A Phase 2, Open Label, Ascending Dose Study of ACE-536 for the Treatment of Anemia in Patients With Low or Intermediate-1 Risk Myelodysplastic Syndromes (MDS)
Phase: PHASE2
Conditions: Anemia
Sponsor: Acceleron Pharma, Inc., a wholly-owned subsidiary of Merck & Co., Inc., Rahway, NJ USA

Official Protocol Title: 
NCT number: 
Document Date: 
A phase 2, open-label, ascending dose study of ACE-536 for the 
treatment of anemia in patients with low or intermediate-1 risk 
myelodysplastic syndromes (MDS).
05-Jul-2016
NCT01749514

Protocol A536-03  
 
 
 
 
 
 
 
 
 
 
 
 
 
                         CONFIDENTIAL 
Revision Level: 05 
 
05-Jul-2016                                                               Page 4 of 74                                                                      
Acceleron Pharma Inc. 
 
 
 
SITE PRINCIPAL INVESTIGATOR SIGNATURE PAGE 
 
 
 
 
 
 
Signature: 
 
 
 
Date: 
 
 
 
Name (print): 
 
 
 
 
 
DD/MMM/YYYY 
 
 
 
 
 
 
Institution Name and Address: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
By my signature I have read the protocol and agree to personally supervise and conduct the study 
as outlined in the protocol.  The study will be conducted in accordance to current United States 
Food and Drug Administration (FDA) regulations, International Conference of Harmonization 
(ICH) Guidelines, Good Clinical Practices (GCP), the Declaration of Helsinki, and local ethical 
and legal requirements. 

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1. 
PROTOCOL SYNOPSIS 
Name of Sponsor/Company:  
Acceleron Pharma Inc. 
 
128 Sidney Street 
 
Cambridge, MA 02139 USA 
Name of Investigational Product:  Luspatercept (ACE-536) 
Name of Active Ingredient: ACE-536 is a recombinant fusion protein consisting of a modified 
form of the extracellular domain (ECD) of the human activin receptor IIB (ActRIIB) linked to 
the human IgG1 Fc domain. 
Title of Study: A phase 2, open-label, ascending dose study of ACE-536 for the treatment of 
anemia in patients with low or intermediate-1 risk myelodysplastic syndromes (MDS). 
Study Centers: Up to 20 
Phase of Development: 2 
Objectives: 
Primary:  
x To evaluate the proportion of patients who have a modified erythroid response 
(mHI-E), defined as a hemoglobin increase of ≥ 1.5 g/dL from baseline for ≥ 14 days 
(in the absence of red blood cell [RBC] transfusions) in non-transfusion dependent 
patients, or a reduction of either ≥ 4 units or ≥ 50% of units of RBCs transfused 
compared to pre-treatment in transfusion dependent patients. 
Secondary: 
x To evaluate safety and tolerability of ACE-536 
x To examine rates of erythroid, neutrophil and platelet (HI-E, HI-N and HI-P) 
responses (International Working Group [IWG] 2006 criteria) 
x To evaluate time to mHI-E and HI-E response and duration of mHI-E and HI-E 
response 
x To evaluate frequency of RBC transfusions in transfusion dependent patients 
x To examine the pharmacokinetic (PK) profile of ACE-536 
x To examine other pharmacodynamic (PD) effects (e.g., iron metabolism, 
erythropoietin, reticulocytes, and bone biomarkers) 
Exploratory: 
x To evaluate biomarkers related to the TGF-E superfamily 
 

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x Evaluation of self-reported quality of life in the expansion cohort using tools 
including but not limited to the Functional Assessment of Cancer Therapy-Anemia 
Scale (FACT-An) questionnaire  
Methodology:  
This is a phase 2, open-label, ascending dose study to evaluate the effects of ACE-536 on 
anemia in patients with low or intermediate-1 risk MDS who are not currently receiving 
treatment with an erythropoiesis-stimulating agent (ESA).  Patients who meet the study 
eligibility criteria will be enrolled within 28 days of screening.  Patients in all cohorts will 
receive ACE-536, administered subcutaneously (SC), every 3 weeks for up to 5 cycles.  Dose 
delay(s) and dose reduction(s) may be required for individual patients as outlined in the Patient 
Dose Modification Rules (Section 10.8.1).   
Each dose escalation cohort will consist of a minimum of 3 patients.  The dose level of 
ACE-536 for the first cohort will be 0.125 mg/kg and the dose level(s) for subsequent cohort(s) 
will follow a modified Fibonacci dose escalation scheme, with a maximum dose level of 
0.25 mg/kg for cohort 2, 0.50 mg/kg for cohort 3, 0.75 mg/kg for cohort 4, 1.0 mg/kg for cohort 
5, 1.33 mg/kg for cohort 6, 1.75 mg/kg for cohort 7, and a maximum dose level not to exceed 
1.75 mg/kg.  Once a minimum of 3 patients in a cohort have completed Study Day 29, the 
Safety Review Team (SRT) will review preliminary safety and hematologic response data and 
make recommendations to the Sponsor regarding whether or not to enroll an additional 3 
patients in that cohort, enroll a new cohort at a higher or lower dose, or proceed to the 
expansion cohort.   
Expansion cohort 1 (n= approximately 30) will be treated with ACE-536 at a starting dose level 
of 1.0 mg/kg.  Expansion cohort 1 will consist of a minimum of 10 patients who are transfusion 
dependent (TD) and 10 patients who are non-transfusion dependent (NTD), if feasible.   
Expansion cohort 2 will be treated with ACE-536 at a starting dose level of 1.0 mg/kg. 
Expansion cohort 2 will be divided into two groups designated expansion cohort 2A and 2B.  
The targeted accrual for each group will be 25 eligible and evaluable patients but permitted to 
range from 22 to 28 for administrative reasons.  The maximum number of patients treated will 
be 56. 
x Expansion cohort 2A: NTD patients with ≥ 15% ring sideroblasts in the bone marrow 
(RS+), less than 4 weeks of exposure to erythropoietin stimulating agents (ESAs), and 
serum erythropoietin (EPO) level ≤ 200 U/L at screening. 
x Expansion cohort 2B: Patients with < 15% ring sideroblasts in the bone marrow (RS-) 
and ≤ 6 RBC units in 8 weeks prior to C1D1.  This group will consist of a minimum of 
10 patients who have less than 4 weeks of exposure to ESAs and 5 patients who have 
received ≥ 4 weeks of treatment with ESAs. 
In the expansion cohorts, a patient’s dose level may be titrated based on criteria listed in 
Section 10.8.2, Expansion Cohorts Patient Dose Titration.  The maximum dose level given to a 
patient will not exceed the maximum dose level evaluated in the dose escalation cohorts.  
Patients in the expansion cohorts will be treated with up to 5 doses of ACE-536 administered 
once every 3 weeks.  

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Dose Escalation Table 
Cohortsa 
ACE-536 Dose Levelb (mg/kg) 
Number of 
Patients 
1 
0.125 
3-6 
2 
0.25 
3-6 
3 
0.50 
3-6 
4 
0.75 
3-6 
5 
1.0 
3-6 
6 
1.33 
3-6 
7 
1.75 
3-6 
Expansion 1 
1.0 
30 
Expansion 2 
1.0 
up to 56 
Planned Total:  
 
 
 
 
 
                         up to 128 
a Cohort escalation is based on SRT review and recommendation to enroll additional cohorts 
and/or the expansion cohorts. 
b The ACE-536 dose level for cohort 1 is 0.125 mg/kg.  The dose level indicated for all 
subsequent dose escalation cohorts is the maximum dose level that can be recommended by 
the SRT for escalation per the modified Fibonacci dose escalation scheme. Dose escalation 
will not exceed 1.75 mg/kg. 
Maximum Number of Patients (Planned): Up to 128 patients 
Duration of Treatment: The total duration of participation for a patient is approximately 28 
weeks (4 week screening period, 12 week treatment period and 12 week follow up period).  If a 
patient has a positive anti-drug antibody (ADA) result at the last visit, the patient may be asked 
to return for additional ADA testing every three months, until a negative result is obtained or 
the result is considered to be stabilized. 
Diagnosis and Main Criteria for Eligibility 
Inclusion Criteria: 
1. Men or women ≥ 18 years of age.  
2. Documented diagnosis of idiopathic/de novo MDS or non-proliferative chronic 
myelomonocytic leukemia (CMML) according to WHO criteria (white blood count [WBC] 
< 13,000/μL) that meets International Prognostic Scoring System (IPSS) classification 
(Appendix 2) of low or intermediate-1 risk disease as determined by microscopic and 
standard cytogenetic analyses of the bone marrow and peripheral complete blood count 
(CBC) obtained during screening. 
3. Anemia defined as: 

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x Mean hemoglobin concentration < 10.0 g/dL of 2 measurements (one performed 
within one day prior to Cycle 1 Day 1 and the other performed 7-28 days prior to 
Cycle 1 Day 1, not influenced by RBC transfusion within 7 days of measurement) 
for non-transfusion dependent patients (defined as having received ˂ 4 units of 
RBCs within 8 weeks prior to Cycle 1 Day 1) (Participation in all cohorts), OR 
x Transfusion dependent, defined as having received ≥ 4 units of RBCs within 8 weeks 
prior to Cycle 1 Day 1 (transfusion dependent patients are allowed in dose escalation 
cohorts and expansion cohort 1 only; patients with ≤ 6 units of RBCs within 8 weeks 
prior to Cycle 1 Day 1 may be allowed in cohort 2B). 
4. 
Serum erythropoietin levels and prior erythropoiesis-stimulating agent (ESA) treatment:  
x Dose escalation cohorts and expansion cohort 1 patients: Serum erythropoietin level 
> 500 U/L, OR, if ≤ 500 U/L, patient is non-responsive, refractory, or intolerant to 
erythropoiesis-stimulating agents (ESAs), or ESAs are contraindicated or 
unavailable. 
x Expansion cohort 2 patients: If patient is RS+ (defined as having ≥ 15% ring 
sideroblasts in the bone marrow), has less than 4 weeks’ exposure to ESAs and 
serum erythropoietin level ≤ 200 U/L. If a patient is RS- (defined as having < 15% 
ring sideroblasts in the bone marrow), prior ESA treatment and any serum 
erythropoietin level is allowed.   
5. 
No alternative treatment options, per national MDS guidelines, are available and/or 
appropriate for the patient, at the discretion of the investigator. 
6. ECOG performance status of 0, 1, or 2 (if related to anemia). 
7. Adequate renal (creatinine ≤ 2 x upper limit of normal [ULN]) and hepatic (total bilirubin 
< 2 x ULN and AST and ALT < 3 x ULN) function. 
8. Adequate transferrin saturation (≥ 15%), ferritin (≥ 50 μg/L), folate (≥ 4.5 nmol/L 
[≥ 2.0 μg/L]) and vitamin B12 (≥ 148 pmol/L [≥ 200 pg/mL]) during screening 
(supplementation and retest during screening is acceptable). 
9. Females of child bearing potential (defined as sexually mature women who have not 
undergone hysterectomy or bilateral oophorectomy, or are not naturally postmenopausal 
≥ 24 consecutive months) must have negative urine or blood pregnancy test prior to 
enrollment and use adequate birth control methods (abstinence, oral contraceptives, barrier 
method with spermicide, or surgical sterilization) during study participation and for 
12 weeks following the last dose of ACE-536.  Males must agree to use a latex condom 
during any sexual contact with females of child-bearing potential while participating in the 
study and for 12 weeks following the last dose of ACE-536, even if he has undergone a 
successful vasectomy.  Patients must be counseled concerning measures to be used to 
prevent pregnancy and potential toxicities prior to the first dose of ACE-536. 
10. Patients are able to adhere to the study visit schedule, understand and comply with all 
protocol requirements. 
11. Patient understands and is able to provide written informed consent. 

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Exclusion Criteria: 
1. Prior treatment with azacitidine (injectable or oral) or decitabine. 
2. Treatment within 28 days prior to Cycle 1 Day 1 with: 
x Erythropoiesis stimulating agent (ESA), 
x Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage 
colony-stimulating factor (GM-CSF), 
x Lenalidomide. 
3. Iron chelation therapy if initiated within 56 days prior to Cycle 1 Day 1. 
4. Treatment with another investigational drug or device, or approved therapy for 
investigational use ≤ 28 days prior to Cycle 1 Day 1, or if the half-life of the previous 
product is known, within 5 times the half-life prior to Cycle 1 Day 1, whichever is longer.  
5. Major surgery within 28 days prior to Cycle 1 Day 1.  Patients must have completely 
recovered from any previous surgery prior to Cycle 1 Day 1.  
6. Platelet count < 30 x 109/L.  
7. Any active infection requiring parenteral antibiotic therapy within 28 days prior to Cycle 1 
Day 1 or oral antibiotics within 14 days of Cycle 1 Day 1.  
8. History of stroke, deep venous thrombosis (DVT) or arterial embolism within 6 months 
prior to Cycle 1 Day 1. 
9. Known positive for human immunodeficiency virus (HIV), active infectious hepatitis B 
(HBV) or active infectious hepatitis C (HCV).  
10. Any malignancy other than MDS which has not been in remission and/or has required 
systemic therapy including radiation, chemotherapy, hormonal therapy or surgery, within 
the last year prior to Cycle 1 Day 1. 
11. Uncontrolled hypertension, defined as systolic blood pressure (BP) ≥ 150 mm Hg or 
diastolic BP ≥ 100 mm Hg. 
12. Pregnant or lactating females. 
13. History of severe allergic or anaphylactic reactions or hypersensitivity to recombinant 
proteins or excipients in the investigational drug.  
14. Any other condition not specifically noted above which, in the judgment of the investigator, 
would preclude the patient from participating in the study. 
15. Transfusion event within 7 days prior to Cycle 1 Day 1. 
16. Prior treatment with sotatercept (ACE-011) or ACE-536. 
17. Secondary MDS. 

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Investigational Product and Mode of Administration: 
ACE-536 drug product will be provided as either a sterile, liquid formulation or a lyophilized 
powder formulation for reconstitution with water.  Each single-use vial of the liquid formulation 
contains 25 mg of ACE-536 in a 0.5 mL Tris-buffered saline solution (50 mg/mL).  Each single-
use vial of the lyophilic formulation contains 50 mg ACE-536 for reconstitution with 1 mL 
water for injection to form a citrate-buffered solution (50 mg/mL). 
ACE-536 will be administered by subcutaneous (SC) injection on Day 1 of each 21 (±2) day 
cycle.   
Safety Evaluation and Dose Escalation: 
Safety will be evaluated by the Safety Review Team (SRT), which is comprised at minimum of 
the coordinating investigator, medical monitor, and an independent hematologist.  The role of 
the SRT will be described in greater detail in the SRT Charter.  The SRT will review safety data 
when a minimum of 3 patients in a cohort have completed Study Day 29, including 
dose-limiting toxicities (DLTs), adverse events (AEs), serious adverse events (SAEs), 
laboratory results (including hematology and chemistry), vital signs, and erythroid response 
data.  The SRT may make one or more of the following recommendations to the sponsor: 
x Enroll 3 additional patients in the current cohort. 
x Enroll 3 patients in a new cohort at a higher or lower dose level, not to exceed the 
modified Fibonacci dose escalation scheme (see Section 9.1). 
x Proceed to expansion cohort 1, with a recommended starting dose level not to exceed 
the maximum dose level evaluated in the dose escalation cohorts. 
x Postpone a decision pending collection of additional data from the current cohort. 
A DLT, using the current active minor version of the National Cancer Institute Common 
Toxicity Criteria for Adverse Events, version 4.0 (NCI-CTCAE v4.0), is defined as any of the 
following toxicities at any dose level occurring within 28 days of the first administered dose: 
x Treatment-related serious adverse event (SAE) of Grade ≥ 3 
x Treatment-related non-hematologic and non-infectious adverse event (AE) of Grade 
≥ 3 
x Treatment-related hematologic or infectious AE of Grade ≥ 4 
SRT recommendations to escalate or reduce the dose level of ACE-536 in a subsequent cohort 
or to continue dosing in the current cohort will be based in part upon the following criteria: 
x If a DLT occurs in 0 out of a minimum of 3 patients in a cohort within 28 days 
following the initial dose, dose escalation may occur. 
x If a DLT occurs in 1 out of 3 patients in a cohort within 28 days following the initial 
dose, an additional 3 patients should be enrolled in the current cohort. 
o If a DLT occurs in 1 out of 6 patients in a cohort within 28 days 
following the initial dose, dose escalation may occur. 

