Hematopoietic stem cell

A hematopoietic stem cell is the stem cell at the root of hematopoiesis, the making of blood. It lives mainly in the red bone marrow, with small numbers in the circulating blood, and before birth it also works in the liver; umbilical cord blood is rich in these cells. Like other stem cells, it can divide to make copies of itself, keeping the supply from running out, or produce daughter cells that commit to more specialized paths. It is multipotent: it can form every kind of blood cell but not other tissues.

Prompted by growth factors, its offspring split into two main branches. Myeloid progenitors give rise to red blood cells, the megakaryocytes that shed platelets, monocytes and the granulocytes, namely neutrophils, eosinophils and basophils. Lymphoid progenitors give rise to B cells, T cells and natural killer cells. The stem cells themselves divide rarely, while their descendants multiply to produce hundreds of billions of new blood cells every day.

A hematopoietic stem cell transplant, often still called a bone marrow transplant, replaces diseased or destroyed marrow with healthy stem cells taken from the patient (autologous) or from a matched donor (allogeneic), using marrow, blood or cord blood. It treats leukemia, lymphoma, sickle cell disease and other disorders and was the first routine stem cell therapy.