Molecular characterization of high avidity CD4+ T cells in HIV Controllers

Background: HIV Controllers spontaneously control HIV replication to levels undetectable by standard assays in the absence of antiretroviral treatment. We previously reported that HIV Controllers harbour a pool of memory CD4+ T cells able to respond to the immunodominant Gag293 peptide with particularly high TCR avidity. We set to functionally analyze high avidity CD4+ T cells and to characterize their TCRs at the molecular level. Methods: HIV Controllers from the ANRS CODEX CO21 cohort (n=8) were compared to efficiently treated patients (HAART group, n=8). Primary CD4+ T cell lines were generated by stimulating PBMCs with decreasing doses of Gag293 peptide. Next, Gag293-specific CD4+ T cells were analyzed for cytokine production by IFNγ ELISPOT and for Gag293/MHC-classII tetramer binding ability. TCR diversity in sorted Gag293/Tetramer+ cells was evaluated by immunoscope analysis. Results: Stimulation with low Gag293 peptide doses generated IFNγ-positive CD4+ T cell lines in HIV Controllers (response rate: 6/8 at 10-9M, 2/8 at 10-11M), but not in HAART patients, confirming the presence of high-avidity Gag-293-specific cells in the HIC group. The immunoscope analysis revealed major amplifications of certain TCR Vα and Vβ chains in the sorted tetramer+ Gag293-specific population, indicating the presence of dominant clonotypes. Conclusion: We identified a number of TCR Vα and Vβ chains preferentially expressed by the high-avidity population of Gag293-specific CD4+ T cells. Transfer of these TCRs to heterologous cells will help determine whether they are sufficient to confer the efficient Gag-specific responses characteristic of HIV Controllers.