Porcine Reproductive and Respiratory Syndrome (PRRS) is the most economically important disease in swine in North America, Europe and Asia. PRRS is caused via infection of the pulmonary alveolar macrophages (PAMs) with the PRRS virus (PRRSV) causing respiratory illness and high fever in young growing pigs that predisposes them to secondary bacterial infections. PRRSV also causes severe reproductive failure in sows and boars. Although research is ongoing, PRRSV continues to elude a successful vaccine. In 2014, piglets were born with a gene edit in exon 7 of the Cluster of differentiation 163 (CD163) gene introduced by using the CRISPR/Cas9 site-directed nucleases system. The resulting litters of pigs were either challenged with multiple PRRSV isolates at 3 weeks of age or bred at maturity for a challenge with pregnant sows. The challenges demonstrated that the pigs were completely resistant to infectivity to both Type 1 and 2 isolates as measured by clinical signs, viremia, antibody response and lung histopathology. In a follow-up study, pregnant CD163-/- pigs were also challenged with PRRSV to determine if absence of CD163 in the dam should be sufficient to protect the CD163+/- fetuses that have functional CD163 protein. The wild-type sow and fetuses were actively infected with the PRRSV and one sow aborted. The CD163-/- sows carrying both the CD163-/- and CD163+/- fetuses were all negative for PRRSV nucleic acid and showed no sign of fetal or placental failure. The results of this study clearly demonstrate that the absence of CD163 in the sow is sufficient to protect a PRRSV-susceptible CD163+/- fetus. Gene editing of CD163 in pigs, via CRISPR/Cas9, successfully blocked PRRSV infectivity in young growing pigs and pregnant sows and their fetuses. This is a great example of the potential of utilizing gene editing to improve animal agriculture.

Genetic polymorphisms within immunity-related candidate genes in pigs have been identified to control variations in immune functions and/or disease resistance. It has become necessary to evaluate the effects of other genetic markers of economically important traits prior to introducing them into marker-assisted selection programs. In this study, polymorphisms of porcine genes coding Interferon-induced Gunylate binding protein 1 (GBP1), GBP2, CD163, and CD169 were investigated for their association with growth and meat quality traits in a Korean native pig breed -Yorkshire inter-crossed F2 pig population (KY-F2). KY-F2 animals (n=346) have been successfully used for linkage mapping to identify quantitative loci that control meat quality, growth, and immunity traits. In our results, polymorphisms in genes GBP1 and GBP2 showed association with pig growth rate as well as meat quality traits such as crude fat, drip loss, and meat color (yellowness) in the KY-F2 population. The polymorphism in gene CD163 only showed association with crude fat, as a meat quality trait. CD169 gene was associated with pork tenderness. In conclusion, four immune-related genetic markers were validated for their association with growth and meat quality traits to gauge their potential use in a swine selection program. The results warrant further studies in other commercial pig populations.