Neutralizing antibody response during acute and chronic hepatitis C virus infection

Biomarkers in Detection of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infection affects 58 million people worldwide. In the United States, the incidence rate of acute hepatitis C has doubled since 2014; during 2021, this increased to 5% from 2020. Acute hepatitis C is defined by any symptom of acute viral hepatitis plus either jaundice or elevated serum alanine aminotransferase (ALT) activity with the detection of HCV RNA, the anti-HCV antibody, or hepatitis C virus antigen(s). However, most patients with acute infection are asymptomatic. In addition, ALT activity and HCV RNA levels can fluctuate, and a delayed detection of the anti-HCV antibody can occur among some immunocompromised persons with HCV infection. The detection of specific biomarkers can be of great value in the early detection of HCV infection at an asymptomatic stage. The high rate of HCV replication (which is approximately 1010 to 1012 virions per day) and the lack of proofreading by the viral RNA polymerase leads to enormous genetic diversity, creating a major challenge for the host immune response. This broad genetic diversity contributes to the likelihood of developing chronic infection, thus leading to the development of cirrhosis and liver cancer. Direct-acting antiviral (DAA) therapies for HCV infection are highly effective with a cure rate of up to 99%. At the same time, many patients with HCV infection are unaware of their infection status because of the mostly asymptomatic nature of hepatitis C, so they remain undiagnosed until the liver damage has advanced. Molecular mechanisms induced by HCV have been intensely investigated to find biomarkers for diagnosing the acute and chronic phases of the infection. However, there are no clinically verified biomarkers for patients with hepatitis C. In this review, we discuss the biomarkers that can differentiate acute from chronic hepatitis C, and we summarize the current state of the literature on the useful biomarkers that are detectable during acute and chronic HCV infection, liver fibrosis/cirrhosis, and hepatocellular carcinoma (HCC).

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.

Prospects for developing an Hepatitis C virus E1E2-based nanoparticle vaccine

Globally, more than 58 million people are chronically infected with Hepatitis C virus (HCV) with 1.5 million new infections occurring each year. An effective vaccine for HCV is therefore a major unmet medical and public health need. Since HCV rapidly accumulates mutations, vaccines must elicit the production of broadly neutralising antibodies (bnAbs) in a reproducible fashion. Decades of research have generated a number of HCV vaccine candidates. Based on the available data and research through clinical development, a vaccine antigen based on the E1E2 glycoprotein complex appears to be the best choice, but robust induction of humoral and cellular responses leading to virus neutralisation has not yet been achieved. One issue that has arisen in developing an HCV vaccine (and many other vaccines as well) is the platform used for antigen delivery. The majority of viral vaccine trials have employed subunit vaccines. However, subunit vaccines often have limited immunogenicity, as seen for HCV, and thus multiple formats must be examined in order to elicit a robust anti-HCV immune response. Nanoparticle vaccines are gaining prominence in the field due to their ability to facilitate a controlled multivalent presentation and trafficking to lymph nodes, where they can interact with both arms of the immune system. This review discusses the potential for development of a nanoparticle-based HCV E1E2 vaccine, with an emphasis on the potential benefits of such an approach along with the major challenges facing the incorporation of E1E2 into nanoparticulate delivery systems and how those challenges can be addressed.

Two Novel Adenovirus Vectors Mediated Differential Antibody Responses via Interferon-α and Natural Killer Cells

Recombinant adenovirus vectors have been widely used in vaccine development. To overcome the preexisting immunity of human adenovirus type 5 (Ad5) in populations, a range of chimpanzee or rare human adenovirus vectors have been generated. However, these novel adenovirus vectors mediate the diverse immune responses in the hosts. In this study, we explored the immune mechanism of differential antibody responses to SARS-CoV-2 S protein in mice immunized by our previously developed two novel simian adenovirus type 23 (Sad23L) and human adenovirus type 49 (Ad49L), and Ad5 vectored COVID-19 vaccines. Sad23L-nCoV-S and Ad5-nCoV-S vaccines induced the low level of interferon-α (IFN-α) and the high level of antigen-specific antibody responses in wild-type and IFN-α/β receptor defective (IFNAR-/-) C57 mice, while Ad49L-nCoV-S vaccine induced the high IFN-α and low antibody responses in C57 mice but the high antibody response in IFNAR-/- mice. In addition, the high antibody response was detected in natural killer (NK) cells-blocked but the low in follicular helper T (TFH) cells -blocked C57 mice immunized with Ad49L-nCoV-S vaccine. These results showed that Ad49L vectored vaccine stimulated IFN-α secretion to activate NK cells, and then reduced the number of TFH cells, generation center (GC) B cells and plasma cells, and subsequently reduced antigen-specific antibody production. The different novel adenovirus vectors could be selected for vaccine development according to the need for either humoral or cellular or both immune protections against a particular disease. IMPORTANCE Novel adenovirus vectors are an important antigen delivery platform for vaccine development. Understanding the immune diversity between different adenoviral vectors is critical to design the proper vaccine against an aim disease. In this study, we described the immune mechanism of Sad23L and Ad49L vectored vaccines for raising the equally high specific T cell response but the different level of specific antibody responses in mice. We found that Ad49L-vectored vaccine initiated the high IFN-α and activated NK cells to inhibit antibody response via downregulating the number of CD4+ TFH cells leading to the decline of GC B cells and plasma cells.

GB Virus B and Hepatitis C Virus, Distantly Related Hepaciviruses, Share an Entry Factor, Claudin-1

Due to increased and broadened screening efforts, the last decade has seen a rapid expansion in the number of viral species classified into the Hepacivirus genus. Conserved genetic features of hepaciviruses suggest that they have undergone specific adaptation and have evolved to hijack similar host proteins for efficient propagation in the liver. Here, we developed pseudotyped viruses to elucidate the entry factors of GB virus B (GBV-B), the first hepacivirus described in an animal after hepatitis C virus (HCV). GBV-B-pseudotyped viral particles (GBVBpp) were shown to be uniquely sensitive to the sera of tamarins infected with GBV-B, validating their usefulness as a surrogate for GBV-B entry studies. We screened GBVBpp infection of human hepatoma cell lines that were CRISPR/Cas9 engineered to ablate the expression of individual HCV receptors/entry factors and found that claudin-1 is essential for GBV-B infection, indicating the GBV-B and HCV share an entry factor. Our data suggest that claudin-1 facilitates HCV and GBV-B entry through distinct mechanisms since the former requires the first extracellular loop and the latter is reliant on a C-terminal region containing the second extracellular loop. The observation that claudin-1 is an entry factor shared between these two hepaciviruses suggests that the tight junction protein is of fundamental mechanistic importance during cell entry. IMPORTANCE Hepatitis C virus (HCV) is a major public health burden; approximately 58 million individuals have chronic HCV infection and are at risk of developing cirrhosis and liver cancer. To achieve the World Health Organization's target of eliminating hepatitis by 2030, new therapeutics and vaccines are needed. Understanding how HCV enters cells can inform the design of new vaccines and treatments targeting the first stage of infection. However, the HCV cell entry mechanism is complex and has been sparsely described. Studying the entry of related hepaciviruses will increase the knowledge of the molecular mechanisms of the first stages of HCV infection, such as membrane fusion, and inform structure-guided HCV vaccine design; in this work, we have identified a protein, claudin-1, that facilitates the entry of an HCV-related hepacivirus but with a mechanism not described for HCV. Similar work on other hepaciviruses may unveil a commonality of entry factors and, possibly, new mechanisms.

