Cloned animals don't age unusually fast, Dolly the sheep's heirs show

The heirs of Dolly the sheep areenjoying a healthy old age, proving cloned animals can livenormal lives and offering reassurance to scientists hoping touse cloned cells in medicine.

Dolly, cloning's poster child, was born in Scotland in 1996.She died prematurely in 2003, aged six, after developingosteoarthritis and a lung infection, raising concerns thatcloned animals may age more quickly than normal offspring.

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Now researchers have allayed those fears by reporting that13 cloned sheep, including four genomic copies of Dolly, arestill in good shape at between seven and nine years of age, orthe equivalent of 60 to 70 in human years.

"Overall, the results are suggesting that these animals areremarkably healthy," said Kevin Sinclair of the University of
Nottingham, whose team reported their findings in the journalNature Communications on Tuesday.

It is the first time experts have made such a detailedage-related health assessment of cloned animals, looking atfactors such as blood pressure, diabetes risk and joint damage.

While no animals were lame, there were signs of mildosteoarthritis in some sheep and one had moderate disease, whichscientists said was to be expected at their age.

Dolly was the first mammal to be cloned from an adult cell,using a process called somatic cell nuclear transfer (SCNT).

This involved taking a sheep egg, removing its DNA andreplacing it with DNA from a frozen udder cell of a sheep that
died years before. The egg was then zapped with electricity tomake it grow like a fertilized embryo. No sperm were involved.

Dolly's creation triggered fears of human reproductivecloning, or producing genetic copies of living or dead people,
but mainstream scientists have ruled this out as far toodangerous.

Instead, the hope is to develop "therapeutic cloning", inwhich cloned cells could be used to regenerate faulty tissue.

Dolly's healthy heirs offer encouragement for regenerativemedicine, although the SCNT process remains tricky and manywould-be clones still fail to develop properly, despitetechnical advances since Dolly's birth.

"This shows cells can undergo complete reprogramming andit's reassuring to know that cells can be perfectly normal,"
Sinclair said. "The challenge going forward is to increase theproportion of cells that undergo this complete reprogamming orbetter select for that."

Parkinson's disease

The four sheep cloned using the same genetic material as forDolly called Debbie, Denise, Dianna and Daisy have just hadtheir ninth birthdays and, together with nine other clones, arepart of a unique flock based in Nottingham.

Unlike Dolly, who was housed indoors for security reasons,today's clones live mainly outside, which may be one factorbehind their relative health, since sheep kept in barns can besusceptible to infections.

Cloning is already used in some U.S. food production,although not in Europe. But the big hope is to produce humanstem cells that could replace damaged tissue in devastatingconditions like Parkinson's disease or spinal cord injuries.

Work on stem-cell medicine has been hobbled in the past bytechnical challenges as well as ethical issues but it received aboost three years ago when biologists finally created human stemcells using the same process that produced Dolly.

Until then, the most natural source of human stem cells washuman embryos left over from IVF treatment, whose use in
research is controversial.

Another approach involves adding genes to adult cells toturn back their biological clocks, creating so-called induced
pluripotent stem cells that behave like embryonic ones. Thelong-term safety of these cell has still to be established.

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