Suppression of T cell function is mediated through PD-1 signalling with its ligands PD-L1 and PD-L2 in murine (Zhang et al., 2009), patient tumours (Sato et al., 2005), and the successful reduction of the tumours has been achieved with checkpoint inhibitors (Lin et al., 2015; Andrews et al., 2019; Errico, 2015; Tumeh et al., 2014; Philippou et al., 2020). This evidence concerns the gene PDCD1LG2 and neoplasm.