What is bone marrow transplantation?
Bone marrow transplantation is used when the immune and blood-forming systems of the body are malfunctioning or have been severely damaged. Without adequate white blood cells, a person will soon die from infection. Transplantation is an attempt to cure or arrest diseases such as leukemia, cancer, and sickle cell disease and conditions such as brain tumors and hereditary diseases. Bone marrow transplantation is used when all other methods of treatment have failed. The procedure is usually performed on patients who are younger than fifty years old, with the greatest success rates found in children.
Before the procedure can be performed, a suitable donor must be found. The donor can be the patient (autologous transplantation) or someone else (allogeneic transplantation). Once the donor is identified, the bone marrow is harvested. This procedure is usually done under general anesthesia and takes one to two hours. A needle is inserted in the hip, and marrow is sucked out from different locations in the pelvic bone. Approximately 1 to 3 pints of marrow are taken. The donor usually stays overnight in the hospital and may be sore for one or two weeks following the operation.
The marrow, which contains the stem cells necessary to reestablish the blood-producing and immune systems of the patient, is processed and stored until the patient is prepared for the transplantation. During the hospital stay, the patient is kept in a sterile room to prevent infection. If the surgery is being performed on a cancer patient, the patient receives extensive chemotherapy and/or radiation before the donor marrow is transplanted; this action destroys any cancer cells in the patient, as well as his or her immune system.
The patient then receives the bone marrow transplantation in a manner similar to a blood transfusion: The donor cells are introduced through the veins and into the bloodstream. Until the transplanted cells begin to function (usually two to four weeks), the patient receives blood and platelet transfusions, as well as antibiotics to fight infection. The patient is usually discharged from the hospital in a month but must take antibiotics and antiviral medications for six months to two years after the transplantation because the recovery of the immune system is slow.
Bone marrow transplantation is a risky procedure with a success rate that ranges from 10 to 90 percent. One of the greatest obstacles is finding a suitable donor. The best possible match is between siblings, but even here the probability of a correct match is only 25 percent. Unrelated donor and patient matches made with marrow from donor banks increase the risk of a mismatch.
Finding a suitable donor is imperative because of the risk of graft-versus-host disease (GVHD). GVHD occurs when the donor cells recognize the host’s body as foreign and react against it. This reaction may occur within a hundred or more days after the transplant and can vary in severity from a mild rash to the fatal destruction of tissue and organs. For correctly matched donors and recipients, the risk of life-threatening GVHD is 10 to 20 percent. For mismatched donors and recipients, the risk rises to 80 percent. In some cases, especially with leukemia and cancerous blood diseases, patients who suffer mild GVHD have an improved chance of survival because part of GVHD is a graft-versus-leukemia (GVL) effect. In these cases, the transplanted immune system acts against any remaining leukemia cells.
When the patient does not have a condition that damages the bone marrow, transplantation can be performed with his or her own marrow. After marrow has been collected from the patient, radiation and/or chemotherapy can be used to destroy the remaining immune system. Autologous transplantation eliminates the need to find a compatible donor and the risk of GVHD. This method can be used for treating solid tumors and has shown promise in curing brain tumors that were once considered fatal, with a success rate of 20 percent.
In April 2013 scientists at the Abramson Cancer Center of the University of Pennsylvania published a study of 300,000 bone marrow translplant recipients. According to the study, transplant recipients are at increased risk for suicide and accadential death.
Research on bone marrow transplantation began in the early 1950s, with the first successful transplantations performed on children in 1968. By the 1990s, more than five thousand bone marrow transplantations were being performed worldwide every year. The development of drugs that work to suppress the immune system has increased the chances for survival for these patients.
Several areas of research promise even better results in the future. A growing understanding of disease at the genetic level offers the possibility of separating unhealthy bone marrow cells from healthy ones. Methods of growing cells outside the body for use in transplantation are being developed. Progress has also been made in increasing the donor pool. National and international programs actively seek potential donors. Healthy people may begin storing their own bone marrow for a possible need in the future.
Perhaps one of the most promising potential sources of donor bone marrow is umbilical cord blood, which is rich in stem cells. Transplants using umbilical cord blood were first used in 1989 and have proven very successful. If established, umbilical cord blood banks could greatly increase the quantity of available donor marrow.
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