Now Christianson’s company, which is a division of the British animal genetics firm Genus, is trying something different. Instead of trying to seal animals off from the environment, it’s changing the pigs themselves. At an experimental facility in the central US (the location kept secret for security reasons), the company has a swine IVF center and a lab where pig eggs are being genetically edited using CRISPR, the revolutionary gene scissors.
In experiments on pig cells, the Genus researchers have tried many possible edits to the CD163 gene, looking for those that occur most predictably. Even with such efforts, the pigs being born have the right edit only about 20 to 30% of the time. Those piglets whose genomes have errors end up in a compost heap.
Antonio RegaladoI want to convey that this technology is not simple. You can be good at this technology or bad at it, says Mark Cigan, a molecular biologist with a senior role in the program.We need to be rigorous, because we want a predictable change in all the pigs. It has to be the same change every time.
Reading past the misleading title – the resulting hundreds of gene-edited pigs are kept in experimental stations and regulatory approval for commercial use is unlikely to arrive before 2025 – the approach seems slow and wasteful to me. While CRISPR shows a lot of promise in many areas, an error rate of 70–80% in mammals is quite high, producing many animals with unwanted mutations that have to be sacrificed. And because you need the pigs with the correct mutation to breed in order to establish a viable population, this slows down trials and results quite a lot.
It’s not clear yet whether the PRRS-resistant pigs, with only one receptor removed, are healthy and otherwise normal. Cigan says the company thinks they are; researchers can’t see other differences in their tests, which measure things like how much the pigs eat and gain weight. But unplanned changes could be subtle.
Richt says a decade ago he was involved in making cattle resistant to mad cow disease. After removing one gene, he sensed they were changed.
The way they stood up was funny—it was hard to get them back up, he says.The caretaker told me they are stupid, so maybe intelligence was affected.With only a dozen cows, he never was sure, but he suspects the cattle lost a “luxury function”—one that wasn’t vital to survival but whose removal led to a degradation of the sensory system.
The hard part is double-checking if the gene-editing, however precise, has not introduced unforeseen side-effects. Obviously, it is highly unethical to apply this technique to humans – as a Chinese scientist did in 2018 in an attempt to gene-engineer HIV resistance. I wonder if these research efforts would not be better spend trying to develop a vaccine for PRRS – since pigs are genetically similar to humans, I imagine the process would be relatively similar as well (and, unlike people, farm animals would not object against vaccination and spread false rumors about its supposed ill effects).
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