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

Abstract

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.

Antibodies to Escherichia coli-Expressed C-Terminal Domains of Plasmodium falciparum Variant Surface Antigen 2-Chondroitin Sulfate A (VAR2CSA) Inhibit Binding of CSA-Adherent Parasites to Placental Tissue

“…While antibodies raised against DBL5ε expressed in Pichia (25) and baculovirus (20) were not inhibitory or had very limited inhibition activity, antibodies raised against E. coli-expressed FCR3 strain DBL5ε were inhibitory against several laboratory lines selected for CSA binding using a flow binding inhibition assay (26). Our results, obtained in a static assay, support and expand the data of the latter work, further demonstrating not only inhibition of lab CSA-binding strains but also inhibition of maternal field isolates.…”

Multilaboratory Approach to Preclinical Evaluation of Vaccine Immunogens for Placental Malaria

“…A pregnancy malaria vaccine is expected to induce immune responses with qualities similar to those of naturally acquired immunity, including broad recognition and functional activity against diverse placental parasites. Previous studies reported that immunization with recombinant VAR2CSA domains can elicit antibodies that recognize the surface of homologous (33)(34)(35) and heterologous (22,27,28,36,37) IRBCs. Naturally acquired antiadhesion antibodies are associated with protection from PM (29), and therefore, an effective PM vaccine should elicit antibodies that can inhibit parasite adhesion.…”

High Levels of Antibodies to Multiple Domains and Strains of VAR2CSA Correlate with the Absence of Placental Malaria in Cameroonian Women Living in an Area of High Plasmodium falciparum Transmission

“…Each of the domains has been characterized in previous studies (Table 1). Cloning and production of recombinant proteins for DBL1 through DBL6 (except for DBL2) from parasite strains 7G8 (South America), 3D7 (origin ambiguous), and FCR3 (origin ambiguous, genotype most close to South East Asia) (39) were performed in Pichia pastoris (Pp in protein designations) as previously described (7,10). All proteins contained a histidine tag at the C terminus.…”