Regulation of hematopoiesis.

Normal hematopoiesis is a well-regulated process in which the generation of mature blood elements occurs from a primitive pluripotent stem cell in an ordered sequence of maturation and proliferation. Regulation occurs at the level of the structured microenvironment (stroma), via cell-cell interactions and by way of the generation of specific hormones and cytokines: erythropoietin, interleukin 3, granulocyte-monocyte colony-stimulating factor (GM-CSF), monocyte-macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), interleukin 5, interleukin 4, and other less well-defined factors, including the megakaryocyte growth factors. Understanding of this complex process has revealed insights into the pathophysiology of human disease and provided a theoretical framework for the therapeutic use of bone marrow transplantation and potential gene transfer therapy. Furthermore, ongoing clinical trials suggest that the hematopoietic growth factors may represent a significant new group of therapeutic reagents for patients with hematological and oncologic disease.