Broadly neutralizing antibodies from an individual that naturally cleared multiple hepatitis C virus infections uncover molecular determinants for E2 targeting and vaccine design

B cell characteristics define HCV reinfection outcome

BACKGROUND AND AIMS

In individuals highly exposed to hepatitis C virus (HCV), reinfection is common, suggesting that natural development of sterilising immunity is difficult. In those that are reinfected, some will develop a persistent infection, while a small proportion repeatedly clear the virus, suggesting natural protection is possible. The aim of this study was to characterise immune responses associated with rapid natural clearance of HCV reinfection.

METHODS

Broad neutralising antibodies (BnAbs) and Envelope 2 (E2)-specific memory B cell (MBCs) responses were examined longitudinally in 15 subjects with varied reinfection outcomes.

RESULTS

BnAb responses were associated with MBC recall, but not with reinfection clearance. Strong evidence of antigen imprinting was found, and the B cell receptor repertoire showed a high level of clonality with ongoing somatic hypermutation of many clones over subsequent reinfection events. Single cell transcriptomic analyses showed that cleared reinfections featured an activated transcriptomic profile in HCV-specific B cells that rapidly expanded upon reinfection.

CONCLUSIONS

MBC quality, but not necessarily breadth of nAb responses, is important for protection against antigenically diverse variants, which is encouraging for HCV vaccine development.

The bright side of chemistry: Exploring synthetic peptide-based anticancer vaccines

The present review focuses on synthetic peptide-based vaccine strategies in the context of anticancer intervention, paying attention to critical aspects such as peptide epitope selection, adjuvant integration, and nuanced classification of synthetic peptide cancer vaccines. Within this discussion, we delve into the diverse array of synthetic peptide-based anticancer vaccines, each derived from tumor-associated antigens (TAAs), including melanoma antigen recognized by T cells 1 (Melan-A or MART-1), mucin 1 (MUC1), human epidermal growth factor receptor 2 (HER-2), tumor protein 53 (p53), human telomerase reverse transcriptase (hTERT), survivin, folate receptor (FR), cancer-testis antigen 1 (NY-ESO-1), and prostate-specific antigen (PSA). We also describe the synthetic peptide-based vaccines developed for cancers triggered by oncovirus, such as human papillomavirus (HPV), and hepatitis C virus (HCV). Additionally, the potential synergy of peptide-based vaccines with common therapeutics in cancer was considered. The last part of our discussion deals with the realm of the peptide-based vaccines delivery, highlighting its role in translating the most promising candidates into effective clinical strategies. Although this discussion does not cover all the ongoing peptide vaccine investigations, it aims at offering valuable insights into the chemical modifications and the structural complexities of anticancer peptide-based vaccines.

Neutralizing antibodies evolve to exploit vulnerable sites in the HCV envelope glycoprotein E2 and mediate spontaneous clearance of infection

Individuals who clear primary hepatitis C virus (HCV) infections clear subsequent reinfections more than 80% of the time, but the mechanisms are poorly defined. Here, we used HCV variants and plasma from individuals with repeated clearance to characterize longitudinal changes in envelope glycoprotein E2 sequences, function, and neutralizing antibody (NAb) resistance. Clearance of infection was associated with early selection of viruses with NAb resistance substitutions that also reduced E2 binding to CD81, the primary HCV receptor. Later, peri-clearance plasma samples regained neutralizing capacity against these variants. We identified a subset of broadly NAbs (bNAbs) for which these loss-of-fitness substitutions conferred resistance to unmutated bNAb ancestors but increased sensitivity to mature bNAbs. These data demonstrate a mechanism by which neutralizing antibodies contribute to repeated immune-mediated HCV clearance, identifying specific bNAbs that exploit fundamental vulnerabilities in E2. The induction of bNAbs with these specificities should be a goal of HCV vaccine development.

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.

Signatures of VH1-69-derived hepatitis C virus neutralizing antibody precursors defined by binding to envelope glycoproteins

An effective preventive vaccine for hepatitis C virus (HCV) remains a major unmet need. Antigenic region 3 (AR3) on the E1E2 envelope glycoprotein complex overlaps with the CD81 receptor binding site and represents an important epitope for broadly neutralizing antibodies (bNAbs) and is therefore important for HCV vaccine design. Most AR3 bNAbs utilize the VH1-69 gene and share structural features that define the AR3C-class of HCV bNAbs. In this work, we identify recombinant HCV glycoproteins based on a permuted E2E1 trimer design that bind to the inferred VH1-69 germline precursors of AR3C-class bNAbs. When presented on nanoparticles, these recombinant E2E1 glycoproteins efficiently activate B cells expressing inferred germline AR3C-class bNAb precursors as B cell receptors. Furthermore, we identify critical signatures in three AR3C-class bNAbs that represent two subclasses of AR3C-class bNAbs that will allow refined protein design. These results provide a framework for germline-targeting vaccine design strategies against HCV.

