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Company says it is near U.S. approval for pigs safe from porcine reproductive and respiratory syndrome.
Pigs, cattle, and other livestock with edited genes are still far from most dinner plates, but a U.K. company has taken a big step toward the supermarket by engineering several commercial breeds of pigs to be resistant to a virus that devastates the swine industry. The firm, Genus plc, hopes that by year’s end the U.S. Food and Drug Administration (FDA) will formally approve the pigs for widespread human consumption, a first for a gene-edited animal.
Alison Van Eenennaam, an animal geneticist at the University of California, Davis, is cheering the news. “There’s no point having a pig getting sick and dying if there’s an approach to genetically prevent it from doing so,” she says, adding that this benefits farmers, the pigs, and, ultimately, the consumer.
But Van Eenennaam laments the regulatory hoops the company is having to jump through. FDA views the DNA change made by the genome editor CRISPR as an “investigational new drug” that requires multiple submissions from Genus to establish the altered gene’s safety, ability to be inherited, and stability over generations, as well as the resulting pigs’ resistance to the virus. “You’re talking about a very, very expensive regulatory pathway,” she says, arguing it is unnecessary because unlike genetically modified organisms, to which DNA from other species has been added, the gene editing involved the pigs’ own DNA, creating changes that could happen naturally.
The gene edit made by Genus outwits a virus that kills nearly all the suckling pigs it infects and weakens older ones as well. The virus, which causes a condition called porcine reproductive and respiratory syndrome (PRRS), has spread worldwide and costs the pork industry an estimated $2.7 billion annually. Eight years ago, a team led by Randall Prather at the University of Missouri reported it could make pigs resistant to PRRS by using CRISPR to disable a receptor, CD163, on pig cells that the virus uses to establish an infection.
Now, Genus, which specializes in breeding livestock with desired traits, has translated “proof-of-concept work to a commercial scale,” it reports in the February issue of The CRISPR Journal. Scientists at the company modified animals in four lines of pigs that are used in commercial production of pork, by doing a CRISPR edit in early embryos that are transferred into gilts and then further breeding of the progeny. This ultimately creates breeds with both their copies of the CD163 gene disabled.
Rodolphe Barrangou, a food scientist at North Carolina State University who is also editor-in-chief of The CRISPR Journal but not involved with the work, says the study is the “end of the beginning” of bringing gene-edited livestock to the wide market because so many farmers will likely want PRRS-resistant pigs. “It’s not just a nice study in a nice model,” says Barrangou, who did pioneering CRISPR work himself. “It’s actually doing it in the real world.”
Vaccines exist for PRRS but they lack the 100% protection seen with the gene edit. Prather, whose university holds patents on this modification and has a licensing agreement with Genus, says the CRISPR edit has several benefits beyond reducing financial losses in the pork industry. The virus, he says, threatens food security and creates “psychological and emotional issues” for producers that have to euthanize the sick pigs. “CD163-edited pigs are a solution.”
FDA has so far formally approved two genetically modified food animals, but neither is widely consumed. One is a salmon that has a gene from another fish species and grows faster, but consumer concerns have limited sales. The second, known as the GalSafe pig and made by Revivicor, had DNA inserted to cripple a gene for a sugar molecule on the surface of its cells. (The engineering included a new gene to track resistance to an antibiotic.) Some people have mild to severe allergic reactions to eating pork as a result of this sugar, and Revivicor expects GalSafe pigs will go into commercial production later this year for this specialized market. (Experimental xenotransplants of organs from GalSafe pigs have also been performed in three people who were brain-dead in the hope the sugar modification would lower the risk of rejection.)
FDA more recently gave less formal endorsements of CRISPR’ed food to five pigs edited to be sterile by a Washington State University team and a line of cattle edited by Acceligen Inc. to have short hair to better withstand heat. But neither received full approval for human consumption or is being produced at a commercial scale: The pigs received an “investigational food use authorization,” which took 2 years and more than $200,000 to obtain, and two short-haired cattle and their future offspring were given a “low risk determination” for marketing. In both cases, the introduced changes occur naturally in the animals—and the cattle ultimately may not need FDA approval.
The CD163 modification used to protect against PRRS could well occur naturally but has never been observed in pigs, creating higher hurdles for FDA clearance, says Clint Nesbitt, a molecular biologist who oversees regulatory affairs at Genus. As a result, he says, “We have to go through the full, complete review system at FDA. There are no shortcuts for us.” Still, he says, Genus has made “good progress” with the agency. “There are just a couple of little [submissions] left that we’re still working on” before submitting a formal request for approval.
The challenging regulatory environment in the United States will be among the topics at a National Academies of Sciences, Engineering, and Medicine workshop on gene-edited food animals next week. Other countries are less restrictive.
Regulators in Colombia in October 2023 indicated that because the edited pigs from Genus do not involve transgenics, they will treat the swine the same as conventionally bred animals. The company is also seeking regulatory approval in China, the largest consumer of pork. “Our decision about when to commercially start selling the pigs is going to be based upon whether we have the right combination of regulatory approvals globally,” Nesbitt says, because the U.S. and other countries export pork worldwide.
Once the modified pigs are approved, Nesbitt says it will take time for producers to breed them into their herds. “Nowhere on the planet is it going to be a light switch, where suddenly everybody’s got the edited pigs,” he says. “It’s going to be much more like a dimmer switch. … And we still have to have a lot of conversations about market acceptance.”
