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Leukemia Stem Cells

Sean Morrison, Ph.D. discusses hematopoietic stem cells and stem cell self-renewal.

What are blood-forming stem cells?

Hematopoietic, or blood-forming, stem cells are found in the bone marrow. These stem cells generate a fresh supply of new blood and immune cells to replace old, worn-out cells that are destroyed by the body. Stem cells give rise to partially restricted progenitor cells, such as myeloid and lymphoid progenitors. Myeloid progenitors generate red blood cells, platelets and a few other types of white blood cells. Lymphoid progenitors give rise to lymphocytes, or white blood cells that help the body fight infection and disease.

When a blood-forming stem cell divides, it uses a process called self-renewal to make one copy of itself and one progenitor cell. The new stem cell remains in a primitive, undeveloped state, but the new progenitor cell keeps dividing. Eventually, these progenitor cells give rise to all the different types of mature cells in blood and the immune system.

The body normally keeps tight controls on the process of self-renewal in stem cells. There's an elaborate network of tumor suppressor genes and other feedback mechanisms that slow down the self-renewal process and prevent it from happening too often.

In leukemia, however, the self-renewal process is out of control. Mutations that inactivate tumor suppressors or activate growth promoting signals allow malignant stem cells to disable or ignore the body's natural control mechanisms. It's like the cancer gets the go signals, but not the stop signals - as if the accelerator gets stuck in the "on" position -- and the stem cells make many more cells than the body can use.

Updated 3/2011

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