Novel E2 Glycoprotein Tetramer Detects Hepatitis C Virus-Specific Memory B Cells

Coordinated expansion of memory T follicular helper and B cells mediates spontaneous clearance of HCV reinfection

Introduction

Follicular helper T cells are essential for helping in the maturation of B cells and the production of neutralizing antibodies (NAbs) during primary viral infections. However, their role during recall responses is unclear. Here, we used hepatitis C virus (HCV) reinfection in humans as a model to study the recall collaborative interaction between circulating CD4 T follicular helper cells (cTfh) and memory B cells (MBCs) leading to the generation of NAbs.

Methods

We evaluated this interaction longitudinally in subjects who have spontaneously resolved primary HCV infection during a subsequent reinfection episode that resulted in either another spontaneous resolution (SR/SR, n = 14) or chronic infection (SR/CI, n = 8).

Results

Both groups exhibited virus-specific memory T cells that expanded upon reinfection. However, early expansion of activated cTfh (CD4+CXCR5+PD-1+ICOS+FoxP3-) occurred in SR/SR only. The frequency of activated cTfh negatively correlated with time post-infection. Concomitantly, NAbs and HCV-specific MBCs (CD19+CD27+IgM-E2-Tet+) peaked during the early acute phase in SR/SR but not in SR/CI. Finally, the frequency of the activated cTfh1 (CXCR3+CCR6-) subset correlated with the neutralization breadth and potency of NAbs.

Conclusion

These results underscore a key role for early activation of cTfh1 cells in helping antigen-specific B cells to produce NAbs that mediate the clearance of HCV reinfection.

Characterization of antibody-dependent cellular phagocytosis in patients infected with hepatitis C virus with different clinical outcomes

Early neutralizing antibodies against hepatitis C virus (HCV) and CD8 + T cell effector responses can lead to viral clearance. However, these functions alone are not sufficient to protect patients against HCV infection, thus undefined additional antiviral immune mechanisms are required. In recent years, Fc-receptor-dependent antibody effector functions, particularly, antibody-dependent cellular phagocytosis (ADCP) were shown to offer immune protection against several RNA viruses. However, its development and clinical role in patients with HCV infection remain unknown. In this study, we found that patients with chronic GT1a or GT3a HCV infection had significantly higher concentrations of anti-envelope 2 (E2) antibodies, predominantly IgG1 subclass, than patients that cleared the viruses while the latter had antibodies with higher affinities. 97% of the patients with HCV had measurable ADCP of whom patients with chronic disease showed significantly higher ADCP than those who naturally cleared the virus. Epitope mapping studies showed that patients with antibodies that target antigenic domains on the HCV E2 protein that are known to associate with neutralization function are also strongly associated with ADCP, suggesting antibodies with overlapping/dual functions. Correlation studies showed that ADCP significantly correlated with plasma anti-E2 antibody levels and neutralization function regardless of clinical outcome and genotype of infecting virus, while a significant correlation between ADCP and affinity was only evident in patients that cleared the virus. These results suggest ADCP was mostly driven by antibody titer in patients with chronic disease while maintained in clearers due to the quality (affinity) of their anti-E2 antibodies despite having lower antibody titers.

Immunological Monitoring in Hepatitis C Virus Controlled Human Infection Model

Controlled human infection model trials for hepatitis C virus represent an important opportunity to identify correlates of protective immunity against a well-characterized inoculum of hepatitis C virus and how such responses are modified by vaccination. In this article, we discuss the approach to immunological monitoring during such trials, including a set of recommendations for optimal sampling schedule and preferred immunological assays to examine the different arms of the immune response. We recommend that this approach be adapted to different trial designs. Finally, we discuss how these studies can provide surrogate predictors of the success of candidate vaccines.

