FDA Greenlights Navsunli Therapy
FDA Reverses Stance on Regenxbio's Navsunli Gene Therapy, Greenlights Accelerated Approval Pathway
Key Points
In February, the FDA rejected Navsunli and said the issue stemmed from “uncertainty over the trial design,” which Reuters reported was the stated reason for the denial before the later reversal.
Reuters also linked the FDA’s broader rare-disease gene-therapy stance shift to engagement by FDA leadership, noting that FDA Commissioner Kyle Diamantas met with advocacy groups earlier in the month.
Gurufocus reported that Regenxbio’s stock jump was more specifically “up $1.97 or 25%” to $9.77 in premarket trading, and added that insiders sold about $0.2 million worth of shares in the past three months.
Endpoints reported Regenxbio will refile “without new study,” attributing the latest FDA ‘walk back’ to “leadership departures,” highlighting internal regulatory upheaval as part of the context for the change in stance.
Separately, Regenxbio’s one-time gene-therapy program NAVSUNLI is positioned by the company as addressing an “unmet medical need” for patients with MPS II (Hunter syndrome), per a company-linked update.
The FDA has reversed its rejection of Regenxbio's Hunter syndrome gene therapy, Navsunli, agreeing that existing data is enough to support an accelerated approval application, Reuters reported. The agency will not require new patient enrollment or a placebo-controlled trial — a major shift from the February 2026 rejection that had stunned the company.
Regenxbio plans to request a formal FDA meeting in July and resubmit its application in the third quarter of 2026. News of the reversal sent the stock up $1.97, or 25%, to $9.77 in premarket trading, according to GuruFocus.
February Rejection Gave Way to June Reversal
In February 2026, the FDA issued a Complete Response Letter rejecting Navsunli. The agency cited "uncertainty over trial design," specifically questioning the lack of a placebo arm and the reliability of the surrogate biomarker used to measure brain disease, according to Reuters. That rejection blindsided Regenxbio and wiped out significant shareholder value.
Now, the FDA says none of that additional evidence is needed. The agency told Regenxbio that existing data — including trial results showing an 80% reduction in a key brain biomarker — is sufficient. Endpoints News reported that Regenxbio will refile "without new study," attributing the FDA's reversal in part to "leadership departures" at the agency.
New FDA Leadership Drove the Policy Shift
The reversal follows significant turnover at the top of the FDA. Former Commissioner Marty Makary and CBER Director Vinay Prasad — both advocates of stricter trial designs — departed their roles earlier this year. Acting Commissioner Kyle Diamantas stepped in on May 13 and quickly signaled a different direction, meeting with 15 rare-disease advocacy groups to promise greater focus on patient access, according to Reuters.
The Navsunli reversal is not an isolated case. On June 17, the FDA also reversed its rejection of uniQure's Huntington's disease therapy. Analysts from Guggenheim Securities said the moves show an "appreciation of the challenges in rare disease" under the new leadership, as reported by ca.finance.yahoo.com.
What Navsunli Does for Hunter Syndrome Patients
Hunter syndrome, or MPS II, affects roughly 2,000 patients worldwide, with about 500 new cases diagnosed each year. Patients lack an enzyme needed to break down complex sugars. Over time, this causes progressive organ damage and cognitive decline. Current enzyme replacement therapies cannot reach the brain because they cannot cross the blood-brain barrier.
Navsunli is a one-time gene therapy delivered directly to the central nervous system. It carries a working copy of the missing gene using an AAV9 vector — a specially engineered shell that transports genetic material into cells. Regenxbio CEO Curran Simpson called the decision vital for families facing an "irreversible ultra-rare disease," according to bellinghamherald.com.
Investors Cheer, But Financial Picture Is Mixed
The 25% premarket stock jump reflects real optimism that Navsunli could soon reach market. If approved, Regenxbio expects to receive a Priority Review Voucher — a tradeable certificate that other drug companies typically buy for $100 million or more. The company also expects a $100 million milestone payment from AbbVie for a separate program in the near term.
Still, some caution remains. GuruFocus noted that insiders sold about $0.2 million worth of shares in the past three months. NS Pharma, a subsidiary of Japan's Nippon Shinyaku, is set to handle U.S. commercialization of Navsunli once approval is secured. The FDA is expected to begin labeling discussions soon after Regenxbio refiles in Q3 2026.
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