New way to make stem cells is safer: U.S. research

"We are in the process already of trying to make integration-free iPS cells in human cells," Hochedlinger said.

"It is a little more tricky because human reprogramming takes a little while longer than mouse reprogramming."

If it works, some day doctors may be able to make tailor-made transplants to treat diseases in people by removing a few cells, transforming them in the lab and transplanting the new tissue or organs back in.

(Reporting by Maggie Fox, editing by Will Dunham)