Lessons from Nature: Understanding Immunity to HCV to Guide Vaccine Design

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].

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.

Change in hepatitis C virus positivity among needle-stick injury source patients: a 10-year experience in a Japanese tertiary hospital

Background

As a blood-borne pathogen, hepatitis C virus (HCV) has long been a major threat associated with needle-stick injuries (NSIs) mainly because no vaccine is available for HCV. Following an NSI, we usually test the source patient for HCV antibody (HCV-Ab). Since HCV-Ab positivity does not necessarily indicate current infection, HCV RNA is further examined in patients positive for HCV-Ab. Direct-acting antivirals (DAAs) have enabled us to treat most HCV-infected patients; therefore, we speculate that the rate of HCV RNA positivity among HCV-Ab-positive patients decreased after the emergence of DAAs. This cross-sectional study was performed to investigate the change in the actual HCV RNA positivity rate in source patients before and after the interferon (IFN)-free DAA era.

Methods

This was a cross-sectional study of NSI source patients at a tertiary academic hospital in Japan from 2009 to 2019. IFN-free DAA regimens were first introduced in Japan in 2014. Accordingly, we compared HCV status of NSI source patients that occurred between 2009 and 2014 (the era before IFN-free DAAs) with those that occurred between 2015 and 2019 (the era of IFN-free DAAs) in a tertiary care hospital in Japan.

Results

In total, 1435 NSIs occurred, and 150 HCV-Ab-positive patients were analyzed. The proportion of HCV RNA-positive patients significantly changed from 2009 through 2019 (p = 0.005, Cochran–Armitage test). Between 2009 and 2014, 102 source patients were HCV-Ab-positive, 78 of whom were also positive for HCV RNA (76.5%; 95%CI, 67.4–83.6%). Between 2015 and 2019, 48 patients were HCV-Ab-positive, 23 of whom were also positive for HCV RNA (47.9%; 95%CI, 34.5–61.7%; p = 0.0007 compared with 2009–2014). In the era of IFN-free DAAs, 9 of 23 HCV RNA-negative patients (39.1%) and 2 of 22 HCV RNA-positive patients (9.1%) were treated with an IFN-free combination of DAAs (p = 0.0351). Regarding the departments where NSIs occurred, HCV RNA-negative patients were predominant in departments not related to liver diseases in the era of IFN-free DAAs (p = 0.0078, compared with 2009–2014).

Conclusions

Actual HCV RNA positivity in source patients of NSIs decreased after the emergence of IFN-free DAAs. IFN-free DAAs might have contributed to this reduction, and HCV RNA-negative patients were predominant in departments not related to liver diseases in the era of IFN-free DAAs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06117-4.

Evaluation of miR-122 Serum Level and IFN-λ3 Genotypes in Patients with Chronic HCV and HCV-Infected Liver Transplant Candidate

BACKGROUND

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are the most common markers of liver damage, but serum level interpretation can be complicated. In hepatocytes, microRNA-122 (miR-122) is the most abundant miRs and its high expression in the serum is a characteristic of liver disease.

OBJECTIVE

We aimed to compare the circulatory level of miR-122 in patients with Chronic Hepatitis C (CHC), Hepatitis C Virus (HCV) infected Liver Transplant Candidates (LTC) and healthy controls to determine if miR-122 can be considered as an indicator of chronic and advanced stage of liver disease.

METHODS

MiR-122 serum level was measured in 170 Interferon-naïve (IFN-naïve) CHC patients, 62 LTC patients, and 132 healthy individuals via TaqMan real-time PCR. Serum levels of miR-122 were normalized to the serum level of Let-7a and miR-221. Also, the ALT and AST levels were measured.

RESULTS

ALT and AST activities and the expression of circulatory miR-122 were similar in the CHC and LTC groups, but it had significantly increased compared to healthy individuals (P<0.001 and P<0.001, respectively). Up-regulation of miR-122 in the sample of patients with normal ALT and AST activities was also observed, indicating that miR-122 is a good marker with high sensitivity and specificity for diagnosing liver damage.

CONCLUSION

miR-122 seemed to be more specific for liver diseases in comparison with the routine ALT and AST liver enzymes. Since the lower levels of circulating miR-122 were observed in the LTC group compared to the CHC group, advanced liver damages might reduce the release of miR-122 from the hepatocytes, as a sign of liver function deficiency.

Antibody Responses to Immunization With HCV Envelope Glycoproteins as a Baseline for B-Cell-Based Vaccine Development

BACKGROUND & AIMS

We investigated antibody responses to hepatitis C virus (HCV) antigens E1 and E2 and the relevance of animal models for vaccine development. We compared antibody responses to vaccination with recombinant E1E2 complex in healthy volunteers, non-human primates (NHPs), and mice.

METHODS

We analyzed 519 serum samples from participants in a phase 1 vaccine trial (ClinicalTrials.gov identifier NCT00500747) and compared them with serum or plasma samples from C57BL/6J mice (n = 28) and rhesus macaques (n = 4) immunized with the same HCV E1E2 antigen. Blood samples were collected at different time points and analyzed for antibody binding, neutralizing activity, and epitope specificity. Monoclonal antibodies from the immunized NHPs were isolated from single plasmablasts and memory B cells, and their immunogenetic properties were characterized.

RESULTS

Antibody responses of the volunteers, NHPs, and mice to the non-neutralizing epitopes on the E1 N-terminus and E2 hypervariable region 1 did not differ significantly. Antibodies from volunteers and NHPs that neutralized heterologous strains of HCV primarily interacted with epitopes in the antigen region 3. However, the neutralizing antibodies were not produced in sufficient levels for broad neutralization of diverse HCV isolates. Broadly neutralizing antibodies similar to the human V_H1-69 class antibody specific for antigen region 3 were produced in the immunized NHPs.

