Heitger Expression of the putatively regulatory T - cell marker FOXP 3 by CD 4 + CD 25 + T cells after pediatric hematopoietic stem cell transplantation

CD4 CD25 T cells have been implicated in two apparently opposing functions, namely an activated effector function but also a regulatory function. In human hematopoietic stem cell transplantation (HSCT), the frequency of CD4CD25 T cells is increased and this increase was reported to correlate with graft-versus-host disease (GvHD), suggesting that the effector function predominates. In mice, CD4CD25 cells have been proposed to maintain self-tolerance and protect from GvHD, thus representing regulatory (Treg) cells. FOXP3, a transcriptional repressor in Treg-cells, was suggested to specifically identify CD4CD25 cells as regulatory cells, because its deficiency leads to a lack of Treg cells, and overexpression increases the number of Treg cells. Hence, FOXP3 is considered necessary and sufficient for Treg activity. Here, we investigated whether different levels of FOXP3 expression in highly purified CD4CD25 cells after allogeneic HSCT would indicate the regulatory capacity of a given CD4CD25 cell population and thus be related to the risk of GvHD.