In humans. In the US (and other jurisdictions that follow FDA guidelines). That's important to keep in mind. If the chain were off, you'd see some real problems. For example, in rats if you give too many cells too quickly, you can easily cause a blood clot that is fatal. I'm sure this kind of thing happens at fly-by-night clinics in developing countries and probably isn't well reported. The FDA can be a big pain in the ass, and I'm all for speeding up the drug discovery process, but they also serve as a very important check on people who don't mind experimenting on humans. The bottom line is that industry and the FDA shouldn't be adversaries. We should work together to build safe products while stifling innovation as little as possible.So far as I know there is not one documented case of autologous stem cell reintroduction having any negative effects.