AUTOLOGOUS PERIPHERAL-BLOOD PROGENITOR-CELL TRANSPLANTATION

Harvesting of autologous peripheral blood stem cells (PBSCs) has been facilitated by using currently available, efficient apheresis technolo gy at the time of rebound from chemotherapy while patients are receivi ng recombinant growth factors, i.e., granulocyte (G) or granulocyte-ma crophage (GM) colony stimulating factor (CSF). Ideally pheresis should be done before patients have had extensive stem cell toxins, i.e., al kylating agents or nitrosoureas. This strategy has facilitated the use of high dose chemoradiotherapy given as a single regimen or in a divi ded dose for patients with solid tumors or hematologic malignancies an d results in more rapid engraftment than bone marrow transplantation ( BMT). Although there are no assays which measure repopulating stem cel ls, enumeration of CD34(+) cells within PBSCs is a direct and rapid as say which provides an index of both early and late long-term reconstit utive capacity, since it correlates with colony-forming unit (CFU)-GMs , as well as pre-progenitor or delta assays and long-term culture-init iating cells (LTC-IC). A threshold of greater than or equal to 2 x 10( 6) CD34(+) cells/kg recipient body weight has been reported to be requ ired for engraftment, but may vary depending upon the clinical setting . Strategies for mobilization of normal PBSCs also increase tumor cell contamination within PB in the setting of both hematologic malignanci es and solid tumors, but the significance of these tumor cells in term s of patient outcome is unclear. Recently isolation of CD34(+) cells f rom PBSCs has been done using magnetic beads or immunoabsorption on co lumns or rigid plates in order to enrich for normal hematopoietic prog enitors and potentially decrease tumor cell contamination. As for othe r cellular blood components, standards have been developed to assure e fficient collection and processing, thawing, and reinfusion, and to ma intain optimal PBPC viability. Finally, future directions of clinical research include expansion of hematopoietic progenitor cells ex vivo; use of umbilical cord or placenta as rich sources of progenitor cells; syngeneic hematopoietic stem cell transplantation; related and unrela ted allogeneic hematopoietic stem cell transplantation; treatment of i nfections, i.e., Epstein Barr virus, or tumor relapse after allogeneic BMT using donor PBSC infusions; and gene therapy approaches. (C) 1995 Wiley-Liss, Inc.