Immune responses of at-risk but HIV-free women

An ideal AIDS vaccine might be one that stimulates the cellular immune system so efficiently that, despite repeat-ed exposure to the virus, an individual never shows signs of viremia or even seroconverts against HIV epitopes. It is still far from clear how to provide anyone this level of pro-tection, but accumulating data from a cohort of at-risk women � sex workers in the AIDS-ravaged community of Nairobi � hint at some of the properties of an immune system that can apparently repel the virus despite ongoing exposure. Kaul et al. have followed this group for some years, and they have found that persistently seronegative women seem to be protected by a vigorous T cell�mediated response to infected cells, while those who have seroconverted eventually succumb to the dis-ease. These authors now report on the HIV epitopes rec-ognized by cytotoxic T lymphocytes from presympto-matic but seropositive women and from persistently seronegative women. The authors previously identified several class I MHC alleles that are associated with this protected status, suggesting a genetic basis for the differ-ence in disease progression. Following up on this work, they now show that the protective alleles present a dis-tinct set of HIV epitopes in the two groups of women. Those epitopes that are exclusively or preferentially rec-ognized in persistently seronegative women could pro-vide the basis of a vaccine that can activate T-cell respons-es that block progression of the disease.