Immunogenicity and protective efficacy of a DNA vaccine encoding a chimeric protein of avian influenza hemagglutinin subtype H5 fused to CD154 (CD40L) in Pekin ducks

Production and characterization of a chimeric antigen, based on nucleocapsid of SARS-CoV-2 fused to the extracellular domain of human CD154 in HEK-293 cells as a vaccine candidate against COVID-19

Despite that more than one hundred vaccines against SARS-CoV-2 have been developed and that some of them were evaluated in clinical trials, the latest results revealed that these vaccines still face great challenges. Among the components of the virus, the N-protein constitutes an attractive target for a subunit vaccine because it is the most abundant, highly conserved and immunogenic protein. In the present work, a chimeric protein (N-CD protein) was constructed by the fusion of the N-protein to the extracellular domain of human CD154 as the molecular adjuvant. HEK-293 cells were transduced with lentiviral vector bearing the N-CD gene and polyclonal cell populations were obtained. The N-CD protein was purified from cell culture supernatant and further characterized by several techniques. Immunogenicity studies in mice and non-human primates showed the N-CD protein induced high IgG titers in both models after two doses. Moreover, overall health monitoring of non-human primates demonstrated that animals were healthy during 228 days after first immunization. Data obtained support further investigation in order to develop this chimeric protein as vaccine candidate against COVID-19 and other coronavirus diseases.

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

A Highly Immunogenic, Protective, and Safe Adenovirus-Based Vaccine Expressing Middle East Respiratory Syndrome Coronavirus S1-CD40L Fusion Protein in a Transgenic Human Dipeptidyl Peptidase 4 Mouse Model

Background

Infection control measures have played a major role in limiting human/camel-to-human transmission of Middle East respiratory syndrome coronavirus (MERS-CoV); however, development of effective and safe human or camel vaccines is warranted.

Methods

We extended and optimized our previous recombinant adenovirus 5 (rAd5)–based vaccine platform characterized by in vivo amplified and CD40-mediated specific responses to generate MERS-CoV S1 subunit-based vaccine. We generated rAd5 constructs expressing CD40-targeted S1 fusion protein (rAd5-S1/F/CD40L), untargeted S1 (rAd5-S1), and Green Fluorescent Protein (rAd5-GFP), and evaluated their efficacy and safety in human dipeptidyl peptidase 4 transgenic (hDPP4 Tg⁺) mice.

Results

Immunization of hDPP4 Tg⁺ mice with a single dose of rAd5-S1/F/CD40L elicited as robust and significant specific immunoglobulin G and neutralizing antibodies as those induced with 2 doses of rAd5-S1. After MERS-CoV challenge, both vaccines conferred complete protection against morbidity and mortality, as evidenced by significantly undetectable/reduced pulmonary viral loads compared to the control group. However, rAd5-S1– but not rAd5-S1/F/CD40L–immunized mice exhibited marked pulmonary perivascular hemorrhage post–MERS-CoV challenge despite the observed protection.

Conclusions

Incorporation of CD40L into rAd5-based MERS-CoV S1 vaccine targeting molecule and molecular adjuvants not only enhances immunogenicity and efficacy but also prevents inadvertent pulmonary pathology after viral challenge, thereby offering a promising strategy to enhance safety and potency of vaccines.

Molecular cloning, expression and characterization of Pekin duck programmed death-1

Programmed death-1 (PD-1) has a pivotal role in the attenuation of adaptive immune responses and peripheral tolerance. Here we describe the identification of the Pekin duck programmed death-1 orthologue (duPD-1). The duPD-1 cDNA encodes a 283-amino acid polypeptide that has an amino acid identity of 70%, 32% and 31% with chicken, murine and human PD-1, respectively. The duck PD-1 gene shares five conserved exons with chicken, murine and human PD-1 genes. A cluster of putative regulatory elements within the conserved region B (CR-B) of the basal promotor is conserved. Homology modeling was most compatible with the two β-sheet IgV domain structure of murine PD-1. Contact residues, shown to be critical for binding of the respective human and murine PD-1 ligands are mostly conserved between avian and mammalian species, whereas residues that define the cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM) are highly conserved across higher vertebrates and frog. Constitutive expression of duPD-1 transcripts was predominantly found in lymphocyte-rich tissues, and mitogen-stimulation of duck peripheral blood mononuclear cells transiently increased duPD-1 mRNA expression. A soluble duPD-1 protein was expressed and shown to engage the identified duck PD-1 ligands. Our observations show considerable evolutionary conservation between mammalian and avian PD-1 orthologues. This work will facilitate further investigation of the role of PD-1 signaling in adaptive immunity in the Pekin duck, a non-mammalian vertebrate and pathogen host with relevance for human and animal health.