Functional HIV-1/HCV cross-reactive antibodies isolated from a chronically co-infected donor

Despite prolific efforts to characterize the antibody response to human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) mono-infections, the response to chronic co-infection with these two ever-evolving viruses is poorly understood. Here, we investigate the antibody repertoire of a chronically HIV-1/HCV co-infected individual using linking B cell receptor to antigen specificity through sequencing (LIBRA-seq). We identify five HIV-1/HCV cross-reactive antibodies demonstrating binding and functional cross-reactivity between HIV-1 and HCV envelope glycoproteins. All five antibodies show exceptional HCV neutralization breadth and effector functions against both HIV-1 and HCV. One antibody, mAb688, also cross-reacts with influenza and coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We examine the development of these antibodies using next-generation sequencing analysis and lineage tracing and find that somatic hypermutation established and enhanced this reactivity. These antibodies provide a potential future direction for therapeutic and vaccine development against current and emerging infectious diseases. More broadly, chronic co-infection represents a complex immunological challenge that can provide insights into the fundamental rules that underly antibody-antigen specificity.

Identification of human progenitors of exhausted CD8(+) T cells associated with elevated IFN-γ response in early phase of viral infection

T cell exhaustion is a hallmark of hepatitis C virus (HCV) infection and limits protective immunity in chronic viral infections and cancer. Limited knowledge exists of the initial viral and immune dynamics that characterise exhaustion in humans. We studied longitudinal blood samples from a unique cohort of individuals with primary infection using single-cell multi-omics to identify the functions and phenotypes of HCV-specific CD8⁺ T cells. Early elevated IFN-γ response against the transmitted virus is associated with the rate of immune escape, larger clonal expansion, and early onset of exhaustion. Irrespective of disease outcome, we find heterogeneous subsets of progenitors of exhaustion, based on the level of PD-1 expression and loss of AP-1 transcription factors. Intra-clonal analysis shows distinct trajectories with multiple fates and evolutionary plasticity of precursor cells. These findings challenge the current paradigm on the contribution of CD8⁺ T cells to HCV disease outcome and provide data for future studies on T cell differentiation in human infections.

Induction of cross-neutralizing antibodies by a permuted hepatitis C virus glycoprotein nanoparticle vaccine candidate

Hepatitis C virus (HCV) infection affects approximately 58 million people and causes ~300,000 deaths yearly. The only target for HCV neutralizing antibodies is the highly sequence diverse E1E2 glycoprotein. Eliciting broadly neutralizing antibodies that recognize conserved cross-neutralizing epitopes is important for an effective HCV vaccine. However, most recombinant HCV glycoprotein vaccines, which usually include only E2, induce only weak neutralizing antibody responses. Here, we describe recombinant soluble E1E2 immunogens that were generated by permutation of the E1 and E2 subunits. We displayed the E2E1 immunogens on two-component nanoparticles and these nanoparticles induce significantly more potent neutralizing antibody responses than E2. Next, we generated mosaic nanoparticles co-displaying six different E2E1 immunogens. These mosaic E2E1 nanoparticles elicit significantly improved neutralization compared to monovalent E2E1 nanoparticles. These results provide a roadmap for the generation of an HCV vaccine that induces potent and broad neutralization.

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.

The Neutralizing Antibody Responses of Individuals That Spontaneously Resolve Hepatitis C Virus Infection

Hepatitis C virus (HCV) infection is a major global health problem. In the majority of cases the virus is not cleared by the host immune response and progresses to chronic infection. Studies of the neutralizing antibody responses in individuals that naturally clear infection are limited. Understanding what constitutes a successful antibody response versus one that has 'failed' and resulted in chronic infection is important to understand what type of antibody response would need to be elicited by a protective vaccine. Samples from spontaneous clearers are difficult to obtain therefore studies are often limited. In our study through HCV Research UK, we had access to a cohort of over 200 samples. We identified the samples that contained HCV neutralizing antibodies using ELISA and HCV pseudoparticle (HCVpp) assays. We then utilised mutagenesis and cross-competition analysis to determine the profile of the neutralizing antibody responses. In addition, we analysed a cohort of samples from chronic infection using the same techniques to enable direct comparison of the antibody profiles observed in both cohorts. We conclude that similar profiles are present in both cohorts indicating that it is not the neutralizing antibody response per se that determines the outcome of infection. These data will provide useful information for future HCV vaccine design.

Computational identification of HCV neutralizing antibodies with a common HCDR3 disulfide bond motif in the antibody repertoires of infected individuals

Despite recent success in hepatitis C virus (HCV) treatment using antivirals, an HCV vaccine is still needed to prevent reinfections in treated patients, to avert the emergence of drug-resistant strains, and to provide protection for people with no access to the antiviral therapeutics. The early production of broadly neutralizing antibodies (bNAbs) associates with HCV clearance. Several potent bNAbs bind a conserved HCV glycoprotein E2 epitope using an unusual heavy chain complementarity determining region 3 (HCDR3) containing an intra-loop disulfide bond. Isolation of additional structurally-homologous bNAbs would facilitate the recognition of key determinants of such bNAbs and guide rational vaccine design. Here we report the identification of new antibodies containing an HCDR3 disulfide bond motif using computational screening with the Rosetta software. Using the newly-discovered and already-known members of this antibody family, we review the required HCDR3 amino acid composition and propose determinants for the bent versus straight HCDR3 loop conformation observed in these antibodies.

