DNA Methyltransferase Inhibition Promotes Th1 Polarization in Human CD4CD25 FOXP3 Regulatory T Cells but Does Not Affect Their Suppressive Capacity.

Regulatory T cells (Treg) can show plasticity whereby FOXP3 expression, the master transcription factor for Treg suppressor function, is lost and proinflammatory cytokines are produced. Optimal FOXP3 expression strongly depends on hypomethylation of the gene. 5-Azacytidine (Aza) and its derivative 5-aza-2'-deoxycytidine (DAC) are DNA methyltransferase inhibitors (DNMTi) that are therapeutically used in hematological malignancies, which might be an attractive strategy to promote Treg stability. Previous research primarily focused on Treg induction by DAC from naïve conventional CD4 T cells (Tconv). Here, we examined the effect of DAC on the stability and function of FACS-sorted human naturally occurring CD4CD25 FOXP3 Treg. We found that activation of Treg in the presence of DAC led to a significant inhibition of Treg proliferation, but not of Tconv. Although Treg activation in the presence of DAC led to increased IFN expression and induction of a Thelper-1 phenotype, the Treg maintained their suppressive capacity. DAC also induced a trend towards increased IL-10 expression. studies in patients with hematological malignancies that were treated with 5-azacytidine (Vidaza) supported the findings. In conclusion, despite its potential to increase IFN expression, DAC does preserve the suppressor phenotype of naturally occurring Treg.