A Plant-Produced Pfs230 Vaccine Candidate Blocks Transmission of Plasmodium falciparum

Abstract

Plasmodium falciparum is transmitted to a new host after completing its sexual cycle within a mosquito. Developing vaccines against the parasite sexual stages is a critical component in the fight against malaria. We are targeting multiple proteins of P. falciparum which are found only on the surfaces of the sexual forms of the parasite and where antibodies against these proteins have been shown to block the progression of the parasite's life cycle in the mosquito and thus block transmission to the next human host. We have successfully produced a region of the Pfs230 antigen in our plant-based transient-expression system and evaluated this vaccine candidate in an animal model. This plant-produced protein, 230CMB, is expressed at approximately 800 mg/kg in fresh whole leaf tissue and is 100% soluble. Administration of 230CMB with >90% purity induces strong immune responses in rabbits with high titers of transmission-blocking antibodies, resulting in a greater than 99% reduction in oocyst counts in the presence of complement, as determined by a standard membrane feeding assay. Our data provide a clear perspective on the clinical development of a Pfs230-based transmissionblocking malaria vaccine.

Malaria vaccine candidate antigen targeting the pre‐erythrocytic stage ofPlasmodium falciparumproduced at high level in plants

“…2014, 9, 1435-1445 sion vectors in combination with the p19 silencing inhibitor. For example, an antibody light chain was expressed at 15% TSP using a comparable system [31] and a recombinant sexual stage malaria vaccine candidate was produced at 0.8 mg/g FLW [32]. Thus far, higher yields (>70%) have been achieved either by stable chloroplast transformation [33], a system that does not offer the flexibility and speed of transient systems, or advanced transient systems based on viral replicons [34,35].…”

Structural and Immunological Characterization of Recombinant 6-Cysteine Domains of the Plasmodium falciparum Sexual Stage Protein Pfs230

“…Pfs230 has been speculated to have a male gamete function because parasites with a truncated form of Pfs230 were shown to adhere to uninfected erythrocytes, even though their capacity to infect mosquitoes was severely decreased by greater than 95% (22). Various forms or domains of Pfs230 have been expressed in several recombinant expression systems, including Saccharomyces cerevisiae, Escherichia coli, plants, and wheat germ (9,12,13,23) but to date none of the recombinant forms of Pfs230 have been suitable for extensive biochemical and biophysical characterization to effectively characterize a functional antibody response. A primary bottleneck in recombinant protein production has been the presence of an unique disulfide bond structure initially modeled by Gerloff et al (24).…”

Structure of thePlasmodium6-cysteine s48/45 domain

“…To date, no experimentally determined molecular structure for any s48/45 domain has been reported, mainly because of proteinexpression challenges (29)(30)(31)(32)(33)(34). However, considering the importance of structural information in the effective design of subunit vaccine candidates, we present the solution three-dimensional structure of the s48/45 domain obtained by NMR spectroscopy of the C-terminal domain of Pf12 expressed in Escherichia coli.…”