PRF1 and melanoma: GZMK cells had low expression of cytotoxic genes (PRF1/GNLY/GZMB) but harbored high expression of both transcription factors TCF7 and EOMES. TCF7-expressing CD8+ cells mediate and sustain immune responses via stem-like activities in a melanoma murine model treated with a PD-1 inhibitor, and following infection with lymphocytic choriomeningitis virus80–82.