For the first time, researchers have genetically modified cows to be resistant to the bacterium that causes bovine tuberculosis. This disease is well-controlled in most developed countries, but it can often be fatal for cattle in developing countries and spread to people and other animals.
Researchers from China’s Northwest A&F University used a technique called CRISPR to insert a gene associated with tuberculosis resistance into 20 cows, 11 of which lived past the age of 3 months. These animals were more resistant to tuberculosis than animals who weren’t modified. They also didn’t show any unintended consequences of genetic modification. A study describing these findings was published in the journal Genome Biology on January 31.
CRISPR is an intensively researched tool developed in the last couple years, which relative to previous techniques, can quickly and cheaply insert genes into specific locations in an organism’s genome. It has been used to tweak many organisms, including modifying human embryos in the lab and correcting the gene responsible for Duchenne muscular dystrophy in mice.
In this case, the scientists used a new version of the technique, which inserts a gene into a single snip within one strand of DNA at a desired location in the cow genome. Previously, CRISPR involved the use of a molecular “scissors” that cleaved both strands of DNA. The advantage of this new technique is that it is potentially safer, says Suk See De Ravin, a researcher with the Laboratory of Host Defenses, part of the U.S. National Institutes of Allergy and Infectious Diseases, who wasn’t involved in the paper.
“I think this is a very neat study that demonstrates the feasibility of introducing a desired gene of interest via a potentially safer way,” De Ravin says. But “obviously further studies to demonstrate the safety of the outcome are necessary.”
He adds that the ability to raise animals “with improved resistance to infections has the potential to dramatically reduce the overuse of antibiotics in livestock,” which is a significant problem.
Harry Malech, chief of the Laboratory of Host Defenses and the National Institutes of Allergy and Infectious Diseases, says that having such resistant animals could help reduce the transmission of tuberculosis through milk, which is a significant health problem in developing countries. (The widespread use of pasteurization in the United States and most of the western world has “pretty much eliminated tuberculosis risk from milk, though the faddish enthusiasm for raw milk and cheeses… has reintroduced that risk,” he notes.)
Chuck Sattler, the vice president of genetic programs at a cow-breeding company Select Sires, says that the inserted gene is already found naturally in some cattle. The researchers used CRISPR to make changes that could occur with traditional breeding, but much more quickly and in a more specific manner, he adds.
For such transgenic cattle to be approved in the United States, they’d have to be vetted by the Food and Drug Administration. That’s cost-prohibitive at this point, Sattler adds.