FDA Issues Complete Response Letter for REGENXBIO's RGX-121 Gene Therapy BLA

summarizeSummary

REGENXBIO announced that the FDA issued a Complete Response Letter (CRL) for its Biologics License Application (BLA) for RGX-121, an investigational gene therapy for Mucopolysaccharidosis type II (MPS II), citing concerns with the study design and endpoints.

check_boxKey Events

• FDA Issues Complete Response Letter (CRL)

  The U.S. Food and Drug Administration (FDA) issued a CRL regarding REGENXBIO's Biologics License Application (BLA) for RGX-121, an investigational gene therapy for Mucopolysaccharidosis type II (MPS II).

• Reasons for BLA Rejection

  The FDA's CRL cited concerns including uncertainty regarding study eligibility criteria, comparability of the natural history external control, and the appropriateness of CSF HS D2S6 as a surrogate endpoint.

• Company Plans Path Forward

  REGENXBIO plans to request a Type A meeting with the FDA to discuss the CRL and a planned BLA resubmission, aiming to provide additional evidence and longer-term clinical data.

• Impact on Development Timeline

  The CRL suggests potential paths forward such as a new study, treating additional patients with longer-term follow-up, or using an untreated control arm, all of which would significantly delay the approval process.

auto_awesomeAnalysis

REGENXBIO Inc. received a Complete Response Letter (CRL) from the FDA, rejecting its Biologics License Application (BLA) for RGX-121, a gene therapy for Mucopolysaccharidosis type II (MPS II). This is a significant setback for the company's lead gene therapy candidate, delaying its potential commercialization and introducing substantial uncertainty regarding its approval pathway. The FDA cited concerns about study eligibility criteria, comparability of the natural history control, and the appropriateness of the surrogate endpoint. While REGENXBIO plans to engage with the FDA to find a path forward and resubmit the BLA, this will likely entail further studies or longer-term follow-up, extending the development timeline and increasing costs. This news follows a previous clinical hold on both RGX-111 and RGX-121 programs announced on January 28, 2026, indicating ongoing regulatory challenges for the company's gene therapy pipeline.