HIV-1 ENVELOPE-ELICITED NEUTRALIZING ANTIBODY-TITERS CORRELATE WITH PROTECTION AND VIRUS LOAD IN CHIMPANZEES

In an attempt to compare the protective effect of vaccination with two forms of envelope antigens, and to define immunological correlates of protection against HIV infection, chimpanzees were vaccinated with ei ther recombinant gp160 or gp120. Homologous HIV challenge was performe d 3 weeks after the fourth immunization. The animal with the highest l evel of serum neutralizing antibodies (gp160 immunogen) was protected against HIV infection. All other chimpanzees became infected, but disp layed various levels of infected PBMCs. The postchallenge data gave ri se to the following conclusions. (1) protection correlated with the le vel of the serological immune response, but not with the nature of the immunogen (gp120 versus gp160); (2) the virus-neutralizing titre at d ay of challenge col related with protection from infection, (3) the re lative magnitude of the lymphoproliferative T-cell response at day of challenge did not correlate with any protective effect; (4) the peak n umbers of virus-infected PBMCs in vaccinated animals were lower than t hose observed in control animals, and this effect was correlated with the intensity of the antibody response at day of challenge. This raise s the possibility that a beneficial effect of HIV vaccination may be a chieved in a situation where sterile immunity is not consistently obta ined.