We evaluated the strength of three established transmission-blocking mAbs against naturally acquiredP. Sequencing of oocysts that survived high mAb concentrations did not suggest enrichment of escape genotypes. mAb 2A2 (-Pfs230) only reduced transmission of parasites from a minority of the donors, suggesting that it targets a non-conserved epitope. Using six laboratory-adapted strains, we revealed that mutations in one Pfs230 domain name correlate with mAb gamete surface binding and functional TRA. Our findings demonstrate that, despite the conserved nature of sexual stage antigens, minor sequence variance can significantly impact the efficacy of transmission-blocking mAbs. Since mAb 45.1 shows high potency against genetically diverse strains, our findings support its further clinical development and may inform Pfs48/45 vaccine design. Subject terms:Parasitic contamination, Vaccines, Microbiology == Introduction == Malaria, caused by the unicellular parasitePlasmodiumspp., continues to cause high mortality and morbidity worldwide1. Current tools, while demonstrating great impact, are considered insufficient to eliminate malaria from most African regions2. One huge challenge for malaria control and removal is the efficient spread of malaria to mosquitoes that starts with the uptake of circulating sexual stage parasites, gametocytes, by the mosquito vector during a blood meal on an infected individual. In the mosquito midgut, gametocytes egress from your host red blood cells and develop into gametes. Male gametocytes produce up to eight motile microgametes upon exflagellation and female gametocytes develop into one immotile macrogamete. Zygotes are created upon fertilization of a macrogamete by a microgamete3,4. The zygote evolves into a motile ookinete that is able to traverse the JNJ-17203212 midgut wall to establish an oocyst5. After differentiation and replication inside the oocyst, parasites are released as sporozoites that migrate to the salivary glands and render the mosquito infectious. Transmission-blocking vaccines (TBVs) aim to induce antibodies that are taken up by the mosquito vector together with the infectious blood meal made up of gametocytes. In the mosquito midgut, these antibodies bind to surface antigens on sexual stage parasites and thereby interfere with sexual development. Three sexual stage antigens are currently under clinical development and are leading TBV candidates: Pfs48/45, Pfs230, and Pfs25. Pfs48/45 and Pfs230 are expressed on the surface of gametes and antibodies targeting these antigens prevent fertilization69. Antibodies against Pfs25 target zygotes JNJ-17203212 and ookinetes and prevent oocyst formation6,8,9. Development of these vaccine candidates has been hampered by difficulties with recombinant protein expression and replication of pre-clinical successes. The first versions of Pfs25-based vaccines have been tested in both naive healthy adults and in malaria-exposed individuals1013. Recently, Pfs230-based vaccines have also entered phase I studies (ref.14and clinicaltrials.gov:NCT02942277), as well as a vaccine targeting Pfs48/45 (clinicaltrials.gov:NCT04862416). While the development of a highly effective TBV formulation is still challenging, a panel of potent monoclonal antibodies (mAbs) targeting JNJ-17203212 these antigens is usually readily available. These have been isolated from immunized rodents and block development of cultured parasites in in vitro standard membrane feeding assays (SMFAs)15. These mAbs provide insight into protective epitopes and as such may inform vaccine design and development16. In addition, passive immunization with mAbs can form an alternative immunization strategy that conveys predictable high-level protection. Fc modifications that lengthen the serum half-life of immunoglobulin (IgGs)17make it conceivable that efficacious concentrations of mAbs can be sustained for periods that are sufficiently long to support malaria removal initiatives, contain outbreaks or span seasonal peaks of transmission. Given the genetic diversity of parasites in endemic settings, cross-strain protection is crucial for the efficacy of both active and passive immunization strategies. Asexual stage antigens in particular are highly polymorphic and vaccines targeting these antigens Rabbit Polyclonal to TNFAIP8L2 face challenges to induce cross-strain protection18. The general consensus is usually that sexual stage antigens are well conserved (Supplementary Fig.1); natural genetic variance may thus have limited impact on TBVs and antibody efficacy. Nevertheless, genetic variance has been observed, especially in Pfs23019. Given their JNJ-17203212 increasing prominence in malaria vaccine development, it is both timely and important to assess whether active and passive immunization strategies are likely to encounter challenges due to genetic diversity. Here we compared the efficacy of mAbs targeting Pfs48/45, Pfs230 and Pfs25 JNJ-17203212 in membrane feeding assays against cultured parasite strains and parasites derived from naturally infected gametocyte service providers in Cameroon and Burkina Faso. == Results == == Three mAbs strongly reduce transmission of reference strain NF54 == Transmission-reducing activity (TRA) was determined by SMFA for three potent mAbs: 45.1 (-Pfs48/45)20, 2A2 (-Pfs230)21,22, and 4B7 (-Pfs25)23. mAbs 45.1 and 2A2 are the most potent transmission-blocking mAbs described to date; 4B7 targets Pfs25 that currently forms the most advanced TBV. All mAbs were raised againstPlasmodium falciparumNF54. Cultured NF54 parasites were mixed with serial dilutions of.