Intrahepatic regulatory T cells are phenotypically distinct from their peripheral counterparts in chronic HBV patients

The Role of CTLA-4 in T Cell Exhaustion in Chronic Hepatitis B Virus Infection

Patients with chronic hepatitis B (CHB) gradually develop T cell exhaustion, and the inhibitory receptor molecule, cytotoxic T-lymphocyte antigen-4 (CTLA-4), may play a role in this phenomenon. This systematic review investigates the role of CTLA-4 in the development of T cell exhaustion in CHB. A systematic literature search was conducted on PubMed and Embase on 31 March 2023 to identify relevant studies. Fifteen studies were included in this review. A majority of the studies investigating CD8⁺ T cells demonstrated increased expression of CTLA-4 in CHB patients, though one study found this only in HBeAg-positive patients. Three out of four studies investigating the expression of CTLA-4 on CD4⁺ T cells found upregulation of CTLA-4. Several studies showed constitutive expression of CLTA-4 on CD4⁺ regulatory T cells. CTLA-4 blockade resulted in heterogeneous responses for all T cell types, as it resulted in increased T cell proliferation and/or cytokine production in some studies, while other studies found this only when combining blockade of CTLA-4 with other inhibitory receptors. Although mounting evidence supports a role of CTLA-4 in T cell exhaustion, there is still insufficient documentation to describe the expression and exact role of CTLA-4 in T cell exhaustion in CHB.

Immune checkpoints on T and NK cells in the context of HBV infection: Landscape, pathophysiology and therapeutic exploitation

In hepatitis B virus (HBV) infection, the interplay between the virus and the host immune system is crucial in determining the pathogenesis of the disease. Patients who fail to mount a sufficient and sustained anti-viral immune response develop chronic hepatitis B (CHB). T cells and natural killer (NK) cells play decisive role in viral clearance, but they are defective in chronic HBV infection. The activation of immune cells is tightly controlled by a combination of activating and inhibitory receptors, called immune checkpoints (ICs), allowing the maintenance of immune homeostasis. Chronic exposure to viral antigens and the subsequent dysregulation of ICs actively contribute to the exhaustion of effector cells and viral persistence. The present review aims to summarize the function of various ICs and their expression in T lymphocytes and NK cells in the course of HBV infection as well as the use of immunotherapeutic strategies targeting ICs in chronic HBV infection.

Critical role of TLR activation in viral replication, persistence, and pathogenicity of Theiler's virus

Theiler's murine encephalomyelitis virus (TMEV) establishes persistent viral infections in the central nervous system and induces chronic inflammatory demyelinating disease in susceptible mice. TMEV infects dendritic cells, macrophages, B cells, and glial cells. The state of TLR activation in the host plays a critical role in initial viral replication and persistence. The further activation of TLRs enhances viral replication and persistence, leading to the pathogenicity of TMEV-induced demyelinating disease. Various cytokines are produced via TLRs, and MDA-5 signals linked with NF-κB activation following TMEV infection. In turn, these signals further amplify TMEV replication and the persistence of virus-infected cells. The signals further elevate cytokine production, promoting the development of Th17 responses and preventing cellular apoptosis, which enables viral persistence. Excessive levels of cytokines, particularly IL-6 and IL-1β, facilitate the generation of pathogenic Th17 immune responses to viral antigens and autoantigens, leading to TMEV-induced demyelinating disease. These cytokines, together with TLR2 may prematurely generate functionally deficient CD25-FoxP3+ CD4⁺ T cells, which are subsequently converted to Th17 cells. Furthermore, IL-6 and IL-17 synergistically inhibit the apoptosis of virus-infected cells and the cytolytic function of CD8+ T lymphocytes, prolonging the survival of virus-infected cells. The inhibition of apoptosis leads to the persistent activation of NF-κB and TLRs, which continuously provides an environment of excessive cytokines and consequently promotes autoimmune responses. Persistent or repeated infections of other viruses such as COVID-19 may result in similar continuous TLR activation and cytokine production, leading to autoimmune diseases.

Heterogeneity of immune control in chronic hepatitis B virus infection: Clinical implications on immunity with interferon-α treatment and retreatment

Hepatitis B virus (HBV) infection is a global public health issue. Interferon-α (IFN-α) treatment has been used to treat hepatitis B for over 20 years, but fewer than 5% of Asians receiving IFN-α treatment achieve functional cure. Thus, IFN-α retreatment has been introduced to enhance antiviral function. In recent years, immune-related studies have found that the complex interactions between immune cells and cytokines could modulate immune response networks, in-cluding both innate and adaptive immunity, triggering immune responses that control HBV replication. However, heterogeneity of the immune system to control HBV infection, particularly HBV-specific CD8⁺ T cell heterogeneity, has consequ-ential effects on T cell-based immunotherapy for treating HBV infection. Altogether, the host’s genetic variants, negative-feedback regulators and HBV components affecting the immune system's ability to control HBV. In this study, we reviewed the literature on potential immune mechanisms affecting the immune control of HBV and the clinical effects of IFN-α treatment and retreatment.

Peripheral Immune Cells Exhaustion and Functional Impairment in Patients With Chronic Hepatitis B

After infection of hepatitis B virus (HBV), the virus induces a variety of immune disorders in the host, leading to immune escape and, finally, the chronicity of the disease. This study investigated immune cell defects and functional impairment in patients with chronic hepatitis B (CHB). We analyzed the percentage, function, and phenotypes of various immune cell subpopulations in the peripheral blood along with the concentrations of cytokines in the plasma. We compared the results between patients with CHB and healthy individuals. It was found that in patients with CHB, the cell function was impaired and, there was increased expression of inhibitory receptors, such as NKG2A and PD-1 in both NK and T cells. The impairment of function was mainly in cytokine secretion, and the cytotoxicity was not significantly diminished. We also found that the proportion of dendritic cells (DC) decreased and regulatory B cells (Breg) increased in CHB. In addition, the Breg cells were negatively correlated with T cell cytokine and positively correlated with ALT and HBV viral load. Taken together, various disorders and functional impairments were found in the immune cells of peripheral blood in CHB patients, especially NK and T cells. These cells showed exhaustion and the increase of regulatory B cells may be one of the reasons for this phenomenon.

