RESISTANCE OF CHIMPANZEES IMMUNIZED WITH RECOMBINANT GP120(SF2) TO CHALLENGE BY HIV-1(SF2)

Objective: To determine whether vaccination with recombinant HIV-1(SF2 ) gp120 in a novel oil-in-water adjuvant emulsion, MF59, protects chim panzees against challenge with HIV-1(SF2), the homologous virus isolat e. Methods: Two vaccinated chimpanzees and two control animals were ch allenged with 25-50 animal infectious doses of a stock of HIV-1(SF2) t hat had been grown in mitogen-activated human peripheral blood mononuc lear cells (PBMC). The animals were monitored by a series of serologic [enzyme-linked immunosorbent assay (ELISA), Western blot, and neutral ization assays] and virologic [virus culture, RNA and DNA polymerase c hain reaction (PCR)] assays for infection. Results: Both control anima ls showed evidence of seroconversion in ELISA and Western blot assays. In addition, virus was detected in the early, acute phase of infectio n of both control animals by (1) plasma RNA PCR, (2) virus culture, an d (3) PBMC DNA PCR assays. One vaccinated animal showed no serologic o r virologic evidence of infection. The other vaccinated animal has not seroconverted, and there was no evidence of plasma viremia. However, virus was detected at early timepoints in this animal's PBMC, and tran sient lymphoproliferation to HIV-1 proteins not in the vaccine was obs erved. These observations suggest that the former animal was protected from challenge while the latter may have experienced a transient or c urtailed infection. Conclusion: Two types of vaccine-induced protectiv e immune responses were observed when chimpanzees immunized with rgp12 0(SF2) were challenged with the homologous virus isolate: a response c onsistent with the 'sterilizing immune response' documented in the chi mpanzee model in previous studies, as well as one that did not complet ely protect from infection, showing curtailment of the acute phase and a failure of the animal to seroconvert.