For instance, programmed cell death-1 (PD-1)/PD-L1 axis, and the cytotoxic T-lymphocyte antigen 4 (CTLA-4)/B7 axis, which contribute cancer cell protection through their suppressive role in tumor microenvironment and negatively regulate cancer cell eradication by immune destruction methods (Pardoll, 2012; Lyford-Pike et al., 2013). Here, PDCD1 is linked to cancer.