This is a non-randomized, open-label, multi-site, single-dose, Phase 3 study in approximately 35 adults and pediatric subjects ≥2 and ≤50 years of age with sickle cell disease (SCD). The study will evaluate hematopoietic stem cell (HSC) transplantation (HSCT) using bb1111 (also known as LentiGlobin BB305 Drug Product for SCD). On 20 December 2021, bluebird bio., Inc. announced that the FDA placed the study on partial clinical hold for pediatric patients (patients less than 18 years of age). This suspension includes that no new enrollment, cell collection, conditioning, or drug product infusion be initiated in pediatric patients. The study remains open to patients 18 years of age and older.