PDCD1 and neoplasm: The interaction between PD‐1 and PD‐L1 blocks CD8+ cytotoxic T cell proliferation and survival, leads to apoptosis of tumor‐infiltrating lymphocytes, and promotes differentiation of CD4+ T lymphocytes into Tregs.1 5 6 Most cancer cells possess the ability to express inhibitory ligands such as PD-L1, for example, in response to interferons (IFN).