Prospects for an AIDS vaccine.

The development of a vaccine against HIV meets with considerable difficulties. The virus shows considerable genetic variability. Neutralizing antibodies raised against one HIV-1 isolate do not cross-neutralize other HIV-1 isolates. HIV can also spread directly from cell to cell without entering extracellular fluids, thus escaping neutralization. It can remain latent in the body for long periods of time, probably as an integrated provirus in the genome of the host cell. Moreover, the HIV envelope glycoprotein appears to be poorly immunogenic for primates. It elicits only weak neutralizing antiviral antibody titers, perhaps due to epitopic suppression. Preliminary data suggest, however, that neutralizing antibodies might be protective, and there is evidence from work with SIV that certain types of vaccines might induce protection against infection. These findings foster the hope that it will eventually be possible to develop a HIV vaccine.