A Safety and Efficacy Study Evaluating CTX001 in Participants With Transfusion-Dependent β-Thalassemia

Key Inclusion Criteria:

* Diagnosis of transfusion-dependent β-thalassemia (TDT) as defined by

1. Documented homozygous β-thalassemia 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
2. History of at least 100 mL/kg/year or ≥10 units/year of packed RBC transfusions in the prior 2 years before signing the consent or the last rescreening for patients going through re-screening
* 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 allo-HSCT
* Participants with associated α-thalassemia and \>1 alpha deletion or alpha multiplications
* Participants with sickle cell beta thalassemia variant
* Clinically significant and active bacterial, viral, fungal, or parasitic infection as determined by the investigator
* White blood cell (WBC) count \<3 × 10\^9/L or platelet count \<50 × 10\^9/L not related to hypersplenism

Other protocol defined Inclusion/Exclusion criteria may apply.