Long-term Follow-up Data From bluebird’s Gene Therapy Program in Sickle Cell Disease Support Durable, Potentially Curative Benefits Through Stable Production of Anti-Sickling Adult Hemoglobin and Resolution of Vaso-Occlusive Events

Oral presentation to include data on 47 patients through five years of follow-up (median 35.5 months, range 0.3-61 months)

Endpoints of sVOE-CR and VOE-CR achieved in 94% (32/34) and 88% (30/34) of evaluable patients respectively

100% of adolescents (10/10) experienced complete resolution of VOEs and sVOEs, providing evidence of potential benefit for this population

Impact on hemolysis markers and health-related quality of life measures further support potential therapeutic benefits

bluebird bio, Inc. (NASDAQ: BLUE) (“bluebird bio” or “bluebird”) today announced new and updated efficacy, safety and health-related quality of life (HRQoL) data from the Phase 1/2 HGB-206 Group C and Phase 3 HGB-210 studies of lovotibeglogene autotemcel (lovo-cel) gene therapy for sickle cell disease through five years of follow-up (median 35.5 months, range 0.3-61 months). Data were highlighted in a press briefing at the 65^th American Society of Hematology (ASH) Annual Meeting & Exposition and will be presented in an oral presentation on Monday, December 11, 2023 at 4:30 p.m. Pacific Time.

“Years of long-term follow-up continue to suggest that lovo-cel has the potential to address the underlying cause of sickle cell disease and provide robust clinical benefits for patients,” said Richard Colvin, M.D., Ph.D., chief medical officer, bluebird bio. “The data presented at ASH give us confidence that these results can be sustained over time and may translate to meaningful and lasting impact on quality of life for people living with sickle cell disease who need and deserve new treatment options.”

The analysis presented at ASH focused on 47 people living with sickle cell disease who received lovo-cel in the HGB-206 Group C and HGB-210 studies following enhancements to the treatment process and manufacturing protocols. Over 85% of patients required ≤2 mobilization cycles prior to infusion. As of the February 13, 2023 cutoff date, all patients had stable production of anti-sickling adult hemoglobin after infusion through last follow-up (median >40% HbA^T87Q), and vaso-occlusive events (VOEs) and severe vaso-occlusive events (sVOEs) were eliminated or significantly reduced in all patients, further suggesting that lovo-cel has shown a durable impact on the underlying cause of sickle cell disease. The majority of adverse events in treated patients were attributed to underlying sickle cell disease or conditioning with busulfan.

Lovo-cel is the most deeply studied gene therapy in development for sickle cell disease, with the most patients treated and longest follow-up in the field. As of February 13, 2023, 59 patients were treated across the entire clinical development program with follow-up beyond 8 years in the earliest treated patients.

The therapy was approved on December 8, 2023 by the U.S. Food and Drug Administration and is currently marketed as LYFGENIA in the U.S.

Updated efficacy data continue to support transformational impact on VOE burden

In the studies, VOEs are defined as episodes of acute pain with no medically determined cause other than a vaso-occlusion, lasting more than two hours and severe enough to require care at a medical facility. This includes acute chest syndrome requiring oxygen treatment and/or blood transfusion, acute hepatic sequestration, acute priapism lasting 2 hours and requiring care at a medical facility and acute splenic sequestration. sVOEs require a 24-hour hospital stay or emergency room visit, or at least two visits to a hospital or emergency room over a 72-hour period, with both visits requiring intravenous treatment; all VOEs of priapism are also considered sVOEs.

As of February 13, 2023, 34 of the 47 patients treated in HGB-206 Group C and HGB-210 were evaluable for the primary and secondary endpoints of complete resolution of VOEs and sVOEs with a median follow-up 36.3 months (12.1, 61).

