RGX-121 is an investigational one-time AAV9 gene therapy candidate for mucopolysaccharidosis type II (MPS II, Hunter syndrome). The program is intended to deliver iduronate-2-sulfatase gene expression through CNS-directed administration and has been evaluated in Phase I/II studies. As of January 29, 2026, partner disclosures reported an FDA clinical hold on RGX-121.
A class action lawsuit was filed against REGENXBIO covering the period from February 9, 2022 to January 27, 2026, following FDA clinical holds on gene therapies RGX-111 and RGX-121 after a CNS tumor was discovered in a trial participant.
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The FDA placed clinical holds on Regenxbio's RGX-111 and RGX-121 gene therapies following a tumor case in an MPS I patient. The company's stock fell nearly 18% on the news.
