Primary or cryopreserved human hepatocytes (h-heps) have been used as the gold standard for in vitro metabolism and hepatotoxicity studies; however, the supply of h-heps is limited and they cannot grow in vitro. We achieved approximately 1000-fold propagation of h-heps in the liver of albumin promoter/enhancer-driven urokinase-type plasminogen activator transgenic/severe combined immunodeficiency disease (uPA/SCID) mice with genetically induced liver disease and immunodeficiency. When h-heps are transplanted into the uPA/SCID mouse liver via the spleen, the h-heps engraft in the mouse liver, resulting in its repopulation with h-heps. We have named this model “chimeric mouse with humanized liver, PXB-mouse^®.” Fresh h-heps can be isolated from the chimeric mice (PXB-cells^®) and have been used for in vitro studies.

The efficacy and safety of chemical entities for use in humans are estimated using experimental animals such as rats and mice. The drug development of many chemical entities has been halted because of metabolic differences between humans and animals during clinical studies. Therefore, chimeric mice with humanized liver have been used to predict human-type metabolism and safety conditions for h-heps. In addition, until recently there were no suitable hepatitis B or C virus (HBV or HCV) susceptible animal models aside from chimpanzees. Chimeric mice are the sole persistent infectious small animal model for HBV and HCV and they have been used to investigate the efficacy of new anti-HBV or HCV agents.

In this chapter, we describe a method for producing chimeric mice with humanized liver using uPA/SCID mice.