Molecular characterization of CD28 and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) of woodchuck (Marmota monax)

Identification of antibodies cross-reactive with woodchuck immune cells and activation of virus-specific and global cytotoxic T cell responses by anti-PD-1 and anti-PD-L1 in experimental chronic hepatitis B and persistent occult hepadnaviral infection

Woodchuck (Marmota monax) infected with woodchuck hepatitis virus (WHV) is the most pathogenically compatible naturally occurring model of human hepatitis B virus (HBV) infection, chronic hepatitis B, and HBV-induced hepatocellular carcinoma. This system plays a crucial role in discovery and preclinical evaluation of anti-HBV therapies. Its utilization remains tempered by the relatively narrow range of validated immunologic and molecular tools. We evaluated commercial antibodies against immune cell phenotypic markers and T cell molecules for cross-reactivity with woodchuck antigenic equivalents. The confirmed antibodies against programed cell death protein-1 (PD-1) and its ligand (PD-L1) were examined for ex vivo ability to activate WHV-specific, global and bystander cytotoxic T cells (CTLs) in chronic hepatitis and asymptomatic infection persisting after self-resolved acute hepatitis. Examination of 65 antibodies led to identification or confirmation of 23 recognizing woodchuck T, regulatory T, B and natural killer cells, T cell-associated PD-1, PD-L1, CTLA-4 and TIM-3 molecules, CD25 and CD69 markers of T cell activation, and interferon gamma (IFNγ). Antibodies against woodchuck PD-1 and PD-L1 triggered in vitro highly individualized WHV-specific and global activation of CTLs in both chronic hepatitis and persistent occult infection. WHV-specific CTLs were more robustly augmented by anti-PD-1 than by anti-PD-L1 in chronic hepatitis, while global IFNγ-positive CTL response was significantly suppressed in chronic hepatitis compared to persistent occult infection. Anti-PD-1 and anti-PD-L1 also occasionally activated CTLs to specificities other than those tested suggesting their potency to trigger side effects. This was particularly apparent when T cells from chronic hepatitis were treated with anti-PD-L1. The current findings indicate that inhibition of the PD-1/PD-L1 pathway could reactivate virus-specific and global T cell responses in both chronic hepatitis and asymptomatic persistent infection. They suggest a mechanism of potential reactivation of clinically silent infection during anti-PD-1/PD-L1 treatment and indicate that this therapy may also subdue occult HBV infection.

The Woodchuck, a Nonprimate Model for Immunopathogenesis and Therapeutic Immunomodulation in Chronic Hepatitis B Virus Infection

The woodchuck hepatitis virus (WHV) and its host, the eastern woodchuck, is a very valuable model system for hepatitis B virus infection. Many aspects of WHV replication and pathogenesis resemble acute and chronic hepatitis B infection in patients. Since the establishment of immunological tools, woodchucks were used to develop new therapeutic vaccines and immunomodulatory approaches to treat chronic hepadnaviral infections. Combination therapy of nucleos(t)ide analogs, with prime-boost vaccination and triple therapy, including immunomodulatory strategies by blocking the interaction of the programmed death-1 (PD-1) receptor with its ligand inducing a potent T-cell response in chronic WHV carrier woodchucks, suppression of viral replication, and complete elimination of the virus in 30% of the animals. Both strategies may be used for future therapies in patients with chronic hepatitis B.

Therapeutic vaccination and immunomodulation in the treatment of chronic hepatitis B: preclinical studies in the woodchuck

Infection with hepatitis B virus (HBV) may lead to subclinical, acute or chronic hepatitis. In the prevaccination era, HBV infections were endemic due to frequent mother to child transmission in large regions of the world. However, there are still estimated 240 million chronic HBV carriers today and ca. 620,000 patients die per year due to HBV-related liver diseases. Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to satisfactory results. Induction of HBV-specific T cells by therapeutic vaccination or immunomodulation may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients with or without therapeutic reduction of viral load did not result in effective immune control of HBV infection, suggesting that combination of antiviral treatment with new formulations of therapeutic vaccines is needed. The woodchuck (Marmota monax) and its HBV-like woodchuck hepatitis virus are a useful preclinical animal model for developing new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments using nucleos(t)ide analogues, with prime-boost vaccination using DNA vaccines, new hepadnaviral antigens or recombinant adenoviral vectors were tested in the woodchuck model. In this review, we summarize these encouraging results obtained with these therapeutic vaccines. In addition, we present potential innovations in immunostimulatory strategies by blocking the interaction of the inhibitory programmed death receptor 1 with its ligand in this animal model.

