Heterosubtypic protection against avian influenza virus by live attenuated and chimeric norovirus P-particle-M2e vaccines in chickens

Diversity and Complexity of Internally Deleted Viral Genomes in Influenza A Virus Subpopulations with Enhanced Interferon-Inducing Phenotypes

Influenza A virus (IAV) populations harbor large subpopulations of defective-interfering particles characterized by internally deleted viral genomes. These internally deleted genomes have demonstrated the ability to suppress infectivity and boost innate immunity, rendering them promising for therapeutic and immunogenic applications. In this study, we aimed to investigate the diversity and complexity of the internally deleted IAV genomes within a panel of plaque-purified avian influenza viruses selected for their enhanced interferon-inducing phenotypes. Our findings unveiled that the abundance and diversity of internally deleted viral genomes were contingent upon the viral subculture and plaque purification processes. We observed a heightened occurrence of internally deleted genomes with distinct junctions in viral clones exhibiting enhanced interferon-inducing phenotypes, accompanied by additional truncation in the nonstructural 1 protein linker region (NS1Δ76-86). Computational analyses suggest the internally deleted IAV genomes can encode a broad range of carboxy-terminally truncated and intrinsically disordered proteins with variable lengths and amino acid composition. Further research is imperative to unravel the underlying mechanisms driving the increased diversity of internal deletions within the genomes of viral clones exhibiting enhanced interferon-inducing capacities and to explore their potential for modulating cellular processes and immunity.

Development of in ovo-compatible NS1-truncated live attenuated influenza vaccines by modulation of hemagglutinin cleavage and polymerase acidic X frameshifting sites

Emerging avian influenza viruses pose a high risk to poultry production, necessitating the need for more broadly protective vaccines. Live attenuated influenza vaccines offer excellent protective efficacies but their use in poultry farms is discouraged due to safety concerns related to emergence of reassortant viruses. Vaccination of chicken embryos inside eggs (in ovo) induces early immunity in young chicks while reduces the safety concerns related to the use of live vaccines on farms. However, in ovo vaccination using influenza viruses severely affects the egg hatchability. We previously engineered a high interferon-inducing live attenuated influenza vaccine candidate with an enhanced protective efficacy in chickens. Here, we asked whether we could further modify this high interferon-inducing vaccine candidate to develop an in ovo-compatible live attenuated influenza vaccine. We first showed that the enhanced interferon responses induced by the vaccine is not enough to attenuate the virus in ovo. To reduce the pathogenicity of the virus for chicken embryos, we replaced the hemagglutinin cleavage site of the H7 vaccine virus (PENPKTR/GL) with that of the H6-subtype viruses (PQIETR/GL) and disrupted the ribosomal frameshifting site responsible for viral polymerase acidic X protein expression. In ovo vaccination of chickens with up to 10⁵ median egg infectious dose of the modified vaccine had minimal effects on hatchability while protecting the chickens against a heterologous challenge virus at two weeks of age. This study demonstrates that targeted genetic mutations can be applied to further attenuate and enhance the safety of live attenuated influenza vaccines to develop future in ovo vaccines for poultry.

Self-assembled multiepitope nanovaccine based on NoV P particles induces effective and lasting protection against H3N2 influenza virus

Current seasonal influenza vaccines confer only limited coverage of virus strains due to the frequent genetic and antigenic variability of influenza virus (IV). Epitope vaccines that accurately target conserved domains provide a promising approach to increase the breadth of protection; however, poor immunogenicity greatly hinders their application. The protruding (P) domain of the norovirus (NoV), which can self-assemble into a 24-mer particle called the NoV P particle, offers an ideal antigen presentation platform. In this study, a multiepitope nanovaccine displaying influenza epitopes (HMN-PP) was constructed based on the NoV P particle nanoplatform. Large amounts of HMN-PP were easily expressed in Escherichia coli in soluble form. Animal experiments showed that the adjuvanted HMN-PP nanovaccine induced epitope-specific antibodies and haemagglutinin (HA)-specific neutralizing antibodies, and the antibodies could persist for at least three months after the last immunization. Furthermore, HMN-PP induced matrix protein 2 extracellular domain (M2e)-specific antibody-dependent cell-mediated cytotoxicity, CD4+ and CD8+ T-cell responses, and a nucleoprotein (NP)-specific cytotoxic T lymphocyte (CTL) response. These results indicated that the combination of a multiepitope vaccine and self-assembled NoV P particles may be an ideal and effective vaccine strategy for highly variable viruses such as IV and SARS-CoV-2.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s12274-023-5395-6.

