A Study Evaluating the Safety and Efficacy of LentiGlobin BB305 Drug Product in β-Thalassemia Major (Also Referred to as Transfusion-dependent β-Thalassemia [TDT]) and Sickle Cell Disease

Neutrophil engraftment was defined as the first of absolute neutrophil count (ANC) > or = 0.5 × 10^9/ liter (L) for 3 consecutive days (or 3 consecutive measurements done on separate days), after a post-transplant value less than (<) 0.5 × 10^9/L. Platelet engraftment was defined as the first of 3 consecutive platelet values > or =20 × 10^9/L for participants with TDT and values > or =50 × 10^9/L for participants with SCD obtained on different days with no platelet transfusions administered for 7 days immediately preceding and during the evaluation period. The day of engraftment is the first day of the 3 consecutive platelet measurements.

Neutrophil engraftment was defined as the first of ANC > or = 0.5 × 10^9/ liter (L) for 3 consecutive days (or 3 consecutive measurements done on separate days), after a post-transplant value < 0.5 × 10^9/L). Platelet engraftment was defined as the first of 3 consecutive platelet values > or =20 × 10^9/L for participants with TDT and values > or =50 × 10^9/L for participants with SCD obtained on different days with no platelet transfusions administered for 7 days immediately preceding and during the evaluation period. The day of engraftment is the first day of the 3 consecutive platelet measurements.

This was the safety outcome measure related to mortality. Transplant related mortality was defined as any death occurring in the study post drug product infusion deemed related to the transplant by the investigator.

Overall survival was defined as time from date of LentiGlobin BB305 Drug Product infusion (Day 1) to date of death. Overall survival was censored at the date of last visit if the participant was still alive. Number of participants with OS events were reported.

Blood samples were analyzed for detection of RCL using RCL co-culture assay.

Clonal dominance was defined as an ISA result greater than (>) 90% of the total insertion sites (IS) at any time and a vector copy number (VCN) > or =0.3, or an initial ISA result of > 30% of the total IS with a VCN > or =0.3 followed by a result > 30% and less than or equal to (< or =) 90% at first repeat and a result > 50% at second repeat.

An AE was any untoward medical occurrence associated with the use of a drug in participants, whether or not considered drug related. An AE may include a change in physical signs, symptoms, and/or clinically significant laboratory change occurring in any phase of a clinical study. This definition includes inter-current illnesses or injuries, and exacerbation of pre-existing conditions. An SAE was any AE, occurring at any dose and regardless of causality, that resulted in death, was life-threatening, required in-patient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, a congenital anomaly/birth defect, or was considered an important medical event that may jeopardize the participant and may require medical or surgical intervention to prevent an outcome listed previously. The number of participants with AEs and SAEs were evaluated.

TI was defined as a weighted average hemoglobin (Hb) > or =9 grams per deciliter (g/dL) without any pRBC transfusions for a continuous period of > or =12 months at any time during the study after drug product infusion, where calculation of time period of TI starts when participants achieve a Hb > or =9 g/dL with no transfusions in the preceding 60 days.

TI was defined as a weighted average hemoglobin (Hb) > or =9 grams per deciliter (g/dL) without any pRBC transfusions for a continuous period of > or =12 months at any time during the study after drug product infusion, where calculation of time period of TI starts when participants achieve a Hb > or =9 g/dL with no transfusions in the preceding 60 days.

TI was defined as a weighted average Hb > or =9 grams per deciliter (g/dL) without any pRBC transfusions for a continuous period of > or =12 months at any time during the study after drug product infusion, where calculation of time period of TI starts when participants achieve a Hb > or =9 g/dL with no transfusions in the preceding 60 days. To meet the initial TI criteria, the weighted Hb must be > or =9 g/dL at the end of the 12-month period, to remain in the TI state beyond the 12-month period, the treated participant needs to maintain a weighted Hb of > or =9 g/dL from that point forward, without receiving a pRBC transfusion. This outcome measure reports the duration of TI and was evaluated in the TDT Transplant Population (TP) that reached TI.

TI was defined as a weighted average Hb > or =9 grams per deciliter (g/dL) without any pRBC transfusions for a continuous period of > or =12 months at any time during the study after drug product infusion, where calculation of time period of TI starts when participants achieve a Hb > or =9 g/dL with no transfusions in the preceding 60 days. To meet the initial TI criteria, the weighted Hb must be > or =9 g/dL at the end of the 12-month period, to remain in the TI state beyond the 12-month period, the treated participant needs to maintain a weighted Hb of > or =9 g/dL from that point forward, without receiving a pRBC transfusion. This endpoint reports the time from infusion to the last pRBC transfusion prior to achieving TI.

TI was defined as a weighted average Hb > or =9 grams per deciliter (g/dL) without any pRBC transfusions for a continuous period of > or =12 months at any time during the study after drug product infusion, where calculation of time period of TI starts when participants achieve a Hb > or =9 g/dL with no transfusions in the preceding 60 days. To meet the initial TI criteria, the weighted Hb must be > or =9 g/dL at the end of the 12-month period, to remain in the TI state beyond the 12-month period, the treated participant needs to maintain a weighted Hb of > or =9 g/dL from that point forward, without receiving a pRBC transfusion. This outcome measure reports the time from infusion to achievement of TI.

Weighted average Hb nadir was defined as an average area under the curve where the Hb closest but within 3 days prior to a transfusion was used as the Hb nadir. Hb values on the day of the transfusion were considered for nadir calculations.

Percent change from baseline in the average annual transfusion volume from 6 months post-drug product infusion through last visit were reported.

Percentage change from baseline in annualized number of pRBC transfusions from 6 months post-drug product infusion through last visit were reported.

Number of VOCs, ACS, and vaso-occlusive events (VOEs; which included both VOC and ACS) through 24 months after drug product infusion.

Therapeutic globin expression was measured by HbA^T87Q in peripheral blood and the ratio of alpha(α)- globin to all beta (β)-like-globins. The relative amount of each globin produced by a participant (including βA^A-T87Q globin) was determined in peripheral blood throughout the study.

LentiGlobin BB305 lentiviral vector (LVV) transduction efficiency was measured by VCN. The presence of vector sequences in the genomic DNA of cells is detected using quantitative polymerase chain reaction (qPCR), and results were expressed as VCN.