In patients who were at least six months post-treatment with
LentiGlobin for SCD, median level of abnormal sickle hemoglobin (HbS)
was reduced to ≤50 percent of total Hb

At up to 15 months post-treatment with LentiGlobin, there were no
reports of serious vaso-occlusive crisis or acute chest syndrome in
Group C

CAMBRIDGE, Mass.–(BUSINESS WIRE)–bluebird
bio, Inc. (Nasdaq:BLUE) announced new data from patients in Group C
of its ongoing Phase 1/2 HGB-206 study of the company’s investigational
LentiGlobin^® gene therapy for sickle cell disease (SCD) today
at the 24th European Hematology Association (EHA) Congress in Amsterdam,
the Netherlands.

SCD is a serious, progressive and debilitating genetic disease caused by
a mutation in the β-globin gene that leads to the production of abnormal
sickle hemoglobin (HbS), causing red blood cells (RBCs) to become
sickled and fragile, resulting in chronic hemolytic anemia, vasculopathy
and painful vaso-occlusive events (VOEs). For adults and children living
with SCD, this means unpredictable episodes of excruciating pain due to
vaso-occlusion as well as other acute complications—such as acute chest
syndrome (ACS), stroke, and infections, which can contribute to early
mortality in these patients.

LentiGlobin for SCD adds functional copies of a modified form of the
β-globin gene (β^A-T87Q-globin gene) into a patient’s own
hematopoietic (blood) stem cells (HSCs). Once patients have the β^A-T87Q-globin
gene, they have the potential to make functional RBCs, with the goal of
reducing sickled RBCs, hemolysis, and other complications.

“The latest Group C data from our ongoing Phase 1/2 study show robust
production of gene therapy-derived anti-sickling hemoglobin, HbA^T87Q,
such that patients with six or more months of follow-up after treatment
with LentiGlobin for sickle cell disease had median sickle hemoglobin
levels reduced to 50 percent or less of total hemoglobin, in the absence
of blood transfusions. The potential for gene therapy with LentiGlobin
to fundamentally alter the pathophysiology of sickle cell disease was
also supported by the normalization of hemolysis markers, increase in
total hemoglobin and substantial reduction in vaso-occlusive crises
relative to baseline,” said David Davidson, M.D., chief medical officer,
bluebird bio. “Further insight into these encouraging clinical results
was provided by findings from an exploratory assay used to evaluate the
expression of HbA^T87Q, which demonstrated 70 percent or more
of patient red blood cells contain HbA^T87Q at nine months
after treatment.”

Phase 1/2: HGB-206

HGB-206 is an ongoing, Phase 1/2 open-label study designed to evaluate
the efficacy and safety of LentiGlobin gene therapy for SCD that
includes three treatment cohorts: Groups A, B and C. As of March 7,
2019, 25 patients were enrolled and a total of 13 patients had been
treated with LentiGlobin in Group C, with a median post-treatment
follow-up of nine months (1.0 – 15.2 months).

“The severity of sickle cell disease is not always recognized, and many
people are unaware that individuals are debilitated by the effects of
sickle cell disease,” said Julie Kanter, M.D., University of Alabama at
Birmingham, Birmingham, Ala. “Group C of the Phase 1/2 HGB-206 study of
LentiGlobin now includes multiple patients with at least one year of
follow-up, and in these individuals, many with a history of
vaso-occlusive crises, their symptoms appear to be resolving. There have
been no incidents of acute chest syndrome or serious vaso-occlusive
crises reported, and many of their labs are approaching normal.”

Eight of the 13 treated patients in Group C had at least six months of
follow-up at the time of the data cutoff. In these patients, production
of gene therapy-derived hemoglobin (HbA^T87Q) ranged from
4.5–8.8 g/dL and total unsupported hemoglobin (Hb) levels ranged from
10.2–15.0 g/dL at the last study visit.

The median concentration of HbA^T87Q continued to increase,
accounting for ≥50 percent of total Hb in patients with at least 12
months of follow up (n=4).

