PDCD1 and viral infectious disease: This suggests that (1) GC potentiation of the inhibitory effects of PD-1/PD-L1 signaling may be useful in therapeutic strategies for autoimmune diseases; (2) using GCs as adjuvant treatment during cancer therapy may lead to therapeutic failure in some tumors [95]; and (3) GC-induced expression of PD-1 on NK cells may lead to protection against cytokine-mediated disease during viral infection [96,97].