Plasmodium falciparum Merozoite Surface Protein 1 (MSP-1)-MSP-3 Chimeric Protein: Immunogenicity Determined with Human-Compatible Adjuvants and Induction of Protective Immune Response

Abstract

ABSTRACT A chimeric gene, MSP-Fu 24 , was constructed by genetically coupling immunodominant, conserved regions of the two leading malaria vaccine candidates, Plasmodium falciparum merozoite surface protein 1 (C-terminal 19-kDa region [PfMSP-1 19 ]) and merozoite surface protein 3 (11-kDa conserved region [PfMSP-3 11 ]). The recombinant MSP-Fu 24 protein was produced in Escherichia coli cells and purified to homogeneity by a two-step purification process with a yield of ∼30 mg/liter. Analyses of conformational properties of MSP-Fu 24 using PfMSP-1 19 -specific monoclonal antibody showed that the conformational epitopes of PfMSP-1 19 that may be critical for the generation of the antiparasitic immune response remained intact in the fusion protein. Recombinant MSP-Fu 24 was highly immunogenic in mice and in rabbits when formulated with two different human-compatible adjuvants and induced an immune response against both PfMSP-1 19 and PfMSP-3 11 . Purified anti-MSP-Fu 24 antibodies showed invasion inhibition of P. falciparum 3D7 and FCR parasites, and this effect was found to be dependent on antibodies specific for the PfMSP-1 19 component. The protective potential of MSP-Fu 24 was demonstrated by in vitro parasite growth inhibition using an antibody-dependent cell inhibition (ADCI) assay with anti-MSP-Fu 24 antibodies. Overall, the antiparasitic activity was mediated by a combination of growth-inhibitory antibodies generated by both the PfMSP-1 19 and PfMSP-3 11 components of the MSP-Fu 24 protein. The antiparasitic activities elicited by anti-MSP-Fu 24 antibodies were comparable to those elicited by antibodies generated with immunization with a physical mixture of two component antigens, PfMSP-1 19 and PfMSP-3 11 . The fusion protein induces a protective immune response with human-compatible adjuvants and may form a part of a multicomponent malaria vaccine.