A team of researchers at Nottingham University announced on Tuesday that four of Dolly the Sheep's genetic identicals are showing no signs of premature aging—evidence that "somatic cell nuclear transfer," or cloning, can result in healthy adult mammals.
An article today in the scientific journal Nature Communications lays out findings by biologist Kevin Sinclair and his team. They found that adult sheep clones Debbie, Denise, Diana, and Daisy—all created from the same cell line as the original clone, Dolly—are just as healthy as any normal sheep their age.
Twenty years after Dolly became the first mammal ever to be cloned, this is the first research aimed at investigating healthy ageing in clones made by somatic cell nuclear transfer, or SCNT.
Still a relatively inefficient technology, SCNT is performed by taking the nucleus from an adult cell (such as a mammary gland, as with Dolly and her clones) and swapping it with the nucleus of a donated egg cell. Then, the embryo is implanted in a surrogate, which will give birth to the clone. However, many attempts at SCNT still fail before the embryo can fully develop, and although scientists say the technology is significantly better than it was in the 1990s, it is by no means perfect.
The Nottingham study is notable because it has disproven the notion that cloned mammals will die from the early onset of diseases linked to ageing, a fear that percolated after Dolly's untimely death at age six from a lung disease that generally affects elderly sheep. A 2002 Japanese study of cloned mice who died early from a handful of various age-related diseases also seemed to support the theory that clones will develop obesity and diabetes and pass away relatively young.
Sinclair's findings show that it was likely environmental factors, not genetic ones, that led to problems with clones.
"There have been a large number of mice studies and in most cases, by and large, most of the mice [cloned] offspring seem relatively healthy," said Sinclair. "It's difficult sometimes to know why [mice can show reduced lifespan] and it comes back to the specific conditions used at the time to generate these clones… The devil is often in the details."
Besides the four Dolly clones, nine other cloned sheep from three different cell lines were included in the study, giving a total of 13 sheep between seven and nine years old (making them senior citizens in human years). All 13 were tested for osteoarthritis (which Dolly also suffered from), as well as glucose tolerance and insulin sensitivity, which could be linked to diabetes—all health issues known to afflict elderly humans, as well as sheep.
The sheep all showed normal results, comparable to another, naturally-bred herd of sheep kept in similar conditions. And although Debbie showed "moderate" osteoarthritis, Sinclair considers all the cloned sheep to be in good health. The study concludes that SCNT is safe for "long-lived species."
"From the current series of assessments we conclude that there are no long-term detrimental effects of cloning by SCNT," Sinclair and his coauthors wrote in their paper.
Two decades after Dolly's emergence set off a fiery global debate about the ethics of cloning, Sinclair believes that this study and others before it can contribute to calming the general public.
"A lot of the fears that were in people's minds back then have dissipated," he said. "They know we aren't making Frankenstein monsters."
Bioethicists and scientists agree, however, that further testing must be undertaken to make sure SCNT and other methods of cloning continue to be safe, especially as the burgeoning stem cell industry researches the use of SCNT in reproductive and regenerative therapies in humans.