The search for protection against HIV infection.

More than 25 years after the recognition of AIDS and the isolation of the causative agent, human immunodeficiency virus (HIV), we have been unable to develop a vaccine to protect against infection. The major obstacle to development of a vaccine has been the absence of naturally acquired protective immunity, which is characteristic of most infectious agents. We and others, however, have identified individuals who appear to be resistant to infection. Using a combination of epidemiology, molecular biology, and genetics, we hypothesize that these individuals are able to resist infection by clearing low doses of HIV from their systems. We further hypothesize that they are able to clear the virus through a highly efficient system of processing and presentation of HIV epitopes (antigens) to CD8+ cytotoxic cells, which activate them to remove virally infected cells. Subsequent studies have lent support to this hypothesis.