Celgene Corporation and Acceleron Pharma Announce Submission of Luspatercept Biologics License Application to U.S. FDA

Celgene Corporation (NASDAQ: CELG) and Acceleron Pharma Inc. (NASDAQ:
XLRN) today announced that Celgene has submitted a Biologics License
Application (BLA) for luspatercept, an erythroid maturation agent, for
the treatment of adult patients with very low to intermediate risk
myelodysplastic syndromes (MDS)-associated anemia who have ring
sideroblasts and require red blood cell (RBC) transfusions and for the
treatment of adult patients with beta-thalassemia-associated anemia who
require RBC transfusions.

The submission is based on the safety and efficacy results of the
pivotal phase 3 studies MEDALIST and BELIEVE, both recently presented at
the American Society of Hematology annual meeting, where MEDALIST was
included in the plenary session.

“There remains a high unmet medical need for patients with MDS or
beta-thalassemia who suffer from the effects of their disease-related
anemia. The primary treatment option for these patients currently is
chronic transfusion of red blood cells which can be associated with
complications such as iron overload,” said Jay Backstrom, M.D., Chief
Medical Officer for Celgene. “New treatment options are urgently needed
for these patients. With this submission, we look forward to working
with the Agency to deliver luspatercept to patients with these serious
blood diseases.”

The companies also plan to submit a marketing application to the
European Medicines Agency in the second quarter of 2019.

“The BLA submission is a key milestone for Acceleron and a credit to our
longstanding collaboration with Celgene,” said Habib Dable, President
and Chief Executive Officer of Acceleron. “We believe luspatercept’s
positive clinical trial results demonstrate its potential as a novel
treatment for patients with lower-risk MDS as well as in
beta-thalassemia. All involved have worked diligently to develop
luspatercept for patients with chronic anemias associated with these
serious blood disorders.”

Luspatercept is an investigational therapy that is not approved for any
use in any country for any indication.

About Luspatercept

Luspatercept is a first-in-class erythroid maturation agent (EMA) that
regulates late-stage red blood cell maturation. Acceleron
and Celgene are jointly developing luspatercept as part of a global
collaboration. A phase 3 trial (COMMANDS) in ESA-naïve, lower-risk MDS
patients, the BEYOND phase 2 trial in non-transfusion-dependent
beta-thalassemia, and a phase 2 trial in myelofibrosis are ongoing. For
more information, please visit www.clinicaltrials.gov.

About MEDALIST

MEDALIST is a phase 3, randomized, double blind, placebo-controlled,
multi-center study evaluating the safety and efficacy of luspatercept in
adults with very low-, low-, or intermediate-risk myelodysplastic
syndromes (MDS). All patients were RBC transfusion dependent and were
either refractory or intolerant to prior erythropoiesis-stimulating
agent (ESA) therapy or were ESA naïve with endogenous serum
erythropoietin ≥ 200 U/L and had no prior treatment with disease
modifying agents. The median age of the patients enrolled in the trial
was 71 years in the luspatercept treatment group and 72 years in the
placebo group. Median transfusion burden in both treatment arms was 5
RBC units/8 weeks. 229 patients were randomized to receive either
luspatercept 1.0 mg/kg (153 patients) or placebo (76 patients) by
subcutaneous injection once every 21 days. The study was conducted at 65
sites in 11 countries.

About BELIEVE

BELIEVE is a phase 3, randomized, double blind, placebo-controlled
multicenter study comparing luspatercept + best supportive care (BSC)
versus placebo + BSC in adults with beta-thalassemia patients who
require regular RBC transfusions. The median age of the patients was 30
years in both treatment arms. 336 patients were randomized to receive
either luspatercept 1.0 mg/kg (224 patients) or placebo (112 patients)
by subcutaneous injection every 21 days for up to 48 weeks. Crossover to
the luspatercept treatment groups was allowed after unblinding based on
the recommendation of an independent Data Safety Monitoring Committee;
patients treated with luspatercept will be followed for up to 3 years.
The study was conducted at 65 sites in 15 countries.

