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Former Cloner Now
Says Cloning of No Practical Relevance By David Prentice Editor’s note. This first appeared in a slightly different form on Dr. Prentice's blog at www.frcblog.com/2011/03/cloner-nuclear-transfer-cloning-of-no-practical-relevance
The latest issue of The Scientist has a profile of Rudolf Jaenisch of the Whitehead Institute [www.the-scientist.com/2011/3/1/52/1/]. Jaenisch has a lot of experience in research involving cloning, embryonic stem cells, and induced pluripotent stem (iPS) cells. His very negative take on cloning in this profile is an about-face from his previous stance, and a wake-up call to all those who continue to promote cloning. The technical term for cloning is "somatic cell nuclear transfer." An embryo is created by transplanting the nucleus (the chromosomes) of a normal body cell (a somatic cell, such as a skin cell) into an egg cell that has had its own chromosomes removed. The resulting embryo can develop just as an embryo created by fertilization. (You can view a diagram of the cloning process, as well as the method of making iPS cells, at www.frcblog.com/wp-content/uploads/2010/07/stemcells-fert-clone-iPS-ASC2.jpg] If the cloned embryo is implanted in an attempt at live birth, it is termed "reproductive cloning," whereas if the same embryo is instead disaggregated for its embryonic stem cells, the process is termed "therapeutic cloning." Proponents of the latter insist it is different than the former. But both are cloning, only in one instance the embryo is implanted in a womb, in the other it is killed by extracting stem cells. The newly-published Jaenisch profile claims that Jaenisch succeeded with "therapeutic cloning" in mice, but that is incorrect. Not only did he fail to get the embryonic stem cells from cloned mouse embryos to "take" and produce a complete new blood system, the real success required growing cloned mice to birth and then using their adult stem cells to regenerate normal blood formation in the sick mice. In this latest interview, Jaenisch makes several strong statements on nuclear transfer cloning in general: “In my view, you cannot make normal clones. Dolly looked normal. But after six years they had to kill her because she was so sick. Mice are the same. Most die very early [in development]. A few make it to birth. And the ones that survive look pretty nice for a year. But many die by 15 months. So I would argue that the animals that survive are just less abnormal than ones that die early. With nuclear transfer you never get normal embryos.” Regarding the uselessness of so-called “therapeutic cloning”--somatic cell nuclear transfer, followed by the destruction of the young embryo to harvest its stem cells--Jaenisch said: “Ten years ago, we talked about the potential of nuclear transfer for therapy. But it turns out the technique was of no practical relevance. You would never do it in humans for a number of reasons. First, it’s very inefficient. With mice, that doesn’t matter because we can do hundreds of transfers to get a few mice. But human cloning is another order of magnitude more difficult than in mice. And people can’t even get the eggs to practice [on]. My former student Kevin Eggan, along with his colleagues at Harvard, spent years putting in place a protocol to get volunteer egg donors. They spent a couple hundred thousand dollars just in advertising. And I think they got one or two donors. Kevin’s postdoc, Dieter Egli, who went to Columbia, told me that he got a couple [of] human nuclear transfers going, but they all arrested at the 6- or 8-cell stage. So there’s something we don’t understand going on in human [embryos]. It should work, but we’re not there yet.” Cloning proponents like Panos Zavos and Irving Weissman should take note. Those interested in actual science-based treatments for patients should look at the successes of adult stem cells, in treating spinal cord injury, chronic heart failure, sickle cell anemia, multiple sclerosis, corneal blindness, and juvenile diabetes, to name a few examples. |
