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What is "therapeutic cloning?"
 Therapeutic cloning is a technique that would be used to produce cloned embryos, but only to create stem cells that can in turn be used to repair damaged or defective tissue in the parent of the cloned cells. Such stem cells could theoretically be used to grow replacement livers or hearts (or any of a variety of organs) for transplant without fear of rejection. They might be used to create healthy nerve cells for people with Alzheimer's or Parkinson's disease. Skin cells could be derived from cloned stem cells for burn victims.
The person who needed the healthy stem cells would provide a non-egg, non-sperm cell from which the DNA would be removed. That DNA, containing two copies of each human chromosome, would be inserted into a donor egg that has had its own nucleus and DNA removed. The technical term for this procedure is somatic cell nuclear transfer. The egg with the introduced DNA would act like it had just been fertilized and begin to divide, forming an embryo. Stem cells from that embryo would be removed and cultured to provide the needed healthy tissue.
Although human stem cells hold a lot of promise for regeneration of damaged organs and tissues throughout the body, in many cases scientists are a very long way from harnessing the therapeutic potential of these cells. For example, it is easy to say that stem cells may be able to replace damaged neurons in the brain or spinal cord. However, actually getting the stem cells to turn into neurons, implant them in the brain, and then have them make the right connections within the nervous system is something that is not technically feasible at the present time, and is not likely to be for many years.
In other cases, the therapeutic potential of human stem cells will likely be realized in a much more immediate fashion. Examples of such applications are using human stem cells to repair a damaged liver or to provide new bone marrow for patients whose own marrow has been irreversibly damaged by chemotherapy. In short, stem cells hold a lot of promise, but like any therapeutic strategy, a great deal of research will be needed before their potential therapeutic value can be fully evaluated and realized.
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