Recent Insights into the Role of B Cells in Chronic Hepatitis B and C Infections

Chronic viral hepatitis infections, caused by the hepatitis B or C virus, are a major global health problem causing an estimated one million deaths each year. Immunological studies have classically focused on T cells, while B cells have largely been neglected. Emerging evidence, however, highlights a role for B cells in the immunopathogenesis of chronic hepatitis B and C infections. B cell responses appear to be altered across different clinical phases of chronic HBV infection and across stages of disease in chronic HCV infection. These B cell responses show signs of a more activated state with a simultaneous enrichment of phenotypically exhausted atypical memory B cells. Despite the fact that studies show an activating B cell signature in chronic viral hepatitis infection, antibody responses to HBsAg remain impaired in chronic HBV infection, and glycoprotein E2-specific neutralizing antibody responses remain delayed in the acute phase of HCV infection. At the same time, studies have reported that a subset of HBV- and HCV-specific B cells exhibit an exhausted phenotype. This may, at least in part, explain why antibody responses in chronic HBV and HCV patients are suboptimal. Here, we summarize recent findings and discuss upcoming research questions while looking forward to how new single-cell technologies could provide novel insights into the role of B cells in chronic viral hepatitis infections.

Differential immune transcriptomic profiles between vaccinated and resolved HCV reinfected subjects

Successive episodes of hepatitis C virus (HCV) infection represent a unique natural rechallenge experiment to define correlates of long-term protective immunity and inform vaccine development. We applied a systems immunology approach to characterize longitudinal changes in the peripheral blood transcriptomic signatures in eight subjects who spontaneously resolved two successive HCV infections. Furthermore, we compared these signatures with those induced by an HCV T cell-based vaccine regimen. We identified a plasma cell transcriptomic signature during early acute HCV reinfection. This signature was absent in primary infection and following HCV vaccine boost. Spontaneous resolution of HCV reinfection was associated with rapid expansion of glycoprotein E2-specifc memory B cells in three subjects and transient increase in E2-specific neutralizing antibodies in six subjects. Concurrently, there was an increase in the breadth and magnitude of HCV-specific T cells in 7 out of 8 subjects. These results suggest a cooperative role for both antibodies and T cells in clearance of HCV reinfection and support the development of next generation HCV vaccines targeting these two arms of the immune system.

Serum neutralization activity declines but memory B cells persist after cure of chronic hepatitis C

The increasing incidence of hepatitis C virus (HCV) infections underscores the need for an effective vaccine. Successful vaccines to other viruses generally depend on a long-lasting humoral response. However, data on the half-life of HCV-specific responses are lacking. Here we study archived sera and mononuclear cells that were prospectively collected up to 18 years after cure of chronic HCV infection to determine the role of HCV antigen in maintaining neutralizing antibody and B cell responses. We show that HCV-neutralizing activity decreases rapidly in potency and breadth after curative treatment. In contrast, HCV-specific memory B cells persist, and display a restored resting phenotype, normalized chemokine receptor expression and preserved ability to differentiate into antibody-secreting cells. The short half-life of HCV-neutralizing activity is consistent with a lack of long-lived plasma cells. The persistence of HCV-specific memory B cells and the reduced inflammation after cure provide an opportunity for vaccination to induce protective immunity against re-infection.

B cell overexpression of FCRL5 and PD-1 is associated with low antibody titers in HCV infection

Antibodies targeting the hepatitis C virus (HCV) envelope glycoprotein E2 are associated with delayed disease progression, and these antibodies can also facilitate spontaneous clearance of infection in some individuals. However, many infected people demonstrate low titer and delayed anti-E2 antibody responses. Since a goal of HCV vaccine development is induction of high titers of anti-E2 antibodies, it is important to define the mechanisms underlying these suboptimal antibody responses. By staining lymphocytes with a cocktail of soluble E2 (sE2) glycoproteins, we detected HCV E2-specific (sE2+) B cells directly ex vivo at multiple acute infection timepoints in 29 HCV-infected subjects with a wide range of anti-E2 IgG titers, including 17 persistently infected subjects and 12 subjects with spontaneous clearance of infection. We performed multi-dimensional flow cytometric analysis of sE2+ and E2-nonspecific (sE2-) class-switched B cells (csBC). In sE2+ csBC from both persistence and clearance subjects, frequencies of resting memory B cells (rMBC) were reduced, frequencies of activated MBC (actMBC) and tissue-like MBC (tlMBC) were increased, and expression of FCRL5, an IgG receptor, was significantly upregulated. Across all subjects, plasma anti-E2 IgG levels were positively correlated with frequencies of sE2+ rMBC and sE2+ actMBC, while anti-E2 IgG levels were negatively correlated with levels of FCRL5 expression on sE2+ rMBC and PD-1 expression on sE2+ actMBC. Upregulation of FCRL5 on sE2+ rMBC and upregulation of PD-1 on sE2+ actMBC may limit anti-E2 antibody production in vivo. Strategies that limit upregulation of these molecules could potentially generate higher titers of protective antibodies against HCV or other pathogens.

