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 used individually. Methods A chimeric protein composed of fragments of Pbg37 and PSOP25 was designed and expressed the recombinant protein in Escherichia coli Rosetta-gami B (DE3). After immunizing mice with individual recombinant proteins Pbg37 and PSOP25, mixed proteins (Pbg37+PSOP25), or the fusion protein (Pbg37-PSOP25), the antibody titers of individual sera were analyzed by ELISA. IFA and Western blot were performed to test the reactivity of the antisera with the native proteins in the parasite. The transmission-blocking activity of the different immunization schemes was assessed using in vitro and in vivo assays. 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 mixed proteins or the fusion protein induced antibodies with significantly stronger transmission-reducing activities in vitro and in vivo than individual antigens. Conclusions There was no immunological interference between Pbg37 and PSOP25. The bivalent vaccines, which expand the portion of the sexual development during which the transmission-blocking antibodies act, produced significantly stronger transmission-reducing activities than single antigens. Altogether, these data provide the theoretical basis for the development of combination TBVs targeting different sexual stages. Graphic Abstract

A dual-antigen malaria vaccine targeting Pb22 and Pbg37 was able to induce robust transmission-blocking activity

“…Two studies additionally showed that the protective immunity induced by dual-antigen malaria vaccines PfCSP-Pfs25 or Pvs25-PvCSP was able to provide a promising high level of transmission-reducing activity (TRA; > 99% for PfCSP-Pfs25; 82% for Pvs25-PvCSP) [ 28 , 29 ]. Comparable to the results of these reports, in our recent work, we showed that fusing or mixing Pbg37 with ookinete surface antigen PSOP25 for immunization was able to enhance the TRA efficiency afforded by Pbg37 alone [ 30 ]. These findings provide support that dual-antigen malaria vaccines, which provide greater overall protection, cost-effectiveness and durability than a single-stage vaccine, will be a powerful tool for malaria control.…”

“…After blocking with 5% skim milk, the parasites were incubated with sera from immunized mice (dilution: 1:500) for 1 h, then co-labeled with rabbit antisera against P47 (dilution: 1:500), α-tubulin II (dilution: 1:500) or Pbs25 (dilution: 1:500) as stage-specific markers for female gametocytes/gametes, male gametocytes/gametes and zygotes/ookinetes, respectively, followed by three washing steps in PBS. The polyclonal antibodies against P47, α-tubulin II and Pbs25 were made in our laboratory [ 30 ]. Alexa Fluor 488-conjugated goat anti-mouse IgG antibodies (dilution: 1:500; Invitrogen, Thermo Fisher Scientific) and Alexa Fluor 555-conjugated goat anti-rabbit IgG antibodies (dilution: 1:500; Invitrogen, Thermo Fisher Scientific) were used as secondary antibodies.…”

A nanoparticle vaccine displaying the ookinete PSOP25 antigen elicits transmission-blocking antibody response against Plasmodium berghei

“…The AP205-2*SpyTag was expressed in E. coli Rosetta-gami B (DE3) cells under induction with 1 mM IPTG (Sigma) at 20 °C for 16 h. Bacterial cells from the overnight culture were pelleted by centrifugation at 4 °C. The pellet was resuspended with a HIS-binding buffer containing 50 mM sodium phosphate buffer and 300 mM NaCl (pH 8.0) and was lysed by sonication [ 28 ]. The bacterial lysate was centrifuged, and the pellet was suspended in Buffer B solution (100 mM NaH 2 PO 4, 10 mM Tris, 8 M Urea, pH 8.0).…”

Characterization of PSOP26 as an ookinete surface antigen with improved transmission-blocking activity when fused with PSOP25

“…Negative controls were HA-tagged ookinetes incubated with the secondary antibodies alone, or WT ookinetes incubated with the anti-HA mAb. The antibodies against PbMSP1, Pbg377, α-tubulin II, and PSOP25 were made in our laboratory [ 25 ]. Parasites were visualized using a Nikon C2 fluorescence confocal laser scanning microscope (Nikon, Tokyo, Japan).…”