The preceding chapter described how developments in the knowledge and potencies of stem cells are now holding out the promise of transplantation replacement therapies to restore organ functions that have been damaged or diseased, for example in Parkinson's disease, various types of heart disease and diabetes. Since these developments are currently drawing significant attention not only from biologists but also from the media, ethicists, governments, politicians, and indeed the general public, this chapter will explore the ethical issues causing concern. For further explanation of concepts and terminology, the reader is referred back to the previous chapter.

Much of the current ethical and societal debate is about spare embryos ‘left over’ from in vitro fertilisation (IVF) procedures, and the even more revolutionary alternative of embryos created specifically for the purpose by transfer of a cell nucleus from the patient's mature tissue (for example the skin) to a donor egg from which the nucleus has been removed. Cells from the latter would be ‘autologous’ (meaning: from the same organism) with the patient, holding out the promise of eliminating or at least substantially reducing the problem of graft rejection which normally bedevils transplantation surgery. This would have important benefits, for example for the sensitive human brain in the treatment of patients suffering from neurological or neurodegenerative disorders and handicaps, by improving on its natural advantage of suffering less violent immune reactions than other organs.