CD274 and autoimmune disease: PD-L1 (B7-H1), a crucial immune checkpoint, is not only expressed on cancer cells and hematopoietic cells including T cells, macrophages, dendritic cells (DCs), et al, but also in some non-hematopoietic tissues including pancreas, vascular endothelium, muscle, skin tissues, et al. PD-L1/PD-1 signaling pathway, as a negative regulatory mechanism against the immune response, plays an important role in tumor evasion from immune surveillance and the occurrence of autoimmune diseases 17.