Stem cells are a form of human life: they are alive and contain human DNA. They have a unique feature in that they can be coaxed into developing into some or all of the 220 cell types found in the human body. Of the three types of stem cells, embryonic stem cells have the greatest potential in that they can theoretically become any of the 220 cell types. Adult stem cells are less useful in that they have already started to specialize and can only become one of a few cell types. Induced pluripotent stem cells are specially treated cells that can be processed to behave somewhat like embryonic stem cells.