A Study Evaluating the Efficacy and Safety of the LentiGlobin® BB305 Drug Product in Participants With Transfusion-Dependent β-Thalassemia, Who do Not Have a β0/β0 Genotype

Inclusion Criteria

• Participants = 8 transfusions of pRBCs per year in the 2 years preceding enrollment (participants >= 12 years).
• Clinically stable and eligible to undergo (HSCT).
• Treated and followed for at least the past 2 years in a specialized center that maintained detailed medical records, including transfusion history.

Exclusion Criteria

• Presence of a mutation characterized as β0 mutation at both alleles of the β-globin gene HBB.
• Positive for presence of human immunodeficiency virus type 1 or 2 (HIV-1 and HIV-2), hepatitis B virus (HBV), or hepatitis C (HCV).
• A white blood cell (WBC) count less than (<) 3×10^9/Liter (L), and/or platelet count < 100×10^9/L not related to hypersplenism.
• Uncorrected bleeding disorder.
• Any prior or current malignancy.
• Immediate family member with a known Familial Cancer Syndrome.
• Prior HSCT.
• Advanced liver disease.
• A cardiac T2* < 10 ms by MRI.
• Any other evidence of severe iron overload that, in the Investigator's opinion, warrants exclusion.
• Participation in another clinical study with an investigational drug within 30 days of Screening.
• Any other condition that would render the participant ineligible for HSCT, as determined by the attending transplant physician or investigator.
• Prior receipt of gene therapy.
• Pregnancy or breastfeeding in a postpartum female or absence of adequate contraception for fertile participant.
• A known and available Human leukocyte antigen (HLA) matched family donor.
• Any contraindications to the use of granulocyte colony stimulating factor (G-CSF) and plerixafor during the mobilization of hematopoietic stem cells and any contraindications to the use of busulfan and any other medicinal products required during the myeloablative conditioning, including hypersensitivity to the active substances or to any of the excipients.