Antibodies to Plasmodium Vivax Transmission-blocking Vaccine Candidate Antigens Pvs25 and Pvs28 Do Not Show Synergism

Transmission-blocking vaccines against malaria parasites target molecules expressed by sexual stage parasites to elicit antibodies that prevent the infection of the mosquito vector. Pvs25 and Pvs28, expressed on the surface of ookinetes, are potential candidates for such a vaccine and induce antibodies that block the infectivity of Plasmodium vivax in immunized animals. To improve the ability to induce transmission-blocking antibodies, Pvs25 and Pvs28 were produced as a single fusion protein by the yeast Saccharomyces cerevisiae. Mice immunized with a low dose of the chimeric molecule (Pvs25-28) developed higher antibody responses compared with mice immunized with either Pvs25 or Pvs28. In membrane feeding assays, both anti-Pvs25-28 and anti-Pvs25 antisera had similarly potent transmission-blocking activities (and both were much greater than anti-Pvs28). Furthermore, serum from mice simultaneously immunized with both Pvs25 and Pvs28, or serum mixtures of anti-Pvs25 alone and anti-Pvs28 alone did not enhance the efficacy over anti-Pvs25 serum alone, demonstrating that there is no synergism in the ability to block transmission of P. vivax between anti-Pvs25 and anti-Pvs28 antibodies.