Excessive Innate Immunity Steers Pathogenic Adaptive Immunity in the Development of Theiler's Virus-Induced Demyelinating Disease

Several virus-induced models were used to study the underlying mechanisms of multiple sclerosis (MS). The infection of susceptible mice with Theiler’s murine encephalomyelitis virus (TMEV) establishes persistent viral infections and induces chronic inflammatory demyelinating disease. In this review, the innate and adaptive immune responses to TMEV are discussed to better understand the pathogenic mechanisms of viral infections. Professional (dendritic cells (DCs), macrophages, and B cells) and non-professional (microglia, astrocytes, and oligodendrocytes) antigen-presenting cells (APCs) are the major cell populations permissive to viral infection and involved in cytokine production. The levels of viral loads and cytokine production in the APCs correspond to the degrees of susceptibility of the mice to the TMEV-induced demyelinating diseases. TMEV infection leads to the activation of cytokine production via TLRs and MDA-5 coupled with NF-κB activation, which is required for TMEV replication. These activation signals further amplify the cytokine production and viral loads, promote the differentiation of pathogenic Th17 responses, and prevent cellular apoptosis, enabling viral persistence. Among the many chemokines and cytokines induced after viral infection, IFN α/β plays an essential role in the downstream expression of costimulatory molecules in APCs. The excessive levels of cytokine production after viral infection facilitate the pathogenesis of TMEV-induced demyelinating disease. In particular, IL-6 and IL-1β play critical roles in the development of pathogenic Th17 responses to viral antigens and autoantigens. These cytokines, together with TLR2, may preferentially generate deficient FoxP3⁺CD25^- regulatory cells converting to Th17. These cytokines also inhibit the apoptosis of TMEV-infected cells and cytolytic function of CD8⁺ T lymphocytes (CTLs) and prolong the survival of B cells reactive to viral and self-antigens, which preferentially stimulate Th17 responses.

Rapid Expansion of Virus-Specific CD4+ T Cell Types in the CNS of Susceptible Mice Infected with Theiler's Virus

The infection of susceptible mice with Theiler's murine encephalomyelitis virus (TMEV) induces a T cell-mediated demyelinating disease. This system has been studied as a relevant infection model for multiple sclerosis (MS). Therefore, defining the type of T cell responses and their functions is critically important for understanding the relevant pathogenic mechanisms. In this study, we adoptively transferred naive VP2-specific TCR-Tg CD4⁺ T cells into syngeneic susceptible SJL mice and monitored the development of the disease and the activation and proliferation of CD4⁺ T cells during the early stages of viral infection. The preexisting VP2-specific naive CD4⁺ T cells promoted the pathogenesis of the disease in a dose-dependent manner. The transferred VP2-specific CD4⁺ T cells proliferated rapidly in the CNS starting at 2-3 dpi. High levels of FoxP3⁺CD4⁺ T cells were found in the CNS early in viral infection (3 dpi) and persisted throughout the infection. Activated VP2-specific FoxP3⁺CD4⁺ T cells inhibited the production of IFN-γ, but not IL-17, via the same VP2-specific CD4⁺ T cells without interfering in proliferation. Thus, the early presence of regulatory T cells in the CNS with viral infection may favor the induction of pathogenic Th17 cells over protective Th1 cells in susceptible mice, thereby establishing the pathogenesis of virus-induced demyelinating disease.

Circulating CTLA-4 levels and CTLA4 polymorphisms associate with disease condition and progression and hepatocellular carcinoma patients' survival in chronic hepatitis B virus infection

BACKGROUND

CTLA-4 is involved in the immune dysfunction of hepatitis B virus (HBV) infection and hepatocellular carcinoma (HCC). This study analyzed the association of circulating CTLA-4 levels and CTLA4 polymorphisms with disease condition and progression in chronic HBV infection.

METHODS

Serum CTLA-4 levels and CTLA4 rs231775 and rs5742909 polymorphisms were determined in patients with various HBV-related diseases [53 asymptomatic HBV carrier status (ASC), 147 chronic hepatitis, 130 cirrhosis and 102 HCC] and nearly a 10-year follow-up.

RESULTS

Serum CTLA-4 levels were stepwisely increased from ASC, chronic hepatitis, cirrhosis to HCC and independently associated with HCC (OR 2.628, P < 0.001). HCC patients had lower frequencies of rs231775 genotype GA, genotype AA and allele A than ASC, chronic hepatitis and cirrhosis patients. Rs231775 genotype GG was independently associated with HCC (OR 2.324, P = 0.010) and higher CTLA-4 levels in patients with HBV infection. In the follow-up, higher baseline CTLA-4 levels and CTLA4 rs231775 genotype GG significantly associated with disease progression from chronic hepatitis to cirrhosis (OR 2.561, P = 0.011 and OR 2.799, P = 0.015, respectively) or from cirrhosis to HCC (OR 2.673, P = 0.008 and OR 2.097, P = 0.023, respectively) and with a shorter overall survival in HCC patients (HR 0.317, P = 0.018 and HR 0.682, P = 0.026, respectively). Rs5742909 had no significant association with CTLA-4 levels and disease progression.

CONCLUSION

CTLA-4 levels and CTLA4 rs231775 polymorphism associate with the disease condition and progression and HCC development in chronic HBV infection and their determination may be used for monitoring disease progression and predicting patient prognosis.

Checkpoint Inhibitors and Therapeutic Vaccines for the Treatment of Chronic HBV Infection

Treatment of chronic hepatitis B virus (HBV) infection is highly effective in suppressing viral replication, but complete cure is rarely achieved. In recent years, substantial progress has been made in the development of immunotherapy to treat cancer. Applying these therapies to improve the management of chronic HBV infection is now being attempted, and has become an area of active research. Immunotherapy with vaccines and checkpoint inhibitors can boost T cell functions in vitro, and therefore may be used to reinvigorate the impaired HBV-specific T cell response. However, whether these approaches will suffice and restore antiviral T cell immunity to induce long-term HBV control remains an open question. Recent efforts have begun to describe the phenotype and function of HBV-specific T cells on the single epitope level. An improved understanding of differing T cell specificities and their contribution to HBV control will be instrumental for advancement of the field. In this review, we outline correlates of successful versus inadequate T cell responses to HBV, and discuss the rationale behind therapeutic vaccines and checkpoint inhibitors for the treatment of chronic HBV infection.

The effects of nucleoside/nucleotide analogues on host immune cells: the baseline for future immune therapy for HBV?

HBV is a non-cytopathic virus and the progression of liver fibrosis is attributed to the host immune response. Complete suppression of viral replication using nucleotide or nucleoside analogues (NUCs) can prevent most complications related to chronic HBV infection. Unfortunately, antiviral treatment has to be administered lifelong to the majority of patients as HBV persists in the hepatocytes. However, although NUCs are very frequently administered in clinical practice, their effects on vital parts of the host immune response to HBV are not well established. In this review we summarize the currently available data gathered from longitudinal studies that investigated treatment-associated alterations of HBV-specific CD4⁺ and CD8⁺ T-cells, regulatory T-cells and natural killer (NK) cells. These observations are important, as they can guide the design of studies that investigate the efficacy of new immune therapeutic agents. Novel experimental compounds will likely be added to ongoing NUC treatment, which leads to a functional cure in only a small minority of patients.

Liver sampling: a vital window into HBV pathogenesis on the path to functional cure

In order to optimally refine the multiple emerging drug targets for hepatitis B virus (HBV), it is vital to evaluate virological and immunological changes at the site of infection. Traditionally liver biopsy has been the mainstay of HBV disease assessment, but with the emergence of non-invasive markers of liver fibrosis, there has been a move away from tissue sampling. Here we argue that liver biopsy remains an important tool, not only for the clinical assessment of HBV but also for research progress and evaluation of novel agents. The importance of liver sampling has been underscored by recent findings of specialised subsets of tissue-resident immune subsets capable of efficient pathogen surveillance, compartmentalised in the liver and not sampled in the blood. Importantly, the assessment of virological parameters, such as cccDNA quantitation, also requires access to liver tissue. We discuss strategies to maximise information obtained from the site of infection and disease pathology. Fine needle aspirates of the liver may allow longitudinal sampling of the local virus/host landscape. The careful utilisation of liver tissue and aspirates in conjunction with blood will provide critical information in the assessment of new therapeutics for the functional cure of HBV.