Convergent antibody responses are associated with broad neutralization of hepatitis C virus

Introduction

Early development of broadly neutralizing antibodies (bNAbs) targeting the hepatitis C virus (HCV) envelope glycoprotein E2 is associated with spontaneous clearance of infection, so induction of bNAbs is a major goal of HCV vaccine development. However, the molecular antibody features important for broad neutralization are not known.

Methods

To identify B cell repertoire features associated with broad neutralization, we performed RNA sequencing of the B cell receptors (BCRs) of HCV E2-reactive B cells of HCV-infected individuals with either high or low plasma neutralizing breadth. We then produced a monoclonal antibody (mAb) expressed by pairing the most abundant heavy and light chains from public clonotypes identified among clearance, high neutralization subjects.

Results

We found distinctive BCR features associated with broad neutralization of HCV, including long heavy chain complementarity determining region 3 (CDRH3) regions, specific VH gene usage, increased frequencies of somatic hypermutation, and particular VH gene mutations. Most intriguing, we identified many E2-reactive public BCR clonotypes (heavy and light chain clones with the same V and J-genes and identical CDR3 sequences) present only in subjects who produced highly neutralizing plasma. The majority of these public clonotypes were shared by two subjects who cleared infection. A mAb expressing the most abundant public heavy and light chains from these clearance, high neutralization subjects had features enriched in high neutralization clonotypes, such as increased somatic hypermutation frequency and usage of IGHV1-69, and was cross-neutralizing.

Discussion

Together, these results demonstrate distinct BCR repertoires associated with high plasma neutralizing capacity. Further characterization of the molecular features and function of these antibodies can inform HCV vaccine development.

Neutralization and receptor use of infectious culture-derived rat hepacivirus as a model for HCV

BACKGROUND AND AIMS

Lack of tractable immunocompetent animal models amenable to robust experimental challenge impedes vaccine efforts for HCV. Infection with rodent hepacivirus from Rattus norvegicus (RHV-rn1) in rats shares HCV-defining characteristics, including liver tropism, chronicity, and pathology. RHV in vitro cultivation would facilitate genetic studies on particle production, host factor interactions, and evaluation of antibody neutralization guiding HCV vaccine approaches.

APPROACH AND RESULTS

We report an infectious reverse genetic cell culture system for RHV-rn1 using highly permissive rat hepatoma cells and adaptive mutations in the E2, NS4B, and NS5A viral proteins. Cell culture-derived RHV-rn1 particles (RHVcc) share hallmark biophysical characteristics of HCV and are infectious in mice and rats. Culture adaptive mutations attenuated RHVcc in immunocompetent rats, and the mutations reverted following prolonged infection, but not in severe combined immunodeficiency (SCID) mice, suggesting that adaptive immune pressure is a primary driver of reversion. Accordingly, sera from RHVcc-infected SCID mice or the early acute phase of immunocompetent mice and rats were infectious in culture. We further established an in vitro RHVcc neutralization assay, and observed neutralizing activity of rat sera specifically from the chronic phase of infection. Finally, we found that scavenger receptor class B type I promoted RHV-rn1 entry in vitro and in vivo.

CONCLUSIONS

The RHV-rn1 infectious cell culture system enables studies of humoral immune responses against hepacivirus infection. Moreover, recapitulation of the entire RHV-rn1 infectious cycle in cell culture will facilitate reverse genetic studies and the exploration of tropism and virus-host interactions.

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.

Taking cues from convalescence to improve vaccines against hepatitis C virus

Hepatitis C virus (HCV) infection remains a worldwide public health issue despite direct-acting antivirals. A substantial proportion of infected individuals (15%–45%) spontaneously clear repeated HCV infections with genetically different viruses by generating broadly neutralizing antibodies (bNAbs). However, translating this response into an effective vaccine strategy has been unsuccessful. In this issue of the JCI, Frumento and colleagues report on their study of bNAb evolution longitudinally in convalescent individuals with repeated infections. Using pseudotyped viruses, well-characterized monoclonal antibodies, and complex modeling, the authors show that multiple exposures to antigenically related, antibody-sensitive viral envelope proteins induced potent bNAbs. This work provides valuable insight into the best strategies for developing HCV vaccines in the future that may successfully reproduce the immunity induced during natural exposures.

Repeated exposure to heterologous hepatitis C viruses associates with enhanced neutralizing antibody breadth and potency

A prophylactic hepatitis C virus (HCV) vaccine that elicits neutralizing antibodies could be key to HCV eradication. However, the genetic and antigenic properties of HCV envelope (E1E2) proteins capable of inducing anti-HCV broadly neutralizing antibodies (bNAbs) in humans have not been defined. Here, we investigated the development of bNAbs in longitudinal plasma of HCV-infected persons with persistent infection or spontaneous clearance of multiple reinfections. By measuring plasma antibody neutralization of a heterologous virus panel, we found that the breadth and potency of the antibody response increased upon exposure to multiple genetically distinct infections and with longer duration of viremia. Greater genetic divergence between infecting strains was not associated with enhanced neutralizing breadth. Rather, repeated exposure to antigenically related, antibody-sensitive E1E2s was associated with potent bNAb induction. These data reveal that a prime-boost vaccine strategy with genetically distinct, antibody-sensitive viruses is a promising approach to inducing potent bNAbs in humans.

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.

Negative impact of HIV infection on broad-spectrum anti-HCV neutralizing antibody titers in HCV-infected patients with advanced HCV-related cirrhosis

OBJECTIVES

The current study aimed to assess the impact of HIV on the production of anti-HCV antibodies in HCV-infected individuals with advanced HCV-related cirrhosis before and 36 weeks after the sustained virological response (SVR) induced by direct-acting antivirals (DAAs) therapy.