Antiviral immunity relies on production of protective immunoglobulin G (IgG) by B cells, but many hepatitis C virus (HCV)-infected individuals have very low levels of HCV-specific IgG in their serum. Elucidating mechanisms underlying this suboptimal IgG expression remains paramount in guiding therapeutic and vaccine strategies. In this study, we developed a highly specific method to capture HCV-specific B cells and characterized their surface protein expression. Two proteins analyzed were Fc receptor-like protein 5 (FCRL5), a cell surface receptor for IgG, and programmed cell death protein-1 (PD-1), a marker of lymphocyte activation and exhaustion. We measured serum levels of anti-HCV IgG in these subjects and demonstrated that overexpression of FCRL5 and PD-1 on memory B cells was associated with reduced anti-E2 IgG levels. This study uses HCV as a viral model, but the findings may be applicable to many viral infections, and they offer new potential targets to enhance antiviral IgG production.

Towards a Systems Immunology Approach to Understanding Correlates of Protective Immunity against HCV

Over the past decade, tremendous progress has been made in systems biology-based approaches to studying immunity to viral infections and responses to vaccines. These approaches that integrate multiple facets of the immune response, including transcriptomics, serology and immune functions, are now being applied to understand correlates of protective immunity against hepatitis C virus (HCV) infection and to inform vaccine development. This review focuses on recent progress in understanding immunity to HCV using systems biology, specifically transcriptomic and epigenetic studies. It also examines proposed strategies moving forward towards an integrated systems immunology approach for predicting and evaluating the efficacy of the next generation of HCV vaccines.

Early T follicular helper cell activity accelerates hepatitis C virus-specific B cell expansion

Early appearance of neutralizing antibodies during acute hepatitis C virus (HCV) infection is associated with spontaneous viral clearance. However, the longitudinal changes in antigen-specific memory B cell (MBCs) associated with divergent HCV infection outcomes remain undefined. We characterized longitudinal changes in E2 glycoprotein-specific MBCs from subjects who either spontaneously resolved acute HCV infection or progressed to chronic infection, using single-cell RNA-seq and functional assays. HCV-specific antibodies in plasma from chronically infected subjects recognized multiple E2 genotypes, while those from spontaneous resolvers exhibited variable cross-reactivity to heterotypic E2. E2-specific MBCs from spontaneous resolvers peaked early after infection (4-6 months), following expansion of activated circulating T follicular helper cells (cTfh) expressing interleukin 21. In contrast, E2-specific MBCs from chronically infected subjects, enriched in VH1-69, expanded during persistent infection (> 1 year), in the absence of significantly activated cTfh expansion. Early E2-specific MBCs from spontaneous resolvers produced monoclonal antibodies (mAbs) with fewer somatic hypermutations and lower E2 binding but similar neutralization as mAbs from late E2-specific MBCs of chronically infected subjects. These findings indicate that early cTfh activity accelerates expansion of E2-specific MBCs during acute infection, which might contribute to spontaneous clearance of HCV.

The next generation of HCV vaccines: a focus on novel adjuvant development

INTRODUCTION

Considerable efforts have been made to treat and prevent acute and chronic infections caused by the hepatitis C virus (HCV). Current treatments are unable to protect people from reinfection. Hence, there is a need for development of both preventive and therapeutic HCV vaccines. Many vaccine candidates are in development to fight against HCV, but their efficacy has so far proven limited partly due to low immunogenicity.

AREAS COVERED

We explore development of novel and powerful adjuvants to achieve an effective HCV vaccine. The basis for developing strong adjuvants is to understand the innate immunity pathway, which subsequently stimulates humoral and cellular immune responses. We have also investigated immunogenicity of developed adjuvants that have been used in recent studies available in online databases such as PubMed, PMC, ScienceDirect, Google Scholar, etc.

