HEPLISAV-B Breaks Immune Tolerance and Induces HBV Control via CD4 T Cell-Dependent Mechanism in Chronic HBV Mouse Model

Background: Chronic hepatitis B virus (HBV) infection (CHB) affects nearly 300 million individuals globally and remains incurable with current antiviral therapies, which suppress viral replication but rarely achieve a functional cure, defined by sustained loss of hepatitis B surface antigen (HBsAg). CHB is characterized by profound virus-induced immune tolerance that limits the efficacy of conventional therapeutic vaccination strategies. Objective: To evaluate the therapeutic efficacy and immunological mechanisms of HEPLISAV-B, a CpG-1018 adjuvanted HBsAg vaccine, in breaking immune tolerance and inducing functional cure-like responses in a murine model of CHB. Design: Using the adeno-associated virus-HBV (AAV-HBV) mouse model, mice with high levels of persistent HBV viremia were vaccinated with two doses of HEPLISAV-B. Virological outcomes in the blood and liver, immune responses and mechanisms were assessed. Results: HEPLISAV-B induced rapid and durable HBsAg clearance, markedly reduced circulating and intrahepatic HBV DNA and RNA, and suppressed viral replication without hepatocellular injury. Vaccination elicited robust, sustained anti-HBs IgG1 and IgA responses, enhanced HBsAg-specific T- and B-cell immunity, reduced CD4 regulatory T cells, and decreased PD-1 expression on CD4 T cells. Therapeutic efficacy was strictly dependent on CD4 T cells and the CD40/CD40L signaling pathway, but independent of CD8 T cells, indicating a CD4-driven, non-cytolytic antiviral mechanism critical for HEPLISAV-B-induced HBV control. Conclusions: HEPLISAV-B effectively breaks HBV-induced immune tolerance and restores coordinated antiviral immunity through a CD4 T cell/CD40L-dependent pathway. The findings support its potential as a therapeutic vaccine in CHB patients.