Development of humanized NOG mice reconstituted with human hepatocytes and their applications in drug discovery and infectious disease research.

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The aim of this study, which was designed to establish a drug evaluation model and infectious disease model, was "to develop a reconstituted mouse with human hepatocytes". The research plan consisted of the following three steps, and the results at each step are described.First step : Development of genetically modified mice with sustained hepatic injury.We established a transgenic mouse (Alb-HSV-Tk), which carries the herpes simplex virus thymidine kinase gene with an albumin enhancer and promoter, to induce hepatocyte specific cell injury by ganciclovir (GCV). Two-hundred and eight pups were obtained by DNA microinjection experiments and we succeeded in obtaining 9 founder mice that showed positive reactions in the first screening by the PCR genotyping test.Second step : Induction of hepatocyte specific cell injury by GCV administration.Transgenic pups were obtained from nine Alb-HSV-Tk founders, and the ability to induce hepatic injury by GCV injection was examined. According to the results, elevated levels of AST and ALT were observed only in the Tg-Alb-HSV-Tk #7-2 line (Tg-Tk#7-2). Furthermore, Tg-Tk#7-2 showed apparent jaundice in the ears. Histological investigation of the mouse liver revealed a number of abnormalities, including hepatocyte vaculation and hepatocyte megalocytosis.Third step : Application in a drug evaluation study with reconstituted mice with human hepatocytes.Unfortunately, the third step could not be completed within the planned period. The main reason was the sterility in the Tg-Tk#7-2 line, which made large-scale production using in vitro fertilization and embryo transplantation techniques impossible, and drastically delayed our production plan. However, we obtained a few Tg-Tk#7-2 NOG mice, and have already started a human hepatocyte transplantation experiment with weekly evaluations for signs of humanization (Hu-Liver NOG). The Hu-Liver NOG mouse will be a useful model to facilitate the evaluation of drug efficacy and pharmacokinetics.