Defective Interfering Particles of Influenza Virus and Their Characteristics, Impacts, and Use in Vaccines and Antiviral Strategies: A Systematic Review

Defective interfering particles (DIPs) are particles containing defective viral genomes (DVGs) generated during viral replication. DIPs have been found in various RNA viruses, especially in influenza viruses. Evidence indicates that DIPs interfere with the replication and encapsulation of wild-type viruses, namely standard viruses (STVs) that contain full-length viral genomes. DIPs may also activate the innate immune response by stimulating interferon synthesis. In this review, the underlying generation mechanisms and characteristics of influenza virus DIPs are summarized. We also discuss the potential impact of DIPs on the immunogenicity of live attenuated influenza vaccines (LAIVs) and development of influenza vaccines based on NS1 gene-defective DIPs. Finally, we review the antiviral strategies based on influenza virus DIPs that have been used against both influenza virus and SARS-CoV-2. This review provides systematic insights into the theory and application of influenza virus DIPs.

Expression of Influenza M2e-NP Recombinant Fusion Protein in Escherichia coli BL21 (DE3) and Its Binding to Antibodies

The current influenza vaccines only confer protection against the circulating influenza subtypes, therefore universal vaccines are needed to prevent upcoming influenza outbreaks caused by emerging influenza subtypes. The extracellular domain of influenza A M2 protein (M2e) is highly conserved among different subtypes of influenza A viruses, and it is able to elicit protective immunity against the viruses. The influenza nucleoprotein (NP) was used to display the M2e in this study due to its promising T-cell response and adjuvanticity. The M2e gene was fused to the 5'-end of the NP gene and then cloned into pRSET B vector. The DNA sequencing analysis revealed six point mutations in the M2e-NP fusion gene, including one mutation in the M2e peptide and five mutations in the NP. The mutations were reverted using PCR site-directed mutagenesis. The recombinant plasmids (pRSET B-M2e-NP and pRSET B-mM2e-NP) were introduced into Escherichia coli (E. coli) BL21 (DE3) for protein expression. The mutated and non-mutated proteins were subsequently expressed and named mM2e-NP and M2e-NP, respectively. The expression of mM2e-NP and M2e-NP was not affected by the mutations. The binding of anti-M2e antibody to the purified native mM2e-NP and M2e-NP also remained active. However, when the anti-NP antibody was tested, the signal produced by mM2e-NP was very weak. The results implied that the amino acid changes in the NP had adversely impacted on the conformation of mM2e-NP and subsequently affected the antibody binding. In light of the remarkable antibody binding to the M2e-NP fusion protein, this study highly recommends the potential of M2e-NP as a universal influenza vaccine candidate.

Recent Progress in Recombinant Influenza Vaccine Development Toward Heterosubtypic Immune Response

Flu, a viral infection caused by the influenza virus, is still a global public health concern with potential to cause seasonal epidemics and pandemics. Vaccination is considered the most effective protective strategy against the infection. However, given the high plasticity of the virus and the suboptimal immunogenicity of existing influenza vaccines, scientists are moving toward the development of universal vaccines. An important property of universal vaccines is their ability to induce heterosubtypic immunity, i.e., a wide immune response coverage toward different influenza subtypes. With the increasing number of studies and mounting evidence on the safety and efficacy of recombinant influenza vaccines (RIVs), they have been proposed as promising platforms for the development of universal vaccines. This review highlights the current progress and advances in the development of RIVs in the context of heterosubtypic immunity induction toward universal vaccine production. In particular, this review discussed existing knowledge on influenza and vaccine development, current hemagglutinin-based RIVs in the market and in the pipeline, other potential vaccine targets for RIVs (neuraminidase, matrix 1 and 2, nucleoprotein, polymerase acidic, and basic 1 and 2 antigens), and deantigenization process. This review also provided discussion points and future perspectives in looking at RIVs as potential universal vaccine candidates for influenza.

Protective immunity induced by oral vaccination with a recombinant Lactococcus lactis vaccine against H5Nx in chickens

BACKGROUND

The development of an influenza vaccine for poultry that provides broadly protective immunity against influenza H5Nx viruses is a challenging goal.

RESULTS

Lactococcus lactis (L. lactis)/pNZ8149-HA1-M2 expressing hemagglutinin-1 (HA1) of A/chicken/Vietnam/NCVD-15A59/2015 (H5N6) and the conserved M2 gene of A/Vietnam/1203/2004 (H5N1) was generated. L. lactis/pNZ8149-HA1-M2 could induce significant humoral, mucosal and cell-mediated immune responses, as well as neutralization antibodies. Importantly, L. lactis/pNZ8149-HA1-M2 could prevent disease symptoms without significant weight loss and confer protective immunity in a chicken model against lethal challenge with divergent influenza H5Nx viruses, including H5N6 and H5N1.