EXPERT OPINION

Adjuvants are used as a part of vaccine formulation to boost vaccine immunogenicity and antigen delivery. Several FDA-approved adjuvants are used in licensed human vaccines. Unfortunately, no adjuvant has yet been proven to boost HCV immune responses to the extent needed for an effective vaccine. One of the promising approaches for developing an effective adjuvant is the combination of various adjuvants to trigger several innate immune responses, leading to activation of adaptive immunity.[Figure: see text].

Global characterization of B cell receptor repertoire in COVID-19 patients by single-cell V(D)J sequencing

The world is facing a pandemic of Corona Virus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Adaptive immune responses are essential for SARS-CoV-2 virus clearance. Although a large body of studies have been conducted to investigate the immune mechanism in COVID-19 patients, we still lack a comprehensive understanding of the BCR repertoire in patients. In this study, we used the single-cell V(D)J sequencing to characterize the BCR repertoire across convalescent COVID-19 patients. We observed that the BCR diversity was significantly reduced in disease compared with healthy controls. And BCRs tend to skew toward different V gene segments in COVID-19 and healthy controls. The CDR3 sequences of heavy chain in clonal BCRs in patients were more convergent than that in healthy controls. In addition, we discovered increased IgG and IgA isotypes in the disease, including IgG1, IgG3 and IgA1. In all clonal BCRs, IgG isotypes had the most frequent class switch recombination events and the highest somatic hypermutation rate, especially IgG3. Moreover, we found that an IgG3 cluster from different clonal groups had the same IGHV, IGHJ and CDR3 sequences (IGHV4-4-CARLANTNQFYDSSSYLNAMDVW-IGHJ6). Overall, our study provides a comprehensive characterization of the BCR repertoire in COVID-19 patients, which contributes to the understanding of the mechanism for the immune response to SARS-CoV-2 infection.

Evidence for B cell maturation but not trained immunity in uninfected infants exposed to hepatitis C virus

OBJECTIVES

Vertical transmission of hepatitis C virus (HCV) is rare compared with other chronic viral infections, despite that newborns have an immature, and possibly more susceptible, immune system. It further remains unclear to what extent prenatal and perinatal exposure to HCV affects immune system development in neonates.

DESIGN

To address this, we studied B cells, innate immune cells and soluble factors in a cohort of 62 children that were either unexposed, exposed uninfected or infected with HCV. Forty of these infants were followed longitudinally from birth up until 18 months of age.

RESULTS

As expected, evidence for B cell maturation was observed with increased age in children, whereas few age-related changes were noticed among innate immune cells. HCV-infected children had a high frequency of HCV-specific IgG-secreting B cells. Such a response was also detected in some exposed but uninfected children but not in uninfected controls. Consistent with this, both HCV-exposed uninfected and HCV-infected infants had evidence of early B cell immune maturation with an increased proportion of IgA-positive plasma cells and upregulated CD40 expression. In contrast, actual HCV viraemia, but not mere exposure, led to alterations within myeloid immune cell populations, natural killer (NK) cells and a distinct soluble factor profile with increased levels of inflammatory cytokines and chemokines.

CONCLUSION

Our data reveal that exposure to, and infection with, HCV causes disparate effects on adaptive B cells and innate immune cell such as myeloid cells and NK cells in infants.

Immune system control of hepatitis C virus infection

Hepatitis C virus (HCV) remains a global public health problem even though more than 95% of infections can be cured by treatment with direct-acting antiviral agents. Resolution of viremia post antiviral therapy does not lead to protective immunity and therefore reinfections can occur. Immune cell detection of HCV activates signaling pathways that produce interferons and trigger the innate immune response against the virus, preventing HCV replication and spread. Cells in the innate immune system, including natural killer, dendritic, and Kupffer cells, interact with infected hepatocytes and present viral antigens to T and B cells where their effector responses contribute to infection outcome. Despite the immune activation, HCV can evade the host response and establish persistent infection. Plans to understand the correlates of protection and strategies to activate proper innate and adaptive immune responses are needed for development of an effective prophylactic vaccine that stimulates protective immunity and limits HCV transmission.

