Transgenic mice replicating hepatitis B virus but lacking expression of the major HBsAg

Tg1.4HBV-s-rec mice, a crossbred hepatitis B virus-transgenic model, develop mild hepatitis

Hepatitis B virus (HBV)-transgenic mice exhibit competent innate immunity and are therefore an ideal model for considering intrinsic or cell-based mechanisms in HBV pathophysiology. A highly replicative model that has been little used, let alone characterized, is the Tg1.4HBV-s-rec strain derived from cross breeding of HBV-transgenic mouse models that either accumulate (Alb/HBs, Tg[Alb1-HBV]Bri44) or lack (Tg1.4HBV-s-mut) the hepatitis B surface antigen (HBsAg). Tg1.4HBV-s-rec hepatocytes secreted HBsAg, Hepatitis B extracellular antigen (HBeAg) and produced HBV virions. Transmission electron microscopy visualised viral particles (Tg1.4HBV-s-rec), nuclear capsid formations (Tg1.4HBV-s-mut and Tg1.4HBV-s-rec) and endoplasmic reticulum malformations (Alb/HBs). Viral replication in Tg1.4HBV-s-rec and Tg1.4HBV-s-mut differed in HBsAg expression and interestingly in the distribution of HBV core antigen (HBcAg) and HBV × protein. While in Tg1.4HBV-s-mut hepatocytes, the HBcAg was located in the cytoplasm, in Tg1.4HBV-s-rec hepatocytes, the HBcAg appeared in the nuclei, suggesting a more productive replication. Finally, Tg1.4HBV-s-rec mice showed symptoms of mild hepatitis, with reduced liver function and elevated serum transaminases, which appeared to be related to natural killer T cell activation. In conclusion, the study of Alb/HBs, Tg1.4HBV-s-mut and their F1 progeny provides a powerful tool to elucidate HBV pathophysiology, especially in the early HBeAg-positive phases of chronic infection and chronic hepatitis.

Poly(I:C) Induces Distinct Liver Cell Type-Specific Responses in Hepatitis B Virus-Transgenic Mice In Vitro, but Fails to Induce These Signals In Vivo

Immunopathology in hepatitis B virus (HBV) infection is driven by innate and adaptive immunity. Whether the hepatitis B surface antigen (HBsAg) affects hepatic antiviral signalling was investigated in HBV-transgenic mouse models that either accumulate (Alb/HBs, Tg[Alb1HBV]Bri44), lack (Tg1.4HBV-s-mut3) or secrete (Tg1.4HBV-s-rec (F1, Tg1.4HBV-s-mut × Alb/HBs) the HBsAg. Herein, the responsiveness of TLR3 and RIG-I in primary parenchymal and non-parenchymal liver cells was determined in vitro and in vivo. Cell type-specific and mouse strain-dependent interferon, cytokine and chemokine expression were observed by LEGENDplex™ and validated by quantitative PCR. In vitro, the hepatocytes, liver sinusoidal endothelial cells and Kupffer cells of Tg1.4HBV-s-rec mice showed poly(I:C) susceptibilities similar to the wild-type controls, while in the remaining leucocyte fraction the interferon, cytokine and chemokine induction was reduced. On the contrary, poly(I:C)-injected 1.4TgHBV-s-rec mice showed suppressed interferon, cytokine and chemokine levels in hepatocytes but increased levels in the leucocyte fraction. Thus, we concluded that liver cells of Tg1.4HBV-s-rec mice, which produce HBV particles and release the HBsAg, responded to exogenous TLR3/RIG-I stimuli in vitro but exhibited a tolerogenic environment in vivo.

Endogenously Expressed Antigens Bind Mammalian RNA via Cationic Domains that Enhance Priming of Effector CD8 T Cells by DNA Vaccination

