Orthotopic liver transplantation (OLT) is the only curative treatment currently available for life threatening genetic disorders of the liver and acute liver failure. However, there is a shortage of donor livers and an increasing number of patients die waiting for a liver transplant. Our overall goal is to develop clinical application of human embryonic (hESCs) and human induced pluripotent stem cells (hiPSCs) differentiated into hepatocytes, the cells responsible for liver metabolism. The rationale of our liver-directed regenerative medicine approach is based on clinical trials showing that transplantation of allogeneic human hepatocytes is a safe therapeutic alternative to OLT. Engrafted hepatocytes improved the clinical outcome of several patients with inborn liver diseases. Between 2 to 5 billion hepatocytes must be transplanted to improve the hepatic metabolic function, which are lacking in patients. However, the supply of good quality donor livers for hepatocyte isolation is a major challenge because donor liver organs are scarce and when available prioritized for OLT. In addition, isolated hepatocytes cannot be expanded in culture with current methods. This emphasizes the critical need to develop new, renewable and reliable sources of hepatocytes. Human ESCs and hiPSCs can generate functional hepatocytes (pStemHep) in vitro that can efficiently engraft into the mouse liver. Still, the clinical application of pStemHep faces major challenges. First, dramatic differences between pluripotent stem cell lines have been observed in terms of hepatic differentiation. In addition, so far the results have been obtained with research grade hESC, which quality is insufficient to be used clinically. Thereby, the production of pStemHep from existing GMP (Good Manufacturing Practices) grade hESCs remains to be achieved and GMP-grade hiPSCs has still to be generated. Second, immunodeficient mouse with chronic or acute liver injury is currently the prevalent model for in vivo validation of human pStemHep. However, these models possess limited relevance to inherited liver diseases, thus necessitate the development of more reliable animal models. For instance, in hereditary liver diseases, hepatocytes must be engrafted in the liver and be functional in the long term whereas in acute liver failure, only transient support of hepatic metabolic functions and liver regeneration is required. Thereby, the specific aims of this proposal are as follows: 1. To constitute a GMP-grade cell bank of hESC-derived hepatocytes fulfilling all criteria for clinical application. 2. To generate GMP-grade hiPSCs with validated hepatic differentiation ability. 3. To perform safety and efficacy studies in a relevant rat model of metabolic liver diseases (Crigler-Najjar) that we will create. 4. To provide the proof-of-principle that hepatocytes differentiated from non-human primate stem cells can stably and safely engraft in the liver of recipient animals with sufficient efficacy to expect clinical benefits for transplanted patients. In this closest species to humans with respect to human liver physiology and anatomy, we will use the clinically-relevant cell transplantation procedure that we developed to obtain 5-10% of liver chimerism with 400 millions injected cells. 5. To create a database of patients in order to identify and follow up those are potentially eligible to liver cell therapy, which will accelerate the translation of StemHepTher regenerative medicine to the clinic.