Luspatercept

Luspatercept is a recombinant fusion protein, not a short peptide, consisting of a modified extracellular domain of the human activin receptor type IIB linked to the Fc portion of human immunoglobulin G1. It was developed by Acceleron Pharma in partnership with Celgene, which later became part of Bristol Myers Squibb. Rather than stimulating erythropoietin signalling, it acts as a ligand trap for selected members of the transforming growth factor-beta superfamily that restrain late red blood cell maturation.

Luspatercept was approved by the FDA in 2019 and subsequently by the EMA, marketed as Reblozyl, for anaemia associated with beta-thalassaemia and with lower-risk myelodysplastic syndromes. Phase 3 trials in these conditions were notable because they introduced a mechanism distinct from erythropoiesis-stimulating agents, acting on late-stage erythroid precursors. In research, luspatercept is a tool for studying ineffective erythropoiesis, the regulatory role of GDF11 and related ligands, and the balance of SMAD signalling in haematopoiesis. It is listed by WADA as a prohibited substance because of its effects on red cell production.

Luspatercept binds and sequesters TGF-beta superfamily ligands, particularly growth differentiation factor 11, GDF8 and activin B, preventing them from engaging endogenous activin type II receptors. In conditions such as beta-thalassaemia and myelodysplastic syndromes, excessive signalling through these ligands activates SMAD2 and SMAD3, which impairs the terminal maturation of erythroid precursors and contributes to ineffective erythropoiesis. By reducing this SMAD2/3 signalling, luspatercept promotes differentiation of late-stage erythroblasts into mature red cells in in vitro studies and animal models.">preclinical and clinical studies. This mechanism acts downstream of erythropoietin, distinguishing it from agents that stimulate early erythroid progenitors.