Introduction
Aplastic anemia (AA) [1] is a common and potentially life-threatening condition in children that leads to bone marrow loss. The two main AA treatment options are hematopoietic stem cell transplantation (HSCT) and immunosuppressive therapy. However, immunosuppressive treatment effectiveness is limited due to non-responsiveness, relapse, and clonal evolution. Therefore, allogeneic HSCT is recommended as the first-line treatment for patients aged <40 years with a matched sibling donor (MSD). HSCT [2] is currently the primary cell treatment used for therapeutic purposes in both malignant and nonmalignant hematologic disorders. Transplantation success is influenced by sex, human leukocyte antigen (HLA) compatibility, donor age, and cytomegalovirus (CMV) status. However, the effect of ABO compatibility remains debated [3-4]. Particularly, it is uncertain whether ABO incompatibility affects HSCT outcomes in high-risk groups, such as patients who have received long-term transfusion treatment. Existing knowledge about ABO-mismatched transplantation in pediatric HSCT is mostly based on studies on adults. Therefore, we investigated the effect of donor–recipient ABO blood type matching on the outcomes of pediatric patients with severe AA receiving HSCT. This is the first report to address this specific research question.