• 32/34 patients (94%) experienced complete resolution of sVOEs, maintained for a median (min, max) of 35.8 months (20.2, 61).
• 30/34 patients (88.2%) experienced complete resolution of all VOEs, maintained for a median (min, max) of 35.8 months (20.2, 61).
• Patients who experienced VOEs at any time post-treatment through long-term follow-up (n=8) experienced significant reduction in VOE frequency and severity compared to before treatment.
  • All 8 patients experienced a reduction in VOEs of at least 50%.
  • Hospital days and admissions were reduced by as much as 100% (annualized median hospital days reduced from 15.75 (3.5, 136) pre-treatment to 2.20 (0.0, 25.4); (annualized median reduction in hospital days was 85.5% (31.7%, 100%).
• Results of a sub-analysis of data from adolescent patients, presented for the first time, showed complete resolution of VOEs and sVOEs in 10/10 (100%) of patients during the 6-18 month enrollment period.

“These new data provide further evidence that lovo-cel can provide significant improvements in quality of life for people living with sickle cell disease and that the effects are durable for at least five years,” said Julie Kanter, M.D., a lovo-cel investigator and director of the University of Alabama Birmingham Adult Sickle Cell Clinic and associate professor in the Division of Hematology and Oncology. “We see meaningful changes in hemoglobin, excellent production of anti-sickling hemoglobin, and improvement in all markers of hemolysis which further reinforces the clinical effects of lovo-cel. This one-time, transformative therapy has the potential to target the underlying cause of the disease and reduce both pain and fatigue—outcomes that matter to people living with sickle cell disease and their families. These findings support the positive impact of lovo-cel on the biology of sickle cell disease and on patients’ clinical outcomes and quality of life.”

Clinical outcomes were further supported by improvements in total hemoglobin and markers of hemolysis

Red blood cells normally break down in the body through a naturally occurring process called hemolysis. In sickle cell disease, hemolysis happens too quickly due to the fragility of sickled red blood cells, resulting in hemolytic anemia. With the exception of patients with alpha-thalassemia trait, all patients had improvement in total hemoglobin and markers of hemolysis; improvements were sustained through last follow-up. As of the February 13, 2023 cut-off date:

• Following engraftment, non‑transfused total Hb and %Hb fractions stabilized by approximately 6 months after lovo-cel infusion.
• Median percent of gene-therapy derived anti-sickling adult hemoglobin (HbA^T87Q) was maintained generally at >40% of non-transfused total Hb throughout follow-up.
• From six months post-infusion through the last visit, several indicators of the health of red blood cells suggest that treatment with lovo-cel improved biological markers for sickle cell disease to normal or near-normal levels. Lactate dehydrogenase and indirect bilirubin levels normalized and reticulocyte counts approached normal levels.

The majority of patients experienced sustained improvements in key domains of health-related quality of life measures

The burden of sickle cell disease impacts every aspect of patients' lives. Health-related quality of life (HRQoL) findings in patients treated in HGB-206 Group C were generated using the Patient Reported Outcomes Measurement Information System 57 (PROMIS-57), a validated instrument in sickle cell disease.

Improvements in key domains including pain interference, pain intensity, and fatigue were demonstrated, showing statistically significant improvements as early as month six which were sustained up to 36 months for pain intensity and 48 months for pain interference and fatigue. These findings provide a broader understanding of the potential impact to daily life over time following treatment with lovo-cel.

Safety results summary

The majority of adverse events in patients treated in HGB-206 Group C and HGB-210 were attributed to underlying sickle cell disease or conditioning with busulfan. Nonserious adverse events related to lovo-cel included infusion reactions (abdominal discomfort, decreased diastolic blood pressure, and nasal congestion) each in one patient (2.1% each). Serious adverse events related to lovo-cel were reported in two patients with comorbid alpha-thalassemia trait and they included two SAEs each of Anemia (4.3%) and 1 SAE of Myelodysplastic syndrome (2.1%), the diagnosis of which remains under evaluation. One patient died due to sudden cardiac death which was deemed unrelated to lovo-cel.

As previously reported, cases of acute myeloid leukemia were observed in two patients from the HGB-206 Group A cohort who were treated with an earlier version of the therapy prior to enhancements to the treatment and manufacturing processes. Both patients died due to aforementioned leukemia.

