Minor ABO-Incompatible Bone Marrow Transplantation in β-Thalassemia Major

Background: Allogeneic bone marrow transplantation (BMT) primarily requires human leukocyte antigen (HLA) compatibility, whereas ABO blood group compatibility is not mandatory. However, transplantation across major or minor ABO incompatibility may result in clinically significant complications, including hemolysis, delayed engraftment, and Passenger Lymphocyte Syndrome (PLS). Elevated anti-ABO antibody titers in either donor or recipient can compromise transplant outcomes. Careful pre-transplant immunohematological evaluation is therefore essential to minimize these risks. Aim: This study aimed to prevent hemolytic complications, optimize engraftment, and improve clinical outcomes in a case of major ABO-incompatible allogeneic BMT. Methods: A retrospective descriptive case study was conducted on a nine-year-old female patient diagnosed with major β-thalassemia, blood group B, scheduled for allogeneic BMT from her HLA-identical (100% match) brother with blood group O. Donor anti-ABO antibody titers were measured using the standard tube agglutination method with serial serum dilutions. Testing was performed using immediate spin (IS) and anti-human globulin (AHG) phases against B-group red blood cells. Based on antibody titration results, the harvested bone marrow graft underwent appropriate cell manipulation prior to infusion. Post-transplant monitoring included clinical assessment and laboratory evaluation for evidence of PLS and engraftment kinetics. Results: Donor anti-B antibody titers were 1:32 at the IS phase and 1:256 at the AHG phase, indicating significant IgG-mediated reactivity. Following graft manipulation, total nucleated cell recovery was 98.5%, while CD34⁺ stem cell recovery was 88.3%, remaining within an acceptable therapeutic range. The patient received the manipulated graft without acute hemolytic complications. Serial clinical and laboratory evaluations revealed no evidence of PLS. Successful hematopoietic engraftment was subsequently achieved. Conclusion: Pre-transplant quantification of anti-ABO antibodies and appropriate graft manipulation can effectively mitigate hemolytic risk in major ABO-incompatible BMT. This individualized approach supports safe engraftment and favorable clinical outcomes, emphasizing the importance of immunohematological assessment in ABO-mismatched transplantation settings.