MELBOURNE: Four new studies in mice report advances in making cloned stem cells which - if successful in humans - would sidestep some of the major ethical barriers to their use.

Many people frown on the idea of cloning human beings, but cloning your own stem cells to repair failing organs is hailed as a great idea. This is the promise of so-called therapeutic cloning.

There are two ethical snags, however. One is that the technique requires the creation of a cloned embryo, which is later destroyed to obtain its stem cells. The other is that creating that clone embryo relies on women donating their unfertilised eggs – a procedure which exposes them to some health risks, however small.

To clone an embryo, researchers currently take the nucleus of a skin cell (which contains the DNA in chromosomes), and place it in an egg whose own chromosomes have been removed. Some of its 'Promethean factor'