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x If a DLT occurs in ≥ 2 patients in a cohort within 28 days of the initial dose, the dose 
level for the next cohort (if any) should not be escalated; a lower dose level may be 
recommended. 
x If a hemoglobin increase of ≥ 2.0 g/dL occurs in ≥ 2 patients in a cohort within 28 
days of the initial dose, the dose level for the next cohort (if any) should not be 
escalated; a lower dose level may be recommended. 
In addition, during enrollment of the expansion cohorts, the SRT will review safety data 
periodically throughout the trial, including AEs, SAEs, laboratory results (including hematology 
and chemistry), vital signs, and erythroid response data. 
Criteria for Evaluation 
x Safety: All patients will be assessed for safety by monitoring adverse events, clinical 
laboratory tests, vital signs, ECG and physical examination.   
x Efficacy: Patients will be assessed for erythroid response for up to 24-weeks following 
initiation of treatment.  Erythroid response endpoints will be determined by monitoring 
hematologic laboratory values and RBC transfusions. 
Secondary efficacy endpoints will be assessed by examining other hematology, 
erythropoiesis, iron metabolism, and bone metabolism parameters. 
o Erythropoiesis parameters include serum erythropoietin levels, reticulocytes, and 
nucleated RBCs 
o Iron metabolism parameters include serum iron, total iron binding capacity 
(TIBC), transferrin, soluble transferrin receptor, ferritin, non-transferrin bound 
iron (NTBI), and hepcidin 
o Bone metabolism parameters include bone specific alkaline phosphatase (BSAP) 
and C-telopeptide of type I collagen (CTX) 
x Exploratory endpoints will include: 
o Evaluation of biomarkers related to the TGF-E superfamily 
o Evaluation of self-reported quality of life in the expansion cohort using tools 
including but not limited to the FACT-An questionnaire 
Statistical methods  
Sample Size Calculation:  
There is no formal sample size calculation for the dose escalation portion of the study.  A 
sample size of 30 evaluable patients in the expansion cohort 1 will provide approximately 90% 
power with 1-sided significance level of 0.05 to differentiate an erythroid response rate of 30% 
from a minimal erythroid response rate of 10% based on Fisher exact test. 
A sample size of 25 evaluable patients in each group of expansion cohort 2 will provide 
approximately 80% power with 1-sided significance level of 0.05 to differentiate an erythroid 
response rate of 30% from a minimal erythroid response rate of 10% based on Fisher exact test 

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Analysis Populations: 
For all analysis populations, patients will be analyzed according to assigned cohort. 
The Intent-to-Treat (ITT) Population: All patients enrolled in the study who have received at 
least one dose of ACE-536 (Safety Population). 
Efficacy Evaluable (EE) Population: All patients who received at least one dose of ACE-536 
and have 1) at least two hemoglobin assessments ≥ 14 days apart post-treatment OR, 2) at least 
8 consecutive weeks of transfusion frequency data between Cycle 1 Day 1 and End of 
Treatment visit in transfusion dependent patients. 
Safety Population: All patients who received at least 1 dose of ACE-536. 
Pharmacokinetics Population: All patients who have received at least 1 dose of ACE-536 and 
have sufficient pharmacokinetic samples collected and assayed for PK analysis. 
Efficacy/Pharmacodynamic Effects Analysis:  
The primary efficacy endpoint is modified erythroid response (mHI-E), defined as the 
proportion of patients who have a hemoglobin increase of ≥ 1.5 g/dL from baseline for ≥ 14 
days (in the absence of RBC transfusions) in non-transfusion dependent patients, or, a reduction 
of either ≥ 4 units or ≥ 50% of units of RBCs transfused over a period of 8 consecutive weeks, 
compared to the number of units of RBCs transfused in the 8 weeks immediately prior to Cycle 
1 Day 1  in transfusion dependent patients (defined as having received ≥ 4 units of RBCs within 
8 weeks prior to Cycle 1 Day 1).  The erythroid response will be summarized using both a point 
estimate and its exact 95% confidence interval based on binomial distribution.  The primary 
efficacy analysis will be performed using the EE population. 
No direct comparison testing with concurrent or historical controls will be performed.   
Baseline hemoglobin will be the average of at least two measures (not influenced by transfusion 
within 7 days of measurement); one measure performed within one day prior to Cycle 1 Day 1 
and the other performed 7-28 days prior to Cycle 1 Day 1.   
The secondary efficacy/pharmacodynamic analysis will be performed using the ITT and EE 
populations and include: 
x Modified erythroid response (mHI-E), as described above for primary endpoint, 
performed using the ITT population. 
x HI-E response rate as defined by IWG 2006 criteria (Appendix 5).  Improvements 
must last ≥ 8 weeks.  For non-transfusion dependent patients, an increase of 
≥ 1.5 g/dL from pre-treatment hemoglobin.  For transfused patients, a reduction by 
≥ 4 units of RBCs transfused (for a hemoglobin ≤ 9.0 g/dL) during any 8-week 
period on study, compared with the 8-week period prior to Cycle 1 Day 1.  
x Time to mHI-E and HI-E response and duration of mHI-E and HI-E response as per 
the IWG 2006 criteria. 
x Frequency of RBC transfusion, and rate of RBC transfusion independence in 
transfusion dependent patients. 
x Other pharmacodynamic (PD) endpoints including: 

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o Biomarkers for iron metabolism 
o Biomarkers for bone metabolism 
o Relationship of biomarkers to response 
o Rates of HI-N and HI-P 
The exploratory endpoints will include: 
o 
Evaluation of biomarkers related to the TGF-E superfamily. 
o 
Evaluation of self-reported quality of life in the expansion cohort using tools 
including but not limited to the FACT-An questionnaire 
All binary endpoints will be summarized using both a point estimate and its exact confidence 
interval based on the binomial distribution.  The time-to-event type secondary endpoints will be 
analyzed using Kaplan-Meier method to estimate the survival curve and median time to event 
and 95% confidence interval. 
Safety analysis: To assess clinical safety, adverse events, vital sign measurements and clinical 
laboratory information will be summarized.  Adverse Events will be coded using the Medical 
Dictionary for Regulatory Activities (MedDRA).  Changes from baseline for clinical laboratory 
values and vital signs will be summarized over time.  Descriptive statistics and shift tables will 
be generated as appropriate. 
Pharmacokinetics analysis: Non-compartmental PK parameters for ACE-536, such as 
maximum plasma concentration (Cmax), time to maximum plasma concentration (tmax), and area 
under the concentration/time curve (AUC), will be estimated.  Dose proportionality may be 
assessed using the exposure data (e.g. Cmax, AUC) after the first dose if sufficient dose levels are 
studied.  Descriptive statistics will be provided for serum concentrations and PK parameters.  
The relationship between ACE-536 exposure and response (i.e., safety, efficacy, and 
biomarkers) may be explored, if appropriate. 
Anti-drug antibody analysis: The results of anti-drug and neutralizing antibody testing for 
ACE-536 and human ActRIIB protein versus time will be presented.  Exploratory analysis will 
be performed on the potential effect of anti-drug antibodies on ACE-536 PK and drug exposure 
if anti-drug antibody tests are deemed positive. 

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2. 
SCHEDULE OF EVENTS 
 
 
Screen 
Treatment Period 
Follow up period 
Cycle 1 
Cycle 2 
Cycle 3 
Cycle 4 
Cycle 5 
EOT12 
Post-
Treatment 
Follow Up 
EOS13 
C1D12 
C1D8 
C1D11 
C1D15 C2D12,15 C2D8 
C2D15 
C3D12,15 
C3D8 C3D15 C4D12,15 
C4D8 C4D15 C5D12,15 C5D8 
C5D15 
Day 
113 
(± 7d) 
Day 
141 
(± 7d) 
Day 
169 
(± 7d) 
Day 
-28 
Day 
1 
Day 
8 
(± 1d) 
Day 
11 
(± 1d) 
Day 
15 
(± 1d) 
Day14 
22 
(± 2d) 
Day 
29 
(± 2d) 
Day 
36 
(± 2d) 
Day14 
43 
(± 2d) 
Day 
50 
(± 2d) 
Day 
57 
(± 2d) 
Day14 
64 
(± 2d) 
Day 
71 
(± 2d) 
Day 
78 
(± 2d) 
Day14 
85 
(± 2d) 
Day 
92 
(± 2d) 
Day 
99 
(± 2d) 
Informed consent 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Inclusion/Exclusion  
X 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Medical history 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
QoLQuestionnaires18 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
X18 
 
 
X19 
 
X 
Physical examination  
X 
X 
 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
X 
Vital signs1  
X 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
 
ECOG Status 
X 
 
 
 
 
 
 
 
X 
 
 
X 
 
 
 
 
 
X 
 
X 
ECG (12 lead) 
X 
 
 
 
 
X 
 
 
 
 
 
 
 
 
 
 
 
X 
 
 
Bone marrow 
aspirate/biopsy3  
X 
 
 
 
 
 
 
 
X3 
 
 
 
 
 
 
 
 
X 
 
 
Serum iron studies4 
X 
X 
 
 
 
X 
X 
 
X 
 
 
X 
 
 
X 
 
 
X 
X 
X 
Serum folate and B12 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Erythropoietin levels  
X 
X 
X 
 
X 
X 
 
 
 
 
 
X 
 
 
 
 
 
X 
X 
X 
Hematology5 
X 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Peripheral blood smear 
X 
X 
 
 
 
X 
 
 
 
 
 
 
 
 
X 
 
 
X 
 
 
Serum chemistry6 
X 
X 
 
 
X 
X 
X 
 
X 
X 
 
X 
X 
 
X 
X 
 
X 
 
X 
Urinalysis and Urine 
Chemistry7  
 
X 
 
 
 
X 
 
 
 
 
 
X 
 
 
 
 
 
X 
 
X 
Anti-drug antibody16 
 
X 
 
 
 
 
 
 
 
 
 
X 
 
 
 
 
 
X 
 
X16 
PK collection 
 
X 
X 
X 
X 
X 
X 
 
 
 
 
X 
 
 
X 
X 
X 
X 
X 
X 
PD biomarkers8 
 
X 
 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
X 
Bone biomarkers9 
 
X 
 
 
 
 
 
 
 
 
 
X 
 
 
 
 
 
X 
 
 
Pregnancy test10 
X 
X 
 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
 
X 
 
X 
Evaluate transfusion 
frequency11 
X 
X 
 
 
 
X 
 
 
X 
 
 
X2 
 
 
X 
 
 
X 
X 
X 
Concomitant 
medications and AEs 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Administer ACE-536 17 
 
X 
 
 
 
X14 
 
 
X14 
 
 
X14 
 
 
X14 
 
 
 
 
 

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1  Vital signs: Weight, heart rate, systolic and diastolic blood pressure, respiration rate and temperature (measured in degrees Celsius).  Height is 
measured only at Screening.   
2  Study procedures must be done prior to administration of study drug.    
3  Bone marrow aspirate/biopsy including cytogenetics at screening must be performed ≤ 3 months prior to C1D1 for evaluation of patient eligibility 
and other PD biomarkers to be determined (e.g., GDF15, GDF8, and GDF11).  
x 
For all patients, at the end of treatment visit, a bone marrow aspirate must be performed (a bone marrow biopsy is optional).  
x 
Dose escalation cohorts and expansion cohort 1 patients only: a bone marrow aspirate must be performed within 21 days after C3D1 (a bone 
marrow biopsy is not required). Note: A bone marrow aspirate is not required within 21 days after C3D1 for expansion cohort 2 patients. 
x 
Dose escalation cohorts and expansion cohort 1 patients only: If hemoglobin increases ≥ 2 g/dL, an optional bone marrow aspirate can be 
performed within 7 days of the result. 
4  Iron Studies: Serum iron, TIBC, transferrin, soluble transferrin receptor, NTBI, ferritin. 
5  Hematology: RBC, WBC with differential, hemoglobin, hematocrit, nRBC, reticulocyte count, platelet count, MCV, MCH, MCHC, and RDW.  On 
dosing days, hemoglobin values are to be drawn and resulted (up to 1 day) prior to dosing (see Section 10.8.1, Patient Dose Modification Rules).  
Historical hemoglobin data will be collected for 24 weeks, where available, prior to C1D1.  During the screening period, hemoglobin will be measured 
twice; one measure performed within one day prior to Cycle 1 Day 1 and the other performed 7-28 days prior to Cycle 1 Day 1.  Neither hemoglobin 
measure should be influenced by transfusion within 7 days of measurement. 
6  Chemistry: Sodium, potassium, AST, ALT, lactate dehydrogenase (LDH), total bilirubin, direct bilirubin, alkaline phosphatase, blood urea nitrogen 
(BUN)/urea, creatinine, GGT, calcium, phosphorus, glucose, amylase, lipase, total protein, albumin, and uric acid.  
7  Urinalysis by dipstick analysis (local lab): pH, specific gravity, protein, glucose, ketones, blood, leukocyte esterase, and nitrite, with microscopic 
examination if indicated.  Urine Chemistry (central lab): Microalbumin and creatinine. 
8   PD Biomarkers: Hepcidin, GDF15, GDF8, GDF11, and others to be determined. 
9   Bone Biomarkers: BSAP and CTX. Not required for expansion cohort 2 patients. 
10  Pregnancy test: (urine or serum) is required for female patients of child bearing potential at screening and prior to each dose of ACE-536. 
11  Transfusion history will be collected for 24 weeks, where available, prior to C1D1. 
12  End of Treatment (EOT): Should be performed 28 days (± 7 days) after the last dose of ACE-536.  Patients who discontinue treatment early should 
complete the end of treatment visit at the time of discontinuation and complete the post-treatment follow-up (PTFU) and EOS follow-up visits 28 days 
(± 7 days) and 56 days (± 7 days) after the EOT visit. 
13  End of Study (EOS): Should be performed 56 days (± 7 days) after the Day 113/EOT visit.  
14  Day 85 ± 2 days is the last possible study day that ACE-536 may be administered, regardless of the cycle. 
15  If a dose delay is required per the dose modification rules the patient will not be dosed.  The patient will return weekly to assess hematology results and 
adverse events until the patient is eligible to administer the next dose of ACE-536.  The patient should resume the study at the planned dosing cycle (e.g. if 
the patient missed a dose at C4D1, then they would resume dosing at C4D1 and not skip to C5D1).  Note: study days may vary if a dose delay occurred 
during the treatment period. 
16  If the patient has a positive ADA result at their last assessment, the patient may be asked to return approximately every three months for additional testing, 
until a negative result is obtained or the result is considered stabilized. 
17  For the first dose of ACE-536, dosing should occur after a minimum of 7 days post-transfusion and a minimum of 24 hours prior to a scheduled transfusion. 
18  Expansion cohorts only, administration of quality of life questionnaires.  Quality of life questionnaire not required for expansion cohort 2 patients at C5D1. 
19  Quality of life questionnaires should be completed at the EOT visit for patients that discontinue treatment early and for all expansion cohort 2 patients. 
 

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3. 
TABLE OF CONTENTS 
1. 
PROTOCOL SYNOPSIS .............................................................................................6 
2. 
SCHEDULE OF EVENTS .........................................................................................15 
3. 
TABLE OF CONTENTS ...........................................................................................17 
4. 
LIST OF ABBREVIATIONS AND DEFINITIONS OF TERMS.............................21 
5. 
ETHICS ......................................................................................................................24 
5.1. 
Institutional Review Board .........................................................................................24 
5.2. 
Ethical Conduct of the Study ......................................................................................24 
5.3. 
Patient Information and Consent ................................................................................24 
5.4. 
Patient Data Protection ...............................................................................................25 
6. 
INVESTIGATORS AND STUDY ADMINISTRATIVE STRUCTURE .................26 
7. 
INTRODUCTION ......................................................................................................27 
7.1. 
Overview of Target Indication ....................................................................................27 
7.2. 
Summary of Nonclinical Studies ................................................................................29 
7.2.1. 
Pharmacology Studies ................................................................................................29 
7.2.2. 
Toxicology Studies .....................................................................................................30 
7.3. 
Summary of Clinical Experience ................................................................................31 
7.4. 
Potential Risks of Human Use ....................................................................................32 
8. 
TRIAL OBJECTIVES ................................................................................................34 
8.1. 
Primary Objective .......................................................................................................34 
8.2. 
Secondary Objectives .................................................................................................34 
8.3. 
Exploratory Objective .................................................................................................34 
9. 
OVERALL STUDY DESIGN AND PLAN: DESCRIPTION ..................................35 
9.1. 
Study Design ...............................................................................................................35 
9.2. 
Discussion of Study Design ........................................................................................36 
9.3. 
Selection of Study Population ....................................................................................37 
9.3.1. 
Inclusion Criteria ........................................................................................................37 
9.3.2. 
Exclusion Criteria .......................................................................................................38 
9.4. 
Patient Treatment Discontinuation and Withdrawal Criteria .....................................39 
10. 
TREATMENT OF PATIENTS ..................................................................................41 
10.1. 
Selection and Timing of Dose for Each Patient ..........................................................41 
10.2. 
Concomitant Medications ...........................................................................................41 

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10.2.1. 
Other Treatments for MDS .........................................................................................41 
10.2.2. 
RBC Transfusions .......................................................................................................41 
10.3. 
Treatment Compliance ................................................................................................42 
10.4. 
Randomization ............................................................................................................42 
10.5. 
Treatments Administered ............................................................................................42 
10.6. 
Dose-Limiting Toxicity Definition .............................................................................42 
10.7. 
Safety Evaluation and Dose Escalation ......................................................................42 
10.8. 
Patient Dose Modification and Titration ....................................................................43 
10.8.1. 
Patient Dose Modification Rules ................................................................................44 
10.8.2. 
Expansion Cohorts Patient Dose Titration .................................................................45 
10.9. 
Other Considerations for Dose Modification, Delay or Discontinuation ...................46 
11. 
STUDY PROCEDURES ............................................................................................47 
11.1. 
Written Informed Consent ..........................................................................................47 
11.2. 
Clinical Laboratory Tests ...........................................................................................47 
11.3. 
Other Safety Assessments ...........................................................................................48 
11.4. 
Pharmacokinetic and Pharmacodynamic Assessments ..............................................48 
11.4.1. 
Pharmacokinetic Assessments ....................................................................................48 
11.4.2. 
Pharmacodynamic Evaluations ...................................................................................48 
12. 
STUDY SCHEDULE .................................................................................................49 
12.1. 
Screening ....................................................................................................................49 
12.2. 
Dosing Days and Interim Visits ..................................................................................49 
12.3. 
Day 85 .........................................................................................................................50 
12.4. 
End of Treatment Visit ...............................................................................................50 
12.5. 
Post-Treatment Follow Up Visit .................................................................................51 
12.6. 
End of Study Visit ......................................................................................................51 
12.7. 
Termination of Study ..................................................................................................51 
13. 
STUDY DRUG MATERIALS AND MANAGEMENT ...........................................52 
13.1. 
Study Drug ..................................................................................................................52 
13.2. 
Study Drug Packaging and Labeling ..........................................................................52 
13.3. 
Study Drug Storage .....................................................................................................52 
13.4. 
Study Drug Preparation ..............................................................................................52 
13.5. 
Administration ............................................................................................................52 
13.6. 
Study Drug Accountability .........................................................................................52 