METHODS

Prospective study on 62 patients (50 HIV/HCV-coinfected and 12 HCV-monoinfected). Plasma anti-E2 and HCV-nAbs were determined respectively by ELISA and microneutralization assays.

RESULTS

At baseline, the HCV-group had higher anti-E2 levels against Gt1a (p = 0.012), Gt1b (p = 0.023), and Gt4a (p = 0.005) than the HIV/HCV-group. After SVR, anti-E2 titers against Gt1a (p < 0.001), Gt1b (p = 0.001), and Gt4a (p = 0.042) were also higher in the HCV-group than HIV/HCV-group. At 36 weeks post-SVR, plasma anti-E2 titers decreased between 1.3 and 1.9-fold in the HIV/HCV-group (p < 0.001) and between 1.5 and 1.8-fold in the HCV-group (p ≤ 0.001). At baseline, the HCV-group had higher titers of HCV-nAbs against Gt1a (p = 0.022), Gt1b (p = 0.002), Gt2a (p < 0.001), and Gt4a (p < 0.001) than the HIV/HCV-group. After SVR, HCV-nAbs titers against Gt1a (p = 0.014), Gt1b (p < 0.001), Gt2a (p = 0.002), and Gt4a (p = 0.004) were also higher in the HCV-group. At 36 weeks post-SVR, HCV-nAbs decreased between 2.6 and 4.1-fold in the HIV/HCV-group (p < 0.001) and between 1.9 and 4.0-fold in the HCV-group (p ≤ 0.001).

CONCLUSIONS

HIV/HCV-coinfected patients produced lower levels of broad-spectrum anti-HCV antibodies than HCV-monoinfected patients.

Innate and Adaptive Immunopathogeneses in Viral Hepatitis; Crucial Determinants of Hepatocellular Carcinoma

Viral hepatitis B (HBV) and hepatitis C (HCV) infections remain the most common risk factors for the development of hepatocellular carcinoma (HCC), and their heterogeneous distribution influences the global prevalence of this common type of liver cancer. Typical hepatitis infection elicits various immune responses within the liver microenvironment, and viral persistence induces chronic liver inflammation and carcinogenesis. HBV is directly mutagenic but can also cause low-grade liver inflammation characterized by episodes of intermittent high-grade liver inflammation, liver fibrosis, and cirrhosis, which can progress to decompensated liver disease and HCC. Equally, the absence of key innate and adaptive immune responses in chronic HCV infection dampens viral eradication and induces an exhausted and immunosuppressive liver niche that favors HCC development and progression. The objectives of this review are to (i) discuss the epidemiological pattern of HBV and HCV infections, (ii) understand the host immune response to acute and chronic viral hepatitis, and (iii) explore the link between this diseased immune environment and the development and progression of HCC in preclinical models and HCC patients.

Serological Markers of SARS-CoV-2 Reinfection

As public health guidelines throughout the world have relaxed in response to vaccination campaigns against SARS-CoV-2, it is likely that SARS-CoV-2 will remain endemic, fueled by the rise of more infectious SARS-CoV-2 variants. Moreover, in the setting of waning natural and vaccine immunity, reinfections have emerged across the globe, even among previously infected and vaccinated individuals. As such, the ability to detect reexposure to and reinfection by SARS-CoV-2 is a key component for global protection against this virus and, more importantly, against the potential emergence of vaccine escape mutations. Accordingly, there is a strong and continued need for the development and deployment of simple methods to detect emerging hot spots of reinfection to inform targeted pandemic response and containment, including targeted and specific deployment of vaccine booster campaigns. In this study, we identify simple, rapid immune biomarkers of reinfection in rhesus macaques, including IgG3 antibody levels against nucleocapsid and FcγR2A receptor binding activity of anti-RBD antibodies, that are recapitulated in human reinfection cases. As such, this cross-species analysis underscores the potential utility of simple antibody titers and function as price-effective and scalable markers of reinfection to provide increased resolution and resilience against new outbreaks. IMPORTANCE As public health and social distancing guidelines loosen in the setting of waning global natural and vaccine immunity, a deeper understanding of the immunological response to reexposure and reinfection to this highly contagious pathogen is necessary to maintain public health. Viral sequencing analysis provides a robust but unrealistic means to monitor reinfection globally. The identification of scalable pathogen-specific biomarkers of reexposure and reinfection, however, could significantly accelerate our capacity to monitor the spread of the virus through naive and experienced hosts, providing key insights into mechanisms of disease attenuation. Using a nonhuman primate model of controlled SARS-CoV-2 reexposure, we deeply probed the humoral immune response following rechallenge with various doses of viral inocula. We identified virus-specific humoral biomarkers of reinfection, with significant increases in antibody titer and function upon rechallenge across a range of humoral features, including IgG1 to the receptor binding domain of the spike protein of SARS-CoV-2 (RBD), IgG3 to the nucleocapsid protein (N), and FcγR2A receptor binding to anti-RBD antibodies. These features not only differentiated primary infection from reexposure and reinfection in monkeys but also were recapitulated in a sequencing-confirmed reinfection patient and in a cohort of putatively reinfected humans that evolved a PCR-positive test in spite of preexisting seropositivity. As such, this cross-species analysis using a controlled primate model and human cohorts reveals increases in antibody titers as promising cross-validated serological markers of reinfection and reexposure.

Analysis of antibodies from HCV elite neutralizers identifies genetic determinants of broad neutralization

The high genetic diversity of hepatitis C virus (HCV) complicates effective vaccine development. We screened a cohort of 435 HCV-infected individuals and found that 2%-5% demonstrated outstanding HCV-neutralizing activity. From four of these patients, we isolated 310 HCV antibodies, including neutralizing antibodies with exceptional breadth and potency. High neutralizing activity was enabled by the use of the VH1-69 heavy-chain gene segment, somatic mutations within CDRH1, and CDRH2 hydrophobicity. Structural and mutational analyses revealed an important role for mutations replacing the serines at positions 30 and 31, as well as the presence of neutral and hydrophobic residues at the tip of the CDRH3. Based on these characteristics, we computationally created a de novo antibody with a fully synthetic VH1-69 heavy chain that efficiently neutralized multiple HCV genotypes. Our findings provide a deep understanding of the generation of broadly HCV-neutralizing antibodies that can guide the design of effective vaccine candidates.

