Totipotent, pluripotent or unipotent stem cells: a complex regulatory enigma and fascinating biology.

The search for sources of human stem cells has become a controversial topic from an ethical point of view primarily as it has required the destruction of human embryos. The development of alternative techniques that enable the generation of pluripotent stem cells from adult cells has opened new avenues of research but the generation of such cells has again been controversial since it requires the use of human eggs, using a technique called somatic cell nuclear transfer. Since the cells so generated have a very small potential to generate an "embryo" and since the production of the cell lines requires destruction of that "embryo", a further ethical issue arises. This article discusses these issues and suggests a framework that may assist their consideration. Finally, the article reviews some recent developments that have the potential to remove the need for the use of eggs or embryos in the generation of stem cell lines and highlights the danger of developing legislation on only our current knowledge.