[Hematopoietic stem cells and their growth factors].

In vitro culture of haematopoietic cells has provided some surprising insight into humoral regulation of haematopoietic cell growth. Each stage of haematopoiesis is subject to strict regulatory mechanisms involving humoral modulators. These factors called haematopoietins are a family of polypeptide hormones that specifically regulate the proliferation and differentiation of stem cells giving rise to erythrocytes, granulocytes, monocytes, megacaryocytes, and T and B lymphocytes. Mixed colonies consisting of elements of all haematopoietic lineages can be grown from pluripotent progenitors in vitro. Erythropoietin is the primary regulator of the later stages in erythropoiesis, whereas factors with burst-promoting activity or erythroid-potentiating activity stimulate the growth of the more primitive erythroid cells. The in vitro proliferation and differentiation of granulocytic and macrophage cells is dependent on the stimulation by a granulocyte-macrophage colony-stimulating factor. The mode of action of these regulators can well be studied using the homogeneous cell populations of human myeloid and erythroleukemia cell lines. Observations indicate that these factors are likely to function in vivo as in vitro. Knowledge on the biochemistry and physiology of these factors will have substantial impact on the understanding of human diseases involving abnormal haematopoietic cell growth.