Allogeneic hematopoietic stem cell transplantation (HSCT) represents a curative treatment\nfor many patients with hematological malignant or non-malignant disorders. Evaluation of potential\ndonors for HSCT includes a rigorous assessment of the human leukocyte antigens (HLA) match\nstatus of family members, and the identification of suitable unrelated donors. Genes encoding\ntransplantation antigens are placed both within and outside the major histocompatibility complex\n(MHC). The human MHC is located on the short arm of chromosome 6 and contains a series of genes\nencoding two distinct types of highly polymorphic cell surface glycoproteins. Donors for HSCT are\nroutinely selected based on the level of matching for HLA-A, -B, -C, -DRB1, and -DQB1 loci. However,\ndisease relapse, graft-versus-host-disease, and infection remain significant risk factors of morbidity\nand mortality. In the same breath, in high-risk patients, graft-versus-leukemia effects inherent in HLA\nmismatching play a substantial immunological role to limit the recurrence of post-transplant disease.\nThe definition of a suitable donor is ever changing, shaped not only by current typing technology, but\nalso by the specific transplant procedure. Indeed, a more complete understanding of permissible HLA\nmismatches and the role of Killer Immunoglobulin-like receptors� genes increases the availability of\nHLA-haploidentical and unrelated donors.
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