The Search Process
Once the patient’s physician has determined that an allogeneic bone marrow or blood stem cell transplant is the best course of treatment, a suitably matched donor must be identified. This is a multi-step process including immediate and extended family studies and an international unrelated donor search. Patients are encouraged to test immediate family members first. However, frequently time is a patient’s biggest enemy. Thus, if a sibling match is not identified immediately, it is worthwhile to initiate an unrelated donor search concurrently with an extended family study.
It is important that patients maintain regular contact with the transplant center in order to obtain regular updates on the status of the donor search. If they are unable to perform this task, they are entitled to designate an advocate of their choosing, usually a close relative or friend to interface with the transplant center on their behalf.
IMMEDIATE FAMILY STUDY
Logic dictates that the most suitable match for a patient would be a family member.
There is a 25 percent chance that a sibling will be a match. If the sibling is an identical twin, there will be a perfect match, referred to as syngeneic.
Parents share 3 of 6 antigens with their biological children. This is referred to as haploidentical. In some cases, parents will share antigens in common with each other. In these circumstances, patients may share more than 3 of 6 antigens with a parent.
EXTENDED FAMILY STUDY
An extended family study is particularly useful among ethnic groups who tend to marry from within their own ethnic group from generation to generation. As typing information on relatives becomes available, experts can predict the likelihood of finding a related match and provide guidance with the related donor search. Possible strategies include determining which haplotype is less common and focusing on a specific branch of the extended family.
Sometimes, when a patient does not have any immediate or extended family, or if it is clear that their HLA typing is uncommon, engaging in genealogical research may be helpful. By tracing familial roots back several generations, one may be able to locate previously unknown descendants. Constructing family trees starting with one’s ancestors can be beneficial, and there is family tree software available on the market that can simplify the task of tracking this information. In terms of research, there are numerous resources available, including genealogical societies and searchable databases on the World Wide Web. If a patient was adopted, this research becomes crucial in order to find potential siblings or other close relatives. This research will require the cooperation of adoption agencies, hospitals, and local governmental agencies, perhaps with the guidance of private investigators.
UNRELATED DONOR SEARCH
Coordinators at transplant centers should have access to the Bone Marrow Donors Worldwide (www.bmdw.org), a collaborative effort of 72 volunteer stem cell registries in 52 countries. The database contains the phenotypes of more than eight million prospective bone marrow and blood stem cell donors. After obtaining a summary report, the coordinator can narrow the search to a few specific registries that have potential matches, and submit to those specific registries, according to the five-step process outlined in the next section.