HLA DQ and DP locus mismatches and their effect on MLC in HLA class I- and DRB1-matched unrelated patient/donor pairs waiting for allogeneic bone-marrow transplantation.

The frequency of HLA DQA1, DQB1, and DPB1 mismatches was evaluated in 110 HLA class I- and DRB1-matched, unrelated pairs who were tested in mixed lymphocyte culture (MLC) in connection with a potential allogeneic bone-marrow transplantation between unrelated persons. After typing of the DQA1, DQB1, and DPB1 genes retrospectively, it was found that only 22% of the pairs were matched for all the loci tested. However, the frequency of this fully matched group was higher (37%) in pairs where both individuals were of Finnish origin as compared to those where the donor originated from a foreign registry. This suggests that the variety of haplotypes may be limited in small populations and justifies local national registries. The overall correlation between class-II match and stimulation in MLC was clear: better matches gave lower responses. However, the correlation was not definitive; for example, no response was observed in some cases with mismatches only in DPB1.