Induction of humoural and cellular immunity by immunisation with HCV particle vaccine in a non-human primate model

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.

Update on Hepatitis C Vaccine: Results and Challenges

Therapy against the Hepatitis C virus (HCV) has significantly improved with the introduction of direct-acting antiviral drugs (DAAs), achieving over 95% sustained virological response (SVR). Despite this, the development of an effective anti-HCV vaccine remains a critical challenge due to the low number of patients treated with DAAs and the occurrence of HCV reinfections in high-risk groups. Current vaccine strategies aim to stimulate either B-cell or T-cell responses. Vaccines based on E1 and E2 proteins can elicit broad cross-neutralizing antibodies against all major HCV genotypes, though with varying efficiencies and without full protection against infection. In humans, the neutralizing antibodies induced by such vaccines mainly target the AR3 region, but their levels are generally insufficient for broad neutralization. Various HCV proteins expressed through different viral vectors have been utilized to elicit T cell immune responses, showing sustained expansion of HCV-specific effector memory T cells and improved proliferation and polyfunctionality of memory T cells over time. However, despite these advancements, the frequency and effectiveness of T-cell responses remain limited.

Current Hepatitis C Vaccine Candidates Based on the Induction of Neutralizing Antibodies

The introduction of direct-acting antivirals (DAAs) has revolutionized hepatitis C treatment. Short courses of treatment with these drugs are highly beneficial to patients, eliminating hepatitis C virus (HCV) without adverse effects. However, this outstanding success is tempered by the continuing difficulty of eradicating the virus worldwide. Thus, access to an effective vaccine against HCV is strongly needed to reduce the burden of the disease and contribute to the elimination of viral hepatitis. The recent failure of a T-cell vaccine based on the use of viral vectors expressing the HCV non-structural protein sequences to prevent chronic hepatitis C in drug users has pointed out that the induction of neutralizing antibodies (NAbs) will be essential in future vaccine candidates. To induce NAbs, vaccines must contain the main target of this type of antibody, the HCV envelope glycoproteins (E1 and E2). In this review, we summarize the structural regions in E1 and E2 proteins that are targeted by NAbs and how these proteins are presented in the vaccine candidates currently under development.

Inactivated genotype 1a, 2a and 3a HCV vaccine candidates induced broadly neutralising antibodies in mice

OBJECTIVE

A prophylactic vaccine is needed to control the HCV epidemic, with genotypes 1-3 causing >80% of worldwide infections. Vaccine development is hampered by HCV heterogeneity, viral escape including protection of conserved neutralising epitopes and suboptimal efficacy of HCV cell culture systems. We developed cell culture-based inactivated genotype 1-3 HCV vaccine candidates to present natively folded envelope proteins to elicit neutralising antibodies.

DESIGN

High-yield genotype 1a, 2a and 3a HCV were developed by serial passage of TNcc, J6cc and DBN3acc in Huh7.5 cells and engineering of acquired mutations detected by next-generation sequencing. Neutralising epitope exposure was determined in cell-based neutralisation assays using human monoclonal antibodies AR3A and AR4A, and polyclonal antibody C211. BALB/c mice were immunised with processed and inactivated genotype 1a, 2a or 3a viruses using AddaVax, a homologue of the licenced adjuvant MF-59. Purified mouse and patient serum IgG were assayed for neutralisation capacity; mouse IgG and immune-sera were assayed for E1/E2 binding.

RESULTS

Compared with the original viruses, high-yield viruses had up to ~1000 fold increased infectivity titres (peak titres: 6-7 log10 focus-forming units (FFU)/mL) and up to ~2470 fold increased exposure of conserved neutralising epitopes. Vaccine-induced IgG broadly neutralised genotype 1-6 HCV (EC50: 30-193 µg/mL; mean 71 µg/mL), compared favourably with IgG from chronically infected patients, and bound genotype 1-3 E1/E2; immune-sera endpoint titres reached up to 32 000.

CONCLUSION

High-yield genotype 1-3 HCV could be developed as basis for inactivated vaccine candidates inducing broadly neutralising antibodies in mice supporting further preclinical development.

