Bone marrow is the spongy tissue inside some of your bones, such as your hip and thigh bones. It contains immature cells, called stem cells. The stem cells can develop into the red blood cells that carry oxygen through your body, the white blood cells that fight infections, and the platelets help with blood clotting.

If there is a problem with your bone marrow, a transplant can give you healthy new marrow. You could need a transplant because of a disease, such as bone marrow diseases or cancers like leukemia or lymphoma. Or you might need one if a strong cancer treatment kills your healthy blood cells.

People with cancer sometimes donate bone marrow before treatment to be transplanted later. But often the new marrow comes from a donor, either a close family member or someone unrelated.

Disorders that may be treated with stem cell transplantation include:

• Immune deficiency. Children born with severe immune cell deficiencies and are unable to make the cells that help the body combat infection are candidates for stem cell transplants.

• Inherited Severe Blood Cell Deseases. Marrow transplantation is now being used to treat diseases such as thalassemia or sickle cell disease in which a mutant gene is inherited.

• Other Inherited Disorders. There is a group of inherited diseases that have a defect in the monocytes.

• Marrow Failure. Human stem cell transplantation has been used successfully to restore the function of marrow that has been injured. This type of marrow failure, referred to as aplastic anemia, can be drug induced, autoimmune or, more rarely, inherited. As a result of exposure to certain drugs or to an external noxious agent, such as a chemical or unintended radiation exposure, marrow failure can occur.