Engineering a Virus-Like Particle as an Antigenic Platform for a Pfs47-Targeted Malaria Transmission-Blocking Vaccine

Abstract

We recently characterized Pfs47, a protein expressed on the surface of sexual stages and ookinetes of Plasmodium falciparum, as a malaria transmission-blocking vaccine (TBV) target. Mice immunization induced antibodies that conferred strong transmission-reducing activity (TRA) at a concentration of 200 μg/mL. Here, we sought to optimize the Pfs47 vaccine to elicit higher titers of high-affinity antibodies, capable of inducing strong TRA at a lower concentration. We report the development and evaluation of a Pfs47-based virus-like particle (VLP) vaccine generated by conjugating our 58 amino acid Pfs47 antigen to Acinetobacter phage AP205-VLP using the SpyCatcher:SpyTag adaptor system. AP205-Pfs47 complexes (VLP-P47) formed particles of ~22 nm diameter that reacted with polyclonal anti-Pfs47 antibodies, indicating that the antigen was accessible on the surface of the particle. Mice immunized with VLP-P47 followed by a boost with Pfs47 monomer induced significantly higher antibody titers, with higher binding affinity to Pfs47, than mice that received two immunizations with either VLP-P47 (VLP-P47/VLP-P47) or the Pfs47 monomer (P47/P47). Purified IgG from VLP-P47/P47 mice had strong TRA (83–98%) at concentrations as low as 5 μg/mL. These results indicate that conjugating the Pfs47 antigen to AP205-VLP significantly enhanced antigenicity and confirm the potential of Pfs47 as a TBV candidate.

In vivo Characterization of Plasmodium berghei P47 (Pbs47) as a Malaria Transmission-Blocking Vaccine Target

“…A recombinant Del1 protein with a "SpyTag" was expressed, purified and covalently linked to the surface of a AP205-VLP, using the AP205-SpyCatcher:SpyTag platform ( Figures 3A,B). We have previously shown that, for P. falciparum Pfs47, a 95% coupling efficiency was achieved when SpyTag-Pfs47 was mixed with AP205-SpyCatcher at a 1:1 molar ratio (Yenkoidiok-Douti et al, 2019). Thus, AP205-SpyCatcher with Pbs47 SpyTag-Del1 were mixed at 1:1 molar ratio and this resulted in a covalently bound protein of the expected size (48 kDa) under denaturing and reducing conditions ( Figure 3A).…”

“…We have previously shown that prime-boost immunization with P. falciparum VLP-Pfs47 elicits a very strong immune response to the VLP carrier, and a better TRA was obtained when prime immunization with VLP-Pfs47 was followed by a boost with Pfs47 monomer (Yenkoidiok-Douti et al, 2019). Thus, the immunogenicity of antibodies generated with two different immunization strategies were evaluated: (1) Prime-boost with P. berghei, Del1 monomer antigen (Del1/Del1) and (2) VLP-Del1 priming followed by a boost with Del1 monomer (VLP-Del1/Del1).…”

“…Soluble AP205-SpyCatcher was purified following a previously described protocol (Yenkoidiok-Douti et al, 2019). Pellets from 1 L of culture were resuspended at RT in 30 mL HEPES-buffered saline (HBS) lysis buffer (20 mM HEPES, 150 mM NaCl, 0.1% triton X-100, 0.1% Tween 20) and incubated on ice for 10-15 min.…”

“…We have recently shown that Pfs47, a paralog of Pfs48/45, is a promising TBV target ( Alvaro et al, 2013 ; Canepa et al, 2018 ; Yenkoidiok-Douti et al, 2019 ), based on SMFA assays. Plasmodium berghei , a murine malaria model ( Craig et al, 2012 ; Otto et al, 2014 ), also infects mosquitoes that transmit human malaria, including A. gambiae , a major vector in Africa ( Cohuet et al, 2006 ; Dong et al, 2006 ).…”

Historical Perspective and Biotechnological Trends to Block Arboviruses Transmission by Controlling Aedes aegypti Mosquitos Using Different Approaches

“…Therefore, after blood meal on an immunized host, the antibody triggered by vaccination could induce interference in the cell cycle on the vector or/and block virus infection to the vector, thus preventing disease transmission to human hosts (107). Some successful examples against transmission of Plasmodium berghei by Anopheles stephensi (108), P. vivax (109) by A. dirus (110), P. falsiparum by A. gambiae (111), and Leishmania infantum by Lutzomyia longipalpis (112) have been reported in the literature, showing this strategy as promising and possibly helpful in interrupting distinct pathogen transmission cycle. Notwithstanding the potential of TBVs, they do not directly protect humans, so there is resistance to their use in public health programs (113).…”