No graft failure, replication-competent lentivirus or vector-mediated insertional oncogenesis was observed across the entire clinical development program.

About sickle cell disease

Sickle cell disease is a complex and progressive genetic disease associated with debilitating and unpredictable pain crises, anemia, irreversible damage to vital organs, and early death. In SCD, high concentrations of sickle hemoglobin (HbS) in red blood cells (RBCs) cause RBCs to become sickled, sticky, and rigid with a shorter life span, which manifests acutely as hemolytic anemia, vasculopathy, and vaso-occlusion. Pain onset can be sudden and unpredictable, often requiring hospitalization. Fifty to sixty percent of adults with SCD have end organ damage, with 24 percent experiencing damage in multiple organs, and one in four patients have a stroke by the age of 45. The impact of SCD is pervasive and affects every aspect of life for patients and their families and caregivers – from missed work and school, decreased quality of life and mental health, and ability to complete daily tasks. In the U.S., there are approximately 100,000 people living with SCD, and the median age of death is 45 years of age.

About LYFGENIA™ (lovotibeglogene autotemcel) or lovo-cel

LYFGENIA is a one-time ex-vivo lentiviral vector gene therapy approved for the treatment of patients 12 years of age or older with sickle cell disease and a history of vaso-occlusive events (VOEs). LYFGENIA works by adding a functional β-globin gene to patients’ own hematopoietic (blood) stem cells (HSCs). Durable production of adult hemoglobin with anti-sickling properties (HbA^T87Q) is possible following successful engraftment. HbA^T87Q has a similar oxygen-binding affinity to wild-type HbA, limits sickling of red blood cells and has the potential to reduce and VOEs.

The Phase 1/2 HGB-206 study of LYFGENIA is ongoing with enrollment and treatment complete; and the Phase 3 HGB-210 study evaluating LYFGENIA is ongoing. bluebird bio is also conducting a long-term safety and efficacy follow-up study (LTF-307) for patients with sickle cell disease who have been treated with LYFGENIA in bluebird bio-sponsored clinical studies.

Indication

LYFGENIA is indicated for the treatment of patients 12 years of age or older with sickle cell disease and a history of vaso-occlusive events (VOEs).

Limitations of Use

Following treatment with LYFGENIA, patients with α-thalassemia trait (-α3.7/-α3.7) may experience anemia with erythroid dysplasia that may require chronic red blood cell transfusions. LYFGENIA has not been studied in patients with more than two α-globin gene deletions.

Important Safety Information

Boxed WARNING: HEMATOLOGIC MALIGNANCY

Hematologic malignancy has occurred in patients treated with LYFGENIA. Monitor patients closely for evidence of malignancy through complete blood counts at least every 6 months and through integration site analysis at Months 6, 12, and as warranted.

Hematologic Malignancy

Hematologic malignancy has occurred in patients treated with LYFGENIA (Study 1, Group A). At the time of initial product approval, two patients treated with an earlier version of LYFGENIA using a different manufacturing process and transplant procedure (Study 1, Group A) developed acute myeloid leukemia (AML). One patient with α-thalassemia trait (Study 1, Group C) has been diagnosed with myelodysplastic syndrome (MDS).

The additional hematopoietic stress associated with mobilization, conditioning, and infusion of LYFGENIA, including the need to regenerate the hematopoietic system, may increase the risk of a hematologic malignancy. Patients with sickle cell disease have an increased risk of hematologic malignancy as compared to the general population.

Patients treated with LYFGENIA may develop hematologic malignancies and should have lifelong monitoring. Monitor for hematologic malignancies with a complete blood count (with differential) at least every 6 months for at least 15 years after treatment with LYFGENIA, and integration site analysis at Months 6, 12, and as warranted.

In the event that a malignancy occurs, contact bluebird bio at 1-833-999-6378 for reporting and to obtain instructions on collection of samples for testing.

