Vitamin C supports conversion of human γδ T cells into FOXP3-expressing regulatory cells by epigenetic regulation

Human gamma delta T cells are potent cytotoxic effector cells, produce a variety of cytokines, and can acquire regulatory activity. Induction of FOXP3, the key transcription factor of regulatory T cells (Treg), by TGF-beta in human V gamma 9V delta 2T cells has been previously reported. Vitamin C is an antioxidant and acts as multiplier of DNA hydroxymethylation. Here we have investigated the effect of the more stable phospho-modified Vitamin C (pVC) on TGF-beta -induced FOXP3 expression and the resulting regulatory activity of highly purified human V gamma 9V delta 2T cells. pVC significantly increased the TGF-beta -induced FOXP3 expression and stability and also increased the suppressive activity of V gamma 9V delta 2T cells. Importantly, pVC induced hypomethylation of the Treg-specific demethylated region (TSDR) in the FOXP3 gene. Genome-wide methylation analysis by Reduced Representation Bisulfite Sequencing additionally revealed differentially methylated regions in several important genes upon pVC treatment of gamma delta T cells. While Vitamin C also enhances effector functions of V gamma 9V delta 2T cells in the absence of TGF-beta, our results demonstrate that pVC potently increases the suppressive activity and FOXP3 expression in TGF-beta -treated V gamma 9V delta 2T cells by epigenetic modification of the FOXP3 gene.