CONCLUSIONS

L. lactis/pNZ8149-HA1-M2 can serve as a promising vaccine candidate in poultry industry for providing protection against H5Nx virus infection in the field application.

H5 cleavage-site peptide vaccine protects chickens from lethal infection by highly pathogenic H5 avian influenza viruses

Highly pathogenic H5Nx avian influenza viruses constantly threaten the poultry industry and humans and have pandemic potential. These viruses continuously evolve, requiring a universal vaccine to protect chickens from members of diverse clades. The purpose of this study was to develop an H5 cleavage-site peptide vaccine containing polybasic amino acids (RRRK) to completely protect chickens from H5N6, H5N8, and H5N1 avian influenza viruses. Chickens were immunized with various doses of a keyhole limpet hemocyanin (KLH)-conjugated H5 cleavage-site peptide vaccine containing RRRK. The effect of RRRK was evaluated by comparing the survival rates of chickens immunized with vaccines either containing or lacking RRRK. The ability of the RRRK-containing vaccine to confer long-term protective immunity was also assessed. We found that protection was dependent on the number of antigens in the vaccine containing RRRK. Chickens immunized intramuscularly with two doses of 5 μg of the vaccine containing RRRK were completely protected, but those immunized with fewer than two doses of 3 or 1 μg were not protected. Chickens immunized with the vaccine lacking RRRK were not protected, suggesting the importance of the polybasic amino acids in conferring immunity. Our results suggest that conserved H5 cleavage-site peptides with polybasic amino acids may be a potential universal vaccine to protect chickens from various emerging clades of H5Nx avian influenza viruses.

Influenza A virus infection in turkeys induces respiratory and enteric bacterial dysbiosis correlating with cytokine gene expression

Turkey respiratory and gut microbiota play important roles in promoting health and production performance. Loss of microbiota homeostasis due to pathogen infection can worsen the disease or predispose the bird to infection by other pathogens. While turkeys are highly susceptible to influenza viruses of different origins, the impact of influenza virus infection on turkey gut and respiratory microbiota has not been demonstrated. In this study, we investigated the relationships between low pathogenicity avian influenza (LPAI) virus replication, cytokine gene expression, and respiratory and gut microbiota disruption in specific-pathogen-free turkeys. Differential replication of two LPAI H5N2 viruses paralleled the levels of clinical signs and cytokine gene expression. During active virus shedding, there was significant increase of ileal and nasal bacterial contents, which inversely corresponded with bacterial species diversity. Spearman’s correlation tests between bacterial abundance and local viral titers revealed that LPAI virus-induced dysbiosis was strongest in the nasal cavity followed by trachea, and weakest in the gut. Significant correlations were also observed between cytokine gene expression levels and relative abundances of several bacteria in tracheas of infected turkeys. For example, interferon γ/λ and interleukin-6 gene expression levels were correlated positively with Staphylococcus and Pseudomonas abundances, and negatively with Lactobacillus abundance. Overall, our data suggest a potential relationship where bacterial community diversity and enrichment or depletion of several bacterial genera in the gut and respiratory tract are dependent on the level of LPAI virus replication. Further work is needed to establish whether respiratory and enteric dysbiosis in LPAI virus-infected turkeys is a result of host immunological responses or other causes such as changes in nutritional uptake.

M2e-Based Influenza Vaccines with Nucleoprotein: A Review

Discovery of conserved antigens for universal influenza vaccines warrants solutions to a number of concerns pertinent to the currently licensed influenza vaccines, such as annual reformulation and mismatching with the circulating subtypes. The latter causes low vaccine efficacies, and hence leads to severe disease complications and high hospitalization rates among susceptible and immunocompromised individuals. A universal influenza vaccine ensures cross-protection against all influenza subtypes due to the presence of conserved epitopes that are found in the majority of, if not all, influenza types and subtypes, e.g., influenza matrix protein 2 ectodomain (M2e) and nucleoprotein (NP). Despite its relatively low immunogenicity, influenza M2e has been proven to induce humoral responses in human recipients. Influenza NP, on the other hand, promotes remarkable anti-influenza T-cell responses. Additionally, NP subunits are able to assemble into particles which can be further exploited as an adjuvant carrier for M2e peptide. Practically, the T-cell immunodominance of NP can be transferred to M2e when it is fused and expressed as a chimeric protein in heterologous hosts such as Escherichia coli without compromising the antigenicity. Given the ability of NP-M2e fusion protein in inducing cross-protective anti-influenza cell-mediated and humoral immunity, its potential as a universal influenza vaccine is therefore worth further exploration.

