The inhibitory function of Treg cells was enhanced by low-dose decitabine in ITP in vitro. Teff cells (2 × 10⁵ cells per well) were seeded in a 96-well plate with or without Treg cells (5 × 10⁴ cells per well) in the presence of decitabine 100 nM. The cell division index was calculated based on the dilution of CFSE fluorescence measured by flow cytometry and represents the average number of cell divisions that Teff cells in the original population have undergone [division index = sum (i × N(i)/2ⁱ)/sum (N(i)/2ⁱ), “i” is division number (undivided = 0), and “N(i)” is the number of cells in division “i”]. (A,C) Representative histograms of CD4⁺CFSE⁺ Teff cells from one healthy control subject (A) and patient with ITP (C). (B,D) Treg cells suppressed the proliferation of Teff cells. Decitabine (100 nM) enhanced the inhibitory function of Treg cells in ITP (D; n = 24), but not in healthy control subjects (B; n = 13). *P < .05, **P < .01, ***P < .001. Dec, decitabine; HC, healthy control subjects; ns, not significant.