Stem cell transplant is the replacement of damaged bone marrow cells with healthy cells (stem cells). Stem cells are immature cells produced in the bone marrow that make more stem cells, red blood cells, white blood cells, and platelets.

Stem cells used for transplants can be taken from bone marrow, from the bloodstream, or from umbilical cord blood.

Stem cell transplant is used:

• To treat diseases that damage or destroy the bone marrow, such as lymphoma and leukemia.
• To restore the bone marrow after it has been destroyed by high doses of radiation and chemotherapy. Stem cells may be taken from the person's body before the radiation or chemotherapy treatment and then reinfused.
• Experimentally for gene therapy and the treatment of other diseases, such as diabetes and sickle cell disease.

Stem cell transplants that use stem cells donated by someone else are called allogeneic transplants. But when a person's own stem cells are used, it is called an autologous transplant.

The success of a stem cell transplant depends on the person's age and general health condition and whether the donated cells match the body cells. Serious complications that can occur after a stem cell transplant include rejection of the new stem cells, destruction of other cells in the person's body by the new stem cells, or severe, often life-threatening, infection.