ADSORPTION TO ALUMINUM HYDROXIDE PROMOTES THE ACTIVITY OF IL-12 AS ANADJUVANT FOR ANTIBODY AS WELL AS TYPE-1 CYTOKINE RESPONSES TO HIV-1 GP120

A series of protocols were tested to examine the adjuvant effects of I L-12 on humoral and type 1 cytokine responses elicited in mice by reco mbinant gp120 envelope protein from HIV-1. This Ag fails to induce det ectable Ab responses when administered s.c. alone, but stimulates low Ab levels when combined with aluminum hydroxide (alum), Moreover, when i.p. injected rIL-12 was included in the immunization, no increase in Ab production was observed, Importantly, optimal gp120 Ab responses w ere achieved by immunizing mice s.c. with gp120 and rlL-12 simultaneou sly coadsorbed to alum, These animals displayed a highly polarized, ty pe 1 cytokine profile, with the emergence of anti-gp120 Ig belonging t o the lgG2 and lgG3 isotypes, In addition, a major increase occurred i n Ab of the IgG1 subclass. The superior adjuvant activity of alum-adso rbed IL-12 compared with that of the free cytokine correlated with the prolonged detection of IFN-gamma in the sera of animals immunized usi ng the former procedure, In related experiments, in vitro neutralizati on of IL-12 was shown to inhibit IFN-gamma production by spleen cells from mice immunized with gp120 plus alum, but not by splenocytes from mice primed in the presence of IL-12, suggesting that the latter proto col induces a stable type 1 phenotype. These studies demonstrate that presentation of IL-12 on alum enhances its immunomodulatory effects an d establish a protocol for the use of the cytokine as an adjuvant for simultaneously promoting both humoral Ab and type 1 cytokine responses .