In an interview with Saga magazine, the 84-year-old revealed that for the past two decades he has been paying a private Swiss clinic £17,000 every 12 to 18 months for stem cell therapy that he credits for looking "not bad" for his age. So is Cleese making a sound investment? Stem cells have remarkable medical potential. They are the body's master cells that, in the embryo, go on to produce every cell type in the body. Even in adulthood our body retains reserves of less versatile stem cells that mobilise to repair injuries and continually regenerate skin and other tissues.