Efficient development of Plasmodium liver stage-specific memory CD8+ T cells during the course of blood-stage malarial infection

Immunity to Plasmodium liver stages in individuals in malaria-endemic areas is inextricably linked to concomitant blood-stage parasitemia. Although Plasmodium sporozoite infection induces measurable CD8(+) T cell responses, the development of memory T cells during active erythrocytic infection remains uncharacterized. Using transgenic T cells, we assessed antigen-specific effector CD8(+) T cell responses induced by normal (NorSpz) and radiation-attenuated (IrrSpz) Plasmodium yoelii sporozoites. The magnitude, phenotypic activation, and differentiation pathway of CD8(+) T cells were similarly induced by NorSpz and IrrSpz. Moreover, in normal mice, memory T cells elicited after priming with NorSpz and IrrSpz generated identical recall responses after a heterologous boost strategy. Furthermore, these recall responses exhibited comparable in vivo antiparasite activity. Our results indicate that sporozoites that retain their infective capacity induce memory CD8(+) T cells that are robustly recalled by secondary immunization. Thus, erythrocytic infection does not preclude the establishment of memory CD8(+) T cell responses to malarial liver stages.