An Antigenically Diverse, Representative Panel of Envelope Glycoproteins for Hepatitis C Virus Vaccine Development

BACKGROUND & AIMS

Development of a prophylactic hepatitis C virus (HCV) vaccine will require accurate and reproducible measurement of neutralizing breadth of vaccine-induced antibodies. Currently available HCV panels may not adequately represent the genetic and antigenic diversity of circulating HCV strains, and the lack of standardization of these panels makes it difficult to compare neutralization results obtained in different studies. Here, we describe the selection and validation of a genetically and antigenically diverse reference panel of 15 HCV pseudoparticles (HCVpps) for neutralization assays.

METHODS

We chose 75 envelope (E1E2) clones to maximize representation of natural polymorphisms observed in circulating HCV isolates, and 65 of these clones generated functional HCVpps. Neutralization sensitivity of these HCVpps varied widely. HCVpps clustered into 15 distinct groups based on patterns of relative sensitivity to 7 broadly neutralizing monoclonal antibodies. We used these data to select a final panel of 15 antigenically representative HCVpps.

RESULTS

Both the 65 and 15 HCVpp panels span 4 tiers of neutralization sensitivity, and neutralizing breadth measurements for 7 broadly neutralizing monoclonal antibodies were nearly equivalent using either panel. Differences in neutralization sensitivity between HCVpps were independent of genetic distances between E1E2 clones.

CONCLUSIONS

Neutralizing breadth of HCV antibodies should be defined using viruses spanning multiple tiers of neutralization sensitivity rather than panels selected solely for genetic diversity. We propose that this multitier reference panel could be adopted as a standard for the measurement of neutralizing antibody potency and breadth, facilitating meaningful comparisons of neutralization results from vaccine studies in different laboratories.

A Multifunctional Neutralizing Antibody-Conjugated Nanoparticle Inhibits and Inactivates SARS-CoV-2

The outbreak of 2019 coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in a global pandemic. Despite intensive research, the current treatment options show limited curative efficacies. Here the authors report a strategy incorporating neutralizing antibodies conjugated to the surface of a photothermal nanoparticle (NP) to capture and inactivate SARS-CoV-2. The NP is comprised of a semiconducting polymer core and a biocompatible polyethylene glycol surface decorated with high-affinity neutralizing antibodies. The multifunctional NP efficiently captures SARS-CoV-2 pseudovirions and completely blocks viral infection to host cells in vitro through the surface neutralizing antibodies. In addition to virus capture and blocking function, the NP also possesses photothermal function to generate heat following irradiation for inactivation of virus. Importantly, the NPs described herein significantly outperform neutralizing antibodies at treating authentic SARS-CoV-2 infection in vivo. This multifunctional NP provides a flexible platform that can be readily adapted to other SARS-CoV-2 antibodies and extended to novel therapeutic proteins, thus it is expected to provide a broad range of protection against original SARS-CoV-2 and its variants.

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.

Mechanisms of HCV resistance to broadly neutralizing antibodies

Broadly neutralizing antibodies (bNAbs) block infection by genetically diverse hepatitis C virus (HCV) isolates by targeting relatively conserved epitopes on the HCV envelope glycoproteins, E1 and E2. Many amino acid substitutions conferring resistance to these bNAbs have been characterized, identifying multiple mechanisms of bNAb escape. Some resistance substitutions follow the expected mechanism of directly disrupting targeted epitopes. Interestingly, other resistance substitutions fall in E2 domains distant from bNAb-targeted epitopes. These substitutions, which can confer broad resistance to multiple bNAbs, act by less clearly defined mechanisms. Some modulate binding of HCV to cell surface receptors, while others may induce conformational changes in the E2 protein. In this review, we discuss mechanisms of HCV bNAb resistance and implications for HCV vaccine development.

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.

Hepatitis C reference viruses highlight potent antibody responses and diverse viral functional interactions with neutralising antibodies

OBJECTIVE

Neutralising antibodies are key effectors of infection-induced and vaccine-induced immunity. Quantification of antibodies' breadth and potency is critical for understanding the mechanisms of protection and for prioritisation of vaccines. Here, we used a unique collection of human specimens and HCV strains to develop HCV reference viruses for quantification of neutralising antibodies, and to investigate viral functional diversity.

DESIGN

We profiled neutralisation potency of polyclonal immunoglobulins from 104 patients infected with HCV genotype (GT) 1-6 across 13 HCV strains representing five viral GTs. Using metric multidimensional scaling, we plotted HCV neutralisation onto neutralisation maps. We employed K-means clustering to guide virus clustering and selecting representative strains.

RESULTS

Viruses differed greatly in neutralisation sensitivity, with J6 (GT2a) being most resistant and SA13 (GT5a) being most sensitive. They mapped to six distinct neutralisation clusters, in part composed of viruses from different GTs. There was no correlation between viral neutralisation and genetic distance, indicating functional neutralisation clustering differs from sequence-based clustering. Calibrating reference viruses representing these clusters against purified antibodies from 496 patients infected by GT1 to GT6 viruses readily identified individuals with extraordinary potent and broadly neutralising antibodies. It revealed comparable antibody cross-neutralisation and diversity between specimens from diverse viral GTs, confirming well-balanced reporting of HCV cross-neutralisation across highly diverse human samples.

CONCLUSION

Representative isolates from six neutralisation clusters broadly reconstruct the functional HCV neutralisation space. They enable high resolution profiling of HCV neutralisation and they may reflect viral functional and antigenic properties important to consider in HCV vaccine design.

A Tale of Two Viruses: Immunological Insights Into HCV/HIV Coinfection

Nearly 2.3 million individuals worldwide are coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Odds of HCV infection are six times higher in people living with HIV (PLWH) compared to their HIV-negative counterparts, with the highest prevalence among people who inject drugs (PWID) and men who have sex with men (MSM). HIV coinfection has a detrimental impact on the natural history of HCV, including higher rates of HCV persistence following acute infection, higher viral loads, and accelerated progression of liver fibrosis and development of end-stage liver disease compared to HCV monoinfection. Similarly, it has been reported that HCV coinfection impacts HIV disease progression in PLWH receiving anti-retroviral therapies (ART) where HCV coinfection negatively affects the homeostasis of CD4⁺ T cell counts and facilitates HIV replication and viral reservoir persistence. While ART does not cure HIV, direct acting antivirals (DAA) can now achieve HCV cure in nearly 95% of coinfected individuals. However, little is known about how HCV cure and the subsequent resolution of liver inflammation influence systemic immune activation, immune reconstitution and the latent HIV reservoir. In this review, we will summarize the current knowledge regarding the pathogenesis of HIV/HCV coinfection, the effects of HCV coinfection on HIV disease progression in the context of ART, the impact of HIV on HCV-associated liver morbidity, and the consequences of DAA-mediated HCV cure on immune reconstitution and HIV reservoir persistence in coinfected patients.

