Production and effect of infectious Dane particles in transgenic mice

Sequence analysis of integrated hepatitis B virus DNA during HBeAg-seroconversion

Hepatitis B virus (HBV) integration into the host cell genome occurs early on in infection and reportedly induces pro-oncogenic changes in hepatocytes that drive HCC initiation. However, it remains unclear when these changes occur during hepatocarcinogenesis. Extensive expansion of hepatocyte clones with a selective advantage was shown to occur prior to cancer formation during the HBeAg-seroconversion phase of chronic HBV infection. We hypothesized that since integrations occur during the early stages of infection, cell phenotype could be altered and induce a selection advantage (e.g., through insertional mutagenesis or cis-mediated activation of downstream genes). Here, we analyzed the enrichment of genomic and functional patterns in the cellular host sequence adjacent to HBV DNA integration events. We examined 717 unique integration events detected in patients who have and have not undergone HBeAg-seroconversion (n = 41) or in an in vitro model system. We also used an in silico model to control for detection biases. We showed that the sites of HBV DNA integration were distributed throughout the entire host genome without obvious enrichment of specific structural or functional genomic features in the adjacent cellular genome during HBeAg-seroconversion. Currently, this is the most comprehensive characterization of HBV DNA integration events prior to hepatocarcinogenesis. Our results suggest no significant selection for (or against) specific cellular sites of HBV DNA integration occur during the clonal expansion phase of chronic HBV infection. Thus, HBV DNA integration events likely represent passenger events rather than active drivers of liver cancer, which was previously suggested.

Hepatocellular carcinoma mouse models: Hepatitis B virus-associated hepatocarcinogenesis and haploinsufficient tumor suppressor genes

The multifactorial and multistage pathogenesis of hepatocellular carcinoma (HCC) has fascinated a wide spectrum of scientists for decades. While a number of major risk factors have been identified, their mechanistic roles in hepatocarcinogenesis still need to be elucidated. Many tumor suppressor genes (TSGs) have been identified as being involved in HCC. These TSGs can be classified into two groups depending on the situation with respect to allelic mutation/loss in the tumors: the recessive TSGs with two required mutated alleles and the haploinsufficient TSGs with one required mutated allele. Hepatitis B virus (HBV) is one of the most important risk factors associated with HCC. Although mice cannot be infected with HBV due to the narrow host range of HBV and the lack of a proper receptor, one advantage of mouse models for HBV/HCC research is the numerous and powerful genetic tools that help investigate the phenotypic effects of viral proteins and allow the dissection of the dose-dependent action of TSGs. Here, we mainly focus on the application of mouse models in relation to HBV-associated HCC and on TSGs that act either in a recessive or in a haploinsufficient manner. Discoveries obtained using mouse models will have a great impact on HCC translational medicine.

Transgenic expression of entire hepatitis B virus in mice induces hepatocarcinogenesis independent of chronic liver injury

Hepatocellular carcinoma (HCC), the third leading cause of cancer deaths worldwide, is most commonly caused by chronic hepatitis B virus (HBV) infection. However, whether HBV plays any direct role in carcinogenesis, other than indirectly causing chronic liver injury by inciting the host immune response, remains unclear. We have established two independent transgenic mouse lines expressing the complete genome of a mutant HBV ("preS2 mutant") that is found at much higher frequencies in people with HCC than those without. The transgenic mice show evidence of stress in the endoplasmic reticulum (ER) and overexpression of cyclin D1 in hepatocytes. These mice do not show any evidence of chronic liver injury, but by 2 years of age a majority of the male mice develop hepatocellular neoplasms, including HCC. Unexpectedly, we also found a significant increase in hepatocarcinogenesis independent of necroinflammation in a transgenic line expressing the entire wildtype HBV. As in the mutant HBV mice, HCC was found only in aged--2-year-old--mice of the wildtype HBV line. The karyotype in all the three transgenic lines appears normal and none of the integration sites of the HBV transgene in the mice is near an oncogene or tumor suppressor gene. The significant increase of HCC incidence in all the three transgenic lines--expressing either mutant or wildtype HBV--therefore argues strongly that in absence of chronic necroinflammation, HBV can contribute directly to the development of HCC.

Use of RNA interference to modulate liver adenoma development in a murine model transgenic for hepatitis B virus

Chronic hepatitis B virus (HBV) infection is closely related to the development of severe liver complications, including hepatocellular carcinoma. In previous studies, we reported that in vivo long-term HBV suppression in transgenic mice can be achieved without apparent toxicity by short hairpin RNA sequentially delivered using adeno-associated viral (AAV) vectors of different serotypes. Our goal herein was to address the clinical utility of this delivery system and, in particular, to determine whether RNA interference (RNAi) and its ability to induce long-term HBV suppression will modulate the development of HBV-associated liver pathology. As a model system, we used a unique HBV transgenic mouse model, containing a 1.3 times over length of the HBV genome, on the ICR mouse background. These transgenic mice produce high serum HBV titers comparable with human chronic HBV patients, and, importantly, manifest characteristic HBV-associated pathology, including progressive hepatocellular injury and the development of hepatocellular adenoma. Using this system, we injected animals with AAV vectors expressing either HBV-specific or a control luciferase-specific short hairpin RNA and followed animals for a total of 18 months. We report herein that AAV-mediated RNAi therapy profoundly inhibits HBV replication and gene expression, with a significant reduction in hepatic regeneration, liver enzymes and, importantly, the appearance of liver adenomas. Indeed, the therapeutic effect of RNAi correlated with the reduction in HBV titers. Our data demonstrate that appropriately designed RNAi therapy has the potential to prevent formation of HBV-associated hepatocellular adenoma.

