Because T cell-derived interferon gamma (IFNγ) is well known to upregulate PD-L1 expression in various cancer cells30, to determine the effect of IFNγ on PD-L1 expression in CCA cell lines, we treated RMCCA-1 and HuCCT-1 with 10 and 50 ng/ml of IFNγ for 24 and 48 h, and PD-L1 expression was examined by Western blot analysis. The gene discussed is IFNG; the disease is cholangiocarcinoma.