Hepatitis B virus infection and the immune response: The big questions

Clinical events and the host immune response during hepatitis B virus (HBV) infection are intricately linked. Despite decades of research, important questions concerning the immunopathogenesis of chronic HBV infection remain unanswered. For example, it is unclear which immune parameters facilitate persistence, and if HBV can be completely cleared from the human liver. Recent technological breakthroughs now allow researchers to address these seemingly basic, but essential questions surrounding HBV immunity. It will be important to better define the molecular underpinnings of immune cell function and dysfunction during chronic disease and in controlled infection, with particular focus on the liver, as little information is available on the intrahepatic compartment. In the near future, it may be possible to solve some of the controversy surrounding the immune responses to HBV, and establish the features of both the innate and adaptive arms of the immune system required to achieve sustained control of HBV infection.

Regulatory T-cells promote hepatitis B virus infection and hepatocellular carcinoma progression

Regulatory T-cells (Tregs), known for their immune suppressive function, have been reported in higher numbers, with activated phenotypes and greater potency, in hepatitis B virus (HBV)-related liver diseases than in normal conditions. The numbers, phenotypes, and function of intrahepatic and/or tumor-infiltrating Tregs in HBV-related liver diseases also differ from those of Tregs in the peripheral blood. By inhibiting the function of effector T-cells (Teffs), Tregs play a substantial role in the formation and maintenance of the liver's suppressive microenvironment, which might account for the progression of HBV-related hepatitis and hepatocellular carcinoma (HCC). In acute hepatitis B virus infection, Tregs can safeguard the liver from damage at the cost of prolonged antiviral processes, which results in chronic HBV infection in the liver. Furthermore, Tregs play a role in the development of cirrhosis, the transformation of cirrhosis to HCC, and the progression and metastasis of HCC. Higher levels of Tregs in the peripheral blood and/or tumor sites signify a poorer prognosis in HBV-related liver conditions, and observational data from mouse models and human patients support the theory that depleting Tregs may be therapeutic in HBV-related liver diseases by inducing antiviral and antitumor immunity.

Intrahepatic mRNA Expression of FAS, FASL, and FOXP3 Genes Is Associated with the Pathophysiology of Chronic HCV Infection

This study aimed to evaluate the relative mRNA expression of Fas receptor (FAS), Fas ligand (FASL), and forkhead box protein 3 (FOXP3) in liver biopsy specimens obtained from patients with viral and non-viral chronic hepatitis and correlate their expression with the fibrosis stage. A total of 51 liver biopsy specimens obtained from HBV (n = 6), HCV (n = 28), and non-viral hepatic disease (NVHD) (n = 9) patients and from individuals with normal liver histology (n = 8) (control—CT) were analyzed. Quantifications of the target genes were assessed using qPCR, and liver biopsies according to the METAVIR classification. The mRNA expression levels of FAS and FASL were lower in the CT group compared to the groups of patients. The increase in the mRNA expression of FAS and FASL was correlated with higher levels of inflammation and disease progression, followed by a decline in tissues with cirrhosis, and it was also associated with increased levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Higher mRNA expression of FOXP3 was observed in the HCV and NVHD groups, with the peak observed among patients with cirrhosis. The increased FOXP3 mRNA expression was positively correlated with increased FAS and FASL mRNA expression and the AST and ALT levels in all patients. Conclusions: These results suggest that regardless of the cause, the course of chronic liver disease may be modulated by the analyzed genes and correlated with an increase in regulatory T cells during the liver damage followed by hepatocyte destruction by Fas/FasL system and subsequent non specific lymphocytic infiltrate accumulation.

Intrahepatic Toll-Like Receptor 3 in Chronic HBV Infection Subjects: Asymptomatic Carriers, Active Chronic Hepatitis, Cirrhosis, and Hepatocellular Carcinoma

BACKGROUND

The entire disease spectrum of chronic HBV infection (CHB) includes asymptomatic carriers (AC), active chronic hepatitis (ACH), cirrhosis (Cir), and hepatocellular carcinoma (HCC). Previous study have demonstrated that the costimulation profiles from the livers of patients influenced immune responses and played various immunological roles in AC, ACH, Cir, and HCC. In addition, activation of TLR3 signaling in the liver may contribute to HBV clearance, although some HBV components are able to block TLR3 signaling and counteract HBV clearance through positive or negative feedback loops. Previous clinical studies have demonstrated that different TLR3 expressions are present in ACH patients, but no studies investigated the expression of TLR3 proteins in the livers of patients with AC, Cir, or HCC.

OBJECTIVES

This study investigated intrahepatic TLR3 expression throughout the entire disease spectrum of CHB patients and assessed the interrelations between TLR3 and costimulation proteins.

PATIENTS AND METHODS

Patients with ACH, Cir, HCC, and AC and healthy donors (HD) were recruited. TLR3 expression in the livers of patients were investigated using western blot analysis and immunohistochemistry. Correlations between TLR3 and costimulation proteins, including CD80, CD86, CD83, CD28, CTLA-4, CD40, and ICAM-1, were assessed.

RESULTS

The TLR3 protein in the ACH group tended toward reduction although the P Value of the comparison between the ACH group and HD group was not statistically significant. The TLR3 levels in the HCC, AC, and Cir groups were higher than those in the HD and ACH groups. TLR3 was not interrelated with all costimulation proteins in the DCs and T cells in all five groups. No group presented any interrelation between TLR3 and CD40, except the AC group.

CONCLUSIONS

The AC, HCC, and Cir patients displayed increased levels of the intrahepatic TLR3 protein compared to the HD and AC patients. Both activation of TLR3/INF-β signaling and inhibition of TLR3/INF-β signaling by HBV components influenced TLR3 expression in the AC, ACH, Cir, and HCC subjects. However, TLR3 signaling did not influence the expression of costimulatory protein in the ACH, Cir, or HCC patients. TLR3/ IFN-β signaling did influence immune responses in the livers of CHB patients.

Hepatitis B Virus--Specific and Global T-Cell Dysfunction in Chronic Hepatitis B

BACKGROUND & AIMS

T cells play a critical role in viral infection. We examined whether T-cell effector and regulatory responses can define clinical stages of chronic hepatitis B (CHB).

METHODS

We enrolled 200 adults with CHB who participated in the National Institutes of Health-supported Hepatitis B Research Network from 2011 through 2013 and 20 uninfected individuals (controls). Peripheral blood lymphocytes from these subjects were analyzed for T-cell responses (proliferation and production of interferon gamma and interleukin 10) to overlapping hepatitis B virus (HBV) peptides (preS, S, preC, core, and reverse transcriptase), influenza matrix peptides, and lipopolysaccharide. T-cell expression of regulatory markers FOXP3, programmed death-1, and cytotoxic T lymphocyte-associated antigen-4 was examined by flow cytometry. Immune measures were compared with clinical parameters, including physician-defined immune-active, immune-tolerant, or inactive CHB phenotypes, in a blinded fashion.