CONCLUSIONS

In an analysis of vaccinated volunteers, NHPs, and mice, we found that recombinant E1E2 vaccine antigen induces high-antibody titers that are insufficient to neutralize diverse HCV isolates. Antibodies from volunteers and NHPs bind to the same neutralizing epitopes for virus neutralization. NHPs can therefore be used as a preclinical model to develop HCV vaccines. These findings also provide useful baseline values for development of vaccines designed to induce production of neutralizing antibodies.

Quasispecies dynamics in disease prevention and control

Medical interventions to prevent and treat viral disease constitute evolutionary forces that may modify the genetic composition of viral populations that replicate in an infected host and influence the genomic composition of those viruses that are transmitted and progress at the epidemiological level. Given the adaptive potential of viruses in general and the RNA viruses in particular, the selection of viral mutants that display some degree of resistance to inhibitors or vaccines is a tangible challenge. Mutant selection may jeopardize control of the viral disease. Strategies intended to minimize vaccination and treatment failures are proposed and justified based on fundamental features of viral dynamics explained in the preceding chapters. The recommended use of complex, multiepitopic vaccines, and combination therapies as early as possible after initiation of infection falls under the general concept that complexity cannot be combated with simplicity. It also follows that sociopolitical action to interrupt virus replication and spread as soon as possible is as important as scientifically sound treatment designs to control viral disease on a global scale.

Removal of the C6 Vaccinia Virus Interferon-β Inhibitor in the Hepatitis C Vaccine Candidate MVA-HCV Elicited in Mice High Immunogenicity in Spite of Reduced Host Gene Expression

Hepatitis C virus (HCV) represents a major global health problem for which a vaccine is not available. Modified vaccinia virus Ankara (MVA)-HCV is a unique HCV vaccine candidate based in the modified vaccinia virus Ankara (MVA) vector expressing the nearly full-length genome of HCV genotype 1a that elicits CD8⁺ T-cell responses in mice. With the aim to improve the immune response of MVA-HCV and because of the importance of interferon (IFN) in HCV infection, we deleted in MVA-HCV the vaccinia virus (VACV) C6L gene, encoding an inhibitor of IFN-β that prevents activation of the interferon regulatory factors 3 and 7 (IRF3 and IRF7). The resulting vaccine candidate (MVA-HCV ΔC6L) expresses all HCV antigens and deletion of C6L had no effect on viral growth in permissive chicken cells. In human monocyte-derived dendritic cells, infection with MVA-HCV ΔC6L triggered severe down-regulation of IFN-β, IFN-β-induced genes, and cytokines in a manner similar to MVA-HCV, as defined by real-time polymerase chain reaction (PCR) and microarray analysis. In infected mice, both vectors had a similar profile of recruited immune cells and induced comparable levels of adaptive and memory HCV-specific CD8⁺ T-cells, mainly against p7 + NS2 and NS3 HCV proteins, with a T cell effector memory (TEM) phenotype. Furthermore, antibodies against E2 were also induced. Overall, our findings showed that while these vectors had a profound inhibitory effect on gene expression of the host, they strongly elicited CD8⁺ T cell and humoral responses against HCV antigens and to the virus vector. These observations add support to the consideration of these vectors as potential vaccine candidates against HCV.

Hypothesis: RNA and DNA Viral Sequence Integration into the Mammalian Host Genome Supports Long-Term B Cell and T Cell Adaptive Immunity

Viral sequence integration into the mammalian genome has long been perceived as a health risk. In some cases, integration translates to chronic viral infection, and in other instances, oncogenic gene mutations occur. However, research also shows that animal cells can benefit from integrated viral sequences (e.g., to support host cell development or to silence foreign invaders). Here we propose that, comparable with the clustered regularly interspaced short palindromic repeats that provide bacteria with adaptive immunity against invasive bacteriophages, animal cells may co-opt integrated viral sequences to support immune memory. We hypothesize that host cells express viral peptides from open reading frames in integrated sequences to boost adaptive B cell and T cell responses long after replicating viruses are cleared. In support of this hypothesis, we examine previous literature describing (1) viruses that infect acutely (e.g., vaccinia viruses and orthomyxoviruses) followed by unexplained, long-term persistence of viral nucleotide sequences, viral peptides, and virus-specific adaptive immunity, (2) the high frequency of endogenous viral genetic elements found in animal genomes, and (3) mechanisms with which animal host machinery supports foreign sequence integration.

HCV epidemiology in high-risk groups and the risk of reinfection

Injecting risk behaviours among people who inject drugs (PWID) and high-risk sexual practices among men who have sex with men (MSM) are important routes of hepatitis C virus (HCV) transmission. Current direct-acting antiviral treatment offers unique opportunities for reductions in HCV-related liver disease burden and epidemic control in high-risk groups, but these prospects could be counteracted by HCV reinfection due to on-going risk behaviours after successful treatment. Based on existing data from small and heterogeneous studies of interferon-based treatment, the incidence of reinfection after sustained virological response range from 2-6/100 person years among PWID to 10-15/100 person years among human immunodeficiency virus-infected MSM. These differences mainly reflect heterogeneity in study populations with regards to risk behaviours, but also reflect variations in study designs and applied virological methods. Increasing levels of reinfection are to be expected as we enter the interferon-free treatment era. Individual- and population-level efforts to address and prevent reinfection should therefore be undertaken when providing HCV care for people with on-going risk behaviour. Constructive strategies include acknowledgement, education and counselling, harm reduction optimization, scaled-up treatment including treatment of injecting networks, post-treatment screening, and rapid retreatment of reinfections.