Prokaryotic expression of woodchuck cytotoxic T lymphocyte antigen 4 (wCTLA-4) and preparation of polyclonal antibody to wCTLA-4

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an inhibitory T cell receptor predominately expressed on activated T cells and plays an important role in regulation of specific T cell responses to viral infection. The woodchuck model is an informative animal model for hepatitis B virus (HBV) infection. In this study, the extracellular region of woodchuck CTLA-4 (wCTLA-4) was cloned and the fusion protein of GST-wCTLA-4 was expressed and purified. Polyclonal antibody against GST-wCTLA-4 (anti-GST-wCTLA-4) was prepared. The full length wCTLA-4 protein expressed in transfected baby hamster kidney cells was detected by anti-GST-wCTLA-4 in western blot analysis and immunofluorescence staining. Anti-GST-wCTLA-4 provides a useful tool to study the role of CTLA-4 in T-cell response in the woodchuck model. Further, the blocking of CTLA-4 with anti-GST-wCTLA-4, as a novel therapy approach for chronic hepatitis B virus infection, could be studied in woodchuck model now.

Cross-species hybridization of woodchuck hepatitis viral infection-induced woodchuck hepatocellular carcinoma using human, rat and mouse oligonucleotide microarrays

BACKGROUND AND AIM

We aimed to evaluate the transcriptional characteristics of viral infection-induced woodchuck hepatocellular carcinoma (HCC), to compare the use of human, rat and mouse gene arrays for cross-species hybridization, and to look into gene expression profiles in woodchuck HCC by the combined use of these arrays.

METHODS

Commercially available human, rat and mouse oligonucleotide microarrays were used to determine the gene expression profiles on the same woodchuck liver samples. Differentially expressed genes between HCC and the surrounding hepatic tissues found in the arrays were selected for quantitative reverse transcription polymerase chain reaction.

RESULTS

Despite the difference in the number of the probes from each array, the percentage of genes that were detectable was similar. Stringent microarray data analysis using both supervised and unsupervised methods identified 281 differentially expressed genes via the human array with a false discovery rate (FDR) of 0.99%, 107 genes via the rat array with an FDR of 1.85% and 78 genes via the mouse array with an FDR of 7.41%. Eleven genes were differentially changed in all three arrays that include the upregulation of NPM1, H2AFZ, EEF1G, HNRPAB, RPS18, EIF5, CKS2, ARIH1, RPS12 and RPS10, and the downregulation of EGR1. The quantitative reverse transcription polymerase chain reaction with woodchuck-specific primers confirmed the reliability of the microarray results.

CONCLUSION

This study further demonstrated the utility of cross-species hybridization of microarrays on woodchuck HCC. A combined use of three types of arrays identified more differential genes in HCC than individual arrays with the human array providing the richest information among the three arrays used.

Immunomodulation as an option for the treatment of chronic hepatitis B virus infection: preclinical studies in the woodchuck model

New therapeutic approaches for chronic hepatitis B virus infection based on immunomodulation are now under investigation. The woodchuck model for hepatitis B virus infection has emerged as a useful animal model for the evaluation of such approaches, after developing necessary assays and reagents for immunologic studies in this model. Conventional and novel vaccines such as DNA vaccines were tested in woodchucks for their ability to induce protective immune responses against challenge infection with the woodchuck hepatitis virus (WHV). Furthermore, immunotherapeutic approaches for the control of chronic hepadnaviral infection were evaluated in woodchucks. Immunizations with WHV proteins and DNA vaccines led to the development of antibodies to the WHV surface antigen and to a significant decrease of viral load in chronically WHV-infected woodchucks. Viral vector-mediated gene transfer was explored for the delivery of antiviral cytokines IFN-alpha in woodchucks and resulted in the decrease of viral replication. It is now generally accepted that a combination of antiviral treatment and immunization will be necessary to achieve successful immunomodulation with a long-term control of chronic hepatitis B virus infection.

