Aspects of the biology of the neonatal hematopoietic stem cell

Abstract

We have studied the frequency of colony forming cells (CFC) in fetal and neonatal blood in comparison with adult blood and marrow. Fetal/neonatal blood contains at least as many CFC as adult marrow and higher numbers of the more primitive CFC—those CFC giving rise to colonies composed 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 differentiated cells in response to Steel factor plus different hematopoietic growth factors. Steel factor is unable to stimulate cell growth by itself 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 differentiated cells are generated for 15 days and are mainly erythroid or granulocytic, respectively. In contrast, Steel factor plus IL‐3 generates multilineage CFC and differentiated cells for more than one month. When the conditions for these long‐term suspension cultures were optimized (37°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 detectable and all cells had a mast cell phenotype. These cells have been maintained and propagated for more than eight months in the presence of IL‐3 and Steel factor and may represent a useful tool to study human mast cell differentiation. Finally, the addition of oligonucleotides antisense to c‐kit, the receptor for Steel factor, selectively suppresses the generation of erythroid cells, indicating that Steel factor/c‐kit interaction plays a major role in the process of erythroid commitment.