Peripheral blood as a stem cell source for hematopoietic cell transplantation in children: is the effort in vein?

Since 1968 HSCT utilizing bone marrow as a stem cell source has become an accepted treatment modality for a variety of immunologic, hematologic and malignant disorders. However, with widespread use it became apparent that BM donation is inconvenient, uncomfortable and not without risk. These observations led to a search for a more easily and safely acquired hematopoietic stem cell source. Recent experience suggests that peripheral blood may serve as an alternative to marrow. Indeed if the current trend continues PBSC will soon replace BM in adults as the preferred stem cell source for both HLA-matched and unrelated HSCT. Furthermore adults who have experienced both seem to prefer PBSC to BM donation. Recently a number of small trials support the feasibility of PBSC harvest from HLA-matched minor sibling donors. With regard to the recipient, data indicate more rapid engraftment, an acceptable incidence of acute and chronic GVHD, decreased infection and an increased survival for patients with malignancies (suggesting an increased GVT/L effect) when PBSC are utilized. These observations based almost entirely on the adult experience are far from definitive when children are considered. The relatively lower risk and severity of acute and chronic GVHD, the more frequent use of HSCT for non-malignant disorders and the diminished role of GVT/L in the treatment of typical malignancies are factors particular to pediatric HSCT. In addition the sense that mobilization and harvest of PBSC may pose unique and significant risk for the young donor suggest to some that PBSC may not posses sufficient advantage to warrant their use in the pediatric transplant setting. Thus both the available adult-derived data and experience suggest clinical equipoise with regard to the choice of stem cell product, under certain circumstances, when children are considered. This circumstance strongly supports the need for a comprehensive study evaluating the safety and efficacy of PBSC vs. BM HSCT in children.