HLA-G expressing Tregs inhibit bystander immune activation in HIV-1 infection

T cells expressing the HLA class Ib molecule, HLA-G, represent an emerging non-classical population of regulatory T cells (Tregs). However, the functional role of these cells during HIV-1 infection remains unclear. Here, we performed a comprehensive investigation of HLA-G- expressing Tregs in patients with different rates of HIV-1 disease progression. Using flow cytometry, we found the proportion of HLA-G-expressing CD4 and CD8 T cells were significantly reduced in individuals with progressive HIV-1 infection (p<0.001 for both CD4 and CD8 T cells). Moreover, HLA-G expressing Tregs were inversely correlated with phenotypic markers of immune activation, CD38 and HLA-DR (p=0.026 for CD4 and p<0.005 for CD8 T cells), and positively correlated with CD4 T cell counts. Functional co-culture assays indicated that HLA-G-expressing CD4 and CD8 T cells were able to potently inhibit TCR-independent bystander activation, but only weakly inhibited TCR-dependent cytokine-secretion and proliferative properties of HIV-1-specific T cells. Furthermore, in vitro infection assay suggested HLA-G expressing Treg were more susceptible to HIV-1 infection (p=0.0039). These data indicate an important role of HLA-G+ Tregs for balancing bystander immune activation and anti-viral immune activity in HIV-1 infection, and suggest that the loss of these cells during advanced HIV-1 infection may contribute to immune dysregulation and HIV-1 disease progression.