Stem Cell Transplants: Finding A Donor Match
One of the most critical first steps to having a stem cell transplant is ensuring the donor and recipient are a good match. This is of particular concern for those receiving an allogeneic transplant, as these involve the donation of stem cells either by a family member, an unrelated individual, or a cord blood unit from a cord blood bank.
In particular, it is critical that a donor and recipient share a compatible protein called the human leukocyte antigen (HLA). In both cord blood and bone marrow transplants, HLA matching is a key factor in the overall success of the procedure, as well as in preventing any possible complications, such as graft versus host disease (GVHD).
What is HLA Matching? Why is it Important?
HLA is a type of protein made up of six antigens, which is found on the outer surfaces of cells. Our bodies use HLA antigens to help distinguish between cells that are foreign (and therefore need to be expelled), and those that are not. Therefore, a close match in HLA antigens is a reliable determinant of a few complications in stem cell transplant procedures.
Furthermore, because HLA antigens are inherited, the best way of ensuring you find the best HLA match is by using the stem cells of a biological sibling - that is, a sibling who shares both your mother and father. Even then, however, the chances of finding a match are not exceedingly high (25%). It is very rare for siblings to produce a perfect match, except in the case of identical twins - this is referred to as a syngeneic transplant. Parents and half-siblings are generally unsuitable, but may be tested in the absence of other siblings. Over 70% of patients requiring a transplant do not have a compatible donor in their family.
In this respect, cord blood transplants may be the optimal choice. That is because umbilical cord blood contains more primitive stem cells, which are less likely to trigger a negative HLA response. Indeed, with respect to HLA compatibility, many transplant centres have a minimum match requirement of 4/6 for a cord blood transplant, while 5/6 is required for a bone marrow transplant.
Finding a Stem Cell Donor
Patients requiring a stem cell transplant who do not have a suitable match in their family are not responsible for finding a donor, as this will be the job of the transplant centre or your health professional. The National Blood Service (England and Wales) will provide the centre with lists of potential volunteers to be considered.
In addition to stem cell compatibility, a potential donor will also be screened for other potential influencing factors through medical examinations. These will be performed in a hospital, normally over the course of a couple of visits. Once they have been determined to be in good health, their bone marrow stem cells will be collected at the hospital.
Unfortunately, however, only about 1 in 10 patients requiring a stem cell or bone marrow transplant will find a suitable, unrelated donor. Ethnic minorities may find particular difficulty, as the donor population is overwhelmingly Caucasian, and it is rare to find a match outside your ethnic group.
How Long Will it Take to Find a Donor Match?
Wait times for finding a donor can vary significantly. In ideal cases, it can take as little as two weeks to find a cord blood unit match. However, it is much more common for patients to have to wait months, and often much longer, to find a suitable transplant donor, particularly for a bone marrow transplant.
While the search for a donor is being conducted, the patient will continue to receive treatment from their doctor, so that they may notify the transplant centre of any changes to the patient's health.
In the case that a suitable donor cannot be found, alternatives to a stem cell transplant may be suggested.
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