FDA Credibility Reset Signals Evidence Rigor, Not Leniency: Two Assets, Zero Data Disclosed

FDA's Post-Makary Era: A Return to Data-Driven Reliability

Following a period of instability under former leadership, the FDA is actively working to restore its reputation for reliability, integrity, and transparency. Recent regulatory outcomes for Replimune's advanced melanoma drug and Capricor's Duchenne muscular dystrophy cell therapy, deramiocel, are seen by experts as indicators of this shift. While the agency is demonstrating a return to data-driven decisions, this does not necessarily imply an easier regulatory path for drugmakers, who are advised to ensure robust data packages and early alignment with the FDA.

• The FDA, under new leadership, is making a conscious effort to move past the "tumultuous stretch" experienced under former Commissioner Marty Makary and CBER chief Vinay Prasad. This involves a renewed focus on reliability, integrity, and transparency in regulatory decisions, with recent advisory committee meetings for Capricor and Replimune serving as key examples of this data-driven approach.
• Capricor's Duchenne muscular dystrophy cell therapy, deramiocel, faced a challenging advisory committee meeting where the Cellular, Tissue, and Gene Therapies Advisory Committee (CTGTAC) voted 9–3 against its approval, citing "very fragile" pivotal data. Despite this, the FDA has shown receptiveness to augmenting the data package with open-label extension data, potentially leading to an extension of its August 22 PDUFA date and offering a continued regulatory path.
• Replimune's advanced melanoma therapy, Tudriqev (RP1), secured an accelerated approval despite a challenging regulatory journey that included two prior rejections and initial FDA briefing documents calling its submission "not interpretable." The drug ultimately received a 10–3 vote in support of approval from the CTGTAC when reviewed in combination with Bristol Myers Squibb’s Opdivo.

The Unmet Need and Challenges in Duchenne Muscular Dystrophy Treatment

Despite meaningful therapeutic advances in Duchenne muscular dystrophy (DMD), existing treatment modalities continue to face substantial clinical, biological, and mechanistic limitations. No current approach achieves durable disease modification across all patient populations, and each therapeutic class carries distinct constraints that complicate long-term management.

• Gene therapy efficacy and safety uncertainties: Delandistrogene moxeparvovec, the first FDA-approved gene therapy for DMD, has shown transgene expression and early functional signals, but long-term efficacy and durability remain unconfirmed. Immune-mediated toxicities — including myositis, myocarditis, and liver injury — pose significant clinical risks, necessitating immunoprophylaxis, careful patient selection, and rigorous post-treatment monitoring. Patients with pre-existing anti-AAV immunity are currently ineligible for systemic gene transfer, and ongoing efforts to address vector size constraints through dual/triple AAV systems, non-viral platforms, and capsid engineering are still investigational.

• Exon skipping therapy limitations: The clinical utility of antisense oligonucleotide (AON)-based exon skipping remains contested. Eteplirsen, the lead agent in this class, has faced sustained scrutiny over insufficient evidence of therapeutic effect, with ongoing controversy surrounding both its efficacy and the AON sequence employed. Broader challenges include restricted patient eligibility — as applicability is mutation-dependent — and suboptimal tissue delivery.

• Corticosteroid-associated morbidities: Prednisone, the longstanding standard of care, is associated with significant adverse effects including weight gain, hirsutism, and cushingoid appearance at the recommended dose of 0.75 mg/kg/day. Chronic prednisone use also drives gut dysbiosis, inducing a pro-inflammatory phenotype and compromised intestinal barrier integrity that may underlie several well-recognized glucocorticoid side effects. Deflazacort, an alternative corticosteroid, may carry a comparatively greater risk of cataract formation, while potentially conferring less weight gain than prednisone in early treatment years.

• Gaps in cardiac management: Heart failure is a leading cause of morbidity in DMD, yet the specific pathomechanisms driving dilated cardiomyopathy (DCM) in this population remain poorly understood. As a result, cardiac management relies on generalized DCM treatment strategies rather than DMD-targeted interventions, representing a critical gap in precision care for this patient population.

