Singleantigenmismatched related donors

For patients without an HLA-matched related donor, a single-antigen- or allele-mismatched sibling donor is available in less than 5% of cases. Such cases may represent a recombinant HLA haplotype in the patient or donor, which can be demonstrated by family study. Other cases may represent two similar, but entirely unrelated haplotypes being present in the family. For unproven cases and unrelated haplotypes, high-resolution DNA typing and additional locus testing (e.g., Cw, DP) are needed.

Compared to HLA-identical sibling transplants, related single HLA-mismatched transplants have been reported to have equivalent84,85 or reduced76,87,88 overall survival. Increased risk of severe acute GVHD has been reported with both class I and class II (DRB1*) mismatches, although it may be higher with DRB1' mismatches.85,87 Increased risk of graft failure and GVHD is associated with single-antigen PMRD donor transplants, but may be offset in part by lower relapse rates due to GVL effect observed in some studies. The stage of disease when the patient is transplanted is an important variable in transplant outcome. In some76,87 but not all85,88 reports, the negative overall survival effect of mismatch was observed in low- or standard-risk patients but not or less in high-risk patients where relapse may be a more imminent factor. When compared to unrelated donor transplants, single HLA-mis-matched PMRD transplants have been reported to have comparable76,85,87,89 overall survival.

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