According to an announcement dated November 7, 2025, Brii Biosciences Limited disclosed the publication of Phase 2 ENSURE study findings in Nature Medicine. The results focus on an siRNA candidate, elebsiran, in combination with pegylated interferon alfa (PEG-IFNα) compared to PEG-IFNα monotherapy. The study also examines the potential role of the hepatitis B virus therapeutic vaccine BRII-179 in identifying immunologically responsive patients and improving hepatitis B surface antigen (HBsAg) loss rates.

The ENSURE trial was conducted in two parts. In Part I (Cohorts 1-3), participants naïve to BRII-179 were allocated to receive 48 weeks of PEG-IFNα alone or in combination with 200 mg or 100 mg of elebsiran every 4 weeks. At 24 weeks post-end of treatment, HBsAg loss reached 21.1% (4 of 19) in the 200 mg group and 33.3% (6 of 18) in the 100 mg group, compared to 5.6% (1 of 18) for PEG-IFNα monotherapy. Elebsiran and PEG-IFNα combination therapy was generally safe and well tolerated.

In Part II (Cohort 4), 31 participants previously treated with elebsiran and BRII-179 in a completed Phase 2 study were categorized by peak hepatitis B surface antibody responses. After 48 weeks of elebsiran (100 mg every 4 weeks) plus PEG-IFNα, 29.0% achieved HBsAg loss at 24 weeks post-end of treatment, with 42.1% among vaccine responders and 8.3% among non-responders. Those previously treated with BRII-179 and elebsiran appeared to experience a faster decline and loss of HBsAg. The overall findings support a personalized approach that identifies patients most likely to benefit from combination regimens.

A cautionary statement in the announcement notes that there is no assurance elebsiran and BRII-179 will be successfully developed or marketed. Readers are advised to exercise caution and seek professional advice when considering any related transactions.