Post-Marketing Long Term Follow-Up Study: Patients who intend to receive treatment with LYFGENIA are encouraged to enroll in the study, as available, to assess the long-term safety of LYFGENIA and the risk of malignancies occurring after treatment with LYFGENIA by calling bluebird bio at 1-833-999-6378. The study includes monitoring (at pre-specified intervals) for clonal expansion.

Delayed Platelet Engraftment

Delayed platelet engraftment has been observed with LYFGENIA. Bleeding risk is increased prior to platelet engraftment and may continue after engraftment in patients with prolonged thrombocytopenia. Two patients (4%) required more than 100 days post treatment with LYFGENIA to achieve platelet engraftment.

Patients should be made aware of the risk of bleeding until platelet recovery has been achieved. Monitor patients for thrombocytopenia and bleeding according to standard guidelines. Conduct frequent platelet counts until platelet engraftment and platelet recovery are achieved. Perform blood cell count determination and other appropriate testing whenever clinical symptoms suggestive of bleeding arise.

Neutrophil Engraftment Failure

There is a potential risk of neutrophil engraftment failure after treatment with LYFGENIA. Neutrophil engraftment failure is defined as failure to achieve three consecutive absolute neutrophil counts (ANC) ≥ 0.5 × 10⁹ cells/L obtained on different days by Day 43 after infusion of LYFGENIA. Monitor neutrophil counts until engraftment has been achieved. If neutrophil engraftment failure occurs in a patient treated with LYFGENIA, provide rescue treatment with the back-up collection of CD34+ cells.

Insertional Oncogenesis

There is a potential risk of lentiviral vector-mediated insertional oncogenesis after treatment with LYFGENIA.

Hypersensitivity Reactions

Allergic reactions may occur with the infusion of LYFGENIA. The dimethyl sulfoxide (DMSO) or dextran 40 in LYFGENIA may cause hypersensitivity reactions, including anaphylaxis.

Anti-retroviral Use

Patients should not take prophylactic HIV anti-retroviral medications for at least one month prior to mobilization and until all cycles of apheresis are completed. There are some long-acting anti-retroviral medications that may require a longer duration of discontinuation for elimination of the medication. If a patient is taking anti-retrovirals for HIV prophylaxis, confirm a negative test for HIV before beginning mobilization and apheresis of CD34+ cells.

Hydroxyurea Use

Patients should not take hydroxyurea for at least 2 months prior to mobilization and until all cycles of apheresis are completed. If hydroxyurea is administered between mobilization and conditioning, discontinue 2 days prior to initiation of conditioning.

Iron Chelation

Drug-drug interactions between iron chelators and the mobilization process and myeloablative conditioning agent must be considered. Iron chelators should be discontinued at least 7 days prior to initiation of mobilization or conditioning. Do not administer myelosuppressive iron chelators (e.g., deferiprone) for 6 months post-treatment with LYFGENIA. Non-myelosuppressive iron chelation should be restarted no sooner than 3 months after LYFGENIA infusion. Phlebotomy can be used in lieu of iron chelation, when appropriate.

Interference with PCR-based Testing

Patients who have received LYFGENIA are likely to test positive by polymerase chain reaction (PCR) assays for HIV due to integrated BB305 LVV proviral DNA, resulting in a possible false-positive PCR assay test result for HIV. Therefore, patients who have received LYFGENIA should not be screened for HIV infection using a PCR-based assay.

Adverse Reactions

The most common adverse reactions ≥ Grade 3 (incidence ≥ 20%) were stomatitis, thrombocytopenia, neutropenia, febrile neutropenia, anemia, and leukopenia.

Three patients died during LYFGENIA clinical trials; one from sudden cardiac death due to underlying disease and two from acute myeloid leukemia who were treated with an earlier version of LYFGENIA using a different manufacturing process and transplant procedure (Study 1, Group A).

Pregnancy/Lactation

Advise patients of the risks associated with myeloablative conditioning agents, including on pregnancy and fertility.

LYFGENIA should not be administered to women who are pregnant, and pregnancy after LYFGENIA infusion should be discussed with the treating physician.

