Immunogenicity of Plasmodium falciparum and Plasmodium vivax circumsporozoite protein repeat multiple antigen constructs (MAC)

In this study we characterized the immunogenic properties of three different multispecies multiple antigen constructs (MACs) carrying the circumsporozoite protein (CSP) repeats of human malaria parasites, Plasmodium falciparum and P. vivax. We synthesized tetrameric MACs containing the antigenic repeats from the CSP of P. vivax-like parasite in two arms and CSP repeat sequences of either P. vivax type-1 (vivax-like/vivax type-1 MAC), P. vivax type-2 (vivax-like/vivax type-2 MAC), or P. falciparum (vivax-like/falciparum MAC) in the other two arms. Mice of four different genetic backgrounds (H-2 a, H-2 b, H-2 d, and H-2 k) were immunized with these MACs in Freund's adjuvant. All three MAC preparations were found to elicit antibodies to P. vivax-like CSP repeats in B10.BR, B10.A, and C57 BL 6 mice. On the other hand, in B10.D2 mice only vivax-like/vivax type-1 MAC, but not the other two MACs induced antibodies to the P. vivax-like CSP repeats. In mice immunized with vivax-like/vivax type-1 MAC, antibodies to P. vivax type-1 CS repeat peptides were induced in B10.BR, B10.A, and C57 BL 6 mice, but not in B10.D2 mice. Antibody responses to P. vivax type-2 repeats were not induced in any of the four strains of mice that were immunized with vivax-like/vivax type-2 MAC. While B10.BR, B10.A, and C57 BL 6 mice produced antibodies to NANP repeats of P. falciparum CSP following immunization with vivax-like/falciparum MAC, B10.D2 mice failed to elicit antibodies to this repeat. All the sera that showed positive reactivity to peptides in enzyme-linked immunosorbent assay were found to react with sporozoites by IFA. In conclusion, these results showed that naturally immunogenic epitopes from different species of malaria parasites can be incorporated in a single vaccine construct to induce immune responses against multiple epitopes.