Pregnant mothers are susceptible to malaria during pregnancy despite pre-existing immunity. Malaria during pregnancy is responsible for nearly 200,000 infant and 10,000 maternal deaths every year. Placental malaria, a mechanism by which malaria in pregnancy causes adverse perinatal outcomes, is characterised by the sequestration of Plasmodium falciparum-infected erythrocytes in the placenta via chondroitin sulphate A (CSA) cellular receptor. A P. falciparum erythrocyte membrane protein 1 family member, VAR2CSA, is the primary antigen responsible for the sequestration of parasites via CSA. Antibodies to VAR2CSA are acquired over successive pregnancies and have been associated with protection against placental malaria and adverse pregnancy outcomes. Current placental malaria vaccines that target VAR2CSA, PRIMVAC and PAMVAC, can only generate neutralising antibodies to homologous parasite strains, rendering them ineffective against heterologous strains in the field. Recently, there has been growing interest in the use of monoclonal antibodies (mAbs) both as therapeutics and as tools for characterisation of antibody-antigen interactions. To date, no broadly reactive antibodies have been identified against VAR2CSA that can neutralise parasite adherence and induce parasite clearance via phagocytosis by innate immune cells.
In this study, we hypothesized that monoclonal antibodies from multigravida women are cross-reactive across multiple P. falciparum strains and functional in preventing CSA adhesion of infected erythrocytes and inducing antibody-mediated phagocytosis by innate immune cells. So far, 10 multigravida women with high Ab titers for full-length VAR2CSA have been identified in malaria-endemic Madang, Papua New Guinea. VAR2CSA-specific memory B cells were isolated, and variable regions of the corresponding antibodies were used for generating IgG monoclonal antibodies. Developed monoclonals will be characterised for reactivity and functionality across 7 parasite strains expressing heterologous forms of VAR2CSA.
Assays exploring monoclonal recognition of native VAR2CSA from heterologous strains and opsonic phagocytosis by THP-1 cell line and isolated neutrophils will be measured using flow cytometry. Furthermore, antibody-mediated inhibition of opsonised infected erythrocyte binding to CSA will be measured via binding inhibition assay.
Identification of broadly reactive monoclonal functional antibodies with the ability to induce parasite clearance via opsonic phagocytosis of innate immune cells and neutralise parasite sequestration by inhibiting CSA adhesion could inform future vaccine design and therapeutics against placental malaria.