Pre-transplant Immunosuppression and Donor Stem Cell Transplant for the Treatment of Severe Hemoglobinopathies

Inclusion Criteria: * Patients 2-30 years-of-age with confirmed sickle cell disease (SCD) (SS \& sickle beta \[SB\]-thalassemia, both sickle beta 0 \[SB0\] and sickle beta plus \[SB+\]) or severe B-thalassemia major are potentially eligible * Patients with SCD should also meet the following eligibility criteria as outlined by the Center for Medicaid and Medicare Services: sickle cell disease and at least one of the following: * Stroke or neurological deficit lasting \> 24 hours * Recurrent acute chest syndrome (ACS): 2 or more episodes of ACS in 2-year period preceding enrollment * Recurrent vaso-occlusive pain crises: 3 or more episodes per year in 2-year period preceding enrollment or recurrent priapism (3 or more episodes in the 2 years preceding enrollment) * Chronic transfusion program defined as 8 or more packed red blood cells (PRBC) transfusions per year to prevent central nervous system and/or vaso-occlusive complications in 1-year period preceding enrollment * Impaired neuropsychological function and abnormal cerebral magnetic resonance imaging (MRI) scan (silent strokes) * Stage I or II sickle lung disease * Sickle nephropathy (moderate or severe proteinuria or a glomerular filtration rate 30-50% of predicted normal value) * Bilateral proliferative retinopathy and major visual impairment in at least one eye * Osteonecrosis of multiple joints * Echocardiographic finding of tricuspid valve regurgitant jet velocity (TRJV) \>= 2.7 m/sec * Patients…