Failed monkey tests show human cloning may be impossible

IT may be impossible to clone humans because primate cells do not divide properly, a “pothole in the process” that creates chromosomes too abnormal for a pregnancy to begin, scientists have said.

The findings by the University of Pittsburgh researchers come five months after a cult group claimed to have cloned a human. Those claims have not been verified.

The scientists, reporting in the journal Science, attempted to discover why efforts to clone a monkey had been unsuccessful. They found that, from the very start, the cloned primate cells did not divide properly. Humans are primates.

"Most people in the cloning field will be surprised by this," said lead researcher Gerald Schatten.

"This work demonstrates there's a pothole in the process. We now know the depth and breadth of the pothole, and we're designing strategies to get around it."

Dozens of animal clones including cows, pigs, mice, goats and a cat have been born since Dolly the sheep was created from an adult cell in 1997. But it still is an uncertain field. Many are stillborn and some survive only with severe defects.

Thus far, attempts to clone monkeys far closer genetically to people using the Dolly technique have failed. Cloning experts fear it would be dangerous to attempt human cloning because of those failures, as well as the birth defects in cloned animals.

It took 277 attempts before Dolly was born. Mr Schatten's group tried even longer to clone a rhesus monkey 724 eggs that yielded only 33 embryos and not a single pregnancy.

The discovery is very important, said Dr Duane Kraemer, a successful cloner of non-primates at Texas A&M University.

"The fact that they don't get pregnancies at all is suggestive that there is something different going on there than with other species," he said.

"It points to a potential problem that may have to be solved before the next advance can be made."

It is not just bad news for reproductive cloning. It also means the related field of therapeutic cloning using embryonic stem cells to grow customised tissues for medical treatment may also prove harder, Mr Schatten said.

His lab is exploring a way to overcome the problem, by combining cloning with old-fashioned egg fertilisation.