The only curative treatment option for many patients that suffer from a liver disorder remains whole liver transplantation. This is an invasive procedure, which is accompanied by increased morbidity and mortality. In search of alternative treatment options, several research groups have performed animal studies investigating liver-directed cell and gene therapy for the treatment of acture liver failure, chronic liver disease and inherited metabolic liver disorders. A problem is translating results of animal studies to a treatment for patients with liver disease is the difference in liver physiology between humans and rodents. Ebtisam El Filali has set out to develop a mouse with a ‘humanized liver’, which would serve as an excellent in vivo model for studies on liver-directed cell and gene therapy.