Engraftment potential of peripheral and cord blood stem cells evaluated by a long-term culture system.

The experiment was performed in an attempt to seek a suitable indicator of allogeneic transplantation using cord blood cells. The number of colony-forming cells (CFC) recovered after 5 weeks of culture represents that of primitive progenitors present in the initiating cell population. In this study of nine children who underwent autologous peripheral blood stem cell transplantation (PBSCT), we measured the amount of colony-forming units-granulocyte/macrophage (CFU-GM) and total CFC output after 5 weeks in long-term culture (LTC-CFC) contained in the infused grafts and compared them to the speed of hematopoietic recovery after marrow ablation. In this patient population, we found a significant negative correlation between the number of infused CFU-GM/kg body weight and the time to achieve an absolute granulocyte count (AGC) of 0.5 x 10(9)/L (r = -0.867, p < 0.01), but not with the time to achieve a platelet count of 50 x 10(9)/L (r = -0.700, p = 0.05). Although the number of infused LTC-CFC/kg did not correlate with the early phase of granulocyte recovery, a significant correlation was observed with platelet recovery speed (r = -0.930, p < 0.01) and with the time to regain an absolute granulocyte count of 2 x 10(9)/L after the nadir of the transient decrease in the number of AGC, which occurred 3 to 7 weeks following PBSCT (r = 0.967, p < 0.01). On the other hand, CFU-GM/kg showed no significant correlation with this late engraftment speed. Thus, LTC assay may reflect the kinetics of immature progenitor cells which are capable of reconstituting stable hematopoiesis after marrow ablative therapy. The data were then used in a comparative analysis of the transplantation potential of peripheral vs. cord blood stem cells. The numbers of LTC-CFC and CFU-GM per mononuclear cell (MNC) from cord blood were 2.5-fold and two-fold greater than those from peripheral blood cells, respectively. These results suggest the advantage of cord blood as an additional stem cell source in transplantation.