Patient-derived monoclonal antibody neutralizes HCV infection in vitro and vivo without generating escape mutants

In recent years, new direct-acting antivirals for hepatitis C virus (HCV) have been approved, but hepatitis C continues to pose a threat to human health. It is important to develop neutralizing anti-HCV antibodies to prevent medical and accidental infection, such as might occur via liver transplantation of chronic HCV patients and needle-stick accidents in the clinic. In this study, we sought to obtain anti-HCV antibodies using phage display screening. Phages displaying human hepatocellular carcinoma patient-derived antibodies were screened by 4 rounds of biopanning with genotype-1b and -2a HCV envelope E2 protein adsorbed to magnetic beads. The three antibodies obtained from this screen had reactivity against E2 proteins derived from both genotype-1b and -2a strains. However, in epitope analysis, these antibodies did not recognize linear peptides from an overlapping E2 epitope peptide library, and did not bind to denatured E2 protein. In addition, these antibodies showed cross-genotypic neutralizing activity against genotype-1a, -1b, -2a, and -3a cell culture-generated infectious HCV particles (HCVcc). Moreover, emergence of viral escape mutants was not observed after repeated rounds of passaging of HCV-infected cells in the presence of one such antibody, e2d066. Furthermore, injection of the e2d066 antibody into human hepatocyte-transplanted immunodeficient mice inhibited infection by J6/JFH-1 HCVcc. In conclusion, we identified conformational epitope-recognizing, cross-genotypic neutralizing antibodies using phage display screening. Notably, e2d066 antibody did not select for escape mutant emergence in vitro and demonstrated neutralizing activity in vivo. Our results suggested that these antibodies may serve as prophylactic and therapeutic agents.

Neutralization of hepatitis B virus with vaccine-escape mutations by hepatitis B vaccine with large-HBs antigen

Although the current hepatitis B (HB) vaccine comprising small-HBs antigen (Ag) is potent and safe, attenuated prophylaxis against hepatitis B virus (HBV) with vaccine-escape mutations (VEMs) has been reported. We investigate an HB vaccine consisting of large-HBsAg that overcomes the shortcomings of the current HB vaccine. Yeast-derived large-HBsAg is immunized into rhesus macaques, and the neutralizing activities of the induced antibodies are compared with those of the current HB vaccine. Although the antibodies induced by the current HB vaccine cannot prevent HBV infection with VEMs, the large-HBsAg vaccine-induced antibodies neutralize those infections. The HBV genotypes that exhibited attenuated neutralization via these vaccines are different. Here, we show that the HB vaccine consisting of large-HBsAg is useful to compensate for the shortcomings of the current HB vaccine. The combined use of these HB vaccines may induce antibodies that can neutralize HBV strains with VEMs or multiple HBV genotypes.

Lipid nanoparticle-based mRNA vaccines in cancers: Current advances and future prospects

Messenger RNA (mRNA) vaccines constitute an emerging therapeutic method with the advantages of high safety and efficiency as well as easy synthesis; thus, they have been widely used in various human diseases, especially in malignant cancers. However, the mRNA vaccine technology has some limitations, such as instability and low transitive efficiency in vivo, which greatly restrict its application. The development of nanotechnology in the biomedical field offers new strategies and prospects for the early diagnosis and treatment of human cancers. Recent studies have demonstrated that Lipid nanoparticle (LNP)-based mRNA vaccines can address the poor preservation and targeted inaccuracy of mRNA vaccines. As an emerging cancer therapy, mRNA vaccines potentially have broad future applications. Unlike other treatments, cancer mRNA vaccines provide specific, safe, and tolerable treatments. Preclinical studies have used personalized vaccines to demonstrate the anti-tumor effect of mRNA vaccines in the treatment of various solid tumors, including colorectal and lung cancer, using these in a new era of therapeutic cancer vaccines. In this review, we have summarized the latest applications and progress of LNP-based mRNA vaccines in cancers, and discussed the prospects and limitations of these fields, thereby providing novel strategies for the targeted therapy of cancers.

Implementation of a controlled human infection model for evaluation of HCV vaccine candidates

Hepatitis C virus (HCV) remains a major global health concern. Directly acting antiviral (DAA) drugs have transformed the treatment of HCV. However, it has become clear that, without an effective HCV vaccine, it will not be possible to meet the World Health Organization targets of HCV viral elimination. Promising new vaccine technologies that generate high magnitude antiviral T and B cell immune responses and significant new funding have recently become available, stimulating the HCV vaccine pipeline. In the absence of an immune competent animal model for HCV, the major block in evaluating new HCV vaccine candidates will be the assessment of vaccine efficacy in humans. The development of a controlled human infection model (CHIM) for HCV could overcome this block, enabling the head-to-head assessment of vaccine candidates. The availability of highly effective DAA means that a CHIM for HCV is possible for the first time. In this review, we highlight the challenges and issues with currently available strategies to assess HCV vaccine efficacy including HCV "at-risk" cohorts and animal models. We describe the development of CHIM in other infections that are increasingly utilized by trialists and explore the ethical and safety concerns specific for an HCV CHIM. Finally, we propose an HCV CHIM study design including the selection of volunteers, the development of an infectious inoculum, the evaluation of host immune and viral parameters, and the definition of study end points for use in an HCV CHIM. Importantly, the study design (including number of volunteers required, cost, duration of study, and risk to volunteers) varies significantly depending on the proposed mechanism of action (sterilizing/rapid viral clearance vs. delayed viral clearance) of the vaccine under evaluation. We conclude that an HCV CHIM is now realistic, that safety and ethical concerns can be addressed with the right study design, and that, without an HCV CHIM, it is difficult to envisage how the development of an HCV vaccine will be possible.