Sites of vulnerability in HCV E1E2 identified by comprehensive functional screening

The E1 and E2 envelope proteins of hepatitis C virus (HCV) form a heterodimer that drives virus-host membrane fusion. Here, we analyze the role of each amino acid in E1E2 function, expressing 545 individual alanine mutants of E1E2 in human cells, incorporating them into infectious viral pseudoparticles, and testing them against 37 different monoclonal antibodies (MAbs) to ascertain full-length translation, folding, heterodimer assembly, CD81 binding, viral pseudoparticle incorporation, and infectivity. We propose a model describing the role of each critical residue in E1E2 functionality and use it to examine how MAbs neutralize infection by exploiting functionally critical sites of vulnerability on E1E2. Our results suggest that E1E2 is a surprisingly fragile protein complex where even a single alanine mutation at 92% of positions disrupts its function. The amino-acid-level targets identified are highly conserved and functionally critical and can be exploited for improved therapies and vaccines.

Inactivated whole hepatitis C virus vaccine employing a licensed adjuvant elicits cross-genotype neutralizing antibodies in mice

BACKGROUND & AIMS

A prophylactic vaccine is required to eliminate HCV as a global public health threat. We developed whole virus inactivated HCV vaccine candidates employing a licensed adjuvant. Further, we investigated the effects of HCV envelope protein modifications (to increase neutralization epitope exposure) on immunogenicity.

METHODS

Whole virus vaccine antigen was produced in Huh7.5 hepatoma cells, processed using a multistep protocol and formulated with adjuvant (MF-59 analogue AddaVax or aluminium hydroxide). We investigated the capacity of IgG purified from the serum of immunized BALB/c mice to neutralize genotype 1-6 HCV (by virus neutralization assays) and to bind homologous envelope proteins (by ELISA). Viruses used for immunizations were (i) HCV5aHi with strain SA13 envelope proteins and modification of an O-linked glycosylation site in E2 (T385P), (ii) HCV5aHi(T385) with reversion of T385P to T385, featuring the original E2 sequence determined in vivo and (iii) HCV5aHi(ΔHVR1) with deletion of HVR1. For these viruses, epitope exposure was investigated using human monoclonal (AR3A and AR4A) and polyclonal (C211 and H06) antibodies in neutralization assays.

RESULTS

Processed HCV5aHi formulated with AddaVax induced antibodies that efficiently bound homologous envelope proteins and broadly neutralized cultured genotype 1-6 HCV, with half maximal inhibitory concentrations of between 14 and 192 μg/ml (mean of 36 μg/ml against the homologous virus). Vaccination with aluminium hydroxide was less immunogenic. Compared to HCV5aHi(T385) with the original E2 sequence, HCV5aHi with a modified glycosylation site and HCV5aHi(ΔHVR1) without HVR1 showed increased neutralization epitope exposure but similar immunogenicity.

CONCLUSION

Using an adjuvant suitable for human use, we developed inactivated whole HCV vaccine candidates that induced broadly neutralizing antibodies, which warrant investigation in further pre-clinical studies.

LAY SUMMARY

A vaccine against hepatitis C virus (HCV) is needed to prevent the estimated 2 million new infections and 400,000 deaths caused by this virus each year. We developed inactivated whole HCV vaccine candidates using adjuvants licensed for human use, which, following immunization of mice, induced antibodies that efficiently neutralized all HCV genotypes with recognized epidemiological importance. HCV variants with modified envelope proteins exhibited similar immunogenicity as the virus with the original envelope proteins.

Induction of broadly neutralizing antibodies using a secreted form of the hepatitis C virus E1E2 heterodimer as a vaccine candidate

SignificanceHepatitis C virus chronically infects approximately 1% of the world's population, making an effective vaccine for hepatitis C virus a major unmet public health need. The membrane-associated E1E2 envelope glycoprotein has been used in clinical studies as a vaccine candidate. However, limited neutralization breadth and difficulty in producing large amounts of homogeneous membrane-associated E1E2 have hampered efforts to develop an E1E2-based vaccine. Our previous work described the design and biochemical validation of a native-like soluble secreted form of E1E2 (sE1E2). Here, we describe the immunogenic characterization of the sE1E2 complex. sE1E2 elicited broadly neutralizing antibodies in immunized mice, with increased neutralization breadth relative to the membrane-associated E1E2, thereby validating this platform as a promising model system for vaccine development.

Peptides for Vaccine Development

This review discusses peptide epitopes used as antigens in the development of vaccines in clinical trials as well as future vaccine candidates. It covers peptides used in potential immunotherapies for infectious diseases including SARS-CoV-2, influenza, hepatitis B and C, HIV, malaria, and others. In addition, peptides for cancer vaccines that target examples of overexpressed proteins are summarized, including human epidermal growth factor receptor 2 (HER-2), mucin 1 (MUC1), folate receptor, and others. The uses of peptides to target cancers caused by infective agents, for example, cervical cancer caused by human papilloma virus (HPV), are also discussed. This review also provides an overview of model peptide epitopes used to stimulate non-specific immune responses, and of self-adjuvanting peptides, as well as the influence of other adjuvants on peptide formulations. As highlighted in this review, several peptide immunotherapies are in advanced clinical trials as vaccines, and there is great potential for future therapies due the specificity of the response that can be achieved using peptide epitopes.

Evolutionary modeling reveals enhanced mutational flexibility of HCV subtype 1b compared with 1a

Hepatitis C virus (HCV) is a leading cause of liver-associated disease and liver cancer. Of the major HCV subtypes, patients infected with subtype 1b have been associated with having a higher risk of developing chronic infection and hepatocellular carcinoma. However, underlying reasons for this increased disease severity remain unknown. Here, we provide an evolutionary rationale, based on a comparative study of fitness landscape and in-host evolutionary models of the E2 glycoprotein of HCV subtypes 1a and 1b. Our analysis demonstrates that a higher chronicity rate of 1b may be attributed to lower fitness constraints, enabling 1b viruses to more easily escape antibody responses. More generally, our results suggest that differences in evolutionary constraints between HCV subtypes may be an important factor in mediating distinct disease outcomes. Our analysis also identifies antibodies that appear escape-resistant against both subtypes 1a and 1b, providing directions for designing HCV vaccines having cross-subtype protection.

