Human gene and protein expression in chimeric mice. (a) RT-PCR of chimeric liver. The human ALB, FAH, TAT, TF, TTR and UGT1A1 genes were expressed in chimeric mice livers (no. 697 and no. 785). Human hepatocytes and mouse hepatocytes were used as positive and negative control, respectively. (b,c) Blood human albumin concentration of human cell recipients was assayed by enzyme-linked immunosorbent assay (ELISA). The threshold concentration of our system is around 0.005 μg/ml. Primary recipients (b); secondary recipients (c). The degree of difference among secondary recipients was much smaller than primary recipients. Logarithmic plotting shows the doubling time of albumin concentration was around 1 week. (d–g) Human liver–specific gene expression levels (displayed on the y-axis) determined by quantitative RT-PCR and normalized to human cyclophilin (1). Adult, average of nine adult human cell donors; Fetal, five human fetal livers; FRG, average of three highly humanized (>10%) FRG mouse livers. (d=,e) All samples show high levels of albumin (d), but alpha-fetoprotein (AFP) is expressed highly only in fetal liver (e). (f) CytochromeP450 CYP3A4 (f) is highly expressed in adult liver and FRG mice, but not in fetal liver. (g) Similarly, CYP1A2 levels in FRG mice mimic those of adult liver.