GSK Announces Bepirovirsen Trial Data, 19% Functional Cure Rate Achieved
Ionis Pharmaceuticals (IONS) partner GSK (GSK) announced data for bepirovirsen, an investigational antisense oligonucleotide for the treatment of chronic hepatitis B. Results from the two Phase 3 trials, B-Well 1 and B-Well 2, were simultaneously published in the New England Journal of Medicine and presented at the European Association for the Study of the Liver congress. GSK licensed bepirovirsen from Ionis and the two companies have collaborated on its development. Pooled data from both trials showed that six-month treatment with bepirovirsen achieved a statistically significant and clinically meaningful 19% functional cure response rate in the overall study population, meeting the primary endpoints. In a key secondary endpoint, a functional cure rate of 26% was achieved in participants with 1000 IU/ml HBsAg level, a group that represents approximately 45% of diagnosed CHB cases globally. The current standard of care typically requires lifelong therapy, with functional cure rates achieved in less than 1% of patients. Functional cure occurs when the hepatitis B virus DNA and HBsAg are undetectable in the blood for at least six months after stopping all treatment. This indicates the disease is being controlled by the immune system without medication. Notably, in an exploratory analysis, 49% of bepirovirsen recipients achieved a quantitative hepatitis B surface antigen of 100 IU/mL one year after the end of treatment. Medical literature has linked this level of low surface antigen with increased immune control and improved patient outcomes. Moreover, 23% of all bepirovirsen recipients and 31% of bepirovirsen recipients with baseline HBsAg of 1000 IU/mL % achieved a sustained DNA lower limit of quantification at week 72 after stopping all treatment at week 48. The trials showed an acceptable safety and tolerability profile consistent with other studies of bepirovirsen. The three most frequently observed adverse events were injection site erythema, local pain and temporary rise in the blood level of a liver enzyme. Bepirovirsen is currently under priority review by the FDA with both Breakthrough and Fast Track Designation. It is also under review by regulatory authorities in Europe, Japan with SENKU designation and China with Breakthrough Therapy and Priority Review designation. GSK anticipates the first regulatory decisions in Q3 2026 and launch preparations are underway. GSK licensed bepirovirsen from Ionis in 2019 under a collaborative development and licensing agreement. Under the terms of the agreement, Ionis has received an upfront payment, license fee and development and regulatory milestone payments and is eligible to receive additional regulatory and sales milestone payments as well as tiered royalties of 10%-12% on net sales of bepirovirsen.
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- Functional Cure Breakthrough: In the pivotal B-Well 1 and B-Well 2 trials, bepirovirsen achieved a 19% functional cure rate overall and 26% in patients with lower viral activity, significantly outperforming the 0% rate of standard care, providing new hope for chronic hepatitis B patients.
- Significant Treatment Outcomes: Notably, 49% of bepirovirsen recipients achieved a hepatitis B surface antigen level of ≤100 IU/mL one year post-treatment, indicating enhanced immune control associated with a significant reduction in liver cancer risk, potentially improving patient outcomes.
- Global Impact: With over 240 million people affected by chronic hepatitis B, the successful development of bepirovirsen could transform treatment paradigms for this large patient population, reducing reliance on lifelong antiviral therapy and improving quality of life.
- Rapid Regulatory Progress: Bepirovirsen is currently under priority review by the FDA with Breakthrough and Fast Track Designations, with the first regulatory decisions anticipated in Q3 2026, highlighting its potential market value and prospects.
- Clinical Trial Success: GSK's antisense drug bepirovirsen, developed with Ionis Pharma, achieved a 19% functional cure rate in two late-stage trials, significantly surpassing the current standard treatment's less than 1% cure rate, marking a new hope for chronic hepatitis B treatment.
- Significant Treatment Effects: In the B-Well 1 and B-Well 2 Phase 3 trials, six months of bepirovirsen therapy resulted in undetectable hepatitis B virus DNA and surface antigens for at least six months post-therapy, demonstrating clinically meaningful efficacy.