Hepatitis C Virus Vaccine Research: Time to Put Up or Shut Up

Unless urgently needed to prevent a pandemic, the development of a viral vaccine should follow a rigorous scientific approach. Each vaccine candidate should be designed considering the in-depth knowledge of protective immunity, followed by preclinical studies to assess immunogenicity and safety, and lastly, the evaluation of selected vaccines in human clinical trials. The recently concluded first phase II clinical trial of a human hepatitis C virus (HCV) vaccine followed this approach. Still, despite promising preclinical results, it failed to protect against chronic infection, raising grave concerns about our understanding of protective immunity. This setback, combined with the lack of HCV animal models and availability of new highly effective antivirals, has fueled ongoing discussions of using a controlled human infection model (CHIM) to test new HCV vaccine candidates. Before taking on such an approach, however, we must carefully weigh all the ethical and health consequences of human infection in the absence of a complete understanding of HCV immunity and pathogenesis. We know that there are significant gaps in our knowledge of adaptive immunity necessary to prevent chronic HCV infection. This review discusses our current understanding of HCV immunity and the critical gaps that should be filled before embarking upon new HCV vaccine trials. We discuss the importance of T cells, neutralizing antibodies, and HCV genetic diversity. We address if and how the animal HCV-like viruses can be used for conceptualizing effective HCV vaccines and what we have learned so far from these HCV surrogates. Finally, we propose a logical but narrow path forward for HCV vaccine development.

Where to Next? Research Directions after the First Hepatitis C Vaccine Efficacy Trial

Thirty years after its discovery, the hepatitis C virus (HCV) remains a leading cause of liver disease worldwide. Given that many countries continue to experience high rates of transmission despite the availability of potent antiviral therapies, an effective vaccine is seen as critical for the elimination of HCV. The recent failure of the first vaccine efficacy trial for the prevention of chronic HCV confirmed suspicions that this virus will be a challenging vaccine target. Here, we examine the published data from this first efficacy trial along with the earlier clinical and pre-clinical studies of the vaccine candidate and then discuss three key research directions expected to be important in ongoing and future HCV vaccine development. These include the following: 1. design of novel immunogens that generate immune responses to genetically diverse HCV genotypes and subtypes, 2. strategies to elicit broadly neutralizing antibodies against envelope glycoproteins in addition to cytotoxic and helper T cell responses, and 3. consideration of the unique immunological status of individuals most at risk for HCV infection, including those who inject drugs, in vaccine platform development and early immunogenicity trials.

A conserved epitope III on hepatitis C virus E2 protein has alternate conformations facilitating cell binding or virus neutralization

Epitope III, a highly conserved amino acid motif of ⁵²⁴APTYSW⁵²⁹ on the hepatitis C virus (HCV) E2 glycoprotein, resides in the critical loop that binds to the host receptor CD81, thus making it one of the most important antibody targets for blocking HCV infections. Here, we have determined the X-ray crystal structure of epitope III at a 2.0-Å resolution when it was captured by a site-specific neutralizing antibody, monoclonal antibody 1H8 (mAb1H8). The snapshot of this complex revealed that epitope III has a relatively rigid structure when confined in the binding grooves of mAb1H8, which confers the residue specificity at both ends of the epitope. Such a high shape complementarity is reminiscent of the "lock and key" mode of action, which is reinforced by the incompatibility of an antibody binding with an epitope bearing specific mutations. By subtly positioning the side chains on the three residues of Tyr⁵²⁷, Ser⁵²⁸, and Trp⁵²⁹ while preserving the spatial rigidity of the rest, epitope III in this cocrystal complex adopts a unique conformation that is different from previously described E2 structures. With further analyses of molecular docking and phage display-based peptide interactions, we recognized that it is the arrangements of two separate sets of residues within epitope III that create these discrete conformations for the epitope to interact selectively with either mAb1H8 or CD81. These observations thus raise the possibility that local epitope III conformational dynamics, in conjunction with sequence variations, may act as a regulatory mechanism to coordinate "mAb1H8-like" antibody-mediated immune defenses with CD81-initiated HCV infections.

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].

Structural and Biophysical Characterization of the HCV E1E2 Heterodimer for Vaccine Development

An effective vaccine for the hepatitis C virus (HCV) is a major unmet medical and public health need, and it requires an antigen that elicits immune responses to multiple key conserved epitopes. Decades of research have generated a number of vaccine candidates; based on these data and research through clinical development, a vaccine antigen based on the E1E2 glycoprotein complex appears to be the best choice. One bottleneck in the development of an E1E2-based vaccine is that the antigen is challenging to produce in large quantities and at high levels of purity and antigenic/functional integrity. This review describes the production and characterization of E1E2-based vaccine antigens, both membrane-associated and a novel secreted form of E1E2, with a particular emphasis on the major challenges facing the field and how those challenges can be addressed.

HCV Core/NS3 Protein Immunization with "N-Terminal Heat Shock gp96 Protein (rNT (gp96))" Induced Strong and Sustained Th1-Type Cytokines in Immunized Mice

Feeble cellular responses induced by T cell-based vaccines are a major challenge for the development of an effective vaccine against Hepatitis C virus (HCV) infection. To address this challenge, the potential of N-terminal fragment of gp96 heat shock protein (rNT (gp96) as an adjuvant was evaluated and compared to that of the CpG (as a recognized Th1-type adjuvant) in the formulation of HCV core/NS3 antigens in three immunization strategies of protein/protein, DNA/DNA, and DNA/protein. Immunized mice were evaluated for elicited immune responses in week 3 (W3) and 11 post-immunizations. Our results demonstrated that the protein (subunit) vaccine formulated with rNT (gp96) in protein/protein strategy (core/NS3 + gp96) was significantly more efficient than CpG oligodeoxynucleotides (CpG ODN) formulation and all other immunization strategies in the induction of Th1-type cytokines. This group of mice (core/NS3 + gp96) also elicited a high level of anti-Core-NS3 total immunoglobulin G (IgG) with dominant IgG2a isotype at W3. Thus, the co-administration of recombinant NT (gp96) protein with rHCV proteins might be a promising approach in the formulation of HCV subunit vaccine candidates for induction of high levels of Th1 cytokines and humoral responses.

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.

