After a couple of years in hibernation, the notion of “therapeutic cloning” is once again in the headlines. The latest development comes from Shoukhrat Mitalipov, a Russian-educated researcher at Oregon Health and Science University.
In a paper in Nature, his team reports that they have successfully created embryonic stem cells using a technique which bypasses the need for egg cells. Instead, the nucleus from an adult cell and placed in an enucleated zygote at the two-cell stage (which is also called the interphase). For some reason this dramatically increases the chance of the new cell’s successful development.
Scientists had previously thought the interphase stage — a later stage of the cell cycle — was incapable of converting transplanted adult cell nuclei into embryonic stem cells.
Apparently Mitalipov and his team have succeeded because they carefully synchronized the cell cycles of the adult cell nucleus and the recipient embryonic cytoplasm. Both had to be at an almost identical point in their respective cell cycles for the process to work. "That was the secret," Mitalipov said. "When we did that matching, then everything worked." The next stage is using the same process in monkeys and after than, humans.
Reviving the powerful “therapeutic cloning” rhetoric of a decade ago, a university press release claimed that this was a great step forward for regenerative medicine: “Human embryonic stem cells are capable of transforming into any cell type in the body. Scientists believe stem cell therapies hold promise for someday curing or treating a wide range of diseases and conditions — from Parkinson's disease to cardiac disease to spinal cord injuries — by replacing cells damaged through injury or illness.”
Although the technique does seem to advance understanding of cell reprogramming, it still poses significant ethical challenges.
First, the source material. In the past, “therapeutic cloning” was not only difficult but impractical and expensive. It depended on access to a huge supply of human eggs. Extracting these is quite dangerous for women and potentially quite exploitative. A market in eggs would be needed.
However, Milatipov apparently envisages using “surplus” eggs from IVF clinics. There are hundreds of thousands of these frozen and stored in the clinics. Embryos will be far cheaper as a raw material for research than eggs – but also far more controversial ethically.
Second, although media reports and the university press release skirted around this issue, two embryos are destroyed in the process: the “surplus” embryo from the IVF clinic, and the cloned embryo created by the researchers, which is dissected for its stem cells.
Third, although media reports tiptoed around the “c-word”, Milatipov’s process is basically an elaborate form of cloning. It could also be used for human reproductive cloning. There are no hints of this in his paper, of course, but the easier it is to produce pluripotent human embryonic stem cells, the easier it will be for rogue scientists to produce human clones.
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