Schieber, Jennifer

ABO incompatibility is frequent in haematopoietic stem cell transplantation (HSCT), yet the clinical impact of non-ABO red blood cell (RBC) alloimmunisation remains less defined. We describe the clinical course of a man in his 50s with chronic eosinophilic leukaemia who underwent a mismatched unrelated donor (MMUD) HSCT. Despite a major ABO mismatch and high-titre pre-existing anti-E antibodies against an E-antigen positive donor, the patient achieved successful trilineage engraftment without haemolysis. Six months after the transplant, he developed severe pancytopenia and a positive direct antiglobulin test (DAT) with anti-E elution. These serologic findings coincided with disease relapse rather than isolated immune-mediated haemolysis. This case illustrates that successful engraftment is possible across RhE-incompatibility and underscores the need to interpret late serologic abnormalities within the broader context of graft function and disease status.

AbstractBackgroundTandem mass spectrometry (MS/MS) has become a common clinical laboratory testing modality has demonstrated success in distinguishing between small protein variations in transthyretin amyloidosis. Since many common clinically significant RBC antigens are also small protein variations, this study aimed to determine if MS/MS could correctly detect common RBC antigens within the Rh, Kell, Duffy, MNS, Kidd, Diego, and Lutheran blood group systems.Study Design and MethodsResidual samples from serotyped/genotyped blood donors at a hospital‐based blood donation center from February to August 2021 were analyzed. RBC membrane protein preparations underwent protease digestion prior to MS/MS analysis for RhD, RhCE, Kell, atypical chemokine receptor 1 (Duffy), glycophorin A (MNS), glycophorin B (MNS), urea transporter 1 (Kidd), band 3 anion transport protein (Diego), and basal cell adhesion molecule (Lutheran). Untargeted liquid chromatography (LC)‐MS/MS detected protein‐specific peptides, while targeted LC‐selected reaction monitoring (LC‐SRM) detected RBC antigen‐containing peptides.ResultsThrough the use of multiple proteases, untargeted LC–MS/MS detected protein‐specific peptides in all but glycophorin B, with band 3 anion transport protein, basal cell adhesion molecule, Kell, and glycophorin A having the greatest protein sequence coverage. Targeted LC‐SRM detected antigen‐specific peptides for Cw, Dia/Dib, Kpb, and Wra/Wrb, which agreed with the donors' previous typing results.DiscussionMS/MS can successfully detect peptides from several blood group systems but only detected a subset of their common RBC antigens. Further sample enrichment and MS/MS detection improvements will need to occur before MS/MS could be considered a clinical RBC phenotyping modality.