ChIP and qPCR analysis revealed that MLL1 depletion by shRNA dramatically decreased H3K4me3 levels in the PD‐L1 and IDO‐1 promoter regions, as well as PD‐L1 and IDO‐1 mRNA levels in human ESCC cells (Figure 4D–G and Figure S4D). Here, IDO1 is linked to esophageal squamous cell carcinoma.