Reduced Toxicity Fludarabine (Flu) + Cyclophosphamide (CPM) + Rabbit Antithymocyte Globulin (rATG) Conditioning Regimen for Unrelated Donor Transplantation in Severe Aplastic Anemia (SAA)

Inclusion Criteria: 1. Diagnosis of severe aplastic anemia defined by any two or three peripheral blood criteria and either marrow criterion. * Peripheral blood 1. Neutrophils \< 0.5 x 109/l 2. Platelets \< 20 x 109/l 3. Corrected reticulocytes \< 1% * Bone marrow 1. Severe hypocellularity (\< 25%) 2. Moderate hypocellularity (25-30%) with hematopoietic cells representing \< 30% of residual cells 2. No prior hematopoietic stem cell transplantation. 3. Age: no limits. 4. Performance status: ECOG 0-2. 5. Patients must be free of significant functional deficits in major organs, but the following eligibility criteria may be modified in individual cases: * Heart: a shortening fraction \> 30% and ejection fraction \> 45%. * Liver: total bilirubin \< 2 × upper limit of normal; ALT \< 3 × upper * Kidney: creatinine \<2 × normal or a creatinine clearance (GFR) \> 60 ml/min/1.73m2. 6. Patients must lack any active viral infections or active fungal infection. 7. Appropriate donor is available: Matched in 6/6 of A, B, DR loci. 8. Patients (or one of parents if patients age \< 19) should sign informed consent. Exclusion Criteria: 1. Pregnant or nursing women. 2. Malignant or nonmalignant illness that is uncontrolled or whose control may be jeopardized by complications of study therapy. 3. Psychiatric disorder that would preclude compliance. 4. Congenital aplastic anemia including Fanconi anemia. 5. Manipulated bone marrow.