PD-L1 is expressed over a much broader range than PD-L2 in both hematopoietic and non-hematopoietic cells: in non-lymphoid tissues (such as the heart, placenta, and skeletal muscles) and on APCs, including peripheral blood monocytes, activated dendritic cells (DCs), some cancer cells, and keratinocytes [103]. The gene discussed is CD274; the disease is cancer.