Reversal of Hepatitis B Virus-Induced Immune Tolerance By an Immunostimulatory 3p-HBx-siRNAs in a Retinoic Acid Inducible Gene I-Dependent Manner

It is extensively accepted that hepatitis B virus (HBV) escapes from innate immunity by inhibiting type I interferon (IFN) production, but efficient intervention to reverse the immune tolerance is still not achieved. Here, we report that 5'-end triphosphate hepatitis B virus X gene (HBx)-RNAs (3p-HBx-short interfering [si] RNAs) exerted significantly stronger inhibitory effects on HBV replication than regular HBx-siRNAs in stably HBV-expressing hepatoplastoma HepG2.2.15 cells through extremely higher expression of type I IFNs, IFN-induced genes and proinflammatory cytokines, and retinoic acid inducible gene I (RIG-I) activation. Also, 3p-HBx-siRNA were more efficient to stimulate type I IFN response than HBx sequence-unrelated 3p-scramble-siRNA in HepG2.2.15 cells, indicating that a stronger immune-stimulating effect may partly result from the reversal of immune tolerance through decreasing HBV load. In RIG-I-overexpressed HepG2.2.15 cells, 3p-HBx-siRNAs exerted stronger inhibitory effects on HBV replication with greater production of type I IFNs; on the contrary, in RIG-I-silenced HepG2.2.15 cells or after blockade of IFN receptor by monoclocnal antibody, inhibitory effect of 3p-HBx-siRNAs on HBV replication was largely attenuated, indicating that immunostimulatory function of 3p-HBx-siRNAs was RIG-I and type I IFN dependent. Moreover, in HBV-carrier mice, 3p-HBx-siRNA more strongly inhibited HBV replication and promoted IFN production than HBx-siRNA in primary HBV+ hepatocytes and, therefore, significantly decreased serum hepatitis B surface antigen and increased serum IFN-beta. Conclusion: 3p-HBx-siRNAs may not only directly inhibit HBV replication, but also stimulate innate immunity against HBV, which are both beneficial for the inversion of HBV-induced immune tolerance. (HEPATOLOGY 2011;54:1179-1189)