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Stem Cell Transplantation
Stem cells are unspecialized cells from which other more specialized cells can be derived. Stem cells may be obtained from the umbilical cord of a baby after it is born (donated by the mother), from bone marrow (bone marrow transplantation), or from blood. Blood is preferred to bone marrow as a source because the procedure is less invasive and the number (count) of blood cells returns to normal more quickly. Stem cells from umbilical cords are usually used only in children because umbilical cord blood does not contain enough stem cells to use in adults.
Stem cell transplantation can be used as part of the treatment for blood disorders such as leukemia, certain types of lymphoma (including Hodgkin lymphoma), aplastic anemia, thalassemia, sickle cell anemia, and some congenital metabolic or immunodeficiency disorders (such as chronic granulomatous disease). Stem cell transplants may also be given to people who have been treated with high doses of chemotherapy or radiation therapy for certain cancers such as breast cancer. Such treatments destroy bone marrow, which produces stem cells. Occasionally, stem cell transplants can be used to treat cancers in organs, such as breast cancer or neuroblastoma (a common childhood cancer that develops from nerve tissue).
About 30 to 40% of people who had lymphoma and 20 to 50% of those who had leukemia are cancer-free after stem cell transplantation. The procedure prolongs life in people with multiple myeloma. It is less effective for breast cancer.
Stem cells may be the person’s own cells (autologous transplantation) or those of a donor (allogeneic transplantation).
If people with cancer are being given their own stem cells, the cells are collected before chemotherapy or radiation therapy, which can damage stem cells. The cells are injected back into the body after the treatment. If the stem cells come from a donor, the recipient is given drugs to suppress the immune system (immunosuppressants) before stem cells are transplanted.
Stem cells from adults can be obtained from blood during an outpatient procedure. First, the donor is given a drug that causes the bone marrow to release more stem cells into the bloodstream. Then blood is removed through a catheter inserted in one arm and is circulated through a machine that removes stem cells. The rest of the blood is returned to the person through a catheter inserted in the other arm. Usually, about six 2- to 4-hour sessions over a period of several days are needed, until enough stem cells are obtained. Stem cells can be preserved for later use by freezing them.
For bone marrow transplantation, the donor is given a general or local anesthetic. Doctors then remove marrow from the donor’s hip bone with a syringe. Removal of bone marrow takes about 1 hour.
Stem cells are injected into the recipient’s vein over a period of 1 to 2 hours. The injected stem cells migrate to and begin to multiply in the recipient’s bones and produce blood cells.
Stem cell transplantation is risky because the recipient’s white blood cells have been destroyed or reduced in number by chemotherapy or radiation therapy. As a result, the risk of infection is very high for about 2 to 3 weeks—until the donated stem cells can produce enough white blood cells to protect against infections. Recipients are given drugs to stimulate blood cell production and antimicrobial drugs to prevent infections.
Another problem is that the new bone marrow obtained from another person may produce cells that attack the recipient’s cells, causing graft-versus-host disease (see Complications After Transplantation). This disease causes death in about 20 to 40% of people who develop it. Furthermore, the original disorder may recur.
The risk of infection can be reduced by keeping the recipient in isolation for a period of time (until the transplanted cells begin to produce white blood cells). During this time, everyone entering the room must wear masks and gowns and wash their hands thoroughly. The recipient is given growth factors, which stimulate the production of blood cells, and antimicrobial drugs to help reduce the risk of infection. If the stem cells came from another donor, the recipient is given immunosuppressants after transplantation to prevent rejection and graft-versus-host disease.
Recipients of a stem cell transplant usually remain in the hospital for 1 to 2 months. After discharge from the hospital, follow-up visits are necessary at regular intervals. Most people need at least 1 year to recover.
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