Development of Recombinant Expression Systems for the Production of Malaria Antigens.

Malarial erythrocytic-stage antigens produce humoral immunity by inducing protective antibodies to epitopes on surface antigens on the parasites. The merozoite surface protein-1 (MSP1) of P. falciparum is a major malaria erythrocytic-stage vaccine candidate. MSP1 may play a role in binding and/or infection of erythrocytes by merozoites (parasites) during red blood cell invasion. The C-terminal fragment of MSP1, MSP1(42), is highly conserved among all known strains of P. falciparum. However, it is folded into a complex structure containing six possible disulfide bridges. Immunization with recombinant proteins that have native-like conformations may elicit long-lasting protective immunity that mimics the natural development of humoral immunity. We have used a novel bacterial expression system that utilizes tightly regulatable transcription and translation signals to control expression of potentially toxic heterologous proteins. Several plasmids encoding MSP1(42) were constructed and tested for their ability to express recombinant protein. These constructs were designed for purification using Ni(+2)-chelating chromatography. Our results show that the recombinant proteins contained conformationally similar structures to the native parasites. The objectives were to develop recombinant MSP1(42) molecules that were structurally correct, (b) to develop fermentation and purification processes that could be scaled-up for large-scale processes, and ultimately (c) to advance these products into human clinical trials.