PARTIAL PROTECTION AGAINST MALARIA BY IMMUNIZATION WITH LEISHMANIA-ENRIETTII EXPRESSING THE PLASMODIUM-YOELII CIRCUMSPOROZOITE PROTEIN

Since infection with Leishmania species induces CD4(+) and CD8(+) anti -leishmania T cells, we assessed protection against malaria by immuniz ation with Leishmania enriettii transfected with the gene encoding the Plasmodium yoelii circumsporozoite protein (PyCSP). The recombinant p lasmid appeared to be a circular episome in the host cells. Reverse tr anscription PCR showed that the PyCSP was trans-spliced by the additio n of the 39-bp spliced leader of L. enriettii at its 5' end. The trans fectant expressed a protein in a pattern similar to that found in the sporozoite itself. Immunofluorescence and immunoelectron microscopy in dicated that PyCSP was abundantly expressed on the surface of the para site. Mice immunized with the transfectant produced antibodies to spor ozoites, had a delay in onset of parasitemia after challenge, and 4 of 22 (18%) were completely protected. The protected mice had cytotoxic T lymphocytes against the PyCSP. Immunization with recombinant vaccini a, Salmonella typhimurium, and pseudorabies virus expressing the PyCSP induces excellent immune responses, but has not been shown to protect against challenge. Thus, the modest protection found in these initial studies represents a step forward. After further work Leishmania may prove to be an important live vector vaccine system for induction of p rotective immune responses.