Molecular definition of multiple sites of antibody inhibition of malaria transmission-blocking vaccine antigen Pfs25

Abstract

The Plasmodium falciparum Pfs25 protein (Pfs25) is a leading malaria transmission-blocking vaccine antigen. Pfs25 vaccination is intended to elicit antibodies that inhibit parasite development when ingested by Anopheles mosquitoes during blood meals. The Pfs25 three-dimensional structure has remained elusive, hampering a molecular understanding of its function and limiting immunogen design. We report six crystal structures of Pfs25 in complex with antibodies elicited by immunization via Pfs25 virus-like particles in human immunoglobulin loci transgenic mice. Our structural findings reveal the fine specificities associated with two distinct immunogenic sites on Pfs25. Importantly, one of these sites broadly overlaps with the epitope of the well-known 4B7 mouse antibody, which can be targeted simultaneously by antibodies that target a non-overlapping site to additively increase parasite inhibition. Our molecular characterization of inhibitory antibodies informs on the natural disposition of Pfs25 on the surface of ookinetes and provides the structural blueprints to design next-generation immunogens.

A Universal Plug-and-Display Vaccine Carrier Based on HBsAg VLP to Maximize Effective Antibody Response

“…One of the main features of the SpyTag/SpyCatcher technology is the possibility to orientate the antigen on the VLP surface to expose the functional epitopes, which leads to the generation of a better quality of response (22). Recent progresses in the malaria-TBV field unrevealed structures and mapped epitopes of important antigen candidates that had remained elusive for long time (42)(43)(44). The combination of the new insights into the structure of these antigens, including Pfs25, and the possibility to specifically orientate them on HBsAg::SpyCatcher, offers a unique advantage in the design of novel vaccine candidates.…”

Characterization of two in vivo challenge models to measure functional activity of monoclonal antibodies to Plasmodium falciparum circumsporozoite protein

“…Antibodies: AB311 and AB317 are human immunoglobulin G 1 (IgG1) mAbs isolated from an experimental clinical trial of RTS,S, MAL071 [23] clinical trial and both mAbs bind to NANP repeats [16]; mAb1245 is also a human IgG1 mAb, isolated from a Kymab mouse, and binds to a P. falciparum ookinete protein Pfs25, and thus is used as a negative isotype control [24]. All mAbs were expressed by transient transduction 0.5 L TunaCHO cultures followed by protein A purification at Lake Pharma Inc. Belmont, CA.…”

“…AB317 has also been previously tested across a range of doses (30-300 µg) [20] and this guided the selection of dose levels for the present study. The mAb AB1245 [24] that binds to ookinete antigen Pfs25, was used as an IgG1 isotype matched negative control. The main features of the in vivo functional assays here have been described [34] and experimental details of the assays, including the use the parasites expressing luciferase induced bioluminescence as a measure of liver burden, have been recently reported [20].…”

Structural delineation of potent transmission-blocking epitope I on malaria antigen Pfs48/45

“…Transmission-blocking vaccines (TBVs) are based on this principle, and aim to elicit antibodies in humans that can reduce Pf transmission to the vector when mosquitoes ingest these antibodies during feeding 6 . Target proteins for TBV development are located on the surface of gametocytes/gametes (P48/45 7 , P230 8 ) and zygotes/ookinetes (P25, P28) 9 , 10 , or are expressed within the mosquito midgut (e.g. APN1 11 and FREP1 12 ).…”