopes. To determine the ability of CD8+ T cells to suppress replication of HIV-1 containing escape mutations, unstimulated CD4+ T cells of seven HLA*B5703+ ES were infected with either wild type or one of the constructed escape mutant variant viruses and cocultured with autologous CD8+ T cells at three target to effector ratios. Effector CD8+ T cells were either used directly ex vivo or first stimulated with peptides corresponding to either wild type or escape variant HLA-B*5703 Gag epitopes to see if this would induce stronger suppression of replication. Intracellular cytokine staining was performed in order to determine the mechanisms involved in the suppression of these escape variants. Results: In this study, we investigated the effect escape mutations within HLA*B-57+ restricted Gag epitopes have on the ability of ES CD8+ T cells to suppress replication of HIV-1 in autologous CD4+ T cells. Unstimulated CD8+ T cells suppressed replication of all six escape mutants at levels that were comparable to the level of suppression of wild type virus. Intracellular cytokine staining revealed low baseline CD8+ T cells responses to wild type and escape variant peptides; however, culture of PBMC with peptides corresponding to either wild type or escape variant HLA-B*57 Gag epitopes for seven days resulted in increased IFN-γ and perforin expression in response to overnight stimulation with either wild type or escape variant peptides. Conclusions: Our data demonstrate that CD8+ T cells from ES are capable of suppressing replication of virus harboring escape mutations in HLA-B*57 restricted Gag epitopes. Additionally, our data suggest that ES CD8+ T cells are capable of generating effective de novo responses to escape mutants. These results may explain why ES are able to control viral replication despite virologic escape.