The meat and poultry industry is in need of novel methods to stave off infection. A group from the College of Animal Sciences, Jilin University in China has combined the gene-editing tool CRISPR-Cas9 with the gene expression silencing technique of RNA interference (RNAi), to develop genetically modified pigs that are protected from classical swine fever virus (CSFV.)

This work is published in a paper titled, “Genetically modified pigs are protected from classical swine fever virus” published on December 13 in PLOS Pathogens.

Classical swine fever, caused by CSFV, is a highly contagious, often fatal porcine disease that causes significant economic losses in the swine industry. CSFV can be transmitted both horizontally (from one pig to another) and vertically (from mother to offspring), and both domestic pigs and wild boar are highly susceptible to CSFV infection. CSFV can cause severe leukopenia and immunosuppression, which often leads to secondary enteric or respiratory infections. Outbreaks are an ongoing problem, and, despite national efforts, the disease remains widespread. Strategies to control CSFV mainly consist of systematic prophylactic vaccination policy and stamping-out policies.

Recently, genetically modified animals with viral resistance were developed using the gene editing CRISPR-Cas9 system. These technologies have contributed to the development of virus-resistant animals and have provided considerable productivity benefits to producers.

In this study, the researchers successfully produced anti-CSFV transgenic pigs by combining RNAi gene silencing technology and CRISPR-Cas9 technologies.

TG pigs exhibit antiviral responses during CSFV infection. Histopathological changes in the NTG pigs were confirmed by HE staining. These histopathological changes included a decrease in splenic white pulp and hyperaemia; an expansion of splenic red pulp; acidophilic change and accumulation of lipid droplets in hepatocytes; infiltration of inflammatory cells in the portal area of the liver; alveolar effusion, bleeding and infiltration of a large number of inflammatory cells in the lungs; and unclear renal tubular epithelial cell boundaries; and cell cavitation in the kidneys. [Xie Z, et al. (2018)]
To do this, the researchers selected antiviral small hairpin RNAs (shRNAs) which were inserted at the porcine Rosa26 (pRosa26) locus via a CRISPR-Cas9-mediated knock-in strategy. Anti-CSFV transgenic pigs were produced by somatic nuclear transfer (SCNT). Additionally, it was confirmed that the disease resistance traits in the transgenic founders were stably transmitted to their F1-generation offspring.

In addition, viral challenge results confirmed that the pigs would be resistant to infection. The authors wrote, “Notably, in vitro and in vivo viral challenge assays further demonstrated that these transgenic pigs could effectively limit the replication of CSFV and reduce CSFV-associated clinical signs and mortality, and disease resistance could be stably transmitted to the F1-generation.”

The authors write that their work demonstrates that, “RNA interference (RNAi) technology combining CRISPR-Cas9 technology offered the possibility to produce transgenic animals with improved resistance to viral infection and that the use of these transgenic pigs can reduce CSF-related economic losses.” And that news, many can agree, is far better than headlines of bacon shortages.

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