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 (329% 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.