A Study to Determine the Efficacy and Safety of Luspatercept in Adults With Non Transfusion Dependent Beta (β)-Thalassemia

The primary objective is:

- To evaluate the effect of luspatercept in non-transfusion dependent β-thalassemia-patient
versus placebo on anemia, as measured by mean hemoglobin concentration in the absence of
transfusions over a continuous 12-week interval, from Week 13 to Week 24, compared to
baseline.

The secondary objectives are:

- To evaluate the effect of luspatercept versus placebo on β-thalassemia related symptoms,
as measured by non transfusion dependent β-thalassemia-patient reported outcome
(NTDT-PRO) over a continuous 12-week intervals (from Weeks 13 to 24 and from Weeks 37 to
48) compared to baseline.

- To evaluate the effect of luspatercept versus placebo on functional and health-related
quality of life (QoL) as measured by Medical Outcomes Study 36-Item Short Form (SF-36)
and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) questionnaires

- To evaluate the long-term effect of luspatercept versus placebo on anemia, as measured
by mean hemoglobin concentration in the absence of transfusions over a continuous
12-week interval from Week 37 to Week 48, compared to baseline

- To evaluate the effect of luspatercept versus placebo on iron overload, as measured by
liver iron concentration (LIC) and iron chelation therapy (ICT) daily dose

- To evaluate the effect of luspatercept versus placebo on iron overload, as measured by
serum ferritin

- To evaluate the duration of erythroid response

- To evaluate the effect of luspatercept versus placebo on physical activity measured by
6-minute walk test (6MWT)

Safety and Pharmacokinetics (PK) Objectives

- To evaluate safety and tolerability of luspatercept, including immunogenicity

- To evaluate population pharmacokinetics (PK) of luspatercept in subjects with β-
thalassemia

The exploratory objectives are:

- To evaluate the effect of luspatercept versus placebo on measures of extra-medullary
hematopoietic (EMH) masses, bone mineral density, splenomegaly, pulmonary hypertension,
and leg ulcers, when present

- To evaluate the effect of luspatercept versus placebo on the β-thalassemia severity as
measured by the NTDT severity score system

- To examine the relationship of baseline and change in serum Growth Differentiation
Factor 11 (GDF11) and other related biomarkers with response to treatment with
luspatercept

- To examine the effect of luspatercept on fetal hemoglobin (HbF)

- To examine the effect of luspatercept on Health Resource Utilization (HRU)

Inclusion Criteria:

Subjects must satisfy the following criteria to be enrolled in the study:

1. Subjects must be ≥ 18 years of age at the time of signing the informed consent
document (ICF).

2. Subject must understand and voluntarily sign an ICF prior to any study-related
assessments/procedures being conducted.

3. Subject is willing and able to adhere to the study visit schedule (eg, not scheduled
to receive hematopoietic stem cell transplantation) and other protocol requirements.

4. Subject must have documented diagnosis of β-thalassemia or hemoglobin E/
β-thalassemia. Concomitant alpha globin mutation and/or duplication are allowed.

5. Subject must be non-transfusion dependent, defined as 0 to 5 units of RBCs received
during the 24-week period prior to randomization. Note: 1 unit defined for this entry
criterion as approximately 200 to 350 mL of transfused packed RBCs.

6. Subject must not be on a regular transfusion program and must be RBC transfusion-free
for at least ≥ 8 weeks prior to randomization

7. Subject must have mean baseline hemoglobin ≤ 10 g/dL, based on a minimum of 2
measurements ≥ 1 week apart within 4 weeks prior to randomization; hemoglobin values
within 21 days post-transfusion will be excluded.

8. Subject must have performance status: Eastern Cooperative Oncology Group (ECOG)
performance score of 0 to 1.

9. A female of childbearing potential (FCBP) for this study is defined as a female who:

1) has achieved menarche at some point, 2) has not undergone a hysterectomy or bilateral
oophorectomy or 3) has not been naturally postmenopausal (amenorrhea following cancer
therapy does not rule out childbearing potential) for at least 24 consecutive months (ie,
has had menses at any time in the preceding 24 consecutive months). A FCBP participating in
the study must:

1. Have 2 negative pregnancy tests as verified by the Investigator prior to starting
study therapy. She must agree to ongoing pregnancy testing during the course of the
study, and after end of study treatment. This applies even if the subject practices
true abstinence* from heterosexual contact.

