The number of CD4⁺CD25^highFoxp3⁺ Tregs in MDS. (A) The absolute number of Tregs in various subtypes of MDS. The number of Tregs in patients with RAEB was significantly higher compared with low-risk subtypes: 5q− syndrome (P < .001), RA (P < .001), and RCMD (P = .002). (B) The absolute number of Tregs was also significantly higher in patients with 5% or greater bone marrow blasts compared with patients with less than 5% bone marrow blasts (P > .001). (C) Comparison of the absolute number of Tregs from patients with low-risk IPSS (score, 0) to those with intermediate-risk (score, 0.5-2.0) and high-risk IPSS (score, 2.5 or greater). Patients with low-risk MDS demonstrated significantly lower numbers of Tregs than did both intermediate- and high-risk groups (P < .001). (D) In those patients with a complex cytogenetic abnormality, the median number of CD4⁺ Tregs was significantly higher compared with 5q− syndrome (0.5 × 10⁷/L vs 1.4 × 10⁷/L; P = .008). There was no significant difference in the number of Tregs upon comparison of patients with normal or complex cytogenetics (P = .29). Error bars represent the interquartile (IQR) of the median.