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13.7. 
Study Drug Handling and Disposal ............................................................................53 
14. 
ASSESSMENT OF SAFETY .....................................................................................54 
14.1. 
Adverse Event Definitions ..........................................................................................54 
14.2. 
Pregnancy and In Utero Drug Exposure .....................................................................55 
14.3. 
Severity .......................................................................................................................56 
14.4. 
Relationship to Study Drug ........................................................................................56 
14.5. 
Documentation and Methods of Reporting of Adverse Events by 
Investigator .................................................................................................................57 
14.5.1. 
Documentation of Serious Adverse Events ................................................................57 
14.6. 
Reporting Period and Monitoring of Patients with Adverse Events ...........................58 
14.7. 
Notification about Serious Adverse Events ................................................................58 
14.7.1. 
Safety Reporting to Health Authorities, Independent Ethics Committees 
Institutional Review Boards and Investigators ...........................................................58 
15. 
STATISTICS ..............................................................................................................60 
15.1. 
Analysis Populations ..................................................................................................60 
15.2. 
Statistical Plan ............................................................................................................60 
15.2.1. 
Patient Accountability and Demographics .................................................................60 
15.2.2. 
Primary Efficacy Analysis ..........................................................................................60 
15.2.3. 
Secondary Analysis ....................................................................................................61 
15.2.4. 
Pharmacokinetics Analysis .........................................................................................62 
15.2.5. 
Anti-drug Antibody Analysis .....................................................................................62 
15.3. 
Determination of Sample Size ....................................................................................62 
15.4. 
Interim Analysis ..........................................................................................................62 
15.5. 
Deviation from Original Analysis Plan ......................................................................62 
16. 
SOURCE DOCUMENTATION AND INVESTIGATOR FILES .............................63 
16.1. 
Study Monitoring ........................................................................................................63 
16.2. 
Audits and Inspections ................................................................................................63 
17. 
QUALITY CONTROL AND QUALITY ASSURANCE .........................................63 
17.1. 
Data Quality Control and Quality Assurance .............................................................63 
17.1.1. 
Investigator Responsibility .........................................................................................63 
17.1.2. 
Protocol Modifications ...............................................................................................63 
18. 
CONFIDENTIALITY ................................................................................................64 
19. 
PUBLICATION POLICY ..........................................................................................64 
20. 
PROTOCOL AMENDMENTS ..................................................................................64 

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21. 
DATA HANDLING AND RECORDKEEPING .......................................................65 
21.1. 
Case Report Form Completion ...................................................................................65 
21.2. 
Retention of Records ..................................................................................................65 
22. 
STUDY FINANCE AND INSURANCE ...................................................................66 
22.1. 
Study Finance .............................................................................................................66 
22.2. 
Insurance .....................................................................................................................66 
23. 
REFERENCES ...........................................................................................................67 
24. 
APPENDICES ............................................................................................................69 
24.1. 
Appendix 1: WHO Classification and Criteria for the Myelodysplastic 
Syndromes26 ................................................................................................................69 
24.2. 
Appendix 2: International Prognostic Scoring System (IPSS) for 
Myelodysplastic Syndromes (MDS)4 .........................................................................71 
24.3. 
Appendix 3: ECOG Performance Status27 ..................................................................72 
24.4. 
Appendix 4: International Working Group (IWG) Criteria - Erythroid 
Response Evaluation10 ................................................................................................73 
24.5. 
Appendix 5: National Cancer Institute (NCI) Common Terminology 
Criteria for Adverse Events (CTCAE) Version 4.0 ....................................................74 
 

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4. 
LIST OF ABBREVIATIONS AND DEFINITIONS OF TERMS 
Abbreviation 
Definition 
ActRIIB 
Activin receptor IIB 
ADA 
Anti-drug antibody 
AE 
Adverse event 
ALT 
Alanine aminotransferase 
AML 
Acute myeloid leukemia 
AST 
Aspartate aminotransferase 
AUC 
Area under the concentration-time curve 
BFU-E 
Burst forming units - erythroid 
BMP 
Bone morphogenetic protein 
BP 
Blood pressure 
BSAP 
Bone-specific alkaline phosphatase 
BSC 
Best supportive care 
BUN 
Blood urea nitrogen 
CXDY 
Cycle X Day Y 
CBC 
Complete blood count 
CFU-E 
Colony forming units – erythroid 
Cmax 
Maximum concentration 
CMML 
Chronic myelomonocytic leukemia 
CREAT 
Creatinine 
CRF 
Case report form 
CRO 
Contract research organization 
CTX 
C-terminal type I collagen telopeptide 
DLT 
Dose-limiting toxicity 
DVT 
Deep venous thrombosis 
ECD 
Extracellular domain 
ECG 
Electrocardiogram 
ECOG 
Eastern Cooperative Oncology Group 
EE 
Efficacy Evaluable 
ESA 
Erythropoiesis stimulating agent 
EOS  
End of study  

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Abbreviation 
Definition 
EPO 
Erythropoietin 
EOT 
End of treatment  
FACS 
Fluorescence activated cell sorting 
FACT-An 
Functional Assessment of Cancer Therapy-Anemia Scale 
FDA 
United States Food and Drug Administration 
GCP 
Good clinical practices 
G-CSF 
Granulocyte colony-stimulating factor 
GDF 
Growth and differentiation factor 
GGT 
Gamma-glutamyl transpeptidase 
GM-CSF 
Granulocyte-macrophage colony-stimulating factor 
HBV 
Hepatitis B virus 
HCV 
Hepatitis C virus 
Hgb 
Hemoglobin 
HI-E 
Erythroid response   
HI-N 
Neutrophil response 
HI-P 
Platelet response 
HIV 
Human immunodeficiency virus 
IB 
Investigator brochure 
ICF 
Informed consent form 
ICH 
International conference on harmonisation 
IEC 
Independent ethics committee 
IgG1 
Immunoglobulin G1 
ITT 
Intent-to-Treat 
IPSS 
International Prognostic Scoring System 
IWG 
International Working Group  
IB 
Investigator’s brochure 
IV 
Intravenous 
KD 
Dissociation constant 
LDH 
Lactate dehydrogenase 
mHI-E 
Modified erythroid response 
MedDRA 
Medical Dictionary for Regulatory Activities 
MCH 
Mean corpuscular hemoglobin 

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Abbreviation 
Definition 
MCHC 
Mean corpuscular hemoglobin concentration 
MCV 
Mean corpuscular volume 
MDS 
Myelodysplastic syndromes 
NCI-CTCAE 
National Cancer Institute-Common terminology criteria for adverse events 
nRBC 
Nucleated red blood cell 
NTBI 
Non-transferrin bound iron 
ORR 
Objective response rate 
PD 
Pharmacodynamic 
PFS 
Progression free survival 
PHI 
Protected health information 
PK 
Pharmacokinetic 
PTFU 
Post-Treatment Follow-up 
QoL 
Quality of Life 
RBC 
Red blood cell 
RDW 
Red blood cell distribution width 
SAE 
Serious adverse event 
SAP 
Statistical analysis plan 
SC 
Subcutaneous 
SD 
Standard deviation 
SRT 
Safety review team 
SUSAR 
Suspected unexpected serious adverse reaction 
T1/2 
Elimination half-life 
TGF-β 
Transforming growth factor beta 
TIBC 
Total iron binding capacity 
Tmax 
Time to maximum concentration 
ULN 
Upper limit of normal 
WBC 
White blood cell 
WHO 
World Health Organization 

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5. 
ETHICS 
5.1. 
Institutional Review Board 
The investigator will submit this protocol, any protocol modifications, and the patient 
Informed Consent Form (ICF) to be used in this study to the appropriate IEC for review and 
approval.  A letter confirming IEC approval of the protocol and ICF as well as a statement that 
the IEC is organized and operates according to Good Clinical Practice (GCP) and the 
applicable laws and regulations, must be forwarded to the sponsor prior to the enrollment of 
patients into the study.  A copy of the approved ICF will also be forwarded to the sponsor.  
Appropriate reports on the progress of the study will be made to the IEC and the sponsor by 
the principal investigator in accordance with applicable governmental regulations and in 
agreement with the policy established by the sponsor. 
5.2. 
Ethical Conduct of the Study 
The sponsor and the investigator must comply with all instructions, regulations, and 
agreements in this protocol and in the applicable International Conference on Harmonisation 
(ICH) and GCP guidelines, and must also conduct the study in accordance with local 
regulations.   
5.3. 
Patient Information and Consent 
Informed written consent is required from each patient prior to any testing under this protocol, 
including screening tests and evaluations.  The ICF, as specified by the study center’s IEC, 
must follow the Protection of Human Patients regulations listed in the Code of Federal 
Regulations, Title 21, Part 50.  The principles of informed consent in the Declaration of 
Helsinki should be implemented in this clinical study and should comply with local and 
national regulations.  The consent forms must be in a language fully comprehensible to the 
prospective subject.  Information should be given in both oral and written form whenever 
possible and deemed appropriate by the IEC. 
The background of the proposed study and the benefits and risks of the procedures and study 
must be explained to the patients.  It is the responsibility of the investigator to obtain consent 
and to provide the patient with a copy of the signed and dated ICF.  Confirmation of a patient’s 
informed consent must also be documented in the patient’s medical record prior to any testing 
under this protocol, including screening tests and evaluations. 
All ICFs used in this study must be approved by the appropriate IEC and by the Sponsor or 
designee.  The ICF must not be altered without the prior agreement of the relevant IEC and the 
Sponsor.   

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5.4. 
Patient Data Protection 
Prior to any testing under this protocol, including screening tests and evaluations, patients must 
authorize the release and use of protected health information (PHI), as required by local law. 
The patient will not be identified by name in the case report form (CRF) or in any study 
reports.  These reports will be used for research purposes only.  The Sponsor, its designee, and 
various government health agencies may inspect the records of this study.  Every effort will be 
made to keep the patient’s personal medical data confidential. 

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6. 
INVESTIGATORS AND STUDY ADMINISTRATIVE 
STRUCTURE 
Acceleron Pharma is the sponsor for this trial.  The sponsor will serve as the medical monitor 
for the study.  The sponsor or designee also will manage the conduct of the trial and provide 
for clinical monitoring, data management, biostatistics, and report writing.  Clinical monitors 
will monitor each study center on a periodic basis and verify source documentation for each 
patient.  The sponsor’s pharmacovigilance representative will be responsible for timely 
reporting of Serious Adverse Events (SAEs) to health authorities as required. 

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7. 
INTRODUCTION 
ACE-536 is a recombinant fusion protein consisting of a modified form of the extracellular 
domain (ECD) of the human activin receptor type IIB (ActRIIB) linked to the human IgG1 Fc 
domain.  The ActRIIB receptor and its ligands are members of the TGFβ superfamily, a group 
of proteins involved in the development, differentiation, and/or maturation of various tissues.  
No species differences have been described in the ligand-receptor interactions among members 
of the TGFβ family as the ligands and receptors are highly conserved across species.1  Thus, 
observations from pharmacology studies of ACE-536 or its murine analog RAP-536 in animal 
models provide significant insight into the potential of ACE-536 to treat human disease. 
Members of the TGFβ family are reported to play a role in red blood cell (RBC) development, 
although the specific ligands and receptors that influence the process of erythropoiesis are not 
completely understood.  In nonclinical experiments, ACE-536 has been shown to bind with 
high affinity to some TGFβ ligands (e.g., GDF8, GDF11, BMP6 and activin B) but 
substantially less, or not at all, to others (e.g., BMP10 and activin A).  The emerging body of 
evidence on ACE-536 suggests that its mechanism of action is distinct from that of 
erythropoietin (EPO), and involves acceleration of the later maturation phase of erythrocyte 
development. 
The nonclinical pharmacology data using ACE-536/RAP-536 demonstrate that the molecule 
can produce a rapid and robust erythroid response in a variety of settings, and that this 
response is due to its influence on the differentiation of hematopoietic cell types in the later 
stages of erythropoiesis.  In contrast, EPO is active in the early, proliferative stage of 
erythropoiesis.  ACE-536 has shown activity in animal models of various conditions in which 
anemia contributes significantly to disease morbidity, including anemia associated with 
ineffective erythropoiesis.  In a murine model of myelodysplastic syndrome (MDS), RAP-536 
was shown to increase RBC and Hgb in early, mid and late stage disease; normalize myeloid: 
erythroid ratio; increase maturation of erythroid precursors; and decrease erythroid 
hyperplasia. 
7.1. 
Overview of Target Indication 
The target indication for ACE-536 is for the treatment of anemia in patients with 
myelodysplastic syndromes (MDS).  MDS are heterogeneous diseases characterized by 
abnormal proliferation and differentiation of erythropoietic precursor cells in the bone marrow, 
resulting in peripheral cytopenias; approximately 25-30% of patients with MDS have 
progression to acute myeloid leukemia (AML).2,3, 4  
MDS is a hematologic neoplasm primarily of the elderly, with 86% of MDS cases diagnosed in 
individuals age ≥ 60 years (median age at diagnosis, 76 years).  According to the SEERS data, 
approximately 12,000 patients are diagnosed with MDS per year in the United States and 
approximately 20,000 in Europe.5  The incidence rate of MDS in Germany is 4.1 per 100,000,6 
with a median age between 68 and 73 years.7  Looking at a subset of patients in Dusseldorf, the 
incidence of MDS is higher in men than women with the incidence and prevalence increasing 
dramatically with age.8  With the number of people over the age of 65 expected to rise over the 
next four decades in developed countries such as Germany, there will likely be a correlated rise 
in the number of patients diagnosed with MDS.9  

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MDS classification systems have been established to address the heterogeneity of MDS.  The 
International Prognostic Scoring System (IPSS) (Appendix 2) categorizes the different types of 
MDS by the number of bone marrow blasts, the number of cytopenias, and bone marrow 
cytogenetics to predict survival and potential progression to AML.4  The IPSS has four risk 
categories: low, intermediate-1, intermediate-2, and high.  Standardized response criteria for 
clinical trials have been established to evaluate response to the treatment.  The International 
Working Group (IWG) criteria is an evaluation tool often used to quantify the quality of a 
response to treatment and for the consideration of risk based treatment goals.10 
Therapy for MDS is based on patient age, IPSS risk category, and ECOG performance status 
(Appendix 3).11  MDS can be cured by stem cell transplantation; however, most patients 
cannot receive the transplant due to age or limited availability of appropriate donors.  
Therefore, supportive care is often provided for these patients.  The median survival rate for 
low risk MDS is 5.7 years and decreases to 3.5 years for patients with intermediate-1 risk 
MDS.4,12 
Anemia is the predominant cytopenia observed in MDS and is present in 85% of MDS patients 
at the time of diagnosis.13  Refractory anemia resulting from ineffective erythropoiesis is a 
major cause of morbidity and mortality in MDS patients.14  Supportive care with blood 
transfusions, erythropoiesis stimulating agents (ESAs), and other growth factors are used to 
treat anemia.  
Clinical studies have demonstrated that ESAs can provide clinical benefit to MDS patients by 
reducing the need for red blood cell transfusions.  Only one third of unselected patients treated 
with ESAs have an erythroid response.15,16  A significant number of MDS patients have serum 
erythropoietin (EPO) levels in excess of 500 U/L, indicating the anemia in MDS is not a 
consequence of endogenous EPO deficiency and unlikely to respond to exogenous EPO.17  
This observation suggests that impaired erythropoiesis in MDS patients occurs downstream of 
the steps that are regulated by EPO.  Ineffective erythropoiesis leading to anemia in MDS 
patients appears to be associated with intramedullary apoptosis of cells during the later stages 
of erythrocyte development beyond those regulated by EPO.18,19 
The azanucleosides, azacitidine (Vidaza®) and decitabine (Dacogen®), and lenalidomide 
(Revlimid®) have demonstrated activity in patients with MDS.20,21  A randomized phase 3 trial 
comparing azacitidine with best supportive care (BSC) demonstrated hematologic 
improvement, delayed progression to AML or death and improved quality of life.22  A second 
phase 3 trial demonstrated improved 2-year overall survival.23  A phase 3 study comparing 
decitabine with BSC showed improved overall response rate (ORR) and progression-free 
survival (PFS).24 
MDS represents a significant hematologic malignancy of the elderly population, contributing 
to serious comorbidities and increased health care use and cost.  Given the high prevalence of 
cardiac and other comorbidities in this patient population, and the strong association between 
comorbidities, transfusional support, and iron overload, strategies to improve anemia and 
maintain adequate iron balance are critical in managing patients with MDS.2  