Inactivated whole hepatitis C virus vaccine employing a licensed adjuvant elicits cross-genotype neutralizing antibodies in mice

BACKGROUND & AIMS

A prophylactic vaccine is required to eliminate HCV as a global public health threat. We developed whole virus inactivated HCV vaccine candidates employing a licensed adjuvant. Further, we investigated the effects of HCV envelope protein modifications (to increase neutralization epitope exposure) on immunogenicity.

METHODS

Whole virus vaccine antigen was produced in Huh7.5 hepatoma cells, processed using a multistep protocol and formulated with adjuvant (MF-59 analogue AddaVax or aluminium hydroxide). We investigated the capacity of IgG purified from the serum of immunized BALB/c mice to neutralize genotype 1-6 HCV (by virus neutralization assays) and to bind homologous envelope proteins (by ELISA). Viruses used for immunizations were (i) HCV5aHi with strain SA13 envelope proteins and modification of an O-linked glycosylation site in E2 (T385P), (ii) HCV5aHi(T385) with reversion of T385P to T385, featuring the original E2 sequence determined in vivo and (iii) HCV5aHi(ΔHVR1) with deletion of HVR1. For these viruses, epitope exposure was investigated using human monoclonal (AR3A and AR4A) and polyclonal (C211 and H06) antibodies in neutralization assays.

RESULTS

Processed HCV5aHi formulated with AddaVax induced antibodies that efficiently bound homologous envelope proteins and broadly neutralized cultured genotype 1-6 HCV, with half maximal inhibitory concentrations of between 14 and 192 μg/ml (mean of 36 μg/ml against the homologous virus). Vaccination with aluminium hydroxide was less immunogenic. Compared to HCV5aHi(T385) with the original E2 sequence, HCV5aHi with a modified glycosylation site and HCV5aHi(ΔHVR1) without HVR1 showed increased neutralization epitope exposure but similar immunogenicity.

CONCLUSION

Using an adjuvant suitable for human use, we developed inactivated whole HCV vaccine candidates that induced broadly neutralizing antibodies, which warrant investigation in further pre-clinical studies.

LAY SUMMARY

A vaccine against hepatitis C virus (HCV) is needed to prevent the estimated 2 million new infections and 400,000 deaths caused by this virus each year. We developed inactivated whole HCV vaccine candidates using adjuvants licensed for human use, which, following immunization of mice, induced antibodies that efficiently neutralized all HCV genotypes with recognized epidemiological importance. HCV variants with modified envelope proteins exhibited similar immunogenicity as the virus with the original envelope proteins.

Prevalence and assessment of the associated risk factors of hepatitis B and C infections in the low socioeconomic communities

Aim: This study determined the prevalence and risk factors associated with hepatitis B and C among the low socioeconomic population. Materials & methods: A total of 1004 participants were screened for hepatitis B/C infection and risk factors from six different localities of Islamabad, Pakistan Results: The prevalence rate of hepatitis B and C was 1 and 4%, respectively. Chi-square test showed hepatitis B/C infection was related with marital status, hepatitis B vaccination, blood recipients and family income. Multivariable analysis showed hepatitis B vaccination, exposure to therapeutic injections, dental visits, exposure to HCV patients and age of participants were independently associated with hepatitis C infection. Conclusion: The risk of hepatitis B/C infection is multifactorial and the population needs to be vaccinated at a larger scale to avoid outbreaks.

