What are blood stem cells?
Blood stem cells produce the body's blood cells. The white blood cells fight infection, red blood cells carry oxygen throughout the body, and platelets enable blood to clot.
The greatest concentration of blood stem cells is in the bone marrow. However, it is possible to move blood stem cells out of the bone marrow into the bloodstream or “peripheral blood” where they can be collected and used instead of bone marrow for the transplant. Umbilical cord blood also contains blood stem cells that can be used for transplant.
Why are transplants performed?
Sometimes the stem cells in the bone marrow malfunction. They might start producing too many blood cells, too few blood cells or defective cells.
When this happens it may be necessary to replace the patient's blood stem cells with new, healthy stem cells. This is accomplished by a blood stem cell transplant, also called a bone marrow, a peripheral blood stem cell or a cord blood transplant.
Blood stem cell transplants are not just used to treat people with blood disorders. Patients with diseases such as lymphoma, immune system disorders, genetic diseases and some solid tumors may also be a candidate for a blood stem cell transplant.
Types of transplant
Transplants using stem cells collected from the bone marrow are called bone marrow transplants. Those using cells collected from the bloodstream are called peripheral blood stem cell transplants. Transplants using stem cells collected from an umbilical cord are called cord blood transplants.
If a patient provides his or her own bone marrow or stem cells for the transplant, the procedure is called an autologous transplant. If the cells being used for the transplant are donated to you by someone else, the procedure is called an allogeneic transplant. If the donor is an identical twin, the procedure is called a syngeneic transplant.
Sometimes the treatment suggested to patients is two transplants. This most often occurs when a patient's diagnsis is multiple myeloma. These transplants are referred to as tandem transplants.
Your doctor may refer to your transplant a hematopoietic cell transplant. This is a technical term used to describe all types of transplants using blood stem cells.
Transplants also vary according to the amount of chemotherapy and/or radiation a patient is given to destroy the disease prior to transplant. In most transplants, patients receive very high dosages of chemotherapy and/or radiation. This destroys the disease, but also destroys the patient’s immune system. This type of transplant is called a standard or myeloablative transplant.
For patients who cannot tolerate very high dosages of chemotherapy or radiation, or who have a disease that does not require that their marrow be completely destroyed, less intensive dosages of chemotherapy or radiation is sometimes an option. This type of transplant is called a reduced intensity transplant, mini-transplant, or nonmyeloablative transplant.
How transplants are performed
The first step is to identify a source of healthy blood stem cells. In some cases, the patient's own stem cells may be used for transplant. In other cases, it may be necessary to find a stem cell donor.
Next, the patient is given chemotherapy and/or radiation to kill the diseased cells. Most chemotherapy drugs are given through a thin, flexible tube called a central venous catheter or a Hickman®, Groshong®, or Broviac® catheter. The catheter is surgically implanted into a large vein just above the heart. It enables drugs to be given to the patient and blood samples withdrawn painlessly without inserting needles into the patient's arm.
Following chemotherapy and/or radiation therapy, the healthy blood stem cells that were previously collected from the patient or a donor are infused into the patient’s bloodstream through the central venous catheter. The stem cells find their way to the bone marrow where they take up residence or ‘’engraft” and then begin to produce normal blood cells.
Where transplants are performed
If you are having a standard or myeloablative transplant, you will probably be hospitalized for most or all of your treatment. The length of your hospital stay will depend on how quickly you recover normal blood counts after your transplant, and whether or not you experience complications.
It typically takes two to four weeks before patients are discharged from the hospital. If you are being transplanted with cells from a donor, it often takes longer. You will need to remain close to the hospital for several weeks after your discharge for follow up care.
If you are an adult and are having a reduced intensity or nonmyeloablative transplant, much of your treatment may be in the out-patient clinic. You will need to make daily visits to the clinic for several weeks to receive your treatment and be monitored for side effects. If a problem arises, you may be admitted to the hospital.
Pre-transplant check list
The National Marrow Donor Program has developed a transplant planning check list that you may find helpful. It identifies steps you may need to take to prepare for financial, legal, employment, spiritual, caregiving and other issues you and your family will face during transplant.
Embryonic stem cells
The stem cells used in blood stem cell transplants are different than embryonic stem cells that are the subject of much controversy. Blood stem cells are collected from the bone marrow or bloodstream of adult donors, or from an umbilical cord after a child is born. They are not collected from embryos.