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7.2. 
Summary of Nonclinical Studies 
A brief summary of key findings from pharmacology and toxicology studies is provided 
below.   A comprehensive review of ACE-536, as well as details regarding the information 
summarized below, is provided in the Investigators Brocure (IB).  The ACE-536 IB should be 
reviewed prior to initating the study.  
7.2.1. 
Pharmacology Studies 
In vitro and in vivo pharmacology studies have been conducted with ACE-536 or its murine 
orthologue, RAP-536.  The use of RAP-536 allows longer term pharmacology studies in 
rodents without the confounding influence of immune reactivity. 
A total of 26 potential ligands within the TGFβ superfamily were assessed for their in vitro 
binding specificity and affinity to ACE-536 by surface plasmon resonance (Biacore).  Among 
the ligands examined, GDF8, GDF11, BMP6 and activin B bound to ACE-536 with the 
highest affinities at 37°C (KD values in the sub-nanomolar range).  Further studies using a cell 
line reporter gene assay to assess signaling through the activin receptor demonstrate that 
signaling by GDF11 and GDF8 was inhibited by ACE-536. 
During the course of early nonclinical pharmacology studies, an observation of a rapid, robust, 
and sustained increase in erythropoiesis in animals treated with ACE-536 was made.  The 
effect of ACE-536 on bone marrow erythroid progenitor cells in mice was assessed by FACS 
analysis.  Results demonstrate that the increase in RBC results as a consequence of a decrease 
of basophilic erythroblasts and a coordinate increase in subsequent, later stage polychromatic 
and orthochromatic erythroblasts as well as nucleated reticulocytes in both the bone marrow 
and spleen.  Separate studies have confirmed that the increase in RBC occurs without affecting 
the populations of erythropoietin (EPO) responsive cells (BFU-E and CFU-E). 
RAP-536 was evaluated for its ability to improve dyserythropoiesis in the NUP98-HOXD13 
mouse model of MDS.25  Over 20 chromosomal translocations involving the NUP98 gene have 
been identified across a number of hematologic malignancies in humans.  Among these, the 
NHD13 fusion gene has been reported in patients with MDS and acute myeloid leukemia 
(AML).  The NUP98-HOXD13 mouse model reliably recapitulates many of the features of 
MDS in humans, including peripheral blood cytopenias, bone marrow dysplasia, apoptosis of 
bone marrow progenitor cells, and progression to acute leukemia in about 60% of the mice.  
Development and progression of MDS in NUP98-HOXD13 mice is relatively rapid, resulted in 
a shortened lifespan of ~14 months. NUP98-HOXD13 mice were treated with RAP-536 twice 
weekly for 6-8 weeks beginning at 4, 8 or 10 months of age, corresponding to early-, mid- and 
late-stage disease.  Results demonstrate significant improvement in hematologic indices 
following RAP-536 treatment, independent of when treatment is initiated.  Figure 1 illustrates 
the response to RAP-536 treatment in MDS mice.  Further, ACE-536 treatment led to the 
normalization of the M:E ratio in MDS mice. 

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In the three month monkey study, there was a dose dependent increase in BUN and creatinine. 
Histologic changes in the kidney consisted of membranoproliferative glomerulonephritis.  This 
finding was dose dependent in both incidence and severity and was not sex dependent.  At the 
highest dose (30 mg/kg), glomerulonephritis was accompanied by fibrosis and hemorrhage of 
the interstitium.  The presence of immune complexes in renal tissue was demonstrated by 
immunohistochemistry and is suggestive of immune complex deposition; however, a direct 
effect of the drug cannot be excluded.   
7.3. 
Summary of Clinical Experience 
The safety, tolerability, pharmacokinetics, and pharmacodynamic effects of ACE-536 was 
evaluated in healthy postmenopausal women in a phase 1, randomized, double-blind, 
placebo-controlled, multiple ascending dose study (Study A536-02).  The primary objective of 
the study was to evaluate the safety and tolerability of ACE-536 in this population.  Secondary 
objectives of the study are to examine the pharmacokinetic parameters and pharmacodynamic 
effects of ACE-536.  Preliminary data from Study A536-02 as of 05 July 2012 are summarized 
below. 
A total of 32 subjects were enrolled.  The study consisted of 4 cohorts (0.0625 mg/kg x 2 
doses, 0.125 mg/kg x 1 dose, 0.125 mg/kg x 2 doses, and 0.25 mg/kg x 2 doses).  Subjects in 
each cohort were randomized and receive either ACE-536 or placebo (6 active and 2 placebo 
subjects per cohort).  Doses were administered SC on Day 1 and Day 15.  One subject in the 
third cohort and 5 subjects in the fourth cohort received only one dose of ACE-536. 
The mean (SD) age for subjects in this study was 59.4 (5.8) years.  Mean baseline hemoglobin 
level was 13.2 (0.6) g/dL.  Preliminary analysis of PK data demonstrated that maximum 
ACE-536 concentration (Cmax) and area under the curve (AUC0-14d) after the first dose were 
generally dose-proportional from 0.0625 to 0.25 mg/kg.  The mean time to maximum 
concentration (tmax) ranged from 7.7 to 11.7 days and the mean elimination half-life (t½) ranged 
from 15.5 to 18.5 days. Pharmacokinetic results support SC dosing of ACE-536 every 3 weeks.    
ACE-536 was generally safe and well-tolerated in this study of healthy postmenopausal female 
subjects.  No serious or severe adverse events were reported.  The majority of AEs were 
considered mild in severity.  Adverse events that were considered probably or possibly related 
to study drug included injection site hemorrhage (3 subjects on active drug), injection site 
macule (2 subjects), and dry skin, hyperesthesia, muscle spasms, myalgia, generalized pruritis, 
and papular rash (1 subject each). 
Consistent with results from the nonclinical pharmacology studies, ACE-536 administration 
resulted in a mean maximum increase in hemoglobin (at any timepoint during the study) of 
1.3 g/dL in the 0.25 mg/kg group.  The maximum hemoglobin increase from baseline at any 
timepoint for patients in the 0.25 mg/kg group ranged from 0.6 to 2.0 g/dL.  The mean 
hemoglobin increase from baseline in that treatment group was at least 0.6 g/dL from Day 8 
through Day 57, compared with a mean hemoglobin decrease from baseline in the placebo 
group of up to 0.6 g/dL through Day 43 (Figure 2).   
 

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Figure 2: 
Mean (±SD) Change from Baseline of Plasma Hemoglobin (g/dL) in 
Healthy Volunteers Treated with One or Two Doses of ACE-536 
 
The preliminary results from this phase 1 study suggest a positive effect of 0.25 mg/kg 
ACE-536 on increasing hemoglobin in healthy subjects.  Doses up to 0.25 mg/kg were 
generally safe and well-tolerated.   
7.4. 
Potential Risks of Human Use 
Increases in hematologic parameters (RBC, hemoglobin, hematocrit, reticulocytes) are 
expected pharmacologic effects of ACE-536 treatment.  Increases in systolic and diastolic 
blood pressures may occur in concert with increases in hemoglobin values.  Excessive or rapid 
increases in hemoglobin or blood pressure may occur and will be monitored.  Dose 
modifications rules for individual subjects and dose escalation/reduction rules will be utilized 
to minimize risks associated with increased RBC parameters. 
Adverse events observed in the Phase 1 study in healthy volunteers that were considered 
probably or possibly related to study drug included injection site hemorrhage, injection site 
macule, and dry skin, hyperesthesia, muscle spasms, myalgia, generalized pruritis, and papular 
rash. 
Membranoproliferative glomerulonephritis was observed in both rats and monkeys, likely 
secondary to immune complex deposition.  These findings were associated with increases in 
serum BUN and creatinine.  The presence of immune complexes in renal tissue from monkeys 
treated with ACE-536 was demonstrated by immunohistochemistry.  
The growth of heart and lungs was slightly reduced in rats exposed to ACE-536 as compared 
with control animals; these decreased heart and lung weights were reversible and there was no 

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corresponding histology finding.  These findings were not replicated in the monkey toxicology 
studies; the potential for these adverse effects in humans is unknown.  
Based on rat toxicology studies, treatment with ACE-536 may affect the adrenal gland.  These 
findings were specific to the rat as they were not replicated in the monkey toxicology studies.  
As with all biologics, there is the potential for anti-drug antibodies that can be associated with 
increased drug clearance and hypersensitivity reactions.  Anti-drug antibody formation against 
ACE-536 as well as human ActRIIB protein will be monitored in the initial clinical studies. 
Reproductive toxicity studies are currently ongoing and therefore ACE-536 should not be 
administered to pregnant women.  Male and female subjects of childbearing potential 
participating in studies of ACE-536 must be willing to abstain from sexual intercourse or use 
adequate contraception during the treatment and for at least 12 weeks following treatment 
discontinuation.  The effects of ACE 536 on the developing fetus are unknown.  It is not 
known if ACE-536 is secreted in milk; therefore, ACE-536 should not be administered to 
nursing mothers.  
It is unknown if humans will experience any of the effects of ACE-536 that were noted in the 
rat and monkey toxicology studies.  Safety effects will be monitored closely through adverse 
event reporting, clinical laboratory tests, vital signs, and physical examinations.  
A comprehensive review of ACE-536, as well as details regarding the information summarized 
above, is provided in the Investigators Brocure (IB).  The ACE-536 IB should be reviewed 
prior to initating the study.  

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8. 
TRIAL OBJECTIVES  
8.1. 
Primary Objective  
x To evaluate the proportion of patients who have a modified erythroid response 
(mHI-E), defined as a hemoglobin increase of ≥ 1.5 g/dL from baseline for ≥ 14 
days (in the absence of red blood cell [RBC] transfusions) in non-transfusion 
dependent patients, or, a reduction of either ≥ 4 units or ≥ 50% of units of RBCs 
transfused compared to pre-treatment in transfusion dependent patients.  
8.2. 
Secondary Objectives 
x To evaluate safety and tolerability of ACE-536 
x To examine rates of erythroid, neutrophil and platelet (HI-E, HI-N and HI-P) 
responses (International Working Group [IWG] 2006 criteria) 
x To evaluate time to mHI-E and HI-E response and duration of mHI-E and HI-E 
response 
x To evaluate frequency of RBC transfusions in transfusion dependent patients 
x To examine the pharmacokinetic (PK) profile of ACE-536 
x To examine other pharmacodynamic (PD) effects (e.g., iron metabolism, 
erythropoietin, reticulocytes, and bone biomarkers) 
8.3. 
Exploratory Objective  
x To evaluate biomarkers related to the TGFE superfamily 
x Evaluation of self-reported quality of life in the expansion cohort using tools 
including but not limited to the FACT-An questionnaire 

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9. 
OVERALL STUDY DESIGN AND PLAN: DESCRIPTION 
This is a phase 2, open-label, multiple ascending dose study to evaluate the effects of ACE-536 
on anemia in patients with low or intermediate-1 risk MDS who are not currently receiving 
treatment with an erythropoiesis-stimulating agent (ESA).  
9.1. 
Study Design  
Patients who meet the study eligibility criteria will be enrolled within 28 days of screening. 
Patients in all cohorts will receive ACE-536, administered subcutaneously (SC), every 3 weeks 
for up to 5 cycles. Dose delay(s) and dose reduction(s) may be required for individual patients 
as outlined in the Patient Dose Modification Rules (Section 10.8.1).   
Each dose escalation cohort will consist of a minimum of 3 patients.  The dose level of 
ACE-536 for the first cohort will be 0.125 mg/kg and the dose level(s) for subsequent cohort(s) 
will follow a modified Fibonacci dose escalation scheme with a maximum dose level of 
0.25 mg/kg for cohort 2, 0.50 mg/kg for cohort 3, 0.75 mg/kg for cohort 4, 1.0 mg/kg for 
cohort 5, 1.33 mg/kg for cohort 6, 1.75 mg/kg for cohort 7, and a maximum dose level not to 
exceed 1.75 mg/kg.  Once a minimum of 3 patients in a cohort have completed Study Day 29, 
the Safety Review Team (SRT) will review preliminary safety and hematologic response data 
and make recommendations to the Sponsor regarding whether or not to enroll an additional 3 
patients in that cohort, enroll a new cohort at a higher or lower dose, or proceed to expansion 
cohort 1.  
Expansion cohort 1 (n= approximately 30) will be treated with ACE-536 at a starting dose 
level of 1.0 mg/kg.  Expansion cohort 1 will consist of a minimum of 10 patients who are 
transfusion dependent (TD) and 10 patients who are non-transfusion dependent (NTD), if 
feasible.   
Expansion cohort 2 will be treated with ACE-536 at a starting dose level of 1.0 mg/kg. 
Expansion cohort 2 will be divided into two groups designated expansion cohort 2A and 
2B.  The targeted accrual for each group will be 25 eligible and evaluable patients but 
permitted to range from 22 to 28 for administrative reasons. The maximum number of patients 
treated will be 56.  
x Expansion cohort 2A: NTD patients with ≥ 15% ring sideroblasts in the bone marrow 
(RS+), less than 4 weeks of exposure to erythropoietin stimulating agents (ESAs) and 
serum erythropoietin (EPO) level ≤ 200 U/L at screening. 
x Expansion cohort 2B: Patients with < 15% ring sideroblasts in the bone marrow (RS-) 
and ≤ 6 RBC units in 8 weeks prior to C1D1.  This group will consist of a minimum of 
10 patients who have less than 4 weeks of exposure to ESAs and 5 patients who have 
received ≥ 4 weeks of  treatment with ESAs. 
In the expansion cohorts, a patient’s dose level may be titrated based on criteria listed in 
Section 10.8.2 , Expansion Cohorts Patient Dose Titration.  The maximum dose level given to 
a patient will not exceed the maximum dose level evaluated in the dose escalation cohorts.  
Patients in the expansion cohort will be treated with up to 5 doses of ACE-536 administered 
once every 3 weeks. 

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Table 2: 
Dose Escalation 
Cohorta 
ACE-536  
Dose Levelb (mg/kg) 
Number of 
Patients 
1 
0.125 
3-6 
2 
0.25 
3-6 
3 
0.50 
3-6 
4 
0.75 
3-6 
5 
1.0 
3-6 
6 
1.33 
3-6 
7 
1.75 
3-6 
Expansion 1 
1.0 
30 
Expansion 2 
1.0 
up to 56 
Planned Total:    
 
     
 
                             up to 128 
  a Cohort escalation is based on SRT review and recommendation to enroll additional  cohorts 
and/or the expansion cohort. 
b The ACE-536 dose level for cohort 1 is 0.125 mg/kg.  The dose level indicated for all 
subsequent dose escalation cohorts is the maximum dose level that can be recommended by 
the SRT for escalation per the modified Fibonacci dose escalation scheme.  Dose escalation 
will not exceed 1.75 mg/kg. 
9.2. 
Discussion of Study Design 
The efficacy assessment based on modified IWG criteria for erythroid response (mHI-E) was 
selected for this study as a variation of the accepted and widely used endpoint for the 
evaluation of therapies in patients with MDS, appropriate for short-term studies.  This was 
selected as the primary endpoint due to the unknown optimal dosing interval for ACE-536 to 
produce a sustained response and the desire to identify the minimal safe dose level producing 
any erythroid response.  The standard HI-E criteria for response will be evaluated as a 
secondary endpoint.  
The initial dose level of 0.125 mg/kg is less than the maximum dose administered in the phase 
1 study A536-02 of 0.25 mg/kg, which was safe and well tolerated, and produced a 
hemoglobin response in healthy volunteers.  The safety measurements are standard for studies 
with investigational medications.  An open-label study, conducted in a limited number of 
patients, with protocol-specified definitions of dose-limiting toxicity, and with 
protocol-specified procedures for dose escalation and reduction is considered appropriate for a 
proof-of-concept study in this target patient population.  Dose escalation in sequential cohorts 
is designed to minimize the risk of excessive erythroid response and hypertension that may 
result from a robust response to high drug levels.  Individualization of dose level in the 
expansion cohorts, using dose titration rules based on hemoglobin response and dose reduction 
rules based on safety information will maximize the proportion of patients having an erythroid 
response while maintaining safety. 

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9.3. 
Selection of Study Population 
9.3.1. 
Inclusion Criteria 
Eligible patients must meet all of the following criteria: 
1. Men or women ≥ 18 years of age.  
2. Documented diagnosis of idiopathic/de novo MDS or non-proliferative chronic 
myelomonocytic leukemia (CMML) according to WHO criteria (white blood count 
[WBC] < 13,000/μL) that meets IPSS classification (Appendix 2) of low or 
intermediate-1 risk disease as determined by the microscopic and standard 
cytogenetic analyses of the bone marrow and peripheral complete blood count (CBC) 
obtained during screening. 
3. Anemia defined as: 
x Mean hemoglobin concentration < 10.0 g/dL of 2 measurements (one performed 
within one day prior to Cycle 1 Day 1 and the other performed 7-28 days prior 
to Cycle 1 Day 1, not influenced by RBC transfusion within 7 days of 
measurement) for non-transfusion dependent patients (defined as having 
received < 4 units of RBCs within 8 weeks prior to Cycle 1 Day 1) 
(Participation in all cohorts), OR 
x Transfusion dependent, defined as having received ≥ 4 units of RBCs within 8 
weeks prior to Cycle 1 Day 1 (transfusion dependent patients are allowed in 
dose escalation cohorts and expansion cohort 1 only; patients with ≤ 6 units of 
RBCs within 8 weeks prior to Cycle 1 Day 1 may be allowed in cohort 2B) . 
4. Serum erythropoietin levels and prior erythropoiesis-stimulating agent (ESA) 
treatment:  
x Dose escalation cohorts and expansion cohort 1 patients: Serum erythropoietin 
level > 500 U/L, OR, if ≤ 500 U/L, patient is non-responsive, refractory, or 
intolerant to erythropoiesis-stimulating agents (ESAs), or ESAs are 
contraindicated or unavailable. 
x Expansion cohort 2 patients: If patient is RS+ (defined as having ≥ 15% ring 
sideroblasts in the bone marrow), has less than 4 weeks’ exposure to ESAs and 
serum erythropoietin level ≤ 200 U/L.  If a patient is RS- (defined as having < 
15% ring sideroblasts in the bone marrow), prior ESA treatment and any serum 
erythropoietin level is allowed  
5. No alternative treatment options, per national MDS guidelines, are available and/or 
appropriate for the patient, at the discretion of the investigator. 
6. ECOG performance status of 0, 1, or 2 (if related to anemia). 
7. Adequate renal (creatinine ≤ 2.0 x upper limit of normal [ULN]) and hepatic (total 
bilirubin < 2 x ULN and AST and ALT < 3 x ULN) function. 

