OPTIMIZATION OF PERIPHERAL FLOOD STEM-CELL MOBILIZATION

Peripheral blood stem cells (PBSC) are increasingly utilized in lieu o f marrow for hematopoietic support due to the ease of collection and t he rapid kinetics of recovery relative to bone marrow (BM). Neutrophil and platelet recovery times after PBSC transplantation average less t han 8-12 days after infusion in contrast to the usual two to four week s experienced after BM transplantation, This has simplified autologous transplantation and made it safer because patients require fewer days of antibiotic and blood component support and are discharged earlier from the hospital. The administration of hematopoietic growth factors during recovery from high-dose chemotherapy increases the number of ci rculating hematopoietic progenitor cells to levels as much as 1,000-fo ld greater than levels normally found in blood and 10-50 times greater than with chemotherapy alone. More recently, it has been shown that a dequate numbers of PBSC can be collected using growth factors alone wi thout prior chemotherapS'. Although not Set universally accepted, the CD34+ cell content of PBSC appears to be the single most powerful pred ictor of recovery kinetics in patients receiving myeloablative therapy and PBSC infusion, Infusion of >5 x 10(6) CD34+ cells/kg is associate d with a rapid engraftment of neutrophils and platelets, although succ essful engraftment has also been reported with the infusion of 2.5-5 x 10(6) CD34+ cells/kg. By measuring the CD34 or colony forming units-g ranulocyte-macrophage (CFG-GM) content of PBSC collections, mobilizati on chemotherapy and cytokine regimens, age, marrow disease, prior radi ation and prior chemotherapy treatment have been found to be important factors influencing the numbers of stem cells collected, The current challenge for clinical investigators is to improve methods of identify ing patients who will fail to mobilize sufficient numbers of PBSC prio r to collection and to utilize new strategies for stem cell mobilizati on. The relative ease of collection and the rapid engraftment after my eloablative therapy suggest that PBSC will likely supplant marrow for both allogeneic and autologous transplantation in the nest five years.