Though specific data for bepirovirsen remain under wraps, GSK plans to file for approval in the first quarter of 2026.
GSK and Ionis Pharmaceuticals’ antisense oligonucleotide bepirovirsen achieved a functional cure in a pair of late-stage chronic hepatitis B studies, clearing the way for a regulatory submission this quarter.
Without revealing specific data, the pharma said on Wednesday that bepirovirsen met its primary efficacy endpoint in the Phase III B-Well 1 and B-Well 2 trials, eliciting a “statistically significant and clinically meaningful functional cure rate” in treated patients. The studies defined “functional cure” as having no detectable levels of virus in the blood, as measured by the hepatitis B surface antigen and viral DNA for 24 weeks after a “finite course of treatment.”
The partners also reported that bepirovirsen met all of its ranked endpoints, including functional cure in patients with lower baseline levels of the virus’ surface antigen. Bepirovirsen’s safety and tolerability were “acceptable,” according to the companies’ announcement, though the companies did not detail any specific adverse events.
With the caveat that they would need to see more data from the B-Well studies, analysts at William Blair said that bepirovirsen’s results bode well for Ionis. “Expectations for the HBV [hepatitis B virus] program have been low,” the analysts wrote in a Wednesday morning note to investors, arguing that therefore, bepirovirsen “is likely an underappreciated opportunity” for Ionis.
Specifically, William Blair pointed to Gilead’s own hepatitis B drug Vemlidy, which in 2024 made $959 million and is, according to the analysts, on track to break the $1 billion sales barrier in 2025. Still, the group emphasized that more data are needed “to better understand the bepirovirsen product profile.”
GSK has promised to present more detailed findings from the B-Well program at an upcoming medical congress. The pharma also plans to file for approval in the first quarter of 2026.
Bepirovirsen is an investigational antisense oligonucleotide that targets and tags for destruction the genetic material of HBV. In turn, bepirovirsen prevents the virus’ replication inside the body and promotes the activity of the immune system, allowing it to fight against the infection. Bepirovirsen was originally developed by Ionis and came into the GSK fold in August 2019 when it licensed the drug for $25 million upfront and up to $262 million in milestones, plus tiered royalties.
In a statement on Wednesday, GSK chief scientific officer Tony Wood said that 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.”
