PDCD1 and neoplasm: Incorporating a cell-intrinsic PD-1 checkpoint blockade within CAR T cells by engineering the expression of the PD-1-dominant negative receptor (DNR), a decoy receptor that binds PD-L1 on tumour cells, is a promising strategy as the co-transduction of PD1-DNR with a CAR has been shown to enhance T-cell functional persistence and T-cell resistance to tumour-mediated T-cell inhibition, thus disrupting the inhibitory action of this TME element and maintaining T-cell activation [68].