Plasmodium vivax gametocyte proteins, Pvs48/45 and Pvs47, induce transmission-reducing antibodies by DNA immunization

Malaria transmission-blocking vaccines (TBV) aim to interfere with the development of the malaria parasite in the mosquito vector, and thus prevent spread of transmission in a community. To date three TBV candidates have been identified in Plasmodium vivax; namely, the gametocyte/gamete protein Pvs230, and the ookinete surface proteins Pvs25 and Pvs28. The Plasmodium falciparum gametocyte/gamete stage proteins Pfs48/45 and Pfs47 have been studied as TBV candidates, and Pfs48/45 shown to induce transmission-blocking antibodies, but the candidacy of their orthologs in P. vivax, Pvs48/45 (PVX_083235) and Pvs47 (PVX_083240), for vivax TBV have not been tested. Herein we investigated whether targeting Pvs48/45 and Pvs47 can inhibit parasite transmission to mosquitoes, using P. vivax isolates obtained in Thailand. Mouse antisera directed against the products from plasmids expressing Pvs48/45 and Pvs47 detected proteins of approximately 45- and 40-kDa, respectively, in the P. vivax gametocyte lysate, by Western blot analysis under non-reducing conditions. In immunofluorescence assays Pvs48/45 was detected predominantly on the surface and Pvs47 was detected in the cytoplasm of gametocytes. Membrane feeding transmission assays demonstrated that anti-Pvs48/45 and -Pvs47 mouse sera significantly reduced the number of P. vivax oocysts developing in the mosquito midgut. Limited amino acid polymorphism of these proteins was observed among 27 P. vivax isolates obtained from Thailand, Vanuatu, and Colombia; suggesting that polymorphism may not be an impediment for the utilization of Pvs48/45 and Pvs47 as TBV antigens. In one Thai isolate we found that the fourth cysteine residue in the Pvs47 cysteine-rich domain (CRD) III (amino acid position 337) is substituted to phenylalanine. However, antibodies targeting Pvs47 CRDI-III showed a significant transmission-reducing activity against this isolate, suggesting that this substitution in Pvs47 was not critical for recognition by the generated antibodies. In conclusion, our results indicate that Pvs48/45 and Pvs47 are potential transmission-blocking vaccine candidates of P. vivax.