In situ vaccination using unique TLR9 ligand K3-SPG induces long-lasting systemic immune response and synergizes with systemic and local immunotherapy

Although checkpoint inhibitors (CPIs) have changed the paradigm of cancer therapy, low response rates and serious systemic adverse events remain challenging. In situ vaccine (ISV), intratumoral injection of immunomodulators that stimulate innate immunity at the tumor site, allows for the development of vaccines in patients themselves. K3-SPG, a second-generation nanoparticulate Toll-like receptor 9 (TLR9) ligand consisting of K-type CpG oligodeoxynucleotide (ODN) wrapped with SPG (schizophyllan), integrates the best of conventional CpG ODNs, making it an ideal cancer immunotherapy adjuvant. Focusing on clinical feasibility for pancreaticobiliary and gastrointestinal cancers, we investigated the antitumor activity of K3-SPG-ISV in preclinical models of pancreatic ductal adenocarcinoma (PDAC) and colorectal cancer (CRC). K3-SPG-ISV suppressed tumor growth more potently than K3-ISV or K3-SPG intravenous injections, prolonged survival, and enhanced the antitumor effect of CPIs. Notably, in PDAC model, K3-SPG-ISV alone induced systemic antitumor effect and immunological memory. ISV combination of K3-SPG and agonistic CD40 antibody further enhanced the antitumor effect. Our results imply that K3-SPG-based ISV can be applied as monotherapy or combined with CPIs to improve their response rate or, conversely, with CPI-free local immunotherapy to avoid CPI-related adverse events. In either strategy, the potency of K3-SPG-based ISV would provide the rationale for its clinical application to puncturable pancreaticobiliary and gastrointestinal malignancies.

High-Titer Hepatitis C Virus Production in a Scalable Single-Use High Cell Density Bioreactor

Hepatitis C virus (HCV) infections pose a major public health burden due to high chronicity rates and associated morbidity and mortality. A vaccine protecting against chronic infection is not available but would be important for global control of HCV infections. In this study, cell culture-based HCV production was established in a packed-bed bioreactor (CelCradle™) aiming to further the development of an inactivated whole virus vaccine and to facilitate virological and immunological studies requiring large quantities of virus particles. HCV was produced in human hepatoma-derived Huh7.5 cells maintained in serum-free medium on days of virus harvesting. Highest virus yields were obtained when the culture was maintained with two medium exchanges per day. However, increasing the total number of cells in the culture vessel negatively impacted infectivity titers. Peak infectivity titers of up to 7.2 log10 focus forming units (FFU)/mL, accumulated virus yields of up to 5.9 × 1010 FFU, and a cell specific virus yield of up to 41 FFU/cell were obtained from one CelCradle™. CelCradle™-derived and T flask-derived virus had similar characteristics regarding neutralization sensitivity and buoyant density. This packed-bed tide-motion system is available with larger vessels and may thus be a promising platform for large-scale HCV production.

[Development approaches for vaccines against hepatitis C virus infections]

Mehr als 10 Jahre nach der Zulassung der ersten direkt wirkenden antiviralen Wirkstoffe zur Behandlung der Hepatitis C bleibt die Inzidenz der Hepatitis-C-Virus-(HCV-)Infektion ungebrochen hoch. In manchen Ländern stecken sich mehr Menschen neu mit dem Virus an, als Patienten durch eine erfolgreiche Therapie geheilt werden. Die Entwicklung eines prophylaktischen Impfstoffes könnte die Transmission des Virus unterbinden und dadurch einen wesentlichen Beitrag zur Kontrolle dieser weltweit verbreiteten Infektion leisten. In diesem Artikel werden die besonderen Herausforderungen und die aktuellen Ansätze der HCV-Impfstoffentwicklung dargestellt.

HCV ist ein hochgradig diverses und wandlungsfähiges Virus, das zumeist dem Immunsystem entkommt und chronische Infektionen etabliert. Andererseits heilt die HCV-Infektion bei bis zu einem Drittel der exponierten Individuen aus, sodass eine schützende Immunität erreichbar ist. Zahlreiche Untersuchungen zu den Determinanten einer schützenden Immunität gegen HCV zeichnen ein immer kompletteres Bild davon, welche Ziele ein Impfstoff erreichen muss. Sehr wahrscheinlich werden sowohl starke neutralisierende Antikörper als auch wirkungsvolle zytotoxische T‑Zellen gebraucht, um sicher vor einer chronischen Infektion zu schützen. Die Schlüsselfrage ist, welche Ansätze besonders breit wirksame Antikörper und T‑Zellen heranreifen lassen. Dies wird erforderlich sein, um vor der großen Fülle unterschiedlicher HCV-Varianten zu schützen. Die jüngsten Erfolge von mRNA-Impfstoffen öffnen neue Türen auch für die HCV-Impfstoffforschung. Kombiniert mit einem tieferen Verständnis der Struktur und Funktion der viralen Hüllproteine, der Identifizierung kreuzprotektiver Antikörper- und T‑Zellepitope sowie der Nutzung standardisierter Verfahren zur Quantifizierung der Wirksamkeit von Impfkandidaten ergeben sich neue Perspektiven für die Entwicklung eines Impfstoffes.

