An Efficacy and Safety Study of Luspatercept (ACE-536) Versus Placebo in Adults Who Require Regular Red Blood Cell Transfusions Due to Beta (β) Thalassemia

Inclusion Criteria:

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

1. Male or female, ≥18 years of age at the time of signing the informed consent document
(ICF).

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

3. Subject is willing and able to adhere to the study visit schedule and other protocol
requirements.

4. Documented diagnosis of β-thalassemia or Hemoglobin E/β-thalassemia. (β-thalassemia
with mutation and/or multiplication of alpha globin is allowed).

5. Regularly transfused, defined as: 6-20 Red Blood Cell (RBC) units* in the 24 weeks
prior to randomization and no transfusion-free period for ≥ 35 days during that
period.

* Sites who prescribe transfusions and have the transfusion records only in volumes
should use for conversion of volume to units the below criteria, in order to obtain
number of units within the last 24 weeks to assess the eligibility: 1 unit in this
protocol refers to a quantity of packed RBCs approximately 200-350 mL. (i) sites who
use transfusion bags within this range, or ≥ 350 mL, the conversion in units should be
done by dividing the volume transfused to the patient by 350 mL, (ii) sites who use
transfusion bags < 200 mL, the conversion in units should be done by dividing the
volume transfused to the patient by 200 mL.

6. Performance status: Eastern Cooperative Oncology Group (ECOG) score of 0 or 1.

7. 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). FCBP participating in the study must:

1. Have two 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 with, effective*** contraception without interruption, 28 days prior to
starting investigational product, during the study therapy (including dose
interruptions), and for 12 weeks (approximately five times the mean terminal
half-life of luspatercept based on multiple-dose Pharmacokinetic PK) data) after
discontinuation of study therapy.

- True abstinence is acceptable when this is in line with the preferred and
usual lifestyle of the subject. [Periodic abstinence (eg, calendar,
ovulation, symptothermal, post-ovulation methods) and withdrawal are not
acceptable methods of contraception.] *** Agreement to use highly effective
methods of contraception that alone or in combination result in a failure
rate of a Pearl index of less than 1% per year when used consistently and
correctly throughout the course of the study.

Such methods include: Combined (estrogen and progesterone/progestin containing)
hormonal contraception: Oral; Intravaginal; Transdermal; Progestogen/progestin only
hormonal contraception associated with inhibition of ovulation: Oral; Injectable
hormonal contraception; Implantable hormonal contraception; Placement of an
intrauterine device (IUD); Placement of an intrauterine hormone-releasing system
(IUS); Bilateral tubal occlusion; Vasectomized partner; Sexual Abstinence.

8. Male subjects must:

- Practice true abstinence 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 five
times the mean terminal half-life of luspatercept based on multiple-dose PK data)
following investigational product 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. A diagnosis of Hemoglobin S/β-thalassemia or alpha (α)-thalassemia (eg, Hemoglobin H);

5. Evidence of active hepatitis C (HCV) infection as demonstrated by a positive HCV-RNA
test of sufficient sensitivity, or active infectious hepatitis B as demonstrated by
the presence of HBsAg and/or HBVDNA-positive,, or known positive human
immunodeficiency virus (HIV).

Note: Subjects receiving antiviral therapies should have 2 negative HCVRNA tests 3
months apart.(ie, one test at the end of the antiviral therapy and a second test 3
months following the first test).

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

7. Use of chronic anticoagulant therapy is excluded, unless the treatment stopped at
least 28 days prior to randomization. Anticoagulant therapies used for prophylaxis for
surgery or high risk procedures as well as low Molecular Weight (LMW) heparin for
superficial venous thrombosis and chronic aspirin are allowed.

8. Platelet count > 1000 x 109/L

9. Poorly controlled diabetes mellitus within 24 weeks prior to randomization as defined
by short term (eg, hyperosmolar or ketoacidotic crisis) and/or history of diabetic
cardiovascular complications (eg, stroke or myocardial infarction).

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

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

12. Use of an erythropoiesis-stimulating agent (ESA) ≤ 24 weeks prior to randomization.

13. Iron chelation therapy, if initiated ≤ 24 weeks prior to randomization (allowed if
initiated > 24 weeks before or during treatment).

14. Hydroxyurea treatment ≤ 24 weeks prior to randomization.

15. Pregnant or lactating females.

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

17. Major organ damage, including:

1. Liver disease with alanine aminotransferase (ALT) > 3 x the upper limit of normal
(ULN) or history of evidence of cirrhosis;

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 within 6 months of randomization.

3. Lung disease, including pulmonary fibrosis or pulmonary hypertension which are
clinically significant ie, ≥ Grade 3 NCI CTCAE version 4.0 (current active minor
version).

4. Creatinine clearance < 60 mL/min (per Cockroft-Gault formula).

18. Proteinuria ≥ Grade 3 according to NCI CTCAE version 4.0 (current active minor
version).

19. Chronic systemic glucocorticoids ≤ 12 weeks prior to randomization (physiologic
replacement therapy for adrenal insufficiency is allowed). Single day glucocorticoid
treatment (eg, for prevention or treatment of transfusion reactions, is allowed).

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

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

22. Cytotoxic agents, immunosuppressants ≤ 28 days prior to randomization (ie,
antithymocite globulin (ATG) or cyclosporine)

23. History of malignancy with the exception of:

1. Curatively resected nonmelanoma skin cancer.

2. Curatively treated cervical carcinoma in situ.

3. Other solid tumor with no known active disease in the opinion of the
investigator.