Frequent HLA Class I and DP Sequence Mismatches in Serologically (HLA-A, HLA-B, HLA-DR) and Molecularly (HLA-DRB1, HLA-DQA1, HLA-DQB1) HLA-Identical Unrelated Bone Marrow Transplant Pairs

The rates of graft-versus-host disease (GVHD) and rejec-tion are significantly higher among recipients of unrelated donor marrow (BM) than in recipients of marrow from HLA-identical siblings, even when donors and recipients are mixed lymphocyte culture (MLC) compatible and serologi-cally and Dw identical. It has been hypothesized that phe-notypically silent HLA class I and DP sequence mismatches might be associated with these differences, but little is known about their incidence. We have sequenced the HLA-A, HLA-B, HLA-C, HLA-DPA1, and HLA-DPB1 genes ex-pressed by 12 unrelated marrow transplant pairs, 11 of whom were molecularly matched at DRB, DQA1, and DQBl loci. Nine of these pairs were also HLA-A and HLA-B matched by serology. Six of these nine "HLA-identical" pairs were HLA-A (2 of 6). HLA-B (1 of 6). and HLA-C (