The prospect of being able to clone human embyros efficiently for medical treatments has been raised by a technical breakthrough that has enabled scientists to make dozens of cloned embryos from adult monkeys for the first time.
Although primates have been cloned before using old fashioned “embryo splitting” methods, attempts to use the more efficient Dolly cloning technique have faced technical problems and saw a major setback with the controversy over fraudulent research in South Korea.
The new technique promises to revolutionise the efficiency by which scientists can turn human eggs into cloned embryos for use in so called therapeutic cloning to grow replacement cells and tissues for a vast range of treatments, though some commentators pointed out that while it looks promising, the team has not yet provided enough evidence to weigh up the full significance of today’s work.
If confirmed, the research by Shoukhrat Mitalipov at the Oregon National Primate Research Centre in Beaverton marks the first time that scientists have been able to use the Dolly cloning method to create large numbers of cloned embryos from an adult primate – in this case a 10-year-old male rhesus macaque monkey.
The findings were presented in June to a meeting in Australia and will appear in a peer reviewed journal within weeks.
Dr Mitalipov and his team will also demonstrate that they have been able to extract what appear to be stem cells from some of the cloned embryos and that they have managed to encourage these embryonic cells to develop in the laboratory into what seem to be mature heart cells and brain cells, neurons.
The development, which has seen by most in the field as inevitable given the wide range of species that can now be cloned, will stir unease among opponents of cloning who will argue that the new technique of manipulating primate eggs to improve cloning efficiency will lead to increased attempts at creating – and destroying – cloned human embryos for research purposes.
Although going one step further is illegal in many countries, such as Britain, this advance will increase the chances of its being applied to produce a cloned baby.
However, the Oregon team is believed to have tried with colleagues in China to implant about 100 cloned monkey embryos into the wombs of around 50 surrogate rhesus macaque mothers but have not yet succeeded with the birth of any cloned offspring.
Scientists in South Korea reported in 2004 that they had created the first cloned human embryo but in 2006 their study was retracted after it emerged that its main author, Hwang Woo-suk, had committed fraud, though there is still debate about what his team actually achieved.
Newcastle University in the UK did produce a documented example of a cloned human embryo, but there has since been little progress in this field.
Dr Mitalipov said he was unable to comment on the study until it was published in the journal Nature.
But he told colleagues at the International Society for Stem Cell Research in Cairns, Queensland, earlier this year that he had made two batches of stem cells from 20 cloned embryos and tests had shown they were true clones.
Earlier cloning attempts in monkeys used ultraviolet light and dyes as a guide while the DNA was being removed from eggs before DNA from a donor - the animal to be cloned - was introduced.
The Oregon researchers believe this damaged the resulting embryos.
Instead, their technique uses polarised light to visualise the egg’s interior during the process of “nuclear transfer”. In this basic method, the DNA containing nucleus of a healthy, unfertilised egg is removed and another nucleus from the mature skin cell of an adult animal is placed inside the egg.
With careful timing and the use of electrical pulses, an embryo can be created which is a genetic clone of the skin tissue donor.
"It’s proof of principle for human therapeutic cloning," said team member Don Wolf, also of the Oregon National Primate Research Centre.
The Oregon team has yet to show cells derived from the clones have all the characteristics of embryonic stem cells.
But already, other researchers are planning to try the same methods on human cells.
"The primate stuff really does give us renewed hope," New Scientist was told by Renee Reijo Pera, who heads a team using therapeutic cloning at Stanford University in California.
Dr Simon Best, Chair of the UK BioIndustry Association, said that “this sounds promising and could well mark significant progress - Oregon is a highly respected lab - however, there is no evidence that the stem-cells created are pluripotent (cardio and neuro are default derivatives for many types of stem-cells ) and functional in any type of grafting/transplantation - and no evidence yet that the embryos are viable - some established pregnancies and a birth would be required to bolster this.”