In response to antigen stimulation, naïve CD4 T cells differentiate into several subsets including effector helper T (Th1, Th2 and Th17) and inducible regulatory T (iTreg) cells. Although these differentiated CD4 T cell subsets are more plastic than previously thought, Th1 cells are one of the most stable subsets, and conversion of Th1 to iTreg cells has been shown to rarely happen. The methods of converting effector Th1 cells into iTreg cells are urged to be established for the treatment of Th1-mediated inflammatory and autoimmune diseases.
Here we report that Foxp3+ cells can be induced in vitro from differentiated Th1 cells by simply culturing Th1 cells in the absence of TCR stimulation for 4 days (resting procesure), then culturing with TGF-β. We named these Th1-derived Foxp3+ cells Th1Reg cells. Th1Reg cells showed both Th1 and iTreg-like phenotypes and possessed suppressive ability in vitro. Vitamin C facilitated stable Foxp3 expression in Th1Reg cells both in vitro and in vivo. Th1Reg cells could also be induced from in vivo-derived Th1 cells that are prepared from mice with graft versus host disease. Surprisingly, the resting process did not induce apparent changes in epigenetic modifications at the Foxp3 enhancer and promoter regions, but down-regulated the mTOR activity of Th1 cells. The resting procedure suppressed glycolysis, which is downstream of the mTOR pathway, but enhanced oxidative phosphorylation. Pharmacologic and gene expression analyses suggested that metabolic shift from glycolysis to oxidative phosphorylation is important for the induction of Th1Reg cells. In addition, both expression of Smad3 and its TGF-β-induced phosphorylation, which is reported to be suppressed by mTOR, were reduced in Th1 cells, and recovered after the resting. These data indicate that the metabolic reprograming is important for the conversion from Th1 cells into iTreg-like cells.