A Hepatitis C Virus DNA Vaccine Encoding a Secreted, Oligomerized Form of Envelope Proteins Is Highly Immunogenic and Elicits Neutralizing Antibodies in Vaccinated Mice

Adenoviruses vectored hepatitis C virus vaccine cocktails induce broadly specific immune responses against multi-genotypic HCV in mice

BACKGROUND

Hepatitis C virus (HCV) vaccines are an urgent need to prevent hepatitis C and its further progression of hepatocellular carcinoma. Since the promising T cell based chimpanzee adenovirus and modified vaccinia virus Ankara vectorial HCV vaccines were failed in clinical phase II trial, the vaccine designs to improve protection efficacy in combination of cellular and humoral immunity have been hypothesized against multi-genotypic HCV.

METHODS

Eight HCV vaccine strains were constructed with two novel adenovirus vectors (Sad23L and Ad49L) encoding E1E2 or NS3-5B proteins of HCV genotype (Gt) 1b and 6a isolates, covering 80 % HCV strains prevalent in south China and south-east Asia. Eight HCV vaccine strains were grouped into Sad23L-based vaccine cocktail-1 and Ad49L-based vaccine cocktail-2 for vaccinating mice, respectively.

RESULTS

The immunogenicity of a single dose of 107-1010 PFU HCV individual vaccines was evaluated in mice, showing weak specific antibody to E1 and E2 protein but a dose-dependent T cell response to E1E2/NS3-5B peptides, which could be significantly enhanced by boosting with an alternative vector vaccine carrying homologous antigen. Prime-boost vaccinations with vaccine cocktail-1 and cocktail-2 induced significantly higher cross-reactive antibody and stronger T cell responses to HCV Gt-1b/6a. The high frequency of intrasplenic and intrahepatic NS31629-1637 CD8+ T cell responses were identified, in which the high proportion of TRM and TEM cells might play an important role against HCV infection in liver.

CONCLUSIONS

Prime-boost regimens with HCV vaccine cocktails elicited the broad cross-reactive antibody and robust T cell responses against multi-genotypic HCV in mice.

Gene-encoded nanoparticle vaccine platforms for in vivo assembly of multimeric antigen to promote adaptive immunity

Nanoparticle vaccines are a diverse category of vaccines for the prophylaxis or treatment of various diseases. Several strategies have been employed for their optimization, especially to enhance vaccine immunogenicity and generate potent B-cell responses. Two major modalities utilized for particulate antigen vaccines include using nanoscale structures for antigen delivery and nanoparticles that are themselves vaccines due to antigen display or scaffolding-the latter of which we will define as "nanovaccines." Multimeric antigen display has a variety of immunological benefits compared to monomeric vaccines mediated through potentiating antigen-presenting cell presentation and enhancing antigen-specific B-cell responses through B-cell activation. The majority of nanovaccine assembly is done in vitro using cell lines. However, in vivo assembly of scaffolded vaccines potentiated using nucleic acids or viral vectors is a burgeoning modality of nanovaccine delivery. Several advantages to in vivo assembly exist, including lower costs of production, fewer production barriers, as well as more rapid development of novel vaccine candidates for emerging diseases such as SARS-CoV-2. This review will characterize the methods for de novo assembly of nanovaccines in the host using methods of gene delivery including nucleic acid and viral vectored vaccines. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Oligomerization and Adjuvant Activity of Peptides Derived from the VirB4-like ATPase of Clostridioides difficile