About Celgene

Celgene Corporation, headquartered in Summit, New Jersey, is an
integrated global biopharmaceutical company engaged primarily in the
discovery, development and commercialization of innovative therapies for
the treatment of cancer and inflammatory diseases through
next-generation solutions in protein homeostasis, immuno-oncology,
epigenetics, immunology and neuro-inflammation. For more information,
please visit www.celgene.com.

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and YouTube.

About Acceleron

Acceleron is a clinical-stage biopharmaceutical company dedicated to the
discovery, development, and commercialization of therapeutics to treat
serious and rare diseases. The Company's leadership in the understanding
of TGF-beta biology and protein engineering generates innovative
compounds that engage the body's ability to regulate cellular growth and
repair.

Acceleron focuses its research and development efforts in hematologic,
neuromuscular, and pulmonary diseases. In hematology, the Company and
its global collaboration partner, Celgene, are developing luspatercept
for the treatment of chronic anemia in myelodysplastic syndromes,
beta-thalassemia, and myelofibrosis. Acceleron is also advancing its
neuromuscular program with ACE-083, a locally-acting Myostatin+ agent in
Phase 2 development in facioscapulohumeral muscular dystrophy and
Charcot-Marie-Tooth disease and is conducting a Phase 2 pulmonary
program with sotatercept in pulmonary arterial hypertension.

For more information, please visit www.acceleronpharma.com.
Follow Acceleron on Social Media: @AcceleronPharma and LinkedIn.

FORWARD-LOOKING STATEMENTS

This press release contains forward-looking statements within the
meaning of The Private Securities Litigation Reform Act of 1995. Such
forward-looking statements include those regarding the potential
benefits of, and plans relating to the collaboration between Acceleron
and Celgene; the potential of luspatercept as a therapeutic drug; and
the benefit of each company’s strategic plans and focus. The words
“anticipate,” “believe,” “estimate,” “expect,” “intend,” “may,” “plan,”
“predict,” “project,” “will,” “would,” “could,” “potential,” “possible,”
“hope” and similar expressions are intended to identify forward-looking
statements, although not all forward-looking statements contain these
identifying words. Such statements are subject to numerous important
factors, risks and uncertainties that may cause actual events or results
to differ materially from current expectations and beliefs. For example,
there can be no guarantee that luspatercept will be successfully
developed or complete necessary clinical phases. Forward-looking
statements in this press release could also be affected by risks and
uncertainties relating to a number of other important factors,
including: results of clinical trials, including subsequent analysis of
existing data and new data received from ongoing and future studies; the
content and timing of decisions made by the U.S. FDA and other
regulatory authorities, investigational review boards at clinical trial
sites and publication review bodies; the ability to obtain and maintain
requisite regulatory approvals and to enroll patients in planned
clinical trials; the ability to obtain, maintain and enforce patent and
other intellectual property protection for luspatercept; the ability to
maintain key collaborations; and general economic and market conditions.
These and other risks are described in greater detail under the caption
"Risk Factors" included in each company’s public filings with
the Securities and Exchange Commission and with respect to Celgene
includes risk factors related to the proposed transaction between
Bristol-Myers Squibb and Celgene, such as, but not limited to, the risks
that: management’s time and attention is diverted on transaction related
issues; disruption from the transaction makes it more difficult to
maintain business, contractual and operational relationships; and
Bristol-Myers Squibb, Celgene or the combined company is unable to
retain key personnel. Any forward-looking statements contained in this
press release speak only as of the date hereof, and neither company has
any obligation to update any forward-looking statements, whether as a
result of new information, future events or otherwise, except as may be
required by law.

Hyperlinks are provided as a convenience and for informational
purposes only. Neither Celgene nor Acceleron bears responsibility for
the security or content of external websites or websites outside of
their respective control.

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