Embryonic stem cells （ESCs） derived from the early embryos possess two important characteristics：self-renewal and pluripotency,which make ESCs ideal seed cells that could be potentially utilized for curing a number of degenerative and genetic diseases clinically.However,ethical concerns and immune rejection after cell transplantation limited the clinical application of ESCs.Fortunately,the recent advances in induced pluripotent stem cell （iPSC） research have clearly shown that differentiated somatic cells from various species could be reprogrammed into pluripotent state by ectopically expressing a combination of several transcription factors,which are highly enriched in ESCs.This ground-breaking achievement could circumvent most of the limitations that ESCs faced.However,it remains challenging if the iPS cell lines,especially the human iPSCs lines,available are fully pluripotent.Therefore,it is prerequisite to establish a molecular standard to distinguish the better quality iPSCs from the inferior ones.
Recent studies have demonstrated that differentiated somatic cells from various mammalian species can be reprogrammed into induced pluripotent stem （iPS） cells by the ectopic expression of four transcription factors that are highly expressed in embryonic stem （ES） cells. The generation of patient-specific iPS cells directly from somatic cells without using oocytes or embryos holds great promise for curing numerous diseases that are currently unresponsive to traditional clinical approaches. However, some recent studies have argued that various iPS cell lines may still retain certain epigenetic memories that are inherited from the somatic cells. Such observations have raised concerns regarding the safety and efficacy of using iPS cell derivatives for clinical applications. Recently, our study demonstrated full pluripotency of mouse iPS cells by tetraploid complementation, indicating that it is possible to obtain fully reprogrammed iPS cells directly from differentiated somatic cells. Therefore, we propose in this review that further comprehensive studies of both mouse and human iPS cells are required so that additional information will be available for evaluating the quality of human iPS cells.
