Tissue‐resident memory T cells are epigenetically cytotoxic with signs of exhaustion in human urinary bladder cancer

Tissue‐resident memory T (T(RM)) cells are CD8(+) T lymphocytes that reside in the tissues, including tumours. This T cell subset possesses a magnitude of cytotoxicity, but its epigenetic regulation has not been studied. Here, we investigate the impact of perforin DNA methylation in T(RM) cells and correlate it with their functional potential. Fifty‐three urothelial urinary bladder cancer (UBC) patients were recruited prospectively. The DNA methylation status of the perforin gene (PRF1) locus in T(RM) cells was investigated by pyrosequencing. Flow cytometry with ViSNE analysis and in‐vitro stimulation were used to evaluate T(RM) cell phenotypes. We discovered that tumour T(RM) cells have low DNA methylation in the PRF1 locus (32·9% methylation), which corresponds to increased numbers of perforin‐expressing T(RM) cells. Surprisingly, programmed cell death 1 (PD‐1) expression is high in tumour T(RM) cells, suggesting exhaustion. Following interleukin‐15 and T cell receptor stimulation, perforin and T‐bet expressions are enhanced, indicating that T(RM) cells from tumours are not terminally exhausted. Moreover, a high number of T(RM) cells infiltrating the tumours corresponds to lower tumour stage in patients. In conclusion, T(RM) cells from UBC tumours are epigenetically cytotoxic with signs of exhaustion. This finding identifies T(RM) cells as potential new targets for cancer immunotherapy.