Expression of CD39 Identifies Activated Intratumoral CD8+ T Cells in Mismatch Repair Deficient Endometrial Cancer.

Identification of human cancer-reactive CD8+ T cells is crucial for the stratification of patients for immunotherapy and determination of immune-therapeutic effects. To date, these T cells have been identified mainly based on cell surface expression of programmed cell death protein 1 (PD-1) or co-expression of CD103 and CD39. A small subset of CD103- CD39+ CD8+ T cells is also present in tumors, but little is known about these T cells. Here, we report that CD103- CD39+ CD8+ T cells from mismatch repair-deficient endometrial tumors are activated and characterized predominantly by expression of . In vitro, transforming growth factor-beta (TGF-β) drives the disappearance of this subset, likely through the conversion of CD103- CD39+ cells to a CD103+ phenotype. On the transcriptomic level, T cell activation and induction of CD39 was associated with a number of tissue residence and TGF-β responsive transcription factors. Altogether, our data suggest CD39+ CD103- CD8+ tumor-infiltrating T cells are recently activated and likely rapidly differentiate towards tissue residence upon exposure to TGF-β in the tumor micro-environment, explaining their relative paucity in human tumors.