Immunization with VAR2CSA-DBL5 Recombinant Protein Elicits Broadly Cross-Reactive Antibodies to Placental Plasmodium falciparum-Infected Erythrocytes

Pregnancy-associated malaria is a severe clinical syndrome associated with the sequestration of Plasmodium falciparum-infected erythrocytes in the placenta. Placental binding is mediated by VAR2CSA, a member of the large and diverse P. falciparum erythrocyte membrane 1 (PfEMP1) protein family. To better understand if conserved regions in VAR2CSA can be targeted by antibodies, we immunized rabbits with VAR2CSA-DBL1 and -DBL5 recombinant proteins produced in Pichia pastoris and developed a panel of seven chondroitin sulfate A (CSA)-binding parasites from diverse geographic origins. Overall, no two parasites in the panel expressed the same VAR2CSA sequence. The DBL1 domains averaged 80% amino acid identity (range, 72 to 89%), and the DBL5 domains averaged 86% amino acid identity (range, 83 to 99%), similar to a broader sampling of VAR2CSA sequences from around the world. Whereas antibodies generated against the VAR2CSA-DBL1 recombinant protein had only limited breadth and reacted with three or four parasites in the panel, immunization with DBL5 recombinant proteins elicited broadly cross-reactive antibodies against all or most parasites in the panel, as well as to fresh clinical isolates from pregnant women. These findings demonstrate that the major PfEMP1 variant expressed by placental isolates exposes strain-transcendent epitopes that can be targeted by vaccination and may have application for pregnancy malaria vaccine development.