The clones are all right.
Three weeks after the 20th anniversary of the birth of Dolly, the first animal cloned from an adult of its species, scientists reported on Tuesday that 13 other sheep clones from the same batch of cells are aging normally, showing no signs of hypertension, diabetes, or serious arthritis at their relatively young age. Dolly’s knee arthritis, which developed when she was only 5 and raised concerns that cloning accelerated aging, was apparently an anomaly.
“Were cloning to accelerate aging, we would have seen it in this group,” said developmental biologist Kevin Sinclair of the University of Nottingham, who led the study published in Nature Communications.
Since cloning people is a near-global taboo, the results have no relevance to questions of whether human Mini-Me’s would become wrinkled and gray-haired in their teens. But large animals from cattle to polo ponies are being cloned, as are dogs and cats, so the study — the first to examine the long-term health of animals created as Dolly was — provides assurance that cloning does not cause premature aging.
More relevant to people is that the technique that created Dolly is also used to produce cell lines for research and, perhaps one day, treatment for diseases. The sheep results suggest that “somatic cell nuclear transfer” does not make the resulting cells old before their time by, as some scientists feared, shortening telomeres, molecules at the ends of chromosomes that seem to influence aging.
The study fits with what other scientists had noticed about other clones. For instance, “one of the two bantengs we cloned in 2003 was healthy and lived a long life at the San Diego Zoo with a herd of other bantengs,” said cloning pioneer Dr. Robert Lanza, chief scientific officer at the Astellas Institute for Regenerative Medicine. Bantengs are an endangered species of cattle native to Southeast Asia.
The 13 sheep in the new study were created from 2005 to 2007, when biologist Keith Campbell, a key member of the Dolly team, was trying to improve cloning — creating more viable embryos to implant in the wombs of surrogate mothers, more pregnancies, and more live offspring. Four of these “Nottingham Dollies” — Debbie, Denise, Dianna, and Daisy, now 9 — were created from the same mammary cell line as Dolly, making them her twin sisters. (After developing a rare lung disease, Dolly died at age 6, less than half the lifespan her species can reach.) The other nine clones came from fetal cells and were born from 2006 to 2008.
None showed signs of diabetes, hypertension, or serious arthritis, the diseases the scientists focused on because they strike aged sheep just as they do elderly humans. Five had mild arthritis in the elbow, as do non-cloned sheep of that age: one sheep year is about eight human ones, so the Dollies are aging normally through the equivalent of 70 or so birthdays. (The Dollies, who will continue to be studied, are considered a legacy to science from Campbell, who committed suicide on Oct. 5, 2012.)
The scientists did not, however, test molecular markers, such as telomere length or epigenetic changes. The latter alter which genes are on and which are off, and have been linked to age-related chronic diseases. It’s possible that the Nottingham Dollies have a biological time bomb in their DNA, but if so, it hasn’t detonated.