Genetic analysis and functional evaluation of the C/T(-318) and A/G(-1661) polymorphisms of the CTLA-4 gene in patients affected with Graves' disease

In this study, we evaluated the A/G(-1661), C/T(-318), A/G49 and A/G6230 single nucleotide polymorphisms (SNPs) of the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene for association with Graves' disease (GD) in 126 Russian simplex families. The conditional TDT analysis revealed significant overtransmission of the A(-1661)G(-318) haplotype (P = 0.033) and undertransmission of the GT haplotype (P = 0.0043) from parents homozygous for both +49 and +6230 polymorphisms. Parents homozygous for both (-1661) and (-318) markers significantly overtransmitted the G49G6230 haplotype (P = 0.0013) and undertransmitted the AG haplotype (P = 0.035) to affected offspring. This suggests in favor of the independent genetic effects of the 3' and 5'ends of CTLA-4 in conferring the susceptibility to GD. Both SNPs located at the 5' untranslated region of CTLA-4 were functionally analyzed using the luciferase reporter assay. We observed differential activation of the C/T(-318) promoter variant when Jurkat T cells and HeLa cells were cotransfected with a plasmid expressing lymphoid enhancing factor 1 (LEF1) and various CTLA-4 promoter constructs. The (-318) SNP modifies a putative binding site for LEF1 so that it alters the stimulating effect of LEF1 on the expression ability of the CTLA-4 promoter. The (-1661) dimorphism modifies a potential binding site for myocyte enhancer factor 2 (MEF2). No significant correlation between the (-1661) SNP and MEF2 activity in cotransfection experiments was found. Observed data help for further understanding a functional role of CTLA-4 promoter polymorphisms in the pathogenic mechanism of GD.

Immunization with the gene expressing woodchuck hepatitis virus nucleocapsid protein fused to cytotoxic-T-lymphocyte-associated antigen 4 leads to enhanced specific immune responses in mice and woodchucks

A number of options are available to modify and improve DNA vaccines. An interesting approach to improve DNA vaccines is to fuse bioactive domains, like cytotoxic-T-lymphocyte-associated protein 4 (CTLA-4), to an antigen. Such fusion antigens are expressed in vivo and directed to immune cells by the specific bioactive domain and therefore possess great potential to induce and modulate antigen-specific immune responses. In the present study, we tested this new approach for immunomodulation against hepadnavirus infection in the woodchuck model. Plasmids expressing the nucleocapsid protein (WHcAg) and e antigen (WHeAg) of woodchuck hepatitis virus (WHV) alone or in fusion to the extracellular domain of woodchuck CTLA-4 and CD28 were constructed. Immunizations of mice with plasmids expressing WHcAg or WHeAg led to a specific immunoglobulin G2a (IgG2a)-dominant antibody response. In contrast, fusions of WHcAg to CTLA-4 and CD28 induced a specific antibody response with comparable levels of IgG1 and IgG2a. Furthermore, the specific IgG1 response to WHcAg/WHeAg developed immediately after a single immunization with the CTLA-4-WHcAg fusion. Woodchucks were immunized with plasmids expressing WHeAg or the CTLA-4-WHcAg fusion and subsequently challenged with WHV. CTLA-4-WHcAg showed an improved efficacy in induction of protective immune responses to WHV. In particular, the anti-WHsAg antibody response developed earlier after challenge in woodchucks that received immunizations with CTLA-4-WHcAg, consistent with the hypothesis that anti-WHs response is dependent on a Th cell response to WHcAg. In conclusion, the use of fusion genes represents a generally applicable strategy to improve DNA vaccination.