Ionis Pharmaceuticals (IONS) stock gained in pre-market trading after GSK reported positive late-stage data for bepirovirsen in chronic hepatitis B. The results strengthened the drug’s regulatory case, while FDA priority review added a stronger market catalyst. IONS fell sharply to $75.34, down 1.50% after dropping from an early high near $78.
Ionis Pharmaceuticals, Inc., IONS
Ionis Pharmaceuticals advanced after partner GSK released pivotal Phase 3 results for bepirovirsen. The drug targets chronic hepatitis B through an antisense oligonucleotide approach. GSK licensed the treatment from Ionis in 2019 under a development and commercialization deal.
The two Phase 3 trials, B-Well 1 and B-Well 2, met their main goals. Pooled data showed a 19% functional cure response rate after six months of treatment. By comparison, the placebo group recorded no functional cure response across both studies.
The data covered adults with hepatitis B surface antigen levels at or below 3000 IU/mL. Patients with levels at or below 1000 IU/mL showed a 26% functional cure rate. This subgroup represents about 45% of diagnosed chronic hepatitis B cases worldwide.
Bepirovirsen now sits under priority review at the U.S. Food and Drug Administration. The treatment also carries Breakthrough Therapy and Fast Track designations in the United States. Therefore, the latest Phase 3 data arrived during an important regulatory window.
GSK has also submitted the therapy to regulators in Europe, Japan and China. Japan granted the drug SENKU designation, while China granted Breakthrough Therapy and Priority Review status. GSK expects the first regulatory decisions in the third quarter of 2026.
The review progress matters because current chronic hepatitis B care often requires lifelong treatment. Standard therapies also achieve functional cure in less than 1% of patients. Bepirovirsen could create a different treatment path if regulators approve the therapy.
Ionis and GSK have worked together on bepirovirsen since the 2019 licensing agreement. Under that deal, Ionis has already received upfront, license, development, and regulatory milestone payments. The company can also receive more regulatory and sales milestone payments.
Ionis remains eligible for tiered royalties of 10% to 12% on net sales. That structure gives the company commercial exposure without leading the global launch process. GSK has said launch preparations are already underway.
The trial safety profile also supported the regulatory package. The most common adverse events included injection site redness, local pain, and temporary liver enzyme increases. Overall, the data gave IONS a clear pre-market boost as traders reacted to the drug’s progress.
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