PDCD1 and melanoma: First, we classified 472 melanoma samples from the TCGA cohort into hot tumor samples and cold tumor samples using an unsupervised clustering method on the basis of hot tumor signature genes (CCL5, CD8A, PDCD1, CD8B, CXCR3, CXCL9, CXCL10, CD4, CD3E, CXCL11, CD274, and CXCR4; Figures 7A–D and Supplementary Table S6).