PDCD1LG2 and neoplasm: PD‐L1 is physiologically expressed by immune cells as well as in lung tissue, vascular endothelium, mesenchymal stem cells, astrocytes, and keratinocytes.9 PD‐L2 expression is more restricted to antigen‐presenting cells and does not show physiologically relevant expression in activated T cells or keratinocytes.4, 9 PD/PD‐L signaling is likely not monodirectional from antigen‐presenting cells or tumor cells to T cells.