Challenges in HLA and ABO typing of deceased organ donors with prior hematopoietic stem cell transplantation: two cases and practical considerations for evaluation

BACKGROUND: Prior allogeneic hematopoietic stem cell transplantation (HSCT) can complicate HLA and ABO typing of deceased organ donors because circulating hematopoietic cells and organs may originate from different sources. CASE PRESENTATIONS: We describe two deceased organ donors with prior HSCT. In Case 1, historical records demonstrated discordance at HLA-C and HLA-DQ between the HSCT donor and the constitutional pre-HSCT typing. Peripheral-blood HLA typing reflected the HSCT donor, while a kidney blood-vessel specimen yielded four DPB1 alleles from mixed sources, permitting only a presumptive kidney DPB1 assignment. In Case 2, HLA assignments were concordant after childhood HSCT, but ABO serology was O/A ambiguous, resulting in allocation as blood group AB. Retrospective molecular ABO genotyping and chimerism testing demonstrated mixed donor- and recipient-derived DNA in buccal specimens. CONCLUSIONS: HSCT-associated chimerism can complicate deceased-donor HLA and ABO typing. Interpretation should integrate transplant history, historical records, specimen source, serology, and molecular testing when indicated.