Efficacy of vaccines containing rhoptry-associated proteins RAP1 and RAP2 of Plasmodium falciparum in Saimiri boliviensis monkeys

A vaccine trial was conducted with rhoptry-associated proteins 1 and 2 (RAP 1 and RAP2) of Plasmodium falciparum in Saimiri boliviensis monkeys to comp are the ability of parasite-derived (PfRAP1 and 2) and recombinant proteins (rRAP1 and 2) to induce protective immune responses and to find adjuvants suitable for use in humans. Eight groups of 6 monkeys each were immunized w ith parasite-derived or recombinant RAP1 and 2 with Freund's complete adjuv ant (FCA) followed by Freund's incomplete adjuvant (FIA), Montanide ISA720 adjuvant, or CRL1005 adjuvant. Recombinant RAP1 and RAP2 were also administ ered separately, with Montanide ISA720. After 3 immunizations, monkeys were challenged by iv inoculation of 50,000 parasites of the Uganda Pale Alto s train of P. falciparum. Of the animals vaccinated using FCA/FIA, I of 6 con trol monkeys, 3 of 6 immunized with PfRAP1 and 2, and 2 of 6 with rRAP1 and 2 did not require drug treatment. Of the monkeys vaccinated with Montanide ISA720 adjuvant, 0 of the 6 control monkeys, 2 of 6 immunized with RAP1 an d 2, 1 of 6 immunized with rRAP1, and 4 of 6 immunized with RAP2 did not re quire drug treatment. Two of 6 monkeys immunized with PfRAP1 and 2 with CRL 1005 did not require treatment. All groups receiving RAP1, RAP2, or both ha d a significant decrease in initial parasite multiplication rates and there was a significant negative correlation between anti-RAP2 antibody and mult iplication rates. Animals were rechallenged with the homologous parasite 12 6 days after the first challenge. Of the monkeys that did not require drug treatment after the first challenge, none developed detectable parasitemia following rechallenge.