Cloning advance calls for careful regulation

Human oocytes reprogram somatic cells to a pluripotent state Until now, it has not been possible to achieve reprogramming of a somatic cell nucleus and derivation of embryonic stem (ES) cells by somatic-cell nuclear transfer — the established laboratory technique for creating an egg with a donor nucleus in other mammals — using human cells. But Dieter Egli and colleagues now report the successful derivation of triploid human pluripotent stem-cell lines through somatic genome transfer into human oocytes. Human oocytes reconstructed using the traditional method (enucleating the oocyte then fusing the donor cell to the karyoplast) invariably arrested during the cleavage stages of development, but when the oocyte genome was not removed and the somatic cell genome was added, the resultant triploid cells efficiently developed to the blastocyst stage. Although the study falls short of generating pristine diploid nuclear-transfer-derived ES cells, it shows that such reprogramming is possible in humans. This work is relevant to regenerative and reproductive medicine, developmental biology and the study of stem-cell pluripotency. It also raises interesting ethical questions related to altruistic egg donation. The research and ethical implications are discussed in a News & Views article by George Daley and Jan Helge Solbakk, and in a Correspondence by Insoo Hyun and Paul Tesar.