4 years ago

Evaluation of a Plasmodium-specific carrier protein to enhance production of recombinant Pfs25, a leading transmission-blocking vaccine candidate.

Parzych, Long, Ramanathan, Miura, Burns
Challenges with the production and suboptimal immunogenicity of malaria vaccine candidates have slowed the development of a Plasmodium falciparum multi-antigen vaccine. Attempting to resolve these issues, we focused on the use of the highly immunogenic merozoite surface protein 8 (MSP8) as a vaccine carrier protein. Previously, we showed that genetic fusion of the C-terminal 19 kDa fragment of merozoite surface protein 1 (MSP119) to PfMSP8 facilitated antigen production, folding and induction of neutralizing antibodies to conformational B cell epitopes of MSP119 Here, using the PfMSP1/8 construct, we further optimized the rPfMSP8 carrier by introduction of two cysteine to serine substitutions (CΔS) to improve the yield of monomeric product. We then sought to test the broad applicability of this approach using the transmission-blocking vaccine candidate, Pfs25. Production of rPfs25-based vaccines has presented challenges. Antibodies directed against the four highly constrained EGF-like domains of Pfs25 block sexual stage development in mosquitoes. The sequence encoding mature Pfs25 was codon-harmonized for expression in E. coli We produced a rPfs25-PfMSP8 fusion protein (rPfs25/8(CΔS)) as well as unfused, mature rPfs25. rPfs25 was purified with a modest yield but required incorporation of refolding protocols to obtain proper conformation. In comparison, chimeric rPfs25/8(CΔS) was expressed and easily purified, with the Pfs25 domain bearing proper conformation without renaturation. Both antigens were immunogenic in rabbits, inducing IgG that bound native Pfs25 and exhibited potent transmission reducing activity. These data further demonstrate the utility of PfMSP8 as a parasite specific carrier protein to enhance production of complex malaria vaccine targets.

Publisher URL: http://doi.org/10.1128/IAI.00486-17

DOI: 10.1128/IAI.00486-17

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