Abstract
Pfs230 is a leading malaria transmission blocking vaccine (TBV) candidate. Comprising 3135 amino acids (aa), the large size of Pfs230 necessitates the use of sub-fragments as vaccine immunogens. Therefore, determination of which regions induce functional antibody responses is essential. We previously reported that of 27 sub-fragments spanning the entire molecule, only five induced functional antibodies. A “functional” antibody is defined herein as one that inhibits Plasmodium falciparum parasite development in mosquitoes in a standard membrane-feeding assay (SMFA). These five sub-fragments were found within the aa 443–1274 range, and all contained aa 543–730. Here, we further pinpoint the location of epitopes within Pfs230 that are recognized by functional antibodies using antibody depletion and enrichment techniques. Functional epitopes were not found within the aa 918–1274 region. Within aa 443–917, further analysis showed the existence of functional epitopes not only within the aa 543–730 region but also outside of it. Affinity-purified antibodies using a synthetic peptide matching aa 543–588 showed activity in the SMFA. Immunization with a synthetic peptide comprising this segment, formulated either as a carrier-protein conjugate vaccine or with a liposomal vaccine adjuvant system, induced antibodies in mice that were functional in the SMFA. These findings provide key insights for Pfs230-based vaccine design and establish the feasibility for the use of synthetic peptide antigens for a malaria TBV.
Highlights
Morbidity and mortality from malaria decreased significantly from 2000 to 2015, but progress has stalled since 2015
The five original total IgGs were independently applied to an affinity column which was coupled with cPro/CM1-2 to deplete antibodies that bind to either cPro, CM1, or CM2 (Fig. 2a)
We confirmed that the cPro/CM1-2depleted IgGs from anti-cPro/CM1-4 and anti-cPro/CM1-3 total IgGs reacted with a CM3-4 recombinant protein measured by ELISA (Fig S1a) and with native Pfs[230] molecule by western blot (Fig S1b)
Summary
Morbidity and mortality from malaria decreased significantly from 2000 to 2015, but progress has stalled since 2015. The mouse antibodies generated against the five constructs in the previous study[17] were tested by SMFA, and IC80 values, the concentration of IgG which shows an 80% reduction in oocyst density (%TRA), were estimated as 157–634 μg/mL depending on the constructs
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