Bone marrow transplantation

Bone marrow, sponge-like tissue found in the center of certain bones, contains stem cells that are the precursors of white blood cells, red blood cells, and platelets. These blood cells are vital for normal body functions. Blood cells have a limited life span and are constantly being replaced; therefore, healthy stem cells are vital.

In association with certain diseases, stem cells may produce too many, too few, or otherwise abnormal blood cells. Also, medical treatments, particularlychemotherapy or radiation treatment, may destroy stem cells or alter blood cell production. The resultant blood cell abnormalities can be life threatening.

Bone marrow transplantation involves extracting bone marrow from a healthy donor and transferring it to a recipient whose body cannot manufacture proper quantities of normal blood cells. The goal of the transplant is to rebuild therecipient's blood cells and immune system and cure the underlying disease. Ailments that may be treated with a bone marrow transplant include both cancerous and noncancerous diseases.

Cancer may or may not specifically involve blood cells, but cancer treatmentcan destroy the body's ability to manufacture new blood cells. Bone marrow transplantation may be used in conjunction with additional treatments, such aschemotherapy, for various types of leukemia, Hodgkin's disease, lymphoma, breast and ovarian cancer. Noncancerous diseases for which bone marrow transplantation can be a treatment option include aplastic anemia, sickle-cell anemia,thalassemia, and severe immunodeficiency.

Bone marrow transplants are accompanied by a risk of infection, transplant rejection by the recipient's immune system, and other complications. The procedure has a lower success rate the greater the recipient's age. Complications are more likely in people whose health is already impaired. Even in the absence of complications, the transplant and associated treatments are hard on therecipient. A person's ability to withstand the rigors of the transplant is akey consideration in deciding to use this treatment.

Two important requirements for a bone marrow transplant are the donor and therecipient. Sometimes, the donor and the recipient are the same person (an autologous transplant). Typically this happens when a person's bone marrow is healthy but will be destroyed due to medical treatment. If a person's bone marrow is unsuitable for an autologous transplant, the bone marrow must be acquired from another person (an allogeneic transplant).

Allogeneic transplants are more complicated because of proteins called humanlymphocyte antigens (HLA) that are on the surface of bone marrow cells. If the donor and the recipient have very dissimilar antigens, the recipient's immune system regards the donor's bone marrow cells as invaders and tries to destroy them. Such an attack negates any benefits offered by the transplant.

HLA matching, a complex procedure, must be done between donor and recipient.A suitable match is more likely if the donor and recipient are related, particularly if they are siblings.

The bone marrow extraction is the same for an autologous or allogeneic transplant. Harvesting is done under general anesthesia, and discomfort is usuallyminimal. Bone marrow is drawn from the hip bone with a special needle and a syringe. Approximately 1-2 quarts of bone marrow is removed from the donor. This amount is only a small percentage of the total bone marrow and is typically replaced within 4 weeks. The donor remains at the hospital for 24-48 hoursand can resume normal activities within a few days.

If the bone marrow is meant for an autologous transplant, it is stored frozenuntil it is needed. Bone marrow for an allogeneic transplant is sometimes treated to remove the donor's T cells (a type of white blood cell) or to removeABO (blood type) antigens; otherwise, it is transplanted without modification.

The bone marrow is administered to the recipient via a catheter (a narrow, flexible tube) inserted into a large vein in the chest. From the bloodstream, it migrates to the cavities within the bones where bone marrow is normally stored. If the transplant is successful, the bone marrow begins to produce normal blood cells once it is in place.

A bone marrow transplant recipient to spends 4-8 weeks in the hospital. In preparation for receiving the transplant, the recipient undergoes a regimen inwhich the bone marrow and abnormal cells are destroyed making room for the new marrow to be transplanted. Unfortunately, this treatment also destroys healthy cells and has many side effects such as extreme weakness, nausea, vomiting, and diarrhea.

A two- to four-week waiting period follows the marrow transplant before its success can begin to be judged. The marrow recipient is kept in isolation during this time to minimize potential infections. The recipient also receives antibiotic medications and blood and platelet transfusions to help fight infection and prevent excessive bleeding.

Following discharge from the hospital, the recipient is monitored through forup to a year. For several months the recipient needs to be careful in avoiding potential infections. Barring complications, the recipient can return to normal activities about 6-8 months after the transplant.

Bone marrow transplants are costly and are accompanied by life-threatening risks. Approximately 30% of people receiving allogeneic transplants do not survive. Autologous transplants have a survival rate near 90%, but are not appropriate in all situations.

There is the danger of pneumonia or other infectious disease, excessive bleeding, or liver disorder caused by blocked blood vessels. The transplant may berejected by the recipient's immune system, or the donor bone marrow may launch an immune-mediated attack against the recipient's tissues. Approximately 25-50% of bone marrow transplant recipients develop long-term, serious complications.

In a successful bone marrow transplant, the donor's marrow migrates to the cavities in the recipient's bones and produces normal numbers of healthy bloodcells. Bone marrow transplants can extend a person's life, improve quality oflife, and may aid in curing the underlying ailment.

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