Who can be a donor?
Stem cells–the healthy immature blood cells used in blood and marrow transplants–are harvested from a variety of donors: self, sibling, parent, relatives or non-related individuals, or are collected from the umbilical cord blood from a related or non-related newborn infant.
Family members of a sick child can be typed to see if they are potential donors. Other times, individuals who have a desire to help will be typed and list themselves on national or international registries as potential donors.
If a potential donor is located as a match, additional tests will be required of the donor to ensure genetic compatibility. Once a match is determined, a donor's stem cells are collected, either from the donor's bone marrow or from the bloodstream. In the case of umbilical cord stem cells, these are collected at the time of birth of the infant and the stem cells are tested, typed and frozen until they are needed.
How are a donor and recipient matched?
Finding a well-matched donor for a patient is an essential first step to a successful transplant. Unfortunately, a transplant recipient cannot receive just anyone's stem cells. Although the tests are done on blood samples, it should not be confused with typing for blood donation and involves matching for what is called human leukocyte antigens (HLA). HLA molecules are present on the surface of white blood cells and other tissues. If these are greatly mismatched, it may lead to complications in the transplant recipient.
HLA is a complex genetic system in which more than 1,000 different HLA antigens have been identified. Each person has inherited one set of HLA antigens, called a haplotype, from each parent. A 25 percent chance exists that two siblings in a family are HLA-identical. The chances are very small that two unrelated people happen to have the same HLA type. In bone marrow transplantation, the search for an HLA-matched unrelated donor requires access to a large population of HLA-typed volunteer donors such as the National Marrow Donor Program's Registry. While such searches are often successful, sometimes only partially matched donors become available for the patient.
In order to know if a recipient and a potential donor are HLA-matched, a small amount of blood from each is sent to a tissue-typing laboratory. For the purposes of blood and marrow transplantation, six major HLA antigens are considered. The role of other antigens is not clear and at this time is thought to be minor. In general, more matched antigens mean a better engraftment of donated marrow. However, in certain circumstances some degree of mismatch is permissible. Engraftment of the stem cells occurs when the donated cells make their way to the marrow and begin to produce new blood cells.
Medical research continues to investigate the role of HLA antigens in blood and marrow transplantation.
Preparation for the Donor
Once a match is found for a child needing a bone marrow transplant (BMT), stem cells will be collected from the donor either by a bone marrow harvest (collection of stem cells with a needle placed into the soft center of the bone marrow) or peripheral blood stem cell collection (stem cells collected from the circulating cells in the blood). Cord blood has already been collected at the time of a birth and stored for later use.
After a potential related or unrelated donor is identified, that individual will undergo additional tests to confirm the tissue match with the recipient, assess donor health status, and determine his/her ability to undergo bone marrow harvest or stem cell collection procedure(s). The details of method of donation, scheduling, informed consent and other pertinent issues will be discussed by the transplant team.
Sibling Donor
If your child will be receiving a bone marrow transplant using bone marrow that is donated, or "harvested," from a sibling, it is very important that the sibling is aware of what will happen both prior to and during the bone marrow harvest procedure. The Child Life Specialist will help to explain this process to the donor sibling.
The sibling may be scared about donating the marrow. This is normal. The Child Life Specialist will be available to explore the sibling's feelings and emotions. It is imperative that the sibling not feel as though the life of the brother or sister is in his/her hands. This is a huge responsibility. Many siblings wonder if their marrow will be "good enough." The sibling needs to understand that a BMT is a type of treatment for the brother or sister's disease. If the transplant is not successful, it is because of the disease, not because of the sibling's bone marrow. The Child Life Specialist will talk with the sibling about this before the harvest procedure.
How are stem cells collected?
A blood and marrow transplant is done by transferring stem cells from one person to another. Stem cells can either be collected from the circulating cells in the peripheral blood or from the bone marrow. For umbilical cord transplants blood is collected at the time of a birth and stored.
Peripheral Blood Stem Cells
Peripheral blood stem cells (PBSCs) are collected by an apheresis, a process in which the donor is connected to a special cell separation machine via a needle inserted in the vein. Blood is taken from one vein and is circulated through the machine, which removes the stem cells and returns the remaining blood and plasma back to the donor through another needle inserted into the opposite arm. Several sessions may be required to collect enough stem cells to assure a chance of successful engraftment in the recipient.
Bone Marrow Harvest
Bone marrow harvesting involves collecting stem cells with a needle placed into the soft center of the bone, the marrow. Most sites used for bone marrow harvesting are located in the hip bones and the sternum. The procedure takes place in the operating room. The donor is anesthetized during the harvest and will not feel the needle. In recovery, the donor may experience some pain in the areas where the needle was inserted.
Umbilical Cord Blood Collection
Cord blood is collected after delivery, when the placenta and umbilical cord are separated from the infant. The site of collection is prepared to prevent bacteria from entering the collection process. The blood that is contained in the cord is collected in a sterile container. The blood is tested for viruses or disease and the stem cells are counted. The cord blood is then stored in a special freezer and is registered in national and international registries for potential recipient matches.
In the News
BMT Survivor Meets Donor
Pittsburgh Post-Gazette (6/11/01)
