Cloned cows are as healthy as their conventionally bred counterparts, say US researchers. The finding could enhance prospects for the use of human therapeutic cloning to make replacement tissues and organs.
To date, most cloned animals have been sickly. Few survive to birth, and many die shortly after. They often have genetic defects and physical deformities, and tend to be bigger than normal.
This was not Robert Lanza's experience. "In contrast to the horrific scenarios you see in the press, our cloned animals seemed healthy," he says.
Lanza, a researcher at Advanced Cell Technology in Worcester, Massachusetts, and his colleagues examined 24 cloned cows between one and four years old
The cloned cows passed a battery of tests - on their behaviour, physiology, immune systems and genetic make-up - with flying colours. "They're vigorous, healthy and normal," says Lanza.
The finding is "encouraging", says Ian Wilmut of the Roslin Institute near Edinburgh, UK, the creator of Dolly the cloned sheep. But, he adds, "these results do not in any way eradicate the previous history of unusual deaths in animals cloned by essentially the same procedure".
A death rate of 20%, plus the many more embryos that spontaneously aborted, suggests that it is still too early to begin widespread cloning of livestock, he says. More must be known about the biology of a cloned animal.
Lanza puts his team's high success rate down to six years of cloning practice and to their methods. They use actively dividing skin cells, for example, as opposed to the non-dividing cells from which Dolly was cloned. Care of the newborn calf in its first few days also makes a big difference.
"Years of experience do seem to make a difference," comments John Gurdon, a cell biologist at the University of Cambridge. "But that only affects the percentage that survive, not whether they're normal or not." No one really knows why cloning has such hit-and-miss results, he says.
Wilmut and Lanza stress that these results give no support for the reproductive cloning of humans. But Lanza is evangelical about the prospects for therapeutic cloning.
A combination of cloning and tissue engineering will be able to produce neurons, insulin-producing cells, skin and blood vessels within the next few years, and more complex organs, such as kidneys, are about a decade away, Lanza believes. "Tens of millions of people could benefit from this technology," he says.
"The general feeling is that there's everything to be gained by pursuing therapeutic cloning," agrees Gurdon.