An experimental GSK drug in development for treating chronic hepatitis B now has results from two pivotal studies showing the therapy brought levels of the virus low enough to allow the immune system to then control the infection without further medication.
This outcome amounts to a functional cure, where the virus can no longer be detected in the blood. Without reporting specific figures, GSK said Wednesday the drug, bepirovirsen, led to statistically significant and clinically meaningful functional cure rates, meeting the main goal of the studies. With the preliminary data in hand, the company is now preparing regulatory submissions for the drug globally.
Hepatitis B virus can cause both acute and chronic liver disease. The infection becomes chronic when the immune system is unable to clear the virus. More than 250 million people worldwide are estimated to have chronic hepatitis B infection, which can lead to liver cancer. Standard treatment is antiviral therapies, such as Gilead Sciences’ Vemlidy, that must be taken chronically and achieve low functional cure rates. Gilead reported $783 million in global Vemlidy sales for the first nine months of 2025, a 12% increase compared to the same period in the prior year.
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Bepirovirsen is an antisense oligonucleotide designed to target RNA to inhibit the production of proteins associated with hepatitis B virus infection and replication. In addition to inhibiting the replication of viral DNA, GSK says this drug also suppresses the level of hepatitis B surface antigen in the blood and stimulates the immune system to increase the chances of a durable response to the therapy.
The preliminary data reported Wednesday are from two Phase 3 studies that enrolled more than 1,800 total patients from 29 countries. The treatment period was 24 weeks. GSK said the functional cure rates were significantly higher with the study drug plus standard of care antivirals compared to standard therapy alone. The company added that if approved, bepirovirsen could become the first finite, six-month therapy for chronic hepatitis B infection. Full clinical trial results will be submitted for presentation at an upcoming scientific meeting and published in a peer-reviewed journal.
“Today’s result supports our plans to progress bepirovirsen as a treatment and also continue its development as a backbone in future sequential therapies,” GSK Chief Scientific Officer Tony Wood said in a prepared statement. “We’re pleased by this major advance in our expanding hepatology pipeline, aimed to transform outcomes in liver disease.”
Bepirovirsen came from the labs of Ionis Pharmaceuticals. In 2010, Ionis began a drug discovery partnership with GSK that included infectious diseases. After bepirovirsen posted positive Phase 2 results in 2019, GSK licensed the hepatitis B virus program, making the big pharma company responsible for further development and regulatory submissions for the drug worldwide. In its 2024 annual report, Ionis said it had received more than $105 million in payments to date from the collaboration.
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In a note sent to investors, Leerink Partners analyst Mani Foroohar wrote that bepirovirsen’s positive data readout was largely expected, given the program’s successful Phase 2 results. The firm is waiting for detailed data before it can place a value on the asset. He added that while chronic hepatitis B represents a large, underserved market, the commercial opportunity will depend on the positioning of antisense oligonucleotide/siRNA therapies in this market. Foroohar said Ionis could receive up to $150 million in remaining milestone payments plus royalties from sales of bepirovirsen.
Public domain image by the CDC