MDA5 can be exploited as efficacious genetic adjuvant for DNA vaccination against lethal H5N1 influenza virus infection in chickens

The Dual Role of the Innate Immune System in the Effectiveness of mRNA Therapeutics

Advances in molecular biology have revolutionized the use of messenger RNA (mRNA) as a therapeutic. The concept of nucleic acid therapy with mRNA originated in 1990 when Wolff et al. reported successful expression of proteins in target organs by direct injection of either plasmid DNA or mRNA. It took decades to bring the transfection efficiency of mRNA closer to that of DNA. The next few decades were dedicated to turning in vitro-transcribed (IVT) mRNA from a promising delivery tool for gene therapy into a full-blown therapeutic modality, which changed the biotech market rapidly. Hundreds of clinical trials are currently underway using mRNA for prophylaxis and therapy of infectious diseases and cancers, in regenerative medicine, and genome editing. The potential of IVT mRNA to induce an innate immune response favors its use for vaccination and immunotherapy. Nonetheless, in non-immunotherapy applications, the intrinsic immunostimulatory activity of mRNA directly hinders the desired therapeutic effect since it can seriously impair the target protein expression. Targeting the same innate immune factors can increase the effectiveness of mRNA therapeutics for some indications and decrease it for others, and vice versa. The review aims to present the innate immunity-related 'barriers' or 'springboards' that may affect the development of immunotherapies and non-immunotherapy applications of mRNA medicines.

In silico design of recombinant multi-epitope vaccine against influenza A virus

Background

Influenza A virus is one of the leading causes of annual mortality. The emerging of novel escape variants of the influenza A virus is still a considerable challenge in the annual process of vaccine production. The evolution of vaccines ranks among the most critical successes in medicine and has eradicated numerous infectious diseases. Recently, multi-epitope vaccines, which are based on the selection of epitopes, have been increasingly investigated.

Results

This study utilized an immunoinformatic approach to design a recombinant multi-epitope vaccine based on a highly conserved epitope of hemagglutinin, neuraminidase, and membrane matrix proteins with fewer changes or mutate over time. The potential B cells, cytotoxic T lymphocytes (CTL), and CD4 T cell epitopes were identified. The recombinant multi-epitope vaccine was designed using specific linkers and a proper adjuvant. Moreover, some bioinformatics online servers and datasets were used to evaluate the immunogenicity and chemical properties of selected epitopes. In addition, Universal Immune System Simulator (UISS) in silico trial computational framework was run after influenza exposure and recombinant multi-epitope vaccine administration, showing a good immune response in terms of immunoglobulins of class G (IgG), T Helper 1 cells (TH1), epithelial cells (EP) and interferon gamma (IFN-g) levels. Furthermore, after a reverse translation (i.e., convertion of amino acid sequence to nucleotide one) and codon optimization phase, the optimized sequence was placed between the two EcoRV/MscI restriction sites in the PET32a⁺ vector.

Conclusions

The proposed “Recombinant multi-epitope vaccine” was predicted with unique and acceptable immunological properties. This recombinant multi-epitope vaccine can be successfully expressed in the prokaryotic system and accepted for immunogenicity studies against the influenza virus at the in silico level. The multi-epitope vaccine was then tested with the Universal Immune System Simulator (UISS) in silico trial platform. It revealed slight immune protection against the influenza virus, shedding the light that a multistep bioinformatics approach including molecular and cellular level is mandatory to avoid inappropriate vaccine efficacy predictions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04581-6.

hnRNPH2 as an Inhibitor of Chicken MDA5-Mediated Type I Interferon Response: Analysis Using Chicken MDA5-Host Interactome