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.

Fowl adenovirus serotype 4-induced apoptosis, autophagy, and a severe inflammatory response in liver

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotrophic virus that causes severe liver diseases. Upon histological examination, the most remarkable findings in the liver are small multifocal areas of necrosis and mononuclear cell infiltration, including basophilic intranuclear inclusion bodies in hepatocytes surrounded by a clear halo or which fill the entire nucleus. Here, we examined the mechanism responsible for FAdV-4-mediated hepatocyte damage in vivo and in vitro. The results showed that FAdV-4 impaired liver integrity and function, which decreased albumin and blood glucose concentrations and increased the plasma activity of aspartate aminotransferase and lactate dehydrogenase, compared with a non-infected control group (P<0.05). FAdV-4 induced hepatocyte apoptosis in a time-dependent manner in vivo and in vitro. Additionally, we found that FAdV-4 also induced the autophagy of hepatocytes, which promoted the conversion of microtubule-associated protein light chain 3 (LC3-I) to LC3-II, which is a hallmarks of autophagy. Furthermore, the mRNA expressions of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in vivo and in vitro showed a statistically significant increase (P<0.05) compared to that of the control group. However, the molecular mechanisms underlying the FAdV-4-induced apoptotic and autophagic cell death remain unclear. In summation, our observations suggested that FAdV-4 induced liver injury via apoptosis, autophagy, and a severe inflammatory response.

Host Immune Response to Influenza A Virus Infection

Influenza A viruses (IAVs) are contagious pathogens responsible for severe respiratory infection in humans and animals worldwide. Upon detection of IAV infection, host immune system aims to defend against and clear the viral infection. Innate immune system is comprised of physical barriers (mucus and collectins), various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, which provide first line of defense against IAV infection. The adaptive immunity is mediated by B cells and T cells, characterized with antigen-specific memory cells, capturing and neutralizing the pathogen. The humoral immune response functions through hemagglutinin-specific circulating antibodies to neutralize IAV. In addition, antibodies can bind to the surface of infected cells and induce antibody-dependent cell-mediated cytotoxicity or complement activation. Although there are neutralizing antibodies against the virus, cellular immunity also plays a crucial role in the fight against IAVs. On the other hand, IAVs have developed multiple strategies to escape from host immune surveillance for successful replication. In this review, we discuss how immune system, especially innate immune system and critical molecules are involved in the antiviral defense against IAVs. In addition, we highlight how IAVs antagonize different immune responses to achieve a successful infection.

Transcriptome Analysis and Identification of Differentially Expressed Transcripts of Immune-Related Genes in Spleen of Gosling and Adult Goose

The goose (Anser cygnoides), having high nutritional value, high-quality feathers and high economic benefit, is an economically important poultry species. However, the molecular mechanisms underlying the higher susceptibility to pathogens in goslings than in adult geese remains poorly understood. In this study, the histological sections of spleen tissue from a two-week-old gosling and an adult goose, respectively, were subjected to comparative analysis. The spleen of gosling was mainly composed of mesenchyma, accompanied by scattered lymphocytes, whereas the spleen parenchyma was well developed in the adult goose. To investigate goose immune-related genes, we performed deep transcriptome and gene expression analyses of the spleen samples using paired-end sequencing technology (Illumina). In total, 50,390 unigenes were assembled using Trinity software and TGICL software. Moreover, these assembled unigenes were annotated with gene descriptions and gene ontology (GO) analysis was performed. Through Kyoto encyclopedia of genes and genomes (KEGG) analysis, we investigated 558 important immune-relevant unigenes and 23 predicted cytokines. In addition, 22 immune-related genes with differential expression between gosling and adult goose were identified, among which the three genes showing largest differences in expression were immunoglobulin alpha heavy chain (IgH), mannan-binding lectin serine protease 1 isoform X1 (MASP1) and C-X-C chemokine receptor type 4 (CXCR4). Finally, of these 22 differentially expressed immune-related genes, seven genes, including tumor necrosis factor receptor superfamily member 13B (TNFRSF13B), C-C motif chemokine 4-like (CCL4), CXCR4, interleukin 2 receptor alpha (IL2RA), MHC class I heavy chain (MHCIα), transporter of antigen processing 2 (TAP2) IgH, were confirmed by quantitative real-time PCR (qRT-PCR). The expression levels of all the candidate unigenes were up-regulated in adult geese other than that of TNFRSF13B. The comparative analysis of the spleen transcriptomes of gosling and adult goose may promote better understanding of immune molecular development in goose.

