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

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.