Beyond the Erythroid Maturation Brake: A Multilayered and Falsifiable Hypothesis for Inadequate Luspatercept Response in Myelodysplastic Neoplasms

Luspatercept (ACE-536) acts as a recombinant fusion protein trap for transforming growth factor-beta (TGF-β) superfamily ligands, diminishing SMAD2/3 signaling to alleviate late-stage erythroid maturation arrest in myelodysplastic neoplasms (MDS). However, a distinct subset of patients exhibits absolute primary inefficacy despite adequate dosing. We propose a multilayered systems-biology hypothesis: luspatercept failure in high-risk molecular phenotypes is governed by an uncoupling between downstream maturation relief and persistent upstream niche/epigenetic stress. Analyzing an index profile featuring co-mutated ASXL1/EZH2/TET2, grade 3/3 marrow fibrosis, elevated hepcidin (185.8 ng/mL), hyperferritinemia (1671 ng/mL), and discordant erythropoietic indices (elevated immature reticulocyte fraction with depressed reticulocyte production index), we construct a tripartite model. We hypothesize that: (1) ASXL1/PRC2-mediated epigenetic dysregulation drives continuous progenitor exhaustion refractory to terminal signaling modulation; (2) severe architectural fibrosis mechanically compromises the vascular niche; and (3) hyperhepcidinemia and parenchymal iron toxicity maintain a pro-inflammatory (IL-6-driven) oxidative loop. Consequently, relieving the terminal SMAD2/3 brake alone is insufficient to generate functional circulating erythrocytes when upstream clonal architecture is structurally and epigenetically disrupted. We propose that restoring erythropoiesis in this refractory phenotype requires a synchronized dual-level therapeutic approach combining hypomethylating epigenetic modulation (5-azacitidine) to quiet the stromal/clonal niche with luspatercept to unlock terminal maturation.