Long-term antigen reduction does not achieve durable HBV control in mice but enhances therapeutic vaccine efficacy.

BACKGROUND & AIMS: Chronic HBV infection has an increasing death toll, but curative therapies are lacking. The study aimed to determine whether long-term suppression of viral antigens using RNA-interference restores HBV-specific immunity and achieves durable virus control, and how long HBV antigens must be suppressed to enable therapeutic vaccination to restore immunity.

METHODS

HBV-transgenic or AAV-HBV-infected, HBV-carrier mice were treated for up to 7 months with liver-directed small interfering RNAs (siRNAs) or short-hairpin RNAs (shRNAs) that target all HBV transcripts. The antiviral effect and development of B- and T-cell immunity were evaluated. A subcohort of mice received the heterologous prime/boost therapeutic vaccine, TherVacB, before cessation of siRNA.

RESULTS

Continuous siRNA therapy reduced HBsAg by up to 4 log10, but a threshold effect was observed after 12-16 weeks. Suppression of viral antigens for up to 7 months did not lead to spontaneous reconstitution of T-cell immunity; this required stimulation by therapeutic vaccination. Without vaccination, HBV replication rebounded after discontinuation of siRNA therapy, even though HBsAg and HBeAg seroconversion had occurred. However, a longer duration of siRNA pretreatment correlated with increasing interferon type I signaling in the liver. siRNA pretreatment for 8 instead of 3.5 weeks improved the ability of therapeutic vaccination to activate functional antiviral T cells, fully control HBV replication, and significantly reduce the number of HBV-positive hepatocytes (p <0.01 to p <0.001).

CONCLUSIONS

Our data show that, in addition to suppressing viral antigens, immune stimulation is necessary to achieve long-lasting HBV control after treatment discontinuation. These results will help design clinical trials that can ultimately achieve HBV control.

IMPACT AND IMPLICATIONS: Drug entities in development to cure chronic hepatitis B include direct-acting antivirals, nucleic acid-based therapeutics, immunotherapies, and combinations thereof. In our study, long-term suppression of HBV in HBV-carrier mice using siRNAs targeting all HBV antigens neither allowed spontaneous reconstitution of T-cell immunity nor sustained HBV control, even when accompanied by anti-HBs seroconversion. However, prolonged viral antigen suppression by siRNA enhanced the efficacy of therapeutic vaccination. Our study highlights that achieving loss of viral parameters from serum, or even anti-HBe/HBs seroconversion, should not represent the ultimate goal of curative therapy, but rather be viewed as a prerequisite that empowers immunostimulatory drugs to induce curative T-cell responses.