Immunogenicity and Efficacy in AotusMonkeys of Four Recombinant Plasmodium falciparumVaccines in Multiple Adjuvant Formulations Based on the 19-Kilodalton C Terminus of Merozoite Surface Protein 1

ABSTRACTThe immunogenicity and protective efficacy of four versions of recombinant C-terminal 19-kDa epidermal growth factor-like region of the major surface protein 1 (rMSP119) of Plasmodium falciparumwas studied in Aotusmonkeys. Vaccination with each of the four rMSP119constructs elicited high levels of antibodies to MSP119but only one construct, the 19-kDa fragment expressed as a secreted fusion protein fromSaccharomyces cerevisiae(yP30P2MSP119), induced a high degree of protective immunity in Aotus nancymaiagainst lethal P. falciparumchallenge. Protective formulation required Freund's adjuvant; vaccination with yP30P2MSP119in six other adjuvants that are suitable for human use induced lower levels of antibody response and no protection. These results emphasize the need to continue the search for an adjuvant that is comparable to Freund's adjuvant in potency and is safe for use in humans.