An Optimized Hepatitis C Virus E2 Glycoprotein Core Adopts a Functional Homodimer That Efficiently Blocks Virus Entry

Hepatitis C virus modified sE2F442NYT as an antigen in candidate vaccine facilitates human immune cell activation

The rational selection of hepatitis C virus (HCV) vaccine antigen will aid in the prevention of future chronic liver disease burden and associated healthcare costs. We have previously shown that HCV E2 glycoprotein is not highly immunogenic, and the modification of E2 reduced CD81 binding and displayed altered cytokine and protective immune responses in vitro and in a surrogate mouse model. Here, we compared the influence of a parental and a modified sE2F442NYT glycoprotein region from HCV genotype 1a for the activation of peripheral blood mononuclear cell (PBMC)-derived dendritic cells (DCs), CD4+T cells, and B cells. Modified sE2F442NYT, when incubated with DCs, induced a higher number of CD86-positive cells. The sE2F442NYT or parental sE2 encapsulated as mRNA-lipid nanoparticle (sE2F442NYT mRNA-LNP) primed DCs co-cultured with autologous CD4+T cells did not induce CD25 or forkhead box P3 expression. PBMC-derived CD4+T cells treated with sE2F442NYT exhibited enhanced signal transducer and activator of transcription (Stat)1/Stat4 phosphorylation in response to anti-CD3/CD28 stimulation in comparison to parental sE2 treatment and facilitated isotype switching in B cells, leading to the generation of a broader subclass of antibodies. Cells treated with modified sE2F442NYT displayed an increase in activated Stat3 and extracellular signal-regulated kinase (ERK). Likewise, PBMC-derived naïve B cells upon in vitro stimulation with sE2F442NYT induced an increased proliferation, Stat3 and ERK activation, and protein kinase B (Akt) suppression. Thus, the modified sE2F442NYT antigen from HCV facilitates improved DC, CD4+T, and B cell activation compared to parental sE2 to better induce a robust protective immune response, supporting its selection as an HCV candidate vaccine antigen for preclinical and clinical HCV vaccine trials.IMPORTANCEThe nature of an enhanced immune response induced by sE2F442NYT will help in the selection of a broad cross-protective antigen from hepatitis C virus genotypes, and the inclusion of relatively conserved sE1 with sE2F442NYT may further strengthen the efficacy of the candidate vaccine in evaluating it for human use.

Testing a vaccine candidate against Hepatitis C virus designed by combinatorial optimization

This paper presents a new procedure for vaccine design against highly variable viruses such as Hepatitis C. The procedure uses an optimization algorithm to design vaccines that maximize the coverage of epitopes across different virus variants. Weighted epitopes based on the success ratio of immunological assays are used to prioritize the selection of epitopes for vaccine design. The procedure was successfully applied to design DC vaccines loaded with two HCV peptides, STG and DYP, which were shown to be safe, immunogenic, and able to induce significant levels of anti-viral cytokines, peptide-specific cellular immune responses and IgG antibodies. The procedure could potentially be applied to other highly variable viruses that currently lack effective vaccines.

Two-component vaccine consisting of virus-like particles displaying hepatitis C virus envelope protein 2 oligomers

Development of B-cell-based hepatitis C virus (HCV) vaccines that induce broadly neutralizing antibodies (bNAbs) is hindered by extensive sequence diversity and low immunogenicity of envelope glycoprotein vaccine candidates, most notably soluble E2 (sE2). To overcome this, we employed two-component approaches using self-assembling virus-like particles (cVLPs; component 1), displaying monomeric or oligomeric forms of HCV sE2 (sE2mono or sE2oligo; component 2). Immunization studies were performed in BALB/c mice and the neutralizing capacity of vaccine-induced antibodies was tested in cultured-virus-neutralizations, using HCV of genotypes 1–6. sE2-cVLP vaccines induced significantly higher levels of NAbs (p = 0.0065) compared to corresponding sE2 vaccines. Additionally, sE2oligo-cVLP was superior to sE2mono-cVLP in inducing bNAbs. Interestingly, human monoclonal antibody AR2A had reduced binding in ELISA to sE2oligo-cVLP compared with sE2mono-cVLP and competition ELISA using mouse sera from vaccinated animals indicated that sE2oligo-cVLP induced significantly less non-bNAbs AR2A (p = 0.0043) and AR1B (p = 0.017). Thus, cVLP-displayed oligomeric sE2 shows promise as an HCV vaccine candidate.