In the era of rapid mRNA-based vaccines: Why is there no effective hepatitis C virus vaccine yet?

Hepatitis C virus (HCV) is responsible for no less than 71 million people chronically infected and is one of the most frequent indications for liver transplantation worldwide. Despite direct-acting antiviral therapies fuel optimism in controlling HCV infections, there are several obstacles regarding treatment accessibility and reinfection continues to remain a possibility. Indeed, the majority of new HCV infections in developed countries occur in people who inject drugs and are more plausible to get reinfected. To achieve global epidemic control of this virus the development of an effective prophylactic or therapeutic vaccine becomes a must. The coronavirus disease 19 (COVID-19) pandemic led to auspicious vaccine development against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus, which has renewed interest on fighting HCV epidemic with vaccination. The aim of this review is to highlight the current situation of HCV vaccine candidates designed to prevent and/or to reduce HCV infectious cases and their complications. We will emphasize on some of the crossroads encountered during vaccine development against this insidious virus, together with some key aspects of HCV immunology which have, so far, hampered the progress in this area. The main focus will be on nucleic acid-based as well as recombinant viral vector-based vaccine candidates as the most novel vaccine approaches, some of which have been recently and successfully employed for SARS-CoV-2 vaccines. Finally, some ideas will be presented on which methods to explore for the design of live-attenuated vaccines against HCV.

Antigenic and immunogenic evaluation of permutations of soluble hepatitis C virus envelope protein E2 and E1 antigens

Yearly, about 1.5 million people become chronically infected with hepatitis C virus (HCV) and for the 71 million with chronic HCV infection about 400,000 die from related morbidities, including liver cirrhosis and cancer. Effective treatments exist, but challenges including cost-of-treatment and wide-spread undiagnosed infection, necessitates the development of vaccines. Vaccines should induce neutralizing antibodies (NAbs) against the HCV envelope (E) transmembrane glycoprotein 2, E2, which partly depends on its interaction partner, E1, for folding. Here, we generated three soluble HCV envelope protein antigens with the transmembrane regions deleted (i.e., fused peptide backbones), termed sE1E2 (E1 followed by E2), sE2E1 (E2 followed by E1), and sE21E (E2 followed by inverted E1). The E1 inversion for sE21E positions C-terminal residues of E1 near C-terminal residues of E2, which is in analogy to how they likely interact in native E1/E2 complexes. Probing conformational E2 epitope binding using HCV patient-derived human monoclonal antibodies, we show that sE21E was superior to sE2E1, which was consistently superior to sE1E2. This correlated with improved induction of NAbs by sE21E compared with sE2E1 and especially compared with sE1E2 in female BALB/c mouse immunizations. The deletion of the 27 N-terminal amino acids of E2, termed hypervariable region 1 (HVR1), conferred slight increases in antigenicity for sE2E1 and sE21E, but severely impaired induction of antibodies able to neutralize in vitro viruses retaining HVR1. Finally, comparing sE21E with sE2 in mouse immunizations, we show similar induction of heterologous NAbs. In summary, we find that C-terminal E2 fusion of E1 or 1E is superior to N-terminal fusion, both in terms of antigenicity and the induction of heterologous NAbs. This has relevance when designing HCV E1E2 vaccine antigens.

Difluoromethylornithine (DFMO), an Inhibitor of Polyamine Biosynthesis, and Antioxidant N-Acetylcysteine Potentiate Immune Response in Mice to the Recombinant Hepatitis C Virus NS5B Protein

Hepatitis C virus (HCV) is one of the main triggers of chronic liver disease. Despite tremendous progress in the HCV field, there is still no vaccine against this virus. Potential vaccines can be based on its recombinant proteins. To increase the humoral and, especially, cellular immune response to them, more effective adjuvants are needed. Here, we evaluated a panel of compounds as potential adjuvants using the HCV NS5B protein as an immunogen. These compounds included inhibitors of polyamine biosynthesis and urea cycle, the mTOR pathway, antioxidants, and cellular receptors. A pronounced stimulation of cell proliferation and interferon-γ (IFN-γ) secretion in response to concanavalin A was shown for antioxidant N-acetylcysteine (NAC), polyamine biosynthesis inhibitor 2-difluoromethylornithine (DFMO), and TLR9 agonist CpG ODN 1826 (CpG). Their usage during the immunization of mice with the recombinant NS5B protein significantly increased antibody titers, enhanced lymphocyte proliferation and IFN-γ production. NAC and CpG decreased relative Treg numbers; CpG increased the number of myeloid-derived suppressor cells (MDSCs), whereas neither NAC nor DFMO affected MDSC counts. NAC and DFMO suppressed NO and interleukin 10 (IL-10) production by splenocytes, while DFMO increased the levels of IL-12. This is the first evidence of immunomodulatory activity of NAC and DFMO during prophylactic immunization against infectious diseases.