RIG-I and MDA5 are two key pattern recognition receptors that sense the invasion of RNA viruses and initiate type I interferon (IFN) response. Although these receptors are generally conserved in vertebrates, RIG-I is absent in chickens, whereas MDA5 is present. Chicken MDA5 (chMDA5) plays a pivotal role in sensing the invasion of RNA viruses into cells. However, unlike mammalian MDA5, where there are in-depth and extensive studies, regulation of the chMDA5-mediated signaling pathway remains unexplored. In this study, we performed a pulldown assay and mass spectrometry analysis to identify chicken proteins that could interact with the N terminal of chMDA5 (chMDA5-N) that contained two CARDs responsible for binding of the well-known downstream adaptor MAVS. We found that 337 host proteins could potentially interact with chMDA5-N, which were integrated to build a chMDA5-N–host association network and analyzed by KEGG pathway and Gene Ontology annotation. Results of our analysis revealed that diverse cellular processes, such as RNA binding and transport and protein translation, ribosome, chaperones, and proteasomes are critical cellular factors regulating the chMDA5-mediated signaling pathway. We cloned 64 chicken genes to investigate their effects on chMDA5-mediated chicken IFN-β production and confirmed the association of chicken DDX5, HSPA8, HSP79, IFIT5, PRDX1, and hnRNPH2 with chMDA5-N. In particular, we found that chicken hnRNPH2 impairs the association between chMDA5-N and MAVS and thus acts as a check on the chMDA5-mediated signaling pathway. To our knowledge, this study is the first to analyze the chicken MDA5–host interactome, which provides fundamental but significant insights to further explore the mechanism of chicken MDA5 signaling regulation in detail.

Differential immunomodulatory effect of vitamin D (1,25 (OH)2 D3) on the innate immune response in different types of cells infected in vitro with infectious bursal disease virus

It has been demonstrated that vitamin D (Vit D) included in diets offers a beneficial effect by improving innate immune responses in chickens. However, its mechanisms of action and the effect on immunosuppressive pathogens, such as infectious bursal disease virus, are not yet known. In the present study, we have studied the immunomodulatory effect of Vit D on the innate immune response in 3 cell lines: fibroblast cells (DF-1), macrophages (HD11), and B cells (DT-40) infected with IBDV (intermediate vaccine) at 2 multiplicity of infections (MOI) (1 and 0.1). Genes associated with innate immune responses (TLR-3, TLR-21, MDA-5, MyD88, TRIF, IRF-7, INF-α, INF-β, PKR, OAS, viperin, IL-1β, IL-6, and IL-12) were evaluated at different time points (3, 6, 12, 24, and 36 h after infection, h.p.i). Virus production reached a maximum at 24 h.p.i., which was significantly (P < 0.05) higher in DF-1 cells, followed by HD-11 and DT-40 cells. Mainly in HD-11 cells, there was a significant (P < 0.05) effect of Vit D supplementation on receptors TLR-3, TLR-21, and MDA-5 after 12 h.p.i, independent of MOI. DT-40 cells showed the highest antiviral activity, with a significant (P < 0.05) effect on IRF-7, IFN-β, OAS, and PKR gene expression, where expression of IRF-7 and IFN-β correlated positively with Vit D supplementation, while OAS and PKR were independent of Vit D. Proinflammatory cytokines were significantly (P < 0.05) upregulated and found to be Vit D and MOI dependent. In conclusion, this study demonstrated the capacity of IBDV to trigger a strong innate immune response in chicken cells and contributes to the understanding of the activation pathways of innate immunity induced by IBDV and further shows the benefitial effect of Vit D supplementation as an immunomodulator.

Transcriptomic Analysis of the Chicken MDA5 Response Genes

RIG-I and MDA5 are two key pattern recognition receptors that sense RNA virus invasion, but RIG-I is absent in chickens. Although chickens have intact MDA5, the genes downstream of chicken MDA5 (chMDA5) that may mediate antiviral response are not well studied. We compared the transcriptional profile of chicken embryonic fibroblasts (DF1) transfected with chMDA5, and poly(I:C), using RNA-seq. Transfected chMDA5 and poly(I:C) in DF1 cells were associated with the marked induction of many antiviral innate immune genes compared with control. Interestingly, nine interferon-stimulated genes (ISGs) were listed in the top 15 upregulated genes by chMDA5 and poly(I:C) transfection. We used real-time PCR to confirm the upregulation of the nine ISGs, namely, MX1, IFI6, IFIT5, RSAD2, OASL, CMPK2, HELZ2, EPSTI1, and OLFML1, by chMDA5 and poly(I:C) transfection in DF1 cells. However, avian influenza virus H5N6 infection only increased MX1, IFI6, IFIT5, RSAD2, and OASL expression levels. Further study showed that the overexpression of these five genes could significantly inhibit H5N6 virus replication. These results provide some insights into the gene expression pattern induced by chMDA5, which would be beneficial for understanding and identifying innate immune genes of chicken that may lead to new antiviral therapies.

