Influence of HLA-DPB1 mismatches on MLR responses: the role of high resolution HLA class II typing and MLC in unrelated donor selection for BMT.

Twenty eight Hungarian patients lacking a compatible related donor and their 61 HLA-A,B,DR serologically identical potential unrelated donors (selected from BMDW) were investigated in this study. Out of the 61 donor-recipient pairs only 7 (11,5%) proved to be HLA-identical at DNA level. Thirty one pairs (50,8%) differed in DP alleles, 1 pair (1,6%) has a DQ mismatch only and 22 (36,1%) pairs differed in more alleles. More than one potential donor was found for 26 patients and 5 of them have several donors with DP mismatches only. Among the 31 donor-recipient pairs differing only in DP alleles, 0, 1 and 2 mismatches were observed in GvH direction in 7, 10 and 14 cases, respectively. In the MLC assay no proliferative response was observed when no DP mismatch has been found. Among the 1 and 2 DP mismatched cases 11 (35,5%) gave negative and 13 (41,9%) gave positive MLR results. We have found a large scatter in RR values. On the basis of the DNA typing and MLR results we have found that HLA-DPB10101-0201 stimulator-responder combination always gave negative MLR in both direction. HLA-DPB10201-0301 and DPB1*0301-0401 allele combinations were reactive in all cases. In conclusion MLC assay might indicate the low immunogeneicity in certain DP allele combinations as well as the avoidable positive combinations, which may help to select the best fitting donor for BMT.