Repertoire and Neutralizing Activity of Antibodies Against Hepatitis C Virus E2 Peptide in Patients With Spontaneous Resolution of Hepatitis C

Neutralizing antibodies can prevent hepatitis C virus (HCV) infection, one of the leading causes of cirrhosis and liver cancer. Here, we characterized the immunoglobulin repertoire of memory B-cell antibodies against a linear epitope in the central front layer of the HCV envelope (E2; amino acids 483-499) in patients who were infected in a single-source outbreak. A reverse transcription polymerase chain reaction-based immunoglobulin gene cloning and recombinant expression approach was used to express monoclonal antibodies from HCV E2 peptide-binding immunoglobulin G-positive memory B cells. We identified highly mutated antibodies with a neutralizing effect in vitro against different genotype isolates sharing similar gene features. Our data confirm the importance of VH1-69 use for neutralizing activity. The data offer a promising basis for vaccine research and the use of anti-E2 antibodies as a means of passive immunization.

Blockade of BAFF Reshapes the Hepatic B Cell Receptor Repertoire and Attenuates Autoantibody Production in Cholestatic Liver Disease

Defects in biliary transport proteins, MDR3 in humans and Mdr2 in mice, can lead to a spectrum of cholestatic liver disorders. Although B cell disorders and the aberrant Ab production are the leading extrahepatic manifestations of cholestatic liver diseases, the mechanism underlying this phenomenon is incompletely understood. Using mice with deficiency of Mdr2 that progressively develop cholestatic liver disease, we investigated the contributions of BAFF to aberrant IgG autoantibody production and hepatic fibrosis. In Mdr2^-/- mice, hepatic B lymphocytes constitutively produced IgG during fibrosis progression, which correlated with elevated serum levels of BAFF, antinuclear Abs (ANA) and immune complexes. The elevated BAFF and ANA titers were also detected in human patients with primary sclerosing cholangitis and hepatobiliary cholangiopathies. Consistent with the higher BAFF levels, liver-specific selection of the focused BCR IgH repertoire was found on hepatic B cells in Mdr2^-/- mice. Interestingly, the administration of anti-BAFF mAb in Mdr2^-/- mice altered the BCR repertoire on hepatic B lymphocytes and resulted in reduced ANA and immune complex titers. However, anti-BAFF treatment did not attenuate hepatic fibrosis as measured by collagen deposition, hepatic expressions of collagen-1a, α-smooth muscle actin, and mononuclear cell infiltration (CD11b⁺ Ly-6c^hi monocytes and CD11b⁺ Gr1⁺ neutrophils). Importantly, depletion of B cells by anti-CD20 mAb reduced both hepatic fibrosis and serum levels of ANA and immune complexes. Our findings implicate B cells as the potential therapeutic targets for hepatic fibrosis and targeting BAFF specifically for attenuating the autoantibody production associated with cholestatic liver disease.

Comparative characterization of B cells specific for HBV nucleocapsid and envelope proteins in patients with chronic hepatitis B

BACKGROUND & AIMS

Knowledge about the regulation of anti-HBV humoral immunity during natural HBV infection is limited. We recently utilized dual fluorochrome-conjugated HBsAg to demonstrate, in patients with chronic HBV (CHB) infection, the functional impairment of their HBsAg-specific B cells. However, the features of their HBcAg-specific B cells are unknown. Here we developed a method to directly visualize, select and characterize HBcAg-specific B cells in parallel with HBsAg-specific B cells.

METHODS

Fluorochrome-conjugated HBcAg reagents were synthesized and utilized to directly detect ex vivo HBcAg-specific B cells in 36 patients with CHB. The frequency, phenotype, functional maturation and transcriptomic profile of HBcAg-specific B cells was studied by flow cytometry, in vitro maturation assays and NanoString-based detection of expression of immune genes, which we compared with HBsAg-specific B cells and total B cells.

