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 multigravida women who acquired specific immunity to CSA-binding parasites, or by antibodies from animals immunized with antigens that mediate parasite binding to CSA. Highlighted in this years summary are results from our publications: Antibody levels to recombinant VAR2CSA domains vary with Plasmodium falciparum parasitaemia, gestational age, and gravidity, but do not predict pregnancy outcomes. Women become resistant to Plasmodium falciparum pregnancy malaria over successive pregnancies as they acquire antibodies to the variant surface antigen VAR2CSA, a leading vaccine candidate. We assessed VAR2CSA antibody levels among pregnant women enrolled in a longitudinal cohort study of mother-infant pairs in Ouelessebougou, Mali. Antibody levels to VAR2CSA were higher in multigravidae than primigravidae. Nntibody levels to VAR2CSA domains during infection, then declined sharply in primigravidae but not in secundigravidae or multigravidae. A relationship between any VAR2CSA antibody specificity and protection from adverse pregnancy outcomes was not detected. The lack of an association between VAR2CSA domain antibody reactivity and improved pregnancy outcomes suggests that the recombinant proteins that are being considered as vaccine immunogens may not present native epitopes targeted by protective antibodies. In addition to our published findings, we completed preclinical studies to assess a variety of PMV candidates, and we will prepare manuscripts based on many of these results in FY19: We examined rodent IgG induced by DNA vaccine with different inserts (full length extracellular VAR2CSA; ID1-ID2; DBL3-6) for functional anti-adhesion activity with fresh parasite samples collected from pregnant women in Mali. The ID1-ID2 VAR2CSA fragments are similar to a vaccine candidate currently in clinical development; the DBL3-DB6 fragments were designed based on in silico predictions of a stable soluble structure. The DBL3-DBL6 immunogens but not full length VAR2CSA and ID1-ID2 fragment induced heterologous activity against a fraction of fresh parasite samples. We examined nonhuman primate IgG induced by recombinant protein vaccine candidates: 2 clinical vaccine candidates (from our European collaborators) and 1 preclinical vaccine candidate (developed at LMIV). IgG were assessed after immunization of Aotus monkeys, and also after episodes of placental malaria when the Aotus monkeys became pregnant to assess boosting of vaccine responses. Unblinding the study and data analysis is on-going, however the blinded data do not suggest that functional antibody responses were boosted by placental malaria infections. We examined rodent IgG induced by viral vectored vaccines (2 different alleles of PfVAR2CSA in gorilla adenoviruses (GCAd) prepared by our collaborator GenVec, now absorbed in the company Precigen). In a pilot study, the GCAd vaccines induced could induce serum reactivity to native antigen expressed on infected red cells, and boosting of the response using membrane fraction of infected rbc (adjuvanted with Freunds adjuvant) showed yielded strong reactivity to native antigen as well as functional activity that blocked iRBC adhesion to the placental receptor CSA. We also achieved a notable technical advance at LMIV in FY18: 5 different alleles of full-length PfVAR2CSA were cloned into a mammalian secreted protein expression vector and successfully transfected into suspension CHO cells (CHO-S). Full-length PfVAR2CSA was detected in the cell supernatant and purified by nickel affinity chromatography. Purified PfVAR2CSA reacted by ELISA to a conformational dependent antibody that only recognize full-length folded PfVAR2CSA, suggesting full-length PfVAR2CSA generated by CHO cells is correctly folded.