2. Either commit to true abstinence* from heterosexual contact (which must be reviewed on
a monthly basis and source documented). If a FCBP engages in sexual activity that may
result in a pregnancy, she must agree to use, and be able to comply during the study
therapy (including dose interruptions), and for 12 weeks (approximately 5 times the
mean terminal half-life of luspatercept based on multiple dose pharmacokinetics [PK]
data) after discontinuation of study therapy.

10. Male subjects must:

a. Practice true abstinence (which must be reviewed on a monthly basis) or agree to use a
condom during sexual contact with a pregnant female or a female of childbearing potential
while participating in the study, during dose interruptions and for at least 12 weeks
(approximately 5 times the mean terminal half-life of luspatercept based on multiple-dose
PK data) following IP discontinuation, even if he has undergone a successful vasectomy

Exclusion Criteria:

The presence of any of the following will exclude a subject from enrollment:

1. Any significant medical condition, laboratory abnormality, or psychiatric illness that
would prevent the subject from participating in the study.

2. Any condition including the presence of laboratory abnormalities, which places the
subject at unacceptable risk if he/she were to participate in the study.

3. Any condition that confounds the ability to interpret data from the study.

4. Diagnosis of hemoglobin S/β-thalassemia or alpha (α)-thalassemia (eg,Hemoglobin H).

5. Active hepatitis C (HCV) infection

6. Deep vein thrombosis (DVT) or stroke requiring medical intervention ≤ 24 weeks prior
to randomization.

7. Subjects on chronic anticoagulant therapy are excluded, unless they stopped the
treatment at least 28 days prior to randomization. Anticoagulant therapies for
prophylaxis and for surgery or high-risk procedures as well as low molecular weight
(LMW) heparin for superficial vein thrombosis (SVT) and chronic aspirin are allowed
before and during the study.

8. Treatment with another investigational drug or device ≤ 28 days prior to
randomization.

9. Prior exposure to sotatercept (ACE-011) or luspatercept (ACE-536).

10. Platelet count > 1000 x 109/L.

11. Subjects on iron chelation therapy (ICT) at the time of ICF signature must have
initiated the treatment with ICT at least 24 weeks before the predicted randomization
date. ICT can be initiated at any time during treatment and should be used according
to the label.

12. Subject had Hydroxyurea and ESA treatment ≤ 24 weeks prior to randomization, and no
prior gene therapy.

13. Subject is pregnant or a lactating female.

14. Uncontrolled hypertension. Controlled hypertension for this protocol is considered ≤
Grade 1 according to National Cancer Institute Common Terminology for Adverse Events
(NCI CTCAE) version 4.0 (current active minor version).

15. Subject has major organ damage, including:

1. Liver disease with alanine aminotransferase (ALT) > 3 x upper limit of normal
(ULN) or history/evidence of cirrhosis, as well as presence of masses/tumor
detected by ultrasound at screening.

2. Heart disease, heart failure as classified by the New York Heart Association
(NYHA) classification 3 or higher, or significant arrhythmia requiring treatment,
or recent myocardial infarction (MI) within 6 months of randomization.

3. Severe lung disease, including pulmonary fibrosis or pulmonary hypertension, ie,
≥G3 NCI CTCAE version 4.0 (current active minor version).

4. Estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m2 (per Modification
of Diet in Renal Disease [MDRD] formula).

16. Subject has received chronic systemic glucocorticoids ≤ 12 weeks prior to
randomization (physiologic replacement therapy for adrenal insufficiency is allowed).

17. Major surgery ≤ 12 weeks prior to randomization (subjects must have completely
recovered from any previous surgery prior to randomization).

18. History of severe allergic or anaphylactic reactions or hypersensitivity to
recombinant proteins or excipients in the investigational product (see Investigator
Brochure).

19. Subject has received immunosuppressants ≤ 28 days prior to randomization.

20. History or current malignancies (solid tumors and hematological malignancies) unless
the subject has been free of the disease (including completion of any active or
adjuvant treatment for prior malignancy) for ≥ 5 years. However, subjects with the
following history/concurrent conditions are allowed:

- Basal or squamous cell carcinoma of the skin

- Carcinoma in situ of the cervix

- Carcinoma in situ of the breast

- Incidental histologic finding of prostate cancer (T1a or T1b using the tumor,
nodes, metastasis [TNM] clinical staging system)