Cellular immune response to hepatitis-C-virus in subjects without viremia or seroconversion: is it important?

The Role of Cluster of Differentiation 39 (CD39) and Purinergic Signaling Pathway in Viral Infections

CD39 is a marker of immune cells such as lymphocytes and monocytes. The CD39/CD73 pathway hydrolyzes ATP into adenosine, which has a potent immunosuppressive effect. CD39 regulates the function of a variety of immunologic cells through the purinergic signaling pathways. CD39+ T cells have been implicated in viral infections, including Human Immunodeficiency Virus (HIV), Cytomegalovirus (CMV), viral hepatitis, and Corona Virus Disease 2019 (COVID-19) infections. The expression of CD39 is an indicator of lymphocyte exhaustion, which develops during chronicity. During RNA viral infections, the CD39 marker can profile the populations of CD4+ T lymphocytes into two populations, T-effector lymphocytes, and T-regulatory lymphocytes, where CD39 is predominantly expressed on the T-regulatory cells. The level of CD39 in T lymphocytes can predict the disease progression, antiviral immune responses, and the response to antiviral drugs. Besides, the percentage of CD39 and CD73 in B lymphocytes and monocytes can affect the status of viral infections. In this review, we investigate the impact of CD39 and CD39-expressing cells on viral infections and how the frequency and percentage of CD39+ immunologic cells determine disease prognosis.

Dose-Dependent Hepacivirus Infection Reveals Linkage between Infectious Dose and Immune Response

More than 70 million people worldwide are still infected with the hepatitis C virus 30 years after its discovery, underscoring the need for a vaccine. To develop an effective prophylactic vaccine, detailed knowledge of the correlates of protection and an immunocompetent surrogate model are needed. In this study, we describe the minimum dose required for robust equine hepacivirus (EqHV) infection in equids and examined how this relates to duration of infection, seroconversion, and transcriptomic responses. To investigate mechanisms of hepaciviral persistence, immune response, and immune-mediated pathology, we inoculated eight EqHV naive horses with doses ranging from 1-2 copies to 1.3 × 106 RNA copies per inoculation. We characterized infection kinetics, pathology, and transcriptomic responses via next generation sequencing. The minimal infectious dose of EqHV in horses was estimated at 13 RNA copies, whereas 6 to 7 copies were insufficient to cause infection. Peak viremia did not correlate with infectious dose, while seroconversion and duration of infection appeared to be affected. Notably, seroconversion was undetectable in the low-dose infections within the surveillance period (40 to 50 days). In addition, transcriptomic analysis revealed a nearly dose-dependent effect, with greater immune activation and inflammatory response observed in high-dose infections than in low-dose infections. Interestingly, inoculation with 6-7 copies of RNA that did not result in productive infection, but was associated with a strong immune response, similar to that observed in the high-dose infections. IMPORTANCE We demonstrate that the EqHV dose of infection plays an important role for inducing immune responses, possibly linked to early clearance in high-dose and prolonged viremia in low-dose infections. In particular, pathways associated with innate and adaptive immune responses, as well as inflammatory responses, were more strongly upregulated in high-dose infections than in lower doses. Hence, inoculation with low doses may enable EqHV to evade strong immune responses in the early phase and therefore promote robust, long-lasting infection.

Occult Infection with Hepatitis C Virus: Looking for Clear-Cut Boundaries and Methodological Consensus

The sustained virologic response and elimination of HCV is widely viewed as a true cure of chronic hepatitis C as it associates with amelioration of histological liver damage and improved clinical outcomes. Therefore, the existence and clinical burden of occult HCV infection (OCI) has been a controversial issue for many years. In this review, we summarize recently published data that adds new information on the molecular and clinical background of OCI and its epidemiological significance. We also identify and discuss the most important methodological pitfalls, which can be a source of inconsistency between studies. Data that have accumulated so far, strongly support the existence of extrahepatic HCV replication in individuals negative for serum HCV-RNA by conventional clinical tests. OCI emerges as a condition where the immune system is unable to fully resolve infection but it is continuously stimulated by low levels of HCV antigens, leading to progression of liver pathology and extrahepatic HCV-related complications. Moreover, the development of monitoring strategies or management guidelines for OCI is still hampered by the lack of clear definition and the confusion regarding its clinical significance. Careful study design and the introduction of uniform protocols for the detection of low-level HCV-RNA are crucial for obtaining reliable data on OCI.

