GSK has gained FDA approval in US for its novel chronic hepatitis B therapy Hibsago (bepirovirsen)
GSK has gained US approval for its novel chronic hepatitis B therapy Hibsago, which could transform treatment by offering around 20% of patients a functional cure.
Hibsago (bepirovirsen) is a first-in-class antisense oligonucleotide developed by Ionis and licensed to GSK, and works by blocking production of the hepatitis B virus’ RNA. In patients who response fully, this allows their immune system to regain control and clear the virus completely from the liver, letting them stop all treatment. This makes it a huge step forward for the 1.7 million patients in the US, the vast majority of whom currently have to remain on antiviral therapy indefinitely.
The US Food and Drug Administration approval of the drug, which had been granted a breakthrough therapy designation, was announced on Oct. 20, 2026 ahead of its target action date, following a priority review. It allows Hibsago to be used in combination with nucleos(t)ide analogue reverse transcriptase inhibitor (NrtI) therapy in adult patients without cirrhosis, receiving NrtI therapy for at least six months, who have suppressed hepatitis B DNA, and with hepatitis B virus surface antigen (HBsAg) levels of 3000IU/ml or below, as determined by an FDA-authorised test.
This equates to a broad group of around 120,00 US patients eligible for treatment, which involves six-months of weekly subcutaneous administration, with the option of self-administration after the first dose.
A same-day note from analysts at Jefferies commented that this label was in line with expectations, and supported its existing $3bn peak-sales forecast, though GSK has not yet confirmed a US launch price or launch date.
However, the label also comes with a black box warning for on-treatment hepatic flares and thrombocytopenia, and treatment must be accompanied by weekly or fortnightly laboratory monitoring. This is likely to complicate the patient experience and could slow its adoption outside specialist hepatology centers.
The approval was based on results from GSK’s B-WELL Phase III trials showing functional cure rates of 19% in adults with ≤3000IU/ml HBsAg, compared with current standard of care alone, which typically achieves less than 1% functional cure rate after one year of treatment.
Functional cure occurs when hepatitis B DNA and viral protein – HBsAg – are undetectable for at least 24 weeks after stopping all treatment, indicating the disease is controlled by the immune system without medication.
Room For Expansion And Improvement
The 19%-20% benchmark clearly leaves room for improvement for GSK and future competitors, but the UK-headquartered firm is keen to maximise its lead in the field.
Exploratory analyses of its pivotal studies also showed bepirovirsen reduced HBsAg to ≤100IU/ml in 49% of participants (598 of 1220) in the overall study population, and in 62% of those with a much lower viral load, ≤1000 IU/ml (476 of 768), after 18 months of treatment, supporting existing observations that patients with lower levels respond more readily to treatment.
Precisely why around 80% of patients do not respond is still not fully understood and GSK is looking to boost functional cure rates with novel combinations. These include GSK’s siRNA asset dapulsiran/tomligisiran, which it is using to reduce HBsAg levels in higher-baseline patients before bepirovirsen administration. Results from the ongoing Phase IIb B-UNITED study of this regimen are expected in early 2027.
GSK signed a marketing deal Sino Biopharmaceutical in May to market the drug in China, the world’s biggest hepatitis B market where around 75 million people carry the virus, and around six million people are currently on nucleoside analogue treatment.
Bepirovirsen has breakthrough therapy designation in China and was accepted for priority review in April 2026.
Competitors will also look to build on and surpass bepirovirsen’s functional cure rate. US-based AusperBio Therapeutics’ unconjugated antisense oligonucleotide, AHB-137, has completed a global Phase I study and is now in a Phase III China-only trial.