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

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.

Exploring T-Cell Immunity to Hepatitis C Virus: Insights from Different Vaccine and Antigen Presentation Strategies

The hepatitis C virus (HCV) is responsible for approximately 50 million infections worldwide. Effective drug treatments while available face access barriers, and vaccine development is hampered by viral hypervariability and immune evasion mechanisms. The CD4+ and CD8+ T-cell responses targeting HCV non-structural (NS) proteins have shown a role in the viral clearance. In this paper, we reviewed the studies exploring the relationship between HCV structural and NS proteins and their effects in contributing to the elicitation of an effective T-cell immune response. The use of different vaccine platforms, such as viral vectors and virus-like particles, underscores their versability and efficacy for vaccine development. Diverse HCV antigens demonstrated immunogenicity, eliciting a robust immune response, positioning them as promising vaccine candidates for protein/peptide-, DNA-, or RNA-based vaccines. Moreover, adjuvant selection plays a pivotal role in modulating the immune response. This review emphasizes the importance of HCV proteins and vaccination strategies in vaccine development. In particular, the NS proteins are the main focus, given their pivotal role in T-cell-mediated immunity and their sequence conservation, making them valuable vaccine targets.

Vaccinia Virus: From Crude Smallpox Vaccines to Elaborate Viral Vector Vaccine Design

Various vaccinia virus (VACV) strains were applied during the smallpox vaccination campaign to eradicate the variola virus worldwide. After the eradication of smallpox, VACV gained popularity as a viral vector thanks to increasing innovations in genetic engineering and vaccine technology. Some VACV strains have been extensively used to develop vaccine candidates against various diseases. Modified vaccinia virus Ankara (MVA) is a VACV vaccine strain that offers several advantages for the development of recombinant vaccine candidates. In addition to various host-restriction genes, MVA lacks several immunomodulatory genes of which some have proven to be quite efficient in skewing the immune response in an unfavorable way to control infection in the host. Studies to manipulate these genes aim to optimize the immunogenicity and safety of MVA-based viral vector vaccine candidates. Here we summarize the history and further work with VACV as a vaccine and present in detail the genetic manipulations within the MVA genome to improve its immunogenicity and safety as a viral vector vaccine.

Poxvirus Interactions with the Host Ubiquitin System

The ubiquitin system has emerged as a master regulator of many, if not all, cellular functions. With its large repertoire of conjugating and ligating enzymes, the ubiquitin system holds a unique mechanism to provide selectivity and specificity in manipulating protein function. As intracellular parasites viruses have evolved to modulate the cellular environment to facilitate replication and subvert antiviral responses. Poxviruses are a large family of dsDNA viruses with large coding capacity that is used to synthetise proteins and enzymes needed for replication and morphogenesis as well as suppression of host responses. This review summarises our current knowledge on how poxvirus functions rely on the cellular ubiquitin system, and how poxviruses exploit this system to their own advantage, either facilitating uncoating and genome release and replication or rewiring ubiquitin ligases to downregulate critical antiviral factors. Whilst much remains to be known about the intricate interactions established between poxviruses and the host ubiquitin system, our knowledge has revealed crucial viral processes and important restriction factors that open novel avenues for antiviral treatment and provide fundamental insights on the biology of poxviruses and other virus families.

Injection site vaccinology of a recombinant vaccinia-based vector reveals diverse innate immune signatures

Poxvirus systems have been extensively used as vaccine vectors. Herein a RNA-Seq analysis of intramuscular injection sites provided detailed insights into host innate immune responses, as well as expression of vector and recombinant immunogen genes, after vaccination with a new multiplication defective, vaccinia-based vector, Sementis Copenhagen Vector. Chikungunya and Zika virus immunogen mRNA and protein expression was associated with necrosing skeletal muscle cells surrounded by mixed cellular infiltrates. The multiple adjuvant signatures at 12 hours post-vaccination were dominated by TLR3, 4 and 9, STING, MAVS, PKR and the inflammasome. Th1 cytokine signatures were dominated by IFNγ, TNF and IL1β, and chemokine signatures by CCL5 and CXCL12. Multiple signatures associated with dendritic cell stimulation were evident. By day seven, vaccine transcripts were absent, and cell death, neutrophil, macrophage and inflammation annotations had abated. No compelling arthritis signatures were identified. Such injection site vaccinology approaches should inform refinements in poxvirus-based vector design.

