Optimized HepaRG is a suitable cell source to generate the human liver chimeric mouse model for the chronic hepatitis B virus infection

The human liver chimeric mouse with primary human hepatocytes (PHHs) engraftment has been demonstrated to be a useful animal model to study hepatitis B virus (HBV) pathogenesis and evaluate anti-HBV drugs. However, the disadvantages of using PHHs include the inability for cellular expansion in vitro, limited donor availability, individual differences, and ethical issues, necessitating the development of alternatives. To obtain in vitro expandable hepatocytes, we optimized the hepatic differentiation procedure of the human liver progenitor cell line, HepaRG, using four functional small molecules (4SM) and enriched the precursor hepatocyte-like cells (HLCs). HepaRG cells of different hepatic differentiation states were engrafted to immunodeficient mice (FRGS) with weekly 4SM treatment. The HepaRG-engrafted mice were challenged with HBV and/or treated with several antivirals to evaluate their effects. We demonstrated that the 4SM treatment enhanced hepatic differentiation and promoted cell proliferation capacity both in vitro and in vivo. Mice engrafted with enriched HepaRG of prehepatic differentiation and treated with 4SM displayed approximately 10% liver chimerism at week 8 after engraftment and were maintained at this level for another 16 weeks. Therefore, we developed a HepaRG-based human liver chimeric mouse model: HepaRG-FRGS. Our experimental results showed that the liver chimerism of the mice was adequate to support chronic HBV infection for 24 weeks and to evaluate antivirals. We also demonstrated that HBV infection in HepaRG cells was dependent on their hepatic differentiation state and liver chimerism in vivo. Overall, HepaRG-FRGS mice provide a novel human liver chimeric mouse model to study chronic HBV infection and evaluate anti-HBV drugs.

Latitudinal Diversity of Culex pipiens Biotypes and Hybrids in Farm, Peri-Urban, and Wetland Habitats in Europe

Despite the presence of Culex (Cx.) pipiens mosquitoes and circulation of West Nile virus (WNV), WNV outbreaks have so far not occurred in northern Europe. The species Cx. pipiens consists of two morphologically identical biotypes, pipiens and molestus, which can form hybrids. Until now, population dynamic studies of Cx. pipiens have not differentiated between biotypes and hybrids at the European scale, nor have they used comparative surveillance approaches. We therefore aimed to elucidate the relative abundance of Cx. pipiens biotypes and hybrids in three habitat types at different latitudes across Europe, using two different surveillance traps. BG-Sentinel and Mosquito-Magnet Liberty Plus traps were placed in three habitat types (farms, peri-urban, wetlands), in three European countries (Sweden, The Netherlands, Italy). Collected Cx. pipiens mosquitoes were identified to biotype with real-time PCR. Both trap types collected equal ratios of the biotypes and their hybrids. From northern to southern latitudes there was a significant decrease of pipiens and an increase of molestus. Habitat types influenced the relative ratios of biotypes and hybrids, but results were not consistent across latitudes. Our results emphasize the need to differentiate Cx. pipiens to the biotype level, especially for proper future WNV risk assessments for Europe.

Chimeric mouse model for the infection of hepatitis B and C viruses

While the chimpanzee remains the only animal that closely models human hepatitis C virus (HCV) infection, transgenic and immunodeficient mice in which human liver can be engrafted serve as a partial solution to the need for a small animal model for HCV infection. The established system that was based on mice carrying a transgene for urokinase-type plasminogen activator (uPA) gene under the control of the human albumin promoter has proved to be useful for studies of virus infectivity and for testing antiviral drug agents. However, the current Alb-uPA transgenic model with a humanized liver has practical limitations due to the inability to maintain non-engrafted mice as dizygotes for the transgene, poor engraftment of hemizygotes, high neonatal and experimental death rates of dizygous mice and a very short time window for hepatocyte engraftment. To improve the model, we crossed transgenic mice carrying the uPA gene driven by the major urinary protein promoter onto a SCID/Beige background (MUP-uPA SCID/Bg). These transgenic mice are healthy relative to Alb-uPA mice and provide a long window from about age 4 to 12 months for engraftment with human hepatocytes and infection with hepatitis C or hepatitis B (HBV) viruses. We have demonstrated engraftment of human hepatocytes by immunohistochemistry staining for human albumin (30-80% engraftment) and observed a correlation between the number of human hepatocytes inoculated and the level of the concentration of human albumin in the serum. We have shown that these mice support the replication of both HBV and all six major HCV genotypes. Using HBV and HCV inocula that had been previously tittered in chimpanzees, we showed that the mice had approximately the same sensitivity for infection as chimpanzees. These mice should be useful for isolating non-cell culture adapted viruses as well as testing of antiviral drugs, antibody neutralization studies and examination of phenotypic changes in viral mutants.