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8. Adequate transferrin saturation (≥ 15%), ferritin (≥ 50 μg/L), folate (≥ 4.5 nmol/L 
[≥2.0 μg/L]) and vitamin B12 (≥ 148 pmol/L [≥ 200 pg/mL]) during screening 
(supplementation and retest during screening is acceptable). 
9. Females of child bearing potential (defined as sexually mature women who have not 
undergone hysterectomy or bilateral oophorectomy, or are not naturally 
postmenopausal ≥ 24 consecutive months) must have negative urine or blood 
pregnancy test prior to enrollment and use adequate birth control methods 
(abstinence, oral contraceptives, barrier method with spermicide, or surgical 
sterilization) during study participation and for 12 weeks following the last dose of 
ACE-536.  Males must agree to use a latex condom during any sexual contact with 
females of child-bearing potential while participating in the study and for 12 weeks 
following the last dose of ACE-536, even if he has undergone a successful 
vasectomy.  Patients must be counseled concerning measures to be used to prevent 
pregnancy and potential toxicities prior to the first dose of ACE-536. 
10. Patients are able to adhere to the study visit schedule, understand and comply with all 
protocol requirements. 
11. Patient understands and is able to provide written informed consent. 
9.3.2. 
Exclusion Criteria 
Eligible patients must not meet any of the following criteria. 
1. Prior treatment with azacitidine (injectable or oral) or decitabine. 
2. Treatment within 28 days prior to Cycle 1 Day 1 with: 
x Erythropoiesis stimulating agent (ESA), 
x Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage 
colony-stimulating factor (GM-CSF), 
x Lenalidomide. 
3. Iron chelation therapy if initiated within 56 days prior to Cycle 1 Day 1. 
4. Treatment with another investigational drug or device, or approved therapy for 
investigational use ≤ 28 days prior to Cycle 1 Day 1, or if the half-life of the previous 
product is known, within 5 times the half-life prior to Cycle 1 Day 1, whichever may 
be longer.  
5. Major surgery within 28 days prior to Cycle 1 Day 1. Patients must have completely 
recovered from any previous surgery prior to Cycle 1 Day 1. 
6. Platelet count < 30 x 109/L.  
7. Any active infection requiring parenteral antibiotic therapy within 28 days prior to 
Cycle 1 Day 1 or oral antibiotics within 14 days of Cycle 1 Day 1. 
8. History of stroke, deep venous thrombosis (DVT) or arterial embolism within 6 
months prior to Cycle 1 Day 1. 
9. Known positive for human immunodeficiency virus (HIV), active infectious hepatitis 
B (HBV) or active infectious hepatitis C (HCV).  

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10. Any malignancy other than MDS which has not been in remission and/or has required 
systemic therapy including radiation, chemotherapy, hormonal therapy or surgery, 
within the last year prior to Cycle 1 Day 1. 
11. Uncontrolled hypertension defined as systolic blood pressure (BP) ≥ 150 mm Hg or 
diastolic BP ≥ 100 mm Hg. 
12. Pregnant or lactating females. 
13. History of severe allergic or anaphylactic reactions or hypersensitivity to recombinant 
proteins or excipients in the investigational drug. 
14. Any other condition not specifically noted above which, in the judgment of the 
investigator, would preclude the patient from participating in the study. 
15. Transfusion event within 7 days prior to Cycle 1 Day 1. 
16. Prior treatment with sotatercept (ACE-011), or ACE-536. 
17. Secondary MDS. 
9.4. 
Patient Treatment Discontinuation and Withdrawal Criteria 
Patients will be informed that they have the right to discontinue treatment and/or withdraw 
from the study at any time for any reason without prejudice to their medical care.   
A patient may be discontinued from treatment for any of the following reasons:  
x Patient’s request 
x Patient’s unwillingness or inability to comply with the protocol 
x Pregnancy 
x Use of prohibited medication (e.g., ESA) 
x Medical reason or adverse event, at the discretion of the investigator and/or the 
medical monitor 
x Lack of effect (e.g., worsening anemia for NTD patients as evidenced by sustained 
reduction in Hgb by ≥ 2 g/dL over 8 weeks or transfusion dependence), to be discussed 
with the medical monitor  
x Disease progression (any of the following):  

For patients with <5% blasts at baseline: ≥ 50% increase in blasts to > 5% blasts 
 
For patients with 5-10% blasts at baseline: ≥ 50% increase in blasts to > 10% blasts 
(For patients with 5-10% blasts, a 2nd bone marrow sample may be collected 
within 4 weeks to confirm progression before discontinuing patients from 
treatment) 
x Hypersensitivity reaction to study drug  
x At the discretion of the sponsor (e.g., termination of the study or a dose level) 
A patient may be withdrawn from the study for any of the following reasons: 

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x Patient’s request 
x Patient’s unwillingness or inability to comply with the protocol 
x Death 
x Loss to follow-up 
x At the discretion of the sponsor (e.g., termination of the study) 
The reasons for study withdrawal and/or treatment discontinuation must be recorded in the 
patient’s CRF.  The investigator must notify the sponsor, the medical monitor and the contract 
research organization (CRO) immediately when a patient has been discontinued/withdrawn 
due to an AE.  Patients who discontinue treatment early should complete the end of treatment 
(EOT) follow-up visit at the time of discontinuation and then complete the post-treatment 
follow-up (PTFU) and end of study (EOS) follow-up visits approximately 28 and 56 days later, 
respectively. 
The investigator must notify the sponsor and the CRO when a patient has been 
discontinued/withdrawn for reasons unrelated to the study or study drug (e.g., withdrawn 
consent, lost to follow up).  

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10. 
TREATMENT OF PATIENTS 
10.1. 
Selection and Timing of Dose for Each Patient 
Once a patient is enrolled, the appropriate dose of ACE-536 will be administered as a 
subcutaneous injection on Cycle 1 Day 1.  Subsequent doses will be administered every 3 
weeks on Day 1 of the cycle.  Study day 85 ± 2 days is the last possible study day that 
ACE-536 can be administered, regardless of the cycle.  Dose reductions may be required for 
individual patients as outlined in the Patient Dose Modifications Rules (Section 10.8.1).  If a 
dose delay is required, the patient will return weekly for assessment of hematology results and 
adverse events until the patient is eligible to receive the next dose of ACE-536.  Patients will 
be asked to return to the clinic for three follow up visits, occurring approximately 28, 56, and 
84 days after their last dose of ACE 536.  If a patient has a positive anti-drug antibody (ADA) 
result at the last visit, the patient may be asked to return for additional ADA testing every three 
months, until a negative result is obtained or the result is considered to be stabilized. 
10.2. 
Concomitant Medications 
During screening and throughout the study, patients may take stable doses of medications for 
chronic conditions that are not specifically excluded by the protocol (see Section 9.3.1 
Inclusion Criteria and Section 9.3.2 Exclusion Criteria).  If a patient requires treatment with 
any new medications that are specifically excluded by the eligibility criteria, the patient will be 
discontinued from the study and should complete the end of treatment visit and enter the 
follow-up period of the study.  The investigator should consult the medical monitor regarding 
any questions about whether a new medication or dosage of existing medication would require 
the patient to discontinue from the study.  Concomitant medications will be collected 
beginning at study screening and will include all medications taken within 28 days prior to 
Cycle 1 Day 1.  
10.2.1. 
Other Treatments for MDS 
If treatment with azacitidine, decitabine, lenalidomide, ESA, or G-CSF is required during the 
ACE-536 treatment period, the patient should be discontinued from treatment with study drug 
and complete the end of treatment visit and enter the follow up period.  Iron chelation therapy 
is allowed unless initiated within 56 days prior to C1D1.  
10.2.2. 
RBC Transfusions 
For the first dose of ACE-536, dosing should occur after a minimum of 7 days post-transfusion 
and prior to any scheduled transfusions.  Each TD patient will have a “pre-transfusion 
hemoglobin threshold” for requiring transfusion, which will be calculated based on transfusion 
history and will be used for determining when to transfuse during the study.  The baseline pre-
transfusion hemoglobin threshold will be the mean of all documented pre-transfusion 
hemoglobin values during the 12 weeks prior to C1D1.  During treatment, if the pre-
transfusion hemoglobin level is increased by ≥ 1 g/dL compared to the baseline pre-transfusion 
hemoglobin threshold for that patient, transfusion should be delayed by a minimum of 7 days 
and/or the number of units transfused should be reduced by 1 or more RBC units.  Patients 

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should not be transfused if hemoglobin is ≥ 9 g/dL unless indicated for symptoms related to 
anemia or other reasons at the investigator’s discretion. 
10.3. 
Treatment Compliance 
ACE-536 will be administered as a SC injection at the clinical site by the study staff and will 
be documented in the study record.  Monitoring for patient compliance with the treatment 
regimen is therefore unnecessary.  
10.4. 
Randomization  
This is an open-label study and a randomization scheme is not needed for this study. 
10.5. 
Treatments Administered 
Patients will continue to receive the same dose level of study drug as they were assigned at 
study entry unless a dose modification is required (see Section 10.8, Patient Dose Modification 
Rules).   
10.6. 
Dose-Limiting Toxicity Definition  
A Dose-Limiting Toxicity (DLT), using the current active minor version of the National 
Cancer Institute Common Toxicity Criteria for Adverse Events version 4.0 (NCI-CTCAE 
v4.0), is defined as any of the following toxicities, at any dose level occurring within 28 days 
of the first administered dose: 
x Treatment-related serious adverse event (SAE) of Grade ≥ 3 
x Treatment-related non-hematologic and non-infectious adverse event (AE) of Grade 
≥ 3 
x Treatment-related hematologic or infectious AE of Grade ≥ 4 
10.7. 
Safety Evaluation and Dose Escalation 
Safety will be evaluated by the Safety Review Team (SRT), which is comprised at minimum 
of the coordinating investigator, medical monitor, and an independent hematologist.  The role 
of the SRT will be described in greater detail in the SRT Charter.  The SRT will review safety 
data when a minimum of 3 patients in a cohort have completed Study Day 29, including dose-
limiting toxicities (DLTs), adverse events (AEs), serious adverse events (SAEs), laboratory 
results (including hematology and chemistry), vital signs, and erythroid response data.  The 
SRT may make one or more of the following recommendations to the sponsor: 
x Enroll 3 additional patients in the current cohort. 
x Enroll 3 patients in a new cohort at a higher or lower dose level, not to exceed 
modified Fibonacci dose escalation scheme (see Section 9.1). 
x Proceed to expansion cohort 1, with a recommended starting dose level not to 
exceed the maximum dose level evaluated in the dose escalation cohorts. 
x Postpone a decision pending collection of additional data from the current cohort. 

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SRT recommendations to escalate or reduce the dose level of ACE-536 in a subsequent cohort 
or to continue dosing in the current cohort will be based in part upon the following criteria: 
x If a DLT occurs in 0 out of a minimum of 3 patients in a cohort within 28 days 
following the initial dose, dose escalation may occur. 
x If a DLT occurs in 1 out of 3 patients in a cohort within 28 days following the 
initial dose, an additional 3 patients should be enrolled in the current cohort.  
o If a DLT occurs in 1 out of 6 patients in a cohort within 28 days 
following the initial dose, dose escalation may occur. 
x If a DLT occurs in ≥ 2 patients in a cohort within 28 days of the initial dose, the 
dose level for the next cohort (if any) should not be escalated; a lower dose level 
may be recommended. 
x If a hemoglobin increase of ≥ 2.0 g/dL occurs in ≥ 2 patients in a cohort within 28 
days of the initial dose, the dose level for the next cohort (if any) should not be 
escalated; a lower dose level may be recommended. 
In addition, during enrollment of the expansion cohorts, the SRT will review safety data 
periodically throughout the trial, including AEs, SAEs, laboratory results (including 
hematology and chemistry), vital signs, and erythroid response data. 
10.8. 
Patient Dose Modification and Titration 
Patients in the dose escalation cohorts have a pre-determined starting dose based on cohort 
number (see modified Fibonacci Dose Escalation Scheme, Section 9.1).  Dose level titration 
(i.e., increase) is not allowed for patients in the escalation cohorts, but dose delay or reduction 
may be required according to Patient Dose Modification Rules (Section 10.8.1).  Examples of 
dose level reductions for patients in dose escalation cohorts are included in Table 3 below.      
All patients in the expansion cohorts will be initially treated with ACE-536 at a starting dose 
level of 1.0 mg/kg, which has been deemed to be safe, well tolerated, and at least minimally 
effective by the SRT.  The expansion cohorts starting dose level and associated modifications 
(reductions and titrations) are in Table 3.  Rules for reductions and titrations are described in 
Section 10.8.1 and Section 10.8.2.  
 
 

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Table 3: 
Starting Dose Levels, Dose Level Reductions (All Cohorts), and Dose Level 
Titrations (Expansion Cohorts Only) 
2nd Dose 
Reduction 
1st Dose 
Reduction 
Starting 
Dose Level 
1st Dose 
Titration 
2nd Dose 
Titration 
0.125 mg/kg 
0.25 mg/kg 
0.50 mg/kg 
0.75 mg/kg 
1.0 mg/kg 
0.25 mg/kg 
0.5 mg/kg 
0.75 mg/kg 
1.0 mg/kg 
1.33 mg/kg 
0.5 mg/kg 
0.75 mg/kg 
1.0 mg/kga,b 
1.33 mg/kga 
1.75 mg/kga,c 
0.75 mg/kg 
1.0 mg/kg 
1.33 mg/kg 
1.75 mg/kgc 
N/A 
1.0 mg/kg 
1.33 mg/kg 
1.75 mg/kgc 
N/A 
N/A 
a Dose titration is only applicable to patients in the expansion cohorts. 
b Expansion cohorts starting dose level is 1.0 mg/kg 
c Dose titration will not exceed 1.75 mg/kg, which is the maximum dose level tested in the dose escalation cohorts 
and determined to be safe and well tolerated by the SRT. 
N/A = Not Applicable. 
10.8.1. 
Patient Dose Modification Rules 
The following dose modification rules include both pharmacodynamic and safety parameters 
which may require a dose delay and possibly a dose reduction.  These rules should be assessed 
prior to dosing.  If a dose delay is required the patient should have weekly visits to assess 
hematology results and adverse events until the patient is eligible to receive the next dose of 
ACE-536.  
 
 

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Table 4: 
Patient Dose Modification Rules 
Observation on 
Dosing Day 
Action 
ACE-536 Dose 
Modificationa 
Hemoglobin ≥ 12 g/dL  
 
Hold dose and monitor patient weekly 
until hemoglobin < 11 g/dL 
Resume dosing once 
hemoglobin < 11 g/dL  
Hemoglobin  ≥ 2 g/dL 
increase from the 
previous dosing day 
(not attributable to 
RBC transfusion) 
Continue dosing 
Reduce the dose by 1 
dose levela 
Non-hematologic 
adverse event ≥ Grade 
3, at least possibly 
related to study drug 
Hold dose and monitor patient weekly 
until resolution of AE to ≤ Grade 1 or 
baseline 
Resume dosing upon 
resolution of the AE to 
≤ Grade 1 or baseline, 
and reduce the dose by 1 
dose levela,b 
White blood cell 
(WBC) count ≥ 
13,000/μL
c 
x Dose delay until WBC < 13,000/μL 
and resolution of associated 
condition (e.g., infection) within 6 
weeks 
x Discontinue treatment if WBC ≥ 
13,000/μL persists for more than 6 
weeks 
x Discontinue treatment if clinically 
significant cytomorphologic 
changes on bone marrow aspirate 
compared to baseline. 
 
a Dose level refers to dose levels listed in Table 3. 
b Patients who require more than 2 dose reductions due to an AE should be discontinued from treatment and 
complete the EOT, PTFU and EOS visits.  
c The investigator may contact the medical monitor and forward appropriate supporting documents for review 
and discussion prior to making decision regarding treatment discontinuation. 
10.8.2. 
Expansion Cohorts Patient Dose Titration 
For the expansion cohorts, the starting dose level to be administered on Cycle 1 Day 1 will be 
1.0 mg/kg.  The starting dose level with the associated dose reductions and titrations are shown 
in Table 3.  The dose level should be titrated individually for each patient, not to exceed the 
maximum dose level tested of 1.75 mg/kg.  Please note that all dose modification rules (i.e., 
dose delay and reduction rules in Section 10.8.1) supersede all dose titration rules. 
For NTD patients, the dose level will be assessed for titration beginning at C3D1.  Dose 
titration rules are as follows, using dose levels in Table 3. 
x If hemoglobin increase from baseline is < 1.5 g/dL throughout the previous two 
cycles at a single dose level, the dose level should be increased by 1 dose level.  

