Cellular therapy is the replacement of unhealthy or damaged cells or tissuesby new ones. Embryonic stem (ES) cells are undifferentiated cells that can generate all the cell typesof the body, and therefore hold the potential to cure a broad range of diseases and injuries, rangingfrom diabetis, liver and heart diseases, to neurological diseases, such as Alzheimer's and Parkinson'sdiseases. The derivation of human ES (hES) cells has been a major step toward bringing ES cell researchto therapy. However, there are several challenges to the advent of ES cell research to therapy. Amongthem, the derivation of hES cell lines devoid of animal contaminants, the maintenance of their normalkaryotypes, their potentials to form tumors upon grafting, and the derivation of isogenic hES cell lines.Stringent ethical and political guidelines are also limiting the use of human embryos for research, therebylimiting progress in ES cell research. Recently, several investigators have devised protocols to derivehES cells free of feeder layer and animal serum, reported that some established cell lines remain stableovertime, pre-differentiated ES cells in vitro to circumvent the risk of tumor formation, and derivedES cell lines without destroying embryos. In this manuscript, we will review and discuss these developmentsthat may unlock ES cell research and therapy.

Keywords: Cloning, Organism - ethics, Nuclear Transfer Techniques, Stem Cells - cytology