Importance of allogeneic T-cells for disease control after stem cell transplantation for high-risk Langerhans cell histiocytosis.

Reduced intensity conditioning followed by allogeneic SCT (RIC-SCT) has recently emerged as promising new salvage option for children suffering from Langerhans cell histiocytosis (LCH) with risk organ involvement and failure to conventional therapy. We report on the posttransplant course of female toddler with high-risk LCH, who achieved complete remission after RIC-SCT, despite a posttransplant chimerism constellation, in which only the T-cell subset proved to be of donor origin in the long-term. We therefore suggest that allogeneic T-cells have played a crucial role in controlling disease activity in this patient and may exert the major curative effect after RIC-SCT for LCH.