Immunization of Mice with DNA-Based Pfs25 Elicits Potent Malaria Transmission-Blocking Antibodies

Abstract

Immunological intervention, in addition to vector control and malaria chemotherapy, will be needed to stop the resurgence of malaria, a disease with a devastating impact on the health of 300 to 500 million people annually. We have pursued a vaccination strategy, based on DNA immunization in mice with genes encoding two antigens present on the sexual stages of Plasmodium falciparum, Pfs25 and Pfg27, to induce biologically important antibodies that can block development of the parasite in the Anopheles mosquito and thus transmission of the disease. DNA encoding Pfs25 when administered by the intramuscular route, either alone or with DNA encoding Pfg27, had the most potent transmission-blocking effects, resulting in up to a 97% decrease in oocyst numbers in mosquito midguts and a 75% decrease in rate of infection. Immunization with DNA encoding a Pfg27-Pfs25 fusion protein was less effective and DNA encoding Pfg27 elicited antibodies in sera that had only modest effects on the infectivity of the parasite. These results show for the first time that DNA vaccination can result in potent transmission-blocking antibodies in mice and suggest that the Pfs25 gene should be included as part of a multicomponent DNA vaccine.

Effects of transmission-blocking vaccines simultaneously targeting pre- and post-fertilization antigens in the rodent malaria parasite Plasmodium yoelii

“…More surprisingly, immunization with both DNA constructs produced decreased humoral responses to each of the two antigens as compared with immunization with individual DNA constructs, suggesting of interference between the two DNA vaccine constructs. This phenomenon is consistent with an earlier report showing a similar interference effect of DNA vaccination with Pfs25 and the gametocyte antigen Pfg27, which showed lower TB activity in the combination vaccination group [ 29 ]. Alternatively, the reduced antibody responses to individual antigens produced in the mixed vaccination scheme could be a dosage effect, as the doubled amount of DNA used for combination immunization may interfere with antigen presentation.…”

“…Since the immunogenicity of a vaccine depends on the formation of natural conformational epitopes, and it is especially important for P48 which contains a unique arrangement of six cysteine-containing domains [ 43 ], we expect that DNA vaccine would circumvent the difficulties in obtaining conformationally correct P48 [ 44 ] as shown for the Pvs48/45 [ 45 ]. Consistent with DNA vaccine results for the Pfs25 [ 29 ] as well as the Pvs48/45 [ 45 ], DNA vaccines with the Pys25 and Pys48/45 individually and in combination produced evident, specific antibody responses, and the antibodies recognized the respective native proteins in parasites and possessed significant TB activity. In both in vitro ookinete conversion and direct mosquito feeding assays, immunization with the Pys25 plasmid produced much better TB activity than with the Pys48/45 construct, which agrees with P25 being one of the best TBV candidates in numerous experiments [ 22 , 46 ].…”

“…DNA vaccine may overcome the need for such requirements associated with conventional protein immunization and has been shown to induce protective immune responses against several pathogens by eliciting both humoral and cellular immune responses [ 23 – 28 ]. DNA vaccines for Pfs25 have been shown to induce effective TB activity in mice and rhesus monkey [ 29 – 31 ]. Another problem is that most TBVs could not induce sterile TB activity to completely block the development of oocysts in mosquitoes.…”

Hemolytic C-Type Lectin CEL-III from Sea Cucumber Expressed in Transgenic Mosquitoes Impairs Malaria Parasite Development

“…Mature gametocytes of P. falciparum (3D7) were produced in vitro as previously described [ 41 ]. Membrane feeding assays were performed to test infectivity of the P. falciparum gametocytes for mosquitoes as previously described [ 42 ]. Briefly, mature gametocyte cultures (0.3 to 0.4% final gametocytemia) were fed for 30 min at 37 °C to transgenic and non-transgenic mosquitoes through a Parafilm membrane.…”

Heat‐precipitation allows the efficient purification of a functional plant‐derived malaria transmission‐blocking vaccine candidate fusion protein

“…The first macrogamete/zygote surface antigen investigated as a TBV was Pfs 25 (Carter et al, ; Fries et al, ), a 21 kDa protein comprising four epidermal growth factor (EGF)‐like domains, and antibodies raised against recombinant Pfs 25 variants expressed in different expression systems and administrated in different ways have shown strong transmission‐blocking activity (Kaslow et al, ; Lobo et al, ; Miura et al, ; Wu et al, ). Among the gamete/gametocyte antigens, Pfs 230 has also received attention as a TBV candidate.…”