Background: Pluripotent stem cells (PSCs) such as embryonic stem cells and induced pluripotent stem cells are\npromising target cells for cell regenerative medicine together with recently advanced technology of in-vitro\ndifferentiation. However, residual undifferentiated stem cells (USCs) during in-vitro differentiation are considered a\npotential risk for development of cancer cells and nonspecific lineage cell types. In this study we observed that\nUSCs still exist during hepatic differentiation, consequently resulting in poor quality of the hepatic population and\nforming teratoma in vivo. Therefore, we hypothesized that effectively removing USCs from in-vitro differentiation\ncould improve the quality of the hepatic population and guarantee safety from risk of teratoma formation.\nMethods: Human PSCs were differentiated to hepatocytes via four steps. YM155, a known BIRC5 inhibitor, was\napplied for removing the residual USCs on the hepatic differentiation. After YM155 treatment, hepatocyte\ndevelopment was evaluated by measuring gene expression, immunostaining and hepatic functions at each stage of\ndifferentiation, and forming teratomas were confirmed by cell transplantation with or without YM155.\nResults: The selected concentrations of YM155 removed USCs (NANOG+ and OCT4+) in a dose-dependent manner.\nAs a result, expression of endodermal markers (SOX17, FOXA2 and CXCR4) at stage II of differentiation and hepatic\nmarkers (ALB, AFP and HNF4A) at stage III was up-regulated by YM155 treatment as well as the hepatic population\n(ALB+), and functions (ALB/urea secretion and CYP450 enzyme activity) were enhanced at the final stage of\ndifferentiation (stage IV). Furthermore, we demonstrated that NANOG and OCT4 expression remaining until stage III\n(day 15 of differentiation) completely disappeared when treated with YM155 and teratoma formation was\neffectively prevented by YM155 pretreatment in the in-vitro study.
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