A key breakthrough in medical science may already have been achieved at a California biotech firm. Andrew French and his team at Stemagen in La Jolla reported last week that they have cloned human embryos. The also say they have extracted and grown cells from these embryos, but both French and the rest of us will have to wait a bit longer to find out whether these turn out to be the precious human embryonic stem cells (hESCs) from which all tissues originate when embryos grow in the womb.
If the cells do turn out to be hESCs, they will be the first ever created through the cloning technique that produced Dolly the sheep. They would bring closer the possibility of growing replacement tissue from a patient鈥檚 own cells, and so overcome shortages of donated organs and avoid problems of tissue rejection.
So far, no one is celebrating, though. The company鈥檚 progress is being monitored every step of the way by fellow researchers still scarred by the scandal that broke in 2005, when it emerged that Woo Suk Hwang of Seoul National University in South Korea had fooled the world into thinking he had made cloned hESCs. Since Hwang was exposed as a fraud, stem cell researchers have greeted every claimed breakthrough with deep scepticism.
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鈥淪ince Hwang was exposed as a fraud, stem cell researchers have greeted every claimed breakthrough with caution鈥�
Last week was no exception. 鈥淚鈥檓 not sold yet. We need to be ultra-cautious after the Hwang scandal, and not make the same mistake all over again,鈥� says Robert Lanza, chief scientist at Advanced Cell Technology in Worcester, Massachusetts.
French says his team created an embryo by fusing DNA taken from one of his own skin cells with a human egg that had been emptied of its DNA. This matured into an early human embryo called a blastocyst, from which it should in theory be possible to extract hESCs matched to French.
Subsequent tests published in Stem Cells () appear to show that the embryo was indeed a clone of French鈥檚 skin cell. It contained his DNA, along with traces of mitochondrial DNA from the woman who donated the egg.
Only one other cloned human blastocyst has ever been made. In 2005 Lyle Armstong and colleagues at the University of Newcastle upon Tyne in the UK grew a blastocyst from a cloned embryonic stem cell. But because adults don鈥檛 have ESCs, this could never be a route to providing personalised tissue.
Of 21 embryos created through the Stemagen process, five survived and grew into blastocysts, which contained between 40 and 72 cells. Only one contained both French鈥檚 DNA and the DNA from the woman鈥檚 egg.
Rival stem cell researchers question why French didn鈥檛 go the whole hog and extract hESCs from the embryo he had created. They are also concerned that the blastocysts he produced looked abnormal. 鈥淚 couldn鈥檛 see an inner cell mass in any of them,鈥� says Stephen Minger, a stem cell researcher at King鈥檚 College London. The inner cell mass is the area of the blastocyst where any ESCs would reside.
French says the blastocysts had to be destroyed in order to prove that they were indeed cloned 鈥� and that this took priority over trying to extract stem cells. 鈥淲e had to be cautious because of the controversy involved,鈥� he says. French also agrees that the blastocysts were not 鈥渢op grade鈥�, but says the company has since made many more that are much improved in appearance.
He told New Scientist that cells extracted from the embryos are currently being grown in the lab, but that it was too soon to say if any were hESCs.
Stem Cells 鈥� Learn more about the promise and the controversy in our cutting edge special report .
