Arbutus doses first patient in additional treatment arm of Phase 2a triple combination clinical trial that includes a PD-1 monoclonal antibody

WARMINSTER, Pa., June 21, 2023 — Arbutus Biopharma Corporation (Nasdaq: ABUS) (“Arbutus” or the “Company”), a clinical-stage biopharmaceutical company leveraging its extensive virology expertise to develop novel therapeutics that target specific viral diseases, today announced that the first patient has been dosed in the additional treatment arm of the AB-729 Phase 2a triple combination clinical trial that has been expanded to include a PD-1 monoclonal antibody, nivolumab. Nivolumab is approved for a number of types of cancer under the brand name, Opdivo^®. The objective of the additional treatment arm is to assess if a low dose of nivolumab, in combination with the booster dose(s) of Vaccitech plc’s (Nasdaq: VACC) VTP-300, will further stimulate immune mediated reduction of HBsAg after the initial treatment with AB-729 and ongoing nucleos(t)ide analogue (NA) therapy in patients with chronic hepatitis B infection (cHBV).

“We are excited to explore the addition of low dose nivolumab to our existing combination of AB-729 and VTP-300, and assess if this will further stimulate HBsAg reduction,” said Dr. Karen Sims, Vice President of Clinical Development at Arbutus Biopharma. “We are hopeful that if we can lower HBsAg and stimulate the immune system with the combination of AB-729 and the first dose of VTP-300 and further enhance this stimulation by administering a low dose of a PD-1 monoclonal antibody with the subsequent dose or doses of VTP-300, we may enhance the ability of the immune system to fully suppress the virus and in turn achieve functional cure. We look forward to reporting preliminary data from this additional treatment arm in 2024.”

AB-729 was specifically designed to reduce all HBV viral proteins and antigens, including hepatitis B surface antigen, which is thought to be a key prerequisite to enable reawakening of a patient’s immune system to respond to the virus. The Phase 2a triple combination clinical trial, AB-729-202, has been expanded to evaluate the safety, antiviral activity and immunogenicity of nivolumab plus Vaccitech’s VTP-300, an antigen-specific immunotherapeutic encoding multiple hepatitis B antigens, following treatment with AB-729 and ongoing NA therapy. Approximately 20 virologically-suppressed chronic hepatitis B (cHBV) patients will be enrolled in the open-label arm to receive AB-729 (60mg every 8 weeks) plus NA therapy for 24 weeks. Patients will then receive a course of VTP-300 which consists of a single dose of ChAdOx-HBV at week 26 and an initial dose of MVA-HBV plus low dose nivolumab at week 30. Patients with HBsAg levels ≥10 IU/mL at Week 34 will receive a second dose of MVA-HBV plus low dose nivolumab at week 38. Patients will remain on their NA therapy throughout the VTP-300 administration period through week 48. At week 48, all patients will be evaluated for eligibility to discontinue their NA therapy.

Enrollment is complete in the original portion of the clinical trial, which is currently evaluating the triple combination of AB-729, NA therapy and VTP-300 or placebo. Preliminary data from the original portion of the trial is expected in the second half of 2023.

About AB-729

AB-729 is an RNA interference (RNAi) therapeutic specifically designed to reduce all HBV viral proteins and antigens, including hepatitis B surface antigen, which is thought to be a key prerequisite to enable reawakening of a patient’s immune system to respond to the virus. AB-729 targets hepatocytes using Arbutus’ novel covalently conjugated N-Acetylgalactosamine (GalNAc) delivery technology that enables subcutaneous delivery. Clinical data generated thus far has shown single- and multi-doses of AB-729 to be generally safe and well-tolerated while providing meaningful reductions in hepatitis B surface antigen and hepatitis B DNA. AB-729 is currently in multiple Phase 2a clinical trials.

About HBV

Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus (HBV). HBV can cause chronic infection which leads to a higher risk of death from cirrhosis and liver cancer. Chronic HBV infection represents a significant unmet medical need. The World Health Organization estimates that over 290 million people worldwide suffer from chronic HBV infection, while other estimates indicate that approximately 2.4 million people in the United States suffer from chronic HBV infection. Approximately 820,000 people die every year from complications related to chronic HBV infection despite the availability of effective vaccines and current treatment options.

About Arbutus

Arbutus Biopharma Corporation (Nasdaq: ABUS) is a clinical-stage biopharmaceutical company leveraging its extensive virology expertise to develop novel therapeutics that target specific viral diseases. Our current focus areas include Hepatitis B virus (HBV), SARS-CoV-2, and other coronaviruses. To address HBV, we are developing a RNAi therapeutic, an oral PD-L1 inhibitor, and an oral RNA destabilizer to potentially identify a combination regimen with the aim of providing a functional cure for patients with chronic HBV by suppressing viral replication, reducing surface antigen and reawakening the immune system. We believe our lead compound, AB-729, is the only RNAi therapeutic with evidence of immune re-awakening. AB-729 is currently being evaluated in multiple phase 2 clinical trials. We also have an ongoing drug discovery and development program directed to identifying novel, orally active agents for treating coronaviruses, (including SARS-CoV-2), for which we have nominated a compound and have begun IND-enabling pre-clinical studies. In addition, we are also exploring oncology applications for our internal PD-L1 portfolio. For more information, visit www.arbutusbio.com.