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Comparative analysis of the fitness landscapes of HCV subtypes 1a and 1b

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Subtype 1b evolution is subject to less constraints than 1a

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Subtype 1b appears to evade antibodies more easily compared with 1a

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Antibodies are identified that are difficult to escape for both subtypes 1a and 1b

Challenges and Prospects of Plant-Derived Oral Vaccines against Hepatitis B and C Viruses

Hepatitis B and C viruses chronically affect approximately 3.5% of the global population, causing more than 800,000 deaths yearly due to severe liver pathogenesis. Current HBV vaccines have significantly contributed to the reduction of chronic HBV infections, supporting the notion that virus eradication is a feasible public health objective in the near future. In contrast to HBV, a prophylactic vaccine against HCV infection is not available yet; however, intense research efforts within the last decade have significantly advanced the field and several vaccine candidates are shortlisted for clinical trials. A successful vaccine against an infectious disease of global importance must not only be efficient and safe, but also easy to produce, distribute, administer, and economically affordable to ensure appropriate coverage. Some of these requirements could be fulfilled by oral vaccines that could complement traditional immunization strategies. In this review, we discuss the potential of edible plant-based oral vaccines in assisting the worldwide fight against hepatitis B and C infections. We highlight the latest research efforts to reveal the potential of oral vaccines, discuss novel antigen designs and delivery strategies, as well as the limitations and controversies of oral administration that remain to be addressed to make this approach successful.

Characterization of linear epitope specificity of antibodies potentially contributing to spontaneous clearance of hepatitis C virus

Background

Around 30% of the HCV infected patients can spontaneously clear the virus. Cumulative evidence suggests the role of neutralizing antibodies in such spontaneous resolution. Understanding the epitope specificity of such antibodies will inform the rational vaccine design as such information is limited to date. In addition to conformational epitope targeted antibodies, linear epitope specific antibodies have been identified that are broadly cross reactive against diverse HCV strains. In this study, we have characterized the potential role of three conserved linear epitopes in the spontaneous clearance of HCV.

Methods

We tested the reactivity of sera from chronic patients (CP) and spontaneous resolvers (SR) with linear peptides corresponding to three conserved regions of HCV envelope protein E2 spanning amino acids 412–423, 523–532 and 432–443 using ELISA. Subsequently, we characterized the dependency of HCV neutralization by the reactive serum samples on the antibodies specific for these epitopes using pseudoparticle-based neutralization assay.

In ELISA most of the CP sera showed reactivity to multiple peptides while most of the SR samples were reactive to a single peptide suggesting presence of more specific antibodies in the SR sera. In most of the HCVpp neutralizing sera of particular peptide reactivity the neutralization was significantly affected by the presence of respective peptide. HCV neutralization by CP sera was affected by multiple peptides while 75% of the HCVpp neutralizing SR sera were competed by the 432 epitope.

Conclusions

These findings suggest that individuals who spontaneously resolve HCV infection at the acute phase, can produce antibodies specific for conserved linear epitopes, and those antibodies can potentially play a role in the spontaneous viral clearance. The epitope present in the 432–443 region of E2 was identified as the primary neutralizing epitope with potential role in spontaneous viral clearance and this epitope potentiates for the design of immunogen for prophylactic vaccine.

Hepatitis C virus envelope protein dynamics and the link to hypervariable region 1

Conformational dynamics of viral envelope proteins seem to be involved in mediating evasion from neutralizing antibodies (NAbs) by mechanisms that limit exposure of conserved protein motifs. For hepatitis C virus (HCV), molecular studies have only recently begun to unveil how such dynamics of the envelope protein heterodimer, E1/E2, are linked to viral entry and NAb evasion. Here, we review data suggesting that E1/E2 exists in an equilibrium between theoretical 'open' (NAb-sensitive) and 'closed' (NAb-resistant) conformational states. We describe how this equilibrium is influenced by viral sequence polymorphisms and that it is critically dependent on the N-terminal region of E2, termed hypervariable region 1 (HVR1). Finally, we discuss how it appears that the virus binding site for the HCV entry co-receptor CD81 is less available in 'closed' E1/E2 states and that NAb-resistant viruses require a more intricate entry pathway involving also the entry co-receptor, SR-BI.