Beyond Metabolism: Role of the Immune System in Hepatic Toxicity

The liver is primarily thought of as a metabolic organ; however, the liver is also an important mediator of immunological functions. Key perspectives on this emerging topic were presented in a symposium at the 2018 annual meeting of the American College of Toxicology entitled "Beyond metabolism: Role of the immune system in hepatic toxicity." Viral hepatitis is an important disease of the liver for which insufficient preventive vaccines exist. Host immune responses inadequately clear these viruses and often potentiate immunological inflammation that damages the liver. In addition, the liver is a key innate immune organ against bacterial infection. Hepatocytes and immune cells cooperatively control systemic and local bacterial infections. Conversely, bacterial infection can activate multiple types of immune cells and pathways to cause hepatocyte damage and liver injury. Finally, the immune system and specifically cytokines and drugs can interact in idiosyncratic drug-induced liver injury. This rare disease can result in a disease spectrum that ranges from mild to acute liver failure. The immune system plays a role in this disease spectrum.

Ginsenoside Rb1 is an immune-stimulatory agent with antiviral activity against enterovirus 71

ETHNOPHARMACOLOGICAL RELEVANCE

According to the theory of traditional Chinese medicine, the main pathogenesis of severe hand, foot and mouth disease (HFMD) is that the heat and wet poisons are deeply trapped in the viscera, which causes the deficiency of Qi and Yin in the patient's body. Ginsenoside Rb1 (Rb1) is the most abundant triterpenoid saponin in Panax quinquefolius L., which has the function of Qi-invigorating and Yin-nourishing. Enterovirus 71 (EV71) is one of the causative pathogens of HFMD, especially the form associated with some lethal complications. Therefore, the therapeutic effect of Rb1 on this disease caused by EV71 infection is worth exploring.

AIM OF THE STUDY

We explored the effective antiviral activities of Rb1 against EV71 in vitro and in vivo and investigated its preliminary antiviral mechanisms.

MATERIAL AND METHODS

EV71-infected two-day-old suckling mice model was employed to detect the antiviral effects of Rb1 in vivo. To detect the antiviral effects of Rb1 in vitro, cytopathic effect (CPE) reduction assay was performed in EV71-infected Rhabdomyosarcoma (RD) cells. Interferon (IFN)-β interference experiment was employed to detect the antiviral mechanism of Rb1.

RESULTS

In this paper, we first found that Rb1 exhibited strong antiviral activities in EV71-infected suckling mice when compared to those of ribavirin. Administration of Rb1 reduced the CPE of EV71-infected RD cells in a dose-dependent manner. Moreover, EV71-induced viral protein-1 (VP-1) expression was significantly reduced by Rb1 administration in vitro and in vivo. Furthermore, Rb1 treatment could induce high cellular and humoral immune responses in vivo. Meanwhile, Rb1 contributed to the enhanced Type I IFN responses and IFN-β knockdown reversed the antiviral activity of Rb1 in vitro.

CONCLUSION

In summary, our findings suggest that Rb1 is an immune-stimulatory agent and provide an insight into therapeutic potentials of Rb1 for the treatment of EV71 infection.

Interferon lambda 4 can directly activate human CD19+ B cells and CD8+ T cells

Compared with the ubiquitous expression of type I (IFNα and IFNβ) interferon receptors, type III (IFNλ) interferon receptors are mainly expressed in epithelial cells of mucosal barriers of the of the intestine and respiratory tract. Consequently, IFNλs are important for innate pathogen defense in the lung and intestine. IFNλs also determine the outcome of hepatitis C virus (HCV) infections, with IFNλ4 inhibiting spontaneous clearance of HCV. Because viral clearance is dependent on T cells, we explored if IFNλs can directly bind to and regulate human T cells. We found that human B cells and CD8+ T cells express the IFNλ receptor and respond to IFNλs, including IFNλ4. IFNλs were not inhibitors but weak stimulators of B- and T-cell responses. Furthermore, IFNλ4 showed neither synergistic nor antagonistic effects in co-stimulatory experiments with IFNλ1 or IFNα. Multidimensional flow cytometry of cells from liver biopsies of hepatitis patients from IFNλ4-producers showed accumulation of activated CD8+ T cells with a central memory-like phenotype. In contrast, CD8+ T cells with a senescent/exhausted phenotype were more abundant in IFNλ4-non-producers. It remains to be elucidated how IFNλ4 promotes CD8 T-cell responses and inhibits the host immunity to HCV infections.

A Neutralizing Antibody-Conjugated Photothermal Nanoparticle Captures and Inactivates SARS-CoV-2

The outbreak of 2019 coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in a global pandemic. Despite intensive research including several clinical trials, currently there are no completely safe or effective therapeutics to cure the disease. Here we report a strategy incorporating neutralizing antibodies conjugated on the surface of a photothermal nanoparticle to actively capture and inactivate SARS-CoV-2. The photothermal nanoparticle is comprised of a semiconducting polymer core and a biocompatible polyethylene glycol surface decorated with neutralizing antibodies. Such nanoparticles displayed efficient capture of SARS-CoV-2 pseudoviruses, excellent photothermal effect, and complete inhibition of viral entry into ACE2-expressing host cells via simultaneous blocking and inactivating of the virus. This photothermal nanoparticle is a flexible platform that can be readily adapted to other SARS-CoV-2 antibodies and extended to novel therapeutic proteins, thus providing a broad range of protection against multiple strains of SARS-CoV-2.

HCV Glycoprotein Structure and Implications for B-Cell Vaccine Development

Despite the approval of highly efficient direct-acting antivirals in the last decade Hepatitis C virus (HCV) remains a global health burden and the development of a vaccine would constitute an important step towards the control of HCV. The high genetic variability of the viral glycoproteins E1 and E2, which carry the main neutralizing determinants, together with their intrinsic structural flexibility, the high level of glycosylation that shields conserved neutralization epitopes and immune evasion using decoy epitopes renders the design of an efficient vaccine challenging. Recent structural and functional analyses have highlighted the role of the CD81 receptor binding site on E2, which overlaps with those neutralization epitopes within E2 that have been structurally characterized to date. This CD81 binding site consists of three distinct segments including “epitope I”, “epitope II” and the “CD81 binding loop”. In this review we summarize the structural features of the HCV glycoproteins that have been derived from X-ray structures of neutralizing and non-neutralizing antibody fragments complexed with either recombinant E2 or epitope-derived linear peptides. We focus on the current understanding how neutralizing antibodies interact with their cognate antigen, the structural features of the respective neutralization epitopes targeted by nAbs and discuss the implications for informed vaccine design.

