GSK's bepirovirsen heads to FDA decision on positive Phase 3 cure data
The October 26 PDUFA date tests whether two positive Phase 3 trials translate into the first approved functional-cure therapy for chronic hepatitis B.
Executive Summary
- The FDA is set to rule on GSK's Phase 3 bepirovirsen program for chronic hepatitis B, a Priority Review application built on two trials that already met their primary endpoint.
- Unlike the nucleos(t)ide analogues that dominate current treatment, bepirovirsen is designed to produce a durable functional cure rather than lifelong viral suppression.
- Breakthrough Therapy and Priority Review designations, plus a Fast Track designation granted earlier in development, signal that the agency has treated this application as addressing a serious unmet need throughout its review.
- Bepirovirsen sits alone at Phase 3 among therapies targeting HBV messenger RNA, with the broader chronic hepatitis B pipeline dominated by mechanistically distinct small molecules and immunotherapies still in earlier-phase testing.
The filing
The FDA accepted GSK's New Drug Application for bepirovirsen for Priority Review and set a PDUFA target action date of October 26, 2026. The agency also granted the drug Breakthrough Therapy designation, and it had previously granted Fast Track designation in February 2024. The application is supported by the Phase 3 B-Well 1 trial (NCT05630807), which enrolled 981 nucleos(t)ide analogue-treated participants and completed in November 2025, and the Phase 3 B-Well 2 trial (NCT05630820). Ionis+1Ionis partner GSK announces bepirovirsen accepted for Priority Review and granted Breakthrough Therapy Designation by U.S. FDA as a potential first-in-class medicine for chronic hepatitis BApr 28, 2026Study of Bepirovirsen in Nucleos(t)Ide Analogue-treated Participants With Chronic Hepatitis B (B-Well 1)NCT05630807
Probability of SuccessBased on the AppliedXL Probability of Success model. For more information about the methodology, read the research here.
The result behind the filing
Both trials met their primary endpoint. GSK reported that B-Well 1 and B-Well 2 each achieved "a statistically significant and clinically meaningful functional cure rate" for bepirovirsen combined with standard of care, versus standard of care alone, with a greater effect in patients with lower baseline HBsAg (hepatitis B surface antigen) levels. Functional cure requires undetectable HBV DNA and HBsAg for at least 24 weeks after all treatment stops, a bar current nucleos(t)ide analogue therapy rarely clears; GSK's own filing materials describe functional cure rates on the standard of care as typically around 1%. B-Well 1's primary endpoint was the number of participants achieving functional cure with baseline HBsAg at or below 3,000 IU/mL. Ionis+1Ionis partner GSK announces bepirovirsen accepted for Priority Review and granted Breakthrough Therapy Designation by U.S. FDA as a potential first-in-class medicine for chronic hepatitis BApr 28, 2026Study of Bepirovirsen in Nucleos(t)Ide Analogue-treated Participants With Chronic Hepatitis B (B-Well 1)NCT05630807
Why this matters
Brett Monia, chief executive officer of Ionis Pharmaceuticals, which licensed bepirovirsen to GSK in 2019 and is eligible for royalties on net sales, said in the announcement that bepirovirsen is positioned as "the first medicine to deliver clinically meaningful functional cure rates" for the roughly 1.7 million people living with chronic hepatitis B in the United States and more than 250 million worldwide. Achieving functional cure is tied to a reduction in long-term liver complications, including liver cancer, according to the same disclosure. IonisIonis partner GSK announces bepirovirsen accepted for Priority Review and granted Breakthrough Therapy Designation by U.S. FDA as a potential first-in-class medicine for chronic hepatitis BApr 28, 2026
Trial operations
B-Well 1 grew its enrollment target from 534 to 981 participants between 2023 and 2025 as the trial progressed toward completion, and its primary completion date moved from October 2025 to November 11, 2025 over three revisions. The trial completed on schedule with its final enrollment and closed in May 2026, a pattern consistent with a large, multi-country registrational study rather than a sign of readout risk. NCT05630807Study of Bepirovirsen in Nucleos(t)Ide Analogue-treated Participants With Chronic Hepatitis B (B-Well 1)NCT05630807
The competitive field
Among therapies targeting HBV messenger RNA specifically, bepirovirsen is the only asset to reach Phase 3; GSK's own earlier-stage HBV mRNA program, GSK3965193, remains in Phase 1/2 testing. The broader chronic hepatitis B pipeline is more populated but mechanistically distinct: RNA-based candidates from other sponsors, including AusperBio's AHB-171 and Epigenic Therapeutics' EPI-003, and antigen-targeted or small-molecule programs such as Daewoong's Vemliver, are all earlier in development and work through different mechanisms. That leaves bepirovirsen positioned as the most advanced attempt to convert antisense suppression of viral transcripts into a functional cure, a bar no other Phase 3 program in this indication has yet been tested against on the same endpoint.
This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.