CD4 and cholangiocarcinoma: At present, there are relatively few studies on the role played by Tregs in CCA, but its important role in CCA has been confirmed: Kim et al. showed that the number of FOXP3 + CD4 + regulatory T cells in extrahepatic CCA was more than that in CCA, and the number of FOXP3 + CD4 + regulatory T cells at the tumor margin predicted a better prognosis 58.