January 18, 2008

scientists react to paper on human embryo cloning as published in the journal Stem Cells

Samuel Wood, a researcher at the Stemagen Coroporation in La Jolla, California, created a cloned embryo using his own skin cells, which were injected into donated eggs.

Dr Stephen Minger, Stem Cell Biologist, King’s College London, said:

“This is academically interesting research that shows that another group have managed to create clone human embryos using nuclear transfer. This is good news, but we are still not much closer to using this technique efficiently, as we still need to use a large number of donor eggs to create a small number of embryos. And disappointingly, the researchers did not go on to do the next step: to create embryonic stem cell lines from cloned embryos. The community is waiting to baited breath to see if anyone can do both steps together. Having access to patient specific stem cell lines would allow us to do research studying major diseases such as Motor Neurone Disease, Parkinson’s Disease and Spinal Muscular Atrophy.”

Prof Robin Lovell-Badge, Head of Division of Stem Cell Biology, MRC National Institute for Medical Research, said:

“This is another step along what has turned out to be a tortuous road. The authors ultimate aim is to be able to use cloning techniques to obtain early human embryos from which they can derive patient-specific Embryonic Stem cell lines, which in turn could be used for research and ultimately for treatment of many debilitating conditions.

“They used adult skin cells as the nuclear donor, and enucleated eggs (oocytes) from woman that were surplus to requirements for fertility treatments. Their success may be attributable to the use of eggs specifically from young women, although this is uncertain as no direct comparison was done with older egg donors.

“They used a DNA stain (Hoechst 33342) to check for correct enucleation of the eggs. This is in contrast to the recent paper showing successful cloning and ES cell derivation in the Rhesus monkey, where a simple (polarised) light microscopy method was chosen as it is likely to be much less harmful. Perhaps adoption of this method in human cloning would also simplify the procedure and improve success rates.

“The authors began with 23 oocytes, of which 7 died soon after enucleation. 14 of the remainder responded correctly to the activation step by showing pronuclear formation, and 10 of these progressed over the next three days to form cleavage stage embryos with at least 5 cells. Half of these then went on to make blastocysts, the stage most commonly used to derive ES cells, although they did not attempt to do this. DNA tests failed on 2 of the blastocysts so it was impossible to know if they were truly clones or not. However the remaining 3 all had nuclear DNA corresponding to the donor skin cells.

“This is the most successful description so far of the use of the cloning techniques with purely human material. However, it is still a long way from achieving the goal of obtaining ES cells. In the recent Rhesus monkey experiments, two ES cell lines were obtained from about 300 starting oocytes, so it is likely that many more attempts will be necessary before anyone can calculate rates and claim real success in humans.

“It still makes sense to explore the use of non-primate eggs first, until the methods can be improved, rather than using valuable human eggs. Although we do not know the wishes of the donors in this case, there is an enormous demand for spare eggs for use in fertility treatments.”