Hepatitis B virus (HBV) core (HBV-C) antigens with homologous or heterologous HIV-tat48-57-like (HBV-C149tat) cationic domains non-specifically bind cellular RNA in vector-transfected cells. Here, we investigated whether RNA-binding to cationic domains influences the immunogenicity of endogenously expressed antigens delivered by DNA vaccination. We initially evaluated induction of HBV-C (K^b/C93)-specific CD8⁺ T cell responses in C57BL/6J (B6) and 1.4HBV-S^mut transgenic (tg) mice that harbor a replicating HBV genome in hepatocytes by DNA immunization. RNA-binding HBV-C and HBV-C149tat antigens moderately enhanced K^b/C93-specific CD8⁺ T cells in B6 mice as compared with RNA-free HBV-C149 antigen (lacking cationic domains). However, only the RNA-binding antigens elicited K^b/C93-specific CD8⁺ T cells that inhibited HBV replication in 1.4HBV-S^mut tg mice. Moreover, RNA-binding to designer antigens, which express a K^b/p15E epitope from an endogenous murine leukemia virus-derived tumor-specific gp70 protein, was crucial to prime tumor-rejecting effector CD8⁺ T cells in B6 mice. Antigen-bound endogenous RNAs function as a Toll-like receptor 7 (TLR-7) ligand and stimulated priming of K^b/p15E-specific CD8⁺ T cells in B6, but not TLR-7^−/−, mice. Antigen-bound cellular RNAs thus function as an endogenous natural adjuvant in in vivo vector-transfected cells, and thus are an attractive tool to induce and/or enhance effector CD8⁺ T cell responses directed against chronic viral infections or tumor self-antigens by DNA vaccination.

Cationic domains in particle-forming and assembly-deficient HBV core antigens capture mammalian RNA that stimulates Th1-biased antibody responses by DNA vaccination

The HBV core protein self-assembles into particles and encapsidates immune-stimulatory bacterial RNA through a cationic COOH-terminal (C150-183) domain. To investigate if different cationic domains have an impact on the endogenous RNA-binding of HBV-C antigens in mammalian cells, we developed a strep-tag (st) based expression/purification system for HBV-C/RNA antigens in vector-transfected HEK-293 cells. We showed that HBV-stC but not HBV-stC149 particles (lacking the cationic domain) capture low amounts of mammalian RNA. Prevention of specific phosphorylation in cationic domains, either by exchanging the serine residues S155, S162 and S170 with alanines (HBV-stCAAA) or by exchanging the entire cationic domain with a HIV-tat_48-57-like sequence (HBV-stC149tat) enhanced the encapsidation of RNA into mutant core particles. Particle-bound mammalian RNA functioned as TLR-7 ligand and induced a Th1-biased humoral immunity in B6 but not in TLR-7^-/- mice by exogenous (protein) and endogenous (DNA) vaccines. Compared to core particles, binding of mammalian RNA to freely exposed cationic domains in assembly-deficient antigens was enhanced. However, RNA bound to non-particulate antigens unleash its Th1-stimulating adjuvant activity by DNA- but not protein-based vaccination. Mammalian RNAs targeted by an endogenously expressed antigen thus function as a natural adjuvant in the host that facilitates priming of Th1-biased immune responses by DNA-based immunization.

Hepatitis B virus genome replication triggers toll-like receptor 3-dependent interferon responses in the absence of hepatitis B surface antigen

The hepatitis B virus (HBV) has been described as stealth virus subverting immune responses initially upon infection. Impaired toll-like receptor signaling by the HBV surface antigen (HBsAg) attenuates immune responses to facilitate chronic infection. This implies that HBV replication may trigger host innate immune responses in the absence of HBsAg. Here we tested this hypothesis, using highly replicative transgenic mouse models. An HBV replication-dependent expression of antiviral genes was exclusively induced in HBsAg-deficient mice. These interferon responses attributed to toll-like receptor 3 (TLR3)-activated Kupffer and liver sinusoidal endothelial cells and further controlled the HBV genome replication. However, activation of TLR3 with exogenous ligands indicated additional HBs-independent immune evasion events. Our data demonstrate that in the absence of HBsAg, hepatic HBV replication leads to Tlr3-dependent interferon responses in non-parenchymal liver cells. We hypothesize that HBsAg is a major HBV-mediated evasion mechanism controlling endogenous antiviral responses in the liver. Eradication of HBsAg as a therapeutic goal might facilitate the induction of endogenous antiviral immune responses in patients chronically infected with HBV.

Comparative analysis of immunization schedules using a novel adenovirus-based immunotherapeutic targeting hepatitis B in naïve and tolerant mouse models

