Definitions
AA is characterized by pancytopenia and hypocellular bone marrow without abnormal infiltrate or marrow fibrosis [6]. ABO blood type compatibility between the donor and patient is crucial in blood group systems [7]. ABO iso-group (match) refers to donors and patients with the same ABO blood types [8]. The major ABO-incompatible group consists of iso-agglutinins directed against donor red blood cell antigens from type A, AB, or B donors to type O recipients. The minor ABO-incompatible group consists of iso-agglutinins directed against red blood cell antigens from type O donors to type A, B, or AB recipients. Bidirectional ABO incompatibility, e.g., type A donor to type B recipient, occurs when iso-agglutinins are present against both the donor and patient red blood cell antigens. OS (overall survival) was measured from the first day of therapy until death or the last follow-up. GFFS (graft failure-free survival) was defined as survival without grade III–IV acute GVHD (aGVHD), moderate-to-severe chronic GVHD (cGVHD), or treatment failure, including death, primary or secondary graft failure, and relapse [9]. Neutrophil engraftment was defined as an absolute neutrophil count > 0.5 × 109/L for three consecutive days. Platelet engraftment was defined as an absolute platelet count > 20 × 109/L for three consecutive days without transfusion. Failure to achieve engraftment by day +28 was considered indicative of low donor chimerism, and primary graft failure was assumed in such cases. The diagnostic and classification criteria for aGVHD and cGVHD were based on the Glucksberg-Seattle criteria [10,11].TA-TMA is diagnosed and treated according to the criteria proposed by the IWG (International Working Group)[12].