Long-lasting protective immunity against rodent malaria parasite infection at the blood stage by recombinant BCG secreting merozoite surface protein-1.

Previously, we constructed a recombinant live BCG (rBCG) secreting a 15 kDa C-terminal region of MSP-1 from Plasmodium yoelii (MSP-1(15)) and succeeded in the induction of more efficient protective immunity against parasite infection than observed with artificial adjuvants (Matsumoto S, Yukitake H, Kanbara H, Yamada T. Recombinant Mycobacterium bovis bacillus Calmette-Guerin secreting merozoite surface protein 1 (MSP-1) induces protection against rodent malaria parasite infection depending on MSP-1-stimulated interferon gamma and parasite-specific antibodies. J Exp Med 1998;188:845-54 [1]). In this study, we examined the endurance of the protective effects. The protective effect generated by rBCGMSP-1(15) was observed even 9 months after final immunization, whereas the effects of immunization by MSP-1(15) together with incomplete Freund adjuvant (IFA) were found to last only 4 months.