- Good Safety Profile: Conducted across 29 countries with chronic hepatitis patients, the studies indicated that bepirovirsen has an acceptable safety and tolerability profile consistent with previous trials, laying a solid foundation for its future market application.
- Long-term Impact Potential: GSK's science chief Tony Wood emphasized that bepirovirsen not only offers the potential for significantly improved functional cure rates but also may reduce the risk of long-term liver complications, including cancer, indicating a major advancement in chronic hepatitis B treatment.
- Analyst Rating Upgrade: Citi analyst Eric Joseph initiated Buy ratings on five biotech companies including Ionis (IONS), Alnylam (ALNY), and BioMarin (BMRN), reflecting a positive outlook for significant growth in the cardiovascular, metabolism, and endocrine sectors, which indicates strong confidence in the biotech industry.
- Ionis Price Target: The analyst set a $115 price target for Ionis, emphasizing that its pipeline based on antisense oligonucleotides provides a solid foundation for durable growth, showcasing confidence in its future performance.
- BioMarin Valuation Discount: BioMarin received a $75 price target, with analysts noting its EV/Rev ratio of 4x is significantly lower than peers' 8-9x, indicating a substantial valuation discount that may attract investor interest.
- Alnylam Investment Opportunity: Alnylam's price target is set at $380, with analysts arguing that despite its year-to-date underperformance, the impressive market launch of its heart disease therapy Amvuttra presents an attractive buying opportunity, signaling potential for future growth.
- Clinical Trial Results: Biogen's Phase 2 CELIA study indicates that diranersen, an experimental therapy for Alzheimer's disease, slowed clinical decline across all doses in early-stage patients, highlighting the drug's potential in treating Alzheimer's.
- Biomarker Impact: The study demonstrated significant reductions in tau pathology associated with Alzheimer's, providing the first evidence from a randomized Phase 2 trial of a tau-directed therapy showing robust biomarker impact and cognitive benefits.
- Safety and Tolerability: In the 416-patient trial, diranersen's safety and tolerability profile was consistent with data from a Phase 1b trial, reinforcing confidence in its safety characteristics for further development.
- Registration Development Outlook: Biogen expressed that the Phase 2 data gives them the confidence to advance diranersen into registrational development, indicating the drug's promising future in the Alzheimer's treatment landscape.

Stock Sale Announcement: Ionis Pharmaceuticals' director, Joseph Loscalzo, plans to sell 54,321 shares of the company's common stock on May 4, with an estimated market value of around $4.35 million.
Reduction in Shareholding: Loscalzo has decreased his shareholding in Ionis Pharmaceuticals by 1,032 shares since March 3, 2026, with a total value of approximately $82,833.
- Investor Conference Schedule: Ionis Pharmaceuticals announced participation in the Bank of America Securities 2026 Health Care Conference on May 12, 2026, the RBC Capital Markets Global Healthcare Conference on May 19, 2026, and the Goldman Sachs 47th Annual Global Healthcare Conference on June 10, 2026, showcasing its innovations in RNA-targeted medicines.
- Live Webcast and Replays: Presentations will be accessible via a live webcast on the Investors & Media section of the Ionis website, with replays available within 48 hours post-event, ensuring investors stay updated on the company's latest developments.
- Company Background: For three decades, Ionis has focused on inventing medicines that improve the futures of patients with serious diseases, currently boasting marketed medicines and a leading pipeline in neurology, cardiometabolic diseases, and areas of high patient need, reflecting its deep expertise in the biopharmaceutical sector.
- Innovation-Driven Technology: As a pioneer in RNA-targeted medicines, Ionis continues to drive innovation in RNA therapies while advancing new approaches in gene editing, demonstrating a profound understanding of disease biology and industry-leading technology aimed at delivering life-changing treatments for patients.









