Tumour cells and tumour-associated myeloid cells such as TAMs and MDSCs can express high levels of checkpoint ligands such as PD-L1 and PD-L2 [73], which can potentially switch off tumour-infiltrating immune cells—particularly CAR T cells—before they get the chance to exert their cytotoxic effect. The gene discussed is PDCD1LG2; the disease is neoplasm.