RESULTS

HBcAg-specific B cells are present at a higher frequency than HBsAg-specific B cells in patients with CHB and, unlike HBsAg-specific B cells, they mature efficiently into antibody-secreting cells in vitro. Their phenotypic and transcriptomic profiles show that HBcAg-specific B cells are preferentially IgG+ memory B cells. However, despite their phenotypic and functional differences, HBcAg- and HBsAg-specific B cells from patients with CHB share an mRNA expression pattern that differs from global memory B cells and is characterized by high expression of genes indicative of cross-presentation and innate immune activity.

CONCLUSIONS

During chronic HBV infection, a direct relation exists between serological detection of anti-HBs and anti-HBc antibodies, and the quantity and function of their respective specific B cells. However, the transcriptomic analysis performed in HBsAg- and HBcAg-specific B cells suggests additional roles of HBV-specific B cells beyond the production of antibodies.

LAY SUMMARY

Protection of viral infection necessitates the production of antibodies that are generated by specialized cells of the immune system called B cells. During chronic HBV infection, antibodies against the internal part of the virus (core or HBcAg) are detectable while the antibodies directed against the virus envelope (surface or HBsAg) are not present. Here we developed a method that allows us to directly visualize ex vivo the B cells specific for these 2 viral components, highlighting their differences and similarities, and showing how 2 components of the same virus can have different impacts on the function of antiviral B cells.

Circulating CXCR3+ Tfh cells positively correlate with neutralizing antibody responses in HCV-infected patients

Circulating T follicular helper (cTfh) cells have been identified as counterparts of germinal center Tfh (GC Tfh) cells in humans and can support T-dependent B cell maturation and antibody production in vitro. However, the role of cTfh cells in neutralizing antibody (nAb) responses in HCV infection remains unclear. Here, we characterized the phenotype and function of cTfh cells and demonstrated the associations of cTfh cells and their subsets with nAb responses in HCV infection. A total of 38 HCV-infected individuals and 28 healthy controls were enrolled from a pool of injection drug users. The frequency and function of blood Tfh cells were analyzed by flow cytometry. The titers and breadths of serum nAbs were measured using HCV pseudo-particle neutralization assays. Herein, we report several key observations. First, HCV infection skewed cTfh toward CXCR3⁺ cTfh cell differentiation. Second, the frequency of CXCR3⁺ cTfh cells positively correlated with HCV nAb titers and breadths. Third, CXCR3⁺ cTfh cells showed higher expression of Tfh-associated molecules (PD-1, ICOS, IL-21, Bcl-6) compared with CXCR3⁻ cTfh cells from individuals with HCV infection. Coculture of cTfh cells and autologous memory B cells in vitro indicated that CXCR3⁺ cTfh cells show a superior ability to support HCV E2-specific B cell expansion compared with CXCR3⁻ cTfh cells from individuals with HCV infection. HCV infection skews cTfh cells toward CXCR3-biased Tfh cell differentiation, which positively correlates with the magnitude and breadth of the HCV nAb response. It is our hope that these findings will provide insights for the rational design of a nAb-based HCV vaccine.

A method for detecting hepatitis C envelope specific memory B cells from multiple genotypes using cocktail E2 tetramers

Hepatitis C (HCV) is a rapidly mutating RNA virus, with a strong propensity to cause chronic infection and progressive liver disease. Recent evidence has shown that early appearance of neutralizing antibodies in primary infection is associated with clearance. Little is known about the characteristics of HCV-specific B cells and their correlation with outcomes in primary infection, as there is a lack of sensitive tools for HCV-specific B cells which are present at very low frequency. We describe the development and optimisation of tetramer staining for flow cytometric detection of HCV-specific B cells using a cocktail of two recombinant HCV Envelope-2 (rE2) glycoproteins (from genotype 1a and 3a; Gt1a and Gt3a) and streptavidin dyes. The optimal weight to weight (w/w) ratio of streptavidin-phycoerythrin (PE) and rE2 proteins were determined for sensitive detection using HCV E2-specific hybridoma cell lines and peripheral blood mononuclear cells (PBMC) from HCV-infected individuals. In a cross-sectional set of PBMC samples collected from 33 subjects with either chronic infection or previous clearance, HCV E2-specific B cells (CD19⁺CD20⁺CD10^-IgD^-tetramer⁺) were detected in 29 subjects (87.8%), with a mean frequency of 0.45% (0.012-2.20%). To validate the specificity of tetramer staining, 367 HCV E2-specific B cells were single cell sorted from 9 PBMC samples before monoclonal antibodies (mAbs) were synthesised, with 87.5% being reactive to E2 via ELISA. Of these mAbs, 284 and 246 clones were reactive to either Gt1a or Gt3a E2 proteins, respectively. This is a sensitive and robust method for future studies investigating B cell responses against the HCV Envelope protein.

