PDCD1 and neoplasm: Whereas the plasma concentrations of sPD-L1, sPD-1, and sCTLA-4 were not correlated with expression of the corresponding genes (CD274, PDCD1, and CTLA4, respectively) in tumor specimens (Supplemental Figure 15, A–C), that of sPD-L1 was moderately correlated with the expression of CD274 in whole-blood cells (Supplemental Figure 15D), suggesting that sPD-L1 might be preferentially derived from blood cells rather than tumor tissue, possibly as a result of the induction of peripheral PD-L1 expression by circulating IFN-γ (Figure 6D).