118. Inhibition of Hepatitis B Virus Replication In Vivo Following Delivery of Antiviral TALENs With Recombinant Adeno-Associated Viral Vectors

Hepatitis B virus (HBV) is hyperendemic to sub-Saharan Africa where there are approximately 600 000 deaths per year associated with chronic HBV infection. HBV may have long periods of dormancy in carriers of the virus, which is dependent on persistence of the nuclear replication intermediate covalently closed DNA (cccDNA). Current HBV therapies, including nucleot(s)ide analogs, target the actively transcribed virus. The cccDNA is not cleared and may act as a reservoir for re-initiation of viral replication following treatment withdrawal. This poses a significant challenge for the successful treatment of chronic HBV sufferers, and makes the cccDNA intermediate an important target for novel HBV treatments. Employing gene editing technology to disable cccDNA has emerged as a promising novel therapeutic strategy. TALENs targeting the surface and the core viral open reading frames, previously described by our group, demonstrated efficacy against HBV targets. To advance this technology to therapeutic application, efficient delivery and evaluation of the TALENs’ safety and target specificity in vivo and in vitro need to be established. This study aimed to evaluate the safety and efficacy of TALENs delivered by adeno-associated viral (AAV) vectors in vivo and in vitro. The HBV-infectable HepG2-hNTCP-C4 cell line was used to establish that the TALENs could disable cccDNA. Capacity for capsid modification, low immunogenicity and good hepatotropic transduction efficiency are favorable features that were considered in selecting these vectors. However, the delivery of TALENs by AAVs is technically complicated, as sequences encoding the two subunits of the complete TALENs exceed the capacity of single stranded AAVs. Consequently, we generated AAVs that encode each of the TALEN subunits. To constitute the complete TALENs, pairs of vectors were thus administered to mice or cultured cells. In vitro testing of AAV-TALENs was undertaken using the HepG2-hNTCP-C4 cell line. These cells present a novel tool for testing anti-HBV therapeutics as they overexpress the human sodium taurocholate co-transporting polypeptide (hNTCP) gene allowing them to be infected by HBV. The viral life-cycle is accurately recapitulated and enables assessment of effects of therapeutic agents on cccDNA. Since viral gene expression is dependent on transcription from the cccDNA intermediate in these cells, measurement of markers of HBV replication may be used as an indicator of cccDNA function. This study evaluated the potential of AAV delivered TALENs in vivo and in vitro by testing their activity and evaluating off-target activity, immunogenicity and liver toxicity. The results provide evidence for the utility of applying AAVs to the delivery of anti-HBV TALENs and offers further support for the feasibility of employing TALENs to treat chronic HBV infection.