Brii Bio Announces Topline End-of-Treatment Data from Phase 2b ENRICH and ENHANCE Studies for the Treatment of Chronic Hepatitis B

• End-of-treatment data from ENRICH demonstrated higher HBsAg loss rates, consistent with ENSURE Cohort 4, confirming the role of BRII-179 in priming immune responses for functional cure strategies
• End-of-treatment data from ENHANCE did not demonstrate improved HBsAg loss rates compared to ENSURE Cohorts 2 and 3, informing selection of combination regimen going forward
• As previously disclosed, advancement of ENRICH into Phase 3 remains subject to the outcome of arbitration with Vir Biotechnology regarding the elebsiran manufacturing technology transfer

DURHAM, N.C. and BEIJING, July 2, 2026 /PRNewswire/ -- Brii Biosciences Limited ("Brii Bio" or the "Company", stock code: 2137.HK), a biotechnology company developing therapies to improve patient health and choice across diseases with high unmet medical need, today announced end-of-treatment (EOT) results from its ongoing Phase 2b ENRICH and ENHANCE studies investigating sequential versus concurrent combination regimens of BRII-179 with elebsiran and PEG-IFNα for chronic hepatitis B virus (HBV) infection.

The ENRICH and ENHANCE studies are two Phase 2b studies designed to further define the role of BRII-179 in chronic HBV treatment and to select the optimal combination regimen for future development. The ENRICH study evaluates BRII-179 as a priming therapy administered prior to elebsiran and PEG-IFNα treatment. The ENHANCE study evaluates a concurrent triple combination regimen of BRII-179, elebsiran, and PEG-IFNα to enhance the functional cure rates.

At EOT, the ENRICH study evaluating pre-treatment with BRII-179 followed by elebsiran and PEG-IFNα demonstrated hepatitis B surface antigen (HBsAg) loss rates of 42.9% (42/98) and 40.0% (20/50) across two different BRII-179 dosing schedules, being 5 doses administered once every 3 weeks versus 7 doses administered once every 2 weeks, respectively. These results were consistent with the HBsAg loss rate observed in ENSURE Cohort 4, 41.9% (13/31) in patients with prior BRII-179 treatment, supporting the immune priming role of BRII-179. The Company had engaged with the Center for Drug Evaluation of the National Medical Products Administration of China and reached preliminary alignment regarding a potential registrational study.

At EOT, the ENHANCE (Part A-1) study evaluating a concurrent triple combination did not demonstrate improved HBsAg loss rates compared with ENSURE Cohorts 2 and 3, 29.7% (11/37), with an observed rate of 25.5% (25/98). However, higher HBsAg loss rates were observed compared with the PEG-IFNα control arm, 10.2% (5/49).

Subgroup analyses from the ENRICH study suggest potential differentiation in subjects with higher baseline HBsAg levels (1000-3000 IU/mL), consistent with prior findings from ENSURE Cohort 4, indicating that BRII-179 may induce beneficial immune responses regardless of baseline HBsAg levels in this difficult-to-treat population.

The ENHANCE study, Part A-2, also evaluated a sequential approach designed to potentially shorten PEG-IFNα therapy by administering BRII-179 plus elebsiran during the first 24 weeks followed by 24 weeks of elebsiran and PEG-IFNα. At EOT, this combination regimen achieved an HBsAg loss rate of 22.5% (18/80), suggesting full course of PEG-IFNα therapy is needed for optimal curative outcome.

HBsAg loss is an important endpoint when evaluating functional cure regimens, but requires confirmation during off-treatment follow-up to assess rebound and durability of functional cure. No new safety concerns were identified in either study. The Company plans to present detailed data, including additional efficacy, safety, subgroup analyses and follow-up results, at a scientific conference in the second half of 2026.

"These initial EOT data provide important insights into the relative performance of the ENRICH and ENHANCE study designs," said Dr. David Margolis, M.D., the Chief Medical Officer of the Company. "While longer-term follow-up is needed to assess durability of the HBsAg loss, the data observed to date, together with EOT and post-EOT findings from multiple prior studies, are very consistent, suggesting that the ENRICH study design is preferred for a registrational study. We look forward to sharing the more complete dataset later this year."

As previously disclosed, in light of the ongoing arbitration between the Company and Vir Biotechnology, Inc., and the unknown nature and timing of the outcome of the Arbitration or any mutual resolution of the claims, the Company considers the future of the elebsiran program to be uncertain. In particular, the Company cannot invest in a Phase 3 clinical study of any elebsiran-containing combination therapy for HBV unless and until the claims in the Arbitration are satisfactorily resolved. The Company will continue to evaluate such developments and assess their impact on the continued viability of the elebsiran program, and update its shareholders and the public as and when appropriate in accordance with relevant requirements.

For more information about Brii Bio's HBV programs visit www.briibio.com.

About Hepatitis B

Hepatitis B virus (HBV) infection is one of the world's most significant infectious disease threats with more than 254 million people infected globally.^[1] Chronic HBV infection is the leading cause of liver disease and an estimated 820,000 people die of complications from chronic HBV infection each year.¹ HBV is of exceptional concern in China, where 87 million people are chronically infected.^[2]

About BRII-179

BRII-179 is a novel recombinant protein-based HBV immunotherapeutic candidate that expresses the Pre-S1, Pre-S2, and S HBV surface antigens, designed to induce enhanced and broad B-cell and T-cell immunity. In November 2023, the Center for Drug Evaluation (the "CDE") of China's National Medical Products Administration (the "NMPA") granted BRII-179 Breakthrough Therapy Designation.

About Elebsiran

Elebsiran is an investigational subcutaneously administered HBV-targeting siRNA designed to degrade HBV RNA transcripts and limit the production of hepatitis B surface antigen. It has the potential to have direct antiviral activity against HBV and HDV. It is the first siRNA in the clinic to include Enhanced Stabilization Chemistry Plus technology to enhance stability and minimize off-target activity, which potentially can result in an increased therapeutic index. Brii Bio licensed exclusive rights to develop and commercialize elebsiran for the Greater China territory from Vir Biotechnology, Inc. in 2020. In May 2024, the CDE of China's NMPA granted elebsiran Breakthrough Therapy Designation.

About Brii Bio

Brii Biosciences Limited ("Brii Bio", stock code: 2137.HK) is a biotechnology company developing therapies to improve patients' health by addressing high unmet medical needs with limited treatment options. The Company is advancing a broad pipeline of unique therapeutic candidates with lead programs against hepatitis B virus (HBV) infection. The Company is led by a visionary and experienced leadership team and has operations in both China and the United States. For more information, visit www.briibio.com.

SOURCE Brii Biosciences Limited