Hepatitis B virus in hepatocarcinogenesis

Hepatitis B virus (HBV) is an important etiologic agent of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Although the mechanism whereby HBV causes HCC is not fully understood, it is likely that there are many relevant molecular pathways that contribute to the development of HBV-associated HCC. This review provides an overview of some of these proposed pathways and their relative importance. It also raises questions on basic and translational research that will signficantly contribute to the better understanding of underlying mechanisms, prevention, and treatment of this tumor type.

Production of antibody to hepatitis B surface antigen (anti-HBs) by murine hepatitis B virus carriers: neonatal tolerance versus antigen presentation by dendritic cells

The inability of hepatitis B virus (HBV) transgenic mice, which express abundant hepatitis B surface antigen (HBsAg) in sera from the neonatal period onwards, to produce antibody to HBsAg (anti-HBs) is considered to be due to defective function of lymphocytes. The defective function is thought to result from neonatal tolerance because antigenic challenge during the neonatal period is considered to be a tolerogenic event rather than an immunogenic one. However, a series of mixed culture experiments in vitro showed that lymphocytes taken from transgenic mice that had been injected with HBsAg in complete Freund's adjuvant (CFA) constitutively produced anti-HBs when cultured with dendritic cells from age-, sex- and major histocompatibility complex (MHC)-matched normal mice, but not when cultured with dendritic cells from transgenic mice. The expression of major histocompatibility complex (MHC) class II and B 7.2 (CD86) antigens on dendritic cells was significantly lower in transgenic mice compared with the same from the normal mice (P < 0.05). Treatment of transgenic mice with interferon-gamma (IFN-gamma) resulted in up-regulation of MHC class II on dendritic cells, and lymphocytes from HBsAg-injected transgenic mice produced anti-HBs in vitro when cultured with dendritic cells from IFN-gamma-treated transgenic mice, but not when cultured with the dendritic cells from untreated transgenic mice. These experiments have shown that defective function of antigen-presenting cells (APC), not immunogenic tolerance, is responsible for the inability of murine HBV-carriers to produce anti-HBs. Production of anti-HBs by lymphocytes from HBsAg-injected transgenic mice in the presence of dendritic cells that express higher levels of MHC class II and CD86 antigens has inspired optimism that a more effective vaccine therapy can be developed for chronic HBV-carriers, injecting vaccine containing HBsAg with modulator(s) of APC function of dendritic cells.

Use of the hemagglutinating virus of Japan (HVJ)-liposome method for analysis of infiltrating lymphocytes induced by hepatitis B virus gene expression in liver tissue

We previously developed a method for introducing foreign genes into liver tissue using liposomes with incorporated hemagglutinating virus of Japan (HVJ, Sendai virus), and found that liver cells transfected with the E. coli beta-galactosidase gene or the gene for hepatitis B virus (HBV) surface protein (HBsAg) expressed these proteins in vivo. Here, we analyzed cellular reactions leading to hepatitis in the liver by expressing the genes of HBV in vivo. Lymphocytes were eluted directly from liver transfected with the HBsAg genes and shown to be cytotoxic only to cells expressing HBsAg in vitro. These lymphocytes were identified as cytotoxic T lymphocytes with the CD4- CD8+ phenotype. Transfer of these lymphocytes to transgenic mice with the whole HBV genome led to elevation of the serum glutamic-pyruvic transaminase (SGPT) level, indicating the induction of hepatitis due to the cytotoxic T lymphocytes in vivo. Similarly, direct transfer of the gene for the HBV secretory core protein (HBeAg) induced expression of HBeAg in hepatocytes and the appearance of antibody against HBeAg in the serum. However, using this system, we found that the lymphocytes infiltrating the transfected liver showed no cytotoxicity specific for HBeAg. These results indicate that expression of HBsAg, one of the components of virions, in animal liver induced hepatitis efficiently through generation of specific cytotoxic T lymphocytes (CTL) without any expression of the other viral components. This in vivo experimental system should be useful for evaluating how expression of a given gene induces cellular reactions and intrinsic functions in the living body.

Characterization of T-cell tolerance to hepatitis B virus (HBV) antigen in transgenic mice

We made three different lines of hepatitis B virus (HBV) transgenic mice which express different amounts of hepatitis B e antigen (HBeAg) and/or hepatitis B core antigen (HBcAg) to analyse the cellular mechanisms of HBcAg specific T-cell tolerance. BS10 (official designation, 1.2HB-BS10) transgenic mice, which contain the whole HBV genome, express relatively high amounts of HBeAg in the serum and HBcAg in the liver. SPC mice, which contain hepatitis B virus core and precore gene, express small amounts of HBeAg in the serum but not HBcAg in the liver. SC33 mice, which contain only hepatitis B core gene, do not express HBeAg in the serum but express HBcAg in the liver. BS10 mice showed a very low anti-HBc antibody response after primary and secondary immunizations with recombinant HBcAg compared to transgenic host C57BL/6 (B6) mice. SPC mice showed an almost equal level of anti-HBc antibody response compared to B6 mice. SC33 mice contained anti-HBc antibody even before immunization and showed high titres of anti-HBc antibody response after immunization with HBcAg. Analysis of cellular site(s) of low responsiveness of BS10 mice revealed that proliferating and helper T cells are specifically tolerant to HBcAg. B cells and antigen-presenting cells in BS10 mice were not defective. SC33, SPC and BS10 mice differ a little in their developmental expression of HBc/HBeAg. Our results suggest critical roles of the nature (circulating versus non-circulating) as well as the time of expression of self-antigens in T-cell tolerance.