Evidence for Gag p24-specific CD4 T cells with reduced susceptibility to R5 HIV-1 infection in a UK cohort of HIV-exposed-seronegative subjects

Aim: To characterize HIV-1 Gag p24-specific CD4 cell responses in HIV-exposed-seronegative (ES) individuals. Methodology: Twelve ES individuals, of diverse ethnicity and wild type for the CCR5 Δ-32 mutation, were identified. Controls were HIV-negative blood donors. Gag p24-specific and total Vβ+ CD4 cells that expressed MIP-1β, IFN-γ and IL-2 were enumerated by intracytoplasmic cytokine staining. β-Chemokine expression was correlated with susceptibility to R5 HIV-1 infection, as measured by polymerase chain reaction for integrated HIV-1 and by p24 enzyme-linked immunosorbent assay. Results: Similar numbers of mitogen-stimulated and Vβ+ MIP-1β+, IFN-γ+ and IL-2+ T cells were found in ES and HIV-negative control subjects. However, all ES subjects tested had an HIV Gag p24-specific MIP-1β+, IFN-γ+ and IL-2+ CD4 T-cell response that was rare in controls. p24-Specific cells of all ES but no control subjects could be expanded by in-vitro Ag/IL-2 stimulation, and when re-stimulated with an overlapping peptide series showed evidence of a broad CD4 cell memory response directed against multiple regions of Gag p24. Mitogen-stimulated ES CD4 cells were as susceptible to HIV infection as those from control subjects, but p24-specific IFN-γ+ CD4 cells of six out of seven ES subjects tested were less susceptible to R5 HIV-1 infection than the counterpart fraction depleted of p24-specific IFN-γ+ cells. The addition of blocking anti-β-chemokine antibodies did not promote R5 HIV-1 infection of p24-specific IFN-γ+ cells. Conclusion: Specific CD4 cell immunity, characterized by a broadly directed memory Gag-p24 CD4 cell response and reduced susceptibility of specific CD4 cells to R5 HIV-1 infection, is a likely correlate of non-transmission. © 2003 Lippincott Williams & Wilkins.