Patients suffering from acute graft-versus-host disease after bone-marrow transplantation have functional CD4+CD25hiFoxp3+ regulatory T cells.

Acute Graft-Versus-Host Disease (aGVHD), mediated by CD4(+) and CD8(+) effector T cells, is a life-threatening complication in hematopoietic stem cell (HSC) transplantation. Naturally-occurring CD4(+)CD25(hi)(Foxp3(+)) regulatory T cells (T(reg)) have been shown to modulate tolerance to aGVHD in murine graft models. In this report, we investigated their role in the prevention of aGVHD in patients transplanted with bone-marrow-derived HSC. When CD4(+)CD25(hi)Foxp3(+) T cells were isolated from bone-marrow grafts, they showed no suppressive activity. The analysis of their function in patients suffering from aGVHD after transplantation revealed a gain of suppressive activity indicating their inability to control the aGVHD induction. Thus, our findings clearly demonstrate that CD4(+)CD25(+) and CD4(+)CD25(hi)Foxp3(+) T cells, when administered in steady-state physiological conditions, do not influence the outcome of aGVHD after bone-marrow transplantation.