Immunization with recombinant duffy binding-like-γ3 induces pan-reactive and adhesion-blocking antibodies against placental chondroitin sulfate A-binding Plasmodium falciparum parasites

Maternal malaria is associated with the sequestration, in the placenta, of Plasmodium falciparum-infected erythrocytes onto chondroitin sulfate A (CSA), via the duffy binding-like (DBL)-γ3 domain of the P. falciparum erythrocyte membrane protein 1 (PfEMPICSA) (DBL-γ3CSA). The production of antibodies against CSA-binding infected erythrocytes (IEsCSA) is correlated with resistance to maternal malaria in multiparous women. We produced recombinant DBL-γ3CSA (rDBL-γ3CSA) in insect cells, corresponding to 2 variant DBL-γ3CSA subtypes that mediate binding to CSA in laboratory lines and placental isolates. Both recombinant cysteine-rich DBL-γ3CSA domains blocked IEsCSA binding to CSA. Immunization of mice, with the rDBL-γ3CSA-FCR3 and rDBL-γ3CSA-3D7 domains, resulted in the generation of antibodies recognizing homologous and heterologous rDBL-γ3CSA, a finding indicating conserved epitopes inducing a pan-reactive immune response. Mouse monoclonal antibodies (MAbs) against both recombinant proteins were pan-reactive with various IEsCSA. One MAb efficiently inhibited and reversed IECSA cytoadhesion to endothelial cells in vitro. Thus, DBL-γ3CSA is the target of inhibitory and pan-reactive antibodies. Saimiri sciureus monkeys immunized with FCR3-rDBL-γ3CSA developed pan-reactive and inhibitory antibodies, a finding suggesting that the development of a vaccine to prevent maternal malaria is feasible.