bluebird bio Announces New Interim Data from Phase 1 (HGB-206) Study of LentiGlobin Gene Therapy in Patients with Severe Sickle Cell Disease at Annual Congress of the European Hematology Association

bio, Inc. (Nasdaq: BLUE) today announced new interim data from the
ongoing HGB-206 Phase 1 multicenter clinical study of LentiGlobin
investigational gene therapy in patients with severe sickle cell disease
(SCD) will be presented in an oral presentation on Saturday, June 16 at
the 23rd Congress of the European Hematology Association
(EHA) by Julie Kanter, M.D., Medical University of South Carolina,
Charleston, South Carolina.

“The consistent production of increased amounts of anti-sickling HbAT87Q in
the Group C patients reflects the substantial positive impact of the
changes introduced with the amended HGB-206 study protocol and refined
manufacturing process. All four Group C patients with greater than or
equal to three months follow-up are making over 30 percent
anti-sickling HbAT87Q. The first patient treated, now
with six months of follow-up, is producing over 60 percent anti-sickling
HbAT87Q with a normal total hemoglobin level of 14.2
g/dL,” said David Davidson, M.D., chief medical officer, bluebird
bio. “The upward trajectory in Group C at these early time points
suggests the potential for these patients to exceed the initially
proposed therapeutic target of 30 percent anti-sickling HbAT87Q.
We continue to define the development plan with regulatory authorities,
and with further follow-up, we hope to see even higher levels of HbAT87Q,
as well as sustained clinical benefit for patients.”

SCD is a genetic disease that causes the protein in red blood cells,
called hemoglobin, to be misshapen. As a result of this abnormal
hemoglobin, many affected individuals live with severe anemia and
vaso-occlusive events which include severe, recurrent pain crises that
lead to organ damage and shortened life span.

“The early data from Group C patients are very exciting and provide
increasing confidence that LentiGlobin has the potential to deliver
transformative benefit to patients. The longer-term data from patients
treated earlier in the study show that levels of anti-sickling HbAT87Q
in patients with SCD treated with LentiGlobin remain stable for at least
two years,” said Dr. Kanter, a lead investigator of the HGB-206 study.
“Treatment options that can address the underlying cause of sickle cell
disease are limited and LentiGlobin gene therapy has the potential to
prevent or substantially reduce damaging symptoms associated with this
debilitating disease.”

Recent Progress in Gene Therapy for Severe Sickle Cell Disease:
Updated Interim Results from a Phase 1 Clinical Study of LentiGlobin
Gene Therapy (Abstract S836)

Presenter: Julie Kanter, M.D., Medical University of South
Carolina, Charleston, SCDate & Time: Saturday, June 16,
2018, 12:30 – 12:45 p.m. CEST (6:30 a.m. EDT)Location: Room

HGB-206 is an ongoing, open-label study designed to evaluate the safety
and efficacy of LentiGlobin gene therapy for the treatment of adults
with severe SCD. Patients in this study are divided into three cohorts:
A, B and C. Patients in Group A were treated under the original study
protocol. Patients in Group B were treated under an amended study
protocol that included a refined Drug Product (DP) manufacturing process
intended to increase DP vector copy number (VCN) as well as changes to
improve engraftment of gene-modified stem cells. Patients in both Group
A and B had DP made from stem cells collected using bone marrow harvest.
Patients in Group C were also treated under the amended study protocol,
but received LentiGlobin gene therapy made from stem cells collected
from peripheral blood after mobilization with plerixafor rather than via
bone marrow harvest. Results, as of May 15, 2018, include:

Conference Call & Webcast Information

bluebird bio will host a conference call and live webcast at 8:00 a.m.
EDT on Friday, June 15, 2018. To access the live webcast, please visit
the “Events & Presentations” page within the Investors and Media section
of the bluebird bio website at
Alternatively, investors may listen to the call by dialing (844)
825-4408 from locations in the United States or +1 (315) 625-3227 from
outside the United States. Please refer to conference ID number 4678706.
A replay of the webcast will be available on the bluebird bio website
for 90 days following the call.

