Immune Responses and Protection of Aotus Monkeys Immunized with Irradiated Plasmodium vivax Sporozoites

A non-human primate model for the induction of protective immunity against the pre-erythrocytic stages of Plasmodium vivax malaria using radiation-attenuated P vivax sporozoites may help to characterize protective immune mechanisms and identify novel malaria vaccine candidates. Immune responses and protective efficacy induced by vaccination with irradiated P vivax sporozoites were evaluated in malaria-naive Aotus monkeys. Three groups of six monkeys received two, five, or ten intravenous inoculations, respectively, of 100,000 irradiated P vivax sporozoites; control groups received either 10 doses of uninfected salivary gland extract or no inoculations. Immunization resulted in the production low levels of antibodies that specifically recognized P vivax sporozoites and the circumsporozoite protein. Additionally, immunization induced low levels of antigen-specific IFN-gamma responses. Intravenous challenge with viable sporozoites resulted in partial protection in a dose-dependent manner. These findings suggest that the Aotus monkey model may be able to play a role in preclinical development of P vivax pre-erythrocytic stage vaccines.