RESULTS

Compared with controls, patients with CHB had weak T-cell proliferative, interferon gamma, and interleukin 10 responses to HBV, with increased frequency of circulating FOXP3(+)CD127(-) regulatory T cells and CD4(+) T-cell expression of programmed death-1 and cytotoxic T lymphocyte-associated antigen-4. T-cell measures did not clearly distinguish between clinical CHB phenotypes, although the HBV core-specific T-cell response was weaker in hepatitis B e antigen (HBeAg)(+) than HBeAg(-) patients (percent responders: 3% vs 23%; P = .00008). Although in vitro blockade of programmed death-1 or cytotoxic T lymphocyte-associated antigen-4 increased T-cell responses to HBV, the effect was weaker in HBeAg(+) than HBeAg(-) patients. Furthermore, T-cell responses to influenza and lipopolysaccharide were weaker in CHB patients than controls.

CONCLUSIONS

HBV persists with virus-specific and global T-cell dysfunction mediated by multiple regulatory mechanisms, including circulating HBeAg, but without distinct T-cell-based immune signatures for clinical phenotypes. These findings suggest additional T-cell-independent or regulatory mechanisms of CHB pathogenesis that warrant further investigation.

The frequency and skewed T-cell receptor beta-chain variable patterns of peripheral CD4(+)CD25(+) regulatory T-cells are associated with hepatitis B e antigen seroconversion of chronic hepatitis B patients during antiviral treatment

The frequency and T-cell receptor beta-chain variable (TCRBV) patterns of peripheral CD4(+)CD25(+) regulatory T-cells (Tregs) are ambiguously altered in chronic hepatitis B (CHB) patients following tenofovir disoproxil fumarate (TDF) treatment. Moreover, the clinical significance of these parameters in relation to hepatitis B e antigen (HBeAg) seroconversion (SC) is largely unknown. In this study, the circulation of Tregs in HBeAg-positive CHB patients was determined by flow cytometry, and the molecular profiles of frequent TCRBV patterns of Tregs were analyzed using a gene melting spectral pattern. The parameters, such as Treg frequency, the number of skewed TCRBV patterns, hepatitis B virus (HBV) DNA levels, and alanine aminotransferase (ALT) levels, were analyzed by comparing their associations in seroconverting and non-seroconverting patients following TDF treatment. The Treg frequency was significantly correlated with the ALT level in seroconverting but not in non-seroconverting patients. Similarly, skewed TCRBV patterns were remarkably associated with HBV DNA levels in the SC group. Six TCRBV families (BV3, BV11, BV12, BV14, BV20, and BV24) were more prevalent than other TCRBV members in seroconverting patients pretreated with TDF, while BV12, BV15, and BV22 were predominant in non-seroconverting patients during TDF treatment. Taken together, the preferential TCRBV patterns may be associated with immune responses related to SC. The dynamic frequency and skewed TCRBV patterns of peripheral Tregs could contribute to predicting SC in CHB patients. Moreover, the conserved TCRBV complementarity-determining region (CDR3) motif may be targeted to develop personalized immunotherapy for CHB patients.

T-cell exhaustion in chronic hepatitis B infection: current knowledge and clinical significance

Hepatitis B virus (HBV) infection is the major cause of inflammatory liver disease, of which the clinical recovery and effective anti-viral therapy is associated with the sustained viral control of effector T cells. In humans, chronic HBV infection often shows weak or absent virus-specific T-cell reactivity, which is described as the ‘exhaustion' state characterized by poor effector cytotoxic activity, impaired cytokine production and sustained expression of multiple inhibitory receptors, such as programmed cell death-1 (PD-1), lymphocyte activation gene-3, cytotoxic T lymphocyte-associated antigen-4 and CD244. As both CD4⁺ and CD8⁺ T cells participate in the immune responses against chronic hepatitis virus through distinct manners, compelling evidences have been proposed, which restore the anti-viral function of these exhausted T cells by blocking those inhibitory receptors with its ligand and will pave the way for the development of more effective immunotherapeutic and prophylactic strategies for the treatment of chronic infectious diseases. A large number of studies have stated the essentiality of T-cell exhaustion in virus-infected diseases, such as LCMV, hepatitis C virus (HCV), human immunodeficiency virus infections and cancers. Besides, the functional restoration of HCV- and HIV-specific CD8⁺ T cells by PD-1 blockade has already been repeatedly verified, and also for the immunological control of tumors in humans, blocking the PD-1 pathway could be a major immunotherapeutic strategy. Although the specific molecular pathways of T-cell exhaustion remain ambiguous, several transcriptional pathways have been implicated in T-cell exhaustion recently; among them Blimp-1, T-bet and NFAT2 were able to regulate exhausted T cells during chronic viral infection, suggesting a distinct lineage fate for this sub-population of T cells. This paper summarizes the current literature relevant to T-cell exhaustion in patients with HBV-related chronic hepatitis, the options for identifying new potential therapeutic targets to treat HBV infection and highlights priorities for further study.

Immunopathogenesis of chronic hepatitis B

Chronic hepatitis B (CHB) is a widespread infectious disease with unfavorable outcomes and life-threatening consequences for patients, in spite of modern vaccination and antiviral treatment modalities. Cutting-edge experimental approaches have demonstrated key pathways that involve cross-talk between viral particles and host immune cells. All events, including penetration of hepatitis B virus (HBV) particles into host cells, establishing persistence, and chronization of CHB infection, and possibility of complete elimination of HBV particles are controlled by the immune system. Researchers have paid special attention to the replication capacity of HBV in host cells, which is associated with cellular changes that reflect presentation of viral antigens and variability of HBV antigen features. In addition, specific HBV proteins have an immune-modulating ability to initiate molecular mechanisms that “avoid” control by the immune system. The relationship between immunological shifts and chronic infection stages has been intensively studied since it was recognized that the immune system is a direct participant in the recurrent (cyclic) nature of CHB. Understanding the wide diversity of molecular pathways and the crosstalk between innate and adaptive immune system components will provide fresh insight into CHB immune pathogenesis and the possibilities of developing new treatment strategies for this disease.

The influences of antiviral therapy on T-cell function in adult patients with chronic hepatitis B

ABSTRACT 

T cells play an important role in the clearance of acute infection and control of hepatitis B virus (HBV) infection during the chronic phase. Chronic HBV is characterized by a weak and limited T-cell response. Several hypotheses, such as presence of Tregs or occurrence of T-cell exhaustion have been proposed to explain these observations. The two registered classes of anti-HBV drugs: pegylated-IFN-α (PEG-IFN-α) and nucleos(t)ide analogs (NUCs) have, next to their antiviral effect, also an immunomodulatory effect. Although NUCs have no direct immunomodulatory effects, they may indirectly positively affect the T-cell response through their viral suppressive action. In this review, effects of both PEG-IFN-α and NUC therapy will be discussed with regard to the cellular immune response against HBV.

