Mixing Spider DNA and Goat Embryos Produces Milk With a Side of Silk
For their adorable antics and the milk they provide for delicious cheese, goats have long been among the most beloved farm residents, as well as the most common livestock on the planet. Now, thanks to genetic engineering, some goats’ milk is being used to make more than just chèvre.
When most people think of agricultural GMOs, long rows of monocropped soy liberally doused with the herbicide Roundup come to mind. Transgenic goats are bred using the same technology, but scientists believe their udders may fulfill the promise of genetic engineering by directly improving and saving lives, making everything from cancer drugs to materials for joint replacements.
The animals look and act just like regular goats: Workers milk them like they would at any dairy, and the goats raid their handlers’ pockets for stuff to chew on—a risk you face around any kid, doe, or billy goat. But scientists have added an extra protein or two to their already nutrient-rich milk.
One of those proteins is from the golden orb-weaver spider. Its silk, tougher than Kevlar, is a hundred times stronger than human ligaments. The potential for a light, incredibly resilient fiber is immense: The future might hold anything from spider knee replacements to spider parachutes. But aside from being viscerally disgusting, a spider farm just won’t work. Golden orb weavers are cannibalistic. In 2000, Nexia Biotechnology figured out a solution to that problem that reads like science fiction—it bred goats that can produce the silk instead.
Scientists like working with goats for several reasons; one imagines their tendency not to eat one another comes in near the top of the list. They’re also easy to breed and handle, and pound-for-pound, goats produce as much milk as cows. But while a goat doesn’t weigh any more than a person, a cow weighs half as much as a car.
“If a hundred-and-fifty-pound goat decides they don’t want to go somewhere, you just push them. You can’t do that with a 1,500-pound cow,” said Randy Lewis, a Utah State University biologist who breeds the goats. Lewis’ team bought the first members of its herd in 2009.
To make the goats, scientists ferreted out the chunk of the golden orb weaver’s genetic code that’s responsible for directing the production of the single protein that makes up its dragline silk, a kind of safety line that connects the spider to its web. Next they tucked that gene into the DNA of goat embryos, alongside the natural milk production genes, to take advantage of the ready-made machinery. The embryos were then implanted into female goats, which gave birth to kids with a little something extra. Now, keeping the line going is easy—just breed a spider-goat with a normal one; half of the babies will carry the spider gene.
The only way to find out if they have the gene is by genetic testing. Lewis has several sets of fraternal twins where only one is part spider. He often asks visitors to guess which makes silk. “Nobody’s better than fifty-fifty guessing which is which,” he said.
Like any other goats, the transgenic ones mature around 18 months. That’s when they start lactating, and the spider silk proteins are mixed in with the milk—which Lewis and his crew extract from the goats’ udders with good old-fashioned milking. “All they want you to do is scratch their head,” Lewis said. “And to milk them, you just turn ’em loose, and they hop up to get milked.”
While getting the silk out is trickier than pouring milk into a bottle, it’s not fundamentally more complicated than making cheese. First the fat is skimmed off, and then the silk proteins are processed out, like separating curds from whey.
Although the herd is regularly producing milk, the silk isn’t being used commercially just yet. There are 50 animals in the spider goat herd at Utah State, about a third of which are normal goats that stick around to increase genetic diversity and provide milk for all of the kids. Lewis also has two other spider silk projects going that use genetically engineered silkworms and bacteria in the same role as the goats.
While we’ve yet to see a star running back get an extra few years on the field thanks to some new spider silk knee ligaments, several goat milk–derived products are on the market. One, an anti-clotting drug called ATryn, is produced by the pharmaceutical company rEVO Biologics. ATryn is how the company is branding the protein antithrombin, which we all have in our blood to regulate the clotting process. Some people don’t naturally produce enough of the molecule, making them susceptible to dangerous clots.
The most common way to treat antithrombin deficiency is by stripping it from plasma that healthy people have donated and injecting it into the sick patients. Some viruses can hitch a ride on the molecule, which means human-derived antithrombin carries a slim risk of infection for the recipient. Protein from a goat’s udder has no such dangers.
And it doesn’t take a blood drive to get goats to give milk, so you don’t have to hope for kind souls to take a needle. "From a manufacturing perspective, the quantity we can make is quite remarkable. There's no limitation to the scale,” said William Gavin, V.P. of operations for rEVO Biologics.
At the moment, rEVO has 600 goats on its 167-acre Massachusetts farm, separated into herds based on which genes they carry. It has had up to 2,000, depending on how many projects it has going. While ATryn is the company’s only product at the moment, its scientists have half a dozen active projects, each with a handful of experimental goats. rEVO, with the help of some partner companies, is researching additional plasma proteins to be used therapeutically. The company is also working to develop goats that produce cutting-edge drugs called monoclonal antibodies.
Monoclonal antibodies work with a sick person’s immune system to help the body better fight off disease. They bind to specific parts of certain cells and can slow down an autoimmune disorder, deliver a radioactive payload to a tumor, and more. They are usually made in cells, either human or bacterial, grown in enormous steel vats—a process that is extremely expensive.
According to Gavin, goat-derived monoclonal antibodies have the potential to be easier to manufacture and more cost-effective. Goats already produce a number of antibodies in their milk—that’s how a kid first develops its immune system. So scientists just add in one more.
“Because a goat can make an antibody at very high levels, it's absolutely perfect for monoclonal antibody production,” he said.
There have been incidents of gross animal neglect and mistreatment at biomedical goat operations. Santa Cruz Biotechnology, which raises biomedical goats, has paid the USDA a string of fines stemming from charges of mistreatment, poor care, and inaccurate reporting. Activist groups such as Stop Animal Exploitation Now have also sued the company. In comparison, GMO goat operations like rEVO have far better track records regarding animal welfare. Inspectors have never found rEVO to be in violation of the Animal Welfare Act. When Lewis was at the University of Wyoming, the school was charged with two Animal Welfare Act violations, paying a fine of $8,571. Researchers treated the sick goats without consulting a veterinarian, which the act requires. The second violation was for having expired veterinarian medications on hand.
“The vet was unavailable, so we went ahead and treated them,” Lewis said of the incident. “We thought that was the only humane thing to do.”
Not all of these scientifically souped-up milks need to be processed to be useful. University of California, Davis, biologist James Murray says he has developed goats whose milk, by itself, could help protect some of the 2 million children who die each year of diarrheal diseases. The UC Davis goats have extra lysozyme in their milk, an enzyme found at high levels in human breast milk, as well as in saliva (and egg whites). Lysozyme protects against a number of bacteria, including E. coli, that cause diarrhea and other diseases.
When fed the upgraded milk, baby pigs with diarrhea caused by E. coli recovered more quickly than those that got regular milk. Unlike broad-spectrum antibiotics, the lysozyme milk is a gentle treatment.
“It doesn’t wipe anything out; it’s not a general antibiotic. It helps inhibit the growth of some of the bacteria that aren’t good,” Murray said.
UC Davis only has between 10 and 20 lysozyme goats at any given time, and the milk hasn’t been approved for human consumption. But Murray is hopeful that human kids will soon be able to get a healthy boost in this easy, low-impact way. “Our goal is to have the milk distributed to at-risk children by NGOs. We’re not trying to make money off this. Ideally, we could provide the goats, and they could produce their own milk,” Murray said.
Goats are an ideal choice for that kind of distribution, for the same reasons they’re the world’s favorite dairy animal. They’re hardy, easy to handle, and most endearingly, extremely personable. Perhaps one day, scientific advances will allow people who rely on goats for nutrition to heal themselves the same way: with a glass of milk.