Influence of demethylation on regulatory T and Th17 cells in myelodysplastic syndrome

Myelodysplastic syndrome (MDS) represents a heterogeneous hematopoietic disorder in which mature blood cells are derived from an abnormal multipotent progenitor cell. The current therapy for MDS involves repeated cycles of DNA methyltransferase (DNMT) inhibitors, particularly the demethylation drug 5-azacytidine (5-azaC) which has been shown to increase the survival of patients with high-risk MDS. The mechanisms behind the therapeutic effects of 5-azaC are not yet clear. In this study the effect of 5-azaC on the development of regulatory T cells (Tregs) and T-helper 17 (Th17) cells was investigated. The numbers of CD4(+) T-cell subsets in 30 patients with intermediate-2/high-risk MDS were serially assessed at diagnosis and following 5-azaC treatment. The number of FoxP3(+) Tregs was significantly higher after 3 months of therapy. However, there was no statistical difference in the number of Th17 cells following treatment. In vitro, 5-azaC enhanced the overall proportion of Tregs, but not Th17, in CD4(+) T cells from patients with MDS. Addition of 5-azaC reduced the proliferative capacity of Tregs, suggesting that the increase in Tregs was due to conversion of conventional CD25(−) cells, rather than proliferation of CD25(+)FoxP3(+) cells. The FoxP3 expression in 5-azaC-treated T effectors was also increased. Interestingly, while Tbet and RORγT mRNA transcription had no obvious changes, due to the demethylation of the FoxP3 promoter, these findings are important in associating the induction of DNA hypomethylation and the clinical response to 5-azaC.