The team around Professor Zhang Yong of the Northwest A&F University’s College of Veterinary Medicine, in Shaanxi province, central China, had made international headlines in early February by presenting a herd of genetically-engineered TB-resistant Holstein-Friesian cattle.
"We are at the experimental stage, with many rounds of validation to follow," Professor Zhang said. "Commercialisation may be possible when the time is ripe but that may take a few years," he added.
To create their TB-resistant herd, Professor Zhang’s research team resorted to a genome modification-technique that had been applied successfully to various species, including mouse, pig, and even monkeys, but never to cattle.
In their research, published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), the team reported the herd efficiently resisted a low dose of Mycobacterium bovis (which causes cattle TB) transmitted from infected cattle in nature, marking a significant a step in creating resistance to bovine TB. Professor Zhang’s research team took a further crucial hurdle by proving that the TB resistance was passed to some of the cattle’s calves.
"Our results contribute to the control and prevention of bovine tuberculosis and provide a previously unidentified insight into breeding animals for disease resistance," the research team said.
The research is now to focus on which of three enzymes able to cut a DNA molecule works best in the genome modification technique, with each having its own advantages and disadvantages in terms of simplicity, efficiency and toxicity. Also, cell types and delivery methods will impact on the success rate, so Professor Zhang’s team will also investigate these issues.
"No reliable rules currently exist to predict nuclease activity before experimental validation," the researchers said.
Bovine tuberculosis leads to hundreds of thousands of cattle being culled and burned or buried globally each year. Research on vaccines has been slow, so that there is no vaccine used within the international bovine TB control programme. The European Union even bans the TB vaccination of cattle due to its interference with the tuberculin skin test for humans. The diagnosis of bovine TB remains unsatisfactory, too; a large share of the cattle culled over TB outbreaks is, in fact, not infected.
But if Professor Zhang’s team is successful, this Chinese research may eventually eliminate the need for a breakthrough on vaccination.