FDA Issues Complete Response Letter for RGX-121, REGENXBIO Shares Fall 11%
REGENXBIO received an FDA Complete Response Letter for its RGX-121 BLA in MPS II, citing eligibility criteria and surrogate endpoint concerns that could require new trials or extended follow-up in the ultra-rare population. Shares fell 11% premarket as management schedules a Type A meeting to plan a BLA resubmission.
1. FDA CRL Details
The FDA issued a Complete Response Letter for the RGX-121 Biologics License Application in MPS II, highlighting issues with patient eligibility criteria and the use of surrogate endpoints. The letter outlined potential next steps including additional trials, dosing more patients, longer follow-up or introduction of untreated control arms in the ultra-rare patient population.
2. Development Impact and Next Steps
REGENXBIO plans to request a Type A meeting to address the FDA’s concerns and shape its strategy for resubmission with supplementary trial evidence. Implementing any of the CRL pathways could extend development timelines by several months to years, given the scarcity of eligible patients with Hunter syndrome.
3. Clinical Data and Safety Context
The RGX-121 filing was backed by positive biomarker, functional and safety results from the CAMPSIITE I/II/III trial through 12 months, demonstrating consistent tolerability across all phases. A prior clinical hold on RGX-111 due to a neoplasm finding has led to heightened regulator scrutiny of both gene therapy programs’ safety profiles.
4. Market Reaction and Analyst View
Shares declined 10.99% in premarket trading on the CRL announcement, reflecting investor concern over regulatory hurdles and potential delays. Despite a consensus Buy rating with an average price target of $31.38, analysts emphasize the FDA’s cautious stance on accelerated pathways lacking placebo-controlled data.