Production and immunogenicity of different prophylactic vaccines for hepatitis C virus (Review)

Hepatitis C virus (HCV) infection is a global health challenge, and prophylactic vaccines are the most effective way to eliminate the infection. To date, numerous forms of preventive vaccines have entered the clinical trial stage, including the virus-like particle (VLP) vaccine, recombinant subunit vaccine, peptide vaccine and nucleic acid vaccine. The rational design makes it easier to obtain specific vaccine structures with a broad spectrum and strong immunogenicity. Different vaccine antigens can evoke different immune responses, including humoral and T-cell immune responses, and can be produced using different expression systems, such as bacteria, yeast, mammals, plants, insects or parasites. Intracellular and insoluble production and a narrow immune spectrum are two difficulties that limit the application of vaccines. The present study summarizes the immunogenicity of different preventive vaccines, evaluates the characteristics of different expression systems used for vaccine production, and analyzes the strategies to enhance the secretion and immune spectrum of vaccine proteins.

Modified E2 Glycoprotein of Hepatitis C Virus Enhances Proinflammatory Cytokines and Protective Immune Response

Hepatitis C virus (HCV) is characterized by a high number of chronic cases owing to an impairment of innate and adaptive immune responses. CD81 on the cell surface facilitates HCV entry by interacting with the E2 envelope glycoprotein. In addition, CD81/E2 binding on immunity-related cells may also influence host response outcome to HCV infection. Here, we performed site-specific amino acid substitution in the front layer of E2 sequence to reduce CD81 binding and evaluate the potential of the resulting immunogen as an HCV vaccine candidate. The modified sE2 protein (F442NYT), unlike unmodified sE2, exhibited a significant reduction in CD81 binding, induced higher levels of proinflammatory cytokines, repressed anti-inflammatory response in primary monocyte-derived macrophages as antigen-presenting cells, and stimulated CD4⁺ T cell proliferation. Immunization of BALB/c mice with an E1/sE2_F442NYT nucleoside-modified mRNA-lipid nanoparticle (mRNA-LNP) vaccine resulted in improved IgG1-to-IgG2a isotype switching, an increase in neutralizing antibodies against HCV pseudotype virus, a B and T cell proliferative response to antigens, and improved protection against infection with a surrogate recombinant vaccinia virus-expressing HCV E1-E2-NS2_aa134-966 challenge model compared to E1/unmodified sE2 mRNA-LNP vaccine. Further investigation of the modified E2 antigen may provide helpful information for HCV vaccine development. IMPORTANCE Hepatitis C virus (HCV) E2-CD81 binding dampens protective immune response. We have identified that an alteration of amino acids in the front layer of soluble E2 (sE2) disrupts CD81 interaction and alters the cytokine response. Immunization with modified sE2_F442NYT (includes an added potential N-linked glycosylation site and reduces CD81 binding activity)-mRNA-LNP candidate vaccine generates improved proinflammatory response and protective efficacy against a surrogate HCV vaccinia challenge model in mice. The results clearly suggested that HCV E2 exhibits immunoregulatory activity that inhibits induction of robust protective immune responses. Selection of engineered E2 antigen in an mRNA-LNP platform amenable to nucleic acid sequence alterations may open a novel approach for multigenotype 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.

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.

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.

Optimized Hepatitis C Virus (HCV) E2 Glycoproteins and their Immunogenicity in Combination with MVA-HCV

Hepatitis C virus (HCV) represents a major global health challenge and an efficient vaccine is urgently needed. Many HCV vaccination strategies employ recombinant versions of the viral E2 glycoprotein. However, recombinant E2 readily forms disulfide-bonded aggregates that might not be optimally suited for vaccines. Therefore, we have designed an E2 protein in which we strategically changed eight cysteines to alanines (E2.C8A). E2.C8A formed predominantly monomers and virtually no aggregates. Furthermore, E2.C8A also interacted more efficiently with broadly neutralizing antibodies than conventional E2. We used mice to evaluate different prime/boost immunization strategies involving a modified vaccinia virus Ankara (MVA) expressing the nearly full-length genome of HCV (MVA-HCV) in combination with either the E2 aggregates or the E2.C8A monomers. The combined MVA-HCV/E2 aggregates prime/boost strategy markedly enhanced HCV-specific effector memory CD4⁺ T cell responses and antibody levels compared to MVA-HCV/MVA-HCV. Moreover, the aggregated form of E2 induced higher levels of anti-E2 antibodies in vaccinated mice than E2.C8A monomers. These antibodies were cross-reactive and mainly of the IgG1 isotype. Our findings revealed how two E2 viral proteins that differ in their capacity to form aggregates are able to enhance to different extent the HCV-specific cellular and humoral immune responses, either alone or in combination with MVA-HCV. These combined protocols of MVA-HCV/E2 could serve as a basis for the development of a more effective HCV vaccine.

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.

Hepatitis C Virus Vaccine: Challenges and Prospects

The hepatitis C virus (HCV) causes both acute and chronic infection and continues to be a global problem despite advances in antiviral therapeutics. Current treatments fail to prevent reinfection and remain expensive, limiting their use to developed countries, and the asymptomatic nature of acute infection can result in individuals not receiving treatment and unknowingly spreading HCV. A prophylactic vaccine is therefore needed to control this virus. Thirty years since the discovery of HCV, there have been major gains in understanding the molecular biology and elucidating the immunological mechanisms that underpin spontaneous viral clearance, aiding rational vaccine design. This review discusses the challenges facing HCV vaccine design and the most recent and promising candidates being investigated.