Development of active targeted immunotherapeutics is a rapid developing field in the arena of chronic infectious diseases. The question of repeated, closely spaced administration of immunotherapeutics to achieve a rapid impact on the replicating agent is an important one. We analyzed here, using a prototype adenovirus-based immunotherapeutic encoding Core and Polymerase from the hepatitis B virus (Ad-HBV), the influence of closely spaced repeated immunizations on the level and quality of induced HBV-specific and vector-specific immune responses in various mouse models. Ad-HBV, whether injected once or multiple times, was able to induce HBV- and adeno-specific T cells both in HBV-free mice and in a HBV tolerant mouse model. Adenovirus-specific T cell responses and titers of neutralizing anti-Ad5 antibodies increased from time of the 3rd injection. Interestingly, single or multiple Ad-HBV injections resulted in detection of Polymerase-specific functional T cells in HBV tolerant mice. Overall no modulation of the levels of HBV-specific cytokine-producing (IFNγ/TNFα) and cytolytic T cells was observed following repeated administrations (3 or 6 weekly injections) when compared with levels detected after a single injection with the exception of two markers: 1. the proportion of HBV-specific IFNγ-producing cells bearing the CD27+/CD43+ phenotype appeared to be sustained in C57BL/6J mice following 6 weekly injections; 2. the percentage of IFNγ/TNFα Core-specific producing cells observed in spleens of HLA-A2 mice as well as of that specific of Polymerase observed in livers of HBV tolerant mice was maintained. In addition, percentage of HBV-specific T cells expressing PD-1 was not increased by multiple injections. Overall these data show that, under experimental conditions used, rapid, closely spaced administrations of an adenovirus-based HBV immunotherapeutics does not inhibit induced T-cell responses including in a HBV-tolerant environment.

Novel Woodchuck Hepatitis Virus (WHV) transgene mouse models show sex-dependent WHV replicative activity and development of spontaneous immune responses to WHV proteins

The woodchuck model is an informative model for studies on hepadnaviral infection. In this study, woodchuck hepatitis virus (WHV) transgenic (Tg) mouse models based on C57BL/6 mice were established to study the pathogenesis associated with hepadnaviral infection. Two lineages of WHV Tg mice, harboring the WHV wild-type genome (lineage 1217) and a mutated WHV genome lacking surface antigen (lineage 1281), were generated. WHV replication intermediates were detected by Southern blotting. DNA vaccines against WHV proteins were applied by intramuscular injection. WHV-specific immune responses were analyzed by flow cytometry and enzyme-linked immunosorbent assays (ELISAs). The presence of WHV transgenes resulted in liver-specific but sex- and age-dependent WHV replication in Tg mice. Pathological changes in the liver, including hepatocellular dysplasia, were observed in aged Tg mice, suggesting that the presence of WHV transgenes may lead to liver diseases. Interestingly, Tg mice of lineage 1281 spontaneously developed T- and B-cell responses to WHV core protein (WHcAg). DNA vaccination induced specific immune responses to WHV proteins in WHV Tg mice, indicating a tolerance break. The magnitude of the induced WHcAg-specific immune responses was dependent on the effectiveness of different DNA vaccines and was associated with a decrease in WHV loads in mice. In conclusion, sex- and age-dependent viral replication, development of autoimmune responses to viral antigens, pathological changes in the liver in WHV Tg mice, and the possibility of breaking immune tolerance to WHV transgenes will allow future studies on pathogenesis related to hepadnaviral infection and therapeutic vaccines.

Human hepatitis B virus production in avian cells is characterized by enhanced RNA splicing and the presence of capsids containing shortened genomes

Experimental studies on hepatitis B virus (HBV) replication are commonly done with human hepatoma cells to reflect the natural species and tissue tropism of the virus. However, HBV can also replicate, upon transfection of virus coding plasmids, in cells of other species. In such cross-species transfection experiments with chicken LMH hepatoma cells, we previously observed the formation of HBV genomes with aberrant electrophoretic mobility, in addition to the those DNA species commonly seen in human HepG2 hepatoma cells. Here, we report that these aberrant DNA forms are mainly due to excessive splicing of HBV pregenomic RNA and the abundant synthesis of spliced DNA products, equivalent to those also made in human cells, yet at much lower level. Mutation of the common splice acceptor site abolished splicing and in turn enhanced production of DNA from full-length pgRNA in transfected LMH cells. The absence of splicing made other DNA molecules visible, that were shortened due to the lack of sequences in the core protein coding region. Furthermore, there was nearly full-length DNA in the cytoplasm of LMH cells that was not protected in viral capsids. Remarkably, we have previously observed similar shortened genomes and non-protected viral DNA in human HepG2 cells, yet exclusively in the nucleus where uncoating and final release of viral genomes occurs. Hence, two effects reflecting capsid disassembly in the nucleus in human HepG2 cells are seen in the cytoplasm of chicken LMH cells.

Animal models of liver cancer: progress and prospects

Primary liver cancer remains one of the most lethal malignancies worldwide. As this disease is lethal in most cases, research has to be done to improve our understanding of the disease and to offer insights for possible treatment options. Animal models have been widely used in the research of primary liver cancer. Here, we review the progress and prospects for the development of animal models of primary liver cancer, highlighting the best candidates for future preclinical investigations.