In a previous study, we demonstrated that the Clostridioides difficile VirB4-like ATPase forms oligomers in vitro. In the current investigation, to study the observed phenomenon in more detail, we prepared a library of VirB4-derived peptides (delVirB4s) fused to a carrier maltose-binding protein (MBP). Using gel chromatography and polyacrylamide gel electrophoresis, we found a set of overlapping fragments that contribute most significantly to protein aggregation, which were represented as water-soluble oligomers with molecular masses ranging from ~300 kD to several megadaltons. Membrane filtration experiments, sucrose gradient ultracentrifugation, and dynamic light scattering measurements indicated the size of the soluble complex to be 15-100 nm. It was sufficiently stable to withstand treatment with 1 M urea; however, it dissociated in a 6 M urea solution. As shown by the changes in GFP fluorescence and the circular dichroism spectra, the attachment of the delVirB4 peptide significantly altered the structure of the partner MBP. The immunization of mice with the hybrid consisting of the selected VirB4-derived peptide and MBP, GST, or GFP resulted in increased production of specific antibodies compared to the peptide-free carrier proteins, suggesting significant adjuvant activity of the VirB4 fragment. This feature could be useful for the development of new vaccines, especially in the case of "weak" antigens that are unable to elicit a strong immune response by themselves.

Pseudotyped Virus for Flaviviridae

Members of Flaviviridae are enveloped single positive-stranded RNA viruses including hepacivirus, pestivirus, pegivirus, and mosquito-transmitted flavivirus, which are important pathogens of infectious diseases and pose serious threats to human health. Pseudotyped virus is an artificially constructed virus-like particle, which could infect host cells similar to a live virus but cannot produce infectious progeny virus. Therefore, pseudotyped virus has the advantages of a wide host range, high transfection efficiency, low biosafety risk, and accurate and objective quantification. It has been widely used in biological characteristics, drug screening, detection methods, and vaccine evaluation of Flaviviridae viruses like hepatitis C virus, Japanese encephalitis virus, dengue virus, and Zika virus.

Individual expression and processing of hepatitis C virus E1/E2 epitopes-based DNA vaccine candidate in healthy humans' peripheral blood mononuclear cells

Purpose

The development and study of hepatitis C virus (HCV) vaccine candidates' individualized responses are of great importance. Here we report on an HCV DNA vaccine candidate based on selected envelope (E1/E2) epitopes. Besides, we assessed its expression and processing in human peripheral blood mononuclear cells (PBMCs) and in vivo cellular response in mice.

Materials and Methods

HCV E1/E2 DNA construct (EC) was designed. The antigen expression of EC was assayed in PBMCs of five HCV-uninfected donors via a real-time quantitative polymerase chain reaction. Serum samples from 20 HCV antibody-positive patients were used to detect each individual PBMCs expressed antigens via enzyme-linked immunosorbent assay. Two groups, five Swiss albino mice each, were immunized with the EC or a control construct. The absolute count of lymph nodes' CD4⁺ and CD8⁺ T-lymphocytes was assessed.

Results

Donors' PBMCs showed different levels of EC expression, ranging between 0.83-2.61-fold in four donors, while donor-3 showed 34.53-fold expression. The antigens expressed in PBMCs were significantly reactive to the 20 HCV antibody repertoire (all p=0.0001). All showed comparable reactivity except for donor-3 showing the lowest reactivity level. The absolute count % of the CD4⁺ T-cell significantly increased in four of the five EC-immunized mice compared to the control group (p=0.03). No significant difference in CD8⁺ T-cells % was observed (p=0.89).

Conclusion

The inter-individual variation in antigen expression and processing dominance was evident, showing independence in individuals' antigen expression and reactivity levels to antibodies. The described vaccine candidate might result in a promising natural immune response with a possibility of CD4⁺ T-cell early priming.

The Transmission Route and Selection Pressure in HCV Subtype 3a and 3b Chinese Infections: Evolutionary Kinetics and Selective Force Analysis

Hepatitis C virus (HCV) genotype 3 (GT-3) represents 22–30% of all infections and is the second most common genotype among all HCV genotypes. It has two main subtypes, GT-3a and GT-3b, that present epidemiological differences in transmission groups. This report generated 56 GT-3a and 64 GT-3b whole-genome sequences to conduct an evolutionary kinetics and selective force analysis with reference sequences from various countries. Evolutionary analysis showed that HCV GT-3a worldwide might have been transmitted from the Indian subcontinent to South Asia, Europe, North America and then become endemic in China. In China, GT-3a may have been transmitted by intravenous drug users (IDUs) and become endemic in the general population, while GT-3b may have originated from IDUs and then underwent mutual transmission between blood donors (BDs) and IDUs, ultimately becoming independently endemic in IDUs. Furthermore, the spread of GT-3a and GT-3b sequences from BD and IDU populations exhibit different selective pressures: the proportion of positively selected sites (PPSs) in E1 and E2 from IDUs was higher than in BDs. The number of positive selection sites was higher in GT-3b and IDUs. These results indicate that different selective constraints act along with the GT-3a and GT-3b genomes from IDUs and BDs. In addition, GT-3a and GT-3b have different transmission routes in China, which allows us to formulate specific HCV prevention and control strategies in China.

