CD274 and neoplasm: Immunostimulatory immune cells such as M1 macrophages, lymphocytes and natural killer (NK) cells play critical roles in tumor cell elimination whereas immunosuppressive immune cells such as myeloid derived suppressor cells (MDSCs), M2 macrophages, T regulatory cells (Tregs) and PD-L1+ immune cells inhibit the tumor suppressing functions of immunostimulatory immune cells, leading to tumor progression [101].