Relevance of 10 Caucasian HLA haplotypes in searches for unrelated bone marrow donors for 100 patients from a single center.

Unrelated donor searches for 100 Caucasian patients were referred to France Greffe de Moelle Registry (FGM) from September 1987 (24600 donors) to December 1993 (71500 donors, 61% DR typed). After DR typing of HLA-A,B matched donors, unsuccessful searches were extended to other European Registries for 36 patients. Twenty two patients had a donor (FGM : 19, other Registries : 3) selected on : (1) HLA-A,B and DRB,DQB1 split identity ; and (2) unidirectional relative response <5% in MLR performed twice. Estimated probability of finding a compatible donor at 9 months in FGM was 12% (s.e. ± 4%) and 25% at 2 years (s.e. ± 6%). This probability was stringently dependent on a phenoidentity to one very common HLA-A,B,DR or B,DR haplotype (25% at 9 months when present, representing 19 of 19 patients with a compatible donor). Without this phenoidentity, the probability was zero per cent (P = 0.0001) in FGM searches and <4% (n=1) in extended searches. The MLR test was shown to be insensitive for screening for DPB1 mismatches. Clinical status influenced the probability of finding a compatible donor at one year ranging from 9% ± 9% for ALL to 23% ±8% for CML (NS). Disregarding DPB1 mismatches is the most efficient way of increasing search efficiency.