A Chimeric Plasmodium falciparum Merozoite Surface Protein Vaccine Induces High Titers of Parasite Growth Inhibitory Antibodies

Abstract

ABSTRACTThe C-terminal 19-kDa domain ofPlasmodium falciparummerozoite surface protein 1 (PfMSP119) is an established target of protective antibodies. However, clinical trials ofPfMSP142, a leading blood-stage vaccine candidate which contains the protective epitopes ofPfMSP119, revealed suboptimal immunogenicity and efficacy. Based on proof-of-concept studies in thePlasmodium yoeliimurine model, we produced a chimeric vaccine antigen containing recombinantPfMSP119(rPfMSP119) fused to the N terminus ofP. falciparummerozoite surface protein 8 that lacked its low-complexity Asn/Asp-rich domain, rPfMSP8 (ΔAsn/Asp). Immunization of mice with the chimeric rPfMSP1/8 vaccine elicited strong T cell responses to conserved epitopes associated with the rPfMSP8 (ΔAsn/Asp) fusion partner. While specific forPfMSP8, this T cell response was adequate to provide help for the production of high titers of antibodies to bothPfMSP119and rPfMSP8 (ΔAsn/Asp) components. This occurred with formulations adjuvanted with either Quil A or with Montanide ISA 720 plus CpG oligodeoxynucleotide (ODN) and was observed in both inbred and outbred strains of mice.PfMSP1/8-induced antibodies were highly reactive with two major alleles ofPfMSP119(FVO and 3D7). Of particular interest, immunization withPfMSP1/8 elicited higher titers ofPfMSP119-specific antibodies than a combined formulation of rPfMSP142and rPfMSP8 (ΔAsn/Asp). As a measure of functionality,PfMSP1/8-specific rabbit IgG was shown to potently inhibit thein vitrogrowth of blood-stage parasites of the FVO and 3D7 strains ofP. falciparum. These data support the further testing and evaluation of this chimericPfMSP1/8 antigen as a component of a multivalent vaccine forP. falciparummalaria.