In a stem cell transplant — also called a 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 people, the aim of the transplant is to cure the disease.
Blood-Forming Stem Cells
Blood-forming, or hematopoietic, stem cells are immature cells that can develop into any type of blood cell, 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 controlling bleeding
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 peripheral blood stem cells (PBSCs) 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.
Types of Transplantation
The are two main types of transplant: autologous transplant, in which a patient's own stem cells are collected and then transplanted back into the patient, and allogeneic transplant, in which the stem cells are obtained from another person, most commonly a brother or sister.
Dr. Sergio Giralt, Chief of the Bone Marrow Transplantation Service, explains how transplantation is used in the treatment of cancer.
Before an autologous or allogeneic transplant, a patient receives either chemotherapy or a combination of chemotherapy and radiation. This treatment, called the preparative regimen or conditioning, eradicates cancerous cells as well as the blood-forming stem cells in the bone marrow, decreasing the number of mature blood cells in a person’s body.
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 new, healthy bone marrow. Allogeneic transplants also give patients a new immune system, which is derived from the donor's stem cells and may provide protection against 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.
Autologous transplantation can be used to treat a person who is diagnosed with:
Allogeneic transplantation can be used to treat a person who is diagnosed with:
Either autologous or allogeneic transplantation can be used to treat people diagnosed with Hodgkin lymphoma, non-Hodgkin lymphoma, or multiple myeloma.
Who Is Eligible for a Transplant?
Transplantation can be an extremely challenging procedure for a patient and family. This is both because of the toxicity of the high-dose preparative regimens and the extended period during which the patient’s immune system is suppressed. For this reason, physicians carefully select patients for this procedure. Newer technology has allowed us to transplant patients who are older and sicker, but an extensive pre-transplant evaluation is still necessary.