For patients without a suitable related donor, searching unrelated donor registries may provide a suitable donor.134 The National Marrow Donor Program (NMDP) is the largest of the registries with over 5 million prospective marrow/PBSC donors and 31,000 CBU135-137 (http://www.nmdpresearch.org/index.html). NMDP searches include donors from Bone Marrow Donors Worldwide, representing registries from 39 countries and bringing the total number of prospective donors to over 9 million (http://www.bmdw.org/ database/donors.htm). As discussed previously, the prospect of finding a match for a patient with uncommon or rare HLA alleles may be different in various populations. Thus, a search of different registries may be more likely to provide a matched donor. In the NMDP registry, five major groups are represented: Caucasian (67.4%), Hispanic (10.6%), African American (9.9%), Asian/Pacific Islander (7.8%), American Indian/Alaska Native (1.6%).136 The CBU Registry has about 30% minority representation. Of the registrants, approximately two-thirds have at least serologic or antigen-level typing for HLA-A, -B, -DR.
When a search is requested a list of potentially matched registrants or CBU is generated. NMDP search reports indicate prospective marrow/PBSC donors with potential for 5/6 and 6/6 (A, B, DR) matches and 4/6, 5/6, and 6/6 for CBU. From among those likely to be matched, a sample for confirmatory and additional HLA testing can be requested. This typing can be performed by the transplant center laboratory or an NMDP reference laboratory. The NMDP requires that both patient and donor be HLA typed at high resolution or allele level for HLA-A*, -B*, and -C* (minimal exons 2 and 3) and DRB1* before donation can occur. This does not indicate that patient and donor must be matched at high resolution for these loci. The intent is to allow analysis of the effect of allele-level matching on transplant outcome.
The prospect of finding a preliminary HLA-A, -B, -DR matched registry donor (i.e. serologic level typing) is 87% for Caucasians, 75% for Asian/Pacific Islander, 85% for Hispanic and 60% for African Americans according to NMDP statistics.135 However, when allele-level matching and other loci are considered, the probability of a full match drops markedly. Tiercy and colleagues138 139 indicated that half or less of their patients with preliminary matches (A, B, DR antigen level) were able to find allele-level matched donors for HLA-A, -B, -Cw, -DRB1, -DRB3, -DRB5, -DQB1. Finding highly matched donors for patients of ethnic minorities is especially difficult.6270
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