Protective immunity induced in Aotus monkeys by a recombinant SERA protein of Plasmodium falciparum: adjuvant effects on induction of protective immunity.

We report the results of vaccination trial 2 of Panamanian Aotus monkeys with a recombinant blood-stage antigen, SERA 1, of the malaria parasite Plasmodium falciparum. Monkeys were immunized with SERA 1, a 262-amino-acid fragment (amino acids 24 to 285) of the 989-amino-acid SERA protein produced by the Honduras 1 strain of the parasite. Immunization mixtures contained 100 micrograms of recombinant SERA 1 protein per dose mixed with one of five different adjuvants. The protein mixed with either Freund's adjuvant or MF75.2 adjuvant stimulated protective immunity. When other P. falciparum antigens were included in the SERA 1-Freund's adjuvant mixture, no protective immunity was observed, although high anti-SERA 1 antibody titers were produced. Three other adjuvants mixed with SERA 1 failed to induce a protective immune response. These results, their relationship to those reported previously in the first vaccination trial (trial 1), and their relationships to the quantitative measurement of anti-SERA 1 antibodies in enzyme-linked immunosorbent assays provided insights into the induction of a protective immune response in vaccinated monkeys.