Bone marrow produces stem cells. These stem cells eventually develop into blood cells. In patients with leukemia, aplastic anemia, and some immune deficiency diseases, the stem cells in the bone marrow malfunction, producing an excessive number of defective or immature blood cells. The immature or defective blood cells interfere with the production of normal blood cells, accumulate in the bloodstream and may invade other tissues.

Bone marrow transplantation have been used to treat patients diagnosed with leukemia, aplastic anemia, lymphomas such as Hodgkin's disease, multiple myeloma, immune deficiency disorders and some solid tumors such as breast and ovarian cancer.

Transplantation may be autologous (an individual's own marrow saved before treatment), allogeneic (marrow donated by someone else), or syngeneic (marrow donated by an identical twin).

Although it's often called a bone marrow transplant, the procedure is really a transplant of the stem cells in the bone marrow - a bit like a blood transfusion. A bone marrow transplant is a very intensive treatment, and patient age and general health will be taken into consideration when deciding whether this is a suitable treatment for him. Generally patient needs to be under the age of 65 to have this treatment. The patient's diagnosis and the stage of the disease are also considered by the physician when determining whether a person should undergo a transplant.

Before you can have the bone marrow transplantation, your leukemia or other cancer needs to be at the lowest possible level. Ideally you should be in remission. If you aren't in remission, the cancer can be reduced using chemotherapy, and possibly radiotherapy.

Stem cell collection:First, the donor receives injections for a few days of a medication that causes stem cells to move out of the bone marrow and into the blood. For the stem cell collection, the donor is connected to a machine by a needle inserted in the vein (like for blood donation).

The transplant:

 The bone marrow is infused into the patient intravenously in much the same way that any blood product is given. The transplant is not a surgical procedure. It takes place in the patient's room, not an operating room.

Engraftment: As the patient waits for the transplanted bone marrow to migrate to the cavities of the large bones, set up housekeeping or "engraft," and begin producing normal blood cells, he or she will be very susceptible to infection and excessive bleeding. Multiple antibiotics and blood transfusions will be administered to the patient to help prevent and fight infection.Once the levels of patient’s blood cells have returned to a safe level, the transplantation is concluded.

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