Increased PD-1 expression in tumor-infiltrating CD8+ T cells (TIL) has been associated with T cell exhaustion and poor clinical outcomes.3 Concurrently, high expression of the ligand PD-L1 has been reported in various cancers, as well as in immunosuppressive cell types such as Tregs, myeloid-derived suppressor cells and cancer-associated fibroblasts. This evidence concerns the gene PDCD1 and cancer.