ABSTRACT
I. INTRODUCTION Efficient mobilization and collection of hematopoietic stem cells (HSCs) from peripheral blood are a prerequisite for a successful peripheral blood stem cell (PBSC) transplantation. Provided that a sufficient number of autologous or allogeneic PBSCs are transplanted, the major advantage of PBSCs compared with bone marrow (BM) is the shortened period of severe cytopenia following high-dose therapy (1,2). Bone marrow has therefore been gradually replaced by mobilized peripheral blood (PB) as a source of HSCs. Circulation of progenitor cells capable of forming granulocytic and monocytic colonies was first observed in 1970 (3). The concentration of these colony-forming units (CFUs) was only 1-10% of that observed in BM. In 1976, Richman et al. found that, in patients with solid tumors, the concentration of circulating CFUs increased up to 20-fold over baseline levels during leukocyte recovery after cytotoxic chemotherapy (4). The introduction of hematopoietic growth factors (HGFs) in the late 1980s resulted in a further significant increase of PBSCs when administered either following cytotoxic chemotherapy or during steadystate hematopoiesis.
