Embryonic stem cells were first isolated in 1981 from mice embryos and were found to have the capacity to transform into any cell of the body. These remarkable cells, however, are derived from 5-day old embryos creating an ethical dilemma for their clinical use. In addition, these cells are genetically destined to build a fetus and in this effort, without proper direction and control they tend to create tumors consisting of unorganized tissues called teratomas. Because of these two issues, embryonic stem cells are used only for basic research.
