CD226 identifies effector CD8⁺ T cells during tuberculosis and costimulates recognition of Mycobacterium...

CD8⁺ T cells defend against Mycobacterium tuberculosis (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 CD226⁺CD8⁺ 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.