CD4 and cholangiocarcinoma: Interestingly, the frequency of peripheral CD4+ Treg cells increased from 0.55% ± 0.49 and 0.71% ± 0.54 (in CCA and HCC, respectively) at T0 to 0.99% ± 0.91 and 1.17% ± 0.33 (in CCA and HCC, respectively) at T1, following tumor resection.