PDCD1 and melanoma: However, the findings that PD-1hiCTLA-4hi TILs that were preferably expanded after anti-PD-1 therapy in melanoma patients (263) counters the findings in preclinical models [PD-1hi T cells were irreversible (178) and anti-PD-1 therapy was effective only in tumors with low frequencies of PD-1+ T cells (24)].