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To study the primary structure of human acetylcholinesterase (AcChoEase; EC 3.1.1.7) and its gene expression and amplification, cDNA libraries from human tissues expressing oocyte-translatable AcChoEase mRNA were constructed and screened with labeled oligodeoxynucleotide probes. Several cDNA clones were isolated that encoded a polypeptide with greater than or equal to 50% identically aligned amino acids to Torpedo AcChoEase and human butyrylcholinesterase (BtChoEase; EC 3.1.1.8). However, these cDNA clones were all truncated within a 300-nucleotide-long G + C-rich region with a predicted pattern of secondary structure having a high Gibbs free energy (-117 kcal/mol) downstream from the expected 5' end of the coding region. Screening of a genomic DNA library revealed the missing 5' domain. When ligated to the cDNA and constructed into a transcription vector, this sequence encoded a synthetic mRNA translated in microinjected oocytes into catalytically active AcChoEase with marked preference for acetylthiocholine over butyrylthiocholine as a substrate, susceptibility to inhibition by the AcChoEase inhibitor BW284C51, and resistance to the BtChoEase inhibitor tetraisopropylpyrophosphoramide. Blot hybridization of genomic DNA from different individuals carrying amplified AcChoEase genes revealed variable intensities and restriction patterns with probes from the regions upstream and downstream from the predicted G + C-rich structure. Thus, the human AcChoEase gene includes a putative G + C-rich attenuator domain and is subject to structural alterations in cases of AcChoEase gene amplification.

Previous studies have demonstrated the feasibility of implantation of human blood cells or tissues in lethally irradiated mice or rats, radioprotected with SCID mouse bone marrow cells: The Trimera system. In the present study, we describe the development of a mouse Trimera model for human hepatitis B virus (HBV) infection. In this model, viremia is induced by transplantation of ex vivo HBV-infected human liver fragments. Engraftment of the human liver fragments, evaluated by hematoxylin-eosin staining and human serum albumin mRNA expression, was observed in 85% of the transplanted animals 1 month postimplantation. Viremia levels were determined in these mice by measuring serum HBV DNA using polymerase chain reaction (PCR), followed by dot-blot hybridization. HBV DNA is first detected 8 days after liver transplantation. Viremia attains a peak between days 18 and 25 when HBV infection is observed in 85% of the transplanted animals. Hepatitis B virus (HBV) infection is a major public health problem affecting millions of people worldwide. 1 Following acute HBV infection, 5% to 10% of the adult patients will develop persistent infection that may lead to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. 2-4 Whereas considerable progress has been achieved regarding the identification and characterization of the virus, the development of new, effective therapies has been impeded because of the lack of a practical small HBV animal model. Attempts to establish animal models to study HBV infection in rats, 5 nude mice, 6 and transgenic mice 7-9 have been described. Other animal models, based on HBV-related hepadnaviruses that infect nonprimates, were developed and successfully used for assessment of antiviral drugs. These models, however, involve relatively large animals that are difficult to handle in most laboratories. In addition, testing of antiviral agents such as nucleoside analogs could produce aberrant results as a consequence of virus-specific differential susceptibility of the viral polymerase. 10 Chimpanzees provide a good HBV animal model in which effects of vaccines and therapeutic agents can be evaluated. 11 Nonetheless, the limited availability and the high cost of these primates severely restrict their use for such purposes.Recently, we have developed a human-mouse radiation chimera in which normal mice, preconditioned by lethal total body irradiation and radioprotected with SCID mouse bone marrow cells, are permissive for engraftment of human hematopoietic cells and tissues. [12][13][14][15][16] This resulting humanmouse model that comprises three genetically disparate sources of tissue is therefore termed ''Trimera.'' The Trimera mouse, engrafted with human peripheral blood lymphocytes, has been adapted successfully to generate human monoclonal antibodies. 17 Likewise, transplantation of Trimera mice with hepatitis C virus-infected human liver tissue was used for the development of an hepatitis C virus infection model. 14 In the present study, we describe in detail the development of an HBV ani...

The lack of small-animal models that are suitable for evaluation of agents used to treat infection with hepatitis C virus (HCV) severely hinders the assessment of potential new therapies for the disease. This study created such a model, termed the "HCV-Trimera" model. The HCV-Trimera model was developed by using lethally irradiated mice, reconstituted with SCID mouse bone marrow cells, in which human liver fragments infected ex vivo with HCV had been transplanted. Viremia (positive-strand HCV RNA levels) in HCV-Trimera mice peaked at approximately day 18 after liver transplantation, and an infection rate of 85% was reached. Viral replication in liver grafts was evidenced by the presence of specific negative-strand HCV RNA. The usefulness of this model for evaluation of anti-HCV agents was demonstrated by the ability of a small molecule (an HCV internal ribosomal entry site inhibitor) and an anti-HCV human monoclonal antibody (HCV AB(XTL)68) to reduce virus loads in HCV-Trimera mice in a dose-dependent manner.