Abstract: Stem cells are primal cells existing in multi-cellular organisms and have held limelight in biomedical research in that they are characterized by the ability to renew themselves through mitotic cell division and to differentiate into diverse range of specialized cells. Stem cell therapy has the potential to change radically the treatment of diseases, and therefore, has been proposed or used to treat Parkinsion's disease, diabetes, spinal cord injury. Stem cells can be classified into embryo stem (ES) cells and adult stem cells or somatic stem cells. The latter, including several subclasses, are undifferentiated cells found in adult bodies and act as a repair system for the body, replenishing specialized cells. ES cells, so-called pluripotent cells, are cells derived from the undifferentiated inner cell mass of embryos, and considered the best stem cells because they have ability to develop into all derivatives of the three germ layers, i.e. ectoderm, endoderm, and mesoderm. Stem cells can also be classified into several subclasses according to their potency: Totipotent; pluripotent （i.e. ES cells）；multipotent (hematopoietcin stem cells); and oligopotent (still have the property of self-renewal). However, recent studies have demonstrated that pluripotent stem cells can be induced from somatic cells, opening a new era for obtaining stem cells. This review summarizes the progress and the discoveries in stem cell research and induced pluripotent stem (iPS) cells.

Key words: stem cells; adult stem cell; differentiation