Evaluation of Safety and Efficacy of CTX001 in Pediatric Participants With Transfusion-Dependent β-Thalassemia (TDT)

Key Inclusion Criteria: * Diagnosis of TDT as defined by: * Documented homozygous or compound heterozygous β-thalassemia including β-thalassemia/hemoglobin E (HbE). Participants can be enrolled based on historical data, but a confirmation of the genotype using the study central laboratory will be required before busulfan conditioning * History of at least 100 mL/kilograms (kg)/year of packed RBC transfusions in the prior 24 months before signing of consent (or the last rescreening for patients going through repeat screening) or, for participants initiating transfusion therapy \<24 months before signing of consent, requirement for packed RBC transfusion at least every 3 to 4 weeks for ≥6 months * Eligible for autologous stem cell transplant as per investigator's judgment. Key Exclusion Criteria: * A willing and healthy 10/10 human leukocyte antigen (HLA)-matched related donor is available per investigator's judgement * Prior hematopoietic stem cell transplant (HSCT) * Participants with associated α-thalassemia and \>1 alpha deletion, or alpha multiplications * Participants with sickle cell β-thalassemia variant * Clinically significant and active bacterial, viral, fungal, or parasitic infection as determined by the investigator Other protocol defined Inclusion/Exclusion criteria may apply.