No ACS or serious vaso-occlusive crisis (VOC) was reported in patients
in Group C at up to 15 months post-treatment with LentiGlobin. In an
exploratory analysis, key markers of hemolysis, including reticulocyte
counts, lactate dehydrogenase (LDH) and total bilirubin concentration,
trended toward normal levels.

As of the data cutoff date, the safety data from all patients in HGB-206
are reflective of underlying SCD, the known side effects of
hematopoietic stem cell (HSC) collection and myeloablative conditioning.
There have been no serious adverse events (SAEs) related to LentiGlobin
for SCD. One mild, non-serious event of hot flush was reported that the
investigator considered to be related to LentiGlobin for SCD; it
occurred and resolved on the day of drug product infusion and did not
require treatment.

Established tools, including high-performance liquid chromatography
(HPLC), are used to measure the amount of HbA^T87Q in a blood
sample. In order to detect HbA^T87Q and HbS protein expression
at a cellular level, bluebird bio has utilized a new, exploratory assay
to demonstrate the pancellular expression of HbA^T87Q in
patients treated with LentiGlobin. The assay enables detection of HbA^T87Q
and HbS protein expression at a cellular level. Results from this
assay showed that in samples from five patients who were at least nine
months post-treatment, on average, at least 70 percent of each patient’s
RBCs expressed HbA^T87Q.

About LentiGlobin for Sickle Cell Disease

LentiGlobin for sickle cell disease (SCD) is an investigational gene
therapy being studied as a potential treatment for SCD. bluebird bio’s
clinical development program for LentiGlobin for SCD includes the
ongoing Phase 1/2 HGB-206 study.

bluebird bio is conducting a long-term safety and efficacy follow-up
study (LTF-303) for people who have participated in bluebird
bio-sponsored clinical studies of LentiGlobin for SCD. For more
information, visit: https://www.bluebirdbio.com/our-science/clinical-trials.

LentiGlobin for SCD received Orphan Medicinal Product designation from
the European Commission for the treatment of SCD.

The U.S. Food and Drug Administration granted Orphan Drug status and
Regenerative Medicine Advanced Therapy designation for LentiGlobin for
the treatment of SCD.

About bluebird bio, Inc.

bluebird bio is pioneering gene therapy with purpose. From
our Cambridge, Mass., headquarters, we’re developing gene therapies for
severe genetic diseases and cancer, with the goal that people facing
potentially fatal conditions with limited treatment options can live
their lives fully. Beyond our labs, we’re working to positively disrupt
the healthcare system to create access, transparency and education so
that gene therapy can become available to all those who can benefit.

bluebird bio is a human company powered by human stories. We’re putting
our care and expertise to work across a spectrum of disorders by
researching cerebral adrenoleukodystrophy, sickle cell disease,
transfusion-dependent β-thalassemia and multiple myeloma using three
gene therapy technologies: gene addition, cell therapy and
(megaTAL-enabled) gene editing.

bluebird bio has additional nests in Seattle, Wash.; Durham, N.C.; and
Zug, Switzerland. For more information, visit bluebirdbio.com.

Follow bluebird bio on social media: @bluebirdbio, LinkedIn, Instagram and YouTube.

LentiGlobin is a trademark of bluebird bio.

Forward-Looking Statements

This release contains “forward-looking statements” within the meaning
of the Private Securities Litigation Reform Act of 1995. 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 risk that the efficacy and safety results from our prior and
ongoing clinical trials of LentiGlobin for SCD will not continue or be
repeated in our ongoing or planned clinical trials of LentiGlobin for
SCD; the risk that the current or planned clinical trials of LentiGlobin
for SCD will be insufficient to support regulatory submissions or
marketing approval in the U.S. and EU; the risk that the production of
HbA^T87Q may not be sustained over extended
periods of time; and the risk that we may not secure adequate pricing or
reimbursement to support continued development or commercialization of
LentiGlobin for SCD following regulatory approval. 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.

Contacts

bluebird bio
Investors:
Elizabeth Pingpank, 617-914-8736
epingpank@bluebirdbio.com
or
Media:
Catherine
Falcetti, 339-499-9436
cfalcetti@bluebirdbio.com