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

Percentage of participants who achieved a red blood cell (RBC) transfusion burden reduction from baseline ≥ 33% with a reduction of at least 2 units during Weeks 37 - 48 compared to the 12-week interval on or prior to Dose 1 Day 1.

Percentage of participants who achieved a red blood cell (RBC) transfusion burden reduction from baseline ≥ 50% with a reduction of at least 2 units during Weeks 13 - 24 compared to the 12-week interval on or prior to Dose 1 Day 1.

Percentage of participants who achieved a red blood cell (RBC) transfusion burden reduction from baseline ≥ 50% with a reduction of at least 2 units during Week 37 to Week 48 compared to the 12-week interval on or prior to Dose 1 Day 1.

Baseline was defined as the total number of Red Blood Cells (RBC) units transfused during the 12-week interval on or prior to Dose 1 Day 1. This is compared to the total number of RBC units transfused during the 12-week interval from treatment weeks 13-24.

Baseline was defined as the last value on or before the first dose of study drug was administered; if multiple values were present for the same date, the average of these values was used. If a participant had 1 postbaseline assessment, it was used as the Week 48 value. If a participant had multiple postbaseline assessments, the last one was used as the Week 48 value. The value of LIC was collected by magnetic resonance imaging. Participants with a LIC value > 43 mg/g were not included in the analysis.

Three different types of Iron Chelation Therapy (ICT) were analyzed: 1. Deferasirox 2. Deferiprone 3. Deferoxamine Mesilate/Deferoxamine The baseline mean daily dose was calculated using the ICT dosage during the 12 weeks prior to first study drug administration and the postbaseline mean daily dose was calculated during the last 12 weeks of the 48-week double-blind Treatment Period or the last 12 weeks of the study treatment for early discontinued participants.

For each participant, the baseline mean serum ferritin level was calculated during the 12 weeks prior to first study drug administration. The postbaseline mean serum ferritin level was calculated during the last 12 weeks of the 48-week double-blind Treatment Period or last 12 weeks of study treatment, if discontinued early. The change was calculated as the difference of post baseline mean serum ferritin level and baseline mean serum ferritin level.

For BMD, the lumbar spine and total hip were measured at baseline and 48 weeks by dual energy x-ray absorptiometry (DXA). Baseline was defined as the last value on or before the first dose of study drug is administered; if multiple values are present for the same date, the average of these values was used. If during the 48 week double-blinded treatment period, a participant has only one assessment, it is counted as 'Week 48' visit; if a participant has multiple assessments, the last one is used as 'Week 48' visit. The analysis was done on the population that had at least 2 measurements.

Myocardial Iron levels were measured by Magnetic Resonance Imaging (MRI), using MRI parameter T2* (Unit: ms). T2* values correlates with heart failure (HF) risk (e.g. T2*<6ms: high HF risk).

The TranQol is a self-administered quality of life tool developed for beta-thalassemia patients. The adult self-report version used in this study, includes 36 questions assessed on a 5-point response, that are grouped into 5 domains (Physical Health, Emotional Health, Sexual Health, Family Functioning, School/Career Functioning). Scores are calculated according to specific scoring algorithms developed by the authors. Both individual domains score and the total score range from 0 (worst) to 100 (best). Total Score and Physical Health domain score are reported. Positive change from baseline values indicate improvement.

The SF-36 (version 2) is a generic, self-administered instrument consisting of 8 multi-item scales that assess 8 health domains. The raw score for each health domain is transformed into a 0 (worst) to 100 (best) domain score. The 0-100 scale score for each health domain is further converted to normbased scores using a T-score transformation, with a mean of 50 and a standard deviation (SD) of 10. Higher norm-based T-scores indicate better heath/QoL. The domains/summaries reported are: 1. Physical Functioning (Range of possible T-scores is 19.26 - 57.54) 2. General Health (Range of possible T-scores is 18.95 - 66.50) 3. Physical Component summary (PCS) (Range of possible T-scores is 5.02 - 79.78). Positive change from baseline values indicate improvement.

Number of participants who had any of the following types of Healthcare Resource Utilization (HRU): - a doctor office visit (non-study scheduled) - an emergency department visit - a hospitalization

Types of hospitals units considered to be 'higher care' are: - Intensive Care Unit - Coronary Care Unit

Transfusion independence was defined as the absence of any transfusion during any consecutive "rolling" 8-week time interval within the treatment period, i.e, Days 1 to 56, Days 2 to 57 and so on.

Responders were defined as subjects who achieved ≥ 33% reduction or ≥ 50% reduction in Red Blood Cells Transfusion (RBC-T) burden from baseline with a reduction of at least 2 RBC units during any rolling 12-week interval. The duration of reduction is calculated as Last Day of Response - First day of response +1

Transfusion independence was defined as the absence of any transfusion during any consecutive "rolling" 8-week time interval within the treatment period, ie, Days 1 to 56, Days 2 to 57 and so on. Longest duration of transfusion independence was estimated based on Kaplan-Meier model.

Time to erythroid response was defined as the time from first dose of the study drug to first erythroid response. This is reported for participants with a ≥ 33% reduction from baseline in RBC transfusion burden (with a reduction of at least 2 units) for any 12-week interval., as well as participants with a ≥ 50% reduction from baseline in RBC transfusion burden (with a reduction of at least 2 units) for any 12-week interval.

The number of transfusion events after start of study treatment were evaluated. For the definition of transfusion events, if multiple transfusions happen on the same date, they are counted as one event; if multiple transfusions happen on two consecutive dates, they are counted as one event; if multiple transfusions happen on three consecutive dates, they are counted as two events. Results are presented in 24-week intervals, up to 96 weeks after start of study treatment

An AE is any noxious, unintended, or untoward medical occurrence that may appear or worsen during the course of a study. A serious AE is any AE occurring at any dose that - Results in death - Is life-threatening - Requires or prolongs existing inpatient hospitalization - Results in persistent or significant disability/incapacity - Is a congenital anomaly/birth defect - Constitutes an important medical event. The Investigator assessed the relationship of each AE to study drug and graded the severity according to the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE, Version 4.03): - Grade 1 = Mild - Grade 2 = Moderate (some limitation in activity; no/minimal medical intervention) - Grade 3 = Severe (limitation in activity; medical intervention required) - Grade 4 = Life-threatening - Grade 5 = Death

Number of participants with positive ADA prior to taking study drug and/or during study. A participant was counted as "treatment-emergent" if there was a positive post-baseline sample while the baseline sample was ADA negative, or there was a positive post-baseline sample with a titer ≥ 4-fold of the baseline titer while the baseline sample was ADA positive. A participant was counted as "preexisting" if the baseline sample was ADA positive and the participant was not qualified for "treatment-emergent."