CD28 and biliary tract neoplasm: Regulatory T cells with similar outcomes included CD28 on CD4+ (OR=0.91, 95% CI=0.84–0.99, P=0.02), CD25 on CD39+ activated Treg (OR=0.87, 95% CI=0.78–0.97, P=0.01), CD25 on CD39+ secreting Treg (OR=0.93, 95% CI=0.88–1.00, P=0.036), and CD4 on CD39+ resting Treg (OR=0.89, 95% CI=0.81–0.99, P=0.028), all of which had a predictive outcome OR of less than 1 and were protective factors for a reduced risk of biliary tract cancer (Figure 6).