Pancreatic β cells are the only cells in the body that produce insulin, and are the cells whose malfunctioning is the proximate cause of diabetes. Consequently, repairing or replacing β cells is one of the major goals of diabetes research. In type I diabetes, where the immune system destroys β cells, need to be replaced outright. In type II diabetes, β cells “disappear” in another way. There is ample evidence that under conditions of chronic high blood sugar, such cells dedifferentiate, becoming less β cell-like over time.