AVIAN INNATE IMMUNITY WITH AN EMPHASIS ON CHICKEN MELANOMA DIFFERENTIATION-ASSOCIATED GENE 5 (MDA5)

Avian species have immune system to fight invading pathogens. The immune system comprises innate and adaptive immunity. Innate immunity relies on pattern recognition receptors to sense particular molecules present in pathogens, i.e. pathogen-associated molecular patterns (PAMPs), or danger signals in the environment, i.e. danger-associated molecular patterns (DAMPs). Cytoplasmic retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs) are the sensors recognizing cytoplasmic PAMP and/or DAMP. Among common avian species, chickens do not have RIG-I whereas ducks and finches do. Therefore, the other RLR member, melanoma differentiation-associated gene 5 (MDA5), is believed to play an important role to recognize intracellular pathogens in chickens. Chicken MDA5 has been identified and its function determined. Chicken MDA5 maintains the same domain architecture compared with MDA5 analogs in other animal species. The expression of chicken MDA5 was upregulated when a synthetic double-stranded RNA (dsRNA), polyriboinosinic:polyribocytidylic acids (poly(I:C)), was transfected into chicken cells, whereas that did not change when cells were incubated with poly(I:C). The enhanced expression of chicken MDA5 in chicken cells upregulated the expression of chicken interferon-[Formula: see text] (IFN-[Formula: see text]). The infection of dsRNA infectious bursal disease virus (IBDV) in non-immune cells triggered the activation of chicken MDA5 signaling pathway, leading to the production of IFN-[Formula: see text] and subsequent response of IFN-stimulated genes. Furthermore, in immune cells like macrophages, chicken MDA5 participated in sensing the infection of IBDV by activating downstream antiviral genes and molecules and modulating adaptive immunity.

On the contrary, one of cytoplasmic NLR member, NLR family pyrin domain containing 3 (NLRP3), was cloned and functionally characterized in chicken cells. Chicken NLRP3 conserved the same domain architecture compared with NLRP3 analogs in other animal species. Chicken NLRP3 was highly expressed in kidney, bursa of Fabricius and spleen. The production of mature chicken interleukin 1 [Formula: see text] (IL-1[Formula: see text] in chicken macrophages was stimulated by lipopolysaccharide (LPS) treatment followed by short ATP exposure.

In summary, chicken MDA5 was a cytoplasmic dsRNA sensor that mediated the production of type I IFN upon ligand engagement, whereas NLRP3 sensed danger signals, such as ATP, in the cytoplasm and cleaved pro-IL-1[Formula: see text] to produce mature IL-1[Formula: see text]. Chicken MDA5 was not only involved in the activation of innate immune responses in non-immune and immune cells, but it also participated in modulating adaptive immunity in immune cells. Chicken NLRP3 participated in the production of mature chicken IL-1[Formula: see text] upon ligand engagement.

Cytolytic Perforin as an Adjuvant to Enhance the Immunogenicity of DNA Vaccines

DNA vaccines present one of the most cost-effective platforms to develop global vaccines, which have been tested for nearly three decades in preclinical and clinical settings with some success in the clinic. However, one of the major challenges for the development of DNA vaccines is their poor immunogenicity in humans, which has led to refinements in DNA delivery, dosage in prime/boost regimens and the inclusion of adjuvants to enhance their immunogenicity. In this review, we focus on adjuvants that can enhance the immunogenicity of DNA encoded antigens and highlight the development of a novel cytolytic DNA platform encoding a truncated mouse perforin. The application of this innovative DNA technology has considerable potential in the development of effective vaccines.

Sequential DNA immunization of chickens with bivalent heterologous vaccines induce highly reactive and cross-specific antibodies against influenza hemagglutinin

Vaccines against avian influenza are mostly based on hemagglutinin (HA), which is the main antigen of this virus and a target for neutralizing antibodies. Traditional vaccines are known to be poorly efficient against newly emerging strains, which is an increasing worldwide problem for human health and for the poultry industry. As demonstrated by research and clinical data, sequential exposure to divergent influenza HAs can boost induction of universal antibodies which recognize conserved epitopes. In this work, we have performed sequential immunization of laying hens using monovalent or bivalent compositions of DNA vaccines encoding HAs from distant groups 1 and 2 (H5, H1, and H3 subtypes, respectively). This strategy gave promising results, as it led to induction of polyclonal antibodies against HAs from both groups. These polyclonal antibodies showed cross-reactivity between different HA strains in ELISA, especially when bivalent formulations were used for immunization of birds. However, cross-reactivity of antibodies induced against H3 and H5 HA subtypes was rather limited against each other after homologous immunization. Using a cocktail of HA sequences and/or sequential DNA vaccination with different strains presents a good strategy to overcome the limited effectiveness of vaccines and induce broader immunity against avian influenza. Such a strategy could be adapted for vaccinating laying hens or parental flocks of different groups of poultry.