LYFGENIA is not recommended for women who are breastfeeding, and breastfeeding after LYFGENIA infusion should be discussed with the treating physician.

Females and Males of Reproductive Potential

A negative serum pregnancy test must be confirmed prior to the start of mobilization and re-confirmed prior to conditioning procedures and before LYFGENIA administration.

Women of childbearing potential and men capable of fathering a child should use an effective method of contraception (intra-uterine device or combination of hormonal and barrier contraception) from start of mobilization through at least 6 months after administration of LYFGENIA.

Advise patients of the options for fertility preservation.

Please see full Prescribing Information for LYFGENIA including Boxed WARNING and Medication Guide.

About bluebird bio, Inc.

bluebird bio is pursuing curative gene therapies to give patients and their families more bluebird days.

Founded in 2010, bluebird has been setting the standard for gene therapy for more than a decade—first as a scientific pioneer and now as a commercial leader. bluebird has an unrivaled track record in bringing the promise of gene therapy out of clinical studies and into the real-world setting, having secured FDA approvals for three therapies in under two years. Today, we are proving and scaling the commercial model for gene therapy and delivering innovative solutions for access to patients, providers, and payers.

With a dedicated focus on severe genetic diseases, bluebird has the largest and deepest ex-vivo gene therapy data set in the field, with industry-leading programs for sickle cell disease, β-thalassemia and cerebral adrenoleukodystrophy. We custom design each of our therapies to address the underlying cause of disease and have developed in-depth and effective analytical methods to understand the safety of our lentiviral vector technologies and drive the field of gene therapy forward.

bluebird continues to forge new paths as a standalone commercial gene therapy company, combining our real-world experience with a deep commitment to patient communities and a people-centric culture that attracts and grows a diverse flock of dedicated birds.

For more information, visit bluebirdbio.com or follow us on social media at @bluebirdbio, LinkedIn, Instagram and YouTube.

LYFGENIA and bluebird bio are trademarks of bluebird bio, Inc.

Forward-Looking Statements

This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements that are not statements of historical facts are, or may be deemed to be, forward-looking statements, such as statements regarding the therapeutic potential of lovo-cel, including with respect to its durable, one-time transformative, and potentially curative benefits and its impact on quality of life for patients. Such forward-looking statements are based on historical performance and current expectations and projections about bluebird’s future goals, plans and objectives and involve inherent risks, assumptions and uncertainties, including internal or external factors that could delay, divert or change any of them in the next several years, that are difficult to predict, may be beyond bluebird’s control and could cause bluebird’s future goals, plans and objectives to differ materially from those expressed in, or implied by, the statements. No forward-looking statement can be guaranteed. Forward-looking statements in this press release should be evaluated together with the many risks and uncertainties that affect bluebird bio’s business, particularly those identified in the risk factors discussion in bluebird bio’s Annual Report on Form 10-K for the year ended December 31, 2022, as updated by its subsequent Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and other filings with the Securities and Exchange Commission. These risks and uncertainties include, but are not limited to: delays and challenges in bluebird’s commercialization and manufacturing of its products; the internal and external costs required for bluebird’s ongoing and planned activities, and the resulting impact on expense and use of cash, has been, and may in the future be, higher than expected which has caused bluebird, and may in the future cause bluebird to use cash more quickly than it expects or change or curtail some of its plans or both; substantial doubt exists regarding bluebird’s ability to continue as a going concern; bluebird’s expectations as to expenses, cash usage and cash needs may prove not to be correct for other reasons such as changes in plans or actual events being different than its assumptions; the risk that the efficacy and safety results from bluebird’s prior and ongoing clinical trials will not continue or be seen in the commercial context; the risk of insertional oncogenic or other safety events associated with lentiviral vector, drug product, or myeloablation; and the risk that lovo-cel will not be successfully commercialized. The forward-looking statements included in this document are made only as of the date of this document and except as otherwise required by applicable law, bluebird bio undertakes no obligation to publicly update or revise any forward-looking statement, whether as a result of new information, future events, changed circumstances or otherwise.

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