Current methods of cloning are repeatable but remain inefficient

The recent report of the derivation of stem cells from a cloned human embryo takes a small, butsignificant, step towards revolutionary new opportunities in biology and medicine.1 By developing these techniques it will become possible to study human genetic diseases in entirely new ways, before in the longer term such cells may be used in the treatment of human disease. However, much remains to be learned about the techniques that are required before these opportunities can be realised. Furthermore, as with all new technical developments, experience will be needed to learn how such cells should best be used.

The procedure that was used in the Korean experiment was essentially the same as that used to produce Dolly, the cloned sheep.2 During a series of trialsa total of 30 of the 242 cloned embryos developed normally for six days to reach the blastocyst stage before attempts were made to derive embryo stem cells.1 Cells were isolated from 20 of these embryos, and from these one stable cell line was derived. As would be expected of embryo stem cells, they had the ability to grow for a prolonged period in culture and to form other cell types. …