Antiviral Goes Viral: Harnessing CRISPR/Cas9 to Combat Viruses in Humans

The clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) systems are RNA-guided sequence-specific prokaryotic antiviral immune systems. In prokaryotes, small RNA molecules guide Cas effector endonucleases to invading foreign genetic elements in a sequence-dependent manner, resulting in DNA cleavage by the endonuclease upon target binding. A rewired CRISPR/Cas9 system can be used for targeted and precise genome editing in eukaryotic cells. CRISPR/Cas has also been harnessed to target human pathogenic viruses as a potential new antiviral strategy. Here, we review recent CRISPR/Cas9-based approaches to combat specific human viruses in humans and discuss challenges that need to be overcome before CRISPR/Cas9 may be used in the clinic as an antiviral strategy. CRISPR/Cas9 technology can be harnessed as a strategy to combat virus infections in humans. CRISPR/Cas9 can be targeted to the viral genome directly or can interfere with the expression of host factors essential for virus infection. Direct targeting of viral genomes by CRISPR/Cas9 limits virus replication, but may induce formation of virus escape variants. Multiplexed CRISPR/Cas9 systems potently inhibit the formation of escape mutants. RNA-guided RNA-targeting Cas endonucleases can be rewired to target human RNA viruses. CRISPR/Cas9 can correct genetic defects in vivo via the use of efficient adeno-associated viral (AAV) vectors. AAV also holds promise as a delivery strategy of antiviral CRISPR/Cas9 to virus-infected cells in vivo.