The Stem Cell Donor
When stem cells are required from someone other than the patient to be transplanted, careful testing called tissue typing or HLA ( Human Leukocyte Antigen ) typing must be done. This testing is somewhat like determining the red blood cell type (A+, O-, AB+, etc.), except the testing is done on white blood cells. The HLA proteins or antigens present on white blood cells are also present on most of the other tissues of the body, so the white cell merely represents an easily obtained "tissue" we can test. Chromosome pair number six (we humans have 23 pair) contains the most important genetic information that determines which proteins or antigens are on the surface of the white blood cell. One of the chromosome pair came from mother and the other came from father. Altogether there are six antigens (three from each parent) that must be identified. These are called HLA A, B and DR--note there are two A antigens, two B antigens, and two DR antigens .
Once a match is found at all six antigens, a second level of testing is required to confirm compatibility. This involves more detailed testing of the antigens. We more precisely determine the degree of compatibility between the HLA A, B, and DR genes of the donor and the recipient using DNA typing.
Among siblings in the family, there is a one-in-four chance of finding a compatible donor. Parents, offspring, aunts, uncles, and cousins rarely are well enough matched to be a donor for an adult recipient. When a sibling is not available to be a donor and stem cells from a healthy donor is required, a matched unrelated donor search will be initiated.
There are several donor registries in the United States and abroad that contain in excess of six million donors, many completely typed but some only typed at HLA A and B. The construction, updating, and maintenance of these registries is a very costly affair and, thus, the process of finding a donor in one of the registries can cost $6,000 to in excess of $20,000. Careful inquiry as to whether insurance will pay for these costs has to be done in all cases.
Once a donor is identified, a very detailed set of guidelines must be followed to insure that the donor is fully counseled and is able to provide informed consent. A complete medical evaluation is required with careful attention paid to possible infections or risks of infections such as hepatitis or AIDS. After it is determined that the donor is medically suited to proceed, the donor signs a form called the Intent to Donate. This form spells out very clearly that once the chemotherapy/radiation therapy is started, backing out by the donor would mean certain death for the patient.
In all cases the donor's stem cells will be harvested in an approved collection center hospital nearest to where they live. The stem cells are then brought by courier to the University of Iowa Hospitals and Clinics where it is received and processed in the Hematopoietic Progenitor Cell Laboratory.
If the donor is a sibling, sometime before chemotherapy and/or radiation begins, the donor is usually seen by a member of the transplant team (or a local physician) for a physical exam, blood tests, chest-X-ray, EKG, and to answer questions about the procedure of collecting stem cells. At that time a unit of blood is usually taken from the donor and stored. This blood is given back to the donor on the day of their stem cell collection. When the transplant team is assured that the donor is a willing and healthy individual, treatment is begun.
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