For example, treatment with anti-PD-1/PD-L1 and anti-CTLA-4 immune checkpoint inhibitors reinvigorate dysfunctional TILs and augment their anti-tumor effects (Wherry and Kurachi, 2015; Zarour, 2016; Miller et al., 2019; Wang et al., 2019a). Here, PDCD1 is linked to neoplasm.