Although more ICIs have been developed already,226,227 anti-CTLA-4 (ipilimumab), PD-1 (pembrolizumab, nivolumab, pidilizumab) and PD-L1 antibodies (atezolizumab, avelumab and durvalumab) have been the focus of current clinical consideration of checkpoint inhibitors.32 PD-1 is a prominent immunosuppressive trans-membrane molecule that is expressed on the surface of T cells.228 In the tumor microenvironment (TME), T cells express high levels of PD-1 molecules, which can bind to PD-L1 on tumor cells or other immune cells and PD-L2 on macrophages and dendritic cells (DCs). Here, CTLA4 is linked to neoplasm.