Poxvirus vector systems have been widely developed for vaccine applications. Despite considerable progress, so far only one recombinant poxvirus vectored vaccine has to date been licensed for human use, with ongoing efforts seeking to enhance immunogenicity whilst minimizing reactogenicity. The latter two characteristics are often determined by early post-vaccination events at the injection site. We therefore undertook an injection site vaccinology approach to analyzing gene expression at the vaccination site after intramuscular inoculation with a recombinant, multiplication defective, vaccinia-based vaccine. This provided detailed insights into inter alia expression of vector-encoded immunoregulatory genes, as well as host innate and adaptive immune responses. We propose that such injection site vaccinology can inform rational vaccine vector design, and we discuss how the information and approach elucidated herein might be used to improve immunogenicity and limit reactogenicity of poxvirus-based vaccine vector systems.

Vaccinia Virus Activation and Antagonism of Cytosolic DNA Sensing

Cells express multiple molecules aimed at detecting incoming virus and infection. Recognition of virus infection leads to the production of cytokines, chemokines and restriction factors that limit virus replication and activate an adaptive immune response offering long-term protection. Recognition of cytosolic DNA has become a central immune sensing mechanism involved in infection, autoinflammation, and cancer immunotherapy. Vaccinia virus (VACV) is the prototypic member of the family Poxviridae and the vaccine used to eradicate smallpox. VACV harbors enormous potential as a vaccine vector and several attenuated strains are currently being developed against infectious diseases. In addition, VACV has emerged as a popular oncolytic agent due to its cytotoxic capacity even in hypoxic environments. As a poxvirus, VACV is an unusual virus that replicates its large DNA genome exclusively in the cytoplasm of infected cells. Despite producing large amounts of cytosolic DNA, VACV efficiently suppresses the subsequent innate immune response by deploying an arsenal of proteins with capacity to disable host antiviral signaling, some of which specifically target cytosolic DNA sensing pathways. Some of these strategies are conserved amongst orthopoxviruses, whereas others are seemingly unique to VACV. In this review we provide an overview of the VACV replicative cycle and discuss the recent advances on our understanding of how VACV induces and antagonizes innate immune activation via cytosolic DNA sensing pathways. The implications of these findings in the rational design of vaccines and oncolytics based on VACV are also discussed.

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

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

Tauopathy Analysis in P301S Mouse Model of Alzheimer Disease Immunized With DNA and MVA Poxvirus-Based Vaccines Expressing Human Full-Length 4R2N or 3RC Tau Proteins

