High-Efficiency Targeted Editing of Large Viral Genomes by RNA-Guided Nucleases

Abstract

A facile and efficient method for the precise editing of large viral genomes is required for the selection of attenuated vaccine strains and the construction of gene therapy vectors. The type II prokaryotic CRISPR-Cas (clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas)) RNA-guided nuclease system can be introduced into host cells during viral replication. The CRISPR-Cas9 system robustly stimulates targeted double-stranded breaks in the genomes of DNA viruses, where the non-homologous end joining (NHEJ) and homology-directed repair (HDR) pathways can be exploited to introduce site-specific indels or insert heterologous genes with high frequency. Furthermore, CRISPR-Cas9 can specifically inhibit the replication of the original virus, thereby significantly increasing the abundance of the recombinant virus among progeny virus. As a result, purified recombinant virus can be obtained with only a single round of selection. In this study, we used recombinant adenovirus and type I herpes simplex virus as examples to demonstrate that the CRISPR-Cas9 system is a valuable tool for editing the genomes of large DNA viruses.

Author Summary

The clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) system was discovered as a component of the bacterial acquired immune system that cleaves foreign DNA. This system is now used for site-specific genome editing in a wide range of organisms, including bacteria, yeasts, plants, and animals. However, the use of this approach in non-cell organisms, such as non-integrating viruses, has not been reported. Because multiple steps are required to construct mutant or recombinant DNA viruses with large genomes using the current approaches, we used the CRISPR-Cas9 system to introduce site-specific indels and insert a foreign gene into an adenoviral vector and wild-type herpes simplex virus. The high efficiency of CRISPR-Cas9 editing allowed for simple construction and purification of recombinant progeny virus. We believe that this new technique will have broad practical significance for selecting attenuated vaccine strains and antiviral drugs, constructing gene therapy vectors, and establishing efficient methods for viral biological studies.