Truncated chicken MDA5 enhances the immune response to inactivated NDV vaccine

Melanoma Differentiation-Associated protein 5 (MDA5) is a cytoplasmic sensor for viral invasion and plays an important role in regulation of the immune response against Newcastle disease virus (NDV) in chickens. MDA5 was used as an adjuvant to enhance the humoral immune response against influenza virus. In the current study, truncated chicken MDA5 [1-483 aa, chMDA5(483aa)] expressed by recombinant adenovirus was administered to specific-pathogen-free (SPF) chickens to improve the immune response induced by inactivated NDV vaccine. A total of 156 SPF chickens were divided into six groups, and after two rounds of immunization, the humoral immune response, cell-mediated immune (CMI) response and the protective efficacy of the vaccines against NDV challenge were evaluated. The results showed that co-administration of chMDA5(483aa) expressed by adenovirus increased the NDV-specific antibody response by 1.7 times and chickens received chMDA5(483aa) also gained a higher level of CMI response. Consistently, the protective efficacy of the inactivated NDV vaccine against virulent NDV (vNDV) challenge was improved by co-administrate with chMDA5(483aa), as indicated by the reduced morbidity and pathological lesions, lower levels of viral load in organs and reduced virus shedding. Our study demonstrated that chMDA5(433aa) expressed by adenovirus could enhance the immune efficacy of inactivated NDV vaccine in chickens and could be a potential adjuvant candidate in developing chicken NDV vaccines.

Improvement Efficacy of Influenza Nanovaccine in Combination with Hemokinin-1 Molecular Adjuvant

BACKGROUND

H9N2 avian influenza viruses have the potential to become the next human pandemic threat and next generation vaccine technologies are needed. Current studies introduce nanoparticles as a proper vaccine delivery vehicle for induction of protective immunity. In this study, the efficacy of chitosan nanoparticle-based H9N2 influenza vaccine with and without hemokinin-1 (HK-1) as a molecular adjuvant to induce protective immunity against the virus was examined.

METHODS

The H9N2 antigen was prepared in MDCK cells and inactivated with formalin. The inactivated antigen alone and in combination with HK-1 was encapsulated into chitosan nanoparticles. Groups of BALB/c mice received chitosan nanoparticle-based H9N2 antigen alone or in combination with HK-1 in a prime/boost platform via eye drop method. To evaluate the efficacy of the adjuvanted-nanovaccine candidate, systemic antibody responses were compared among the groups of animals.

RESULTS

Serological analysis indicated that mice receiving the HK-1/H9N2 nanoparticles formulation induced higher antibody titers that were sustained until the end of experiment. However, in the immunized mice, influenza specific antibody titers were comparable to that in the animals which were immunized either with inactivated antigen alone or the H9N2 nanoparticles without HK-1 adjuvant.

CONCLUSION

The data demonstrate the synergy between HK-1 as an adjuvant and chitosan nanoparticles as a delivery antigen/adjuvant carrier in the improvement of influenza immune responses.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Transcriptome analysis of avian reovirus-mediated changes in gene expression of normal chicken fibroblast DF-1 cells

Background

Avian reovirus (ARV) is an important poultry pathogen that can cause immunosuppression. In this study, RNA-Seq technology was applied to investigate the transcriptome-wide changes of DF-1 cells upon ARV infection at the middle stage.

Results

Total RNA of ARV-infected or mock-infected samples at 10 and 18 h post infection (hpi) was extracted to build RNA-Seq datasets. Analysis of the sequencing data revealed that the expressions of numerous genes were altered, and a panel of differentially expressed genes were confirmed with RT-qPCR. At 10 hpi, 104 genes were down-regulated and 64 were up-regulated, while the expressions of 47 genes were increased and only one was down-regulated, which may play a role in retinoic acid biosynthesis, at 18 hpi in the ARV-infected cells. The similar profiles of up-regulated genes between the two groups of infected cells suggest that ARV infection activated a prolonged antiviral response of host cells. Alternative splicing analysis found no significantly changed events altered by ARV infection.

