Cellular hematopoiesis in the twentieth century.

From work particularly In the last two decades of the century, the cell populations forming blood cells can now be purified and cultured clonally so that blood cell formation can be analyzed in vitro. A large number of specific regulators of this process have been identified and mass-produced in recombinant form. Three of these, erythropoletin, granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) are in extensive clinical use to stimulate hematopoiesis. Similar advances have characterized the processes by which T lymphocytes, B lymphocytes, and dendritic cells are formed and interact to mediate immune responses. In the last decade most research on blood cell formation has involved the generation of animals with inactivation of specific genes involved in hematopolesis. Major unsolved problems are the molecular control of differentiation commitment and maturation in hematopoietic cells, processes that need to be better understood to allow improvements in the management of leukemia and other disorders of hematopoiesis.