Hepatitis C Vaccination: Where We Are and Where We Need to Be

The hepatitis C virus (HCV) is a common cause of chronic liver disease and liver cancer worldwide. Despite advances in curative therapies for HCV, the incidence of new infections is not decreasing at the expected rate to hit the World Health Organization (WHO) target for the elimination of HCV by 2030. In fact, there are still more new cases of infection in the United States and worldwide than are being cured. The reasons for the rise in new cases include poor access to care and the opioid epidemic. The clinical burden of HCV requires a multimodal approach to eradicating the infection. Vaccination would be an excellent tool to prevent incidence of new infections; however, the genetic diversity of HCV and its ability to generate quasispecies within an infected host make creating a broadly reactive vaccine difficult. Multiple vaccine candidates have been identified, but to date, there has not been a target that has led to a broadly reactive vaccine, though several of the candidates are promising. Additionally, the virus is very difficult to culture and testing candidates in humans or chimpanzees is ethically challenging. Despite the multiple barriers to creating a vaccine, vaccination still represents an important tool in the fight against HCV.

Hepatitis C virus DNA vaccines: a systematic review

BACKGROUND

Vaccination against HCV is an effective measure in reduction of virus-related public health burden and mortality. However, no prophylactic vaccine is available as of yet. DNA-based immunization is a promising modality to generate cellular and humoral immune responses. The objective of this study is to provide a systematic review of HCV DNA vaccines and investigate and discuss the strategies employed to optimize their efficacies.

METHODS

MEDLINE (PubMed), Web of Science, Scopus, ScienceDirect, and databases in persian language including the Regional Information Centre for Science & Technology (RICeST), the Scientific Information Database and the Iranian Research Institute for Information Science and Technology (IranDoc) were examined to identify studies pertaining to HCV nucleic acid vaccine development from 2000 to 2020.

RESULTS

Twenty-seven articles were included. Studies related to HCV RNA vaccines were yet to be published. A variety of strategies were identified with the potential to optimize HCV DNA vaccines such as incorporating multiple viral proteins and molecular tags such as HBsAg and Immunoglobulin Fc, multi-epitope expression, co-expression plasmid utilization, recombinant subunit immunogens, heterologous prime-boosting, incorporating NS3 mutants in DNA vaccines, utilization of adjuvants, employment of less explored methods such as Gene Electro Transfer, construction of multi- CTL epitopes, utilizing co/post translational modifications and polycistronic genes, among others. The effectiveness of the aforementioned strategies in boosting immune response and improving vaccine potency was assessed.

CONCLUSIONS

The recent progress on HCV vaccine development was examined in this systematic review to identify candidates with most promising prophylactic and therapeutic potential.

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].

Optimisation and validation of a new method for antibody dependent cellular phagocytosis in hepatitis C virus infection

Lack of a simple, high throughput antibody-dependent cellular phagocytosis (ADCP) assay has limited our understanding of its potential role of in hepatitis C (HCV) infection. Here, we optimised a flow-cytometry based ADCP assay using HCV envelope (E2)-protein coated microbeads that were opsonised with anti-E2 monoclonal IgG antibody (αE2 mAb) and the THP-1 monocyte cell line as effector cells. We found 1.5 × 10⁹/ml microbeads opsonised with 5 μg/ml αE2 mAb and 1.6 × 10⁶/ml THP-1 cells were optimal conditions to distinguish between healthy controls and patients with HCV. This optimised assay was then used to investigate ADCP in plasma obtained from 72 patients with chronic HCV infection and 15 healthy controls. We found that 75% of patients with genotype 1 and 87% of patients with genotype 3 HCV infection had significantly higher levels of ADCP compared to healthy controls. In patients, there was a significant correlation between increase in ADCP and higher concentrations of anti-E2 IgG antibodies in the plasma. Taken together, we established a simple, quick and high throughput ADCP assay for HCV infection that can readily be used for screening of large cohorts of patients and investigation of the role of ADCP in the pathogenesis or protection from this disease.

