Studies using a recombinant vaccinia virus expressing the circumsporozoite protein of Plasmodium berghei

A recombinant vaccinia virus was constructed which expressed the circumsporozoite protein of Plasmodium berghei. Four different strains of mice belonging to different haplotypes were immunized with the recombinant virus. The antibody response to the circumsporozoite protein as well as to vaccinia virus varied among the strains, independently of each other. The anti-circumsporozoite protein titers were comparable to that obtained on immunization with irradiated sporozoites. Spleen cells from H2d mice immunized with P. berghei sporozoites showed a significant proliferative response when cultured in vitro with a low multiplicity of the recombinant vaccinia virus. A weak cytotoxic T lymphocyte response specifically targeting the circumsporozoite protein could be identified in spleens of BALB/c (H2d) mice immunized with vaccinia virus when BALB 3T3 cells transformed with a plasmid expressing the circumsporozoite protein under control of the simian virus 40 promoter were used as target cells in the cytotoxic T lymphocyte assay. However, none of the recombinant virus-immunized animals could be protected from a challenge of sporozoites even at the lowest dose of parasite used.