Abstract

Background: ABO blood group incompatibility in allogeneic hematopoietic stem cell transplantation (HSCT) poses a significant challenge due to the risk of life-threatening acute hemolytic reactions. Traditional processing methods, such as red blood cell depletion from the graft or pre-transplant therapeutic plasma exchange, require advanced technical infrastructure, incur high costs, and lead to substantial stem cell loss, which limits their feasibility in low- and middle-income countries. This study aims to evaluate the safety and efficacy of an antibody adsorption strategy using incremental donor-type packed red blood cell (PRBC) transfusions to manage ABO incompatibility in pediatric patients undergoing allogeneic bone marrow transplantation for severe thalassemia at Hue Central Hospital.

Methods: A non-controlled clinical intervention study combining retrospective and prospective designs was conducted on 21 patients who received allogeneic bone marrow transplantation between September 2024 and June 2026. In cases of ABO incompatibility with pre-transplant antibody titers (anti-A and/or anti-B ≥1/32, incremental small volumes of donor-type PRBCs (5 ml, 10 ml, 20 ml, and 40 ml) were transfused during the conditioning phase. Changes in antibody titers, clinical hemolytic reactions, and toxicities were evaluated.

Results: ABO incompatibility was observed in 7 out of 21 pediatric patients (33.3%), including 3 cases of major incompatibility (42.9%), 3 cases of bidirectional incompatibility (42.9%), and 1 case of minor incompatibility (14.3%). The median age was 6.5 years (range: 2–11 years). Indications for transplantation included severe Beta-thalassemia (n=4) and severe Alpha-thalassemia (n=3). The median antibody titer decreased sharply from 1/256 (range: 1/32 – 1/512) pre-intervention to 1/16 (range: 1/8 – 1/128) after the first transfusion course, and 1/16 (range 1/8 – 1/16) after the second transfusion course. Five out of seven patients (71,4%) achieved the target titer of < 1/32 immediately after the first course. Two patients (case 6, 7) required a second transfusion course on day -11 to reduce the titer from 1/128 to the target level of < 1/32. The median volume of transfused PRBCs was 75 ml (range: 75–149 ml); the median volume of bone marrow infused on day 0 was 285 ml (range: 153–370 ml). Regarding adverse events, febrile reactions occurred in 2 cases (28.6%), and transient hemoglobinuria was noted in 5 cases (71.4%). No severe hemolytic reactions or life-threatening anaphylaxis were observed. All 7 patients safely received unmanipulated bone marrow infusions on day 0.

Conclusion: Immune tolerization via incremental donor-type PRBC transfusion is a simple, safe, and highly effective strategy for managing ABO incompatibility in allogeneic stem cell transplantation. This method preserves the integrity of the bone marrow stem cell count, reduces the financial burden, and is particularly suitable for the practical conditions of bone marrow transplant centers in Vietnam.