Stem cell success may lead to transplant breakthrough

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Scientists have come the closest yet to producing valid stem cells from human embryos created by a similar cloning technique to the one that resulted in the birth of Dolly the sheep – the first clone of an adult mammal.

It is a significant step towards using a patient's own skin cells to create embryonic stem cells in the lab that can be used in transplant operations to treat diseased tissues and organs, from diabetes and heart disease to spinal injuries and Parkinson's disease.

The breakthrough is one of the most significant developments since the discrediting of work published in 2005 by South Korean scientists led by Woo-Suk Hwang, of Seoul National University, who claimed to have produced the first stem cells from cloned human embryos. However, it later emerged that the work was flawed and was eventually retracted.

In the latest study, researchers have merged the genetic material of human skin cells with 270 spare IVF eggs to create embryonic stem cells that appear to be capable of developing into specialised cells and tissues. Unlike the work on Dolly, the study was not aimed at producing cloned embryos for transplant into the womb but at producing stem cells for clinical use.

However, the embryonic stem cells produced by this technique cannot be used as a treatment for patients because they contain three sets of chromosomes rather than the usual two – the extra set coming from the unfertilised egg cell's nucleus which was not removed.

The scientists said that retaining the genetic material of the unfertilised egg, rather than ejecting it before merging it with the skin cell, was the only way they could be sure of producing an embryo that would develop to the crucial "blastocyst" stage, when embryonic stem cells can be extracted.

Although the resulting "triploid" embryonic stem cells carried three sets of chromosomes, tests showed that they were capable of developing normally into specialised tissues, just like ordinary stem cells. The next stage is to find ways eliminating the extra chromosomes so that the stem cells can be used in transplant operations, the scientists said.