CD226 identifies effector CD8 T cells during tuberculosis and costimulates recognition of -infected macrophages.

CD8 T cells defend against (Mtb) infection but variably recognize Mtb-infected macrophages. To define how the diversity of lung parenchymal CD8 T cells changes during chronic infection, cells from C57BL/6J mice infected for 6- and 41-weeks were analyzed by scRNA-seq. We identified an effector lineage, including a cluster that expresses high levels of cytotoxic effectors and cytokines, and dysfunctional lineage that transcriptionally resembles exhausted T cells. The most significant differentially expressed gene between two distinct CD8 T cell lineages is CD226. Mtb-infected IFNγ-eYFP reporter mice revealed IFNγ production is enriched in CD226CD8 T cells, confirming these as functional T cells in vivo. Purified CD226 but not CD226 CD8 T cells recognize Mtb-infected macrophages, and CD226 blockade inhibits IFNγ and granzyme B production. Thus, CD226 costimulation is required for efficient CD8 T cell recognition of Mtb-infected macrophages, and its expression identifies CD8 T cells that recognize Mtb-infected macrophages.