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x If hemoglobin increase from baseline is ≥ 1.5 g/dL but not sustained for at least two 
consecutive study measurements during the previous two cycles at a single dose 
level, the dose level should be increased by 1 dose level.   
x If hemoglobin increase from baseline is ≥ 1.5 g/dL (not influenced by RBC 
transfusion) on two or more consecutive study measurements during the previous 
two cycles, the dose level should remain unchanged.   
For TD patients, the dose level will be assessed for titration beginning at C3D1.  Dose titration 
rule is as follows, using dose levels in Table 3. 
x Rate of transfusion is the number of units of RBCs transfused over a defined period 
of time.  If no decrease from baseline in the rate of transfusion over the previous 
two cycles, the dose should be increased by 1 dose level. 
The SRT will meet periodically to monitor overall safety and erythroid response data for the 
expansion cohorts. 
10.9. 
Other Considerations for Dose Modification, Delay or 
Discontinuation 
For individual patients judged by the investigator to be at an unacceptable risk, but who do not 
meet the protocol-defined conditions for a dose modification or interruption, the investigator 
should consult with the medical monitor to decide whether to continue dosing at the same dose 
level, reduce the dose level, delay the patient’s dose, or discontinue the patient’s treatment 
with ACE-536. 

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11. 
STUDY PROCEDURES  
Please refer to Section 2, Schedule of Events for the schedule of procedures required for each 
visit. 
11.1. 
Written Informed Consent 
Patients will be required to sign an IEC approved ICF prior to any study related procedures, 
including screening evaluations. 
11.2. 
Clinical Laboratory Tests 
The following laboratory assessments will be performed at the clinical site’s local laboratory 
according to the laboratory collection recommendations.  The sponsor may request additional 
safety tests be performed based on ongoing data review during the study.  
x Hematology: RBC, WBC with differential, hemoglobin, hematocrit, reticulocyte 
count, platelet count, MCV, MCH, MCHC, and RDW.  
x Serum chemistry: Sodium, potassium, AST, ALT, lactate dehydrogenase (LDH), 
total bilirubin, direct bilirubin, alkaline phosphatase, blood urea nitrogen 
(BUN)/urea, creatinine, GGT, calcium, phosphorus, glucose, amylase, lipase, total 
protein, albumin, and uric acid.  
x Urinalysis by dipstick analysis: pH, specific gravity, protein, glucose, ketones, 
blood, leukocyte esterase, and nitrite, with microscopic examination if indicated. 
x Pregnancy test: women of child bearing potential must have a negative pregnancy 
test at screening and prior to administration of ACE-536 on each dosing day. 
x Screening visit only: serum folate and B12  
The following laboratory assessments will be performed at the central laboratory according to 
the laboratory collection recommendations.  The sponsor may request additional safety tests be 
performed based on ongoing data review during the study.  
x Iron studies: Serum iron, TIBC, transferrin, soluble transferrin receptor, ferritin, 
NTBI and hepcidin. 
x Nucleated RBC 
x Erythropoietin levels 
x Peripheral blood smear 
x Urine microalbumin and creatinine  
x Bone Biomarkers: serum BSAP and CTX (not collected for expansion cohort 2 
patients).  

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11.3. 
Other Safety Assessments   
x Physical examination 
x Vital signs: weight, heart rate, systolic and diastolic blood pressure, respiration rate 
and temperature (measured in degrees Celsius).  Height is measured only at 
screening.   
x ECOG Status 
x 12-lead ECG  
x Anti-drug antibody testing   
x The occurrence of a new malignancy or premalignant lesion will be monitored as an 
event of interest and should be included as part of the assessment of adverse events 
throughout the course of the study.  Investigators are to report the development of 
any new malignancy or premalignant lesion as a serious adverse event, regardless 
of causal relationship to study drug, occurring at any time for the duration of the 
study, from the time of signing the ICF up to and including 3 months of follow up. 
11.4. 
Pharmacokinetic and Pharmacodynamic Assessments 
11.4.1. 
Pharmacokinetic Assessments 
PK assessment of ACE-536 concentrations will be performed periodically as outlined in 
Section 2, (Schedule of Events).  Blood samples should be drawn and processed on-site for 
serum collection at the time points specified.  Additional details regarding PK collection and 
processing can be found in the Laboratory Manual.   
11.4.2. 
Pharmacodynamic Evaluations 
Pharmacodynamic assessments including hematologic laboratory assessments and transfusion 
information will be used to determine erythroid response to ACE-536. 
Bone marrow biopsy and bone marrow aspirates will be performed for histology, cytogenetics, 
and morphology.  Additional analyses may be included, such as flow cytometry to explore 
erythroid lineage markers and molecular testing to explore MDS-related genetic mutations. 
Blood biomarkers for iron metabolism will include serum iron, TIBC, transferrin, soluble 
transferrin receptor, ferritin, NTBI, and hepcidin. 
Biomarkers related to the TGFE superfamily and/or iron metabolism, such as GDF15, GDF8, 
GDF11, and others may be tested in blood and/or bone marrow samples, to be determined. 
The relationship of biomarkers to erythroid response may be investigated. 
The sponsor may request additional biomarkers for exploratory research purposes only. 
 

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12. 
STUDY SCHEDULE 
Please refer to Section 2, Schedule of Events for the schedule of procedures required for each 
visit.  Note that all windows on visits should be determined relative to the date of the previous 
dose of ACE-536.  
12.1. 
Screening  
x Signature of the current IEC approved ICF should occur prior to initiation of any 
study-specific screening procedures. 
x All screening procedures should occur within 28 days prior to Cycle 1 Day 1. 
x Bone marrow aspirate and biopsy including cytogenetics must be performed within 
3 months prior to Cycle 1 Day 1 for evaluation of patient eligibility. 
x Historical hemoglobin and transfusion history will be collected for 24 weeks prior 
to Cycle 1 Day 1. 
x Baseline hemoglobin will be calculated as the average of two measurements; one 
performed within one day prior to Cycle 1 Day 1, and the other performed 7-28 
days prior to Cycle 1 Day 1. Neither hemoglobin measure should be influenced by 
transfusion within 7 days of measurement.  
x Pregnancy test (urine or serum) is required of female patients of child bearing 
potential only. 
x Concomitant medications taken within 28 days prior to Cycle 1 Day 1 will be 
documented in the CRF. 
x Screen failure information will be maintained to document specific information, 
including but not limited to, reason for failure. 
x For expansion cohort patients only, administration of  quality of life questionnaires. 
12.2. 
Dosing Days and Interim Visits 
x All screening procedure results required to confirm eligibility must be obtained and 
reviewed prior to study drug administration.  Patient eligibility must be confirmed 
from these results.  
x For any RBC transfusions received during the study, the hemoglobin value just 
prior to transfusion should be collected. 
x A patient will be considered enrolled into the study once a multi-digit patient 
identification number has been assigned to the patient.  After assignment of the 
patient identification number and the completion of the required procedures, study 
drug administration may occur.  Note that the patient dose must be calculated based 
on the patient’s weight on the day of dosing.   
x Negative pregnancy test (urine or serum) is required of female patients of child 
bearing potential prior to administration of ACE-536 on each dosing day. 

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x All study procedures on each dosing day must be done prior to administration of 
study drug. 
x For the first dose of ACE-536, dosing should occur after a minimum of 7 days 
post-transfusion and a minimum of 24 hours prior to a scheduled transfusion. 
Patients should be observed for a minimum of 30 minutes following treatment with 
ACE-536. 
x If a dose delay is required per the dose modification rules (Section 10.8.1), the 
patient will not be dosed.  The patient will return weekly for assessment of 
hematology results and adverse events until the patient is eligible to receive the next 
dose of ACE-536.  The patient should resume the study at the planned dosing cycle 
(e.g. if the patient missed a dose at C4D1, then they would resume dosing at C4D1 
and not skip to C5D1). 
x The hematology results can be collected up to 24 hours prior to the dosing day.  For 
Cycle 1 Day 1, the hemoglobin should be available to confirm eligibility within one 
day prior.  
x For dose escalation cohort and expansion cohort 1 patients, a bone marrow aspirate 
must be performed within 21 days after C3D1 (a bone marrow biopsy is not 
required).  Note: a bone marrow aspirate is not required within 21 days after C3D1 
for expansion cohort 2 patients. 
x Any non-serious AEs that occur prior to dosing in cycle 1 should be recorded in the 
Medical History section of the CRF. 
x All AEs that occur after dosing in Cycle 1 should be recorded in the AE page of the 
CRF. 
x On subsequent dosing days, all AEs and abnormal findings that might require 
modification of dosing (see Section 10.8.1) should be reviewed prior to dosing to 
ensure that the patient is still eligible to receive additional doses of ACE-536.  
12.3. 
Day 85 
x Day 85 ± 2 days is the last possible study day that ACE-536 may be administered, 
regardless of the cycle. 
x For expansion cohort 1 patients only, administration of quality of life 
questionnaires.  Not required for expansion cohort 2 patients.   
12.4. 
End of Treatment Visit 
x The end of treatment visit should occur approximately 28 days after the last dose of 
ACE-536.  
x Patients who discontinue treatment early should complete the end of treatment visit 
at the time of discontinuation. 
x Patients who discontinue treatment early and all expansion cohort 2 patients should 
complete the quality of life questionnaires at the end of treatment visit. 

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x A bone marrow aspirate must be performed at the end of treatment visit (a bone 
marrow biopsy is optional). 
12.5. 
Post-Treatment Follow Up Visit 
x The post-treatment follow up visit should occur approximately 28 days after the end 
of treatment visit. 
12.6. 
End of Study Visit 
x The end of study visit should occur approximately 56 days after the end of 
treatment visit.  
x Patients who discontinue treatment early should complete the end of study visit 
approximately 56 days after the end of treatment visit. 
x For expansion cohorts patients only, administration of quality of life questionnaires. 
x If a patient has a positive anti-drug antibody (ADA) result at the last visit, the 
patient may be asked to return for additional ADA testing every three months, until 
a negative result is obtained or the result is considered to be stabilized. 
12.7. 
Termination of Study 
The sponsor may terminate this study or discontinue a cohort, after consultation with the 
investigator(s), or at any time, for safety or administrative reasons.  The sponsor will terminate 
the study if the occurrence of SAEs or other findings suggests unacceptable risk to the health 
of the patients.   
 

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13. 
STUDY DRUG MATERIALS AND MANAGEMENT 
13.1. 
Study Drug 
ACE-536 is a recombinant fusion protein consisting of a modified form of the extracellular 
domain (ECD) of the human activin receptor IIB (ActRIIB) linked to the human IgG1 Fc 
domain. 
13.2. 
Study Drug Packaging and Labeling 
ACE-536 drug product will be provided as either a sterile, liquid formulation or a lyophilized 
powder formulation for reconstitution with water.  Each single-use vial of the liquid 
formulation contains 25 mg of ACE-536 in a 0.5 mL Tris-buffered saline solution (50 mg/mL).   
Each single-use vial of the lyophilic formulation contains 50 mg ACE-536 for reconstitution 
with 1 mL water for injection to form a citrate-buffered solution (50 mg/mL). 
13.3. 
Study Drug Storage 
ACE-536 liquid formulation is stored frozen at d -65˚C until use. 
ACE-536 lyophilized powder formulation is stored between 2 - 8˚C until use. 
13.4. 
Study Drug Preparation 
Please refer to the study drug handling guideline, provided under separate cover, for detailed 
ACE-536 drug handling, administration, and storage instructions.   
13.5. 
Administration 
ACE-536 will be administered by SC injection.  Multiple injections may be required to 
administer the appropriate dose at higher dose levels; however, no more than 4 injections will 
be administered per dose.  The maximum volume per SC injection should not exceed 1.2 mL. 
Patients should be observed for a minimum of 30 minutes following treatment with ACE-536. 
13.6. 
Study Drug Accountability 
Accountability for ACE-536 is the responsibility of the investigator.  Investigational clinical 
supplies must be received by a designated person at the clinical site and kept in a secured 
location.  The clinical site must maintain accurate records demonstrating dates and amounts of 
ACE-536 received, to whom it was dispensed (patient-by-patient accounting), and accounts of 
any ACE-536 accidentally or deliberately destroyed or returned. 
Unless otherwise notified, all vials of ACE-536, both used and unused, must be saved for drug 
accountability purposes.  The used vials may be discarded, per the institution’s standard 
practice, after drug accountability assessment has been completed by the clinical monitor.  At 
the end of the study, the sponsor will provide direction for the outcome of all unused vials.  
Following the sponsor’s instructions, the investigator must either return all unused vials of 
ACE-536 to the sponsor or destroy them at the clinical site.  In either case, the outcome must 
be documented on the drug accountability log.  

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13.7. 
Study Drug Handling and Disposal 
Please refer to the study drug handling guide, provided under separate cover, for detailed 
ACE-536 drug handling, administration, storage, and disposal instructions.  

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14. 
ASSESSMENT OF SAFETY 
14.1. 
Adverse Event Definitions 
Adverse Event 
An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation 
subject administered a study drug, which does not necessarily have a causal relationship with 
this treatment.  An AE can therefore be any unfavorable and unintended sign (including an 
abnormal laboratory finding), symptom, or disease temporally associated with the use of the 
study drug whether or not it is considered related to the study drug.  
Abnormal laboratory and other abnormal investigational findings (e.g. physical exam, ECG) 
should not be reported as AEs unless they are associated with clinical signs and symptoms, lead 
to treatment discontinuation or are otherwise considered clinically relevant by the investigator.  
In cases of surgical or diagnostic procedures, the condition/illness leading to such a procedure is 
considered as the AE rather than the procedure itself.  In case of a fatality, the cause of death is 
considered as the AE, and the death is considered as its outcome. 
Unexpected Adverse Events 
An unexpected AE is an AE that is not described in nature or severity in the Investigator’s 
Brochure.  
Events Not to Be Considered as Adverse Events 
Pre-existing medical conditions/signs/symptoms present before the Screening period that do not 
worsen in severity or frequency during the study are defined as Baseline Medical Conditions, 
and are not to be considered AEs.  Anticipated day-to-day fluctuations of pre-existing 
conditions, including the disease under study, that do not represent a clinically significant 
exacerbation or worsening need not be considered adverse events. 
Serious Adverse Event 
A serious adverse event (SAE) is any AE, occurring at any dose level/regimen and regardless of 
causality that: 
x Results in death. 
x Is life-threatening:  Life-threatening means that the patient was at immediate risk of 
death from the reaction as it occurred (i.e., it does not include a reaction which 
hypothetically might have caused death had it occurred in a more severe form). 
x Requires inpatient hospitalization or prolongation of existing hospitalization; 
however, a hospitalization for an elective procedure will not be considered a SAE.  
x Results in persistent or significant disability/incapacity. 
x Is a congenital anomaly/birth defect. 
x Is an important medical event: an important medical event is an event that may not 
result in death, be life-threatening, or require hospitalization but may be considered 
an SAE when, based upon appropriate medical judgment, it may jeopardize the 

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patient and may require medical or surgical intervention to prevent one of the 
outcomes listed in the definitions for SAEs.  Examples of such medical events 
include allergic bronchospasm requiring intensive treatment in an emergency room or 
at home, blood dyscrasias or convulsions that do not result in inpatient 
hospitalization, or the development of drug dependency or drug abuse.   
For the purposes of reporting per regulations, any suspected transmission of an infectious agent 
via a medical product is by default a suspected, unexpected serious adverse reaction (SUSAR) 
and should be reported in an expedited manner as described in Section 14.7. 
Events Not to Be Considered as Serious Adverse Events 
Elective hospitalizations to administer or to simplify study treatment or procedures are not 
considered SAEs.  
 
