FDA rejects REGENXBIO's RGX-121 BLA for MPS II; company plans resubmission

REGENXBIO Inc.

FDA issued CRL on Feb 7, 2026 for RGX-121 (clemidsogene lanparvovec) to treat MPS II (Hunter syndrome).
CRL cites uncertainty in defining neuronopathic population, external control comparability, and surrogate endpoint CSF HS D2S6.
FDA suggests new study, additional patients, longer follow-up, or untreated control arm; company calls it 'devastating'.
REGENXBIO plans to request Type A meeting and aim for BLA resubmission with additional data.
Company had believed it addressed FDA's concerns during BLA review; independent experts supported data.

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