Pregnancy Malaria Vaccine development

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

Placental malaria (PM) is a major public health problem associated with severe maternal anemia, preeclampsia, pregnancy loss, low birthweight delivery and infant mortality. PM is caused by sequestration in the placenta of parasites that bind the receptor chondroitin sulfate A (CSA). Previous ex vivo experiments have shown that parasite binding to CSA can be inhibited by antibodies from multigravid women who acquired specific immunity to CSA-binding parasites, or by antibodies from animals immunized with antigens that mediate parasite binding to CSA. We report the following unpublished advances in FY2025: 1. In previously published work, we reported that a single full-length ectodomain VAR2CSA recombinant can purify broadly neutralizing antibodies from multigravid women who naturally acquired PM protective antibody. In FY2025, we extended this approach to purify IgG on the core (NTS-ID3) and the flexible (DBL5-6) arms of VAR2CSA representing the full-length ectodomain. We found that IgG purified on the NTS-ID3 fragment which contains the major CSA binding channel had similar blocking activity as that of IgG purified against the full-length ectodomain. Interestingly, purified IgG specific to DBL5-6 also exhibited similar blocking activity pattern. This finding provides evidence that epitopes targeted by antibody with broadly neutralizing activity are located in a fragment of VAR2CSA with no known CSA binding residues, suggesting alternative mechanisms of antibody blocking activity possibly by steric hindrance. 2. We explored factors that impact strain-transcending activity of anti-VAR2CSA antibody, which is key to design more potent PM vaccine candidates. We used mAb PAM1.4 (a broadly reactive anti-VAR2CSA human monoclonal antibody) to identify allelic sequence variations associated with lack of PAM1.4 reactivity in a variant of VAR2CSA that exhibited a distinct dimorphic sequence in the ID1 region of the protein. We showed that replacing the ID1 sequence by that of a variant (NF54) with PAM1.4 reactivity resulted in mAb binding to the transgenic VAR2CSAM920 . This finding highlights a case of major sequence variation in the critically important ID1 region of VAR2CSA that impeded binding of broadly reactive antibody. This observation provides new evidence of VAR2CSA polymorphism impact on the broad functional activity of PM antibody with crucial implication for improved design of potent VAR2CSA-based immunogens. 3. We analyzed VAR2CSA epitopes data generated from screening antibodies acquired by multigravid women and an Aotus monkey who naturally acquired PM protective antibody. We described VAR2CSA peptides uniquely recognized by multigravid women and those associated with the CSA binding inhibition activity in humans and Aotus. Among these peptides, two were identified in the region of VAR2CSA that interacts with CSA, suggesting that antibody targeting these sequences have potential to directly disrupt CSA binding to VAR2CSA. This information can be used in PM vaccine design, while supporting the use of this Aotus model for development of VAR2CSA-based vaccines against PM. This work is being prepared as a manuscript for journal submission. 4. Sera samples from pregnant Aotus that were immunized with one or two allelic forms of full-length ectodomain VAR2CSA have been evaluated for functional activity on parasites isolated from pregnant women. We showed that Aotus monkeys that experienced malaria infection during pregnancy developed antibody with broad blocking activity compared to those that received an immunization boost. This work is being prepared as a manuscript for journal submission. 5. We produced and characterized recombinant human decorin (RH-decorin) for placental malaria vaccine development. RH-decorin is expressed efficiently in HEK293 cells in the CSA modified form and the unmodified protein core. We developed a 2-coumn method to purify the desired modified RH-decoirin. We then compared RH-decorin to the commercially available bovine decorin that is currently used in VAR2CSA binding assays. RH-decorin binds to 5 alleles of recombinant full-length VAR2CSA as well as bovine decorin. Next, we tested the ability of native VAR2CSA to bind RH-decorin in a binding assay. RH-decorin bound erythrocytes infected with 4 different variants (NF54 and 3 maternal isolates) at levels equivalent or better than commercially available decorin. Finally, we demonstrated that RH-decorin performs as well as bovine decorin in the binding inhibition assay. Together, our results support RH-decorin as a suitable reagent for the development of VAR2CSA-based vaccines. These findings are currently being prepared for journal submission.