Adaptive Immune Response against Hepatitis C Virus

A functional adaptive immune response is the major determinant for clearance of hepatitis C virus (HCV) infection. However, in the majority of patients, this response fails and persistent infection evolves. Here, we dissect the HCV-specific key players of adaptive immunity, namely B cells and T cells, and describe factors that affect infection outcome. Once chronic infection is established, continuous exposure to HCV antigens affects functionality, phenotype, transcriptional program, metabolism, and the epigenetics of the adaptive immune cells. In addition, viral escape mutations contribute to the failure of adaptive antiviral immunity. Direct-acting antivirals (DAA) can mediate HCV clearance in almost all patients with chronic HCV infection, however, defects in adaptive immune cell populations remain, only limited functional memory is obtained and reinfection of cured individuals is possible. Thus, to avoid potential reinfection and achieve global elimination of HCV infections, a prophylactic vaccine is needed. Recent vaccine trials could induce HCV-specific immunity but failed to protect from persistent infection. Thus, lessons from natural protection from persistent infection, DAA-mediated cure, and non-protective vaccination trials might lead the way to successful vaccination strategies in the future.

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.

Use of an Outbred Rat Hepacivirus Challenge Model for Design and Evaluation of Efficacy of Different Immunization Strategies for Hepatitis C Virus

BACKGROUND AND AIMS

The lack of immunocompetent small animal models for hepatitis C virus (HCV) has greatly hindered the development of effective vaccines. Using rodent hepacivirus (RHV), a homolog of HCV that shares many characteristics of HCV infection, we report the development and application of an RHV outbred rat model for HCV vaccine development.

APPROACH AND RESULTS

Simian adenovirus (ChAdOx1) encoding a genetic immune enhancer (truncated shark class II invariant chain) fused to the nonstructural (NS) proteins NS3-NS5B from RHV (ChAd-NS) was used to vaccinate Sprague-Dawley rats, resulting in high levels of cluster of differentiation 8-positive (CD8⁺ ) T-cell responses. Following RHV challenge (using 10 or 100 times the minimum infectious dose), 42% of vaccinated rats cleared infection within 6-8 weeks, while all mock vaccinated controls became infected with high-level viremia postchallenge. A single, 7-fold higher dose of ChAd-NS increased efficacy to 67%. Boosting with ChAd-NS or with a plasmid encoding the same NS3-NS5B antigens increased efficacy to 100% and 83%, respectively. A ChAdOx1 vector encoding structural antigens (ChAd-S) was also constructed. ChAd-S alone showed no efficacy. Strikingly, when combined with ChAd-NS, ChAD-S produced 83% efficacy. Protection was associated with a strong CD8⁺ interferon gamma-positive recall response against NS4. Next-generation sequencing of a putative RHV escape mutant in a vaccinated rat identified mutations in both identified immunodominant CD8⁺ T-cell epitopes.

CONCLUSIONS

A simian adenovirus vector vaccine strategy is effective at inducing complete protective immunity in the rat RHV model. The RHV Sprague-Dawley rat challenge model enables comparative testing of vaccine platforms and antigens and identification of correlates of protection and thereby provides a small animal experimental framework to guide the development of an effective vaccine for HCV in humans.

Challenges and Promise of a Hepatitis C Virus Vaccine

An estimated 1.5-2 million new hepatitis C virus (HCV) infections occur globally each year. Critical to the World Health Organization's (WHO) HCV elimination strategy is an 80% reduction in incidence of HCV infections by 2030. However, even among high-income countries, few are on target to achieve the WHO's incident infection-reduction goal. A preventative vaccine could have a major impact in achieving incidence-reduction targets globally. However, barriers to HCV vaccine development are significant and include at-risk populations that are often marginalized: viral diversity, limited options for testing HCV vaccines, and an incomplete understanding of protective immune responses. In part because of those factors, testing of only one vaccine strategy has been completed in at-risk individuals as of 2019. Despite challenges, immunity against HCV protects against chronic infection in some repeated HCV exposures and an effective HCV vaccine could prevent transmission regardless of risk factors. Ultimately, prophylactic vaccines will likely be necessary to achieve global HCV elimination.

Protective cellular immune response against hepatitis C virus elicited by chimeric protein formulations in BALB/c mice

The eradication of hepatitis C virus (HCV) infection is a public health priority. Despite the efficiency of treatment with direct-acting antivirals, the high cost of the therapy and the lack of accurate data about the HCV-infected population worldwide constitute important factors hampering this task. Hence, an affordable preventive vaccine is still necessary for reducing transmission and the future disease burden globally. In this work, chimeric proteins (EnvCNS3 and NS3EnvCo) encompassing conserved and immunogenic epitopes from the HCV core, E1, E2 and NS3 proteins were produced in Escherichia coli, and their immunogenicity was evaluated in BALB/c mice. The impact of recombinant HCV E2.680 protein and oligodeoxynucleotide 39M (ODN39M) on the immune response to chimeric proteins was also assessed. Immunization with chimeric proteins mixed with E2.680 enhanced the antibody and cellular response against HCV antigens and chimeric proteins. Interestingly, the combination of NS3EnvCo with E2.680 and ODN39M as adjuvant elicited a potent antibody response characterized by an increase in antibodies of the IgG2a subclass against E2.680, NS3 and chimeric proteins, suggesting the induction of a Th1-type response. Moreover, a cytotoxic T lymphocyte response and a broad response of IFN-γ-secreting cells against HCV antigens were induced with this formulation as well. This T cell response was able to protect vaccinated mice against challenge with a surrogate model based on HCV recombinant vaccinia virus. Overall, the vaccine candidate NS3EnvCo/E2.680/ODN39M might constitute an effective immunogen against HCV with potential for reducing the likelihood of viral persistence.

CXCL9 chemokine level is associated with spontaneous clearance and sustained virological response in Egyptian Chronic Hepatitis C patients receiving direct acting antivirals

BACKGROUND

Chronic Hepatitis C virus (HCV) infection is associated with progressive liver inflammation which in turn leads to cirrhosis and finally causes hepatocellular carcinoma (HCC). By different escape mechanisms, the virus succeeds to evade the innate and acquired immune responses to establish chronic infection.

AIM

This study aimed to evaluate the level of chemokine CXCL9 and its correlation with some biochemical parameters in different subjects of HCV patients.

MATERIALS AND METHODS

A total of 83 persons participated in this study including healthy subjects without both HCV antibodies and HCV RNA (22.9%), HCV treated responders accomplished SVR post treatment, with HCV antibodies and absence of HCV RNA (24.1%), spontaneous or natural clearance patients, with positive HCV antibodies and negative HCV RNA without treatment (26.5%) and chronic HCV-patients, with both positive HCV antibodies and HCV RNA with no treatment (26.5%). HCV RNA was quantitated by real time PCR and serum CXCL9 level was measured by ELISA commercial kit pre-coated with human MIG/CXCL9 antibody. Assessment of biochemical and hematological parameters was carried out.

