GSK and Ionis Pharmaceuticals announced that their drug candidate bepirovirsen has achieved a functional cure in two late-stage clinical trials for chronic hepatitis B. The companies reported that the Phase III B-Well 1 and B-Well 2 studies met their primary efficacy endpoint, showing a statistically significant and clinically meaningful rate of functional cure. In these trials, functional cure was defined as no detectable hepatitis B virus in the blood, measured by surface antigen and viral DNA levels, for 24 weeks after completing treatment.
Bepirovirsen also met all ranked endpoints in the studies, including demonstrating efficacy among patients with lower baseline levels of hepatitis B surface antigen. The safety and tolerability profile was described as acceptable, though specific adverse events were not detailed.
William Blair analysts commented that expectations for Ionis’ hepatitis B program have been low but now see bepirovirsen as an underappreciated opportunity. They referenced Gilead’s Vemlidy, which generated $959 million in sales in 2024 and is projected to surpass $1 billion in 2025, while noting more data are needed to fully understand bepirovirsen's profile.
GSK intends to present additional findings from the B-Well program at an upcoming medical congress and plans to file for regulatory approval during the first quarter of 2026.
Bepirovirsen is designed as an antisense oligonucleotide that targets the genetic material of HBV for destruction. This approach aims to block viral replication and support immune system activity against infection. Ionis originally developed bepirovirsen before licensing it to GSK in August 2019 under an agreement worth $25 million upfront with potential milestones up to $262 million plus tiered royalties.
In a statement, Tony Wood, chief scientific officer at GSK, said: “If approved, bepirovirsen has the potential to transform treatment goals for people living with [chronic hepatitis B] by achieving significant functional cure rates—a first for the disease.”
