DEVELOPMENT OF A SINGLE-SHOT SUBUNIT VACCINE FOR HIV-1 .3. EFFECT OF ADJUVANT AND IMMUNIZATION SCHEDULE ON THE DURATION OF THE HUMORAL IMMUNE-RESPONSE TO RECOMBINANT MN GP120

HIV-1 prophylaxis may require ''sterilizing immunity'' (i.e., the prev ention of infection), and this is likely to demand a vaccine that give s high, long-lasting antibody titers. Although it is known that vaccin e adjuvants and immunization schedule affect the magnitude of the immu ne response, there are few reports on antibody decay rates and persist ence. Guinea pigs were immunized with recombinant gp120 using differen t adjuvants and immunization schedules, and the anti-gp120 and HIV-1 n eutralization titers were determined over time following the last boos ter immunization. As observed previously in the literature, a longer t ime between boosting gave higher titers, with a slight increase in the decay half-life as the booster was spaced farther out from the primar y immunization. The decay rate of the antibody titers showed surprisin gly little effect of adjuvant, except for sustained-release polymer-ba sed formulations. Adjuvants that gave high titers initially after boos ting showed the greatest persistence of antibody titers (persistence d efined as the residual titers at long times). These data show that hig h, long-lasting titers may be achieved by using sustained-release form ulations, and these are likely the prime vaccine candidates for prophy laxis requiring prolonged sterilizing immunity.