Targeting the HA2 subunit of influenza A virus hemagglutinin via CD40L provides universal protection against diverse subtypes

The influenza viral hemagglutinin (HA) is comprised of two subunits. Current influenza vaccine predominantly induces neutralizing antibodies (Abs) against the HA1 subunit, which is constantly evolving in unpredictable fashion. The other subunit, HA2, however, is highly conserved but largely shielded by the HA head domain. Thus, enhancing immune response against HA2 could potentially elicit broadly inhibitory Abs. We generated a recombinant adenovirus (rAd) encoding secreted fusion protein, consisting of codon-optimized HA2 subunit of influenza A/California/7/2009(H1N1) virus fused to a trimerized form of murine CD40L, and determined its ability of inducing protective immunity upon intranasal administration. We found that mice immunized with this recombinant viral vaccine were completely protected against lethal challenge with divergent influenza A virus subtypes including H1N1, H3N2, and H9N2. Codon-optimization of HA2 as well as the use of CD40L as a targeting ligand/molecular adjuvant were indispensable to enhance HA2-specific mucosal IgA and serum IgG levels. Moreover, induction of HA2-specific T-cell responses was dependent on CD40L, as rAd secreting HA2 subunit without CD40L failed to induce any significant levels of T-cell cytokines. Finally, sera obtained from immunized mice were capable of inhibiting 13 subtypes of influenza A viruses in vitro. These results provide proof of concept for a prototype HA2-based universal influenza vaccine.

Protective efficacy of a single dose of baculovirus hemagglutinin-based vaccine in chickens and ducks against homologous and heterologous H5N1 virus infections

Outbreaks of the highly pathogenic H5N1 virus in poultry and humans are ongoing. Vaccination is an efficient method for prevention of H5N1 infection. Using chickens and ducks, we assessed the efficacy of a vaccine comprising H5N1 hemagglutinin (HA) protein produced in a baculovirus expression system. The immunized chickens and ducks were protected against lethal infection by H5N1 in an antigen dose-dependent manner. Complete protection against homologous challenge and partial protection against heterologous challenge were achieved in chickens immunized with 5 μg HA protein and in ducks immunized with 10 μg HA protein. The IgG antibody subtype was mainly detected in the sera and tissues, including the lungs. The neuraminidase (NA) inhibition assay was negative in immunized chickens and ducks. Our results indicated that the expressed HA protein by baculovirus was immunogenic to both chickens and ducks, and the immunized chickens and ducks were protected from the lethal infections of highly pathogenic H5N1 influenza virus, though ducks required more HA protein than chickens to be protected. Also, baculovirus HA-vaccinated poultry can be differentiated from infected poultry by NA inhibition assay.

Molecular cloning, expression and characterization of Pekin duck interferon-λ

Interferons (IFNs) are the first line of defense against viral infections in vertebrates. Type III interferon (IFN-λ) is recognized for its key role in innate immunity of tissues of epithelial origin. Here we describe the identification of the Pekin duck IFN-λ ortholog (duIFN-λ). The predicted duIFN-λ protein has an amino acid identity of 63%, 38%, 37% and 33% with chicken IFN-λ and human IFN-λ3, IFN-λ2 and IFN-λ1, respectively. The duck genome contains a single IFN-λ gene that is comprised of five exons and four introns. Recombinant duIFN-λ up-regulated OASL and Mx-1 mRNA in primary duck hepatocytes. Our observations suggest evolutionary conservation of genomic organization and structural features implicated in receptor binding and antiviral activity. The identification and expression of duIFN-λ will facilitate further study of the role of type III IFN in antiviral defense and inflammatory responses of the Pekin duck, a non-mammalian vertebrate and pathogen host with relevance for human and animal health.

