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  • Title: Growth factor regulation of the maintenance and differentiation of human long-term culture-initiating cells (LTC-IC).
    Author: Sutherland HJ, Hogge DE, Eaves CJ.
    Journal: Leukemia; 1993 Aug; 7 Suppl 2():S122-5. PubMed ID: 8361214.
    Abstract:
    Current evidence suggests that the most primitive of hematopoietic progenitors detectable in adult human marrow are cells that can give rise to clonogenic cells for > 5 weeks in vitro when co-cultured with certain stromal cells. Procedures developed to isolate these so-called long-term culture-initiating cells (LTC-IC) in highly purified form allow their separation from most other hematopoietic cells as well as from stromal cells and their precursors also present in the marrow. We have used such procedures in conjunction with the LTC system to identify specific growth factors that support human LTC-IC maintenance and differentiation and to make comparisons with effects on later events in hematopoiesis. In some studies, soluble growth factors were added exogenously to the study cultures. In others, marrow-derived fibroblasts were genetically engineered to allow increased levels of specific human growth factors to be endogenously produced. In both of these ways, the influence of granulocyte--macrophage colony-stimulating factor (GM-CSF), G-CSF, Interleukin-3 (IL-3), IL-6, and Steel factor were investigated. Increased provision of GM-CSF alone (or in combination with other factors) enhanced terminal cell differentiation (production of granulocytes and macrophages), although the same conditions had no influence on LTC-IC differentiation (production of clonogenic cells) or on LTC-IC maintenance. In contrast, G-CSF, IL-3 and IL-6 alone (and more so when combined) in the presence of feeders effectively enhanced LTC-IC differentiation and was less active on later stages of granulopoiesis. Provision of additional exogenous Steel factor also enhanced LTC-IC differentiation, although Steel factor alone, without feeders or other growth factors, did not support either the initial differentiation of LTC-IC into clonogenic cells or their subsequent differentiation into mature granulocytes and macrophages. No combination of exogenously added growth factors was found that enhanced LTC-IC maintenance over that achieved with primary marrow feeders. However, some murine fibroblasts (including those of SI/SI origin), as well as certain exogenous growth factors (including Steel factor), were able to substitute for feeders in this regard. These observations highlight the likelihood of redundancy in factors that can elicit similar biological responses at the earliest as well as later stages of hematopoietic cell development. Nevertheless, it appears that the responses of hematopoietic cells at different stages of differentiation to any particular factor may differ markedly and that the nature of any particular response is not yet predictable from a knowledge of effects on earlier or later cell types.
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