Inflammation response and liver stiffness: predictive model of regression of hepatic stiffness after sustained virological response in cirrhotics patients with chronic hepatitis C

Cirrhotic patients with chronic hepatitis C should be monitored for the evaluation of liver function and screening of hepatocellular carcinoma even after sustained virological response (SVR). The stage of inflammatory resolution and regression of fibrosis is likely to happen, once treatment and viral clearance are achieved. However, liver examinations by elastography show that 30-40% of patients do not exhibit a reduction of liver stiffness. This work was a cohort study in cirrhotic patients whose purpose was to identify immunological factors involved in the regression of liver stiffness in chronic hepatitis C and characterize possible serum biomarkers with prognostic value. The sample universe consisted of 31 cirrhotic patients who underwent leukocyte immunophenotyping, quantification of cytokines/chemokines and metalloproteinase inhibitors in the pretreatment (M1) and in the evaluation of SVR (M2). After exclusion criteria application, 16 patients included were once more evaluated in M3 (like M1) and classified into regressors (R) or non-regressors (NR), decrease or not ≥ 25% stiffness, respectively. The results from ROC curve, machine learning (ML) and linear discriminant analysis showed that TCD4 + lymphocytes (absolute) are the most important biomarkers for the prediction of the regression (AUC = 0.90). NR patients presented levels less than R of liver stiffness since baseline, whereas NK cells were increased in NR. Therefore, it was concluded that there is a difference in the profile of circulating immune cells in R and NR, thus allowing the development of a predictive model of regression of liver stiffness after SVR. These findings should be validated in greater numbers of patients.

Association of the polymorphism of the Toll-like receptor (TLR)-3 and TLR-9 genes with hepatitis C virus-specific cell-mediated immunity outcomes among Egyptian health-care workers

Variations in the immune response could explain resistance to hepatitis C virus (HCV) infection. Toll-like receptor gene (TLR)-3 is an innate detector of dsRNA viruses, and the TLR-9 gene recognizes bacterial and viral unmethylated cytosine-phosphate-guanosine (CpG) motifs. We previously reported that the TLR-3.rs3775290 CC genotype was associated with HCV chronicity and that the TLR-9 gene played no major role in this infection. This study identified the role of TLR-3.rs3775290 (c.1377C/T), TLR-9.rs5743836 (-1237T→C) and TLR-9.rs352140 (G2848A) gene polymorphisms in predicting the outcome of HCV-specific cell-mediated immunity (CMI) among Egyptian health-care workers (HCWs). We enrolled 265 HCWs in this study and divided them into four groups. Group 1: 140 seronegative-aviraemic HCWs; group 2: 20 seronegative-viraemic HCWs; group 3: 35 subjects with spontaneously resolved HCV infection; and group 4: 70 chronic HCV HCWs (patients). All subjects were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis for the TLR-3.rs3775290, TLR-9.rs5743836 and TLR-9.rs352140 single nucleotide polymorphisms (SNPs). We also quantified HCV-specific CMI in the four groups using an interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) assay in response to nine HCV genotype 4a, overlapping 15mer peptide pools covering the whole viral genome. No statistically significant difference was found between CMI-responding subjects with different HCV states and TLR-3.rs3775290 or TLR-9.rs352140 genotypes. However, there was a significant relationship between the outcome of the HCV-specific CMI and the TLR-9.rs5743836 genotype among the responding subjects (P = 0·005) and the chronic HCV patients (P = 0·044). In conclusion, TLR-9.rs5743836 SNP, but not TLR-3.rs3775290 or TLR-9.rs352140 genotypes, could predict the outcome of HCV-specific CMI responses among Egyptians infected with genotype-4.

Heterologous Immunity: Role in Natural and Vaccine-Induced Resistance to Infections

The central paradigm of vaccination is to generate resistance to infection by a specific pathogen when the vacinee is re-exposed to that pathogen. This paradigm is based on two fundamental characteristics of the adaptive immune system, specificity and memory. These characteristics come from the clonal specificity of T and B cells and the long-term survival of previously-encountered memory cells which can rapidly and specifically expand upon re-exposure to the same specific antigen. However, there is an increasing awareness of the concept, as well as experimental documentation of, heterologous immunity and cross-reactivity of adaptive immune lymphocytes in protection from infection. This awareness is supported by a number of human epidemiological studies in vaccine recipients and/or individuals naturally-resistant to certain infections, as well as studies in mouse models of infections, and indeed theoretical considerations regarding the disproportional repertoire of available T and B cell clonotypes compared to antigenic epitopes found on pathogens. Heterologous immunity can broaden the protective outcomes of vaccinations, and natural resistance to infections. Besides exogenous microbes/pathogens and/or vaccines, endogenous microbiota can also impact the outcomes of an infection and/or vaccination through heterologous immunity. Moreover, utilization of viral and/or bacterial vaccine vectors, capable of inducing heterologous immunity may also influence the natural course of many infections/diseases. This review article will briefly discuss these implications and redress the central dogma of specificity in the immune system.