HBsAg as an important predictor of HBeAg seroconversion following antiviral treatment for HBeAg-positive chronic hepatitis B patients

Background

Serum quantitative hepatitis B surface antigen (HBsAg) levels may be an important predictor of hepatitis B e antigen (HBeAg) seroconversion (SC) in HBeAg-positive chronic hepatitis B (CHB) patients during antiviral treatment. The pattern of HBsAg variation in CHB patients either with or without SC following tenofovir disoproxil fumarate (TDF) treatment is not clearly understood.

Methods

Twenty patients with full experimental data were enrolled, and liver biochemistry, serum HBV DNA, and circulating CD4⁺CD25⁺ regulatory T cell (Treg) levels were determined at baseline and every 12weeks after the initiation of TDF treatment (for a total of 96weeks). In addition, the relationship between HBsAg or HBeAg and alanine aminotransferase (ALT), HBV DNA and Treg levels in SC and non-SC patients was analyzed.

Results

In all, 9 patients had undergone HBeAg seroconversion by week 72 of TDF treatment, and biochemical and virological indexes and Treg percentages declined to normal levels. Furthermore, the positive correlation between HBsAg and ALT, HBV DNA and Treg levels was significant for SC patients, but not for non-SC patients. However, for HBeAg, significant positive correlations were or not observed for both SC and non-SC patients.

Conclusions

The quantitation of HBsAg is a more useful indicator than HBeAg for distinguishing SC and non-SC patients during TDF treatment. Moreover, HBsAg may be related to immune regulatory property of CHB patients during antiviral treatment.

Effects of costimulation on intrahepatic immunopathogenesis in patients with chronic HBV infection

Objective

Chronic HBV infection can lead to “immune tolerance” in asymptomatic carriers (ACs), “immune injury” in active chronic hepatitis (ACH) patients or “immune abnormality” in cirrhosis (Cir) and hepatocellular carcinoma (HCC) patients. Previous investigations reported that chronic hepatitis presented abnormal expression of costimulatory molecules. We investigated the costimulation profile in the liver of ACs and patients with ACH, Cir and HCC.

Methods

Patients with ACH, Cir and HCC, ACs and normal controls were recruited into the present study. The costimulation profiles and cytokines in the liver of patients were investigated by Western blotting, immunohistochemistry and real-time quantitative PCR. Correlations between serum alanime aminotransferase (ALT) levels, necroinflammation scores, cytokines and costimulatory proteins were assessed.

Results

The ACs presented decreased inflammatory and increased inhibitory costimulation, which was negatively correlated with inflammatory costimulatory proteins and ALT, whereas the ACH patients exhibited increased inflammatory costimulation and decreased inhibitory costimulation, which was correlated with increased ALT. The Cir patients showed both increased inhibitory and inflammatory costimulation. The HCC patients exhibited both decreased inhibitory and inflammatory costimulation.

Conclusion

Costimulation participates in intrahepatic immune responses, and plays important roles in immune tolerance, immune injury and immune abnormalities in patients with chronic HBV infection.

Electronic supplementary material

The online version of this article (doi:10.1007/s00011-013-0691-3) contains supplementary material, which is available to authorized users.

Immune responses elicited by apoB-100-derived peptides in mice

Peptides derived from apolipoprotein B (apoB)-100 have been previously used in vaccine preparations to treat atherosclerosis. Such vaccines have been shown to reduce atherosclerotic plaque development by 50 % in experimental animals, and this effect is associated with induction of T helper (Th)2 immune responses. In this study we immunised apolipoprotein E-deficient (apoE(-/-)) mice with apoB-100-derived peptides P2, P45 and P210. Animals received BSA-conjugated peptides or peptide-loaded bone marrow-derived dendritic cells (DCs). We used enzyme-linked immunosorbent assays to assess the synthesis of anti-peptide-specific IgG1 and IgG2a as well as the levels of interleukin (IL-)10 and interferon gamma (IFN-γ) in plasma of immunised animals. We also measured the effect of immunisation on the number of spleen-derived CD4(+) and CD8(+) regulatory T cells (Tregs) in these animals. Peptide and peptide-loaded DC immunisation significantly increased the levels of peptide-specific immunoglobulins and the number of Tregs in apoE(-/-) mice. This was accompanied by a significant increase in the secretion of IL-10 with no effect on IFN-γ levels. The results also show that the peptides can modulate the homing properties of DCs. Altogether, this study provides novel evidence for the immune mechanisms excerpted by apoB-100-derived peptides and their effect on Tregs and DCs relevant to their use in vaccine preparations.

Interferon alpha induced intrahepatic pSTAT1 inversely correlate with serum HCV RNA levels in chronic HCV infection

BACKGROUND

The Jak-STAT signaling of hepatitis C virus (HCV) infected hepatocyte is critical for the antiviral action of endogenously produced interferon (IFN) as well as exogenously administered interferon alpha (IFN-α). The activation of cellular Jak-STAT signaling by IFN-α results in the phosphorylation and nuclear translocation of pSTAT1 and pSTAT2 proteins to induce antiviral gene transcription. Clinical studies show that chronic HCV patients with high viral load show poor response to interferon alpha and ribavirin combination therapy.

AIM

We seek to determine whether the IFN-α induced activation of pSTAT1 and pSTAT2 in hepatocytes isolated from liver biopsy of patients chronically infected with hepatitis C virus could be related to the viral load.

METHOD

Hepatocytes were isolated from liver biopsies of 18 chronic HCV patients using the collagen digestion method. Induction of pSTAT1 protein in the isolated hepatocyte was measured after IFN-α treatment. The fold change in the levels of pStat1 in the cell lysates due to IFN-treatment was measured by Western blot analysis followed by densitometry analysis.

RESULTS

Results of our study indicate that IFN-α induced pSTAT1 levels vary in chronically infected hepatocytes from chronic HCV patients. Semi-quantitative analysis of the pSTAT1 bands revealed a median induction of 7.4-fold in non-infected primary hepatocytes and 2.3-fold in chronic hepatitis C patients (p < 0.001). Total STAT1 levels were not significantly different between treated and untreated primary hepatocytes. We also found a significantly inverse correlation between the intrahepatic pSTAT1 inductions with the serum HCV RNA levels.

CONCLUSION

We have developed an antibody based Western blot detection method to measure intrahepatic pStat1 and pStat2 levels to assess the cellular response to exogenous IFN-alpha. Our results indicate that pStat1 activation is a good indicator to assess the level of HCV replication in chronic HCV patients.

T-cell responses in hepatitis B and C virus infection: similarities and differences

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection are global health problems affecting 600 million people worldwide. Indeed, HBV and HCV are hepatotropic viruses that can cause acute and chronic liver disease progressing to liver cirrhosis and even hepatocellular carcinoma. Furthermore, co-infections of HBV and HCV with HIV are emerging worldwide. These co-infections are even more likely to develop persistent infection and are difficult to treat. There is growing evidence that virus-specific CD4⁺ and CD8⁺ T-cell responses play a central role in the outcome and pathogenesis of HBV and HCV infection. While virus-specific T-cell responses are able to successfully clear the virus in a subpopulation of patients, failure of these T-cell responses is associated with the development of viral persistence. In this review article, we will discuss similarities and differences in HBV- and HCV-specific T-cell responses that are central in determining viral clearance, persistence and liver disease.