Adverse Events of Special Interest 
Events of new malignancy and premalignant lesions (excluding benign tumors or benign 
neoplasia) are to be reported as described in Section 14.7 within 24 hours of the investigator’s 
knowledge of the event by fax, or other appropriate method, using the SAE Report Form, and 
must be considered an “Important Medical Event” even if no other serious criteria apply; these 
events must also be documented in the appropriate page(s) of the CRF and subject’s source 
documents.  Documentation of the diagnosed malignancy must be provided at the time of 
reporting as a serious adverse event (e.g., any confirmatory histology or cytology results, X-rays, 
CT scans, etc.). 
Malignancies or cancerous tumors are lesions capable of invading into adjacent tissues, and may 
be capable of spreading to distant tissues.  A benign tumor has none of those properties. 
Malignancy or cancer is characterized by anaplasia, invasiveness, and metastasis.  For MDS 
studies, these also include progression to high/very high risk of MDS, myeloproliferation (e.g., 
clinically significant increases in blasts), progression to AML, etc. 
Premalignant or precancerous lesions refer to a state of disordered morphology of cells that is 
associated with an increased risk of cancer.  If left untreated, these conditions may lead to 
cancer.  Such conditions are usually either dysplasia or benign neoplasia (and the dividing line 
between those is sometimes blurry).  Sometimes the term "precancer" is used to describe 
carcinoma in situ, which is a noninvasive cancer that has not progressed to an aggressive, 
invasive stage.  Not all carcinoma in situ will progress to invasive disease. 
Premalignant lesions are morphologically atypical tissue which appears abnormal under 
microscopic examination and in which cancer is more likely to occur than in its apparently 
normal counterpart. 
14.2. 
Pregnancy and In Utero Drug Exposure 
The investigator will attempt to collect pregnancy information if a female patient or a male 
patient’s female partner becomes pregnant while the patient is participating in this study.  The 
pregnancy information will be recorded on the appropriate form and must be submitted to the 
Sponsor within 2 weeks of learning of the pregnancy.  The patient or partner will be followed for 
the outcome of the pregnancy.  Information on the status of the mother and child will be 

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forwarded to the Sponsor or designee.  Generally, follow up will be no longer than 6 to 8 weeks 
following the estimated delivery date.  Any premature termination of the pregnancy will be 
reported. 
14.3. 
Severity 
Investigators must evaluate the severity/intensity of AEs according to the current active minor 
version of the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 
4.0 (NCI-CTCAE v4.0), preferentially using the graded scales.  If there is a change in severity of 
an adverse event, it must be recorded as a separate event.  If a particular AE’s severity/intensity 
is not specifically graded, the investigator should apply the general guidelines for determination 
of Grade 1 through Grade 5 as listed in the NCI-CTCAE v4.0 cover page (as shown below), 
using their best medical judgment: 
Grade 1: Mild; asymptomatic or mild symptoms; clinical or diagnostic observations only; 
intervention not indicated. 
Grade 2: Moderate; minimal, local or noninvasive intervention indicated; limiting 
age-appropriate instrumental activities of daily living (preparing meals, shopping for 
groceries or clothes, using the telephone, managing money, etc.). 
Grade 3: Severe or medically significant but not immediately life-threatening; hospitalization or 
prolongation of hospitalization indicated; disabling; limiting self-care activities of 
daily living (bathing, dressing and undressing, feeding self, using the toilet, taking 
medications, and not bedridden). 
Grade 4: Life-threatening consequences; urgent intervention indicated. 
Grade 5: Death related to AE. 
14.4. 
Relationship to Study Drug 
Investigators must also assess the causal relationship of each AE to ACE-536.  Factors for the 
assessment of causal relationship include, but are not limited to, temporal relationship between 
the AE and the administration of ACE-536, known side effects of ACE-536, medical history, 
concomitant therapy, course of the underlying disease and pertinent study procedures.  
Probable: A causal relationship is clinically/biologically highly plausible and there is a 
plausible time sequence between onset of the AE and administration of ACE-536 and 
there is a reasonable response on withdrawal. 
Possible: A causal relationship is clinically/biologically plausible and there is a plausible time 
sequence between onset of the AE and administration of ACE-536. 
Unlikely: A causal relationship is improbable and another documented cause of the AE is most 
plausible. 
Unrelated: A causal relationship can be definitively excluded and another documented cause of 
the AE is most plausible. 

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14.5. 
Documentation and Methods of Reporting of Adverse Events by 
Investigator 
It is the responsibility of the Investigator to document all adverse events that occur during the 
study. Patients will be evaluated and questioned generally for AEs during the course of the 
study, starting at the signing of the informed consent.  The Investigator must report in detail all 
adverse signs and symptoms which are either volunteered by subjects or observed during or 
following the course of investigational product administration on the appropriate CRF page. All 
non-serious AEs occurring after signing of the ICF until a patient is dosed on Cycle 1 Day 1 are 
to be documented on the medical history CRF.  All AEs and SAEs occurring after the Cycle 1 
Day 1 dose through 84 days after the last study drug administration (End of Study visit) are to be 
reported and documented on the AE CRF. 
All AEs spontaneously reported by the patient and/or in response to an open question from study 
personnel or revealed by observation, physical examination or other diagnostic procedures will 
be recorded on the AE CRF.  Any clinically relevant changes in laboratory assessments, or other 
clinical findings as described in Section 14.1, are considered AEs and must be recorded on the 
AE CRF.  AEs are to be followed for resolution as described in Section 14.6.  
It is important that each AE report include a description of the event, duration (onset and 
resolution dates), severity, relationship with ACE-536, any other potential causal factors, any 
treatment given or other action taken (including dose modification or discontinuation of 
ACE-536) and outcome.  In addition, serious AEs (SAEs) should be identified and the 
appropriate seriousness criteria documented.  AEs categorized as SAEs must also be documented 
using an SAE Report Form as described in Section 14.5.1. 
Specific guidance can be found in the CRF Completion Guidelines provided by the Sponsor or 
designee.  
14.5.1. 
Documentation of Serious Adverse Events 
All SAEs that occur after the first study drug administration on Cycle 1 Day 1 until 84 days after 
the last study drug administration (End of Study visit) are to be documented on the AE CRF.  
SAEs should not be reported for patients who are considered screen failures unless the event is 
deemed due to a protocol required procedure. 
For all SAEs, an SAE form must be completed with as much information as possible and 
submitted within the time frame described in Section 14.7 (Notification about Serious Adverse 
Events).   
When new significant information is obtained as well as when the outcome of an event is known, 
the investigator should record the information on a new SAE form.  If the patient was 
hospitalized, a copy of the discharge summary must be included as part of the patient medical 
file.  In all instances, the investigator should follow up with patients until the outcome of the 
SAE is known. 

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14.6. 
Reporting Period and Monitoring of Patients with Adverse Events 
As described in Section 14.5, all AEs must be recorded in the CRF up until the end of the 
treatment period.  All patients who took at least one dose of study drug, whether they completed 
the treatment period or not, should complete the end of treatment procedures. 
All AEs will be followed until clinical database lock (or resolution if it occurs before database 
lock).  All SAEs will undergo active follow up until resolved or the event becomes chronic or 
stable.  Follow up data for SAEs obtained after clinical database lock will be incorporated into 
the ACE-536 safety database. 
14.7. 
Notification about Serious Adverse Events 
If an SAE occurs during the reporting period, the investigator must immediately, within a 
maximum 24 hours after becoming aware of the event, inform the sponsor via the CRO by 
telephone, fax, or e-mail. 
All written reports should be transmitted using the study specific SAE Report Form, which must 
be completed by the investigator following specific completion instructions.  Names, addresses, 
telephone and fax numbers for SAE reporting are located on the SAE Report Form and in the 
completion instructions provided in the Study Manual.  When an SAE (or follow up information) 
is reported by telephone, a written report must be sent immediately thereafter by fax or e-mail.  
Reporting procedures and timelines for follow up information are the same as for the initially 
reported SAE.  
Relevant pages from the CRF may be provided in parallel (e.g., medical history, concomitant 
therapy).  In all cases, the information provided in the SAE Report Form must be consistent with 
the data that are recorded in the corresponding sections of the CRF. 
The investigator/reporter must respond to any request for follow up information or to any 
question the Sponsor or designee may have on the AE within the same timelines as described for 
initial reports.  This is necessary to permit a prompt assessment of the event by the Sponsor and 
(as applicable) to allow the Sponsor to meet regulatory timelines associated with expedited 
reporting obligations. 
Requests for follow up will usually be made by the responsible clinical research associate or 
Medical Monitor, or an Acceleron pharmacovigilance representative who may contact the 
investigator directly to obtain clarification on a particularly critical event. 
14.7.1. 
Safety Reporting to Health Authorities, Independent Ethics Committees 
Institutional Review Boards and Investigators 
The Sponsor will send appropriate safety notifications to Health Authorities in accordance with 
applicable laws and regulations. 
The investigator must comply with any applicable site-specific requirements related to the 
reporting of SAEs involving his/her patients to the IEC that approved the study. 
In accordance with International Conference on Harmonization (ICH) Good Clinical Practice 
(GCP) guidelines, the Sponsor will inform the investigator of “findings that could adversely 
affect the safety of patients, impact the conduct of the study, or alter the IEC’s 
approval/favorable opinion to continue the study.”  

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The Sponsor will inform the investigator of AEs that are both serious and unexpected and are 
considered to be related to ACE-536 (“suspected unexpected serious adverse reactions” or 
SUSARs).  The investigator should place copies of these Safety Reports in the Investigator Site 
File.  National regulations with regard to Safety Report notifications to investigators will be 
followed. 
When specifically required by regulations and guidelines, the Sponsor will provide appropriate 
Safety Reports directly to the concerned lead IEC and will maintain records of these 
notifications.  When direct reporting by the Sponsor is not clearly defined by national or 
site-specific regulations, the investigator will be responsible for promptly notifying the 
concerned IEC of any Safety Reports and for filing copies of all related correspondence in the 
Investigator Site File. 
For studies covered by the European Union Clinical Trials Directive 2001/20/EC, the Sponsor’s 
responsibilities regarding the reporting of SAEs/SUSARs will be carried out in accordance with 
that Directive and with the related Detailed Guidances. 
  

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15. 
STATISTICS 
15.1. 
Analysis Populations 
For all analysis populations, patients will be analyzed according to assigned treatment groups. 
The Intent-to-Treat Population: All patients enrolled in the study who have received at least 
one dose of ACE-536 (Safety Population). 
Efficacy Evaluable Population: All patients who received at least one dose of ACE-536 and 
have 1) at least two hemoglobin assessments ≥ 14 days apart post-treatment OR 2) at least 8 
consecutive weeks of transfusion frequency data between Cycle 1 Day 1 and End of Treatment 
visit in transfusion dependent patients. 
Safety Population: All patients who received at least 1 dose of ACE-536. 
Pharmacokinetics Population: All patients who have received at least 1 dose of ACE-536 and 
have sufficient pharmacokinetic samples collected and assayed for PK analysis. 
15.2. 
Statistical Plan 
Summary statistics will be presented for continuous/quantitative variables, by way of number of 
patients (n), mean, standard deviation (SD), median, minimum and maximum and by way of 
group frequencies and percentages for categories of qualitative variables.  Percentages will be 
calculated using the total patients per treatment / subgroup. 95% confidence intervals (CIs) will 
be presented as applicable. 
All patient data will be presented in separate data listings. 
15.2.1. 
Patient Accountability and Demographics 
Exposure to study drug and reasons for discontinuation of study will be tabulated, and 
demographics will be presented using descriptive statistics (i.e., mean, standard deviation, 
median, and range).   
15.2.2. 
Primary Efficacy Analysis 
The primary efficacy endpoint is modified erythroid response (mHI-E), defined as the 
proportion of patients who have a hemoglobin increase of ≥ 1.5 g/dL from baseline for ≥ 14 days 
(in the absence of RBC transfusions) in non-transfusion dependent patients, or, a reduction of 
either ≥ 4 units or ≥ 50% of units of RBCs transfused over a period of 8 consecutive weeks, 
compared to the number of units of RBCs transfused in the 8 weeks immediately prior to Cycle 1 
Day 1 in transfusion dependent patients (defined as having received ≥ 4 units of RBCs within 8 
weeks prior to Cycle 1 Day 1).  The erythroid response will be summarized using both a point 
estimate and its exact 95% confidence interval based on binomial distribution.  The primary 
efficacy analysis will be performed using the EE population. 
No direct comparison testing with concurrent or historical controls will be performed.   

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Baseline hemoglobin will be the average of at least two measures (not influenced by transfusion 
within 7 days of measurement); one measure performed within one day prior to Cycle 1 Day 1 
and the other performed 7-28 days prior to Cycle 1 Day 1.   
15.2.3. 
Secondary Analysis 
Safety analysis: To assess clinical safety, adverse events, vital sign measurements and clinical 
laboratory information will be summarized.  Adverse Events will be coded using the Medical 
Dictionary for Regulatory Activities (MedDRA).  Changes from baseline for clinical laboratory 
values and vital signs will be summarized over time.  Descriptive statistics and shift tables will 
be generated as appropriate.  
Secondary efficacy/pharmacodynamic analysis of the study will be performed using the ITT 
and EE populations and will include: 
x Modified erythroid response (mHI-E), as described above for primary endpoint, 
performed using the ITT population. 
x HI-E response rate as defined by IWG 2006 criteria (Appendix 5).  Improvements 
must last ≥ 8 weeks.  For non-transfusion dependent patients, an increase of 
≥ 1.5 g/dL from pre-treatment hemoglobin.  For transfused patients, a reduction by 
≥ 4 units of RBCs transfused (for a hemoglobin ≤ 9.0 g/dL) during any 8-week period 
on study, compared with the 8-week period prior to Cycle 1 Day 1.  
x Time to mHI-E and HI-E response and duration of mHI-E and HI-E response as per 
the IWG 2006 criteria. 
x Frequency of RBC transfusion, and rate of RBC transfusion independence in 
transfusion dependent patients. 
x Other pharmacodynamic (PD) endpoints including: 
o Biomarkers for iron metabolism 
o Biomarkers for bone metabolism 
o Relationship of biomarkers to response 
o Rates of HI-N and HI-P  
Exploratory endpoints will include: 
o Evaluation of biomarkers related to the TGFE superfamily. 
o Evaluation of self-reported quality of life in the expansion cohort using tools 
including but not limited to the FACT-An questionnaire. 

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All binary endpoints will be summarized using both a point estimate and its exact confidence 
interval based on the binomial distribution.  The time-to-event type secondary endpoints will be 
analyzed using Kaplan-Meier method to estimate the survival curve and median time to event 
and 95% confidence interval.   
15.2.4. 
Pharmacokinetics Analysis 
Pharmacokinetics analysis: Non-compartmental PK parameters for ACE-536, such as 
maximum plasma concentration (Cmax), time to maximum plasma concentration (tmax), and area 
under the concentration/time curve (AUC), will be estimated.  Dose proportionality may be 
assessed using the exposure data (e.g. Cmax, AUC) after the first dose if sufficient dose levels are 
studied.  Descriptive statistics will be provided for serum concentrations and PK parameters.  
The relationship between ACE-536 exposure and response (i.e., safety, efficacy, and biomarkers) 
may be explored, if appropriate. 
15.2.5. 
Anti-drug Antibody Analysis 
Anti-drug antibody analysis: The results of anti-drug and neutralizing antibody testing for 
ACE-536 and human ActRIIB protein versus time will be presented.  Exploratory analysis will 
be performed on the potential effect of anti-drug antibodies on ACE-536 PK and drug exposure 
if anti-drug antibody tests are deemed positive. 
15.3. 
Determination of Sample Size 
There is no formal sample size calculation for the dose escalation portion of the study.  A 
standard dose escalation design will be implemented, and up to 42 patients will be enrolled at up 
to 7 different dose levels to further evaluate erythroid response. 
A sample size of 30 evaluable patients in expansion cohort 1 will provide approximately 90% 
power with 1-sided significance level of 0.05 to differentiate an erythroid response rate of 30% 
from a minimal erythroid response rate of 10% based on Fisher exact test.  
A sample size of 25 evaluable patients in each group of expansion cohort 2 will provide 
approximately 80% power with 1-sided significance level of 0.05 to differentiate an erythroid 
response rate of 30% from a minimal erythroid response rate of 10 % based on Fisher exact test. 
15.4. 
Interim Analysis 
There are no planned interim analyses.  However, safety and erythroid response data will be 
reviewed periodically throughout the study. 
15.5. 
Deviation from Original Analysis Plan 
A formal Statistical Analysis Plan (SAP) for the analysis and presentation of data from this study 
will be prepared before the database lock.  Deviations from the statistical analyses outlined in 
this protocol will be indicated in this plan; any further modifications will be noted in the final 
clinical study report. 

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16. 
SOURCE DOCUMENTATION AND INVESTIGATOR FILES 
16.1. 
Study Monitoring 
The clinical monitor will arrange to visit the clinical sites at regular intervals during the study.  
The monitoring visits must be conducted according to the applicable ICH and GCP guidelines to 
ensure protocol adherence, quality of data, drug accountability, compliance with regulatory 
requirements, and continued adequacy of the clinical sites and their facilities.  During these 
visits, CRFs and other data related to the study will be reviewed and any discrepancies or 
omissions will be resolved.  The clinical monitor will be given access to study–relevant source 
documents (including medical records) for purposes of source data verification. 
16.2. 
Audits and Inspections 
The investigators and clinical sites will permit trial-related monitoring, audits, IEC review, and 
regulatory inspections as requested by FDA or other health authorities and the sponsor or 
designee.  In addition to CRFs, the clinical site will permit direct access to source 
data/documents (i.e., original medical records, laboratory reports, hospital documents, progress 
reports, signed ICFs, etc.).  During and/or after completion of the study, quality assurance 
officers named by the sponsor or the regulatory authorities may wish to perform on-site audits.  
The investigator is expected to cooperate with any audit and provide assistance and 
documentation (including source data) as requested. 
17. 
QUALITY CONTROL AND QUALITY ASSURANCE 
17.1. 
Data Quality Control and Quality Assurance 
17.1.1. 
Investigator Responsibility 
The investigator is responsible for ensuring the study is conducted according to the protocol, 
Code of Federal Regulations, GCP, and applicable regulatory requirements.  The investigator’s 
responsibilities are outlined in these documents and must include the responsibility to obtain a 
signed informed consent prior to patient participation in the study. 
17.1.2. 
Protocol Modifications 
The investigator should not modify the protocol without agreement from the sponsor and prior 
review or approval by the IEC, unless an emergency situation requires protocol modification to 
ensure the safety of patients.  Any deviations from the protocol should be documented by the 
investigator or designee.  

