Particle-based, Pfs230 and Pfs25 immunization is effective, but not improved by duplexing at fixed total antigen dose

Abstract

Background: The Plasmodium falciparum sexual-stage surface proteins Pfs25 and Pfs230 are antigen candidates for a malaria transmission-blocking vaccine (TBV), and have been widely investigated as such. It is not clear whether simultaneously presenting these two antigens in a particulate vaccine would enhance the transmission reducing activity (TRA) of induced antibodies. To assess this, immunization was carried out with liposomes containing synthetic lipid adjuvant monophosphoryl lipid A (MPLA), and cobalt-porphyrin-phospholipid (CoPoP), which rapidly converts recombinant, his-tagged antigens into particles. Methods: His-tagged, recombinant Pfs25 and Pfs230C1 were mixed with CoPoP liposomes to form a bivalent vaccine. Antigens were fluorescently labelled to infer duplex particleization serum-stability and binding kinetics using fluorescence resonance energy transfer. Mice and rabbits were immunized with individual or duplexed particleized Pfs25 and Pfs230C1, at fixed total antigen doses. The resulting antibody responses were assessed for magnitude and TRA. Results: Pfs230C1 and Pfs25 rapidly bound CoPoP liposomes to form a serum-stable, bivalent particle vaccine. In mice, immunization with 5 ng of total antigen (individual antigen or duplexed) elicited functional antibodies against Pfs25 and Pfs230. Compared to immunization with the individual antigen, Pfs25 antibody production was moderately lower for the bivalent CoPoP vaccine, whereas Pfs230C1 antibody production was not impacted. All antibodies demonstrated at least 92% inhibition in oocyst density at 750 μg/mL purified mouse IgG in the standard membrane feeding assay (SMFA). At lower IgG concentrations, the bivalent vaccine did not improve TRA; antibodies induced by particleized Pfs25 alone showed stronger function in these conditions. In rabbits, immunization with a 20 µg total antigen dose with the duplexed antigens yielded similar antibody production against Pfs25 and Pfs230 compared to immunization with a 20 µg dose of individual antigens. However, no enhanced TRA was observed with duplexing. Conclusions: Pfs25, Pfs230 or the duplexed combination can readily be prepared as particulate vaccines by mixing CoPoP liposomes with soluble, recombinant antigens. This approach induces potent transmission-reducing antibodies following immunization in mice and rabbits. Immunization with bivalent, particleized, Pfs230 and Pfs25 did not yield antibodies with superior TRA compared to immunization with particleized Pfs25 as a single antigen. Altogether,

Evaluation of Two Sexual-stage Antigens as Bivalent Transmission-blocking Vaccines in Rodent Malaria

“…The combination of RTS,S/AS01 with a viral vector PEV (ChAd63/MVA ME-TRAP) failed to improve the vaccine e cacy as compared to the two vaccines administered individually [33]. For a bivalent TBV design, the combination of Pfs25 and Pfs230C1 did not enhance the antibody response when compared to single antigen immunization [23]. In this study, we tested speci c antibody responses against the rPbg37 and rPSOP25 fragments and demonstrated that these two protein fragments did not interfere with each other in inducing functional antibodies.…”

“…Subsequently, the mice were immunized by two boosters at 2-week intervals with 25 µg of rPbg37, 25 µg of rPSOP25, mixed proteins (25 µg rPbg37 + 25 µg rPSOP25), or 25 µg rPbg37-PSOP25 chimeric proteins, emulsi ed with incomplete Freund's adjuvant. For antisera, blood was collected 10 days after the third immunization and allowed to clot at room temperature [23,28].…”

“…It has been shown that the combination of two blood-stage antigens MSP1 and AMA1 caused immune interference by the immunodominant antigen [19], whereas the two ookinete antigens Pfs25 and Pfs28 did not show immune interference [20,21,22]. Further, two studies showed that dual-antigen vaccines based on Pfs25 and Pfs230C did not elicit better TRA compared to the mono-antigen vaccines [18,23]. However, the Pfs230 and Pfs48/45 fusion proteins were found to elicit functional antibodies in mice with higher TBA than the single proteins alone [24].…”

Progress in Parasite Genomics and Its Application to Current Challenges in Malaria Control

“…Pfs25 is an important glycophosphatidylinositol-linked protein expressed on the surface of ookinetes. It is found only within the Anopheles host and is approximately 25 kDa with 11 disulfie bonds [118]. The parasites require Pfs25 to survive in the Anopheles's midgut and develop into oocysts [119].…”

Experimental and Computational Observations of Immunogenic Cobalt Porphyrin Lipid Bilayers: Nanodomain-Enhanced Antigen Association

“…Other approaches make use of recombinant protein engineering for downstream Pfs25 multimerization [20] or attachment to VLPs [21]. The CoPoP system has been demonstrated for other his-tagged antigens related to malaria transmission-blocking [22,23] and other infectious diseases [24][25][26].…”