A Novel In Vitro Potency Assay Demonstrating the Anti-Fibrotic Mechanism of Action of CDCs in Deramiocel

<b>Background/Objectives:</b> Duchenne muscular dystrophy (DMD) is characterized by progressive skeletal and cardiac muscle degeneration driven by inflammation and fibrosis, ultimately leading to cardiomyopathy and premature death. Deramiocel, an allogeneic cell therapy composed of cardiosphere-derived cells (CDCs), has demonstrated potent anti-fibrotic and immunomodulatory effects in preclinical models and clinical trials, including HOPE-2 and its open-label extension (HOPE-2 OLE), where Deramiocel treatment significantly attenuated progression of skeletal and cardiac muscle dysfunction. <b>Methods:</b> CDCs in Deramiocel were cultured to generate CM enriched with secreted exosomes and factors, which was subsequently applied to primary human dermal fibroblasts (HDFs). Following co-culture, ex-pression of collagen type I alpha 1 (<i>COL1A</i>) and collagen type III alpha 1 (<i>COL3A</i>) was measured by qRT-PCR. Non-conditioned media serves as a control in the assay. Reduction in <i>COL1A</i> and <i>COL3A</i> expression therefore provides a direct and clinically relevant measure of the anti-fibrotic activity of Deramiocel. <b>Results:</b> A novel in vitro potency assay was developed to quantify the anti-fibrotic activity of Deramiocel. Conditioned media (CM) from over one hundred Deramiocel manufacturing lots significantly suppressed expression of collagen type I alpha 1 (<i>COL1A</i>) and collagen type III alpha 1 (<i>COL3A</i>) in primary human dermal fibroblasts compared with non-conditioned media controls, establishing a robust, reproducible readout of anti-fibrotic activity. The effect was dose-dependent and abrogated by sequential depletion of exosomes and soluble proteins, implicating both as critical mediators of Deramiocel's mechanism of action. Importantly, CDCs in Deramiocel lots classified as potent by this assay were shown to exert a clinically meaningful benefit in DMD patients in the HOPE-2 and HOPE-2 OLE studies. <b>Conclusions:</b> This assay represents a mechanistically informative, therapeutically relevant, reproducible, scalable, and regulatory-compliant approach for assessing Deramiocel potency, enabling consistent manufacturing, and facilitating the continued development of Deramiocel as a disease-modifying therapy for DMD.