Long-Term Data for bluebird bio’s betibeglogene autotemcel (beti-cel) Gene Therapy Show Patients Across Ages and β-thalassemia Genotypes Achieve Transfusion Independence and Remain Free from Transfusions Up to Six Years Presented at 62nd ASH Meeting - Seite 2

As of the data cut-off of March 3, 2020, a total of 60 pediatric, adolescent and adult patients, including 10 patients with at least five years of follow-up and one with at least six years, across genotypes of TDT have been treated with beti-cel in the Phase 1/2 HGB-204 (Northstar) and HGB-205 studies, and the Phase 3 HGB-207 (Northstar-2) and HGB-212 (Northstar-3) studies. Data from bluebird bio’s Phase 1/2 and Phase 3 clinical studies represent more than 160 years of patient experience with beti-cel.

Long-term follow-up study LTF-303: Efficacy

After participating in and completing the two years of follow-up in either Phase 1/2 studies (HGB-204, HGB-205), or in one of the Phase 3 studies (HGB-207, HGB-212), patients treated with beti-cel were invited to enroll in the 13-year long-term follow-up study, LTF-303. As of March 3, 2020, 32 patients were enrolled in LTF-303 (22 treated in Phase 1/2 studies, 10 treated in Phase 3 studies) with a median post-infusion follow-up of 49.1 months (min-max: 23.3 – 71.8 months).

Of the 32 patients enrolled in LTF-303, TI was achieved in 14/22 (64%) patients treated in Phase 1/2 and in 9/10 (90%) patients treated in Phase 3. All patients who achieved TI remained free from transfusions [median duration of ongoing TI is 39.4 months (min-max: 19.4 – 69.4 months)].

Weighted average Hb in patients who achieved TI in the Phase 1/2 was 10.4 (min-max: 9.4 – 13.3) g/dL and 12.5 (min-max: 11.9 – 13.5) g/dL in patients who achieved TI in the Phase 3 studies.

Median gene therapy-derived hemoglobin (HbA^T87Q) in all patients treated in the Phase 1/2 studies was stable over time: 6.4 (min-max: 0.5 – 10.1) g/dL at Month 24 (n=22), 6.7 (min-max: 0.4 – 10.1) g/dL at Month 36 (n=22), 6.6 (min-max: 0.5 – 10.7) g/dL at Month 48 (n=22), and 7.1 (min-max: 2.8 – 11.2) g/dL at Month 60 (n=10). Median HbA^T87Q at Month 24 in all patients treated in the Phase 3 studies was 9.5 (min-max: 0.9 – 12.4) g/dL (n=10).

Following an initial increase in liver iron concentration (LIC) after infusion, LIC in patients who achieved TI decreased, particularly in patients with a high iron burden at baseline. Patients with severe (LIC >15 mg/g, n=2) and significant (LIC ≥7 – 15 mg/g, n=5) iron burden at baseline had a median reduction of 59% and 38%, respectively, from baseline to Month 48.

Prior to beti-cel infusion, all patients were on iron chelation, which is needed to reduce excess iron caused by chronic blood transfusions. Of the 23 patients who achieved TI following treatment with beti-cel, the majority (65%, n=15) discontinued iron chelation and 30% (7/23) were able to receive phlebotomy (blood removal), which is a preferred method for iron reduction.