Development of transmission blocking malaria vaccine using recombinant groteins.

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We have studied Pbs21, a major ookinete surface protein of Plasmodium berghei, for the development of a model transmission blocking immunogen. In the mouse, recombinant Pbs21 expressed in the Escherichia coli expression system (EcrPbs21) is not as effective in inducing transmission blocking antibodies as native Pbs21 (nPbs21), possibly because of differences in post-translational processing between EcrPbs21 and nPbs21. In an attempt to improve the efficacy of the recombinant molecule, we describe here the use of a baculovirus expression vector system in the silkworm Bombyx mori. Following an injection of recombinant baculovirus containing Pbs21 cDNA,B.morilarvae produced recombinant Pbs21 (BmrPbs21) with a molecular weight indistinguishable from nPbs21. Fifty micrograms of BmrPbs21 were purified from the hemolymph of one infected larva using affinity chromatography. Monoclonal antibodies reacting with reduction -sensitive epitopes of nPbs21 detected BmrPbs21 but not EcrPbs21 in Western blotting analyzes. Oocyst formation in Anopheles stephensi mosquitoes, which fed on Balb/c mice immuinized with purified BmrPbs21 and infected with P.berghei, wqs blocked by 99.1-100%. These results suggest that the baculovirus-silkworm system produces useful quantities of recombinant Pbs21 which in limited studies is structurally and immunogenically indistinguishable from the native molecule.