CD4+ T cell–mediated HLA class II cross-restriction in HIV controllers

The structural basis of HIV-Gag recognition by class II–restricted T cell receptors in spontaneous controllers. Spontaneous HIV controllers A small number of HIV-infected individuals (<1%) can spontaneously control HIV in the absence of antiretroviral therapy. Because CD4+ and CD8+ T cell responses are thought to contribute to protection, HIV-responsive T cell receptors (TCRs) from these individuals are of considerable interest. Galperin et al. have examined how three public class II–restricted TCRs—F24, F25, and F5—documented in spontaneous controllers are capable of binding a Gag peptide, Gag 293–312, in the context of multiple HLA-DR molecules. By solving the structures of multiple TCR–peptide–HLA-DR complexes, the authors report that the ability of these TCRs to recognize this Gag peptide in the context of multiple HLA-DR allomorphs is shaped by extensive contacts between these TCRs and the peptide itself. Rare individuals, termed HIV controllers, spontaneously control HIV infection by mounting efficient T cell responses against the virus. Protective CD4+ T cell responses from HIV controllers involve high-affinity public T cell receptors (TCRs) recognizing an immunodominant capsid epitope (Gag293) presented by a remarkably broad array of human leukocyte antigen (HLA) class II molecules. Here, we determine the structures of a prototypical public TCR bound to HLA-DR1, HLA-DR11, and HLA-DR15 molecules presenting the Gag293 epitope. TCR recognition was driven by contacts with the Gag293 epitope, a feature that underpinned the extensive HLA cross-restriction. These high-affinity TCRs promoted mature immunological synapse formation and cytotoxic capacity in both CD4+ and CD8+ T cells. The public TCRs suppressed HIV replication in multiple genetic backgrounds ex vivo, emphasizing the functional advantage conferred by broad HLA class II cross-restriction.