PDCD1 and melanoma: Furthermore, the presence of tumor-infiltrating TCF1+ CD8 T cells in the tumors of melanoma patients correlated with the responsiveness to αPD-1 therapy (13), and a higher frequency of Tpex cells among the PD-1+ CD8 TILs was associated with prolonged progression-free survival and overall survival in patients with melanoma who received immune checkpoint blockade therapy (9).