Acceleron Pharma Inc. is a biopharmaceutical company. The Company is focused on its research, development, and commercialization efforts in pulmonary and hematologic diseases. Its research is focused on key natural regulators of cellular growth and repair, particularly the Transforming Growth Factor-Beta (TGF-beta) protein superfamily. The Company's product pipeline includes Sotatercept, ACE-1334 and REBLOZYL (luspatercept-aamt). Its lead pulmonary program, Sotatercept, is an activin receptor type IIA fusion protein that is used for the treatment of patients with pulmonary arterial hypertension (PAH). ACE-1334 is a wholly owned TGF-beta superfamily-based ligand trap designed to bind and inhibit TGF-beta 1 and 3 ligands but not TGF-beta 2. Its REBLOZYL (luspatercept-aamt), is an erythroid maturation agent designed to promote red blood cell (RBC).