Testing of Plasmodium vivax CS proteins in Saimiri monkeys

Recombinant proteins directed against the circumsporozoite (CS) protein of Plasmodium vivax were tested for safety, immunogenicity, and efficacy in Saimiri sciureus boliviensis monkeys. The monkeys were immunized 3 times with either alum or muramyl tripeptide as adjuvant, and were challenged with 10,000 sporozoites (P. vivax, Salvador I strain) from mosquitos infected by membrane feeding on gametocytes from chimpanzees. Antibodies, measured by indirect immunofluorescent antibody tests and enzyme-linked immunosorbent assays, were induced by all the vaccines. Six of 42 monkeys immunized with recombinant or synthetically produced vaccines were protected. Two of 6 monkeys immunized with irradiated sporozoites were protected. Saimiri appear to be less susceptible than are humans to sporozoite infection. Therefore, the predictive usefulness of this model must await the results of comparable trials in monkeys and humans.