ABSTRACT
There has been remarkable progress to date in the identifi cation, derivation, and characterization of stem cells, including embryonic stem (ES) cells and induced-pluripotent stem (iPS) cells. The proliferative capacity and pluripotency of mouse ES cells, which were fi rst established by Evans and colleagues in 1981, enabled the establishment of early developmental model systems and the generation of genetically modifi ed mice, including knockout mice (Evans and Kaufman 1981). The progress of ES cell research slowed markedly once it moved into experimental animals such as in vivo models for cell-transplantation therapy (Fukuda and Yuasa 2006), although the establishment of human ES cells in 1998 reinvigorated attention toward ES cells as a source for regenerative therapy (Thomson et al. 1998). Since then, further progress has been made in directing the differentiation of stem cells into various cell types and tissues with enhanced survival properties following transplantation, although several problems have to be overcome to realize successful clinical application of these cells (Passier et al. 2008). Specifi cally, ethical and legal considerations have inhibited the development of human ES cells as a potential regenerative source because of the associated destruction of early human embryos; furthermore, ES cells do not display the autologous genotype of the donor patient (Evans and Kaufman 1981).
