PDCD1 and neoplasm: Interestingly, some studies suggest that neither knockout nor overexpression of PD-L1 in tumor cells affected the efficacy of PD-L1 inhibitors, but it is the PD-L1 located on immune cells (DCs, macrophages) that correlates with the efficacy of anti-PD-1 alone or in combination with anti-CTLA-4.