Quantitative and qualitative involvement of P3N-PIPO in overcoming recessive resistance against Clover yellow vein virus in pea carrying the cyv1 gene

In pea carrying cyv1, a recessive gene for resistance to Clover yellow vein virus (ClYVV), ClYVV isolate Cl-no30 was restricted to the initially infected cells, whereas isolate 90-1 Br2 overcame this resistance. We mapped the region responsible for breaking of cyv1-mediated resistance by examining infection of cyv1 pea with chimeric viruses constructed from parts of Cl-no30 and 90-1 Br2. The breaking of resistance was attributed to the P3 cistron, which is known to produce two proteins: P3, from the main open reading frame (ORF), and P3N-PIPO, which has the N-terminal part of P3 fused to amino acids encoded by a small open reading frame (ORF) called PIPO in the +2 reading frame. We introduced point mutations that were synonymous with respect to the P3 protein but nonsynonymous with respect to the P3N-PIPO protein, and vice versa, into the chimeric viruses. Infection of plants with these mutant viruses revealed that both P3 and P3N-PIPO were involved in overcoming cyv1-mediated resistance. Moreover, P3N-PIPO quantitatively affected the virulence of Cl-no30 in cyv1 pea. Additional expression in trans of the P3N-PIPO derived from Cl-no30, using White clover mosaic virus as a vector, enabled Cl-no30 to move to systemic leaves in cyv1 pea. Susceptible pea plants infected with chimeric ClYVV possessing the P3 cistron of 90-1 Br2, and which were therefore virulent toward cyv1 pea, accumulated more P3N-PIPO than did those infected with Cl-no30, suggesting that the higher level of P3N-PIPO in infected cells contributed to the breaking of resistance by 90-1 Br2. This is the first report showing that P3N-PIPO is a virulence determinant in plants resistant to a potyvirus.

Challenge pools of hepatitis C virus genotypes 1-6 prototype strains: replication fitness and pathogenicity in chimpanzees and human liver-chimeric mouse models

Chimpanzees represent the only animal model for studies of the natural history of hepatitis C virus (HCV). To generate virus stocks of important HCV variants, we infected chimpanzees with HCV strains of genotypes 1-6 and determined the infectivity titer of acute-phase plasma pools in additional animals. The courses of first- and second-passage infections were similar, with early appearance of viremia, HCV RNA titers of >10(4.7) IU/mL, and development of acute hepatitis; the chronicity rate was 56%. The challenge pools had titers of 10(3)-10(5) chimpanzee infectious doses/mL. Human liver-chimeric mice developed high-titer infections after inoculation with the challenge viruses of genotypes 1-6. Inoculation studies with different doses of the genotype 1b pool suggested that a relatively high virus dose is required to consistently infect chimeric mice. The challenge pools represent a unique resource for studies of HCV molecular virology and for studies of pathogenesis, protective immunity, and vaccine efficacy in vivo.

The role of viral infection in inducing variability in virus-free progeny in tomato

The effect of virus-host interactions on subsequent generations is poorly understood. The evaluation of the effects of viral infection on inheritance of quantitative traits in the progeny of infected plants and elucidation of a possible relationship between chiasma frequency in the infected plants and variability of traits in the progeny were investigated. The current study involved genotypes of four intraspecific hybrids of tomato (Solanum lycopersicum L.), their parental forms and two additional cultivars. Used as infection were the tobacco mosaic virus (TMV) and potato virus X (PVX). The consequences of the effect of viral infection were evaluated based on chromosome pairing in diakinesis and/or by examining quantitative and qualitative traits in the progeny of the infected tomato plants. Tomato plants infected with TMV + PVX were found to differ in chiasma frequency per pollen mother cell or per bivalent. Deviations have been observed for genotypes of both F(1) hybrids and cultivars. At the same time, differences in mean values of the traits under study have only been found for progeny populations (F(2)-F(4)) derived from virus-infected F(1) hybrids, but not in the case of progeny of the infected cultivars. The rate of recombinants combining traits of both parents increased significantly (2.22-8.24 times) in progeny populations of hybrids infected with TMV + PVX. The above suggests that the observed effects could be the result of modification of recombination frequencies that can be manifested in heterozygous hybrids and make small contributions to variability in cases of 'homozygous' tomato genotypes (i.e. cultivars).

