Family pedigree of the patient in the clinical case. An HLA-haploidentical donor has inherited one HLA haplotype in common with the recipient and is mismatched for anywhere between 0 and 5 HLA genes on the unshared haplotype. Biological parents and biological children always share an HLA haplotype with the recipient, unless a rare genetic rearrangement has occurred. In this pedigree analysis, the patient has 3 siblings, none of whom are HLA-matched, but 2 are partially matched related (haploidentical) donors, whereas 1 brother is disparate. Other potential HLA-haploidentical donors include half-siblings, aunts, uncles, nieces, nephews, cousins, or grandchildren.