Regenxbio (RGNX) Stock Plummets 25% as FDA Halts Gene Therapy Trial

Key Takeaways

• Shares of Regenxbio plummeted 25% to $8.05 following FDA’s clinical hold on gene therapy candidate RGX-121
• An expanded imaging surveillance program detected asymptomatic nodules and cystic masses on spinal scans of five trial participants
• Medical experts classified the discoveries as non-serious with probable benign characteristics, yet regulatory intervention followed
• The biotech firm has abandoned near-term plans to resubmit its Biologics License Application for RGX-121
• Despite setbacks, the company maintains plans to file a BLA for its Duchenne treatment this quarter and expects wet AMD trial results in Q4

Shares of Regenxbio tumbled 25% to $8.05 during Monday’s trading session following the FDA’s decision to impose a clinical hold on RGX-121, the company’s experimental gene therapy targeting Hunter syndrome. The stock experienced a temporary trading suspension prior to the announcement.

REGENXBIO Inc., RGNX

The regulatory action stemmed from results of an enhanced MRI surveillance initiative that revealed unexpected observations in five trial participants. Each individual presented with a small nodular formation or cystic structure along their spinal column. The affected patients had all undergone RGX-121 administration approximately three to six years before the imaging discoveries.

Medical investigators determined these observations did not constitute serious adverse events. Radiological specialists evaluated the formations as most likely benign in nature, with no definitive clinical or histopathological evidence establishing a causal relationship to the therapeutic intervention.

Nevertheless, regulatory authorities proceeded with implementing a clinical hold on the development program, prompting Regenxbio to announce it has shelved expectations for near-term BLA resubmission for RGX-121.

As recently as this past June, FDA officials had communicated to Regenxbio that no supplementary clinical investigations were necessary prior to BLA resubmission during the third quarter. That projected timeline has now been completely abandoned.

This marks the second Regenxbio development candidate to face FDA-imposed suspension in recent months. RGX-111, a distinct therapeutic candidate, received a clinical hold earlier this year, occurring just weeks ahead of an anticipated regulatory decision. The suspension was subsequently expanded to encompass RGX-121 due to shared characteristics between the two treatment approaches.

Executive Commentary

Chief Executive Officer Curran Simpson characterized the imaging observations as appearing “unique and limited” to the Hunter syndrome development program, while recognizing they “require longer-term follow-up and additional data analysis” before the organization can comprehensively evaluate RGX-121’s benefit-risk balance.

All five affected individuals maintain overall stability or demonstrate improvement across neurocognitive and neurobehavioral evaluation measures.

Hunter syndrome represents a rare hereditary condition characterized by the body’s inability to metabolize complex carbohydrate molecules. The disorder predominantly impacts male patients and significantly limits lifespan, with most affected individuals surviving only into their third decade.

Pipeline Progress Continues Elsewhere

Regenxbio emphasizes that its Duchenne muscular dystrophy and wet age-related macular degeneration development programs utilize distinct capsid technology and administration pathways and remain unaffected by the regulatory hold.

The biotechnology company intends to submit a BLA for its Duchenne therapeutic candidate within the current fiscal quarter.

Primary endpoint data for its wet AMD candidate, developed in collaboration with AbbVie, is anticipated during Q4. Financial analysts have highlighted this data release as a potentially significant catalyst for Regenxbio’s stock performance.

Other biotechnology firms operating in related therapeutic areas experienced spillover effects. Sarepta Therapeutics declined 3.3% while EyePoint shares dropped 4.3% during the trading session.

Earlier this month, Barclays analyst Eliana Merle revised her rating on Regenxbio to Equal Weight from Overweight, pointing to regulatory uncertainty and intensifying competitive pressures as potential headwinds for both development programs.

The company stated it is coordinating with development partner NS Pharma to review supplementary patient imaging studies and extended follow-up information, and will integrate FDA guidance into the strategic direction for RGX-121 going forward.

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