Donor Selection
As the National Marrow Donor Program explains, one of the first aspects of receiving a bone marrow transplant is finding suitable donor cells. This involves finding bone marrow of the right HLA variety. HLA describes proteins that are found on the surface of the cells. Each person has their own HLA protein combination, and that is one way in which the immune system identifies if the cells are from the body or are foreign. If a person receives marrow cells from someone who is not an HLA match, then the immune system will attack the donated cells, which is known as a transplant rejection. As a result, it is essential to find a donor who has identical HLA tissue types. Bone marrow cells from the patient or from an identical twin are the best sources for transplants, but closely related family members can also serve as donors. Occasionally, if no one else is a match, an outside person is sought though the donor program.
Donation Process
According to the American Cancer Society, there are two different ways in which bone marrow stem cells can be collected. The stem cells can be harvested from the bone marrow itself. For this process, the donor is anesthetized and a large hollow bore needle is inserted into the pelvis, where it extracts some of the bone marrow. Generally, approximately two pints of bone marrow is taken, and the body is able to replace the bone marrow after four to six weeks. Alternately, peripheral blood stem cells can be donated. Peripheral blood stem cells are cells which circulate in the blood and which can also be used for a bone marrow transplant. For this process, the donor is given a shot of a medication called filgrastim, and that increases the amount of stem cells which are in the blood. The donor donates blood, and it is then given to a special machine which separates the stem cells from the normal blood cells. The stem cells are removed and the remaining cells are given back to the donor.
Transplant Process
Before the transplant recipient receives the donated bone marrow stem cells, physicians typically will destroy the recipient's bone marrow, either using high doses of chemotherapy or radiation. This makes room in the recipient's bones for the donated cells, and also eliminates any diseased bone marrow (which may be why the patient needs a transplant). The stem cells are then gradually infused into the recipient's bloodstream. Once the stem cells have entered into the circulation, they will travel to the host's bone marrow and begin to replicate and divide, thus replacing the recipient's bone marrow.
