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Bone marrow transplantation is a medical procedure that involves stem cell transplantation. The common feature of recipients is a need for blood stem cells. Most recipients are leukemia patients or others who have been exposed to high doses of chemotherapy or total body irradiation resulting in destruction of their bone marrow stem cells. Other patients who receive bone marrow transplants include pediatric cases where the patient has an inborn defect such as severe combined immunodeficiency or congenital neutropenia and was born with either no blood stem cells or defective stem cells. Other conditions that bone marrow transplants are considered for include thalassemia major, sickle cell disease and aplastic anemia.
The transplanted cells are bone marrow-derived blood stem cells. These cells can be obtained from a bone marrow donation, peripheral blood donation or donation of the blood from an umbilical cord and placenta after a baby is born. In a bone marrow donation, bone marrow is surgically removed from a large bone of the donor, typically the sternum or the hip, by a large needle that reaches the center of the bone. The technique is referred as a bone marrow harvest and involves literally 100s of insertions of the needle. Peripheral blood cells are collected through a process known as apheresis. The donor's blood is withdrawn through a sterile needle in one arm and passed through a machine that separates the blood-forming cells.
The rest of the blood is returned to the donor. Cord blood is obtained when a mother donates her infant's umbilical cord and placenta after birth. The blood products obtained are either transplanted immediately or frozen for later use. The blood stem cells are infused into the recipient through an IV (intravenous) line, like any other intravenous fluid. The blood stem cells will eventually settle into the recipient's bone and start producing blood cells there.
There are two major types of bone marrow transplantation. Allogeneic bone marrow transplantation involves two people, one is the donor and one is the recipient. Autologous bone marrow transplantation involves isolation of bone marrow-derived blood stem cells from a patient, storage of the stem cells, medical treatment of the patient that destroys stem cells remaining in the body, and return of the patient's own stored stem cells to their body.
Donor limitation
A major limitation of allogeneic bone marrow transplantation is a shortage of donors. To avoid rejection of the transplanted stem cells, the donor should have the same human leukocyte antigens as the recipient. About 25 to 30 percent of bone marrow transplantation recipients have an HLA-identical sibling who donates the required stem cells. For other recipients, registries of volunteer donors can be quickly searched in order to find an exact HLA match. If an exact match cannot be found, HLA-similar donors can be used. However, the results with non-exact donors are sometimes poor due to rejection or severe graft-versus-host disease.
A compatible donor is found by doing blood tests on potential donors. Perfect matches, the donor matches on all six HLA types result in the most successful transplants. Less perfect matches, four or five matches, can also result in successful transplants but the risk of complications is greater.
Medical conditions treated by bone marrow transplantation
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