Conclusions

Overall, the differential expression profile presented in this study can be used to expand our understanding of the comprehensive interactions between ARV and the host cells, and may be helpful for us to reveal the pathogenic mechanism on the molecular level.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4310-5) contains supplementary material, which is available to authorized users.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Improvement influenza HA2 DNA vaccine cellular and humoral immune responses with Mx bio adjuvant

Immunization with DNA vaccines as a novel alternative to conventional vaccination strategy requires adjuvant for improving vaccine efficacy. The conserved immunogenic HA2 subunit, which harbors neutralizing epitopes is a promising vaccine candidate against influenza viruses. In this study, for the first time we explore the idea of using host interferon inducible Mx protein to increase the immunogenicity of HA2 H9N2 influenza DNA vaccine. The potency and safety of the Mx adjuvanted-HA2 vaccine was evaluated in BALB/c mice by different prime-boost strategies. To assess the effect of the vaccination on the virus clearance rate, mice were challenged with homologous influenza virus. Administration of the adjuvanted vaccine and boosting with the same regimen could effectively enhance both humoral and cellular immune responses in treated mice. These data demonstrated that Mx as host defense peptide can be potentiated for improving influenza vaccine efficacy.

Triggering Intracellular Receptors for Vaccine Adjuvantation

Immune adjuvants are components that stimulate, potentiate, or modulate the immune response to an antigen. They are key elements of vaccines in both the prophylactic and therapeutic domains. In the past decade substantial progress in our understanding of innate immunity has paved the way for the design of next-generation adjuvants that stimulate a wide range of receptors. Within the framework of vaccine adjuvant design, this review outlines the interest of targeting endosomal and intracellular receptors to enhance and guide the immune response. We present and compare the molecules as well as potential combinations which are currently in the spotlight. We emphasize how targeting the appropriate receptor can direct immunity towards the appropriate response, such as a cytotoxic or mucosal response.

In Silico Analysis of HA2/Mx Chimera Peptide for Developing an Adjuvanted Vaccine to Induce Immune Responses Against Influenza Viruses

PURPOSE

The direct transmission of avian influenza viruses to human and increasing drug resisted strains posing new threats for public health. Therefore, development of efficient vaccines is needed to generate protective and persistent immunity to the viruses.

METHODS

Three motifs of Mx protein sequence in human, mouse and poultry located in interferon induced (GTP ase) domain were candidate as biologic adjuvant for enhancing the immune responses against influenza virus. Chimera proteins composed with the conserved HA2 subunit of influenza virus and the Mx motifs named HA2/Mx were modeled and evaluated by in silico analysis includes bioinformatics algorithms in order to explore biological characteristics of these peptides.

RESULTS

Amongst the predicted models, HA2/Mx1 peptide showed the better results following protein structures prediction, antigenic epitopes determination and model quality evaluation. Comparative homology modeling was performed with Swiss Model and the model was validated using ProSA. Epitope predictions revealed the construct could induce both B and T cell epitopes that expect a high immune response.

CONCLUSION

Taken together, these data indicate that the HA2/Mx1 chimera peptide can be potentiated for developing an adjuvant-fused influenza vaccine capable of stimulating effective immune response.

Molecular mechanisms for enhanced DNA vaccine immunogenicity

In the two decades since their initial discovery, DNA vaccines technologies have come a long way. Unfortunately, when applied to human subjects inadequate immunogenicity is still the biggest challenge for practical DNA vaccine use. Many different strategies have been tested in preclinical models to address this problem, including novel plasmid vectors and codon optimization to enhance antigen expression, new gene transfection systems or electroporation to increase delivery efficiency, protein or live virus vector boosting regimens to maximise immune stimulation, and formulation of DNA vaccines with traditional or molecular adjuvants. Better understanding of the mechanisms of action of DNA vaccines has also enabled better use of the intrinsic host response to DNA to improve vaccine immunogenicity. This review summarizes recent advances in DNA vaccine technologies and related intracellular events and how these might impact on future directions of DNA vaccine development.

DNA vaccination of poultry: The current status in 2015

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Poultry DNA vaccination studies are regularly being published since 1993.