Solubility Controlling Peptide Tags of Opposite Charges Generate a Bivalent Immune Response Against Dengue ED3 Serotypes 3 and 4

We previously demonstrated that a protein’s immunogenicity could be substantially increased by attaching a hydrophobic solubility controlling peptide tag (SCP-tag) producing small sub-visible aggregates. Here, we report the oligomerization of Dengue envelop protein domain 3 (ED3), and consequently, its immunogenicity increase by mixing ED3s attached with SCP-tags of opposite charges at equimolar concentration. We used ED3 of serotype 3 (D3ED3) and serotype 4 (D4ED3), which are, respectively, moderately and poorly immunogenic, and their SCP tagged variants constructed by attaching either a C-termini 5-Aspartic acid (C5D) or a 5-Lysine (C5K) tag. Light scattering indicated that the isolated tagged ED3s remained monomeric, but mixing the C5D and C5K tagged ED3s at equimolar concentration generated sub-visible aggregates or oligomers of ~500 nm through electrostatic interaction. In addition, the oligomerized ED3s remained in a native-like state, as assessed by fluorescence spectroscopy and circular dichroism. The in vivo immunogenicity of the D3ED3 and D4ED3 oligomers generated by the charged tags increased by 5 and 16 fold, respectively. Furthermore, injection of heterotypic ED3 oligomers (D3C5D+D4C5K) induced an immune response against both D3ED3 and D4ED3 in 3 of 4 responsive mice, and the IgG titer of the bivalent anti-D3C5D-D4C5K sera was over 100 times higher than that generated by co-injecting the untagged D3ED3 and D4ED3 (D3+D4). Altogether, these observations suggest that SCP-tags could be used as a platform for producing a long-sought tetravalent dengue vaccine.

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

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

From hepatitis A to E: A critical review of viral hepatitis

Viral infections affecting the liver have had an important impact on humanity, as they have led to significant morbidity and mortality in patients with acute and chronic infections. Once an unknown etiology, the discovery of the viral agents triggered interest of the scientific community to establish the pathogenesis and diagnostic modalities to identify the affected population. With the rapid scientific and technological advances in the last centuries, controlling and even curing the infections became a possibility, with a large focus on preventive medicine through vaccination. Hence, a comprehensive understanding of hepatitis A, B, C, D and E is required by primary care physicians and gastroenterologists to provide care to these patients. The review article describes the epidemiology, pathogenesis, clinical presentation, diagnostic tools and current medication regimens, with a focus on upcoming treatment options and the role of liver transplantation.

Immuno-Informatics Analysis of Pakistan-Based HCV Subtype-3a for Chimeric Polypeptide Vaccine Design

Hepatitis C virus (HCV) causes chronic and acute hepatitis infections. As there is extreme variability in the HCV genome, no approved HCV vaccine has been available so far. An effective polypeptide vaccine based on the functionally conserved epitopes will be greatly helpful in curing disease. For this purpose, an immuno-informatics study is performed based on the published HCV subtype-3a from Pakistan. First, the virus genome was translated to a polyprotein followed by a subsequent prediction of T-cell epitopes. Non-allergenic, IFN-γ producer, and antigenic epitopes were shortlisted, including 5 HTL epitopes and 4 CTL, which were linked to the final vaccine by GPGPG and AAY linkers, respectively. Beta defensin was included as an adjuvant through the EAAAK linker to improve the immunogenicity of the polypeptide. To ensure its safety and immunogenicity profile, antigenicity, allergenicity, and various physiochemical attributes of the polypeptide were evaluated. Molecular docking was conducted between TLR4 and vaccine to evaluate the binding affinity and molecular interactions. For stability assessment and binding of the vaccine-TLR4 docked complex, molecular dynamics (MD) simulation and MMGBSA binding free-energy analyses were conducted. Finally, the candidate vaccine was cloned in silico to ensure its effectiveness. The current vaccine requires future experimental confirmation to validate its effectiveness. The vaccine construct produced might be useful in providing immune protection against HCV-related infections.

