CD274 and neoplasm: More importantly, by using PD-L1 knockout mice and multiple PD-L1 knockdown or knockout tumor cell lines, we further showed that although PD-L1 was also highly expressed on tumor infiltrating myeloid cells and other stromal cells in the tumor microenvironment, it was the tumor cell-associated PD-L1 expression detected T cell exhaustion and immune suppression inside tumor tissues9.