WHAT ARE STEM CELL TRANSPLANTS?
Stem cell transplants are procedures that restore blood-forming stem cells in people who have had theirs destroyed by the very high doses of chemotherapy or radiation therapy used to treat certain cancers.
Blood-forming stem cells are important because they grow into different types of blood cells. The main types of blood cells are:
- White blood cells, which are part of your immune system and help your body fight infection
- Red blood cells, which carry oxygen throughout your body
- Platelets, which help the blood clots
WHAT ARE THE TYPES OF STEM CELL TRANSPLANTS?
There are three types of transplants:
- Patients receive their own stem cells (autologous transplants).
- Patients receive stem cells from their identical twin (syngeneic transplants).
- Patients receive stem cells from someone other than themselves or an identical twin. The patient’s brother, sister, parent or a person not related to the patient may be used (allogeneic transplants).
- In general, patients are less likely to develop a complication known as graft-versus-host disease (GVHD) if the stem cells of the donor and patient are closely matched.
- After being treated with high-dose anticancer drugs and/or radiation, the patient receives the harvested stem cells. They travel to the bone marrow and begin to produce new blood cells.
- A “mini-transplant” uses lower, less toxic doses of chemotherapy and/or radiation to prepare the patient for transplant.
- A “tandem transplant” involves two sequential courses of high-dose chemotherapy and stem cell transplant.
- The National Marrow Donor Program® maintains an international registry of volunteer stem cell donors.
WHAT ARE BONE MARROW AND HEMATOPOIETIC STEM CELLS?
Bone marrow is the soft, sponge-like material found inside bones. Bone marrow contains a specific kind of cell that creates blood-forming stem cells (hematopoietic). Hematopoietic stem cells divide to form more blood-forming stem cells, or they mature into one of three types of blood cells:
- White blood cells, which fight infection.
- Red blood cells, which carry oxygen.
- Platelets, which help the blood to clot.
- Most hematopoietic stem cells are found in the bone marrow. But some cells, called peripheral blood stem cells (PBSCs), are found in the bloodstream. Blood in the umbilical cord also contains hematopoietic stem cells. Cells from any of these sources can be used in transplants.
WHY ARE STEM CELL TRANSPLANTS USED IN CANCER TREATMENT?
One reason stem cell transplants are used in cancer treatment is to make it possible for patients to receive very high doses of chemotherapy and/or radiation therapy. To understand more about why stem cell transplants used, it is helpful to understand how chemotherapy and radiation therapy work.
- Chemotherapy and radiation therapy generally affect cells that divide rapidly. They are used to treat cancer because cancer cells divide more often than most healthy cells. But, because bone marrow cells also divide frequently, high-dose treatments can severely damage or destroy the patient’s bone marrow. Without healthy bone marrow, the patient is no longer able to make the blood cells needed to:
- Carry oxygen.
- Fight infection.
- Prevent bleeding.
Transplants replace stem cells that were destroyed by treatment. The healthy, transplanted stem cells can restore the bone marrow’s ability to produce the blood cells the patient needs.
HOW ARE THE DONOR’S STEM CELLS MATCHED TO THE PATIENT’S STEM CELLS IN ALLOGENEIC OR SYNGENEIC TRANSPLANTATION?
- To minimize potential side effects, doctors most often use transplanted stem cells that match the patient’s own stem cells as closely as possible. People have different sets of proteins on the surface of their cells. They are called human leukocyte-associated (HLA) antigens. The set of proteins, called the HLA type, is identified by a special blood test.
- In most cases, the success of allogeneic transplantation depends in part on how well the HLA antigens of the donor’s stem cells match those of the recipient’s stem cells. The higher the number of matching HLA antigens, the greater the chance that the patient’s body will accept the donor’s stem cells. In general, patients are less likely to develop a complication known as graft-versus-host disease (GVHD) if the stem cells of the donor and patient are closely matched.
- Close relatives, especially brothers and sisters, are more likely than unrelated people to be HLA-matched. But only 25-35% of patients have an HLA-matched sibling. The chances of obtaining HLA-matched stem cells from an unrelated donor is approximately 50%. Among unrelated donors, HLA-matching is greatly improved when the donor and recipient have the same ethnic and racial background.
- Identical twins have the same genes, so they have the same set of HLA antigens. As a result, the patient’s body will accept a transplant from an identical twin.
HOW ARE PERIPHERAL BLOOD STEM CELLS (PBSC) OBTAINED FOR TRANSPLANTATION?
The stem cells used in PBSC transplants come from the bloodstream and are obtained through a process called apheresis. For 4 or 5 days before apheresis, the donor may be given a medication to increase the number of stem cells released into the bloodstream. In apheresis, blood is removed through a large vein in the arm or a central venous catheter. This is a flexible tube that is placed in a large vein in the neck, chest or groin area. The blood goes through a machine that removes the stem cells. The blood is then returned to the donor. The collected cells are then stored. Apheresis typically takes 4 to 6 hours. The stem cells are then frozen until they are given to the recipient.