Evolving Duchenne Muscular Dystrophy Treatment Landscape Amidst FDA Shifts

Over the past five years, the Duchenne muscular dystrophy (DMD) treatment landscape has been fundamentally reshaped by the approval of the first gene therapy and continued refinement of antisense oligonucleotide (ASO) strategies. Delandistrogene moxeparvovec — an AAV-rh74 vector delivering a functional micro-dystrophin construct — became the first FDA-approved gene therapy for DMD, indicated for ambulatory pediatric patients aged 4 through 5 years with confirmed DMD mutations. The pivotal phase 3 EMBARK trial (N=125, ages 4 to <8 years) administered a single intravenous dose of 1.33 × 10¹⁴ vg/kg but did not meet its primary endpoint at week 52: the between-group difference in North Star Ambulatory Assessment (NSAA) score was 0.65 points (95% CI: −0.45, 1.74; P=0.2441). Nevertheless, secondary functional endpoints — including Time to Rise (−0.64 seconds), 10-meter Walk/Run (−0.42 seconds), and 4-step ascent time (−0.36 seconds) — demonstrated more favorable trends, and mean micro-dystrophin expression reached 34.29% in treated patients versus 0.00% in placebo at week 12. Two-year follow-up data from EMBARK part 1 showed statistically significant benefits versus propensity score-weighted external controls across NSAA and timed function tests, with maintained micro-dystrophin expression and sarcolemmal localization through 64 weeks. Longer-term phase 1/2a data (Study 101; N=4) further showed a statistically significant 9-point NSAA advantage relative to a propensity score-weighted external control cohort at year 4 (least-squares mean difference: 9.4; SE: 3.4; P=0.0125). Safety signals across trials include immune myositis, myocarditis, thrombocytopenia, and hepatotoxicity, with serious treatment-related adverse events reported in 11.1% of EMBARK participants and one death reported post-marketing outside of a trial setting.

On the mutation-specific therapy front, four exon-skipping ASOs — eteplirsen, golodirsen, viltolarsen, and casimersen — have received FDA approval, with casimersen (targeting exon 45, estimated to address ~8% of the DMD population) approved under accelerated approval in February 2021, contingent on confirmatory phase 3 data. While long-term real-world use of these agents suggests a manageable safety profile and some delay in muscle deterioration, their molecular efficacy remains constrained by limited dystrophin protein restoration. This has driven a wave of next-generation ASO development incorporating novel chemical modifications and bioconjugation strategies — including peptide and antibody conjugates — to enhance muscle cell uptake, endosomal escape, and nuclear import. Early clinical trial data on these next-generation compounds indicate clear improvements in molecular efficacy compared to first-generation ASOs, though their long-term safety profiles remain to be fully established.

Beyond gene-targeted approaches, vamorolone has emerged as a clinically differentiated steroidal anti-inflammatory alternative to traditional corticosteroids. Its mechanistic distinctions — non-metabolism by 11β-hydroxysteroid dehydrogenases, mineralocorticoid receptor antagonism, and differential co-factor binding — underpin a more favorable safety profile, particularly with respect to growth. In a 30-month nonrandomized controlled trial (N=46 boys, ages 4.5–7.5 years), vamorolone at doses escalated to 2.0–6.0 mg/kg/day produced no statistically significant decline in timed stand velocity (−0.011 rises/s; 95% CI: −0.068 to 0.046) and showed no statistically significant differences from glucocorticoid-treated historical controls on NSAA or BMI z-score trajectories. Critically, vamorolone-treated participants demonstrated stable height percentiles over time (+0.37 percentile/month; 95% CI: 0.23 to 0.52), in marked contrast to the significant growth suppression observed in glucocorticoid-treated patients in the Duchenne Natural History Study. Taken together, these developments reflect a maturing therapeutic ecosystem that now spans gene therapy, precision ASO strategies, and safer anti-inflammatory agents — each addressing distinct aspects of DMD pathophysiology with an evolving evidence base.