Background.

FOXP3+ regulatory T-cells (Treg) are important regulators of allo-reactivity and may therefore represent an important predictor for the risk of graft versus-host disease (GVHD) after allogeneic stem cell transplantation.

Methods.

To determine the clinical significance of Treg-content in stem cell grafts, we analyzed 58 human leukocyte antigen (HLA)-identical sibling donors (34 patients received myeloablative and 24 patients reduced intense conditioning regimens) and correlated the Treg frequency with clinical outcome after stem cell transplantation (SCT).

Results.

A mean value of 9.1× 10 6 CD4+ FOXP3+ Treg per kg body weight (bw) of the recipient was transplanted (ranging from 0.7 to 33.7× 10 6 Treg/kg bw). Graft content of Treg correlated with mononuclear cells and CD3+ T-cells. Patients receiving low numbers of Treg (Treg low) after myeloablative conditioning for SCT had a significantly increased cumulative incidence of 76% for acute GVHD when compared with 23% for individuals receiving high numbers of Treg (Treg high). This observation, however, was not made in patients after reduced intense conditioning-SCT. Notably, relapse rate was not significantly different between Treg low and Treg high patients in either patient group and overall survival was even increased in Treg high patients after myeloablative SCT. Finally, low Treg graft levels represent an independent prognostic factor in multivariate analysis for the appearance of acute GHVD.

Conclusion.

Donor-derived Treg might be of particular significance for the development of acute GVHD after myeloablative SCT using HLA-identical sibling donors.