A Study of IMR-687 in Subjects With Beta Thalassemia

Inclusion Criteria: 1. Documented diagnosis of β-thalassemia or HbE/ β-thalassemia in their medical history. Concomitant alpha gene deletion, duplication, or triplication is allowed. 2. Documentation of the dates of transfusion events and the number of all pRBC units per event within the 12 weeks prior to the Baseline (Day 1) visit. . 3. Must be willing and able to complete all study assessments and procedures, and to communicate effectively with the investigator and site staff. 4. TDT Subjects: subjects must be regularly transfused, defined as \>3 to 10 pRBC units in the12 weeks prior to Baseline (Day 1) visit and no transfusion-free period for \>35 days during that period. 5. NTDT subjects: Subjects must be transfusion independent, defined as 0 to ≤3 units of pRBCs received during the 12-week period prior to the Baseline (Day 1) visit, must not be on a regular transfusion program, must be RBC transfusion-free for at least ≥ 4 weeks prior to randomization, and must not be scheduled to start a regular 6. hematopoietic stem cell transplantation within 9 months. 7. NTDT subjects: Subjects must have Hb ≤10.0 g/dL at Screening; the screening Hb sample must be collected 7 to 28 days prior to randomization. Hb values within 21 days post-transfusion will be excluded. 8. ECOG performance score of 0 to 1 9. Female subjects must not be pregnant, or breastfeeding and be highly unlikely to become pregnant. Male subjects must be unlikely to impregnate a partner. Exclusion Criteria: 1. Diagnosis of α-thalassemia (e.g., hemoglobin H \[HbH\]) or hemoglobin S (HbS)/ β thalassemia. 2. Body mass index (BMI) \<17.0 kg/m2 or a total body weight \<45 kg; or BMI \>35 kg/m2 3. Subjects with known active hepatitis A, hepatitis B, or hepatitis C, with active or acute event of malaria, or who are known to be positive for human immunodeficiency virus (HIV). 4. Stroke requiring medical intervention ≤24 weeks prior to randomization. 5. Platelet count \>1000 × 109/L. 6. Participated in another clinical study of an investigational agent (or device) within 30 days or 5-half-lives of date of informed consent, whichever is longer, or is currently participating in another study. 7. For Subjects on iron chelation therapy (ICT) at the time of ICF signing, initiation of ICT less than 24 weeks before the predicted randomization date. 8. Prior exposure to sotatercept or luspatercept, IMR-687, or gene therapy within 6 months prior to randomization (Day 1). 9. Subjects who have major organ damage