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18. 
CONFIDENTIALITY 
To maintain patient privacy, all CRFs, study drug accountability records, study reports and 
communications will identify the patient by the assigned patient identification number.  The 
investigator will grant clinical monitor(s) and auditor(s) from the sponsor or designee and 
regulatory authorities’ access to the patient’s original medical records for verification of data 
gathered on the CRFs and to audit the data collection process.  The patient’s confidentiality will 
be maintained and will not be made publicly available.  The patient’s medical information will 
only be released to the extent permitted by the applicable laws and regulations. 
All information regarding the investigational product supplied by the sponsor to the investigator 
is privileged and confidential information.  The investigator agrees to use this information to 
accomplish the study and will not use it for other purposes without consent from the sponsor.  It 
is understood that there is an obligation to provide the sponsor with complete data obtained 
during the study.  The information obtained from the clinical study will be used towards the 
development of the investigational product and may be disclosed to regulatory authorities, other 
investigators, corporate partners, or consultants as required. 
19. 
PUBLICATION POLICY 
All information concerning ACE-536 is considered confidential and shall remain the sole 
property of the sponsor.  The investigator(s) agree to use this information only in conducting the 
study and shall not use it for any other purposes without the sponsor’s written approval.  The 
investigator(s) agree not to disclose the sponsor’s confidential information to anyone except to 
persons involved in the study that need such information to assist in conducting the study, and 
then only on like terms of confidentiality and non-use. 
It is understood by the investigator(s) that the information developed from this clinical study will 
be used by the sponsor in connection with the development of ACE-536, and therefore may be 
disclosed as required to regulatory agencies.  To allow for the use of the information derived 
from clinical studies, it is understood that there is an obligation to provide the sponsor with 
complete test results and all data developed in the study. 
No publication or disclosure of study results will be permitted except as specified in a separate, 
written, agreement between the sponsor and the investigator(s). 
20. 
PROTOCOL AMENDMENTS 
Protocol amendments that impact patient safety, change the scope of the investigation, or affect 
the scientific quality of the study must be approved by the IEC and submitted to the appropriate 
regulatory authorities before implementation. 
In the event that the protocol needs to be modified immediately to eliminate an apparent hazard 
to a patient, the sponsor will implement the protocol change and subsequently amend the 
protocol and notify the regulatory authorities and/or the IEC, as appropriate. 
 

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21. 
DATA HANDLING AND RECORDKEEPING 
21.1. 
Case Report Form Completion 
CRFs will be completed for each enrolled patient.  It is the investigator’s responsibility to ensure 
the accuracy, completeness, and timeliness of the data reported in the patient’s CRF.  Source 
documentation supporting the CRF data should indicate the patient’s participation in the study 
and should document the dates and details of study procedures, AEs, and patient status. 
Investigators will maintain copies of the CRFs at the clinical site.  For patients who discontinue 
or terminate from the study, the CRFs will be completed as much as possible, and the reason for 
the discontinuation or termination clearly and concisely specified on the appropriate CRF. 
21.2. 
Retention of Records 
The investigator will maintain all study records according to ICH-GCP and applicable regulatory 
requirements.  Records will be retained for at least 2 years after the last marketing application 
approval or 2 years after formal discontinuation of the clinical development of the investigational 
product, or according to applicable regulatory requirements.  If the investigator withdraws from 
the responsibility of keeping the study records, custody must be transferred to a person willing to 
accept the responsibility.  The sponsor must be notified in writing if a custodial change occurs. 

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22. 
STUDY FINANCE AND INSURANCE 
22.1. 
Study Finance 
The costs necessary to perform the study will be agreed with each Investigator and will be 
documented in a separate financial agreement that will be signed by the Investigator and 
Acceleron Pharma Inc. or designee, prior to the study commencing.  
Participants may be reimbursed for study-related travel.  
22.2. 
Insurance 
The Sponsor has insurance coverage for study related ACE-536 induced injury and other 
liabilities incurred during clinical studies which will provide compensation for any study related 
injury according to the guidelines set out by the Association of the British Pharmaceutical 
Industry (ABPI), namely “Clinical Studies Compensation for Medicine Induced Injury. 

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23. 
REFERENCES 
1. Massague J. TGF-beta signal transduction. Annu Rev Biochem 1998;67:753-91. 
2. Goldberg SL, Chen E, Corral M, et al. Incidence and Clinical Complications of 
Myelodysplastic Syndromes Among United States Medicare Beneficiaries. J Clin Oncol 2010. 
3. Hofmann W-K, Lubbert, M., Hoelzer, D., Koeffler, HP. Myelodysplastic syndromes. 
Hematol J 2004;5:1-8. 
4. Greenberg P, Cox C, LeBeau MM, et al. International scoring system for evaluating 
prognosis in myelodysplastic syndromes. Blood 1997;89:2079-88. 
5. Germing U, Aul C, Niemeyer CM, Haas R, Bennett JM. Epidemiology, classification and 
prognosis of adults and children with myelodysplastic syndromes. Ann Hematol 2008;87:691-9. 
6. Williamson PJ, Kruger AR, Reynolds PJ, Hamblin TJ, Oscier DG. Establishing the incidence 
of myelodysplastic syndrome. Br J Haematol 1994;87:743-5. 
7. Matsuda A, Germing U, Jinnai I, et al. Difference in clinical features between Japanese and 
German patients with refractory anemia in myelodysplastic syndromes. Blood 2005;106:2633-
40. 
8. Neukirchen J, Schoonen WM, Strupp C, et al. Incidence and prevalence of myelodysplastic 
syndromes: data from the Dusseldorf MDS-registry. Leuk Res 2011;35:1591-6. 
9. Aul C, Gattermann N, Schneider W. Age-related incidence and other epidemiological aspects 
of myelodysplastic syndromes. Br J Haematol 1992;82:358-67. 
10. Cheson BD, Greenberg PL, Bennett JM, et al. Clinical application and proposal for 
modification of the International Working Group (IWG) response criteria in myelodysplasia. 
Blood 2006;108:419-25. 
11. Clinical Practice Guidelines in Oncology: Myelodysplastic Syndromes. V.1.2012. 2012. 
(Accessed at www.nccn.org.) 
12. Casadevall N, Durieux P, Dubois S, et al. Health, economic, and quality-of-life effects of 
erythropoietin and granulocyte colony-stimulating factor for the treatment of myelodysplastic 
syndromes: a randomized, controlled trial. Blood 2004;104:321-7. 
13. Noel P, Solberg LA, Jr. Myelodysplastic syndromes. Pathogenesis, diagnosis and treatment. 
Crit Rev Oncol Hematol 1992;12:193-215. 
14. Platzbecker U, Hofbauer LC, Ehninger G, Holig K. The clinical, quality of life, and 
economic consequences of chronic anemia and transfusion support in patients with 
myelodysplastic syndromes. Leuk Res 2012;36:525-36. 
15. Jadersten M, Montgomery SM, Dybedal I, Porwit-MacDonald A, Hellstrom-Lindberg E. 
Long-term outcome of treatment of anemia in MDS with erythropoietin and G-CSF. Blood 
2005;106:803-11. 
16. Moyo V, Lefebvre P, Duh MS, Yektashenas B, Mundle S. Erythropoiesis-stimulating agents 
in the treatment of anemia in myelodysplastic syndromes: a meta-analysis. Ann Hematol 
2008;87:527-36. 

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17. Aul C, Arning M, Runde V, Schneider W. Serum erythropoietin concentrations in patients 
with myelodysplastic syndromes. Leuk Res 1991;15:571-5. 
18. Claessens YE, Bouscary D, Dupont JM, et al. In vitro proliferation and differentiation of 
erythroid progenitors from patients with myelodysplastic syndromes: evidence for Fas-dependent 
apoptosis. Blood 2002;99:1594-601. 
19. Parker JE, Mufti GJ. The role of apoptosis in the pathogenesis of the myelodysplastic 
syndromes. Int J Hematol 2001;73:416-28. 
20. Quintas-Cardama A, Santos FP, Garcia-Manero G. Therapy with azanucleosides for 
myelodysplastic syndromes. Nat Rev Clin Oncol 2010;7:433-44. 
21. Komrokji RS, List AF. Role of lenalidomide in the treatment of myelodysplastic syndromes. 
Semin Oncol 2011;38:648-57. 
22. Kornblith AB, Herndon JE, 2nd, Silverman LR, et al. Impact of azacytidine on the quality of 
life of patients with myelodysplastic syndrome treated in a randomized phase III trial: a Cancer 
and Leukemia Group B study. J Clin Oncol 2002;20:2441-52. 
23. Fenaux P, Mufti GJ, Hellstrom-Lindberg E, et al. Efficacy of azacitidine compared with that 
of conventional care regimens in the treatment of higher-risk myelodysplastic syndromes: a 
randomised, open-label, phase III study. Lancet Oncol 2009;10:223-32. 
24. Lubbert M, Suciu S, Baila L, et al. Low-Dose Decitabine Versus Best Supportive Care in 
Elderly Patients With Intermediate- or High-Risk Myelodysplastic Syndrome (MDS) Ineligible 
for Intensive Chemotherapy: Final Results of the Randomized Phase III Study of the European 
Organisation for Research and Treatment of Cancer Leukemia Group and the German MDS 
Study Group. J Clin Oncol 2011. 
25. Lin YW, Slape C, Zhang Z, Aplan PD. NUP98-HOXD13 transgenic mice develop a highly 
penetrant, severe myelodysplastic syndrome that progresses to acute leukemia. Blood 
2005;106:287-95. 
26. Vardiman JW, Thiele J, Arber DA, et al. The 2008 revision of the World Health 
Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and 
important changes. Blood 2009;114:937-51. 
27. Oken MM, Creech RH, Tormey DC, et al. Toxicity and response criteria of the Eastern 
Cooperative Oncology Group. Am J Clin Oncol 1982;5:649-55. 
28. Yellen SB,  Cella DF, Webster K, et al. Measuring fatigue and other anemia-related 
symptoms with the Functional Assessment of Cancer Therapy (FACT) measurement system. J 
Pain Symptom Manage 1997;13(2): 63-74. 
29. Cella D, Eaton D, Lai JS, et al. Combining anchor and distribution-based methods to derive 
minimal clinically important differences on the Functional Assessment of Cancer Therapy 
(FACT) anemia and fatigue scales. J Pain Symptom Manage 2002; 24(6):547-561.  
30. Eremenco SL, Cella DF, Arnold BJ. A comprehensive method for the translation and cross-
cultural validation of health-status questionnaires. Evaluation and the Health Professions 2005; 
28(2):212-232. 

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24. 
APPENDICES 
24.1. 
Appendix 1: WHO Classification and Criteria for the 
Myelodysplastic Syndromes26  
 
Disease 
Blood findings 
Bone marrow findings 
Refractory cytopenia with unilineage 
dysplasia (RCUD): (refractory anemia 
[RA]; refractory neutropenia [RN]; 
refractory thrombocytopenia [RT])  
Unicytopenia or 
bicytopenia
a 
 
No or rare blasts  
(< 1%)
b  
Unilineage dysplasia: ≥ 10% of the cells in 
one myeloid lineage  
 
< 5% blasts  
 
< 15% of erythroid precursors are ring 
sideroblasts  
Refractory anemia with ring sideroblasts 
(RARS)  
Anemia 
 
No blasts  
≥ 15% of erythroid precursors are ring 
sideroblasts  
 
Erythroid dysplasia only  
 
< 5% blasts  
Refractory cytopenia with multilineage 
dysplasia (RCMD)  
Cytopenia(s) 
 
No or rare blasts  
(< 1%)b 
 
No Auer rods 
 
< 1 x109/L monocytes  
Dysplasia in ≥ 10% of the cells in ≥ 2 
myeloid lineages (neutrophil and/or 
erythroid precursors and/or megakaryocytes)  
 
< 5% blasts in marrow  
 
No Auer rods  
 
± 15% ring sideroblasts  
Refractory anemia with excess blasts-1 
(RAEB-1)  
Cytopenia(s) 
 
< 5% blastsb 
 
No Auer rods 
< 1 x109/L monocytes  
Unilineage or multilineage dysplasia  
 
5%-9% blastsb  
 
No Auer rods  
Refractory anemia with excess blasts-2 
(RAEB-2)  
Cytopenia(s) 
 
5%-19% blasts
c 
 
Auer rods ±c 
 
< 1 x109/L monocytes  
Unilineage or multilineage dysplasia  
 
10%-19% blastsc  
 
Auer rods ±c  

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Disease 
Blood findings 
Bone marrow findings 
Myelodysplastic syndrome-unclassified 
(MDS-U)  
Cytopenias 
 
< 1% blastsb 
Unequivocal dysplasia in < 10% of cells in 
one or more myeloid lineages when 
accompanied by a cytogenetic abnormality 
considered as presumptive evidence for a 
diagnosis of MDS  
 
< 5% blasts  
MDS associated with isolated del(5q)  
Anemia 
 
Usually normal or 
increased platelet count 
 
No or rare blasts  
(< 1%)  
Normal to increased megakaryocytes with 
hypolobated nuclei  
 
< 5% blasts  
 
Isolated del(5q) cytogenetic abnormality  
 
No Auer rods  
a Bicytopenia may occasionally be observed.  Cases with pancytopenia should be classified as MDS-U.  
b If the marrow myeloblast percentage is < 5% but there are 2% to 4% myeloblasts in the blood, the diagnostic 
classification is RAEB-1.  Cases of RCUD and RCMD with 1% myeloblasts in the blood should be classified as MDS-U.  
c Cases with Auer rods and < 5% myeloblasts in the blood and less than 10% in the marrow should be classified as 
RAEB-2.  Although the finding of 5% to 19% blasts in the blood is, in itself, diagnostic of RAEB-2, cases of RAEB-2 
may have < 5% blasts in the blood if they have Auer rods or 10% to 19% blasts in the marrow or both.  Similarly, cases of 
RAEB-2 may have < 10% blasts in the marrow but may be diagnosed by the other 2 findings, Auer rod+ and/or 5% to 
19% blasts in the blood. 

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24.2. 
Appendix 2: International Prognostic Scoring System (IPSS) for 
Myelodysplastic Syndromes (MDS)4 
 
 
 
 
 
 
 
 
 
 
a Good = normal, –Y, del(5q), del(20q); Intermediate = other abnormalities; 
  Poor = complex (≥ 3 abnormalities) or chromosome 7 anomalies 
b Neutrophils < 1800/μL, hemoglobin < 10 g/dL, platelets < 100,000/μL. 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
IPSS Scoring Value 
Prognostic Variable 
0 
0.5 
1.0 
1.5 
2.0 
Bone Marrow Blasts (%) 
< 5 
5-10 
— 
11-20 
21-30 
Karyotypea 
Good 
Intermediate 
Poor 
 
 
Cytopeniasb 
0-1 
2-3 
 
 
 
 
IPSS Classification 
Risk Group 
Low 
Int-1 
Int-2 
High 
Score 
0 
0.5 - 1.0 
1.5 - 2.0 
≥ 2.5 

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24.3. 
Appendix 3: ECOG Performance Status27 
The ECOG scale is used to assess a patient’s quality of life in an evaluation by a health 
professional of the daily activities and how the activities are affected by the disease of the 
patient. 
 
 
Grade ECOG 
0 
Fully active, able to carry on all pre-disease performance without restriction 
1 
Restricted in physically strenuous activity but ambulatory and able to carry out work of 
a light or sedentary nature, e.g., light house work, office work 
2 
Ambulatory and capable of all self-care but unable to carry out any work activities. Up 
and about more than 50% of waking hours 
3 
Capable of only limited self-care, confined to bed or chair more than 50% of waking 
hours 
4 
Completely disabled.  Cannot carry on any self-care.  Totally confined to bed or chair 
5 
Dead 

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24.4. 
Appendix 4: International Working Group (IWG) Criteria - 
Erythroid Response Evaluation10 
 
Hematologic 
Improvement (HI)a 
Response Criteria 
(Responses must last at least 8 weeks) 
Erythroid response (Hi-E) 
(pretreatment Hgb < 11 g/dL)   
Hgb increase of ≥ 1.5 g/dL for patients not transfused; or, as 
defined by having received less than 4 units of RBCs within 
8 weeks of Cycle 1 Day 1 
Reduction by ≥ 4 units of RBCs transfused (for a Hgb 
≤ 9.0 g/dL) during any 8-week period on study, compared 
with the 8-week period prior to study day 1 
Platelet response (HI-P) 
(pretreatment, < 100 x109/L)   
Absolute increase of ≥ 30 x 109/L for patients starting with 
> 20 x 109/L platelets   
Increase from < 20 x 109/L to > 20 x 109/L and by at least 
100% 
Neutrophil response (HI-N) 
(pretreatment, < 1.0 x109/L)   
At least 100% increase and an absolute increase > 0.5 x 109/L 
a Pre-treatment counts are averages of at least 2 measurements (not influenced by transfusions) ≥ 1 week apart 
within 28 days prior to Day 1.  
Hgb indicates hemoglobin; RBC: red blood cell; HI: hematologic improvement. 
 

Protocol A536-03  
 
 
 
 
 
 
 
 
 
 
 
 
 
                         CONFIDENTIAL 
Revision Level: 05 
 
05-Jul-2016 
Page 74 of 74                                                     
Acceleron Pharma Inc. 
24.5. 
Appendix 5: National Cancer Institute (NCI) Common Terminology 
Criteria for Adverse Events (CTCAE) Version 4.0  
 
See http://evs.nci.nih.gov/ftp1/CTCAE/CTCAE