Effect of CRISPR-Cas9 mediated knockout of IRF3 gene in BHK-21 cells on immune gene expression and foot-and-mouth disease virus replication

Foot-and-mouth disease (FMD) is an acute highly contagious viral disease of cloven-hoofed animals. Currently, FMD vaccine production and research mainly depend on the BHK-21 cell line. BHK-21 is highly sensitive to FMD virus, however, still a lot of room for improvement that can result in higher antigen yield in vaccine production facilities. IRF3 (Interferon regulatory factor 3) is a key transcription regulatory factor involved in the interferon (IFN) pathway, the immediate antiviral response of the cells. In this study, IRF3 knock-out (KO) BHK-21 cells were established using the CRISPR-Cas9 method. The KO cell line was stable in growth and morphological characteristics, unveiled in growth curve analysis. After infection with FMDV, the viral copy number, virus titer, and plaque forming units (PFU) were significantly increased in KO cells than those in parental BHK-21 (NC) cells. The relative gene expression of type I IFNs and ISGs such as IRF3, IRF7, viperin, Mx1 and ISG15 upon FMDV infection was severely reduced in KO cells. Results preliminarily reveal the role of IRF3 in cellular antiviral immune response, and the IRF3-KO cell line could also serve as a useful tool for FMDV research and vaccine production.