To determine the functions of MTHFD1 in cellular redox regulation and CCA gemcitabine chemoresistance, we silenced MTHFD1 in the human CCA cell line QBC939 and its HyPer-low subpopulation cells with a short interfering RNA (siRNA)-mediated gene knockdown approach (Fig. 4F), and siMTHFD1#1 (siM1#1) had a marked decrease in the mRNA levels of both QBC939 and its HyPer-low subpopulation cells (Fig. 4G). This evidence concerns the gene MTHFD1 and cholangiocarcinoma.