TGFB1 and chronic obstructive pulmonary disease: Herein, we first present evidence that CD4+CD25–Foxp3+ T cells differentiate from CD4+CD25+Foxp3+ T cells via the influence of TGFβ1, and then propose a novel mechanism regarding how Th17 cells develop from the transdifferentiation of CD4+CD25− Foxp3+ T cells in COPD patients.