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by a progressive memory loss and cognitive decline that has been associated with an accumulation in the brain of intracellular neurofibrillary tangles (NFTs) formed by hyperphosphorylated tau protein, and extracellular senile plaques formed by β-amyloid peptides. Currently, there is no cure for AD and after the failure of anti β-amyloid therapies, active and passive tau immunotherapeutic approaches have been developed in order to prevent, reduce or ideally reverse the disease. Vaccination is one of the most effective approaches to prevent diseases and poxviruses, particularly modified vaccinia virus Ankara (MVA), are one of the most promising viral vectors used as vaccines against several human diseases. Thus, we present here the generation and characterization of the first MVA vectors expressing human tau genes; the full-length 4R2N tau protein or a 3RC tau fragment containing 3 tubulin-binding motifs and the C-terminal region (termed MVA-Tau4R2N and MVA-Tau3RC, respectively). Both MVA-Tau recombinant viruses efficiently expressed the human tau 4R2N or 3RC proteins in cultured cells, being detected in the cytoplasm of infected cells and co-localized with tubulin. These MVA-Tau vaccines impacted the innate immune responses with a differential recruitment of innate immune cells to the peritoneal cavity of infected mice. However, no tau-specific T cell or humoral immune responses were detected in vaccinated mice. Immunization of transgenic P301S mice, a mouse model for tauopathies, with a DNA-Tau prime/MVA-Tau boost approach showed no significant differences in the hyperphosphorylation of tau, motor capacity and survival rate, when compared to non-vaccinated mice. These findings showed that a well-established and potent protocol of T and B cell activation based on DNA/MVA prime/boost regimens using DNA and MVA vectors expressing tau full-length 4R2N or 3RC proteins is not sufficient to trigger tau-specific T and B cell immune responses and to induce a protective effect against tauopathy in this P301S murine model. In the pursuit of AD vaccines, our results highlight the need for novel optimized tau immunogens and additional modes of presentation of tau protein to the immune system.

Deletion of Vaccinia Virus A40R Gene Improves the Immunogenicity of the HIV-1 Vaccine Candidate MVA-B

Development of a safe and efficacious vaccine against the HIV/AIDS pandemic remains a major scientific goal. We previously described an HIV/AIDS vaccine based on the modified vaccinia virus Ankara (MVA) expressing HIV-1 gp120 and Gag-Pol-Nef (GPN) of clade B (termed MVA-B), which showed moderate immunogenicity in phase I prophylactic and therapeutic clinical trials. Here, to improve the immunogenicity of MVA-B, we generated a novel recombinant virus, MVA-B ΔA40R, by deleting in the MVA-B genome the vaccinia virus (VACV) A40R gene, which encodes a protein with unknown immune function. The innate immune responses triggered by MVA-B ΔA40R in infected human macrophages, in comparison to parental MVA-B, revealed an increase in the mRNA expression levels of interferon (IFN)-β, IFN-induced genes, and chemokines. Compared to priming with DNA-B (a mixture of DNA-gp120 plus DNA-GPN) and boosting with MVA-B, mice immunized with a DNA-B/MVA-B ΔA40R regimen induced higher magnitude of adaptive and memory HIV-1-specific CD4+ and CD8+ T-cell immune responses that were highly polyfunctional, mainly directed against Env. and of an effector memory phenotype, together with enhanced levels of antibodies against HIV-1 gp120. Reintroduction of the A40R gene into the MVA-B ΔA40R genome (virus termed MVA-B ΔA40R-rev) promoted in infected cells high mRNA and protein A40 levels, with A40 protein localized in the cell membrane. MVA-B ΔA40R-rev significantly reduced mRNA levels of IFN-β and of several other innate immune-related genes in infected human macrophages. In immunized mice, MVA-B ΔA40R-rev reduced the magnitude of the HIV-1-specific CD4+ and CD8+ T cell responses compared to MVA-B ΔA40R. These results revealed an immunosuppressive role of the A40 protein, findings relevant for the optimization of poxvirus vectors as vaccines.

An MVA Vector Expressing HIV-1 Envelope under the Control of a Potent Vaccinia Virus Promoter as a Promising Strategy in HIV/AIDS Vaccine Design