Antigenic and immunogenic evaluation of permutations of soluble hepatitis C virus envelope protein E2 and E1 antigens

Yearly, about 1.5 million people become chronically infected with hepatitis C virus (HCV) and for the 71 million with chronic HCV infection about 400,000 die from related morbidities, including liver cirrhosis and cancer. Effective treatments exist, but challenges including cost-of-treatment and wide-spread undiagnosed infection, necessitates the development of vaccines. Vaccines should induce neutralizing antibodies (NAbs) against the HCV envelope (E) transmembrane glycoprotein 2, E2, which partly depends on its interaction partner, E1, for folding. Here, we generated three soluble HCV envelope protein antigens with the transmembrane regions deleted (i.e., fused peptide backbones), termed sE1E2 (E1 followed by E2), sE2E1 (E2 followed by E1), and sE21E (E2 followed by inverted E1). The E1 inversion for sE21E positions C-terminal residues of E1 near C-terminal residues of E2, which is in analogy to how they likely interact in native E1/E2 complexes. Probing conformational E2 epitope binding using HCV patient-derived human monoclonal antibodies, we show that sE21E was superior to sE2E1, which was consistently superior to sE1E2. This correlated with improved induction of NAbs by sE21E compared with sE2E1 and especially compared with sE1E2 in female BALB/c mouse immunizations. The deletion of the 27 N-terminal amino acids of E2, termed hypervariable region 1 (HVR1), conferred slight increases in antigenicity for sE2E1 and sE21E, but severely impaired induction of antibodies able to neutralize in vitro viruses retaining HVR1. Finally, comparing sE21E with sE2 in mouse immunizations, we show similar induction of heterologous NAbs. In summary, we find that C-terminal E2 fusion of E1 or 1E is superior to N-terminal fusion, both in terms of antigenicity and the induction of heterologous NAbs. This has relevance when designing HCV E1E2 vaccine antigens.

Hepatitis C Virus Epitope Immunodominance and B Cell Repertoire Diversity

Despite the advent of effective, curative treatments for hepatitis C virus (HCV), a preventative vaccine remains essential for the global elimination of HCV. It is now clear that the induction of broadly neutralising antibodies (bNAbs) is essential for the rational design of such a vaccine. This review details the current understanding of epitopes on the HCV envelope, characterising the potency, breadth and immunodominance of antibodies induced against these epitopes, as well as describing the interactions between B-cell receptors and HCV infection, with a particular focus on bNAb heavy and light chain variable gene usage. Additionally, we consider the importance of a public repertoire for antibodies against HCV, compiling current knowledge and suggesting that further research in this area may be critical to the rational design of an effective HCV vaccine.

Structure-Based and Rational Design of a Hepatitis C Virus Vaccine

A hepatitis C virus (HCV) vaccine is a critical yet unfulfilled step in addressing the global disease burden of HCV. While decades of research have led to numerous clinical and pre-clinical vaccine candidates, these efforts have been hindered by factors including HCV antigenic variability and immune evasion. Structure-based and rational vaccine design approaches have capitalized on insights regarding the immune response to HCV and the structures of antibody-bound envelope glycoproteins. Despite successes with other viruses, designing an immunogen based on HCV glycoproteins that can elicit broadly protective immunity against HCV infection is an ongoing challenge. Here, we describe HCV vaccine design approaches where immunogens were selected and optimized through analysis of available structures, identification of conserved epitopes targeted by neutralizing antibodies, or both. Several designs have elicited immune responses against HCV in vivo, revealing correlates of HCV antigen immunogenicity and breadth of induced responses. Recent studies have elucidated the functional, dynamic and immunological features of key regions of the viral envelope glycoproteins, which can inform next-generation immunogen design efforts. These insights and design strategies represent promising pathways to HCV vaccine development, which can be further informed by successful immunogen designs generated for other viruses.

From Structural Studies to HCV Vaccine Design

Hepatitis C virus (HCV) is a serious and growing public health problem despite recent developments of antiviral therapeutics. To achieve global elimination of HCV, an effective cross-genotype vaccine is needed. The failure of previous vaccination trials to elicit an effective cross-reactive immune response demands better vaccine antigens to induce a potent cross-neutralizing response to improve vaccine efficacy. HCV E1 and E2 envelope (Env) glycoproteins are the main targets for neutralizing antibodies (nAbs), which aid in HCV clearance and protection. Therefore, a molecular-level understanding of the nAb responses against HCV is imperative for the rational design of cross-genotype vaccine antigens. Here we summarize the recent advances in structural studies of HCV Env and Env-nAb complexes and how they improve our understanding of immune recognition of HCV. We review the structural data defining HCV neutralization epitopes and conformational plasticity of the Env proteins, and the knowledge applicable to rational vaccine design.

To Include or Occlude: Rational Engineering of HCV Vaccines for Humoral Immunity

Direct-acting antiviral agents have proven highly effective at treating existing hepatitis C infections but despite their availability most countries will not reach the World Health Organization targets for elimination of HCV by 2030. A prophylactic vaccine remains a high priority. Whilst early vaccines focused largely on generating T cell immunity, attention is now aimed at vaccines that generate humoral immunity, either alone or in combination with T cell-based vaccines. High-resolution structures of hepatitis C viral glycoproteins and their interaction with monoclonal antibodies isolated from both cleared and chronically infected people, together with advances in vaccine technologies, provide new avenues for vaccine development.

Functional convergence of a germline-encoded neutralizing antibody response in rhesus macaques immunized with HCV envelope glycoproteins

Human IGHV1-69-encoded broadly neutralizing antibodies (bnAbs) that target the hepatitis C virus (HCV) envelope glycoprotein (Env) E2 are important for protection against HCV infection. An IGHV1-69 ortholog gene, VH1.36, is preferentially used for bnAbs isolated from HCV Env-immunized rhesus macaques (RMs). Here, we studied the genetic, structural, and functional properties of VH1.36-encoded bnAbs generated by vaccination, in comparison to IGHV1-69-encoded bnAbs from HCV patients. Global B cell repertoire analysis confirmed the expansion of VH1.36-derived B cells in immunized animals. Most E2-specific, VH1.36-encoded antibodies cross-neutralized HCV. Crystal structures of two RM bnAbs with E2 revealed that the RM bnAbs engaged conserved E2 epitopes using similar molecular features as human bnAbs but with a different binding mode. Longitudinal analyses of the RM antibody repertoire responses during immunization indicated rapid lineage development of VH1.36-encoded bnAbs with limited somatic hypermutation. Our findings suggest functional convergence of a germline-encoded bnAb response to HCV Env with implications for vaccination in humans.

