RNA-guided gene editing of the murine gammaherpesvirus 68 genome reduces infectious virus production.

Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV) are cancer-causing viruses that establish lifelong infections in humans. Gene editing using the Cas9-guideRNA (gRNA) CRISPR system has been applied to decrease the latent load of EBV in human Burkitt lymphoma cells. Validating the efficacy of Cas9-gRNA system in eradicating infection in vivo without off-target effects to the host genome will require animal model systems. To this end, we evaluated a series of gRNAs against individual genes and functional genomic elements of murine gammaherpesvirus 68 (MHV68) that are both conserved with KSHV and important for the establishment of latency or reactivation from latency in the host. gRNA sequences against ORF50, ORF72 and ORF73 led to insertion, deletion and substitution mutations in these target regions of the genome in cell culture. Murine NIH3T3 fibroblast cells that stably express Cas9 and gRNAs to ORF50 were most resistant to replication upon de novo infection. Latent murine A20 B cell lines that stably express Cas9 and gRNAs against MHV68 were reduced in their reactivation by approximately 50%, regardless of the viral gene target. Lastly, co-transfection of HEK293T cells with the vector expressing the Cas9-MHV68 gRNA components along with the viral genome provided a rapid read-out of gene editing and biological impact. Combinatorial, multiplex MHV68 gRNA transfections in HEK293T cells led to near complete ablation of infectious particle production. Our findings indicate that Cas9-gRNA editing of the murine gammaherpesvirus genome has a deleterious impact on productive replication in three independent infection systems.