This is a single-dose, open-label study in participants with transfusion-dependent β-thalassemia (TDT) or severe sickle cell disease (SCD). The study will evaluate the safety and efficacy of autologous CRISPR-Cas9 modified CD34+ human hematopoietic stem and progenitor cells (hHSPCs) using CTX001.
Eligible for autologous stem cell transplant as per investigator's judgment.
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
History of at least 100 milliliter (mL)/kilograms (kg)/year or 10 units/year of packed red blood cells (RBC) transfusions in the prior 2 years before signing the consent or the last rescreening for patients going through re-screening
Documented SCD genotypes
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)
Clinically significant and active bacterial, viral, fungal, or parasitic infection as determined by the investigator
Participants with associated α-thalassemia and >1 alpha deletion, or alpha multiplications