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.

Enhanced T Cell Responses Induced by a Necrotic Dendritic Cell Vaccine, Expressing HCV NS3

A vaccine that induces potent, broad and sustained cell-mediated immunity, resulting in effective memory has the potential to restrict hepatitis C (HCV) virus infection. Early, multi-functional CD4⁺ and CD8⁺ T cell responses against non-structural protein 3 (NS3) have been associated with HCV clearance. Necrotic cells generate strong immune responses and represent a major antigenic source used by dendritic cells (DC) for processing and presentation, but there is conflicting evidence as to their immunogenicity in vaccination. Immunization with DC loaded with viral antigens has been done in the past, but to date the immunogenicity of live vs. necrotic DC vaccines has not been investigated. We developed a DC2.4 cell line stably expressing HCV NS3, and compared the NS3-specific responses of live vs. necrotic NS3 DC. Vaccination of mice with necrotic NS3 DC increased the breadth of T-cell responses and enhanced the production of IL-2, TNF-α, and IFN-γ by effector memory CD4⁺ and CD8⁺T cells, compared to mice vaccinated with live NS3 DC. A single dose of necrotic NS3 DC vaccine induced a greater influx and activation of cross-presenting CD11c⁺ CD8α⁺ DC and necrosis-sensing Clec9A⁺ DC in the draining lymph nodes. Furthermore, using a hydrodynamic challenge model necrotic NS3 DC vaccination resulted in enhanced clearance of NS3-positive hepatocytes from the livers of vaccinated mice. Taken together, the data demonstrate that necrotic DC represent a novel and exciting vaccination strategy capable of inducing broad and multifunctional T cell memory.

Reactivation of human cytomegalovirus inhibits expression of liver fibrosis related cytokines in patients chronically infected with hepatitis C virus genotype 4a

BACKGROUND

The impact of human cytomegalovirus (HCMV) reactivation on the expression pattern of matrix metalloproteinases, their inhibitors and related cytokines during HCV infection poorly understood.

METHODS

Reactivation of CMV in 95 subjects (75 chronically infected HCV patients and 20 healthy subjects) was examined. All studied subjects had detectable IgG antibodies for CMV, but only 35/75 of HCV patients (46.7%) had detectable CMV DNA. The expressions of 11 fibrosis related genes by quantitative real-time PCR were analyzed in subjects' PBMCs. The serum levels of TGFβ2 and PDGFα have been measured by ELISA.

RESULTS

Chronically infected HCV patients with reactivated CMV had less expression of TGF-β1, TGF-β2, PDGFα and STAT1 transcripts than HCV patients with latent CMV (p = 0.037, 0.006, 0.001 and 0.009; respectively) and normal controls (TGF-β2, p = 0.008). Moreover the expression of (TGFβ2 and PDGFα) genes decreased significantly in CMV-reactivated patients during the early stage of fibrosis relative to the comparable stage of HCV infection (p = 0.004 and 0.008; respectively). Besides, the mRNA abundance of STAT1 gene in CMV-reactivated patients decreased dramatically as compared to HCV infections during the late stage of fibrosis (p = 0.014). The TGFβ2 protein level has been declined dramatically in CMV-reactivated patients compared to HCV infected patients and control group (p = 0.001 and 0.033; respectively). Our results suggest that CMV reactivation disrupts the expression of several cytokines as compared to solitary infection with HCV. Noticeably, the expressions of matrix metalloproteinases genes and their inhibitors have not been significantly influenced by reactivation of CMV.

CONCLUSION

The current data reveal that reactivation of CMV partially blocks the upregulation of 2 important pro-inflammatory cytokines i.e. TGFβ 2 and PDGFα at early stages of fibrosis, moreover this CMV mediated blockage of the STAT1 shows statistical significance at late stage of fibrosis.

