Hematopoietic growth factors.

The process of blood cell formation, by which a small number of self-renewing stem cells give rise to lineage committed pro- genitor cells that subsequently proliferate and differentiate to produce the circulating mature blood cells, is sustained through- out life by a group of glycoprotein hormonal growth factors. These hormones are known collectively as the colony-stimulating factors (CSFs)' (1); the term derives from the in vitro observation that the CSFs stimulate progenitor cells of different hemato- poietic cell lineages to form discrete colonies of recognizable maturing cells. The different factors have been operationally de- fined by prefixes denoting the major type of colony produced, e.g., granulocyte maprophage CSF (GM-CSF). Not only is the presence of CSF5 necessary for the proliferation of progenitor cells but these factors affect the function of mature cells as well (2-8); furthermore, they may be the major regulators ofincreased cell production during states of increased demand. It is not yet clear whether they play a pathogenetic role in some forms of leukemia.