STAT3 GOF patients have decreased Treg numbers and functional markers. (A) Flow cytometric analysis of FOXP3+CD25+ Treg populations from patient 4, gated on CD4+ T cells, compared with a healthy control. (B) Decreased Treg percentages in STAT3 GOF patients. Treg populations were determined by flow cytometry. The percentages of CD4+ T cells that were FOXP3+CD25+ Tregs from patients were decreased compared with 6 healthy controls and 2 patients with ALPS who had FAS defects (*P < .05). (C) Tregs from STAT3 GOF patients have decreased expression of CD25. Treg populations (CD4+ FOXP3+CD127low) were determined by flow cytometry and the CD25 expression further analyzed by histogram. Tregs from patients demonstrate lower levels of CD25 expression than healthy controls.