Role of specialised adult cells proved in cloning

Scientists have finally proved that cloning an animal from a fully specialised cell of an adult is possible – something that has been doubted even though Dolly the sheep was supposed to have been created from a skin cell.

There has always been a theoretical possibility that the clones of adult animals were in fact the result of cloning from unspecialised stem cells hidden within the highly specialised tissues of a fully grown animal.

This meant that although it was plausible to believe Dolly had resulted from the cloning of the specialised skin cell of a six-year-old ewe, it was equally plausible that she might have been "accidentally" cloned from an adult stem cell lurking in the skin.

Now two scientists have proved beyond doubt that fully specialised cells can give rise to clones, which opens the prospect of there being two ways to clone from adult tissues – by cloning either from specialised cells or from adult stem cells.

Konrad Hochedlinger and Rudolf Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, published their study yesterday in the online edition of the journal Nature.

"We've proven for the first time that it's possible to clone a mouse from adult cells. This question has not been answered by any of the cloning experiments to date," Dr Hochedlinger said.

The scientists cloned adult mice from mature white blood cells using a new two-step process that might one day be used by doctors to generate replacement tissues for transplant operations from a drop of patient's blood.

Dr Hochedlinger says the likelihood is that adult stem cells may be far easier to clone than specialised adult cells. This means that if adult stem cells can be distinguished from other adult cells – which is easily done at the moment – human cloning for therapeutic purposes may prove to be far easier than originally thought.

"An important question for the future is whether stem cells from adults would give higher efficiencies for cloning. This might be very important for clinical applications," Dr Hochedlinger said.

"We believe that stem cells from adults are easier to reprogramme so it might mean fewer errors in the procedure. It may be safer, but it needs to be shown," he said.

Dr Jaenisch said that if identifying and isolating the rare adult stem cells in human tissues was posssible, then therapeutic cloning would receive an important boost.

"In normal cloning attempts, it would be too inefficient to use mature adult cells. We were able to produce clones from adult cells because we took the two-stem approach," Dr Jaenisch said. "I think this supports the suggestion that many clones are derived not from mature cells but rather from adult stem cells, but we haven't proved this."