18. Delivery of CRISPR/Cas9 or TALENs Against Hepatitis B Virus cccDNA by High-Capacity Adenoviral Vectors
Authors: Maren Schiwon, Thorsten Bergmann, Eric Ehrke-Schulz, Anja Ehrhardt
Journal: Molecular Therapy (2016)

High-capacity adenoviral vectors (HCAdV) are superior tools to deliver large DNA cargos into living cells. These vectors are devoid of all adenoviral coding sequences, leaving only essential adenoviral DNA sequences which are required for virus replication and packaging of HCAdV genomes containing foreign DNA. Here HCAdVs were utilized in combination with designer nucleases to develop a cure for chronic hepatitis B virus (HBV) infection. Although advanced prevention measures are available, chronic HBV infection still presents a serious global health burden for which no cure exists. The hepatitis B virus genome forms a persistent DNA species in infected cells (covalently closed circular DNA, cccDNA) and in that way is able to convert the infection into a chronic state. A chronic carrier state makes the sufferers susceptible for cirrhosis and liver cancer. To date various versions of designer nucleases against the HBV genome were already devised but yet no adequate transfer to HBV-infected cells in vitro and especially in vivo was presented. In the present study the potential of designer nucleases as a tool to cure chronic HBV infection was investigated and the aim was to cut and therefore destroy the HBV-DNA intracellularly. We employed transcription factor-like effector nucleases (TALENs) and the clustered regularly interspaced short palindromic repeats / Cas9 (CRISPR/Cas9) system and additionally adapted HCAdV as an efficient delivery method. This is the advancement of this study in which either both TALEN subunits of a pair or multiple guide RNA expression cassettes alongside with a Cas9 coding sequence including promoter and termination signal were co-delivered in one vector. The expression cassettes including all compounds of both systems were inserted into HCAdVs. Vectors were amplified in large scale, their integrity monitored and then tested on liver cell lines which were infected with HBV. For this purpose we established an HBV infection model which is based on a HBV genome which was also inserted into a HCAdV. The effect of the designer nucleases on the HBV genome and its transcription was assayed by qPCR, a mutation detection assay and HBsAg ELISA. Our data revealed 80% reduction of hepatitis B surface antigen production in designer nuclease treated cells in comparison to untreated or mock treated cells. Furthermore cells treated with nucleases resulted in a decreased HBV genome copy number and the introduction of mutations could be demonstrated by a mutation detection assay using T7 endonuclease I. Note that the CRIRSPR/Cas9 system was superior to the TALEN based construct. In conclusion, we demonstrated delivery of a complete TALEN pair as well as a CRISPR/Cas9 construct containing three guide RNAs by use of just one HCAdV, respectively, which after application resulted in effective reduction of HBV parameters. Future objectives are to test our vectors in animal models of HBV infection and eventually to optimize the vector for the needs of this application.