Stem cell transplantation, sometimes referred to as bone marrow transplant, is a procedure that replaces unhealthy blood-forming cells with healthy cells. Stem cell transplantation allows doctors to give large doses of chemotherapy or radiation therapy to increase the chance of eliminating blood cancer in the marrow and then restoring normal blood cell production. Researchers continue to improve stem cell transplantation procedures, making them an option for more patients.

The basis for stem cell transplantation is that blood cells (red cells, white cells and platelets) and immune cells (lymphocytes) arise from the stem cells, which are present in marrow, peripheral blood and cord blood. Intense chemotherapy or radiation therapy kills the patient's stem cells. This stops the stem cells from making enough blood and immune cells.

How Does It Work?

The patient receives high-dose chemotherapy and/or radiation therapy, followed by the stem cell transplant. A donor's stem cells are then transfused into the patient's blood. The transplanted stem cells go from the patient's blood to his or her marrow.

The donor is usually a brother or a sister if one is available and if he or she is a match for the patient. Otherwise, an unrelated person with stem cells that match the patient's tissue type can be used. These matched unrelated donors (MUDs) can be found through stem cell donor banks or registries.

The new cells grow and provide a supply of red cells, white cells (including immune cells) and platelets. The donated stem cells make immune cells that are not totally matched with the patient's cells. (Patients and donors are matched to major tissue types but not minor tissue types.) For this reason, the donor immune cells may recognize the patient's cancer cells' minor tissue types as foreign and kill the cancer cells. This is called "graft versus cancer effect."

Types of Stem Cell Transplantation

If you're a candidate for a stem cell transplant, your doctor will usually recommend one of three types:

• Autologous. The stem cells come from your own body.
• Allogeneic. The stem cells are from a healthy person (the donor).
• Reduced-intensity stem cell transplantation. Like allogeneic transplant, the stem cells are from a healthy person (the donor), but the chemotherapy given is less intensive.

A fourth type of stem cell transplantation, syngeneic transplantation, is much less common than the other three. Syngeneic transplantation is rare for the simple reason that it's only used on identical twins. In addition, the donor twin and the recipient twin must have identical genetic makeup and tissue type.

Are You a Candidate for Stem Cell Transplantation?

Your doctor considers several factors when deciding whether you're a candidate for stem cell transplantation. For allogeneic stem cell transplantation, your doctor takes into account:

• The likelihood that the disease will respond to the conditioning regimen
• The availability of a suitable donor
• Your overall health
• Your age and medical condition

When considering whether you're a candidate for an autologous stem cell transplantation, your doctor takes into account:

• The likelihood that the disease will respond to other types of treatment
• Your diagnosis (for example, autologous transplant isn't commonly used to treat acute lymphocytic leukemia because of the high relapse rate nor is it used Frequently for myelodysplastic syndromes)
• Whether you have a sufficient number of stem cells that can be collected
• Your overall health
• Your age

Allogeneic stem cell transplant is more successful in younger patients than older patients. About three-quarters of the people who develop a blood cancer are older than 50. In general, older individuals are more likely to:

• Have complicating medical problems
• Develop graft versus host disease
• Have a decreased tolerance for the cumulative effects of the intensive chemotherapy and for radiation treatments needed before the transplant

However, the above factors are generalizations, and there's no specific age cut-off for stem cell transplantation.

Other factors and the response of the underlying disease to initial cancer therapy determine when your doctor considers transplant options. Some patients undergo stem cell transplantation in first remission. For other patients, it's recommended later in the course of treatment for relapsed or refractory disease.

Pretreatment

Before you undergo stem cell transplantation, you'll need pretreatment, also called conditioning treatment. You'll be given high-dose chemotherapy or radiation therapy to:

• Decrease the risk that your immune cells will reject the donor's transplanted cells (for standard allogeneic stem cell transplant)
• Eliminate any disease that might remain at the time of the transplant
• Eliminate the disordered lymphocytes (white cells) that are attacking your developing blood cells, in certain cases involving marrow failure

Pretreatment for a reduced-intensity allogeneic stem cell transplant involves lower dosages of chemotherapy drugs or radiation than for a standard allogeneic stem cell transplant.

Transferring Cells to Patients

Donor stem cells are transferred to patients by infusion, a procedure similar to a blood transfusion. Blood is delivered through a catheter — a thin flexible tube — into a large blood vessel, usually in your chest.

Infusing the stem cells usually takes several hours. You'll be checked frequently for signs of fever, chills, hives, a drop in blood pressure or shortness of breath. You may experience side effects such as headache, nausea, flushing and shortness of breath from the cryopreservative used to freeze the stem cells. If so, you'll be treated and then continue infusion.