Immune checkpoint inhibitors (ICIs), including antibodies targeting the programmed cell death 1 (PD-1)-PD-1 ligand 1 (PD-L1) axis (such as nivolumab and pembrolizumab) and cytotoxic T lymphocyte antigen 4 (CTLA4) (like ipilimumab), have gained approval from the US Food and Drug Administration (FDA) for the treatment of various cancers, which conferring a notable survival advantage to numerous patients 2. Here, PDCD1 is linked to cancer.