Effect of antiviral treatment with nucleoside and nucleotide analogues on cellular immune function in patients with chronic hepatitis B

China is a country where hepatitis B virus (HBV) infection is highly endemic, and a large sample survey shows that chronic HBV infection affects as many as 120 million people in China. Since immune response dysregulation caused by persistent HBV infection and replication is the underlying cause of disease progression in patients with chronic hepatitis B (CHB), effective antiviral therapy should be given to halt the progression of the disease. Nucleoside and nucleotide analogues have been generally accepted as effective anti-HBV drugs and widely used in the clinical setting. They exert antiviral effects against HBV mainly by inhibition of DNA polymerase-mediated DNA replication. In addition, nucleoside and nucleotide analogues also have an impact on the body's immune function. In this article we review recent progress in understanding the effect of antiviral treatment with nucleoside and nucleotide analogues on cellular immune function in CHB patients.

Negative regulation of hepatitis C virus specific immunity is highly heterogeneous and modulated by pegylated interferon-alpha/ribavirin therapy

Specific inhibitory mechanisms suppress the T-cell response against the hepatitis C virus (HCV) in chronically infected patients. However, the relative importance of suppression by IL-10, TGF-β and regulatory T-cells and the impact of pegylated interferon-alpha and ribavirin (PegIFN-α/ribavirin) therapy on these inhibitory mechanisms are still unclear. We revealed that coregulation of the HCV-specific T-cell responses in blood of 43 chronic HCV patients showed a highly heterogeneous pattern before, during and after PegIFN-α/ribavirin. Prior to treatment, IL-10 mediated suppression of HCV-specific IFN-γ production in therapy-naive chronic HCV patients was associated with higher HCV-RNA loads, which suggests that protective antiviral immunity is controlled by IL-10. In addition, as a consequence of PegIFN-α/ribavirin therapy, negative regulation of especially HCV-specific IFN-γ production by TGF-β and IL-10 changed dramatically. Our findings emphasize the importance of negative regulation for the dysfunctional HCV-specific immunity, which should be considered in the design of future immunomodulatory therapies.

Regulatory T cells are the most important determinant factor of hepatitis B infection prognosis: a systematic review and meta-analysis

INTRODUCTION

Association of increased levels of CD4(+)CD25(+) regulatory T cells (Tregs) with impaired immune response and hepatitis B infection progression has been proposed. For determination of Tregs various effects among hepatitis B infected patients we performed a meta-analysis of the available literature.

METHODS

Current content, abstract books of congresses, and electronic databases were searched. Critical appraisal has been done. According to the result of heterogeneity tests (Q, I-squared, and Tau-squared), we used fix/random model for analysis.

RESULT

Twelve studies that fulfilled inclusion criteria entered to analysis. Pooled estimation of reported results showed that CD4(+)CD25(+) Tregs have higher expression of forkhead box P3 (FoxP3) versus CD4(+)CD25(-) Tregs, odd ratio (OR) was 31.49 (95% Confidence Intervals (CI): 5.09-194.94). Tregs level among chronic hepatitis B (CHB) patients was 77% (OR=1.77 95% CI: 1.43-2.19) higher than healthy controls. Patients with more than 10,000,000 HBV copies/ml have higher level of Tregs (OR: 1.24 95% CI: 1.08-1.41) comparing subjects with less than that. CHB patients have increased level of Tregs versus acute hepatitis B patients (OR=1.33 95% CI: 1.16-1.52). CD8 cells activity increased significantly after depletion of circulating Tregs (OR=1.93 CI: 1.37-2.73). Also, Tregs reduce response to treatment and non-responders to INF-α had higher level of Tregs (OR=1.60 95% CI: 1.09-2.36). In addition, Tregs increase risk of hepatocellular carcinoma (HCC) (OR=1.36 95%CI: 1.10-1.69).

CONCLUSION

Tregs influence HBV infected patients in various states. Tregs determine the disease prognosis by leading to infection progression and impairing immune response. So, Tregs are therapeutic target for immunotherapy of HBV infection.

T cell immunopathogenesis and immunotherapeutic strategies for chronic hepatitis B virus infection

Hepatitis B is caused by the host immune response and T cells play a major role in the immunopathogenesis. More importantly, T cells not only destroy hepatocytes infected by hepatitis B virus (HBV), but also control HBV replication or eradicate HBV in a noncytolytic manner. Therefore, analysis of T cell immune response during acute and chronic HBV infection is important to develop a strategy for successful viral control, which could lead to immunotherapy for terminating persistent HBV infection. There have been many attempts at immunotherapy for chronic HBV infection, and some have shown promising results. High viral load has been shown to suppress antiviral immune responses and immunoinhibitory signals have been recently elucidated, therefore, viral suppression by nucleos(t)ide analogs, stimulation of antiviral immune response, and suppression of the immunoinhibitory signals must be combined to achieve desirable antiviral effects.

Porcine reproductive and respiratory syndrome virus induces CD4+CD8+CD25+Foxp3+ regulatory T cells (Tregs)

The aim of this study was to analyze the regulatory T cells (Tregs) induced by the porcine reproductive and respiratory syndrome virus (PRRSV) in pigs. Serum, blood, tonsil, and mediastinal lymph nodes' samples were obtained at different time post-infection (dpi). The frequencies of CD4(+)CD8(-)CD25(+)Foxp3(+), CD4(+)CD8(+)CD25(+)Foxp3(+), or CD4(-)CD8(+)CD25(+)Foxp3(+) phenotypes were determined in PBMC and lymph node cells, and cells producing IL-10 or TGF-β were analyzed. PRRSV increased the number of CD4(+)CD8(+)CD25(+)Foxp3(+) cells at 14 dpi, whereas CD4(+)CD8(-)CD25(+)Foxp3(+) remained constant until 28 dpi. Positive correlation exists between viremia and induced regulatory cells. CD4(+)CD8(+)CD25(+)Foxp3(+)-induced Treg cells were consistently observed in lymphoid tissues. Analysis of IL-10- and TGF-β-producing cell demonstrated that in response to PRRSV, CD4(+)CD8(-)Foxp3(low) and CD4(+)CD8(+)Foxp3(high) cells increase moderately the proportion of IL-10(+) cells. TGF-β was only observed in the CD4(+)CD8(+)Foxp3(high) population after PRRSV stimulation. In conclusion, PRRSV infection increases the frequency of Tregs with the phenotype CD4(+)CD8(+)CD25(+)Foxp3(high) and produces TGF-β.

Foxp3+ regulatory T cells are associated with the natural history of chronic hepatitis B and poor prognosis of hepatocellular carcinoma

BACKGROUND

Recent studies have focused on regulatory T cells (Tregs) in chronic hepatitis B (CHB) and hepatocellular carcinoma (HCC) and they were also conducted independently of each other.

