Conditioning Regimen Containing Low Dose ATG for The Treatment of Acquired SAA Receiving sUCBT

Inclusion Criteria: * Patients diagnosed with severe aplastic anemia who do not respond to initial diagnosis or immunosuppressive therapy; * Patients meet diagnostic criteria for severe aplastic anemia (Camitta criteria); * Age from 1 to 50 years old, male or female; * Patients without HLA-matched sibling or unrelated donors avaliable; * Patients who have undergone unrelated cord blood transplantation need to have HLA high-resolution matching、TNC (before cord blood freezing)≥3.0×107/kg、CD34+(before cord blood freezing)≥1.5×107/kg、tubule recovery rate≥80%; * patients and their family members or guardians agreed to the study and signed informed consent; * No severe organ failure; * ECOG score≤2 and HCT-CI≤2; * serum ferritin (SF)\<1000ug/L; * women of reproductive agemust have a negative pregnancy test and agree to use effective contraception during treatment and for one year thereafter. Exclusion Criteria: * patients with inherited bone marrow failure syndromes; * Positive for HLA-A, B, Cw, DRB1, DQB1, DPB1 site-specific HLA antibodies for donor cord blood with solid-phase fluorescence assay; * patients who have previously received allogeneic hematopoietic stem cell transplantation or solid organ transplantation; * Uncontrolled bacterial, viral, or fungal infections; * HIV infection or active viral hepatitis B or C infection; * Pregnant or breastfeeding women; * patients with a history of primary malignancy within 3 years prior to transplant treatment; * patients receiving …