Envelope-Specific IgG3 and IgG1 Responses Are Associated with Clearance of Acute Hepatitis C Virus Infection

Hepatitis C virus (HCV) can be cleared naturally in a subset of individuals. However, the asymptomatic nature of acute HCV infection makes the study of the early immune response and defining the correlates of protection challenging. Despite this, there is now strong evidence implicating the humoral immune response, specifically neutralising antibodies, in determining the clearance or chronicity outcomes of primary HCV infection. In general, immunoglobulin G (IgG) plays the major role in viral neutralisation. However, there are limited investigations of anti-HCV envelope protein 2 (E2) isotypes (IgM, IgG, IgA) and IgG subclasses (IgG1-4) in early HCV infection. In this study, using a rare cohort of 14 very recently HCV-infected individuals (4-45 days) with varying disease outcome (n = 7 clearers), the timing and potency of anti-HCV E2 isotypes and IgG subclasses were examined longitudinally, in relation to neutralising antibody activity. Clearance was associated with anti-E2 IgG, specifically IgG1 and IgG3, and appeared essential to prevent the emergence of new HCV variants and the chronic infection outcome. Interestingly, these IgG responses were accompanied by IgM antibodies and were associated with neutralising antibody activity in the subjects who cleared infection. These findings provide novel insights into the early humoral immune response characteristics associated with HCV disease outcome.

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

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

A trivalent HCV vaccine elicits broad and synergistic polyclonal antibody response in mice and rhesus monkey

OBJECTIVE

Despite the development of highly effective direct-acting antivirals, a prophylactic vaccine is needed for eradicating HCV. A major hurdle of HCV vaccine development is to induce immunity against HCV with high genome diversity. We previously demonstrated that a soluble E2 (sE2) expressed from insect cells induces broadly neutralising antibodies (NAbs) and prevents HCV infection. The objective of this study is to develop a multivalent HCV vaccine to increase the antigenic coverage.

DESIGN

We designed a trivalent vaccine containing sE2 from genotype 1a, 1b and 3a. Mice and rhesus macaques were immunised with monovalent or trivalent sE2 vaccine, and sera or purified immunoglobulin were assessed for neutralisation against a panel of cell culture-derived virion (HCVcc) of genotype 1-7 in cell culture. Splenocytes from the vaccinated macaques were assessed for HCV-specific T cell response.

RESULTS

We showed that the trivalent vaccine elicited pangenotypic NAbs in mice, which neutralised HCVcc of all the seven genotypes more potently than the monovalent vaccine. Further analyses demonstrated that each sE2 component of this trivalent vaccine elicited unique spectrum of NAbs which acted synergistically to inhibit HCV infection. Finally, the trivalent vaccine triggered stronger and more uniform multigenotypic neutralising antibody response than the monovalent vaccine in rhesus macaques.

CONCLUSIONS

In summary, we developed a trivalent HCV vaccine that induces broad and synergistic-acting neutralising antibodies in mice and non-human primates.

Hypervariable Region 1 in Envelope Protein 2 of Hepatitis C Virus: A Linchpin in Neutralizing Antibody Evasion and Viral Entry

Chronic hepatitis C virus (HCV) infection is the cause of about 400,000 annual liver disease-related deaths. The global spread of this important human pathogen can potentially be prevented through the development of a vaccine, but this challenge has proven difficult, and much remains unknown about the multitude of mechanisms by which this heterogeneous RNA virus evades inactivation by neutralizing antibodies (NAbs). The N-terminal motif of envelope protein 2 (E2), termed hypervariable region 1 (HVR1), changes rapidly in immunoglobulin-competent patients due to antibody-driven antigenic drift. HVR1 contains NAb epitopes and is directly involved in protecting diverse antibody-specific epitopes on E1, E2, and E1/E2 through incompletely understood mechanisms. The ability of HVR1 to protect HCV from NAbs appears linked with modulation of HCV entry co-receptor interactions. Thus, removal of HVR1 increases interaction with CD81, while altering interaction with scavenger receptor class B, type I (SR-BI) in a complex fashion, and decreasing interaction with low-density lipoprotein receptor. Despite intensive efforts this modulation of receptor interactions by HVR1 remains incompletely understood. SR-BI has received the most attention and it appears that HVR1 is involved in a multimodal HCV/SR-BI interaction involving high-density-lipoprotein associated ApoCI, which may prime the virus for later entry events by exposing conserved NAb epitopes, like those in the CD81 binding site. To fully elucidate the multifunctional role of HVR1 in HCV entry and NAb evasion, improved E1/E2 models and comparative studies with other NAb evasion strategies are needed. Derived knowledge may be instrumental in the development of a prophylactic HCV vaccine.