Heterologous Expression and Evaluation of Novel Plasmodium falciparum Transmission Blocking Vaccine Candidates

Abstract

Malaria transmission blocking vaccines (TBV) aim to induce antibodies that can interrupt Plasmodium falciparum development in the mosquito midgut and thereby prevent onward malaria transmission. A limited number of TBV candidates have been identified and only three (Pfs25, Pfs230 and Pfs48/45) have entered clinical testing. While one of these candidates may emerge as a highly potent TBV candidate, it is premature to determine if they will generate sufficiently potent and sustained responses. It is therefore important to explore novel candidate antigens. We recently analyzed sera from naturally exposed individuals and found that the presence and/or intensity of antibodies against 12 novel putative surface expressed gametocyte antigens was associated with transmission reducing activity. In this study, protein fragments of these novel TBV candidates were designed and heterologously expressed in Drosophila melanogaster S2 cells and Lactococcus lactis. Eleven protein fragments, covering seven TBV candidates, were successfully produced. All tested antigens were recognized by antibodies from individuals living in malaria-endemic areas, indicating that native epitopes are present. All antigens induced antigen-specific antibody responses in mice. Two antigens induced antibodies that recognized a native protein in gametocyte extract, and antibodies elicited by four antigens recognized whole gametocytes. In particular, we found that antigen Pf3D7_0305300, a putative transporter, is abundantly expressed on the surface of gametocytes. However, none of the seven novel TBV candidates expressed here induced an antibody response that reduced parasite development in the mosquito midgut as assessed in the standard membrane feeding assay. Altogether, the antigen fragments used in this study did not prove to be promising transmission blocking vaccine constructs, but led to the identification of two gametocyte surface proteins that may provide new leads for studying gametocyte biology.

Highly potent, naturally acquired human monoclonal antibodies against Pfs48/45 block Plasmodium falciparum transmission to mosquitoes

“…Proteins were produced as previously described. 45 In short, Drosophila melanogaster S2 cells (ExpreS 2 ion Biotechnologies, Denmark) were transfected according to manufacturer’s instructions to generate stable polyclonal cell lines. To capture expressed proteins, clarified five-day batch culture supernatant was filtered and directly applied on a cOmplete™ His-Tag purification column (Sigma-Aldrich).…”

“…Transmission reducing activity (TRA) was calculated as the reduction in oocysts compared to a negative control, using a negative binomial regression model as previously described. 45 SMFA data analyses were done in R (version 4.1.2).…”

Potent transmission-blocking monoclonal antibodies from naturally exposed individuals target a conserved epitope on Plasmodium falciparum Pfs230

“…TRA values were calculated using a negative binomial regression model for samples that were tested in a single SMFA experiment and using a mixed-effects negative binomial regression model for samples that were tested in multiple independent SMFA experiments. 74 , 75 IC 80 values were calculated by linear regression analysis on the log 10 transformed ratio of mean oocyst count in control and test sample, and square root of antibody concentration, and the 95% confidence intervals for the IC 80 values were calculated with the delta method. 76 SMFA data analyses were done in R (version 4.1.2).…”