Progress With Developing Use of Gene Editing To Cure Chronic Infection With Hepatitis B Virus

Abstract

Chronic infection with hepatitis B virus (HBV) occurs in approximately 6% of the world's population. Carriers of the virus are at risk for life-threatening complications, and developing curative treatment remains a priority. The main shortcoming of licensed therapies is that they do not affect viral covalently closed circular DNA (cccDNA), a stable intermediate of replication. Harnessing gene editing to mutate cccDNA provides the means to inactivate HBV gene expression permanently. Reports have described use of engineered zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR) with CRISPR-associated (Cas) nucleases. Although inhibition of viral replication has been demonstrated, reliably detecting mutations in cccDNA has been difficult. Also, the dearth of murine models that mimic cccDNA formation has hampered analysis in vivo. To reach a stage of clinical use, efficient delivery of the editors to HBV-infected hepatocytes and limiting unintended off-target effects will be important. Investigating therapeutic efficacy in combination with other treatment strategies, such as immunotherapies, may be useful to augment antiviral effects. Advancing gene editing as a mode of treating HBV infection is now at an interesting stage and significant progress is likely to be made in the immediate future.

Sustained Inhibition of HBV Replication In Vivo after Systemic Injection of AAVs Encoding Artificial Antiviral Primary MicroRNAs

“…Advances with hepatotropic delivery of therapeutic nucleic acids have also been remarkable. Evidence now indicates that gene therapy-based treatment, alone or in combination with other therapeutics, is feasible and may lead to complete or functional cure from HBV infection 9, 35, 36…”

Improved antiviral efficacy using TALEN-mediated homology directed recombination to introduce artificial primary miRNAs into DNA of hepatitis B virus

“…Gene editing has recently shown promise as the means of inactivating cccDNA to achieve a cure from the infection (reviewed in Ref. [6]). The basis of using engineered nucleases to disable cccDNA is that repeated digestion of the target viral DNA eventually results in mutation following error-prone repair of the viral sequences through activation of the NHEJ pathway.…”

“…[6]). Gene editing and gene silencing inactivate HBV and both approaches have been shown to be effective without causing toxicity and other unintended off-target effects.…”

Hepatitis B virus: is a cure possible?

“…phenylpropenamide derivatives, heteroaryldihydropyrimidines) that decrease nucleocapsid assembly/stability, and small interfering RNA-based strategies (e.g. ARC-520 and ISIS-HBVRx) aiming at viral RNA degradation [4,5,7,[9][10][11].…”

“…Other strategies aim at promoting the elimination of infected hepatocytes by restoring antiviral immunity using immunomodulatory compounds (e.g. TLR7 agonists) or antigen-or DNA-based therapeutic vaccines as well as by tumor necrosis factor-mediated killing of HBV-infected hepatocytes using antagonists of cellular inhibitors of apoptosis proteins [4,5,7,[9][10][11][14][15][16]. Interestingly, given that long-term NUC treatment can restore T-cell responses in chronic hepatitis B patients, increasing antiviral T-cell responses by immunotherapeutic strategies might increase the chances of achieving control of HBV infection [17].…”