Evaluation of Efficacy and Safety of a Single Dose of CTX001 in Participants With Transfusion-Dependent β-Thalassemia and Severe Sickle Cell Disease

Key Inclusion Criteria:

• Participants with TDT and SCD:

• Eligible for autologous stem cell transplant as per investigator's judgment.

• Participants with TDT:

• Diagnosis of TDT as defined by:

• Documented homozygous β-thalassemia or compound heterozygous β-thalassemia including β-thalassemia/hemoglobin E (HbE). Participants can be enrolled based on historicaldata, but a confirmation of the genotype using the study central laboratory will berequired before busulfan conditioning

• History of at least 100 milliliter (mL)/kilograms (kg)/year or 10 units/year ofpacked red blood cells (RBC) transfusions in the prior 2 years before signing theconsent or the last rescreening for patients going through re-screening

• Participants with SCD:

• 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 priorto enrollment

Key Exclusion Criteria:

• Participants with TDT and SCD:

• A willing and healthy 10/10 human leukocyte antigen (HLA)-matched related donor isavailable per investigator's judgement

• Prior hematopoietic stem cell transplant (HSCT)

• Clinically significant and active bacterial, viral, fungal, or parasitic infectionas determined by the investigator

• Participants with TDT:

• Participants with associated α-thalassemia and >1 alpha deletion, or alphamultiplications

• Participants with sickle cell β-thalassemia variant

• Participants with SCD:

• History of untreated moyamoya syndrome or presence of moyamoya syndrome at screening

Other protocol defined Inclusion/Exclusion criteria may apply.