Just a year ago, the prospects for "therapeutic" cloning seemed bright. The idea is to create an embryo by inserting the nucleus of a patient's cell into a human egg stripped of its own genetic material. The embryo, genetically matched to the original patient, would be grown for a few days to create a hollow ball of cells called a blastocyst. Embryonic stem cells (ESCs), which have the potential to turn into any type of tissue in the body, would then be extracted from it. So in May 2005, when Woo Suk Hwang of Seoul National University in South Korea claimed that he had created 11 different lines of cloned human ESCs in this way, the goal of treating patients with tissues genetically matched to their own cells seemed to be within reach. Now, with Hwang revealed as a fraud, we are back to square one: no one has yet created a single line of cloned human ESCs. But for groups that are planning to try there are some reasons for optimism.
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