RESULTS

Data showed that, the level of CXCL9 was significantly increased in chronic individuals (627.1 pg/ml) (P< 0.001) than spontaneous clearance (107.76 pg/ml) and responder subjects (117.28 pg/ml) (P⩽ 0.05). No correlation has been found between CXCL9 level and viral load. Furthermore, CXCL9 levels correlated variably with some biochemical and hematological parameters according to each subject.

CONCLUSION

Serum Chemokine CXCL9 level is associated with spontaneous clearance of HCV and response to HCV treatment, which may be identified as a predictive marker among HCV patients.

Hepatitis C Virus: 30 Years after Its Discovery

Evidence for the existence of another hepatitis-causing pathogen, other than the known hepatitis A and B viruses, emerged in the mid-1970s. A frustrating search of 15 years was ended by the identification of the hepatitis C virus in 1989 using a recombinant DNA immunoscreening method. This discovery quickly led to blood tests that eliminated posttransfusion hepatitis C and could show the partial efficacy of type 1 interferon-based therapies. Subsequent knowledge of the viral replication cycle then led to the development of effective direct-acting antivirals targeting its serine protease, polymerase, and nonstructural protein 5A that resulted in the approval of orally available drug combinations that can cure patients within a few months with few side effects. Meanwhile, vaccine strategies have been shown to be feasible, and they are still required to effectively control this global epidemic.

Modeling of patient virus titers suggests that availability of a vaccine could reduce hepatitis C virus transmission among injecting drug users

The major route of hepatitis C virus (HCV) transmission in the United States is injection drug use. We hypothesized that if an HCV vaccine were available, vaccination could affect HCV transmission among people who inject drugs by reducing HCV titers after viral exposure without necessarily achieving sterilizing immunity. To investigate this possibility, we developed a mathematical model to determine transmission probabilities relative to the HCV RNA titers of needle/syringe-sharing donors. We simulated sharing of two types of syringes fitted with needles that retain either large or small amounts of fluid after expulsion. Using previously published viral kinetics data from both naïve subjects infected with HCV and reinfected individuals who had previously cleared an HCV infection, we estimated transmission risk between pairs of serodiscordant injecting drug users, accounting for syringe type, rinsing, and sharing frequency. We calculated that the risk of HCV transmission through syringe sharing increased ~10-fold as viral titers (log₁₀ IU/ml) increased ~25-fold. Cumulative analyses showed that, assuming sharing episodes every 7 days, the mean transmission risk over the first 6 months was >90% between two people sharing syringes when one had an HCV RNA titer >5 log₁₀ IU/ml. For those with preexisting immunity that rapidly controlled HCV, the cumulative risk decreased to 1 to 25% depending on HCV titer and syringe type. Our modeling approach demonstrates that, even with transient viral replication after exposure during injection drug use, HCV transmission among people sharing syringes could be reduced through vaccination if an HCV vaccine were available.

Clearance of hepatitis C virus is associated with early and potent but narrowly-directed, Envelope-specific antibodies

Hepatitis C virus (HCV) is one of very few viruses that are either naturally cleared, or alternatively persist to cause chronic disease. Viral diversity and escape, as well as host adaptive immune factors, are believed to control the outcome. To date, there is limited understanding of the critical, early host-pathogen interactions. The asymptomatic nature of early HCV infection generally prevents identification of the transmitted/founder (T/F) virus, and thus the study of host responses directed against the autologous T/F strain. In this study, 14 rare subjects identified from very early in infection (4–45 days) with varied disease outcomes (n = 7 clearers) were examined in regard to the timing, breadth, and magnitude of the neutralizing antibody (nAb) response, as well as evolution of the T/F strain. Clearance was associated with earlier onset and more potent nAb responses appearing at a mean of 71 days post-infection (DPI), but these responses were narrowly directed against the autologous T/F virus or closely related variants. In contrast, a delayed onset of nAbs (mean 425 DPI) was observed in chronic progressors that appear to have targeted longitudinal variants rather than the T/F strain. The nAb responses in the chronic progressors mapped to known CD81 binding epitopes, and were associated with rapid emergence of new viral variants with reduced CD81 binding. We propose that the prolonged period of viremia in the absence of nAbs in these subjects was associated with an increase in viral diversity, affording the virus greater options to escape nAb pressure once it emerged. These findings indicate that timing of the nAb response is essential for clearance. Further investigation of the specificities of the early nAbs and the factors regulating early induction of protective nAbs is needed.

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.

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.

Broadly Neutralizing Antibodies Targeting New Sites of Vulnerability in Hepatitis C Virus E1E2

Increasing evidence indicates that broadly neutralizing antibodies (bNAbs) play an important role in immune-mediated control of hepatitis C virus (HCV) infection, but the relative contribution of neutralizing antibodies targeting antigenic sites across the HCV envelope (E1 and E2) proteins is unclear. Here, we isolated thirteen E1E2-specific monoclonal antibodies (MAbs) from B cells of a single HCV-infected individual who cleared one genotype 1a infection and then became persistently infected with a second genotype 1a strain. These MAbs bound six distinct discontinuous antigenic sites on the E1 protein, the E2 protein, or the E1E2 heterodimer. Three antigenic sites, designated AS108, AS112 (an N-terminal E1 site), and AS146, were distinct from previously described antigenic regions (ARs) 1 to 5 and E1 sites. Antibodies targeting four sites (AR3, AR4-5, AS108, and AS146) were broadly neutralizing. These MAbs also displayed distinct patterns of relative neutralizing potency (i.e., neutralization profiles) across a panel of diverse HCV strains, which led to complementary neutralizing breadth when they were tested in combination. Overall, this study demonstrates that HCV bNAb epitopes are not restricted to previously described antigenic sites, expanding the number of sites that could be targeted for vaccine development.IMPORTANCE Worldwide, more than 70 million people are infected with hepatitis C virus (HCV), which is a leading cause of hepatocellular carcinoma and liver transplantation. Despite the development of potent direct acting antivirals (DAAs) for HCV treatment, a vaccine is urgently needed due to the high cost of treatment and the possibility of reinfection after cure. Induction of multiple broadly neutralizing antibodies (bNAbs) that target distinct epitopes on the HCV envelope proteins is one approach to vaccine development. However, antigenic sites targeted by bNAbs in individuals with spontaneous control of HCV have not been fully defined. In this study, we characterize 13 monoclonal antibodies (MAbs) from a single person who cleared an HCV infection without treatment, and we identify 3 new sites targeted by neutralizing antibodies. The sites targeted by these MAbs could inform HCV vaccine development.