Silencing of HBV and PD-L1 synergistically enhances the efficacy of therapeutic vaccination in high-titer HBV carrier mice

Therapeutic vaccination represents a promising treatment of chronic hepatitis B; however, high levels of hepatic HBV antigens impede vaccine-mediated immunity. Reducing HBV levels before vaccination by HBV-specific siRNAs (siHBV) enhanced the immunogenicity and antiviral efficacy of our clinical candidate protein-prime/MVA-boost therapeutic vaccine, TherVacB, in high-titer HBV-carrier mice. Non-responsiveness to vaccination was associated with high PD-1 expression on vaccine-elicited CD8 T-cells. We hypothesized that combining siHBV with silencing PD-L1 could further broaden the applicability of TherVacB in high-titer HBV carrires.

We therefore established high-titer persistent HBV infection in C57BL/6J mice using AAV-HBV, resulting in over 80% of HBV-positive hepatocytes. We pretreated mice for eight weeks with siHBV before TherVacB and applied siPD-L1 during the two protein priming immunizations. We followed up with the mice for 7.5 months after the MVA boost.

Mice receiving TherVacB or TherVacB+siPD-L1 demonstrated only a minor decrease in serum HBsAg shortly after treatment. Without vaccination, siHBV+siPD-L1 reduced HBsAg, but the antigen load eventually returned to the baseline values, and no induction of HBV-specific immunity was observed. Combining siHBV+TherVacB reduced HBsAg to undetectable levels for eight weeks, but finally resulted only in a 1-log10 decrease. By contrast, mice receiving siHBV+TherVacB+siPD-L1 cleared HBsAg for 24 weeks; 3/5 mice remained negative for 7.5 months. Overall, the siHBV+TherVacB+siPD-L1 treatment resulted in a≥3-log10 reduction in HBsAg and a 70% reduction in HBV+hepatocytes.

Our data demonstrate that complementary siRNA-mediated silencing of HBV and the immune checkpoint PD-L1 helps to further enhance the efficacy of therapeutic vaccination in high-titer HBV carriers.

Publication History

Article published online:
20 January 2025