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These studies are mainly, but not only, concerned with vaccination against viruses.

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The different strategies of improving DNA vaccine efficacies are presented.

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The fate of the vaccine plasmid, immune properties and other applications are described.

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Despite the compiling preclinical reports, a poultry DNA vaccine is yet unavailable in the market.

DNA vaccination is a promising alternative strategy for developing new human and animal vaccines. The massive efforts made these past 25 years to increase the immunizing potential of this kind of vaccine are still ongoing. A relatively small number of studies concerning poultry have been published. Even though there is a need for new poultry vaccines, five parameters must nevertheless be taken into account for their development: the vaccine has to be very effective, safe, inexpensive, suitable for mass vaccination and able to induce immune responses in the presence of maternal antibodies (when appropriate). DNA vaccination should meet these requirements. This review describes studies in this field performed exclusively on birds (chickens, ducks and turkeys). No evaluations of avian DNA vaccine efficacy performed on mice as preliminary tests have been taken into consideration. The review first describes the state of the art for DNA vaccination in poultry: pathogens targeted, plasmids used and different routes of vaccine administration. Second, it presents strategies designed to improve DNA vaccine efficacy: influence of the route of administration, plasmid dose and age of birds on their first inoculation; increasing plasmid uptake by host cells; addition of immunomodulators; optimization of plasmid backbones and codon usage; association of vaccine antigens and finally, heterologous prime-boost regimens. The final part will indicate additional properties of DNA vaccines in poultry: fate of the plasmids upon inoculation, immunological considerations and the use of DNA vaccines for purposes other than preventing infectious diseases.

Design of a heterosubtypic epitope-based peptide vaccine fused with hemokinin-1 against influenza viruses

Influenza viruses continue to emerge and re-emerge, posing new threats for public health. Control and treatment of influenza depends mainly on vaccination and chemoprophylaxis with approved antiviral drugs. Identification of specific epitopes derived from influenza viruses has significantly advanced the development of epitope-based vaccines. Here, we explore the idea of using HLA binding data to design an epitope-based vaccine that can elicit heterosubtypic T-cell responses against circulating H7N9, H5N1, and H9N2 subtypes. The hemokinin-1 (HK-1) peptide sequence was used to induce immune responses against the influenza viruses. Five conserved high score cytotoxic T lymphocyte (CTL) epitopes restricted to HLA-A*0201-binding peptides within the hemagglutinin (HA) protein of the viruses were chosen, and two HA CTL/HK-1 chimera protein models designed. Using in silico analysis, which involves interferon epitope scanning, protein structure prediction, antigenic epitope determination, and model quality evaluation, chimeric proteins were designed. The applicability of one of these proteins as a heterosubtypic epitopebased vaccine candidate was analyzed.

Improvement of DNA vaccination by adjuvants and sophisticated delivery devices: vaccine-platforms for the battle against infectious diseases

Advantages of DNA vaccination against infectious diseases over more classical immunization methods include the possibilities for rapid manufacture, fast adaptation to newly emerging pathogens and high stability at ambient temperatures. In addition, upon DNA immunization the antigen is produced by the cells of the vaccinated individual, which leads to activation of both cellular and humoral immune responses due to antigen presentation via MHC I and MHC II molecules. However, so far DNA vaccines have shown most efficient immunogenicity mainly in small rodent models, whereas in larger animals including humans there is still the need to improve effectiveness. This is mostly due to inefficient delivery of the DNA plasmid into cells and nuclei. Here, we discuss technologies used to overcome this problem, including physical means such as in vivo electroporation and co-administration of adjuvants. Several of these methods have already entered clinical testing in humans.

Avian influenza vaccines against H5N1 'bird flu'

H5N1 avian influenza viruses (AIVs) have spread widely to more than 60 countries spanning three continents. To control the disease, vaccination of poultry is implemented in many of the affected countries, especially in those where H5N1 viruses have become enzootic in poultry and wild birds. Recently, considerable progress has been made toward the development of novel avian influenza (AI) vaccines, especially recombinant virus vector vaccines and DNA vaccines. Here, we will discuss the recent advances in vaccine development and use against H5N1 AIV in poultry. Understanding the properties of the available, novel vaccines will allow for the establishment of rational vaccination protocols, which in turn will help the effective control and prevention of H5N1 AI.