Mechanisms of Hepatitis C Virus Escape from Vaccine-Relevant Neutralizing Antibodies

Hepatitis C virus (HCV) is a major causative agent of acute and chronic hepatitis. It is estimated that 400,000 people die every year from chronic HCV infection, mostly from severe liver-related diseases such as cirrhosis and liver cancer. Although HCV was discovered more than 30 years ago, an efficient prophylactic vaccine is still missing. The HCV glycoprotein complex, E1/E2, is the principal target of neutralizing antibodies (NAbs) and, thus, is an attractive antigen for B-cell vaccine design. However, the high genetic variability of the virus necessitates the identification of conserved epitopes. Moreover, the high intrinsic mutational capacity of HCV allows the virus to continually escape broadly NAbs (bNAbs), which is likely to cause issues with vaccine-resistant variants. Several studies have assessed the barrier-to-resistance of vaccine-relevant bNAbs in vivo and in vitro. Interestingly, recent studies have suggested that escape substitutions can confer antibody resistance not only by direct modification of the epitope but indirectly through allosteric effects, which can be grouped based on the breadth of these effects on antibody susceptibility. In this review, we summarize the current understanding of HCV-specific NAbs, with a special focus on vaccine-relevant bNAbs and their targets. We highlight antibody escape studies pointing out the different methodologies and the escape mutations identified thus far. Finally, we analyze the antibody escape mechanisms of envelope protein escape substitutions and polymorphisms according to the most recent evidence in the HCV field. The accumulated knowledge in identifying bNAb epitopes as well as assessing barriers to resistance and elucidating relevant escape mechanisms may prove critical in the successful development of an HCV B-cell vaccine.

Antibody Responses in Hepatitis C Infection

Antibody responses in hepatitis C virus (HCV) have been a rather mysterious research topic for many investigators working in the field. Chronic HCV infection is often associated with dysregulation of immune functions particularly in B cells, leading to abnormal lymphoproliferation or the production of autoantibodies that exacerbate inflammation and extrahepatic diseases. When considering the antiviral function of antibody, it was difficult to endorse its role in HCV protection, whereas T-cell response has been shown unequivocally critical for natural recovery. Recent breakthroughs in the study of HCV and antigen-specific antibody responses provide important insights into viral vulnerability to antibodies and the immunogenetic and structural properties of the neutralizing antibodies. The new knowledge reinvigorates HCV vaccine research by illuminating a new path for the rational design of vaccine antigens to elicit broadly neutralizing antibodies for protection.

Design of a native-like secreted form of the hepatitis C virus E1E2 heterodimer

Hepatitis C virus (HCV) is a major worldwide health burden, and a preventive vaccine is needed for global control or eradication of this virus. A substantial hurdle to an effective HCV vaccine is the high variability of the virus, leading to immune escape. The E1E2 glycoprotein complex contains conserved epitopes and elicits neutralizing antibody responses, making it a primary target for HCV vaccine development. However, the E1E2 transmembrane domains that are critical for native assembly make it challenging to produce this complex in a homogenous soluble form that is reflective of its state on the viral envelope. To enable rational design of an E1E2 vaccine, as well as structural characterization efforts, we have designed a soluble, secreted form of E1E2 (sE1E2). As with soluble glycoprotein designs for other viruses, it incorporates a scaffold to enforce assembly in the absence of the transmembrane domains, along with a furin cleavage site to permit native-like heterodimerization. This sE1E2 was found to assemble into a form closer to its expected size than full-length E1E2. Preservation of native structural elements was confirmed by high-affinity binding to a panel of conformationally specific monoclonal antibodies, including two neutralizing antibodies specific to native E1E2 and to its primary receptor, CD81. Finally, sE1E2 was found to elicit robust neutralizing antibodies in vivo. This designed sE1E2 can both provide insights into the determinants of native E1E2 assembly and serve as a platform for production of E1E2 for future structural and vaccine studies, enabling rational optimization of an E1E2-based antigen.

Hepatitis C virus associated hepatocellular carcinoma

Liver cancer is a global problem and hepatocellular carcinoma (HCC) accounts for about 85% of this cancer. In the USA, etiologies and risk factors for HCC include chronic hepatitis C virus (HCV) infection, diabetes, non-alcoholic steatohepatitis (NASH), obesity, excessive alcohol drinking, exposure to tobacco smoke, and genetic factors. Chronic HCV infection appears to be associated with about 30% of HCC. Chronic HCV infection induces multistep changes in liver, involving metabolic disorders, steatosis, cirrhosis and HCC. Liver carcinogenesis requires initiation of neoplastic clones, and progression to clinically diagnose malignancy. Tumor progression associates with profound exhaustion of tumor-antigen-specific CD8⁺T cells, and accumulation of PD-1^hi CD8⁺T cells and Tregs. In this chapter, we provide a brief description of HCV and environmental/genetic factors, immune regulation, and highlight mechanisms of HCV associated HCC. We also underscore HCV treatment and recent paradigm of HCC progression, highlighted the current treatment and potential future therapeutic opportunities.

