PDCD1 and neoplasm: In contrast, in the PD-L1−/CD8high group, immune suppressive mechanisms other than the PD-1/PD-L1 axis [e.g., regulatory T cells, tumor-associated macrophages, or myeloid-derived suppressor cells (MDSCs)], may be activated for the purpose of immune escape [37, 38]; however, the specific details remain unclear.