Luspatercept and sotatercept. (A) Molecular structure of luspatercept and sotatercept. (B) Mechanism of action of luspatercept. ACE, angiotensin-converting enzyme; BasoE, baso erythroblast; BFU-E, burst-forming unit erythroid; CFU-E, colony-forming unit erythroid; OrthoE, ortho erythroblast; PolyE, poly erythroblast; ProE, pro erythroblast; Retic, reticulocyte.