CLINICAL TRIAL / NCT04207320

Inclusion Criteria: - Hemoglobin SS, SC, S-β0 Thalassemia, or SO-Arab Sickle Cell Disease - Between the ages of 2 and 25 years (Stage 1: 10-25 years; Stage II: 2-25 years) - Lack a fully matched family donor or fully matched unrelated donor register in the National Marrow Donor Program - Partially-matched family member with hemoglobin AA (normal) or hemoglobin AS (sickle trait) phenotype - SCD with Severe Phenotype, defined by the following criteria: Neurologic manifestations of sickle disease including cerebral vascular accident (CVA), transient ischemic event (TIA) or abnormal MRI findings suggestive of silent infarct; Two or more episodes of acute chest syndrome (ACS) requiring admission for transfusional or respiratory support including supplemental oxygen within [two years] of enrollment in study despite hydroxyurea therapy. Patients who cannot tolerate hydroxyurea and who experience multiple episodes of ACS will also be eligible; History of severe vaso-occlusive (VOC) disease requiring hospitalization and intravenous narcotics on 3 or more occasions per year over the two years prior to enrollment despite hydroxyurea therapy. Patients who cannot tolerate hydroxyurea and who experience multiple episodes of VOC will also be eligible; Other severe phenotype as evidenced by end organ dysfunction related to sickle cell disease. Exclusion Criteria: - Karnofsky or Lansky score < 60% - Acute hepatitis or evidence of moderate or severe portal fibrosis on biopsy. (Biopsy will be obtained if patient has been on chronic transfusion therapy > 6 months or has a ferritin > 1000 ng/ml) or AST or ALT >5 times the upper limit of normal - Severe renal impairment (as evidenced by creatinine clearance of <50ml/minute glomerular filtration rate (GFR) < 50% predicted normal) - Cardiac function that demonstrates shortening fraction less than 26% by cardiac echocardiogram or pulmonary hypertension. - Pregnant Female. - Lactating female. - Pulmonary function with baseline O2 saturation <85% or Diffusing Capacity for Carbon Monoxide (DLCO) on pulmonary function testing (PFT) with a DLCO <40%.