Pigs that are immune to a disease estimated to cost farmers $2.7 billion a year globally look set to become the first genetically modified farm animals to be used for large-scale meat production.
鈥淲e could very well be the first,鈥澛爏ays Clint Nesbitt of international breeding company , which has created hundreds of the CRISPR-edited pigs in preparation for a commercial launch.
He is confident that the animals, which have been modified to have immunity to porcine reproductive and respiratory syndrome (PRRS), will be given the go-ahead by US regulators by early 2025 or sooner. 鈥淚 think by and large the farmers are quite excited to have it, because this is a fairly devastating disease,鈥� says Nesbitt.
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That approval process by the Food and Drug Administration has been going on for several years and is nearing completion, says Nesbitt. 鈥淲e don鈥檛 have any reason to think that the FDA will not approve the pigs.鈥�
Genus is also applying for the regulatory green light to be given in major export markets for US pork, from Mexico to China, and the full-scale commercial launch will follow this, he says. 鈥淚f those pork products end up in countries where they have not yet approved the pig, that causes all kinds of disruptions,鈥� says Nesbitt. 鈥淚 think we still have two years to go before we鈥檙e likely to start actually selling the pigs.鈥�
PRRS is caused by a virus that may lead to no symptoms in some animals, but severe disease in others. It can damage the immune system, making pigs vulnerable to other infections that have to be treated with antibiotics. There are vaccines available, but they only reduce the severity of symptoms, which is why gene editing is an attractive alternative.
The virus infects cells by binding to a small part of a protein called CD163. Work at the Roslin Institute in the UK showed that using CRISPR gene editing to remove the DNA coding for this part of the protein while allowing the protein in the pigs to continue to function in all other ways.
鈥淭hey are completely immune to the virus,鈥� Nesbitt says. 鈥淎nd we have not found anything else that is impacted in the pig.鈥�
Now, in facilities in the US, Genus has made this gene edit in four different elite breeding lines of pigs, though this wasn鈥檛 straightforward. Only around a fifth of the piglets created by Genus had the desired edit and only in some cells in the body, not all 鈥� a phenomenon called mosaicism. A few also had unintended changes elsewhere in the genome as a result of the editing process. Further rounds of breeding were needed to create animals with the desired change in both copies of the gene and with no unintended changes.
The difficulty and expense of creating a genetically diverse population of animals ready for mass production is partly why modified farm animals aren鈥檛 yet used for meat or dairy production, and, as far as 快猫短视频 is aware, Genus is the first company to overcome this hurdle.
The firm will sell semen rather than pigs, says Nesbitt. This means the first generation of animals produced from this won鈥檛 have immunity to PRRS, as only one of the two copies of the CD163 gene in such offspring will have the edit. Further breeding will be required to produce animals with the edit in both copies, which could take several years.
Genus will also provide a test that reveals if pigs have the edit, and whether they have it in one or both copies. In the US, meat from the pigs won鈥檛 have to be labelled.
In the UK, the National Pig Association has to allow the production and sale of gene-edited plants and animals in England so the PRRS-resistant pigs become available to farmers sooner. The introduction of the resistant pigs would help avoid animal suffering, it says.
But . 鈥淜eeping animals crowded together, and in stressful conditions, provides an ideal environment for pathogens to spread and evolve,鈥� says Catherine Jadav of Compassion in World Farming. 鈥淚f PRRS-resistant pigs are used to perpetuate the current highly intensive model of pig farming, then other diseases will continue to develop 鈥� bringing disease after disease that 鈥榬equires鈥� new gene-edited animals.鈥�
The CRISPR Journal
