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Mice have for the first time been cured of a severe blood disorder through treatment with stem cells created from tissue taken from their own tails.The breakthrough demonstrates for the first time a way of treating severe diseases using stem cells created from a patient's own tissue, thus sidestepping the problem of rejection faced when blood or tissue is donated.Furthermore, by changing tail cells into stem cells, the researchers avoided the ethically controversial alternative of deriving them from embryos.(cut)Jaenisch and his colleagues first extracted skin cells from mice and infected them in the lab with a virus carrying genes that act like four natural gene "switches", known as transcription factors. These switches reprogrammed the skin cells so that they became induced pluripotent stem cells, a form of cell capable of maturing into any tissue in the body.Jaenisch and his colleagues then used a precise gene-editing technique called homologous recombination to replace the defective beta-globin gene with a correct version, restoring the mouse genes to normal, even though the mice still had unhealthy red blood cells.So, the team then used chemical signalling molecules to make the induced pluripotent stem cells mature into blood stem cells, before transplanting them back into the bone marrows of the animals.Here, the corrected cells multiplied, repopulating the blood system of each treated mouse with completely normal blood cells and curing the original disease. Also, because the cells came from the animals themselves, there was no need for them to receive immunosuppressive drugs to overcome rejection.Cancer riskJaenisch says that the experiment shows in principle what could be achieved in humans, especially for blood disorders that result from a single, repairable gene mutation."The only problem with human treatment is that we can't use viruses to ferry the reprogramming genes into cells," says Jaenisch. The viruses themselves could trigger cancer later in life, so Jaenisch's team and other labs are experimenting with other ways to import the genes, such as inside fatty molecules that can penetrate into cells.