The effects of 5-azacytidine on the function and number of regulatory T-cells and T-effectors in myelodysplastic syndrome

Background. Expansion of regulatory T cells occurs in high-risk myelodysplastic syndrome and correlates with a poor prognosis. DNA methyltransferase inhibitors, particularly 5-azacytidine, have been shown to increase the survival of high-risk myelodysplastic syndrome patients. It is not entirely clear whether this improvement in patient survival is related to the effects of DNA methyltransferase inhibitors on the immune system and/or the direct effect of these drugs on the dysplastic clone. In this study we investigated the effect of 5-azacytidine on the function and proliferation capability of regulatory T cells and T helper cells.

Design and methods. The number and function of CD4+ T cell subsets in 68 intermediate-2/high-risk myelodysplastic syndrome patients were serially assessed at diagnosis and following treatment. The in-vitro effects of 5-azacytidine on CD4+ T cell subsets isolated from both healthy donors and myelodysplastic syndrome patients were also investigated.

Results. The number of peripheral blood regulatory T cells was significantly higher in myelodysplastic syndrome patients compared with healthy donors and responders to treatment (p=0.01). The absolute numbers of T-helper 1 and T-helper 2, but not T-helper 17, cells were significantly reduced following 12 months of treatment (p=0.03, p=0.03). The in vitro addition of 5-azacytidine to CD4+ T cells reduced the proliferative capacity of regulatory T cells (p=0.03). In addition, the 5-azacytidine-treated regulatory T cells had reduced suppressive function and produced larger amounts of IL-17. The FOXP3 expression in 5-azacytidine-treated T effectors was also increased. Interestingly, these FOXP3+/IL-17+ cells originated mainly from effector T cells rather than regulatory T cells.

Conclusions. Our data suggest that 5-azacytidine has profound effects on CD4+ T cells, which correlate with disease status post treatment. Furthermore, despite the demethylation of the FOXP3 promoter and increased FOXP3 expression following 5-azacytidine treatment, these phenotypic 'regulatory T cells-like cells' lack the regulatory function and cytokine profile of regulatory T cells. These findings are important in correlating the clinically relevant immunomodulatory effects of 5-azacytidine.