The present pilot study aims to evaluate the frequency and the function of regulatory T (Treg) cells in patients with diffuse cutaneous SSc (dcSSc) before and after autologous hematopoietic SCT (aHSCT). Peripheral blood lymphocytes from seven dcSSc patients were analyzed before and 24 months after aHSCT and were compared with those from seven healthy donors (controls). Immunophenotyping of CD4(+)CD25(high)FoxP3(+) natural Treg (nTreg), CD4(+)CD25(+)TGF-β(+) and CD4(+)CD25(+)IL-10(+) adaptive Treg (aTreg) cell subsets was performed using four-color flow cytometry. Treg-suppressive capability was measured after coculture with autologous T effector cells by evaluation of T-cell proliferation using (3)H-thymidine incorporation. Peripheral CD4(+)CD25(high)FoxP3(+) (2±0.5 vs 4.2±1.1, P<0.01), CD4(+)CD25(+)TGF-β(+) (6.9±1.8 vs 14.6±5.0, P<0.05) and CD4(+)CD25(+)IL-10(+) (10.7±0.5 vs 16.1±3.2, P<0.01) Tregs as well as CD4(+)CD25(high)CD127(low) Tregs suppressive capacity (P<0.05) were decreased in dcSSc patients vs controls. After aHSCT (n=7), the percentages of CD4(+)CD25(high)FoxP3(+) (4.1±1.8) and CD4(+)CD25(+)IL-10(+) (15.7±2.2) Treg cells and the suppressive activity of CD4(+)CD25(high)CD127(low) were restored to the levels in controls. The decreased frequency and the functional defect of peripheral Treg cells from patients with dcSSc are reversed following aHSCT to reach those observed in controls. This pilot study brings evidence of an effective restoration of nTreg and aTreg subsets, and recovery of nTreg suppressive function following aHSCT.