New Approaches to the Treatment of Chronic Hepatitis B

Abstract

The currently recommended treatment for chronic hepatitis B virus (HBV) infection achieves only viral suppression whilst on therapy, but rarely hepatitis B surface antigen (HBsAg) loss. The ultimate therapeutic endpoint is the combination of HBsAg loss, inhibition of new hepatocyte infection, elimination of the covalently closed circular DNA (cccDNA) pool, and restoration of immune function in order to achieve virus control. This review concentrates on new antiviral drugs that target different stages of the HBV life cycle (direct acting antivirals) and others that enhance both innate and adaptive immunity against HBV (immunotherapy). Drugs that block HBV hepatocyte entry, compounds that silence or deplete the cccDNA pool, others that affect core assembly, agents that degrade RNase-H, interfering RNA molecules, and nucleic acid polymers are likely interventions in the viral life cycle. In the immunotherapy category, molecules that activate the innate immune response such as Toll-like-receptors, Retinoic acid Inducible Gene-1 (RIG-1) and stimulator of interferon genes (STING) agonists or checkpoint inhibitors, and modulation of the adaptive immunity by therapeutic vaccines, vector-based vaccines, or adoptive transfer of genetically-engineered T cells aim towards the restoration of T cell function. Future therapeutic trends would likely be a combination of one or more of the aforementioned drugs that target the viral life cycle and at least one immunomodulator.

Keywords: DNA vaccines; capsid inhibitors; cccDNA modifiers; chronic hepatitis B; direct acting antivirals; hepatitis B virus; immunotherapy; siRNA.

Figure 1

The steps of the hepatitis B virus (HBV) life cycle, from viral entry into hepatocytes to release of mature virions into the extracellular space. The target sites of investigational antiviral agents are noted. NTCP, sodium taurocholate cotransporting polypeptide; cccDNA, covalently closed circular DNA; HBsAg, hepatitis B surface antigen; HBeAg, hepatitis B e antigen.

Figure 2

(A) HBsAg, HBeAg, and HBx can interfere with the innate immune response and in particular components of signal transduction pathways or other processes which, in turn, can disregulate IFN and antiviral cytokine production by effector cells such as natural killer (NK), NK T cells (NKT), kuppfer cells (KC) and plasmacytoid dendritic cells (pDC). Such events may inhibit CD4+ and CD8+ T cells; Interferons (INFs (B) The adaptive immune response relies on the production of virus neutralizing antibodies and cytotoxic T cells for lysis of infected hepatocytes. However, chronic HBV infection is characterized by the loss or functional exhaustion of HBV-specific CD8+ T cells due to high levels of HBs antigenaemia and failure to neutralize circulating virions as a result of an insufficient B-cell response. Programmed cell death protein-1 (PD-1).