Distinct patterns of HIV-specific memory T lymphocytes in HIV-exposed uninfected individuals and in HIV-infected patients

Background: Repeated exposure to HIV is not always associated with infection and multiple cohorts of HIV-exposed but seronegative individuals (ESN) have been described. HIV-specific CD4 and CD8 T lymphocytes are detected both in HIV patients and in ESN; we verified whether different patterns of HIV-specific memory T lymphocytes would be detected in individuals in whom exposure to HIV results or does not result in infection. Methods: Gag-specific T cells were analysed in 15 ESN, 14 HIV patients, and 15 healthy controls using extensive flow cytometry analysis. Results: Data confirmed that gag-specific T lymphocytes are present in ESN. Gag-specific T cells mainly secrete interleukin-2 in ESN and interferon-γ in HIV patients. In addition the CD4/CD8 and the memory/naive ratios are altered, central memory (45RA-/CCR7+) CD4 and CD8 T lymphocytes are more abundant, and terminally differentiated (45RA+/ CCR7- and 27-728-) CD8 T lymphocytes are augmented in ESN individuals. Conclusions: Exposure to HIV occurs in high risk seronegative individuals; the observation that naive cells and CM are skewed in ESN indicate that this exposure is robust enough to modulate the CM/EM ratio. The increase in late effectors and in natural killer cells seen in ESN suggests a role for these cells in preventing actual infection.