BACKGROUNDStudies of highly exposed persistently seronegative (HEPS) individuals may provide valuable information on mechanisms of protection and on vaccine design. Cellular immune responses play a critical role in containing human immunodeficiency virus. However, the cellular immune responses in HEPS individuals have not been thoroughly assessed at the entire viral genome level.

METHODSTen HEPS Chinese with a history of frequent penetrative vaginal intercourse (mean frequency, at least once a week), with some unprotected sexual contact occurring in the weeks or days immediately before enrollment, 25 HIV-1 seropositive individuals, 10 HIV-1-seronegative healthy individuals with low-risk sexual behavior and no history suggestive of exposure to HIV-1 infection were enrolled. HIV-1-specific T cell responses were comprehensively analyzed by an interferon-gamma Elispot assay against 770 overlapping peptides spanning all HIV-1 proteins.

RESULTSHIV-1-specific T-cell responses of interferon-gamma secretion were identified in 3 (30%) out of 10 HEPS individuals; the specific cytotoxic T lymphocytes were targeted at Pol (2/10), Env (2/10), and Tat (1/10). HIV-1-specific T-cell responses of interferon-gamma secretion were identified in 20 (80%) out of 25 seropositive intravenous drug users (IDUs), revealing that all HIV-1 proteins and protein subunits could serve as targets for HIV-1-specific CD8(+) T cell responses with 85% recognizing Gag, 80% recognizing Nef, 75% recognizing Pol, 60% recognizing Env, 55% recognizing Vpu, 45% recognizing Vpr, 20% recognizing Vif, 20% recognizing Tat and 15% recognizing Rev in these seropositive individuals. None of the seronegative healthy individuals gave the positive T-cell responses.

CONCLUSIONSAbout 30% of HEPS Chinese mounted HIV-1 specific T cell immune responses. Cell-mediated immunity against HIV-1 may be developed through non-productive infections.