Owing to the evident prognosis benefits of cancer immunotherapy, antibodies targeting the negative immune checkpoint molecules programmed cell death protein 1 (PD-1) or PD-1 ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) (Hodi et al., 2010) has been approved by the FDA in the treatment of several cancer entities. Here, PDCD1 is linked to cancer.