Provided herein is a recombinant non-human mammal having an immune system including human immune cells and having a liver including human liver cells, and methods for producing the same. Also provided are methods of screening a compound for activity in treating hepatitis, comprising: administering a test compound to a recombinant non-human mammal as described herein and then detecting the presence or absence of said activity in said mammal (e.g., by biochemical assay), said presence of said activity in said mammal indicating that said compound has activity in treating hepatitis. Methods of making fusion cells useful for the production of human monoclonal antibodies are also provided.