ARE ANY RISKS ASSOCIATED WITH DONATING BONE MARROW?
- Only a small amount of bone marrow is removed, so donating usually does not pose any significant problems for the donor. The most serious risk involves the use of anesthesia during the procedure.
- The area where the bone marrow was taken out may feel stiff or sore for a few days. And the donor may feel tired. Within a few weeks, the donor’s body replaces the donated marrow. But the time required for a donor to recover varies. Some people are back to their usual routine within 2 or 3 days. Others may take up to 3 to 4 weeks to fully recover their strength.
ARE ANY RISKS ASSOCIATED WITH DONATION?
Apheresis usually causes little discomfort. During apheresis, the patient may feel:
- Numbness around the lips
- Cramping in the hands
The medication that is given to stimulate the release of stem cells from the marrow into the bloodstream may cause:
- Bone and muscle aches
- Difficulty sleeping
These side effects generally stop within 2 to 3 days of the last dose of the medication.
HOW DOES THE PATIENT RECEIVE THE STEM CELLS DURING THE TRANSPLANT?
After being treated with high-dose anticancer drugs and/or radiation, the patient receives the stem cells through an intravenous (IV) line just like a blood transfusion. This part of the transplant takes 1 to 5 hours.
WHAT HAPPENS AFTER THE STEM CELLS HAVE BEEN TRANSPLANTED TO THE PATIENT?
After entering the bloodstream, the stem cells travel to the bone marrow. There they begin to produce new white blood cells, red blood cells and platelets in a process known as engraftment. Engraftment usually occurs within about 2 to 4 weeks after transplantation. Your caregivers monitor it by checking blood counts on a frequent basis. Complete recovery of immune function takes much longer. It can take up to several months for autologous transplant recipients and 1 to 2 years for patients receiving allogeneic or syngeneic transplants. Caregivers evaluate the results of various blood tests to confirm that new blood cells are being produced and that the cancer has not returned. The removal of a small sample of bone marrow through a needle for examination under a microscope (bone marrow aspiration) can also help caregivers determine how well the new marrow is working.
WHAT ARE THE POSSIBLE SIDE EFFECTS?
The major risk is an increased susceptibility to infection and bleeding as a result of the high-dose cancer treatment. Caregivers may give the patient antibiotics to prevent or treat infection. They may also give the patient transfusions of platelets to prevent bleeding and red blood cells to treat anemia. Patients may experience short-term side effects. These include:
- Loss of appetite
- Mouth sores
- Hair loss
- Skin reactions
Potential long-term risks include complications of the pre-transplant chemotherapy and radiation therapy, such as:
- Inability to produce children (infertility).
- Clouding of the lens of the eye (cataracts).
- New cancers
- Damage to the liver, kidneys, lungs, and/or heart
With allogeneic transplants, a complication known as graft-versus-host disease (GVHD) sometimes develops. GVHD occurs when white blood cells from the donor identify cells in the patient’s body as foreign and attack them. The most commonly damaged organs are the skin, liver, and intestines. This complication can develop within a few weeks of the transplant (acute GVHD) or much later (chronic GVHD). To prevent this complication, the patient may receive medications that suppress the immune system. Also, the donated stem cells can be treated to remove the white blood cells that cause GVHD. This is a process called T-cell depletion. If GVHD develops, it is treated with steroids or other immunosuppressive agents. GVHD can be difficult to treat, but some studies suggest that patients with leukemia who develop GVHD are less likely to have the cancer come back.
WHAT IS A “TANDEM TRANSPLANT”?
A “tandem transplant” is a type of autologous transplant. This method is being studied in clinical trials for the treatment of several types of cancer, including multiple myeloma and germ cell cancer. During a tandem transplant, a patient receives two courses of high-dose chemotherapy, one after another (sequential), with stem cell transplant. Typically, the two courses are given several weeks to several months apart. Researchers hope that this method can prevent the cancer from coming back at a later time.
HOW DO PATIENTS COVER THE COST OF PBSC TRANSPLANTS?
- There are options for relieving the financial burden associated with PBSC transplants. A hospital social worker is a valuable resource in planning for these financial needs. Federal Government programs and local service organizations may also be able to help.
- The National Cancer Institute’s (NCI) Cancer Information Service (CIS) can provide additional information about sources of financial assistance.
WHERE CAN PEOPLE GET MORE INFORMATION ABOUT POTENTIAL DONORS AND TRANSPLANT CENTERS?
The National Marrow Donor Program® (NMDP) is a federally funded nonprofit organization. It was created to improve the effectiveness of the search for donors. The NMDP maintains an international registry of volunteers willing to be donors for all sources of blood stem cells used in transplantation:
- Bone marrow.
- Peripheral blood.
- Umbilical cord blood.
The NMDP website contains a list of participating transplant centers. The list includes descriptions of the centers as well as their transplant experience, survival statistics, research interests, pre-transplant costs, and contact information.