Evaluation of Two Sexual-stage Antigens as Bivalent Transmission-blocking Vaccines in Rodent Malaria

Abstract Background: Transmission-blocking vaccine (TBV) is a promising strategy for malaria elimination. It is hypothesized that mixing or fusing two antigens targeting different stages of sexual development may provide higher transmission-blocking activity than these antigens are used individually.Methods: We designed a chimeric protein composed of fragments of Pbg37 and PSOP25 and expressed the recombinant protein in Escherichia coli Rosetta-gami B (DE3). After immunizing mice with mixing or fusing recombinant proteins, the antibody titers of sera were analyzed by ELISA. IFA and Western blot were performed to test the reactivity of the antisera with the native proteins of the parasite. The transmission blocking activity were assessed in vitro and in vivo assay. Results: When Pbg37 and PSOP25 were co-administered in a mixture or as a fusion protein, they elicited similar antibody responses in mice as single antigens without causing immunological interference with each other. Antibodies against the mixed or fused antigens recognized the target proteins in the gametocyte, gamete, zygote and ookinete stages. The two bivalent vaccines (mixed proteins or a fusion protein) produced the superior TBA compared to that of the antibodies against individual antigens.Conclusions: There was no immunological interference between the two antigens of bivalent vaccines. And the bivalent vaccines produced significantly stronger transmission-blocking activities than single antigens. Altogether, these data provide the theoretical basis for the development of combination TBVs targeting different sexual stages.