Background.Acute liver failure (ALF) can occur after acute viral hepatitis, acute-on-chronic liver disease, toxin exposure and/or major liver surgery, and is characterized by massive acute tissue damage that leads to impaired hepatic function. In the most severe cases, liver transplantation is the only useful therapy. Hepatocyte transplantation in acute liver failure is used to support liver functions and enhance regeneration of native liver. A severe shortage of useful hepatocytes limits a wider application of this cellular therapy.  Stem cell sources are being investigated for the production of cells for transplants.  Human amniotic epithelial (hAE) cells have been shown to have characteristics similar to pluripotent stem cells, have the ability to differentiate into cells from all three germ layers, are not tumorigenic and when transplanted into the liver of mice, express human liver genes including CYP450, phase II, hepatic transporter and nuclear hormone receptor genes at levels observed in normal adult human liver.  In addition, hAE have anti-inflammatory and immunomodulatory effects that may play beneficial role in ALF progression.Aim.  We evaluated the possible beneficial effects of hAE cell transplants in ALF-induced liver failure. Materials and Methods.Twenty eight mice received D-galactosamine (Dgal; 5 g/kg) intraperitoneally. Six hours later, half of the mice were directly injected with 2x10⁶ hAE cells in the spleen, whereas the remaining animals were injected with saline (ctrl).  Seven animals in each group were sacrificed at day 2 and remaining surviving animals at day 14. Livers and blood were collected to evaluate histopathological, biochemical and gene expression parameters. Results.Animals that received d-gal developed severe liver failure and all untreated or saline treated animals died within an average of 2.2 days with significant increases in AST, ALT and TGF-beta levels, and liver pathology consistent with ALF. All d-gal-intoxicated animals that received hAE cell transplants survived and appeared healthy until scheduled sacrifice at day 14.  In separate experiments with animals sacrificed 48 hrs. post d-gal treatment, transplant of hAE cells significantly decreased serum AST, ALT, and TGF-beta levels and decreased hepatic expression of Interleukin 1-beta, and Tumor Necrosis Factor alpha, and increased IL-10 expression. Conclusion.Human AE cell transplantation improvedsurvival in mice in a Dgal-induced ALF model. These results suggest that human AE stem cell transplantation may be a useful cellular therapy for ALF and have motivated translation to GMP isolation and banking of hAE at our Institutet for the cellular therapy in liver diseases. Supported in part by the PKU foundation.