Family Members
A suitable donor for bone marrow transplant depends on the degree of matching tissue types of the donor and patient. Genetic markers on the white blood cells called HLA (Human Leukocyte Antigens) determine a person's tissue type. Each person inherits a set of antigens from each parent. A patient's siblings are much more likely to share the same antigens than someone in the general population.

Three major antigens are known to be important in determining the extent of graft rejection or graft-versus-host disease that may occur. These three antigens are known as the HLA-A,

HLA-B and HLA-Dr. These antigens are assigned a number and there can be hundreds of different possibilities and combinations. Therefore, a person's tissue type may look like the following: A-1, A-2, B-7, B-12, Dr-7, Dr-6.

DNA typing is now done to match the antigens of the donor and patient as close as possible.

A "perfect" HLA match can only be seen between full siblings within a family as the antigens are inherited from their parents. Chances of a patient having a fully matched sibling are 25% (one in four).

BMT can be done using a partially matched ("mismatched") family member donor. This means that the donor and patient have one to three antigens that do not match. These mismatches are often referred to as "a five out of six, four out of six or three out of six antigen match. Transplantation using a mismatched donor may increase the risk of graft-versus-host disease or graft rejection.

Unrelated Donors
In the U.S., the National Marrow Donor Program (NMDP) registry facilitates the search for an unrelated bone marrow donor. Additionally, some foreign countries have bone marrow registries. Searching for matched donors within these registries takes only 1-2 days and is done free of charge.

If a suitable donor is found within the registry, the donor is contacted by a person in their community and that are asked whether they still want to donate marrow. If they agree, they are tested and examined by doctors to make sure the marrow will be matched, and that they suitably healthy to donate marrow. The bone marrow is harvested locally and flown via courier for transplantation to Iowa, where it is processed in the laboratory and infused the same day or the following day. The process of searching for an unrelated donor and obtaining the marrow takes 1-3 months.

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