Immune system control of hepatitis C virus infection. Curr Opin Virol. 2021;46:36-44. [PMID: 33137689 DOI: 10.1016/j.coviro.2020.10.002]

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.

Hepatitis C virus vaccine design: focus on the humoral immune response

Despite the recent development of safe and highly effective direct-acting antivirals, hepatitis C virus (HCV) infection remains a significant health problem. In 2016, the World Health Organization set out to reduce the rate of new HCV infections by 90% by 2030. Still, global control of the virus does not seem to be achievable in the absence of an effective vaccine. Current approaches to the development of a vaccine against HCV include the production of recombinant proteins, synthetic peptides, DNA vaccines, virus-like particles, and viral vectors expressing various antigens. In this review, we focus on the development of vaccines targeting the humoral immune response against HCV based on the cumulative evidence supporting the important role of neutralizing antibodies in protection against HCV infection. The main targets of HCV-specific neutralizing antibodies are the glycoproteins E1 and E2. Recent advances in the knowledge of HCV glycoprotein structure and their epitopes, as well as the possibility of getting detailed information on the human antibody repertoire generated by the infection, will allow rational structure-based antigen design to target specific germline antibodies. Although obtaining a vaccine capable of inducing sterilizing immunity will be a difficult task, a vaccine that prevents chronic hepatitis C infections, a more realistic goal in the short term, would have a considerable health impact.

An alternate conformation of HCV E2 neutralizing face as an additional vaccine target

To achieve global elimination of hepatitis C virus (HCV), an effective cross-genotype vaccine is needed. The HCV envelope glycoprotein E2 is the main target for neutralizing antibodies (nAbs), which aid in HCV clearance and protection. E2 is structurally flexible and functions in engaging host receptors. Many nAbs bind to the "neutralizing face" on E2, including several broadly nAbs encoded by the V_H1-69 germline gene family that bind to a similar conformation (A) of this face. Here, a previously unknown conformation (B) of the neutralizing face is revealed in crystal structures of two of four additional E2-V_H1-69 nAb complexes. In this conformation, the E2 front-layer region is displaced upon antibody binding, exposing residues in the back layer for direct antibody interaction. This E2 B structure may represent another conformational state in the viral entry process that is susceptible to antibody neutralization and thus provide a new target for rational vaccine development.

Substitution of the CD81 Binding Site and β-Sandwich Area in E2 of HCV in Cambodia

The high genetic variability of hepatitis C virus (HCV) is the main obstacle to developing a vaccine. E2 has attracted attention for vaccine development because targeting this protein could potentially overcome issues related to the genetic diversity of HCV. In this study, we analyzed HCV genes in the general population of Cambodia and investigated the E2 locus as a candidate for vaccine development. HCV sero-epidemiological surveys were conducted between the period 2010 and 2014, with an HCV RNA–positive rate of 1.3% (11/868). Follow-up blood samples were collected from four anti-HCV– and HCV RNA– positive patients (genotype 1b: 2 cases, 6e: 1 case, 6r: 1 case) after 4.12 years. Analysis of HCV full-length nucleotide sequences in paired specimens revealed that the mutation rates of HCV genotypes 1b and 6e/6r were 1.61–2.03 × 10⁻³ and 2.52–2.74 × 10⁻³ substitutions/site/year, respectively. Non-synonymous substitutions were detected in HVR1, the front layer of the CD81 binding site, and the β-sandwich, but not in the N-terminal region or adjacent to the CD81 binding site. Therefore, we conclude that the CD81 binding site is a promising locus for HCV vaccine development.

Proof of concept for rational design of hepatitis C virus E2 core nanoparticle vaccines

Hepatitis C virus (HCV) envelope glycoproteins E1 and E2 are responsible for cell entry, with E2 being the major target of neutralizing antibodies (NAbs). Here, we present a comprehensive strategy for B cell-based HCV vaccine development through E2 optimization and nanoparticle display. We redesigned variable region 2 in a truncated form (tVR2) on E2 cores derived from genotypes 1a and 6a, resulting in improved stability and antigenicity. Crystal structures of three optimized E2 cores with human cross-genotype NAbs (AR3s) revealed how the modified tVR2 stabilizes E2 without altering key neutralizing epitopes. We then displayed these E2 cores on 24- and 60-meric nanoparticles and achieved substantial yield and purity, as well as enhanced antigenicity. In mice, these nanoparticles elicited more effective NAb responses than soluble E2 cores. Next-generation sequencing (NGS) defined distinct B cell patterns associated with nanoparticle-induced antibody responses, which target the conserved neutralizing epitopes on E2 and cross-neutralize HCV genotypes.

Peptide-Based Vaccines: Current Progress and Future Challenges

Vaccines have had a profound impact on the management and prevention of infectious disease. In addition, the development of vaccines against chronic diseases has attracted considerable interest as an approach to prevent, rather than treat, conditions such as cancer, Alzheimer's disease, and others. Subunit vaccines consist of nongenetic components of the infectious agent or disease-related epitope. In this Review, we discuss peptide-based vaccines and their potential in three therapeutic areas: infectious disease, Alzheimer's disease, and cancer. We discuss factors that contribute to vaccine efficacy and how these parameters may potentially be modulated by design. We examine both clinically tested vaccines as well as nascent approaches and explore current challenges and potential remedies. While peptide vaccines hold substantial promise in the prevention of human disease, many obstacles remain that have hampered their clinical use; thus, continued research efforts to address these challenges are warranted.