Occurrence of Potato virus X on hybrid dock in Czech Republic

Hybrid dock of Uteush (Rumex patientia L. x Rumex tianschanicus A. Los., the family Polygonaceae) is a perspective high productive crop and in the last decade its farming area has continuously grown in Czech Republic. However, the introduction of this non-native perennial crop into a present plant production creates a new potential reservoir for some plant viruses. Also, the hybrid dock could become a host of currently uncommon or insignificant viruses. We screened two dock-farming localities situated in south-west and north-east part of the Czech Republic for the presence of potyviruses, potexviruses, and carlaviruses. In the south-west part of the country, we detected a high incidence of Potato virus X (PVX, the genus Potexvirus). In contrast, in the north-east part of the country we did not detect any dock plants infected with PVX. Next, two other viruses, Turnip yellow mosaic virus (TYMV) and Radish mosaic virus (RaMV) were mechanically inoculated and tested for their survival capacity and multiplication in the hybrid dock. Both viruses were detected 9 months after inoculation in the infected plants.

A chimeric plum pox virus shows reduced spread and cannot compete with its parental wild-type viruses in a mixed infection

The effect of a recombination event in the genomic 3' end on the biological properties and competitiveness of plum pox virus (PPV) was investigated. Therefore, a fragment spanning the coat protein (CP) coding region and a part of the 3' non-translated region of a non-aphid-transmissible strain of PPV (PPV-NAT) was replaced by the corresponding region of a PPV sour cherry isolate (PPV-SoC). The resulting chimera (PPV-NAT/SoC) caused severe symptoms in Nicotiana benthamiana, resembling those of PPV-NAT. In mixed infections with either of the parental viruses, the chimera PPV-NAT/SoC was less competitive. Labelling experiments with DsRed showed that PPV-NAT/SoC (PPV-NAT/SoC-red) moved more slowly from cell to cell than PPV-NAT (PPV-NAT-red). In mixed infections of PPV-NAT/SoC-red with a green fluorescent protein-expressing PPV-NAT (PPV-NAT-AgfpS), spatial separation of the viruses was observed. These data suggest that, in PPV infections, symptom severity and competitiveness are independent aspects and that spatial separation may contribute to the displacement of a recombinant virus.

Infection of human hepatocyte chimeric mouse with genetically engineered hepatitis C virus and its susceptibility to interferon

We developed a reverse genetics system of hepatitis C virus (HCV) genotypes 1a and 2a using infectious clones and human hepatocyte chimeric mice. We inoculated cell culture-produced genotype 2a (JFH-1) HCV intravenously. We also injected genotype 1a CV-H77C clone RNA intrahepatically. Mice inoculated with HCV by both procedures developed measurable and transmissible viremia. Interferon (IFN) alpha treatment resulted in greater reduction of genotype 2a HCV levels than genotype 1a, as seen in clinical practice. Genetically engineered HCV infection system should be useful for analysis of the mechanisms of resistance of HCV to IFN and other drugs.

Analysis of sugarcane mosaic virus resistance in maize in an isogenic dihybrid crossing scheme and implications for breeding potyvirus-resistant maize hybrids

The gene action of 2 sugarcane mosaic virus (SCMV) resistance loci in maize, Scmv1 and Scmv2, was evaluated for potyvirus resistance in an isogenic background. All 4 homozygous and 5 heterozygous isogenic genotypes were produced for introgressions of the resistant donor (FAP1360A) alleles at both loci into the susceptible parent (F7) genetic background using simple sequence repeat markers. For SCMV and maize dwarf mosaic virus (MDMV), virus symptoms appeared rapidly in the 3 homozygous genotypes, with susceptibility alleles fixed at 1 or both loci. Although the 9 isogenic genotypes revealed a high level of resistance to Zea mosaic virus (ZeMV), the same 3 homozygous genotypes were only partially resistant. This indicates that 1 resistance gene alone is not sufficient for complete resistance against SCMV, MDMV, and ZeMV. Scmv1 showed strong early and complete dominant gene action to SCMV, but it gradually became partially dominant. Scmv2 was not detected at the beginning, showing dominant gene action initially and additive gene action at later stages. Both genes interacted epistatically (for a high level of resistance, at least 1 resistance allele at each of both loci is required). This implies that double heterozygotes at the 2 loci are promising for producing SCMVresistant hybrids. Results are discussed with respect to prospects for isolation of SCMV and MDMV resistance genes.

