Summary CD8+ T cells contribute to the control of HIV, but it is not clear whether initial immune responses modulate the viral set point. We screened high-risk uninfected women twice a week for plasma HIV RNA and identified twelve hyperacute infections. Onset of viremia elicited a massive HIV-specific CD8+ T cell response, with limited bystander activation of non-HIV memory CD8+ T cells. HIV-specific CD8+ T cells secreted little interferon-γ, underwent rapid apoptosis and failed to upregulate the interleukin 7 receptor, known to be important for T cell survival. The rapidity to peak CD8+ T cell activation and the absolute magnitude of activation induced by the exponential rise in viremia were inversely correlated with set point viremia. These data indicate that rapid, high magnitude HIV-induced CD8+ T cell responses are crucial for subsequent immune control of acute infection, which has important implications for HIV vaccine design.

Immune control of viral infections is heavily dependent on helper CD4 T cell function. However, the understanding of the contribution of HIV-specific CD4 T cell responses to immune protection against HIV-1, particularly in clade C infection, remains incomplete. Recently, major histocompatibility complex (MHC) class II tetramers have emerged as a powerful tool for interrogating antigen-specific CD4 T cells without relying on effector functions. Here, we defined the MHC class II alleles for immunodominant Gag CD4 T cell epitopes in clade C virus infection, constructed MHC class II tetramers, and then used these to define the magnitude, function, and relation to the viral load of HIV-specific CD4 T cell responses in a cohort of untreated HIV clade C-infected persons. We observed significantly higher frequencies of MHC class II tetramer-positive CD4 T cells in HIV controllers than progressors ( = 0.0001), and these expanded Gag-specific CD4 T cells in HIV controllers showed higher levels of expression of the cytolytic proteins granzymes A and B. Importantly, targeting of the immunodominant Gag41 peptide in the context of HLA class II DRB1*1101 was associated with HIV control ( = -0.5, = 0.02). These data identify an association between HIV-specific CD4 T cell targeting of immunodominant Gag epitopes and immune control, particularly the contribution of a single class II MHC-peptide complex to the immune response against HIV-1 infection. Furthermore, these results highlight the advantage of the use of class II tetramers in evaluating HIV-specific CD4 T cell responses in natural infections. Increasing evidence suggests that virus-specific CD4 T cells contribute to the immune-mediated control of clade B HIV-1 infection, yet there remains a relative paucity of data regarding the role of HIV-specific CD4 T cells in shaping adaptive immune responses in individuals infected with clade C, which is responsible for the majority of HIV infections worldwide. Understanding the contribution of HIV-specific CD4 T cell responses in clade C infection is particularly important for developing vaccines that would be efficacious in sub-Saharan Africa, where clade C infection is dominant. Here, we employed MHC class II tetramers designed to immunodominant Gag epitopes and used them to characterize CD4 T cell responses in HIV-1 clade C infection. Our results demonstrate an association between the frequency of HIV-specific CD4 T cell responses targeting an immunodominant DRB1*11-Gag41 complex and HIV control, highlighting the important contribution of a single class II MHC-peptide complex to the immune response against HIV-1 infections.

No abstract