AIMS

This study tried to characterize Tregs in blood and tumour infiltration, and to explore the correlations between Tregs and the context of chronic hepatitis B in HCC patients.

METHODS

The liver-resident Tregs and CD8(+) T cells on core biopsy were investigated using immunohistochemistry staining in individuals (n = 209) with CHB (n = 47), HCC (n = 137) or healthy controls (n = 25). Circulating Tregs were detected in the above patients with CHB (n = 27) or HCC (n = 101) by flow cytometry.

RESULTS

The number of tumour-infiltrating and circulating FoxP3(+) Tregs was significantly high in patients with CHB (P < 0.001). However, there were fewer intratumoural Tregs in patients with advanced HCC than those in patients with early stage HCC (P = 0.043); In contrast, the circulating Tregs frequency increased during the progression of HCC (P = 0.024). Increased tumour-infiltrating and circulating FoxP3(+) Tregs were associated with poor overall survival (P = 0.041, 0.002 respectively) and a shorter time to recurrence (P = 0.049, 0.002 respectively) in patients with early stage HCC. Tumour-infiltrating Foxp3 + Tregs were related to chronic hepatitis B natural history in HCC (P = 0.012). Neither tumour-infiltrating CD8(+) T cells nor balance of intratumoural Tregs and CD8(+) T cells correlated with prognosis of HCC.

CONCLUSIONS

Increased Foxp3(+) Tregs may represent a prognostic predictor in patients with early stage HCC. The CHB natural history influenced density of tumour-infiltrating Tregs in hepatocellular carcinoma patients with chronic hepatitis B viruses infection.

Therapeutic vaccines and immune-based therapies for the treatment of chronic hepatitis B: perspectives and challenges

The treatment of chronic hepatitis B virus (HBV) infection has greatly improved over the last 10 years, but alternative treatments are still needed. Therapeutic vaccination is a promising new strategy for controlling chronic infection. However, this approach has not been as successful as initially anticipated for chronic hepatitis B. General impairment of the immune responses generated during persistent HBV infection, with exhausted T cells not responding correctly to therapeutic vaccination, is probably responsible for the poor clinical responses observed to date. Intensive research efforts are now focusing on increasing the efficacy of therapeutic vaccination without causing liver disease. Here we describe new approaches to use with therapeutic vaccination, in order to overcome the inhibitory mechanisms impairing immune responses. We also describe innovative strategies for generating functional immune responses and inducing sustained control of this persistent infection.

Activated IL-23/IL-17 pathway closely correlates with increased Foxp3 expression in livers of chronic hepatitis B patients

Background

Foxp3 protein plays a critical role in mediating the inflammatory response and can inhibit the proinflammatory IL-23/IL-17 pathway. However, the molecular interplay of Foxp3 and the IL-23/IL-17 pathway in patients with chronic hepatitis B (CHB) remains unclear. To this end, we analyzed the expression patterns of Foxp3- and IL-23/IL-17 pathway-related proinflammatory cytokines in 39 patients with acute-on-chronic liver failure, 71 patients with CHB and 32 healthy controls.

Results

Foxp3 expression was found to be elevated in and mainly expressed by the CD4⁺ T cell sub-population of peripheral blood mononuclear cells and liver tissues of patients with hepatitis B. The intrahepatic expression of Foxp3 strongly correlated with the copies of HBV DNA and the concentration of surface antigen, HBsAg. IL-23/IL-17 pathway-related proinflammatory cytokines were also found to be significantly increased in patients' liver tissues, as compared to healthy controls. Moreover, Foxp3 expression was strikingly correlated with the production of these cytokines in liver tissues of CHB patients.

Conclusions

The closely-correlated increase of Foxp3 and IL-23/IL-17 pathway activity in HBV-infected livers suggests that the proinflammatory IL-23/IL-17 pathway had not been effectively suppressed by the host immune machinery, such as Treg (Foxp3) cells. Constitutive activation of the IL-23/17 pathway, thus, may support the chronic hepatitis B state.

Retention of CD4+ CD25+ FoxP3+ regulatory T cells in the liver after therapy-induced hepatitis C virus eradication in humans

Following infection with the hepatitis C virus (HCV), in most cases immunity fails to eradicate the virus, resulting in slowly progressing immunopathology in the HCV-infected liver. We are the first to examine intrahepatic T cells and CD4(+) CD25(+) FoxP3(+) regulatory T cells (Treg) in patients chronically infected with HCV (chronic HCV patients) during and after antiviral therapy by collecting multiple aspiration biopsy samples from the liver at different time points. We found that intrahepatic Treg frequencies were increased upon alpha interferon and ribavirin administration in about 50% of chronic HCV patients, suggesting stronger regulation of intrahepatic immunity by Treg during antiviral therapy. After cessation of antiviral therapy, the frequency of intrahepatic Treg remained above baseline in the large majority of livers of individuals who successfully cleared the virus. The phenotype of those Treg that were retained in the liver months after therapy-induced clearance of HCV RNA indicated a reduced contribution of effector memory cells. Our findings, gathered by multiple samplings of the liver, indicate that successful antiviral therapy of chronic HCV patients does not lead to normalization of the local immune response to a resting state comparable to that for healthy livers. The continuous presence of high numbers of Treg, with a phenotype reflecting a relatively weak suppressive activity, suggests ongoing residual regulation of immunopathology. These findings provide important insight into the dynamics of the immune response to HCV, as well as the effect of therapy on intrahepatic immunity.

Regulatory T cells in HBV and HCV liver diseases: implication of regulatory T lymphocytes in the control of immune response

IMPORTANCE OF THE FIELD

Hepatic cirrhosis is a frequent consequence of chronic hepatitis infection (HBV and HCV) or alcohol abuse and the most common cause of hepatocellular carcinoma (HCC). Currently, liver transplantation remains the only effective therapeutic approach for cirrhosis-related HCC patients. The evolution of the pathology strongly depends on immunological mechanisms.

AREAS COVERED IN THIS REVIEW

Despite the presence of specific T cells, viral chronic infection and continuous tumor growth suggest a failure of immune control. It appears that direct suppression of antiviral or antitumor effector cells by regulatory T cells plays a pivotal role in the impairment of immune response. Several types of regulatory T cells have been described, natural regulatory T cells (nTreg) and induced-type 1 regulatory T cells (Tr1) being the best characterized.

WHAT THE READER WILL GAIN

Currently, there is no evidence for a direct implication of regulatory T cells in the evolution of hepatitis, especially concerning chronic infection, cirrhosis late stage and HCC progress. However, recent studies show that regulatory T cells are implicated in the modulation of HBV- and HCV-associated immune response, thus, promoting HCC progress.

TAKE HOME MESSAGE

Therefore, nTreg and Tr1 cells seem to play an important role in the control of immune response leading to chronic hepatitis infection and progression of the pathology to cirrhosis and HCC.

