Background: HBV is hyperendemic to southern Africa and parts of Asia, but licensed antivirals have little effect on limiting life-threatening complications of the infection. Although RNA interference (RNAi)-based gene silencing has shown therapeutic potential, difficulties with delivery of anti-HBV RNAi effectors remain an obstacle to their clinical use. To address concerns about the transient nature of transgene expression and toxicity resulting from immunostimulation by recombinant adenovirus vectors (Ads), utility of RNAi-activating anti-HBV helper-dependent (HD) Ads were assessed in this study.
Methods: Following intravenous administration of 5×10(9) unmodified or pegylated HD Ad infectious particles to HBV transgenic mice, HBV viral loads and serum HBV surface antigen levels were monitored for 12 weeks. Immunostimulation of HD Ads was assessed by measuring inflammatory cytokines, hepatic function and immune response to the co-delivered LacZ reporter gene.
Results: Unmodified and pegylated HD Ads transduced 80-90% of hepatocytes and expressed short hairpin RNAs (shRNAs) were processed to generate intended HBV-targeting guides. Markers of HBV replication were decreased by approximately 95% and silencing was sustained for 8 weeks. Unmodified HD Ads induced release of proinflammatory cytokines and there was evidence of an adaptive immune response to β-galactosidase. However the HD Ad-induced innate immune response was minimal in preparations that were enriched with infectious particles.
Conclusions: HD Ads have potential utility for delivery of therapeutic HBV-silencing sequences and alterations of these vectors to attenuate their immune responses may further improve their efficacy.