“You don't want to have a pluripotent cell in your body, because it can become all types of cells,” says Oliver Brüstle, a professor who studies stem cells at Germany’s Bonn University. Additionally, the few key genes involved in the stem cell conversion process can drive the formation of cancer if left active. That’s why Brüstle and his team have looked for other ways of de-aging cells without going through a pluripotent state.