About SCD

Sickle cell disease (SCD) is a serious, progressively debilitating, and
life-threatening genetic disease. SCD results from production of
abnormal sickle hemoglobin (HbS), which leads to sickled red blood cells
(RBCs) and hemolysis. As a result of this abnormal hemoglobin, many
affected individuals live with severe anemia and vaso-occlusive events
which include severe, recurrent pain crises that lead to organ damage
and shortened life span.

Where adequate medical care is available, common treatments for patients
with SCD largely revolve around prevention of infection, and management
and prevention of acute sickling episodes. Chronic management includes a
limited number of pharmaceutical treatment options and, in certain
cases, chronic transfusions. Allogeneic hematopoietic stem cell
transplant (HSCT) is currently the only available option with the
potential to correct the genetic deficiency in SCD. However, its use is
limited to certain pediatric patients with severe disease who have an
unaffected matched sibling donor. Complications of allogeneic HSCT
include a risk of treatment-related mortality, graft failure,
graft-versus-host disease (GvHD) and opportunistic infections,
particularly in patients who undergo non-sibling-matched allogeneic HSCT.

About bluebird bio, Inc.

With its lentiviral-based gene therapies, T cell immunotherapy expertise
and gene editing capabilities, bluebird bio has built an integrated
product platform with broad potential application to severe genetic
diseases and cancer. bluebird bio’s gene therapy clinical programs
include Lenti-D™ for the treatment of cerebral
adrenoleukodystrophy, and LentiGlobin™ for the treatment of
transfusion-dependent ?-thalassemia, also known as ?-thalassemia major,
and severe sickle cell disease. bluebird bio’s oncology pipeline is
built upon the company’s leadership in lentiviral gene delivery and T
cell engineering, with a focus on developing novel T cell-based
immunotherapies, including chimeric antigen receptor (CAR T) and T cell
receptor (TCR) therapies. bluebird bio’s lead oncology programs, bb2121
and bb21217, are anti-BCMA CAR T programs partnered with Celgene.
bluebird bio also has discovery research programs utilizing
megaTAL/homing endonuclease gene editing technologies with the potential
for use across the company’s pipeline.

bluebird bio has operations in Cambridge, Massachusetts, Seattle,
Washington, Durham, North Carolina and Zug, Switzerland.

LentiGlobin and Lenti-D are trademarks of bluebird bio, Inc.

Forward-Looking Statements

This release contains “forward-looking statements” within the meaning
of the Private Securities Litigation Reform Act of 1995, including
statements regarding the Company’s research, development, manufacturing
and regulatory approval plans for its LentiGlobin product candidate to
treat severe sickle cell disease. Any forward-looking statements are
based on management’s current expectations of future events and are
subject to a number of risks and uncertainties that could cause actual
results to differ materially and adversely from those set forth in or
implied by such forward-looking statements. These risks and
uncertainties include, but are not limited to, the risks that the
preliminary positive efficacy and safety results from our prior and
ongoing clinical trials of LentiGlobin will not continue or be repeated
in our ongoing, planned or expanded clinical trials of LentiGlobin, the
risks that the changes we have made in the LentiGlobin manufacturing
process or the HGB-206 clinical trial protocol will not result in
improved patient outcomes, risks that the current or planned clinical
trials of LentiGlobin will be insufficient to support regulatory
submissions or marketing approval in the US and EU, the risk of a delay
in the enrollment of patients in our clinical studies, and the risk that
any one or more of our product candidates will not be successfully
developed, approved or commercialized. For a discussion of other risks
and uncertainties, and other important factors, any of which could cause
our actual results to differ from those contained in the forward-looking
statements, see the section entitled “Risk Factors” in our most recent
Form 10-Q, as well as discussions of potential risks, uncertainties, and
other important factors in our subsequent filings with the Securities
and Exchange Commission. All information in this press release is as of
the date of the release, and bluebird bio undertakes no duty to update
this information unless required by law.

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