CD40 ligand preferentially modulates immune response and enhances protection against influenza virus

CD40L, a key regulator of the immune system, was studied as both a targeting ligand and a molecular adjuvant in nucleoprotein (NP)-based host defense against influenza in mouse models with different genetic backgrounds. Adenoviral vectors secreting NP-CD40L fusion protein (denoted as rAd-SNP40L) afforded full protection of immunocompetent and immunocompromised mice (CD40L(-/-) and CD4(-/-)) against lethal influenza infection. Mechanistically, rAd-SNP40L preferentially induced early and persistent B cell germinal center formation, and accelerated Ig isotype-switching and Th1-skewed, NP-specific Ab response. Moreover, it drastically augmented primary and memory NP-specific CTL activity and polyfunctional CD8(+) T cells. The markedly enhanced nonneutralizing Abs and CTLs significantly reduced viral burdens in the lungs of mice upon lethal virus challenge. Data generated from CD40L(-/-) and CD4(-/-) mice revealed that the protection was indeed CD40L mediated but CD4(+) T cell independent, demonstrating the viability of the fusion Ags in protecting immunodeficient hosts. Notably, a single dose of rAd-SNP40L completely protected mice from lethal viral challenge 4 mo after immunization, representing the first report, to our knowledge, on NP in conjunction with a molecular adjuvant inducing a robust and long-lasting memory immune response against influenza. This platform is characterized by an increased in vivo load of CD40-targeted Ag upon the secretion of the fusion protein from adenovirus-infected cells and may represent a promising strategy to enhance the breadth, durability, and potency of Ag-specific immune responses.

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.

Genomic structure, molecular characterization and functional analysis of Pekin duck interleukin-10

Here we describe the cloning and expression of Pekin duck IL-10 (duIL-10) and a six exon-5 intron structure of an IL-10 gene. Two transcripts encoding duIL-10 with an alternatively spliced 3'UTR, and a transcript lacking exon 5 with a novel coding sequence for its C-terminus (duIL-10ΔE5) were isolated from splenocytes. The duIL-10 protein has an amino acid identity of 79% and 47% with chicken and human IL-10, respectively. The duck IL-10 gene shares a similar structure of the respective exons 1-5 with the IL-10 genes of other vertebrates but has an alternative exon. The duIL-10 3D structure by homology modeling was similar to that of the human IL-10 monomer, whereas the predicted duIL-10ΔE5 protein lacks helix F. DuIL-10 and duIL-10ΔE5 transcripts were most abundant in primary and secondary immune organs and lung. Recombinant duIL-10 suppressed duck IL-2 transcripts in mitogen-activated PBMCs. Our observation suggests evolutionary conservation of structure and function of the duIL-10 protein but the roles of the novel IL-10 splice variants in the regulation of duck immune responses and evolution of vertebrate immunity remain to be elucidated.

CD40 ligand enhances immunogenicity of vector-based vaccines in immunocompetent and CD4+ T cell deficient individuals

