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

Tissue-resident memory T (T ) 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 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 cells was investigated by pyrosequencing. Flow cytometry with ViSNE analysis and in-vitro stimulation were used to evaluate T cell phenotypes. We discovered that tumour T cells have low DNA methylation in the PRF1 locus (32·9% methylation), which corresponds to increased numbers of perforin-expressing T cells. Surprisingly, programmed cell death 1 (PD-1) expression is high in tumour T cells, suggesting exhaustion. Following interleukin-15 and T cell receptor stimulation, perforin and T-bet expressions are enhanced, indicating that T cells from tumours are not terminally exhausted. Moreover, a high number of T cells infiltrating the tumours corresponds to lower tumour stage in patients. In conclusion, T cells from UBC tumours are epigenetically cytotoxic with signs of exhaustion. This finding identifies T cells as potential new targets for cancer immunotherapy.