Generation of cross-protective antibodies against Plasmodium falciparum sequestration by immunization with an erythrocyte membrane protein 1-duffy binding-like 1 alpha domain.

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is an important virulence factor on the surface of infected erythrocytes. Naturally acquired antibodies to PfEMP1 expressed by parasites causing severe malaria are suggested to be protective and of major interest for the development of a vaccine against severe disease. In this study, the PfEMP1 expressed by a parasite clone displaying a multiadhesive phenotype associated with severe malaria was well recognized by sera of malaria semi-immune children. The efficiency of the Duffy binding-like 1 alpha (DBL1 alpha) domain of this PfEMP1 was therefore, alone or in combination with two additional DBL1 alpha domains, evaluated as a potential vaccine candidate using both a rodent model and a primate model. Antibodies against the DBL1 alpha domain were generated by immunization with recombinant DBL1 alpha-Semliki Forest virus particles and recombinant protein and analyzed in vitro. The immunized animals were challenged in vivo with various parasite strains or clones. Immunization with the PfEMP1-DBL1 alpha domain abolished the PfEMP1-dependent sequestration of the homologous strain in immunized rats and substantially inhibited parasite adhesion in immunized monkeys. Protection against sequestration of heterologous parasite strains was also confirmed by direct or indirect challenge in the rat model. These results strongly support the use of the DBL1 alpha domain in the development of a vaccine targeting severe malaria.