Immunopotentiating and Delivery Systems for HCV Vaccines

Development of preventive vaccines against hepatitis C virus (HCV) remains one of the main strategies in achieving global elimination of the disease. The effort is focused on the quest for vaccines capable of inducing protective cross-neutralizing humoral and cellular immune responses, which in turn dictate the need for rationally designed cross-genotype vaccine antigens and potent immunoadjuvants systems. This review provides an assessment of the current state of knowledge on immunopotentiating compounds and vaccine delivery systems capable of enhancing HCV antigen-specific immune responses, while focusing on the synergy and interplay of two modalities. Structural, physico-chemical, and biophysical features of these systems are discussed in conjunction with the analysis of their in vivo performance. Extreme genetic diversity of HCV-a well-known hurdle in the development of an HCV vaccine, may also present a challenge in a search for an effective immunoadjuvant, as the effort necessitates systematic and comparative screening of rationally designed antigenic constructs. The progress may be accelerated if the preference is given to well-defined molecular immunoadjuvants with greater formulation flexibility and adaptability, including those capable of spontaneous self-assembly behavior, while maintaining their robust immunopotentiating and delivery capabilities.

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.

mRNA vaccine: a potential therapeutic strategy

mRNA vaccines have tremendous potential to fight against cancer and viral diseases due to superiorities in safety, efficacy and industrial production. In recent decades, we have witnessed the development of different kinds of mRNAs by sequence optimization to overcome the disadvantage of excessive mRNA immunogenicity, instability and inefficiency. Based on the immunological study, mRNA vaccines are coupled with immunologic adjuvant and various delivery strategies. Except for sequence optimization, the assistance of mRNA-delivering strategies is another method to stabilize mRNAs and improve their efficacy. The understanding of increasing the antigen reactiveness gains insight into mRNA-induced innate immunity and adaptive immunity without antibody-dependent enhancement activity. Therefore, to address the problem, scientists further exploited carrier-based mRNA vaccines (lipid-based delivery, polymer-based delivery, peptide-based delivery, virus-like replicon particle and cationic nanoemulsion), naked mRNA vaccines and dendritic cells-based mRNA vaccines. The article will discuss the molecular biology of mRNA vaccines and underlying anti-virus and anti-tumor mechanisms, with an introduction of their immunological phenomena, delivery strategies, their importance on Corona Virus Disease 2019 (COVID-19) and related clinical trials against cancer and viral diseases. Finally, we will discuss the challenge of mRNA vaccines against bacterial and parasitic diseases.

Stenotrophomonas-maltophilia inhibits host cellular immunity by activating PD-1/PD-L1 signaling pathway to induce T-cell exhaustion

BACKGROUND

Smalotrophomonas maltophilia(S. maltophilia) is common in nosocomial infections. However, few studies have revealed the effect of S. maltophilia on cellular immunity in the host's immune system up to now. In clinical work, we accidentally discovered that S. maltophilia directly stimulated T cells to secrete IFN-γ.

MATERIALS AND METHODS

S. maltophilia was co-cultured with PBMCs to detect secretion of cytokines (IFN-γ, TNF-α and IL-2) and expression of cell surface molecules (CD3, CD4, CD8, CD69, CD147 and CD152) of T cells. We used light microscopy and electron microscopy to observe the cell morphology and subcellular structure of S. maltophilia co-cultured with lymphocytes. Flow cytometry and Western Blot were used to detect the expression of PD-1/PD-L1 and annexin V in cells.

RESULTS

T cells stimulated by S. maltophilia secreted a large amount of IL-2, IFN-γ, and TNF-α. The expression of CD4 and CD8 on the cell surface were declined, accompanied by the activation of the PD-1/PD-L1 pathway, which eventually led to the massive apoptosis of T cells. Electron microscopy showed that cells showed significant apoptotic morphology. Blocking the PD-1/PD-L1 pathway can inhibit the apoptosis-inducing effect of S. maltophilia on T cells.