Highly attenuated poxviral vectors, such as modified vaccinia virus ankara (MVA), are promising vaccine candidates against several infectious diseases. One of the approaches developed to enhance the immunogenicity of poxvirus vectors is increasing the promoter strength and accelerating during infection production levels of heterologous antigens. Here, we have generated and characterized the biology and immunogenicity of an optimized MVA-based vaccine candidate against HIV/AIDS expressing HIV-1 clade B gp120 protein under the control of a novel synthetic late/early optimized (LEO) promoter (LEO160 promoter; with a spacer length of 160 nucleotides), termed MVA-LEO160-gp120. In infected cells, MVA-LEO160-gp120 significantly increased the expression levels of HIV-1 gp120 mRNA and protein, compared to the clinical vaccine MVA-B vector expressing HIV-1 gp120 under the control of the commonly used synthetic early/late promoter. When mice were immunized with a heterologous DNA-prime/MVA-boost protocol, the immunization group DNA-gp120/MVA-LEO160-gp120 induced an enhancement in the magnitude of gp120-specific CD4⁺ and CD8⁺ T-cell responses, compared to DNA-gp120/MVA-B; with most of the responses being mediated by the CD8⁺ T-cell compartment, with a T effector memory phenotype. DNA-gp120/MVA-LEO160-gp120 also elicited a trend to a higher magnitude of gp120-specific CD4⁺ T follicular helper cells, and modest enhanced levels of antibodies against HIV-1 gp120. These findings revealed that this new optimized vaccinia virus promoter could be considered a promising strategy in HIV/AIDS vaccine design, confirming the importance of early expression of heterologous antigen and its impact on the antigen-specific immunogenicity elicited by poxvirus-based vectors.

Potent Anti-hepatitis C Virus (HCV) T Cell Immune Responses Induced in Mice Vaccinated with DNA-Launched RNA Replicons and Modified Vaccinia Virus Ankara-HCV

Hepatitis C is a liver disease caused by the hepatitis C virus (HCV) affecting 71 million people worldwide with no licensed vaccines that prevent infection. Here, we have generated four novel alphavirus-based DNA-launched self-amplifying RNA replicon (DREP) vaccines expressing either structural core-E1-E2 or nonstructural p7-NS2-NS3 HCV proteins of genotype 1a placed under the control of an alphavirus promoter, with or without an alphaviral translational enhancer (grouped as DREP-HCV or DREP-e-HCV, respectively). DREP vectors are known to induce cross-priming and further stimulation of immune responses through apoptosis, and here we demonstrate that they efficiently trigger apoptosis-related proteins in transfected cells. Immunization of mice with the DREP vaccines as the priming immunization followed by a heterologous boost with a recombinant modified vaccinia virus Ankara (MVA) vector expressing the nearly full-length genome of HCV (MVA-HCV) induced potent and long-lasting HCV-specific CD4⁺ and CD8⁺ T cell immune responses that were significantly stronger than those of a homologous MVA-HCV prime/boost immunization, with the DREP-e-HCV/MVA-HCV combination the most immunogenic regimen. HCV-specific CD4⁺ and CD8⁺ T cell responses were highly polyfunctional, had an effector memory phenotype, and were mainly directed against E1-E2 and NS2-NS3, respectively. Additionally, DREP/MVA-HCV immunization regimens induced higher antibody levels against HCV E2 protein than homologous MVA-HCV immunization. Collectively, these results provided an immunization protocol against HCV by inducing high levels of HCV-specific T cell responses as well as humoral responses. These findings reinforce the combined use of DREP-based vectors and MVA-HCV as promising prophylactic and therapeutic vaccines against HCV.IMPORTANCE HCV represents a global health problem as more than 71 million people are chronically infected worldwide. Direct-acting antiviral agents can cure HCV infection in most patients, but due to the high cost of these agents and the emergence of resistant mutants, they do not represent a feasible and affordable strategy to eradicate the virus. Therefore, a vaccine is an urgent goal that requires efforts to understand the correlates of protection for HCV clearance. Here, we describe for the first time the generation of novel vaccines against HCV based on alphavirus DNA replicons expressing HCV antigens. We demonstrate that potent T cell immune responses, as well as humoral immune responses, against HCV can be achieved in mice by using a combined heterologous prime/boost immunization protocol consisting of the administration of alphavirus replicon DNA vectors as the priming immunization followed by a boost with a recombinant modified vaccinia virus Ankara vector expressing HCV antigens.