Adult cells (for example, skin cells) reprogrammed to an undifferentiated state. This major discovery, made by teams supervised by Dr Shinya Yamanaka (Nobel Prize for medicine 2012) in Japan, enables the “regression” of an adult cell which has already specialized towards a pluripotent state (and even a totipotent state), presenting characteristics similar to those of embryo stem cells, without any ethical mishaps. The modeling and screening of molecules can be carried out efficiently and conclusively with iPS cells, without any need to destroy an embryo.