Use of a novel chimeric mouse model with a functionally active human immune system to study human immunodeficiency virus type 1 infection

The goal of this study was to develop a small-animal model to study human immunodeficiency virus type 1 (HIV-1) pathogenesis in blood and primary and secondary lymphoid organs. Rag2(-/-)gamma(c)(-/-) mice that are neonatally injected with human CD34(+) cells develop a functional human immune system (HIS), with human hematopoietic cells being found in the thymuses, peripheral blood, spleens, and bone marrow of the animals (hereafter these animals are referred to as HIS-Rag2(-/-)gamma(c)(-/-) mice). HIS-Rag2(-/-)gamma(c)(-/-) mice were infected with small amounts of CCR5-tropic HIV-1. Viral replication and immunophenotypic changes in the human cells in peripheral blood and lymphoid organs were examined. The productive infection of human cells in peripheral blood, thymus and spleen tissue, and bone marrow was detected. Ratios of CD4(+) T cells to CD8(+) T cells in the infected animals declined. Although no specific anti-HIV-1 immune responses were detected, immunoglobulin M (IgM) and IgG antibodies to an unidentified fetal calf serum protein present in the virus preparation were found in the inoculated animals. Thus, we have shown that the HIS-Rag2(-/-)gamma(c)(-/-) mouse model can be used for infection with low doses of CCR5-tropic HIV-1, which is most commonly transmitted during primary infections. HIS-Rag2(-/-)gamma(c)(-/-) mice can serve as a small-animal model for investigating HIV-1 pathogenesis and testing potential HIV-1 therapies, and studies with this model may replace some long and costly studies with nonhuman primates.

Construction of a novel SHIV having an HIV-1-derived protease gene and its infection to rhesus macaques: a useful tool for in vivo efficacy tests of protease inhibitors

We generated a novel SHIV (termed SHIV-pr) that possesses the HIV-1-derived protease (PR) gene in the corresponding position in the SIVmac genome. SHIV-pr is replication-competent in human and monkey CD4(+) T lymphoid cell lines as well as rhesus macaque PBMCs. The viral growth of SHIV-pr was completely blocked in the presence of a peptide-analog PR inhibitor at the tissue culture level. When SHIV-pr was intravenously inoculated into two rhesus macaques, it resulted in a weak but long-lasting persistent infection in one monkey, whereas the infection of another was only temporary. To enhance the viral growth competence by adaptation, we then passaged the virus in vivo from a monkey up to the fourth generation. The initial peak values of plasma viral loads as well as the setpoint values increased generation by generation and reached those of a parental virus SIVmac. When a medication using the content of Kaletra capsule (a mixture of two PR inhibitors, lopinavir and ritonavir) was orally given to three SHIV-pr-infected monkeys for 4 weeks, plasma viral loads dropped to near or below the detection limit and quickly rebounded after the cessation of medication. The results suggest that SHIV-pr can be used to evaluate PR inhibitors using monkeys.

Tiered tests to assess the environmental risk of fitness changes in hybrids between transgenic crops and wild relatives: the example of virus resistant Brassica napus

Over the last 20 years, there has been much research aimed at improving environmental risk assessment of transgenic crops. Despite large amounts of data, decisions to allow or prohibit the release of transgenic crops remain confused and controversial. We argue that part of the reason for confusion is the lack of clear definitions of components of the environment that should be protected, and, as a consequence, there is no way to judge the relevance of data collected under the auspices of 'environmental risk assessment'. Although this criticism applies to most aspects of environmental risk assessment of transgenic crops, it is most pertinent to effects that might result from an increase in plant fitness, often referred to as increased weediness. Environmental risk assessment of weediness is regarded as complicated: an increase in the fitness of a transgenic plant compared with non-transgenic counterparts will be the result of an interaction between the altered plant phenotype and an enormous number of environmental variables. This has led to the idea that risk assessment of weediness needs to "understand" these interactions, with the implication that exhaustive data are required. Here we argue that environmental risk assessment of the weediness of transgenic plants need not be complicated. Analysis of the conditions that must be met for increased weediness to occur suggests a series of studies that starts with simple tests in the laboratory under "worst case" assumptions, and becomes increasingly complex and realistic should the simpler studies not indicate negligible risk with sufficient certainty. We illustrate how the approach might work for assessing the risks of increased weediness using the example of possible introgression of a gene for Turnip mosaic virus (TuMV) resistance from oilseed rape to certain wild Brassica species.

Application of functional genomics to the chimeric mouse model of HCV infection: optimization of microarray protocols and genomics analysis

BACKGROUND

Many model systems of human viral disease involve human-mouse chimeric tissue. One such system is the recently developed SCID-beige/Alb-uPA mouse model of hepatitis C virus (HCV) infection which involves a human-mouse chimeric liver. The use of functional genomics to study HCV infection in these chimeric tissues is complicated by the potential cross-hybridization of mouse mRNA on human oligonucleotide microarrays. To identify genes affected by mouse liver mRNA hybridization, mRNA from identical human liver samples labeled with either Cy3 or Cy5 was compared in the presence and absence of known amounts of mouse liver mRNA labeled in only one dye.

