ABSTRACT
Because ES cells can be differentiated into several types of cells in vitro, therapeutic cloning provides a means by which therapeutically useful cells can be derived from specific genotypes. Since the technology is more advanced in mice and oocytes more readily available, mice have been studied as a model of human therapeutic cloning (13). Murine ES cells were successfully derived from somatic cell-cloned blastocysts and further differentiated in vitro to produce neural and bone cells. These differientated cells were transplanted back to mice defective in these tissues, to observe if the transplanted cells can survive and help the host organ to be rescued. Ultimately we would hope to use this technique to restore organ function or to prevent or slow further deterioration in humans. However, attempts to clone human embryos have so far proven unsuccessful, possibly because of the loss of critical factors in primates during enucleation (14).
