The changing role of stem cell transplantation in childhood.

Over the past decade, relevant improvements and refinements have significantly changed the indications, technique and results obtained with allogeneic hematopoietic SCT (HSCT) in childhood. A fundamental turning point in the history of allogeneic HSCT is represented by the use of placental blood, which was first employed in 1988 in a patient with Fanconi anemia, successfully transplanted with cord blood cells from an HLA-identical sibling. Since then, thousands of children were given an allograft of cord blood-derived hematopoietic progenitors, mainly from an unrelated donor. This large clinical experience has documented that, as compared with BMT, cord blood transplantation (CBT) is associated with reduced incidence and severity of GvHD. The outcome of recipients given unrelated CBT has been reported to be at least as good as that of patients transplanted with either BM or peripheral blood mobilized cells of an unrelated volunteer. Another emerging strategy of HSCT is that of using HLA-partially matched relatives as donors of hematopoietic progenitors. The infusion of a huge number of positively in vitro-selected CD34+ cells, with the concomitant removal of T cells, has been demonstrated to permit sustained engraftment of donor hematopoiesis, without the occurrence of GvHD in the majority of patients transplanted from an HLA-disparate relative. In adults given this type of transplantation, the most favorable results have been reported for AMLs and when the donor displays alloreactivity of natural killer cells. It remains to be definitively proved whether these findings documented in adults maintain their value in pediatric patients transplanted from an HLA-disparate family donor. Finally, the last few years have witnessed the emergence of approaches of adoptive cell therapy aimed at optimizing the results of allograft through strategies able to reinforce immune competence against pathogens, as well as against tumor cells, or at modulating donor T-cell alloreactivity.