Nuclear transfer stem cells from monkey Scientists from the Oregon Primate Research Center reported the derivation of two stem cell lines from blastocysts after nuclear transfer in the primate, in this case the monkey1. This publication provides hope that nuclear transfer will eventually work in humans. Although this technology has been successfully applied in a number of other animals, including mice and sheep, until now this feat had not been achieved in primates and it was suspected that the technical difficulties in primates might be insurmountable. Initial claims in 2004 by a South Korean team to have accomplished this in humans were subsequently found to be fraudulent2. In nuclear transfer, the DNA from an egg is removed and replaced by the DNA of a donor cell, for example, a skin cell. The egg is then coaxed into believing it has been fertilized and starts to divide. A few days later, the cells are extracted and put into culture conditions that allow the embryonic stem cells to grow out. For therapeutic purposes, the donor cell might come from a patient who will receive the cells generated from these newly generated ES cells (for more detail, see http://www.isscr.org/public/therapeutic.htm). As the cells are derived from the patient’s own skin cells rejection will not occur. This might sound simple, but the biology is very complex. In the primate, it was feared that it would not be possible to remove the original DNA without irreparably damaging the egg. The Oregon team modified the process, avoiding a toxic compound that is used to visualize the DNA that one wants to extract. Instead, the scientists used a powerful microscope that allowed them to see the DNA and sucked it out of the egg. It is now possible to try this with human eggs and see whether one can also derive nuclear transfer stem cells from the human. While this work is a great scientific achievement and step forward towards potential human application, it also illustrates that therapeutic cloning for humans will be difficult. From 304 eggs, the team obtained only 2 stem cell lines. With such a low efficiency, there might never be enough human eggs available for this procedure to treat the many patients in need of transplants. The publication of the Oregon team is also important for another reason. In an unusual step, the research claim was verified by an independent group before the work was published. Usually scientific claims are corroborated by other groups after they have been published, as according to scientific publishing rules, results remain confidential until the publication date. However, after the fraudulent claims of successful SCNT in humans by Hwang and colleagues2, it was deemed important to verify these new claims prior to publication. Notes 1. Byrne JA, Pedersen DA, Clepper LL, Nelson M, Sanger WG, Gokhale S, Wolf DP, Mitalipov SM (2007). Producing primate embryonic stem cells by somatic cell nuclear transfer. Nature 450, 497-502. 2. Science Magazine ‘Special Online Collection: Hwang et al. Controversy -- *Author Affiliation: Posted February 26, 2008
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