Impairment of host immunity, particularly CD4+ T cell deficiency, presents significant complications for vaccine immunogenicity and efficacy. CD40 ligand (CD40L or CD154), a member of the tumor necrosis factor superfamily (TNFSF), is an important co-stimulatory molecule and, through interactions with its cognate receptor CD40, plays a pivotal role in the generation of host immune responses. Exploitation of CD40L and its receptor CD40 could provide a means to enhance and potentially restore protective immune responses in CD4+ T cell deficiency. To investigate the potential adjuvanticity of CD40L, we constructed recombinant plasmid DNA and adenoviral (Ad) vaccine vectors expressing murine CD40L and the mycobacterial protein antigen 85B (Ag85B). Co-immunization of mice with CD40L and Ag85B by intranasal or intramuscular prime-boosting led to route-dependent enhancement of the magnitude of vaccine-induced circulating and lung mucosal CD4+ and CD8+ T cell responses in both normal (CD4-replete) and CD4+ T cell deficient animals, including polyfunctional T cell responses. The presence of CD40L alone was insufficient to enhance or restore CD4+ T cell responses in CD4-ablated animals; however, in partially depleted animals, co-immunization with Ag85B and CD40L was capable of eliciting enhanced T cell responses, similar to those observed in normal animals, when compared to those given vaccine antigen alone. In summary, these findings show that CD40L has the capacity to enhance the magnitude of vaccine-induced polyfunctional T cell responses in CD4+ T cell deficient mice, and warrants further study as an adjuvant for immunization against opportunistic pathogens in individuals with CD4+ T cell deficiency.

cDNA cloning, genomic structure, molecular characterization and mRNA expression analysis of the Pekin duck interleukin-10 receptor 1

Interleukin-10 (IL-10) mediates its broad anti-inflammatory and immunoregulatory effects through two cell surface receptors by which binding to the IL-10 receptor 1 (IL-10R1) is the initial step that leads to recruitment of IL-10R2 and initiation of the ternary complex signal transduction cascade. The duck IL-10R1 (duIL-10R1) cDNA was obtained by using RT-PCR and 5'RACE. The deduced 574 amino acid protein has an amino acid identity of 62%, 27% and 28% with chicken, mouse and human IL-10R1, respectively. Comparison of the duIL-10R1 cDNA with duck genomic sequences revealed a seven exon-six intron structure of the duck IL-10R1 gene that shares a similar size with the respective exons 1-7 of the chicken and human IL-10R1 genes, but the avian genes are more compact. Promoter analysis identified putative binding sites for regulatory elements such as CCAAT enhancer binding protein-α, specificity protein 1 (Sp1), nuclear factor 1 (NF1), transcriptional regulatory protein Oct-1, nuclear factor (NF) κB and interferon-stimulated gene factor-3 (ISGF-3). A canonical TATA box was absent in proximity of the transcription initiation site, but a CpG island was present. Sequence analysis of the predicted duIL-10R1 protein revealed characteristic features of class-II cytokine receptors (CFR2) family members and a considerable degree of conservation of residues implicated in ligand binding across higher vertebrates. The predicted secondary structure of the duIL-10R1 extracellular domain is compatible with the two-subdomain structure of the human IL-10R1 protein established by its crystal structure. The 3D model structure shows conservation of the positions of conserved contact residues within four of the five ligand-binding loops. Within the cytoplasmic domain, residues implicated in signal transduction were conserved including two redundant peptide motifs GYXXQ essential for recruitment and activation of STAT3. DuIL-10R1 mRNA expression was most abundant in spleen, thymus, peripheral blood mononuclear cells (PBMCs) and lung. Mitogen stimulation of PBMCs transiently increased duIL-10R1 mRNA expression. Our observations suggest significant evolutionary conservation of the IL-10R1 genomic organization, protein structure and receptor function through the JAK/STAT signalling pathway across higher vertebrates.

Immunoglobulin genetics and antibody responses to influenza in ducks

The role of the duck as the natural host and reservoir of influenza and efforts to vaccinate ducks during recent outbreaks of avian influenza has renewed interest in the duck antibody response. Ducks have unique antibody structures and expression, with consequences for their function. Aspects of immunoglobulin genetics, gene expression, and antibody function will be reviewed in the context of the duck immune response to influenza. Ducks have three immunoglobulin isotypes, IgM, IgA and IgY in translocon arrangement. The order of heavy chain genes in the locus is unusual, IGHM, IGHA and IGHY, with IGHA in inverse transcriptional orientation. IgH and IgL gene rearrangement in ducks involves limited V, (D) and J element recombination and diversity is generated by gene conversion from pseudogenes. IgY, the functional equivalent of IgG, is produced in two secreted forms, a full-length form and one lacking the third and fourth C region domains, which predominates later in the immune response and lacks the biological effector functions of IgG. The unusual features of duck antibodies may contribute to weak antibody responses and the perpetuation of the virus in this animal reservoir.