High-Level Expression of the Malaria Blood-Stage Vaccine CandidatePlasmodium falciparumApical Membrane Antigen 1 and Induction of Antibodies That Inhibit Erythrocyte Invasion

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Abstract
Apical membrane antigen 1 (AMA-1) is a highly promising malaria blood-stage vaccine candidate that has induced protection in rodent and nonhuman primate models of malaria. Authentic conformation of the protein appears to be essential for the induction of parasite-inhibitory antibody responses. Here we have developed a synthetic gene with adapted codon usage to allow expression ofPlasmodium falciparumFVO strain AMA-1 (PfAMA-1) inPichia pastoris. In addition, potential N-glycosylation sites were changed, exploiting the lack of conservation of these sites inPlasmodium, to obtain high-level secretion of a homogeneous product, suitable for scale-up according to current good manufacturing procedures. Purified PfAMA-1 displayed authentic antigenic properties, indicating that the amino acid changes had no deleterious effect on the conformation of the protein. High-titer antibodies, raised in rabbits, reacted strongly with homologous and heterologousP. falciparumby immunofluorescence. In addition, purified immunoglobulin G from immunized animals strongly inhibited invasion of red blood cells by homologous and, to a somewhat lesser extent, heterologousP. falciparum.