Antibody Responses to a Quadrivalent Hepatitis C Viral-Like Particle Vaccine Adjuvanted with Toll-Like Receptor 2 Agonists

Is there still hope for the prophylactic hepatitis C vaccine? A review of different approaches

Despite remarkable progress in the treatment of hepatitis C virus (HCV) infection, it remains a significant global health burden, necessitating the development of an effective prophylactic vaccine. This review paper presents the current landscape of HCV vaccine candidates and approaches, including more traditional, based on inactivated virus, and more modern, such as subunit protein, vectored, based on nucleic acids (DNA and mRNA) and virus-like particles. The concept of the HCV vaccine is first put in the context of viral genetic diversity and adaptive responses to HCV infection, an understanding of which is crucial in guiding the development of an effective vaccine against such a complex virus. Because ethical dimensions are also significant in vaccine research, development, and potential deployment, we also address them in this paper. The road to a safe and effective vaccine to prevent HCV infection remains bumpy due to the genetic variation of HCV and its ability to evade immune responses. The progress in cell-culture systems allowed for the production of an inactivated HCV vaccine candidate, which can induce cross-neutralizing antibodies in vitro, but whether this could prevent infection in humans is unknown. Subunit protein vaccine candidates that entered clinical trials elicited HCV-specific humoral and cellular responses, though it remains to be shown whether they translate into effective prevention of HCV infection or progression of infection to a chronic state. Such responses were also induced by a clinically tested vector-based vaccine candidate, which decreased the viral HCV load but did not prevent chronic HCV infection. These disappointments were not readily predicted from preclinical animal studies. The vaccine platforms employing virus-like particles, DNA, and mRNA provide opportunities for the HCV vaccine, but their potential in this context has yet to be shown. Ensuring the designed vaccine is based on conserved epitope(s) and elicits broadly neutralizing immune responses is also essential. Given failures in developing a prophylactic HCV vaccine, it is crucial to continue supporting national strategies, including funding for screening and treatment programs. However, these actions are likely insufficient to permanently control the HCV burden, encouraging further mobilization of significant resources for HCV vaccine research as a missing element in the elimination of viral hepatitis as a global public health.

Development of virus-like particles with inbuilt immunostimulatory properties as vaccine candidates

The development of virus-like particle (VLP) based vaccines for human papillomavirus, hepatitis B and hepatitis E viruses represented a breakthrough in vaccine development. However, for dengue and COVID-19, technical complications, such as an incomplete understanding of the requirements for protective immunity, but also limitations in processes to manufacture VLP vaccines for enveloped viruses to large scale, have hampered VLP vaccine development. Selecting the right adjuvant is also an important consideration to ensure that a VLP vaccine induces protective antibody and T cell responses. For diseases like COVID-19 and dengue fever caused by RNA viruses that exist as families of viral variants with the potential to escape vaccine-induced immunity, the development of more efficacious vaccines is also necessary. Here, we describe the development and characterisation of novel VLP vaccine candidates using SARS-CoV-2 and dengue virus (DENV), containing the major viral structural proteins, as protypes for a novel approach to produce VLP vaccines. The VLPs were characterised by Western immunoblot, enzyme immunoassay, electron and atomic force microscopy, and in vitro and in vivo immunogenicity studies. Microscopy techniques showed proteins self-assemble to form VLPs authentic to native viruses. The inclusion of the glycolipid adjuvant, α-galactosylceramide (α-GalCer) in the vaccine formulation led to high levels of natural killer T (NKT) cell stimulation in vitro, and strong antibody and memory CD8+ T cell responses in vivo, demonstrated with SARS-CoV-2, hepatitis C virus (HCV) and DEN VLPs. This study shows our unique vaccine formulation presents a promising, and much needed, new vaccine platform in the fight against infections caused by enveloped RNA viruses.

Toll-like Receptor Response to Hepatitis C Virus Infection: A Recent Overview

Hepatitis C virus (HCV) infection remains a major global health burden, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that detect pathogen-associated molecular patterns and activate downstream signaling to induce proinflammatory cytokine and chemokine production. An increasing number of studies have suggested the importance of TLR responses in the outcome of HCV infection. However, the exact role of innate immune responses, including TLR response, in controlling chronic HCV infection remains to be established. A proper understanding of the TLR response in HCV infection is essential for devising new therapeutic approaches against HCV infection. In this review, we discuss the progress made in our understanding of the host innate immune response to HCV infection, with a particular focus on the TLR response. In addition, we discuss the mechanisms adopted by HCV to avoid immune surveillance mediated by TLRs.

