THE GENERATION OF COLONY-FORMING CELLS (CFC) AND THE EXPANSION OF HEMATOPOIESIS IN CULTURES OF HUMAN CORD BLOOD-CELLS IS DEPENDENT ON THE PRESENCE OF STEM-CELL FACTOR (SCF)

We have analyzed the effect of stem cell factor (SCF), alone or in com bination with other growth factors, on the generation of colony-formin g cells (CFC) and on the expansion of hematopoiesis in vitro from ligh t density, soybean agglutinin-, CD34+ cord blood cells under serum-dep rived conditions. The growth factors were either added only once at th e onset of the culture or added every few days when the cultures were demidepopulated and refed with fresh medium. No growth factor, alone, generated CFC or expanded hematopoiesis under these conditions. Howeve r, SCF, in combination with interleukin 3 (IL-3) or with ''late-acting factors'' (granulocyte colony-stimulating factor (G-CSF) or erythropo ietin (Epo)), generated large numbers of mature cells as well as CFC. The number of CFC generated depended on the refeeding procedure adopte d. In cultures never refed, the CFC numbers increased from <160 CFC/cu lture at day 0 to >3000 CFC at day 10. The CFC numbers stayed above th e input levels for 25 days before declining. Almost no CFC were detect able after one month. In contrast, in cultures regularly refed, CFC we re detectable for at least 40 days. The lineages of the mature cells a nd the types of CFC generated varied with the different growth factors . In the presence of SCF plus IL-3, erythroid burst-forming cells (BFU -E) and granulocyte/macrophage colony-forming cells (GM-CFC) were gene rated and erythroid as well as myelomonocytic precursors were present among the differentiated cells. In contrast, in the presence of SCF an d G-CSF or Epo, the progenitor cells as well as the differentiated cel ls were dictated by the late-acting growth factor (i.e. mostly G-CFC a nd myeloid cells in the presence of SCF and G-CSF vs. BFU-E, erythroid colony-forming cells (CFU-E) and erythroblasts in the presence of SCF and Epo). Thus, marked expansion of erythropoiesis and granulopoiesis can be achieved in vitro by as few as two factors - SCF acting as the early factor along with the appropriate late-acting factor.