Inflammasomes in antiviral immunity: clues for influenza vaccine development

Inflammasomes are cytosolic multiprotein complexes that sense microbial motifs or cellular stress and stimulate caspase-1-dependent cytokine secretion and cell death. Recently, it has become increasingly evident that both DNA and RNA viruses activate inflammasomes, which control innate and adaptive immune responses against viral infections. In addition, recent studies suggest that certain microbiota induce inflammasomes-dependent adaptive immunity against influenza virus infections. Here, we review recent advances in research into the role of inflammasomes in antiviral immunity.

Innate sensing of viruses by pattern recognition receptors in birds

Similar to mammals, several viral-sensing pattern recognition receptors (PRR) have been identified in birds including Toll-like receptors (TLR) and retinoic acid-inducible gene I (RIG-I)-like receptors (RLR). Avian TLR are slightly different from their mammalian counterparts, including the pseudogene TLR8, the absence of TLR9, and the presence of TLR1La, TLR1Lb, TLR15, and TLR21. Avian TLR3 and TLR7 are involved in RNA virus recognition, especially highly pathogenic avian influenza virus (HPAIV), while TLR15 and TLR21 are potential sensors that recognize both RNA viruses and bacteria. However, the agonist of TLR15 is still unknown. Interestingly, chickens, unlike ducks, geese and finches, lack RIG-I, however they do express melanoma differentiation-associated gene 5 (MDA5) which functionally compensates for the absence of RIG-I. Duck RIG-I is the cytosolic recognition element for HPAIV recognition, while chicken cells sense HPAIV through MDA5. However, the contributions of MDA5 and RIG-I to IFN-β induction upon HPAIV infection is different, and this may contribute to the chicken’s susceptibility to highly pathogenic influenza. It is noteworthy that the interactions between avian DNA viruses and PRR have not yet been reported. Furthermore, the role for avian Nod-like receptors (NLR) in viral immunity is largely unknown. In this review, recent advances in the field of viral recognition by different types of PRR in birds are summarized. In particular, the tissue and cellular distribution of avian PRR, the recognition and activation of PRR by viruses, and the subsequent expression of innate antiviral genes such as type I IFN and proinflammatory cytokines are discussed.

DNA vaccines: a simple DNA sensing matter?

Since the introduction of DNA vaccines two decades ago, this attractive strategy has been hampered by its low immunogenicity in humans. Studies conducted to improve the immunogenicity of DNA vaccines have shown that understanding the mechanism of action of DNA vaccines might be the key to successfully improving their immunogenicity. Our current understanding is that DNA vaccines induce innate and adaptive immune responses in two ways: (1) encoded protein (or polypeptide) antigen(s) by the DNA plasmid can be expressed in stromal cells (i.e., muscle cells) as well as DCs, where these antigens are processed and presented to naïve CD4 or CD8 T cells either by direct or cross presentation, respectively; and (2) the transfected DNA plasmid itself may bind to an un-identified cytosolic DNA sensor and activate the TBK1-STING pathway and the production of type I interferons (IFNs) which function as an adjuvant. Recent studies investigating double-stranded cytosolic DNA sensor(s) have highlighted new mechanisms in which cytosolic DNA may release secondary metabolites, which are in turn recognized by a novel DNA sensing machinery. Here, we discuss these new metabolites and the possibilities of translating this knowledge into improved immunogenicity for DNA vaccines.

Innate Immune Signaling by, and Genetic Adjuvants for DNA Vaccination

DNA vaccines can induce both humoral and cellular immune responses. Although some DNA vaccines are already licensed for infectious diseases in animals, they are not licensed for human use because the risk and benefit of DNA vaccines is still controversial. Indeed, in humans, the immunogenicity of DNA vaccines is lower than that of other traditional vaccines. To develop the use of DNA vaccines in the clinic, various approaches are in progress to enhance or improve the immunogenicity of DNA vaccines. Recent studies have shown that immunogenicity of DNA vaccines are regulated by innate immune responses via plasmid DNA recognition through the STING-TBK1 signaling cascade. Similarly, molecules that act as dsDNA sensors that activate innate immune responses through STING-TBK1 have been identified and used as genetic adjuvants to enhance DNA vaccine immunogenicity in mouse models. However, the mechanisms that induce innate immune responses by DNA vaccines are still unclear. In this review, we will discuss innate immune signaling upon DNA vaccination and genetic adjuvants of innate immune signaling molecules.