PDCD1 and melanoma: The results of a melanoma study identified Tcf1+PD-1+CD8+ T cells as a cluster of tumor reactive TILs with an exhausted phenotype and central memory characteristics by combining the aforementioned two molecules(Tcf1 and PD-1), suggesting that immune checkpoint blockade therapy results not in the functional recovery of highly exhausted cells but in promoting the strong proliferation of Tcf1+PD-1+CD8+ T cells to produce antitumor effects (95).