REGENXBIO Shares Plunge After FDA Places Clinical Hold on RGX-121

REGENXBIO Inc. (NASDAQ:RGNX) shares tumbled 35% after the U.S. Food and Drug Administration placed a clinical hold on RGX-121, the company’s investigational gene therapy for Mucopolysaccharidosis type II (MPS II), also known as Hunter Syndrome.

The regulatory action followed the identification of asymptomatic findings in spine MRI scans from five participants in the CAMPSIITE study. Following the development, REGENXBIO said it no longer expects to resubmit the Biologics License Application for RGX-121 in the near term.

MRI Findings Identified in Five Participants

The company said five study participants were found to have either a small nodule or a small cystic mass on spine MRI scans.

The patients had received RGX-121 through intracisternal or intraventricular administration approximately three to six years earlier.

Investigators classified the findings as nonserious, while radiologists believe they are likely benign. REGENXBIO added that no nodules or masses were detected in brain MRI scans.

All five participants continue to perform well clinically, according to the company, with neurocognitive and neurobehavioral assessments showing overall stability or improvement.

Expanded Monitoring Programme Uncovers Findings

The abnormalities were detected through an expanded MRI surveillance programme introduced by REGENXBIO several months ago following a separate clinical hold involving RGX-111.

Spine MRI scans are not routinely conducted for MPS patients either in standard clinical practice or in clinical trials. As a result, the company said the underlying prevalence and clinical significance of these asymptomatic findings within this patient population are currently unknown.

REGENXBIO believes the observations are unique to and limited to its Hunter Syndrome programme. Longer-term monitoring and further analysis will now be required to better understand their significance and assess the overall benefit-risk profile of RGX-121.

RGX-121 Regulatory Timeline Faces Delay

The FDA clinical hold represents a significant setback for the RGX-121 programme, particularly because REGENXBIO no longer anticipates resubmitting its BLA in the near future.

That uncertainty weighed heavily on NASDAQ:RGNX shares, with the 35% decline reflecting investor concerns about both the programme’s regulatory pathway and the additional work that may be required before development can move forward.

The company will continue evaluating the five participants and gathering longer-term data as it works to determine the relevance of the MRI findings.

Duchenne and Retinal Programmes Remain on Track

Despite the setback involving RGX-121, REGENXBIO said it remains focused on its Duchenne muscular dystrophy and retinal disease programmes.

Those candidates use a different capsid and different administration routes from the Hunter Syndrome therapy, distinguishing them from RGX-121.

REGENXBIO continues to plan a BLA submission for its Duchenne programme during the current quarter. It also expects to report topline pivotal data from its wet age-related macular degeneration programme in the fourth quarter.

These upcoming milestones could become increasingly important for NASDAQ:RGNX as investors assess the implications of the RGX-121 clinical hold and shift their attention towards the company’s remaining late-stage development programmes.

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