Abstract
A Plasmodium falciparum chimeric protein, PfMSP-Fu24, was constructed by genetically coupling immunodominant, conserved regions of two merozoite surface proteins, the 19-kDa region C-terminal region of merozoite surface protein 1 (PfMSP-119) and an 11-kDa conserved region of merozoite surface protein 3 (PfMSP-311), to augment the immunogenicity potential of these blood-stage malaria vaccine candidates. Here we describe an improved, efficient, and scalable process to produce high-quality PfMSP-Fu24. The chimeric protein was produced in Escherichia coli SHuffle T7 Express lysY cells that express disulfide isomerase DsbC. A two-step purification process comprising metal affinity followed by cation exchange chromatography was developed, and we were able to obtain PfMSP-Fu24 with purity above 99% and with a considerable yield of 23 mg/liter. Immunogenicity of PfMSP-Fu24 formulated with several adjuvants, including Adjuplex, Alhydrogel, Adjuphos, Alhydrogel plus glucopyranosyl lipid adjuvant, aqueous (GLA-AF), Adjuphos+GLA-AF, glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE), and Freund's adjuvant, was evaluated. PfMSP-Fu24 formulated with GLA-SE and Freund's adjuvant in mice and with Alhydrogel and Freund's adjuvant in rabbits produced high titers of PfMSP-119 and PfMSP-311-specific functional antibodies. Some of the adjuvant formulations induced inhibitory antibody responses and inhibited in vitro growth of P. falciparum parasites in the presence as well as in the absence of human monocytes. These results suggest that PfMSP-Fu24 can form a constituent of a multistage malaria vaccine.