This is a single-dose, open-label study in pediatric participants with severe SCD and hydroxyurea (HU) failure or intolerance. The study will evaluate the safety and efficacy of autologous CRISPR-Cas9 modified CD34+ human hematopoietic stem and progenitor cells (hHSPCs) (CTX001).
Key Inclusion Criteria: * Diagnosis of severe SCD as defined by: * Documented SCD genotypes * History of at least two severe VOCs events per year for the previous two years prior to enrollment * Hydroxyurea (HU) failure unless HU intolerant * Eligible for autologous stem cell transplant as per investigators judgment Key Exclusion Criteria: * A willing and healthy 10/10 human leukocyte antigen (HLA)-matched related donor * Prior hematopoietic stem cell transplant (HSCT). * Clinically significant and active bacterial, viral, fungal, or parasitic infection Other protocol defined Inclusion/Exclusion criteria may apply.