PHENOTYPIC AND FUNCTIONAL-CHARACTERIZATION OF LONG-TERM CULTURE-INITIATING CELLS PRESENT IN PERIPHERAL-BLOOD PROGENITOR COLLECTIONS OF NORMAL DONORS TREATED WITH GRANULOCYTE-COLONY-STIMULATING FACTOR

Granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blo od progenitor cells (PBPC) have successfully been used as stem cells f or both autologous and allogeneic transplants. However, little is know n concerning the absolute number and phenotype of primitive progenitor s, such as long-term culture-initiating cells (LTC-IC) in mobilized PB PC. The aim of our study was to evaluate the capacity of G-CSF to mobi lize LTC-IC in the PB of normal individuals and to evaluate the phenot ypic and functional characteristics of G-CSF mobilized LTC-IC, G-CSF w as administered to 29 healthy volunteers at 7.5 mu g or 10 mu g/kg/d s ubcutaneously (SC) for 5 consecutive days and PBPC were harvested on d ay 6. Mobilization with G-CSF increased the absolute number of week 5 LTC-IC in PB 60-fold, while the number of CD34(+) cells and committed colony forming cells (CFC) was increased seven-fold to 12-fold. The fr equency of CFC and week 5 LTC-IC In CD34(+) cells selected by fluoresc ence-activated cell sorter (FACS) from mobilized PBPC was 2 +/- 0.3-fo ld and 9 +/- 2.2-fold higher respectively than in CD34(+) cells select ed front unmobilized PBMNC. CFC were enriched in the CD34(+) CD38(+) a nd CD34(+) HLA-DR(+) populations. The absolute number of LTC-IC presen t in CD34(+) CD38(-) and CD34(+) HLA-DR(-) cells selected by FAGS from either mobilized PBPC, unmobilized PBMNC or steady state bone marrow (BM) was similar (0.5% to 2%). In contrast to unmobilized PBMNC or ste ady state BM CD34(+) CD38(+) and CD34(+) HLA-DR(+) cells, which contai n less than 0.1% LTC-IC, CD34(+) CD38(+) and CD34(+) HLA-DR(+) cells s orted from mobilized PBPC contained 0.5% to 5% of cells capable of sus taining hematopoiesis in long-term cultures for 5 weeks. However, 90% to 95% of LTC-IC present in mobilized CD34(+) CD38(+) and CD34(+) HLA- DR(+) cells were not able to sustain hematopoiesis for 8 weeks, while 30% of CD34(+) CD38(-) and CD34(+) HLA-DR(-) LTC-IC present in mobiliz ed PBPC could sustain hematopoiesis for at least 8 weeks, This suggest s that the majority of CD34(+) CD38(+) and CD34(+) HLA-DR(+) week 5 LT C-IC represent progenitors at an intermediate state of differentiation . We conclude that G-CSF effectively mobilizes LTC-IC in the blood of normal individuals. Although a fraction of these cells has functional characteristics similar to those of steady state PBMNC or BM LTC-IC, m ore than 85% of mobilized PBPC LTC-IC are CD34(+) CD38(+) and CD34(+) HLA-DR(+), capable of sustaining hematopoiesis for 5 weeks, but not fo r 8 weeks. The functional and phenotypic characterization of primitive and more mature populations of LTC-IC in mobilized PBPC should prove extremely useful in future studies examining the role of these progeni tors in engraftment following transplantation. (C) 1996 by The America n Society of Hematology.