Acceleron Announces Updated Results from Ongoing Phase 2 Trials of Luspatercept in Beta-Thalassemia at the 23rd Congress of the European Hematology Association

Acceleron Pharma Inc. (Nasdaq:XLRN), a leading biopharmaceutical company
in the discovery and development of TGF-beta therapeutics to treat
serious and rare diseases, today announced updated results from the
ongoing Phase 2 trials of luspatercept in patients with beta-thalassemia
during an oral presentation at the 23rd Congress of the
European Hematology Association (EHA) in Stockholm, Sweden. Luspatercept
is being developed as part of a global collaboration between Acceleron
and Celgene.

“These results reinforce our enthusiasm for luspatercept’s potential as
a safe, efficacious therapy for beta-thalassemia patients over the long
term,” said Habib Dable, President and Chief Executive Officer of

Beta-thalassemia is caused by a genetic defect in the production of
hemoglobin, a protein that carries oxygen to red blood cells throughout
the body. Patients suffer from severe, chronic anemia and often
experience fatigue, organ enlargement, and bone complications. Patients
require lifelong therapy that includes frequent red blood cell
transfusions and corresponding treatment for the iron overload that

“We now have patients with both non-transfusion- and
transfusion-dependent beta-thalassemia continuing on treatment for three
years,” Dable continued. “We look forward to sharing top-line results
from the BELIEVE Phase 3 trial over the next few months.”

Phase 2 Results

A total of 31 non-transfusion-dependent patients have been treated with
luspatercept (dose levels ? 0.6 mg/kg) in the trials.

A total of 32 transfusion-dependent patients have been treated with
luspatercept (dose levels ? 0.6 mg/kg) in the trials.

Phase 2 Safety Summary

The majority of adverse events (AEs) were Grade 1 or 2. Grade 3 AEs
possibly or probably related to study drug were bone pain (n=3
patients), asthenia (n=2 patients), bone infarction (n=1 patient),
headache (n=1 patient), and presyncope (n=1 patient). One serious AE of
biliary colic was reported as possibly related to study drug.

The EHA beta-thalassemia presentation will be available immediately
following the presentation on Saturday, June 16th at the
conference under the Science page of the Company’s website at www.acceleronpharma.com/.

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

About the Phase 2 Trial

Data from two Phase 2 trials were presented at the 23rd Congress of the
EHA: the base study in which beta-thalassemia patients received
treatment with luspatercept for three months and the ongoing long-term
safety extension study in which patients may receive treatment with
luspatercept for up to an additional five years.

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.
Phase 3 clinical trials are underway to evaluate the safety and efficacy
of luspatercept in patients with MDS (the MEDALIST trial) and in
patients with beta-thalassemia (the BELIEVE trial). A Phase 3 trial is
being planned in first-line, lower-risk, MDS patients (the COMMANDS
trial). 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 Acceleron

Acceleron is a Cambridge-based, 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 franchise with two distinct Myostatin+ agents, ACE-083 and
ACE-2494, and a pulmonary program with sotatercept in pulmonary arterial

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

Forward-Looking Statements

This press release contains forward-looking statements about the
Company’s strategy, future plans and prospects, including statements
regarding the development of the Company’s compounds, the timeline for
clinical development and regulatory approval of the Company’s compounds
and the expected timing for reporting of data from ongoing clinical
trials. The words “anticipate,” “believe,” “could,” “estimate,”
“expect,” “goal,” “intend,” “may,” “plan,” “potential,” “project,”
“should,” “target,” “will,” “would,” and similar expressions are
intended to identify forward-looking statements, although not all
forward-looking statements contain these identifying words.

Actual results could differ materially from those included in the
forward-looking statements due to various risks and uncertainties,
including, but not limited to, that preclinical testing of the Company’s
compounds and data from clinical trials may not be predictive of the
results or success of ongoing or later clinical trials, that the
development of the Company’s compounds will take longer and/or cost more
than planned, that the Company or its collaboration partner, Celgene,
will be unable to successfully complete the clinical development of the
Company’s compounds, that the Company or Celgene may be delayed in
initiating, enrolling or completing any clinical trials, and that the
Company’s compounds will not receive regulatory approval or become
commercially successful products. These and other risks and
uncertainties are identified under the heading “Risk Factors” included
in the Company’s most recent Annual Report on Form 10-K, and other
filings that the Company has made and may make with the SEC in the

The forward-looking statements contained in this press release are based
on management’s current views, plans, estimates, assumptions and
projections with respect to future events, and the Company does not
undertake and specifically disclaims any obligation to update any
forward-looking statements.

View source version on businesswire.com: https://www.businesswire.com/news/home/20180615005201/en/