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

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

Prevention of Hepatitis C Virus Infection and Liver Cancer

Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer and the second leading cause of cancer-related death worldwide.

TLR2 Agonistic Small Molecules: Detailed Structure-Activity Relationship, Applications, and Future Prospects

Toll-like receptors (TLRs) are the pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) in microbial species. Among the various TLRs, TLR2 has a special place due to its ability to sense the widest repertoire of PAMPs owing to its heterodimerization with either TLR1 or TLR6, broadening its ligand diversity against pathogens. Various scaffolds are reported to activate TLR2, which include naturally occurring lipoproteins, synthetic lipopeptides, and small heterocyclic molecules. We described a detailed SAR in TLR2 agonistic scaffolds and also covered the design and chemistry for the conjugation of TLR2 agonists to antigens, carbohydrates, polymers, and fluorophores. The approaches involved in delivery of TLR2 agonists such as lipidation of antigen, conjugation to polymers, phosphonic acids, and other linkers to achieve surface adsorption, liposomal formulation, and encapsulating nanoparticles are elaborated. The crystal structure analysis and computational modeling are also included with the structural features that facilitate TLR2 activation.

High antibody titres induced by protein subunit vaccines using Mycobacterium ulcerans antigens Hsp18 and MUL_3720 with a TLR-2 agonist fail to protect against Buruli ulcer in mice

Background

Mycobacterium ulcerans is the causative agent of a debilitating skin and soft tissue infection known as Buruli ulcer (BU). There is no vaccine against BU. The purpose of this study was to investigate the vaccine potential of two previously described immunogenic M. ulcerans proteins, MUL_3720 and Hsp18, using a mouse tail infection model of BU.

Methods

Recombinant versions of the two proteins were each electrostatically coupled with a previously described lipopeptide adjuvant. Seven C57BL/6 and seven BALB/c mice were vaccinated and boosted with each of the formulations. Vaccinated mice were then challenged with M. ulcerans via subcutaneous tail inoculation. Vaccine performance was assessed by time-to-ulceration compared to unvaccinated mice.

Results

The MUL_3720 and Hsp18 vaccines induced high titres of antigen-specific antibodies that were predominately subtype IgG₁. However, all mice developed ulcers by day-40 post-M. ulcerans challenge. No significant difference was observed in the time-to-onset of ulceration between the experimental vaccine groups and unvaccinated animals.

Conclusions

These data align with previous vaccine experiments using Hsp18 and MUL_3720 that indicated these proteins may not be appropriate vaccine antigens. This work highlights the need to explore alternative vaccine targets and different approaches to understand the role antibodies might play in controlling BU.

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.

Pre-clinical evaluation of a quadrivalent HCV VLP vaccine in pigs following microneedle delivery

The introduction of directly acting antiviral agents (DAAs) has produced significant improvements in the ability to cure chronic hepatitis C infection. However, with over 2% of the world’s population infected with HCV, complications arising from the development of cirrhosis of the liver, chronic hepatitis C infection remains the leading indication for liver transplantation. Several modelling studies have indicated that DAAs alone will not be sufficient to eliminate HCV, but if combined with an effective vaccine this regimen would provide a significant advance towards achieving this critical World Health Organisation goal. We have previously generated a genotype 1a, 1b, 2a, 3a HCV virus like particle (VLP) quadrivalent vaccine. The HCV VLPs contain the core and envelope proteins (E1 and E2) of HCV and the vaccine has been shown to produce broad humoral and T cell immune responses following vaccination of mice. In this report we further advanced this work by investigating vaccine responses in a large animal model. We demonstrate that intradermal microneedle vaccination of pigs with our quadrivalent HCV VLP based vaccine produces long-lived multi-genotype specific and neutralizing antibody (NAb) responses together with strong T cell and granzyme B responses and normal Th1 and Th2 cytokine responses. These responses were achieved without the addition of adjuvant. Our study demonstrates that our vaccine is able to produce broad immune responses in a large animal that, next to primates, is the closest animal model to humans. Our results are important as they show that the vaccine can produce robust immune responses in a large animal model before progressing the vaccine to human trials.