A dynamical motif comprising the interactions between antigens and CD8 T cells may underlie the outcomes of viral infections

Some viral infections culminate in very different outcomes in different individuals. They can be rapidly cleared in some, cause persistent infection in others, and cause mortality from immunopathology in yet others. The conventional view is that the different outcomes arise as a consequence of the complex interactions between a large number of different factors (virus, different immune cells, and cytokines). Here, we identify a simple dynamical motif comprising the essential interactions between antigens and CD8 T cells and posit it as predominantly determining the outcomes. Viral antigen can activate CD8 T cells, which in turn, can kill infected cells. Sustained antigen stimulation, however, can cause CD8 T-cell exhaustion, compromising effector function. Using mathematical modeling, we show that the motif comprising these interactions recapitulates all of the outcomes observed. The motif presents a conceptual framework to understand the variable outcomes of infection. It also explains a number of confounding experimental observations, including the variation in outcomes with the viral inoculum size, the evolutionary advantage of exhaustion in preventing lethal pathology, the ability of natural killer (NK) cells to act as rheostats tuning outcomes, and the role of the innate immune response in the spontaneous clearance of hepatitis C. Interventions that modulate the interactions in the motif may present routes to clear persistent infections or limit immunopathology.

Safety and tolerability of mice to repeated subcutaneous injections of a peptide mix as a potential vaccine against HCV infection

BACKGROUND AND AIMS

In this study, the safety and tolerability of new candidate HCV vaccine named Cenv6 were screened in mice. Cenv6 peptide is composed of 6 synthetic HCV peptides (3 structural and 3 nonstructural peptides).

METHODS

Forty eight mice were enrolled in this study, 12 controls and 36 mice (the thirty-six mice were categorized into 3 groups according to administered doses (3 monthly doses of 800 ng, 1600 ng, and 16 μg/25 gm mouse body weight (bw))). Hematological, biochemical and histopathological changes were appraised.

RESULTS

Our data indicated that the doses of 800 ng and 1600 ng of Cenv6 per 25 gm mouse body weight were safe as compared to the dose 16 μg/25 gm bw (10 times more than the potential therapeutic dose) for all examined tissues while the 16 μg Cenv6 dose provoked histopathological changes in kidneys, liver and lungs.

CONCLUSIONS

The extravagant histopathological changes in different organs have exiled the 16 μg dose out of acceptable range and validated that Cenv6 is safe and tolerable at the two lower doses (800 and 1600 ng/25 gm bw).

Sociodemographic and clinical characteristics of persons who experienced spontaneous hepatitis C viral clearance

Background

In the United States Hepatitis C virus (HCV) viral clearance is estimated to range between 20 and 30%. The objective of this study was to estimate the frequency of HCV clearance and identify correlates of viral clearance among patients newly identified as HCV antibody positive in a large urban health system in Los Angeles, California.

Methods

We identified patients between November 2015 and September 2017 as part of a newly implemented HCV screening and linkage-to-care program at University of California Los Angeles (UCLA) Health System. All patients were eligible for screening, though there were additional efforts to screen patients born between 1945 and 1965. We reviewed Medical records to categorize anti-HCV antibody positive patients as having spontaneously cleared HCV infection (HCV RNA not detected) or not (HCV RNA detected). We excluded those with a prior history of anti-HCV positivity or history of HCV treatment. We compared differences between those with and without detectable HCV RNA using chi-square test, Fisher’s exact test, and t-test as appropriate. We assessed factors associated with HCV clearance using logistic regression analysis.

Results

Among the 320 patients included in this study, 56% were male. Baby boomers (52–72 years of age) comprised the single largest age group (62%). We found spontaneous HCV clearance in 58% (n = 185). HCV viral clearance was slightly higher among women as compared to men (63% vs. 53%; p value = 0.07) and varied by race/ethnicity: clearance among Blacks/African Americans was 37% vs. 58% among whites (p value = 0.02). After adjusting for age, race/ethnicity, and sex we found that those diagnosed with chronic kidney disease had a tendency of decreased HCV viral clearance (adjusted OR = 0.34; 95% CI 0.14–1.03).

