About Stem Cell Transplantation

In a stem cell transplant -- also called bone marrow transplant -- a patient's blood-forming stem cells are replaced by infusing new ones into his or her bloodstream. The procedure can be an effective form of treatment for certain forms of cancer, specific genetic diseases, and other types of blood disorders. For most patients, the aim of the transplant is to cure their disease.

What Blood-Forming Stem Cells Are and Where They Are Found

Blood-forming or hematopoietic stem cells are immature cells that can develop into any type of blood cells, including:

• white blood cells, which help the body fight infections
• red blood cells, which carry oxygen throughout the body
• platelets, which are important in blood clotting and the control of bleeding.

The stem cells are produced in the bone marrow, a sponge-like tissue that is found inside large bones (for example, in the breastbone, pelvis, ribs, and spine). Before a transplant, stem cells can be collected from a person's bone marrow or from the bloodstream, where so-called peripheral blood stem cells (PBSC) circulate.

Another source of stem cells is blood from a newborn's umbilical cord and placenta, which can be donated to a stem cell bank by the baby's mother.

The Two Main Types of Transplant and How They Work

The are two main types of transplant: autologous ("auto") transplant, in which a patient's own stem cells are collected and then transplanted back into the patient, and allogeneic ("allo") transplant, in which the stem cells are obtained from a person other than the patient, most commonly a brother or sister.

Before an autologous or allogeneic transplant, either chemotherapy or a combination of chemotherapy and radiation is given. This treatment, called the preparative regimen or conditioning, eradicates cancerous cells as well as the blood-forming stem cells in the bone marrow, causing the number of mature blood cells to drop.

Next, stem cells are infused into the patient's bloodstream through an intravenous catheter, in a procedure that is similar to a blood transfusion. No surgery is required. Over the following days, the transplanted stem cells travel to the bone marrow, where they will grow and develop into new mature blood cells, including red and white blood cells and platelets.

It usually takes several weeks before all the mature blood cells are replenished. During this time, special measures are taken to protect the patient from infections and bleeding.

Successful autologous and allogeneic transplants provide patients with a new, healthy bone marrow. Allogeneic transplants also give patients a new immune system, which is derived from the donor's stem cells and may give protection from cancer.

Diseases Treated with Transplantation

Different types of transplants are known to be more effective for some diseases than others. Your team of doctors will determine which type of transplant is best for you after considering the specifics of your disease and a number of other factors -- for instance, what other treatments you have received and your general health status. Your transplant doctor will discuss these factors in detail with you.

Here are some of the most common diseases treated with autologous or allogeneic transplantation:

Diagnosis	Allogeneic Transplant/ Autologous Rescue
Amegakaryocytosis/Congenital Thrombocytopenia	Allogeneic
Amyloidosis	Autologous
Aplastic Anemia/Refractory Anemia	Allogeneic
Germ Cell Tumors (Testicular Cancer)	Autologous
Paroxysmal Nocturnal Hemoglobinuria	Allogeneic
Hodgkin's Disease	Autologous or Allogeneic
Acute Leukemias	Allogeneic
Chronic Lymphocytic Leukemia	Allogeneic
Familial Erythrophagocytic Lymphohistiocytosis	Allogeneic
Non-Hodgkin Lymphoma	Autologous or Allogeneic
Multiple Myeloma	Autologous or Allogeneic
Osteopetrosis	Allogeneic
Myelodysplastic Syndrome/Other Myelodysplastic Disorders	Allogeneic
Solid Tumors	Autologous
Wiskott-Aldrich Syndrome	Allogeneic