RESULTS

The results indicate that hybridization of mouse mRNA to the corresponding human gene probe on Agilent Human 22 K oligonucleotide microarray does occur. The number of genes affected by such cross-hybridization was subsequently reduced to approximately 300 genes both by increasing the hybridization temperature and using liver samples which contain at least 80% human tissue. In addition, Real Time quantitative RT-PCR using human specific probes was shown to be a valid method to verify the expression level in human cells of known cross-hybridizing genes.

CONCLUSION

The identification of genes affected by cross-hybridization of mouse liver RNA on human oligonucleotide microarrays makes it feasible to use functional genomics approaches to study the chimeric SCID-beige/Alb-uPA mouse model of HCV infection. This approach used to study cross-species hybridization on oligonucleotide microarrays can be adapted to other chimeric systems of viral disease to facilitate selective analysis of human gene expression.

Host-directed processing of Citrus exocortis viroid

Prolonged infection of tomato hybrid (Lycopersicon esculentum x Lycopersicon peruvianum) by Citrus exocortis viroid (CEVd) resulted in viroid-like enlarged structures, detected by gel electrophoresis. This population included two new enlarged variants or D-variants, D-87 and D-76, and three transient species or D-forms, D-38, D-40 and D-43. Sequence analyses exposed a locus near the terminal repeat region where major changes appeared consistently. In transmission tests to CEVd hosts, a variety of progeny populations were recovered, including progeny enlargements of and reversions to CEVd, as well as sequence fidelity to the inoculum. Transmission tests to citrus hosts of the genera Citrus, Poncirus or Fortunella were unsuccessful. The importance of host specificity to the recovery and processing of the various CEVd-related structures, as well as the temporal variability of progeny populations, was demonstrated.

VP5 and the N terminus of VP2 are not responsible for the different pathotype of serotype I and II infectious bursal disease virus

Two serotypes have been identified in infectious bursal disease virus (IBDV), a member of the family BIRNAVIRIDAE: A reverse genetics system was used for generation of chimeras in genome segment A of the two serotypes, in which the complete viral VP5 gene and 3' noncoding region (NCR), or parts thereof, were exchanged. The engineered viruses were characterized in vitro and in vivo in comparison to serotype I and II IBDV. Our results show that IBDV chimeras exhibit a different phenotype in cell culture compared to the wild-type viruses. In in vitro-cultivated bursal-derived cells, chimeric viruses infected B lymphocytes, as does serotype I IBDV. Surprisingly, serotype II virus was also able to infect in vitro-cultivated bursal cells, but these were neither B lymphocytes nor macrophages. After infection of susceptible chickens all chimeras replicated in the bursa of Fabricius (BF), and three chimeric viruses caused mild depletion of bursal cells. In contrast, after infection of chickens with a chimeric IBDV containing exchanged VP5 as well as 3'-NCR, no depletion was detectable. The serotype II strain did not replicate in the BF nor did it cause depletion of bursal cells. Thus, the origin of VP5 does not explain the different pathotype of IBDV serotype I and II.

Characterization of chimeric enzymes between caprine arthritis--encephalitis virus, maedi--visna virus and human immunodeficiency virus type 1 integrases expressed in Escherichia coli

In order to investigate the functions of the three putative lentiviral integrase (IN) protein domains on viral DNA specificity and target site selection, enzymatically active chimeric enzymes were constructed using the three wild-type IN proteins of caprine arthritis-encephalitis virus (CAEV), maedi-visna virus (MVV) and human immunodeficiency virus type 1 (HIV-1). The chimeric enzymes were expressed in Escherichia coli, purified by affinity chromatography and analysed in vitro for IN-specific endonuclease and integration activities on various DNA substrates. Of the 21 purified chimeric IN proteins constructed, 20 showed distinct site-specific cleavage activity with at least one substrate and six were able to catalyse an efficient integration reaction. Analysis of the chimeric IN proteins revealed that the central domain together with the C terminus determines the activity and substrate specificity of the enzyme. The N terminus appears to have no considerable influence. Furthermore, an efficient integration activity of CAEV wild-type IN was successfully demonstrated after detailed characterization of the reaction conditions that support optimal enzyme activities of CAEV IN. Also, under the same in vitro assay conditions, MVV and HIV-1 IN proteins exhibited endonuclease and integration activities, an indispensable prerequisite of domain-swapping experiments. Thus, the following report presents a detailed characterization of the activities of CAEV IN in vitro as well as the analysis of functional chimeric lentiviral IN proteins.