Hepatitis C Vaccines, Antibodies, and T Cells

The development of vaccines that protect against persistent hepatitis C virus (HCV) infection remain a public health priority. The broad use of highly effective direct-acting antivirals (DAAs) is unlikely to achieve HCV elimination without vaccines that can limit viral transmission. Two vaccines targeting either the antibody or the T cell response are currently in preclinical or clinical trials. Next-generation vaccines will likely involve a combination of these two strategies. This review summarizes the state of knowledge about the immune protective role of HCV-specific antibodies and T cells and the current vaccine strategies. In addition, it discusses the potential efficacy of vaccination in DAA-cured individuals. Finally, it summarizes the challenges to vaccine development and the collaborative efforts required to overcome them.

Lectin microarray and mass spectrometric analysis of hepatitis C proteins reveals N-linked glycosylation

We used lectin microarray and mass spectrometric analysis to identify the N-linked glycosylation patterns of hepatitis C virus (HCV) particles. HCV J6/JFH-1 chimeric cell culture (HCVcc) in the culture supernatant was concentrated and purified by ultrafiltration and sucrose gradient ultracentrifugation. Twelve fractions were collected from the top and analyzed for viral infectivity and HCV RNA content after sucrose gradient separation. HCV RNA and proteins were separated by ultracentrifugation in a continuous 10% to 60% sucrose gradient to purify viral particles based on their sedimentation velocities. HCVcc particles were found mainly in fractions 6 to 8, as determined by quantitative polymerase chain reaction (qPCR) analysis for HCV RNA and ELISA of the HCV core protein. The N-glycans on HCV proteins were analyzed by lectin microarray and mass spectrometry. We identified that 32 of 37 lectins displayed the positive binding signals and 16 types of N-glycoforms of which the major HCV glycoforms were high mannose-type N-linked oligosaccharides, hybrid N-glycans, and fucosylated N-glycans. Our study provided new detailed information regarding the majority of the glycan-protein profile, complementing to previous findings of glycan-HCV protein interactions.

Selective expansion of high functional avidity memory CD8 T cell clonotypes during hepatitis C virus reinfection and clearance

The dynamics of the memory CD8 T cell receptor (TCR) repertoire upon virus re-exposure and factors governing the selection of TCR clonotypes conferring protective immunity in real life settings are poorly understood. Here, we examined the dynamics and functionality of the virus-specific memory CD8 TCR repertoire before, during and after hepatitis C virus (HCV) reinfection in patients who spontaneously resolved two consecutive infections (SR/SR) and patients who resolved a primary but failed to clear a subsequent infection (SR/CI). The TCR repertoire was narrower prior to reinfection in the SR/SR group as compared to the SR/CI group and became more focused upon reinfection. CD8 T cell clonotypes expanding upon re-exposure and associated with protection from viral persistence were recruited from the memory T cell pool. Individual CD8 T cell lines generated from the SR/SR group exhibited higher functional avidity and polyfunctionality as compared to cell lines from the SR/CI group. Our results suggest that protection from viral persistence upon HCV reinfection is associated with focusing of the HCV-specific CD8 memory T cell repertoire from which established cell lines showed high functional avidity. These findings are applicable to vaccination strategies aiming at shaping the protective human T cell repertoire.

In this study we examined the diversity and dynamics of the repertoire of receptors of CD8 T cells that are selected and enriched upon real-life multiple exposures to viral infections. Using hepatitis C virus (HCV) infection in a cohort of high risk people who inject drugs, we demonstrate that protection upon two subsequent infections was associated with a narrow repertoire of virus-specific CD8 T cells and selective expansion of cells with high polyfunctionality (increased TNFα production and cytotoxic potential). Our results have important implications in vaccination programs aiming at shaping the CD8 T cell repertoire against viral infections and cancers.