1 United States site
18 to 45 Years
– Diagnosis of sickle cell disease with the homozygous HbSS or an HbSβ thalassemia
variant (ie, HbSβ0 thalassemia or HbSβ+ thalassemia) genotype, confirmed by hemoglobin
– Fetal hemoglobin (HbF) ≤ 15%.
– Severe sickle cell disease symptomatology, defined as any one or more of the
1. ≥ 2 episodes of acute chest syndrome in the last 2 years.
2. ≥ 3 episodes of severe pain events requiring a visit to a medical facility and
treatment with opioids in the last 2 years.
3. > 2 episodes of recurrent priapism in the last 2 years.
4. Red-cell alloimmunization (> 2 antibodies) during long-term transfusion therapy
5. Chronic transfusions for primary or secondary prophylaxis (lifetime history).
6. Trans-thoracic echocardiograph evidence of tricuspid valve regurgitant jet
velocity ≥ 2.7 m/sec (lifetime history).
7. Clinically significant neurologic event (eg, ischemic stroke) or any neurological
deficit lasting > 24 hours.
– Hypoxanthine-guanine phosphoribosyl transferase (HPRT) deficiency.
– Thiopurine S-methyltransferase (TPMT) deficiency.
– Alpha thalassemia.
– Serum ferritin ≥ 2500 ng/mL.
– Inadequate bone marrow function, defined as at least 1 of the following:
1. Absolute neutrophil count < 1000/µL. 2. Platelet count < 120,000/µL.