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

This is a Phase 3, double-blind, randomized, placebo-controlled, multicenter study to determine the efficacy and safety of luspatercept (ACE-536) plus Best supportive care (BSC) versus placebo plus BSC in adults who require regular red blood cell transfusion due to (β)-thalassemia. The study is divided into the following periods: * Historical Period, * Screening/Run-in Period, * Double-blind Treatment Period (48 weeks), * Double-blind Long-term Treatment Period, (at the investigator's discretion an additional 48 weeks), * Open-Label Phase post unblinding and upon Data Monitoring Committee positive recommendation * Post-treatment Follow-up Period