You can only learn so much from laboratory mice. Trials of stem cells conducted in our four-legged friends may serve as a bridge to human studies.
A staple in labs across the world, laboratory rodents are genetically homogenous, closely monitored, and are kept in standard, controllable environments -- and that's a problem. In the human real world, people are genetically different, have various diets and habits, and live in diverse environments. What's more, many times disease is induced in these animals, whereas in humans diseases are rarely planned and may have more than one cause. It's not very surprising that so many promising preclinical experiments do not pan out in human clinical trials. The cost of these failures is sky high, for companies, patients, and society.