CONCLUSIONS

These indicates that T cells are inhibited after being stimulated by S. maltophilia, and then accelerated to induce death without the initiation of an immunologic cascade. This paper demonstrates for the first time the inhibitory effect of S. maltophilia on cellular immunity, and the immunosuppressive effect induced by infection of S. maltophilia should be considered.

Development of a downstream process for the production of an inactivated whole hepatitis C virus vaccine

There is a large unmet need for a prophylactic hepatitis C virus (HCV) vaccine to control the ongoing epidemic with this deadly pathogen. Many antiviral vaccines employ whole viruses as antigens. For HCV, this approach became feasible following the development of infectious cell culture systems for virus production. However, the lack of efficient downstream processes (DSP) for HCV purification poses a roadblock for the development of a whole virus vaccine. Using cell culture-derived genotype 1a HCV we developed a scalable and efficient DSP train, employing commonly used clarification and ultrafiltration techniques, followed by two membrane-based chromatography steps. For virus capture, steric exclusion chromatography using cellulose membranes was established, resulting in a virtually complete virus recovery with > 99% protein and 84% DNA depletion. Virus polishing was achieved by sulphated cellulose membrane adsorbers with ~ 50% virus recovery and > 99% protein and 90% DNA depletion. Additional nuclease digestion resulted in 99% overall DNA depletion with final DNA concentrations of 2 ng/mL. Process results were comparable for cell culture-derived HCV of another major genotype (5a). This study provides proof-of-concept for establishment of an efficient and economically attractive DSP with potential application for production of an inactivated whole virus vaccine against HCV for human use.

Pharmacodynamic and safety considerations for influenza vaccine and adjuvant design

INTRODUCTION

A novel adjuvant evaluation system for safety and immunogenicity is needed. Vaccination is important for infection prevention, for example, from influenza viruses. Adjuvants are considered critical for improving the effectiveness of influenza vaccines. Adjuvant development is an important issue in influenza vaccine design.

AREAS COVERED

A conventional in vivo evaluation method for vaccine safety has been limited in analyzing phenotypic and pathological changes. Therefore, it is difficult to obtain information on the changes at the molecular level. This review aims to explain the recently developed genomics analysis-based vaccine adjuvant safety evaluation tools verified by AddaVax^TM and polyinosinic-polycytidylic acid (poly I:C) using 18 biomarker genes and whole-virion inactivated influenza vaccine as a toxicity control. Genomics analyzes would help provide safety and efficacy information regarding influenza vaccine design by facilitating appropriate adjuvant selection.

EXPERT OPINION

The efficacy and safety profiles of influenza vaccines and adjuvants using genomics technologies provide useful information regarding immunogenicity, which is related to safety and efficacy. This approach provides important information to select appropriate inoculation routes, combinations of vaccine antigens and adjuvants, and dosing amounts. The efficacy of vaccine adjuvant evaluation by genomics analysis should be verified by various studies using various vaccines in the future.

Dietary schizophyllan reduces mitochondrial damage by activating SIRT3 in mice

Schizophyllan (SPG), produced by Schizophyllum commune, is an exopolysaccharide with multiple academic and commercial uses, including in the food industry and for various medical functions. We previously demonstrated that SPG conjugated with c-Src peptide exerted a significant therapeutic effect on mouse models of the acute inflammatory diseases polymicrobial sepsis and ulcerative colitis. Here we extended these results by investigating whether SPG exerted a protective effect against mitochondrial damage in the liver via sirtuin 3 (SIRT3) induction, focusing on the deacetylation of succinate dehydrogenase A (SDHA) and superoxide dismutase 2 (SOD2). Liver damage models induced by alcohol or conjugated linoleic acid (CLA, which simulates lipodystrophy) in SIRT3^-/-, SOD2^-/-, and SDHA^-/- mice were used. Results showed that dietary supplementation with SPG induced SIRT3 activation; this was involved in mitochondrial metabolic resuscitation that countered the adverse effects of alcoholic liver disease and CLA-induced damage. The mitochondrial SIRT3 mediated the deacetylation and activation of SOD2 in the liver and SDHA in adipose tissues, suggesting that SPG supplementation reduced ethanol-induced liver damage and CLA-induced adverse dietary effects via SIRT3-SOD2 and SIRT3-SDHA signaling, respectively. Together, these results suggest that dietary SPG has a previously unrecognized role in SIRT3-mediated mitochondrial metabolic resuscitation during mitochondria-related diseases.