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.

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.

Innate Immune Response against Hepatitis C Virus: Targets for Vaccine Adjuvants

Despite successful treatments, hepatitis C virus (HCV) infections continue to be a significant world health problem. High treatment costs, the high number of undiagnosed individuals, and the difficulty to access to treatment, particularly in marginalized susceptible populations, make it improbable to achieve the global control of the virus in the absence of an effective preventive vaccine. Current vaccine development is mostly focused on weakly immunogenic subunits, such as surface glycoproteins or non-structural proteins, in the case of HCV. Adjuvants are critical components of vaccine formulations that increase immunogenic performance. As we learn more information about how adjuvants work, it is becoming clear that proper stimulation of innate immunity is crucial to achieving a successful immunization. Several hepatic cell types participate in the early innate immune response and the subsequent inflammation and activation of the adaptive response, principally hepatocytes, and antigen-presenting cells (Kupffer cells, and dendritic cells). Innate pattern recognition receptors on these cells, mainly toll-like receptors, are targets for new promising adjuvants. Moreover, complex adjuvants that stimulate different components of the innate immunity are showing encouraging results and are being incorporated in current vaccines. Recent studies on HCV-vaccine adjuvants have shown that the induction of a strong T- and B-cell immune response might be enhanced by choosing the right adjuvant.

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.

Safety Profile of a Multi-Antigenic DNA Vaccine Against Hepatitis C Virus

Despite direct acting antivirals (DAAs) curing >95% of individuals infected with hepatitis C (HCV), in order to achieve the World Health Organization HCV Global Elimination Goals by 2030 there are still major challenges that need to be overcome. DAAs alone are unlikely to eliminate HCV in the absence of a vaccine that can limit viral transmission. Consequently, a prophylactic HCV vaccine is necessary to relieve the worldwide burden of HCV disease. DNA vaccines are a promising vaccine platform due to their commercial viability and ability to elicit robust T-cell-mediated immunity (CMI). We have developed a novel cytolytic DNA vaccine that encodes non-structural HCV proteins and a truncated mouse perforin (PRF), which is more immunogenic than the respective canonical DNA vaccine lacking PRF. Initially we assessed the ability of the HCV pNS3-PRF and pNS4/5-PRF DNA vaccines to elicit robust long-term CMI without any adverse side-effects in mice. Interferon-γ (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay was used to evaluate CMI against NS3, NS4 and NS5B in a dose-dependent manner. This analysis showed a dose-dependent bell-curve of HCV-specific responses in vaccinated animals. We then thoroughly examined the effects associated with reactogenicity of cytolytic DNA vaccination with the multi-antigenic HCV DNA vaccine (pNS3/4/5B). Hematological, biochemical and histological studies were performed in male Sprague Dawley rats with a relative vaccine dose 10–20-fold higher than the proposed dose in Phase I clinical studies. The vaccine was well tolerated, and no toxicity was observed. Thus, the cytolytic multi-antigenic DNA vaccine is safe and elicits broad memory CMI.

NS1 DNA vaccination protects against Zika infection through T cell-mediated immunity in immunocompetent mice

The causal association of Zika virus (ZIKV) with microcephaly, congenital malformations in infants, and Guillain-Barré syndrome in adults highlights the need for effective vaccines. Thus far, efforts to develop ZIKV vaccines have focused on the viral envelope. ZIKV NS1 as a vaccine immunogen has not been fully explored, although it can circumvent the risk of antibody-dependent enhancement of ZIKV infection, associated with envelope antibodies. Here, we describe a novel DNA vaccine encoding a secreted ZIKV NS1, that confers rapid protection from systemic ZIKV infection in immunocompetent mice. We identify novel NS1 T cell epitopes in vivo and show that functional NS1-specific T cell responses are critical for protection against ZIKV infection. We demonstrate that vaccine-induced anti-NS1 antibodies fail to confer protection in the absence of a functional T cell response. This highlights the importance of using NS1 as a target for T cell-based ZIKV vaccines.