The application of immune checkpoint inhibitors (ICI) can inhibit the function of suppressive immune cells by targeting the expression of checkpoint molecules, such as programmed death protein-1 (PD1), programmed death protein-ligand-1 (PD-L1), or cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) on immune cells, thereby reactivating the anti-tumor immune response and killing tumor cells (He et al., 2020). Here, PDCD1 is linked to neoplasm.