An ultralong CDRH2 in HCV neutralizing antibody demonstrates structural plasticity of antibodies against E2 glycoprotein

A vaccine protective against diverse HCV variants is needed to control the HCV epidemic. Structures of E2 complexes with front layer-specific broadly neutralizing antibodies (bNAbs) isolated from HCV-infected individuals, revealed a disulfide bond-containing CDRH3 that adopts straight (individuals who clear infection) or bent (individuals with chronic infection) conformation. To investigate whether a straight versus bent disulfide bond-containing CDRH3 is specific to particular HCV-infected individuals, we solved a crystal structure of the HCV E2 ectodomain in complex with AR3X, a bNAb with an unusually long CDRH2 that was isolated from the chronically-infected individual from whom the bent CDRH3 bNAbs were derived. The structure revealed that AR3X utilizes both its ultralong CDRH2 and a disulfide motif-containing straight CDRH3 to recognize the E2 front layer. These results demonstrate that both the straight and bent CDRH3 classes of HCV bNAb can be elicited in a single individual, revealing a structural plasticity of VH1-69-derived bNAbs.

A stereotyped light chain may shape virus-specific B-cell receptors in HCV-dependent lymphoproliferative disorders

Hepatitis C virus (HCV) causes B-cell lymphoproliferative disorders (LPDs) expressing stereotyped B-cell receptors (BCRs) endowed with rheumatoid factor (RF) activity and putatively recognizing the HCV E2 protein. To further untangle the shaping and function of these BCRs, we analyzed immunoglobulin gene rearrangements of monoclonal B cells from 13 patients with HCV-associated LPDs and correlated their features with the clinical outcomes of antiviral therapy. While only two patients shared a stereotyped heavy-chain complementarity determining region 3 (CDR3) sequence, two kappa chain CDR3 stereotyped sequences accounted for 77% of BCRs. Light chains were enriched in sequences homologous to anti-HCV E2 antibodies compared with heavy chains (7/13 vs. 0/13; p = 0.005). Anti-HCV E2 homology was uniquely associated (7/7 vs. 0/6; p = 0.0006) with a stereotyped CDR3 sequence encoded by IGKV3-20/3D-20 gene(s) accounting for 54% of BCRs. An IGKV3-15/IGKJ1-encoded stereotyped sequence homologous to WA RF accounted for 23% of BCRs. LPDs expressing KCDR3s homologous to anti-HCV E2 antibodies responded more frequently to the eradication of HCV by antiviral therapy (6/6 vs. 1/6; p = 0.015). These findings, although limited by the small sample size, suggest that a stereotyped KCDR3 may predominantly shape anti-HCV specificity of BCRs, possibly providing a signature that may help identifying bona fide HCV-dependent LPDs.

Flexibility and intrinsic disorder are conserved features of hepatitis C virus E2 glycoprotein

The glycoproteins of hepatitis C virus, E1E2, are unlike any other viral fusion machinery yet described, and are the current focus of immunogen design in HCV vaccine development; thus, making E1E2 both scientifically and medically important. We used pre-existing, but fragmentary, structures to model a complete ectodomain of the major glycoprotein E2 from three strains of HCV. We then performed molecular dynamic simulations to explore the conformational landscape of E2, revealing a number of important features. Despite high sequence divergence, and subtle differences in the models, E2 from different strains behave similarly, possessing a stable core flanked by highly flexible regions, some of which perform essential functions such as receptor binding. Comparison with sequence data suggest that this consistent behaviour is conferred by a network of conserved residues that act as hinge and anchor points throughout E2. The variable regions (HVR-1, HVR-2 and VR-3) exhibit particularly high flexibility, and bioinformatic analysis suggests that HVR-1 is a putative intrinsically disordered protein region. Dynamic cross-correlation analyses demonstrate intramolecular communication and suggest that specific regions, such as HVR-1, can exert influence throughout E2. To support our computational approach we performed small-angle X-ray scattering with purified E2 ectodomain; this data was consistent with our MD experiments, suggesting a compact globular core with peripheral flexible regions. This work captures the dynamic behaviour of E2 and has direct relevance to the interaction of HCV with cell-surface receptors and neutralising antibodies.

Plasma deconvolution identifies broadly neutralizing antibodies associated with hepatitis C virus clearance

A vaccine for hepatitis C virus (HCV) is urgently needed. Development of broadly-neutralizing plasma antibodies during acute infection is associated with HCV clearance, but the viral epitopes of these plasma antibodies are unknown. Identification of these epitopes could define the specificity and function of neutralizing antibodies (NAbs) that should be induced by a vaccine. Here, we present development and application of a high-throughput method that deconvolutes polyclonal anti-HCV NAbs in plasma, delineating the epitope specificities of anti-HCV NAbs in acute infection plasma of forty-four humans with subsequent clearance or persistence of HCV. Remarkably, we identified multiple broadly neutralizing antibody (bNAb) combinations that were associated with greater plasma neutralizing breadth and with HCV clearance. These studies have potential to inform new strategies for vaccine development by identifying bNAb combinations in plasma associated with natural clearance of HCV, while also providing a high-throughput assay that could identify these responses after vaccination trials.