Where are we now with vaccines against AIDS?

Abstract

Extensive studies in experimental animal models and phase I and II clinical trials in humans provide some grounds for optimism about developing a vaccine for AIDS. Over 200 monkeys have been protected by simple inactivated vaccines against infection with a lethal challenge dose of simian immunodeficiency virus (SIV). Passive transfer of the antibody to SIV has been shown to prevent infection. Recent vaccination with attenuated, live SIV protected against a challenge with 1000 monkey infectious doses of virus. Studies in chimpanzees have been limited to the unrepresentative IIIB strain of HIV-1. Purified recombinant envelope protein either as the gp 120 surface unit or as the entire gp 160 protein has protected a proportion of chimpanzees against infection. Several experimental immunogens have been tested in phase I and II clinical trials in human volunteers. 5 different recombinant HIV envelope subunits, live recombinant vaccinia virus expressing HIV envelope, and synthetic peptides or virus-like particles derived from yeast, but expressing HIV core proteins, have been used for vaccines that have proved safe. However, large quantities of the subunit HIV antigens are required, and the humoral immune responses are short-lived. Trials with the live recombinant vaccinia virus expressing HIV envelope represent the first use of live recombinant virus in humans. Further studies are under way in France with an avian poxvirus vector, which is host restricted and therefore potentially safer. STudies with combinations of live recombinant virus vaccines followed by immunization with purified subunits indicate that this approach may stimulate both cellular immunity and neutralizing antibodies at higher concentrations than previously observed. The WHO has identified sites in Brazil, Rwanda, Thailand, and Uganda for large scale trials of the efficacy of AIDS vaccines that will probably begin within 5 years.