ASPECTS OF THE BIOLOGY OF THE NEONATAL HEMATOPOIETIC STEM-CELL

We have studied the frequency of colony forming cells (CFC) in fetal a nd neonatal blood in comparison with adult blood and marrow. Fetal/neo natal blood contains at least as many CFC as adult marrow and higher n umbers of the more primitive CFC-those CFC giving rise to colonies com posed of erythroid and myeloid cells. CD34+ cord blood cells (selected either by sorting, panning or affinity chromatography) proliferate in culture over time and generate more CFC (from pre-CFC) and differenti ated cells in response to Steel factor plus different hematopoietic gr owth factors. Steel factor is unable to stimulate cell growth by itsel f under serum-deprived conditions and requires the synergistic action of erythropoietin (Epo), granulocyte colony stimulating factor (G-CSF) or interleukin 3 (IL-3). In the presence of Epo or G-CSF, CFC and dif ferentiated cells are generated for 15 days and are mainly erythroid o r granulocytic, respectively. In contrast, Steel factor plus IL-3 gene rates multilineage CFC and differentiated cells for more than one mont h. When the conditions for these long-term suspension cultures were op timized (37-degrees-C, regular refeeding with fresh growth factors and media without changing the flask), CFC and differentiated cells were generated for more than two months. At this time, CFC were no longer d etectable and all cells had a mast cell phenotype. These cells have be en maintained and propagated for more than eight months in the presenc e of IL-3 and Steel factor and may represent a useful tool to study hu man mast cell differentiation. Finally, the addition of oligonucleotid es antisense to c-kit, the receptor for Steel factor, selectively supp resses the generation of erythroid cells, indicating that Steel factor /c-kit interaction plays a major rote in the process of erythroid comm itment.