Conclusion

Of those patients newly identified as anti-HCV positive, 58% had cleared HCV virus, while the rest showed evidence of active infection. In addition, we found that clearance varied by race/ethnicity and clinical characteristics.

Heterologous Immunity between Adenoviruses and Hepatitis C Virus (HCV): Recombinant Adenovirus Vaccine Vectors Containing Antigens from Unrelated Pathogens Induce Cross-Reactive Immunity Against HCV Antigens

Host immune responses play an important role in the outcome of infection with hepatitis C virus (HCV). They can lead to viral clearance and a positive outcome, or progression and severity of chronic disease. Extensive research in the past >25 years into understanding the immune responses against HCV have still resulted in many unanswered questions implicating a role for unknown factors and events. In our earlier studies, we made a surprising discovery that peptides derived from structural and non-structural proteins of HCV have substantial amino acid sequence homologies with various proteins of adenoviruses and that immunizing mice with a non-replicating, non-recombinant adenovirus vector leads to induction of a robust cross-reactive cellular and humoral response against various HCV antigens. In this work, we further demonstrate antibody cross-reactivity between Ad and HCV in vivo. We also extend this observation to show that recombinant adenoviruses containing antigens from unrelated pathogens also possess the ability to induce cross-reactive immune responses against HCV antigens along with the induction of transgene antigen-specific immunity. This cross-reactive immunity can (a) accommodate the making of dual-pathogen vaccines, (b) play an important role in the natural course of HCV infection and (c) provide a plausible answer to many unexplained questions regarding immunity to HCV.

Hepatitis C virus infection induces endoplasmic reticulum stress and apoptosis in human fetal liver stem cells

The cellular mechanisms by which hepatitis C virus (HCV) replication might mediate cytopathic effects are controversial and not entirely clear. In this study, we found that blood-borne HCV (bbHCV) infection could lead to endoplasmic reticulum (ER)-stress and mitochondria-related/caspase-dependent apoptosis at the early stages of infection based on use of the highly efficient bbHCV cell culture model established previously. Sections of bbHCV-infected human fetal liver stem cells (hFLSCs) revealed convolution and nonlinear ER, cell vacuolization, swelling of mitochondria, and numerous double membrane vesicles (DMVs). The percentage of apoptotic hFLSCs infected by bbHCV reached 29.8% at 16 h postinfection, and the amount of cytochrome c increased remarkably in the cytosolic protein fraction. However, over time, apoptosis was inhibited due to the activation of NF-κB. The expression of NF-κB-p65, Bcl-xL, XIAP, and c-FLIPL in hFLSCs was increased significantly 24 h after in infection by bbHCV. The accelerated cell death cycles involving apoptosis, regeneration and repair by bbHCV infection might give rise to the development of cirrhosis, and ultimately to hepatocellular carcinogenesis. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Association of Toll-like receptor 3 and Toll-like receptor 9 single-nucleotide polymorphisms with hepatitis C virus persistence among Egyptians

Toll-like receptors (TLRs) give the innate immune system a considerable specificity for a large range of pathogens. TLR3 detects dsRNA of viruses while TLR9 recognizes bacterial and viral unmethylated CpG motifs. This study examined whether there is a potential association between single-nucleotide polymorphisms (SNPs) in the TLR3.rs3775290 (c.1377C/T), TLR9.rs5743836 (-1237T→C) and TLR9.rs352140 (G2848A) genes and HCV infection among Egyptian patients and healthcare workers (HCWs). We enrolled 546 subjects (409 HCWs and 137 patients) divided into four groups: group 1 included 265 seronegative, aviremic subjects; group 2 included 25 seronegative, viremic subjects; group 3 included 87 subjects with spontaneously resolved HCV infection; and group 4 included 169 chronic HCV patients. All subjects were genotyped for TLR3.rs3775290, TLR9.rs5743836 and TLR9.rs352140 SNPs by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis. TLR3.rs3775290 "CC" genotype was associated with chronic HCV infection, where there was a significantly greater frequency of this genotype among chronic patients when compared to subjects with spontaneously resolved infection (63.9% vs. 51.9%; p = 0.033; OR = 1.639 and 95% CI = 0.94-2.84). However, this SNP did not correlate with the HCV RNA load among the chronic subjects (p > 0.05). There was no significant difference in TLR9.rs5743836 and TLR9.rs352140 genotype distribution between groups (p > 0.05). Lack of association between the three SNPs was found, as the three SNPs are located on two different chromosomes. In conclusion, the TLR3.rs3775290 "CC" genotype was associated with HCV chronicity, while the TLR9 gene may not play a major role in HCV infection.

