PDCD1 and metastatic melanoma: To characterize the relevance of IFNγ sensing by CD8 T cells during carcinogenesis, we first examined IFNγR expression on T cell subsets in the blood of eight patients with metastatic melanoma before and 21 days after undergoing checkpoint blockade (anti-CTLA-4 and/or anti-PD-1 immunotherapy)10.