A non-pathogenic Leishmania tarentolae vector based- HCV polytope DNA vaccine elicits potent and long lasting Th1 and CTL responses in BALB/c mice model

Despite successful anti-viral (DAAs) treatment of Hepatitis C virus (HCV) infection, recent data indicated the need for an effective vaccine. Preexisting anti-vector immunity is an obstacle for application of live vectors for antigen delivery and development of effective T-cell based HCV vaccines. Herein, we report construction of recombinant Leishmania tarentolae, a lizard (non-human) parasite, expressing an HCV polytope DNA, PT-NT(gp96), encoding for several immunogenic HCV epitopes and evaluation of its immunogenicity in three different prime/boost immunization groups (G) of BALB/c mice. Homologous prime/boost immunization by L.tarentolae-PT-NT(gp96) either with or without CpG (G1 and G2 respectively) and heterologous immunization with a PT-NT(gp96) encoding-pCDNA plasmid followed by L.tarentolae-PT-NT (G3) was undertaken. Immune responses were measured three and nine weeks (W) post immunization. Splenocytes (cultured with antigen-stimulant) of mice in G1 showed the highest percentage of specific CTL-cytolytic activity compared to G2 and G3 at both short (W3:70.98% versus 41.29% and 13.12%) and long (W9: 50% versus 24.5% and 20%) term periods, accompanied with high levels of secreted IFN-γ. Comparison of IFN-γ, IL-4, IL-17 and TNF-α cytokines levels obtained from the supernatant of antigen-stimulated splenocytes as well as antibodies level (as IgG1/IgG2a ratio; obtained from sera of immunized mice) indicated higher Th1 oriented responses for G1, G2 groups and balanced Th1-Th17 for G3. Results indicated the potential of L.tarentolae (+CpG), as a non-pathogenic live vaccine vector, for delivery and enhancement of immune responses against HCV-polytope antigens.

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.

High density Huh7.5 cell hollow fiber bioreactor culture for high-yield production of hepatitis C virus and studies of antivirals

Chronic hepatitis C virus (HCV) infection poses a serious global public health burden. Despite the recent development of effective treatments there is a large unmet need for a prophylactic vaccine. Further, antiviral resistance might compromise treatment efficiency in the future. HCV cell culture systems are typically based on Huh7 and derived hepatoma cell lines cultured in monolayers. However, efficient high cell density culture systems for high-yield HCV production and studies of antivirals are lacking. We established a system based on Huh7.5 cells cultured in a hollow fiber bioreactor in the presence or absence of bovine serum. Using an adapted chimeric genotype 5a virus, we achieved peak HCV infectivity and RNA titers of 7.6 log₁₀ FFU/mL and 10.4 log₁₀ IU/mL, respectively. Bioreactor derived HCV showed high genetic stability, as well as buoyant density, sensitivity to neutralizing antibodies AR3A and AR4A, and dependency on HCV co-receptors CD81 and SR-BI comparable to that of HCV produced in monolayer cell cultures. Using the bioreactor platform, treatment with the NS5A inhibitor daclatasvir resulted in HCV escape mediated by the NS5A resistance substitution Y93H. In conclusion, we established an efficient high cell density HCV culture system with implications for studies of antivirals and vaccine development.

Current status and future development of infectious cell-culture models for the major genotypes of hepatitis C virus: Essential tools in testing of antivirals and emerging vaccine strategies

In this review, we summarize the relevant scientific advances that led to the development of infectious cell culture systems for hepatitis C virus (HCV) with the corresponding challenges and successes. We also provide an overview of how these systems have contributed to the study of antiviral compounds and their relevance for the development of a much-needed vaccine against this major human pathogen. An efficient infectious system to study HCV in vitro, using human hepatoma derived cells, has only been available since 2005, and was limited to a single isolate, named JFH1, until 2012. Successive developments have been slow and cumbersome, as each available system has been the result of a systematic effort for discovering adaptive mutations conferring culture replication and propagation to patient consensus clones that are inherently non-viable in vitro. High genetic heterogeneity is a paramount characteristic of this virus, and as such, it should preferably be reflected in basic, translational, and clinical studies. The limited number of efficient viral culture systems, in the context of the vast genetic diversity of HCV, continues to represent a major hindrance for the study of this virus, posing a significant barrier towards studies of antivirals (particularly of resistance) and for advancing vaccine development. Intensive research efforts, driven by isolate-specific culture adaptation, have only led to efficient full-length infectious culture systems for a few strains of HCV genotypes 1, 2, 3, and 6. Hence research aimed at identifying novel strategies that will permit universal culture of HCV will be needed to further our understanding of this unique virus causing 400 thousand deaths annually.