Transforming growth factor-beta (TGF-beta) is a pivotal cytokine in the differentiation of regulatory T cells, and Foxo transcription factors positively regulate this process. On the other hand, the function of Foxo transcription factors is negatively regulated by PI3K/Akt signaling, which is activated by TGF-beta in many types of cells; yet the role of TGF-beta in Akt activity and its downstream substrates in CD4(+) T cells, including Foxo transcription factors, remains to be determined. Herein, we demonstrate that TGF-beta selectively induces Akt phosphorylation at Ser473 but not at Thr308 in a class I-A PI3K-dependent manner in CD4(+) T cells, resulting in the phosphorylation and inhibition of Foxo transcription factors and negatively regulating the differentiation of induced regulatory T cells (iTregs). These observations reveal a novel negative regulatory mechanism involving Akt and Foxo transcription factors induced by TGF-beta in the iTreg differentiation process. (C) 2016 Elsevier Inc. All rights reserved.