Modeling how reversal of immune exhaustion elicits cure of chronic hepatitis C after the end of treatment with direct-acting antiviral agents

A fraction of chronic hepatitis C patients treated with direct‐acting antivirals (DAAs) achieved sustained virological responses (SVR), or cure, despite having detectable viremia at the end of treatment (EOT). This observation, termed EOT⁺/SVR, remains puzzling and precludes rational optimization of treatment durations. One hypothesis to explain EOT⁺/SVR, the immunologic hypothesis, argues that the viral decline induced by DAAs during treatment reverses the exhaustion of cytotoxic T lymphocytes (CTLs), which then clear the infection after treatment. Whether the hypothesis is consistent with data of viral load changes in patients who experienced EOT⁺/SVR is unknown. Here, we constructed a mathematical model of viral kinetics incorporating the immunologic hypothesis and compared its predictions with patient data. We found the predictions to be in quantitative agreement with patient data. Using the model, we unraveled an underlying bistability that gives rise to EOT⁺/SVR and presents a new avenue to optimize treatment durations. Infected cells trigger both activation and exhaustion of CTLs. CTLs in turn kill infected cells. Due to these competing interactions, two stable steady states, chronic infection and viral clearance, emerge, separated by an unstable steady state with intermediate viremia. When treatment during chronic infection drives viremia sufficiently below the unstable state, spontaneous viral clearance results post‐treatment, marking EOT⁺/SVR. The duration to achieve this desired reduction in viremia defines the minimum treatment duration required for ensuring SVR, which our model can quantify. Estimating parameters defining the CTL response of individuals to HCV infection would enable the application of our model to personalize treatment durations.

Development and characterization of a human monoclonal antibody targeting the N-terminal region of hepatitis C virus envelope glycoprotein E1

Monoclonal antibodies (mAbs) targeting the hepatitis C virus (HCV) envelope have been raised mainly against envelope protein 2 (E2), while the antigenic epitopes of envelope protein 1 (E1) are not fully identified. Here we describe the detailed characterization of a human mAb, designated A6, generated from an HCV genotype 1b infected patient. ELISA results showed reactivity of mAb A6 to full-length HCV E1E2 of genotypes 1a, 1b and 2a. Epitope mapping identified a region spanning amino acids 230-239 within the N-terminal region of E1 as critical for binding. Antibody binding to this epitope was not conformation dependent. Neutralization assays showed that mAb A6 lacks neutralizing capacity and does not interfere with the activity of known neutralizing antibodies. In summary, mAb A6 is an important tool to study the structure and function of E1 within the viral envelope, a crucial step in the development of an effective prophylactic HCV vaccine.

Oxidative Stress and Immune Responses During Hepatitis C Virus Infection in Tupaia belangeri

Hepatitis C virus (HCV) is a leading cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma. To address the molecular basis of HCV pathogenesis using tupaias (Tupaia belangeri), we characterized host responses upon HCV infection. Adult tupaias were infected with HCV genotypes 1a, 1b, 2a, or 4a. Viral RNA, alanine aminotransferase, anti-HCV core and anti-nonstructural protein NS3 antibody titres, reactive oxygen species (ROS), and anti-3β-hydroxysterol-Δ24reductase (DHCR24) antibody levels were measured at 2-week intervals from 0 to 41 weeks postinfection. All HCV genotypes established infections and showed intermittent HCV propagation. Moreover, all tupaias produced anti-core and anti-NS3 antibodies. ROS levels in sera and livers were significantly increased, resulting in induction of DHCR24 antibody production. Similarly, lymphocytic infiltration, disturbance of hepatic cords, and initiation of fibrosis were observed in livers from HCV-infected tupaias. Intrahepatic levels of Toll-like receptors 3, 7, and 8 were significantly increased in all HCV-infected tupaias. However, interferon-β was only significantly upregulated in HCV1a- and HCV2a-infected tupaias, accompanied by downregulation of sodium taurocholate cotransporting polypeptide. Thus, our findings showed that humoral and innate immune responses to HCV infection, ROS induction, and subsequent increases in DHCR24 auto-antibody production occurred in our tupaia model, providing novel insights into understanding HCV pathogenesis.