Increased liver-infiltrating CD8+FoxP3+ regulatory T cells are associated with tumor stage in hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver, and patients who are diagnosed with this tumor typically have a poor prognosis. The suppressive effects of CD4(+)FoxP3(+) regulatory T cells on antitumor immune response in HCC have been studied in great detail. CD8(+)FoxP3(+) regulatory T cells have recently been detected in tumors; however, the role of CD8(+)FoxP3(+) regulatory T cells in HCC is still unknown. Here, the frequency and phenotype of CD8(+)FoxP3(+) regulatory T cells were analyzed by multicolor flow cytometry in liver of HCC patients and healthy donors. We observed that the percentage of these cells in HCC patients was significantly higher than that observed in healthy control donors (p = 0.0155); their phenotype was close to that of CD4(+) regulatory T cells. Furthermore, we show that CD8(+)FoxP3(+) regulatory T cells are activated and act as effector memory cells (EM, CD45RA(-)CCR7(-)CD27(+/-)CD28(+)). Most importantly, a higher percentage of intrahepatic CD8(+)FoxP3(+) regulatory T cells was found in patients with advanced HCC than in those with early HCC in terms of tumor-node-metastasis (TNM) stage (stage I vs III, p = 0.0007). These data suggest that CD8(+)FoxP3(+) regulatory T cells may contribute to HCC immune escape and disease progression.

Characterization and role of intra-hepatic regulatory T cells in chronic hepatitis C pathogenesis

BACKGROUND & AIMS

In chronic hepatitis C (CHC), HCV-specific T-cell responses are often dysfunctionnal. In vitro data point out that regulatory T cells (Treg) are able to suppress HCV-specific lymphocyte proliferation and cytokine secretion but their implication in this pathology is still debated.

METHODS

Three complementary approaches were performed to investigate phenotype, frequency or localization of intra-hepatic Treg in treatment naïve CHC patients. Double immunohistochemical analysis was performed in 20 formalin-fixed biopsies with CD8/FoxP3 and CD4/FoxP3 antibodies. Cellular markers and cytokines were investigated by quantitative RT-PCR in 27 additional frozen biopsies. Eight other fresh liver biopsies were selected for complementary analysis of immunophenotyping and frequency of intra-hepatic Treg.

RESULTS

Immunohistochemical analyses showed the presence of intra-hepatic CD4(+)FoxP3(+)T cells while CD8(+)FoxP3(+)T cells were very scarce. CD4(+)FoxP3(+)T cells were located in necro-inflammatory areas in contact with CD8(+)T cells, suggesting that Treg-mediated inhibition of CD8(+)T cell proliferation may occur by cell-cell contact. RT-PCR analyses showed strong correlations between CD8, FoxP3, and IL-10 with emergence of four distinct gene clusters, CD8-FoxP3, CD8-IL-10, TGF-beta-IL-10, and TNF-alpha-TGF-beta. No correlation was found between serum viral load and any immune markers. Interestingly, the FoxP3(+)/CD8(+) cells ratio significantly decreased in severe fibrosis (F>3) due to the dramatic decline of FoxP3 cells.

CONCLUSIONS

This study provides new insights into the histological localization of Treg within HCV-infected liver, with a special accumulation of CD4(+)FoxP3(+)Treg cells in necro-inflammatory areas, in contact with CD8(+)T cells. Our results suggest a link between Treg, CD8, and IL-10 which altogether could balance immune responses against the virus to avoid immunopathogenesis.

Abundant numbers of regulatory T cells localize to the liver of chronic hepatitis C infected patients and limit the extent of fibrosis

BACKGROUND & AIMS

Weak hepatitis C virus (HCV) specific immunity in peripheral blood has been shown to be partially controlled by regulatory T cells (Treg). However, little is known about Treg present in livers of HCV-infected patients, their association with clinical parameters, and immunopathology resulting in disease progression.

METHODS

The frequency and phenotype of CD4+FoxP3+ Treg, conventional CD4+ T cells, and the distribution of lymphocytes and leukocytes were studied by multi-color flowcytometry in liver and peripheral blood of 43 chronic HCV patients at different phases of liver disease. Comparisons between healthy blood and liver and correlations with disease parameters were made.

RESULTS

An extensive lymphocyte infiltration containing abundant numbers of CD4+FoxP3+ Treg was present in HCV-infected livers, while absent from healthy liver. Moreover, in all patients, intrahepatic CD4+FoxP3+ Treg showed a fully differentiated and highly activated phenotype on the basis of the surface markers CD45RO, CCR7, CTLA-4 and HLA-DR. These Treg were more numerous in those HCV-infected livers showing only limited fibrosis. However, HCV RNA loads or alanine transaminase levels did not correlate with CD4+FoxP3+ Treg frequencies.

CONCLUSIONS

Our data demonstrate that large numbers of highly activated and differentiated CD4+FoxP3+ Treg localize to the infiltrated chronic HCV-infected liver and may result in limiting the extent of fibrosis. This suggests that CD4+FoxP3+ Treg play a pivotal role in limiting collateral damage by suppressing excessive HCV-induced immune activation.

Tissue-specific abundance of regulatory T cells correlates with CD8+ T cell dysfunction and chronic retrovirus loads

Infection of mice with Friend virus induces the activation of CD4(+) regulatory T cells (Tregs) that suppress virus-specific CD8(+) T cells. This suppression leads to incomplete virus clearance and the establishment of virus persistence. We now show that Treg-mediated suppression of CD8(+) T cells is tissue specific, occurring in the spleen but not the liver. Regardless of infection status, there was a 5-fold lower proportion of Tregs in the liver than in the spleen, much lower absolute cell numbers, and the relatively few Tregs present expressed less CD25. Results indicated that reduced expression of CD25 on liver Tregs was due to microenvironmental factors including low levels of IL-2 production by CD4(+) Th cells in that tissue. Low CD25 expression on liver Tregs did not impair their ability to suppress CD8(+) T cells in vitro. Correlating with the decreased proportion of Tregs in the liver was a significantly increased proportion of virus-specific CD8(+) T cells compared with the spleen. The virus-specific CD8(+) T cells from the liver did not appear suppressed given that they produced both IFN-gamma and granzyme B, and they also showed evidence of recent cytolytic activity (CD107a(+)). The functional phenotype of the virus-specific CD8(+) T cells correlated with a 10-fold reduction of chronic Friend virus levels in the liver compared with the spleen. Thus, suppression of CD8(+) T cells by virus-induced Tregs occurs in a tissue-specific manner and correlates with profound effects on localized levels of chronic infection.

Immunology of hepatitis B and hepatitis C virus infections

Hepatitis B (HBV) and hepatitis C (HCV) viruses are the two major causes of chronic liver inflammation worldwide. Despite distinct virologic features, both viruses are preferentially hepatotropic, not directly cytopathic, and elicit liver diseases that share several aspects of their natural history. HBV and HCV infections also share some important features of the adaptive antiviral immune response. We describe the innate immune response in the early phase following infection, and how these early events may influence the development of the adaptive immune response in these two important viral infections. The mechanisms by which high levels of viral antigens, liver immunological features, the presence of regulatory T cells and impaired dendritic cell functions may maintain the HBV- and HCV-specific immunological failure, characteristic of chronic hepatitis B and C patients, are also evaluated.