Identification of Targets of CD8(+) T Cell Responses to Malaria Liver Stages by Genome-wide Epitope Profiling

CD8(+) T cells mediate immunity against Plasmodium liver stages. However, the paucity of parasite-specific epitopes of CD8(+) T cells has limited our current understanding of the mechanisms influencing the generation, maintenance and efficiency of these responses. To identify antigenic epitopes in a stringent murine malaria immunisation model, we performed a systematic profiling of H(2b)-restricted peptides predicted from genome-wide analysis. We describe the identification of Plasmodium berghei (Pb) sporozoite-specific gene 20 (S20)- and thrombospondin-related adhesive protein (TRAP)-derived peptides, termed PbS20(318) and PbTRAP(130) respectively, as targets of CD8(+) T cells from C57BL/6 mice vaccinated by whole parasite strategies known to protect against sporozoite challenge. While both PbS20(318) and PbTRAP(130) elicit effector and effector memory phenotypes in both the spleens and livers of immunised mice, only PbTRAP(130)-specific CD8(+) T cells exhibit in vivo cytotoxicity. Moreover, PbTRAP(130)-specific, but not PbS20(318)-specific, CD8(+) T cells significantly contribute to inhibition of parasite development. Prime/boost vaccination with PbTRAP demonstrates CD8(+) T cell-dependent efficacy against sporozoite challenge. We conclude that PbTRAP is an immunodominant antigen during liver-stage infection. Together, our results underscore the presence of CD8(+) T cells with divergent potencies against distinct Plasmodium liver-stage epitopes. Our identification of antigen-specific CD8(+) T cells will allow interrogation of the development of immune responses against malaria liver stages.