Knock-out human stem cells created

US scientists have managed to remove individual genes from human embryo stem cells, the body's master cells that can potentially grow into any type of tissue. The research, published in the journal Nature Biotechnology, is a step towards developing new cell therapies for diseases such as Parkinson's disease and diabetes. The ability to 'knock-out' specific genes could also help scientists to understand rare genetic conditions, complementing studies carried out on animal models.

The team, based at the University of Wisconsin, has already used the technique to remove a gene which, when it is missing in humans, causes a rare genetic disorder called Lesch-Nyhan syndrome. Mice bred to lack the same gene are apparently healthy, and so shed little light on the cause of the disease symptoms. The altered human stem cells should allow scientists to study the basic molecular mechanisms behind the disease, say the researchers. The method could additionally be used to manipulate the growth of stem cells to produce specific body cells, such as the dopamine-producing brain cells that are lost during Parkinson's disease.    

Study author Dr Thomas Zwaka says that altering human stem cells may also bypass the need for therapeutic cloning, the potential use of genetically matched embryo stem cells in new medical therapies. The genes that cause the body to reject foreign tissue could be removed to create 'universal donor' batches of embryo stem cells, suggests Zwaka. But stem cell researcher John Gearhart, of Johns Hopkins University, points out that despite years of effort, scientists have not been able to grow mouse stem cells that are compatible in all mice. He says that therapeutic cloning research will remain important in the search for treatments for human disease.