REGENXBIO Inc. and Nippon Shinyaku Co., Ltd. have entered a strategic partnership to develop and commercialize RGX-121 for Mucopolysaccharidosis II (MPS II), also known as Hunter syndrome, and RGX-111 for Mucopolysaccharidosis I (MPS I), also known as Hurler syndrome.
Key Terms of the Agreement:
- Financials: REGENXBIO will receive an upfront payment of $110 million, with up to $700 million in additional payments based on development, regulatory, and sales milestones. This includes $40 million for potential development and regulatory achievements and $660 million for potential sales milestones.
- Royalties: REGENXBIO will earn substantial double-digit royalties on net sales in the U.S. and Asia.
- Responsibilities: Nippon Shinyaku will handle commercialization in the Licensed Territory, while REGENXBIO will oversee the clinical development of RGX-121 and RGX-111.
- Priority Review Voucher (PRV): REGENXBIO retains full rights to the PRV for RGX-121 and will receive 100% of any proceeds from its potential sale upon approval.
- Closing Timeline: The transaction is expected to close by the end of Q1 2025, subject to customary conditions and regulatory approvals.
About RGX-121 and RGX-111:
MPS I and II patients lack specific enzymes necessary to break down large sugar molecules, leading to their accumulation in tissues. This accumulation causes a range of physiological and neurological symptoms. Both therapies aim to treat neurological symptoms by addressing enzyme deficiencies through direct gene delivery to the central nervous system (CNS).
RGX-121 (MPS II – Hunter Syndrome):
- Mechanism: Uses an AAV9 vector to deliver the iduronate-2-sulfatase (IDS) gene, reducing glycosaminoglycan (GAG) accumulation in the CNS.
- Clinical Trial: The CAMPSIITE™ study (Phase I/II/III) is ongoing.
- Recent Data: Pivotal trial data shows an 86% median reduction in cerebrospinal fluid (CSF) levels of D2S6, a key biomarker, with no serious drug-related adverse events reported.
RGX-111 (MPS I – Hurler Syndrome):
- Mechanism: Delivers the alpha-L-iduronidase (IDUA) gene via an AAV9 vector to address enzyme deficiency and reduce GAG buildup.
- Clinical Trial: Currently in Phase I/II.
- Recent Data: Interim results from February 2023 indicate RGX-111 is well-tolerated, with positive biomarker and neurodevelopmental outcomes and no serious drug-related adverse events.
Other companies, such as Denali Therapeutics and Ultragenyx, are also advancing treatments for MPS, leveraging biomarker findings to seek accelerated approvals. Denali’s DNL310 is in Phase 2/3 trials for Hunter syndrome, and Ultragenyx has submitted a BLA for its Sanfilippo syndrome type A gene therapy.
This partnership underscores the commitment of both companies to advancing innovative gene therapies for rare genetic disorders, offering hope for improved patient outcomes.

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