Andrić, Biljana (57216181995)Biljana (57216181995)AndrićRadonjić, Zorica (56007079900)Zorica (56007079900)RadonjićŠerbić, Olivera (36618083400)Olivera (36618083400)ŠerbićVujić, Dragana (16647611700)Dragana (16647611700)VujićZečević, Željko (36019685900)Željko (36019685900)ZečevićSimić, Marija (57298543100)Marija (57298543100)SimićGobeljić, Borko (56879227300)Borko (56879227300)GobeljićJovanović-Srzentić, SneŽana (6507184289)SneŽana (6507184289)Jovanović-SrzentićRadović, Ivana (57518394300)Ivana (57518394300)Radović2025-06-122025-06-122024https://doi.org/10.1159/000536176https://www.scopus.com/inward/record.uri?eid=2-s2.0-85194922400&doi=10.1159%2f000536176&partnerID=40&md5=d91ef4c8302e7deb500625936ed12d6bhttps://remedy.med.bg.ac.rs/handle/123456789/1066Introduction: ABO blood type changes after ABOincompatible hematopoietic stem cell transplantation (HSCT). Most non-hematopoietic tissues retain the expression of the patient s own ABO antigens, which may adsorb from the plasma onto the donor s red blood cells (RBCs). Because of this phenomenon, a persistent patient s A and/or B antigen could be detected in the laboratory, despite 100% white cell donor chimerism. Adsorption of the patient s soluble ABO antigens on the newly formed RBCs complicates the interpretation of the patient s blood type and decision of transfusion therapy. Case Presentation: The first case report is a 6-year-old girl, A, D+, with T-cell acute lymphoblastic leukemia (ALL), transplanted with HLAmatched unrelated group O, D+ bone marrow. A second case report describes an 8-year-old girl, AB, D-, with ALL transplanted with an HLA-matched related group B, D+ bone marrow. The presence of persistent antigen A was registered in both patients more than 1 year after HSCT, despite complete donor chimerism. Conclusion: The weak expression of ABO antigens on RBCs after HSCT should be examined in detail for proper planning of transfusion therapies. © 2024 The Author(s).ChildrenHematopoietic stem cellsPersistent antigen ATransplantation