We reported that chimeric mice generated from albumin enhancer/promoter-driven cDNA urokinase-type plasminogen activator/severe combined immunodeficiency (cDNA-uPA/SCID) mice (PXB-mice) exhibited stable repopulation rates of HHs for several months [15], and were useful for studies on drug metabolism and pharmacokinetics, drug-drug interactions [16–18], and chronic infection by hepatitis viruses [19]. This evidence concerns the gene PLAU and severe combined immunodeficiency.