Pharmacological modulation of T cell immunity results in long-term remission of autoimmune arthritis

Significance Chronic inflammatory diseases are characterized by an imbalance between pathogenic T effector cells and regulatory T cells. In this report, we demonstrate that decitabine, a cytosine analog, has a rapid and sustained therapeutic effect in animal models of rheumatoid arthritis. Decitabine selectively targets T effector cells expressing ENT1, a nucleoside transporter, and generates robust regulatory T cells with the capacity to suppress immune-driven inflammation. This study identifies a path toward resetting tolerance in autoimmune disease using a repurposed drug. Chronic inflammatory diseases like rheumatoid arthritis are characterized by a deficit in fully functional regulatory T cells. DNA-methylation inhibitors have previously been shown to promote regulatory T cell responses and, in the present study, we evaluated their potential to ameliorate chronic and acute animal models of rheumatoid arthritis. Of the drugs tested, decitabine was the most effective, producing a sustained therapeutic effect that was dependent on indoleamine 2,3-dioxygenase (IDO) and was associated with expansion of induced regulatory T cells, particularly at the site of disease activity. Treatment with decitabine also caused apoptosis of Th1 and Th17 cells in active arthritis in a highly selective manner. The molecular basis for this selectivity was shown to be ENT1, a nucleoside transporter, which facilitates intracellular entry of the drug and is up-regulated on effector T cells during active arthritis. It was further shown that short-term treatment with decitabine resulted in the generation of a population of regulatory T cells that were able to suppress arthritis upon adoptive transfer. In summary, a therapeutic approach using an approved drug is described that treats active inflammatory disease effectively and generates robust regulatory T cells with the IDO-dependent capacity to maintain remission.