Formulation of HBsAg in Montanide ISA 51VG adjuvant: Immunogenicity study and monitoring long-lived humoral immune responses

Montanide ISA 51VG adjuvant has been approved for human clinical application and stimulates cellular and humoral immune responses. Here, HBsAg was formulated in Montanide ISA51VG adjuvant to compare its potency with the Fendrix and HBsAg-alum vaccines. In particular, the long-term humoral response was assessed up to 220 days after the final immunization. BALB/c mice were allocated into six groups. Treatment groups were injected with HBsAg-Montanide ISA51VG, the Fendrix and commercial HBsAg-alum, respectively. Montanide ISA51 VG, Alum and PBS injected mice were considered as control groups. Mice were immunized three times with 2-week intervals on days 0, 14 and 28 by subcutaneous injection. Lymphocyte proliferation was assessed with the BrdU method. IFN-γ, IL-2 and IL-4 cytokines, specific total IgG and IgG1/IgG2a isotypes were assessed using ELISA. The HBsAg-Montanide ISA51VG vaccine resulted in a significant increase in lymphocyte proliferation versus HBsAg-alum and higher IL-2 cytokine production versus the Fendrix. Comparable IL-4 and IFN-γ cytokines responses were observed for these vaccines. Following the first immunization, IgG increased more in HBs-Montanide 51VG group versus the HBs-alum group, while after the second and third shots comparable responses were observed in comparison to the HBs-alum group. Monitoring for 220 days after the final vaccination showed the superiority of HBsAg-Montanide ISA 51VG vaccine versus HBsAg-alum and even the Fendrix vaccine in the induction of long-term antibody responses. This study suggests that HBsAg-Montanide ISA51VG as a novel vaccine formulation can trigger both cellular and long-lasting humoral immune responses more efficiently than conventional HBsAg vaccines.

Viral Subpopulation Screening Guides in Designing a High Interferon-Inducing Live Attenuated Influenza Vaccine by Targeting Rare Mutations in NS1 and PB2 Proteins

Influenza A viruses continue to circulate among wild birds and poultry worldwide, posing constant pandemic threats to humans. Effective control of emerging influenza viruses requires new broadly protective vaccines. Live attenuated influenza vaccines with truncations in nonstructural protein 1 (NS1) have shown broad protective efficacies in birds and mammals, which correlate with the ability to induce elevated interferon responses in the vaccinated hosts. Given the extreme diversity of influenza virus populations, we asked if we could improve an NS1-truncated live attenuated influenza vaccine developed for poultry (PC4) by selecting viral subpopulations with enhanced interferon-inducing capacities. Here, we deconstructed a de novo population of PC4 through plaque isolation, created a large library of clones, and assessed their interferon-inducing phenotypes. While most of the clones displayed the parental interferon-inducing phenotype in cell culture, few clones showed enhanced interferon-inducing phenotypes in cell culture and chickens. The enhanced interferon-inducing phenotypes were linked to either a deletion in NS1 (NS1Δ76-86) or a substitution in polymerase basic 2 protein (PB2-D309N). The NS1Δ76-86 deletion disrupted the putative eukaryotic translation initiation factor 4GI-binding domain and promoted the synthesis of biologically active interferons. The PB2-D309N substitution enhanced the early transcription of interferon mRNA, revealing a novel role for the 309D residue in suppression of interferon responses. We combined these mutations to engineer a novel vaccine candidate that induced additive amounts of interferons and stimulated protective immunity in chickens. Therefore, viral subpopulation screening approaches can guide the design of live vaccines with strong immunostimulatory properties.IMPORTANCE Effectiveness of NS1-truncated live attenuated influenza vaccines relies heavily on their ability to induce elevated interferon responses in vaccinated hosts. Influenza viruses contain diverse particle subpopulations with distinct phenotypes. We show that live influenza vaccines can contain underappreciated subpopulations with enhanced interferon-inducing phenotypes. The genomic traits of such virus subpopulations can be used to further improve the efficacy of the current live vaccines.

Immunization of turkeys with a DNA vaccine expressing the haemagglutinin gene of low pathogenic avian influenza virus subtype H9N2

Low pathogenic avian influenza H9N2 is still circulating in the Middle East causing respiratory manifestations and severe economic losses in poultry. In the present study, an H9 plasmid-based DNA vaccine targeting the HA gene of H9N2 A/CK/Egypt/SCU8/2014 was developed and evaluated in turkeys. The full length of HA was cloned into vector plasmids under the control of a cytomegalovirus promoter. The in-vitro expression of the recombinant HA was demonstrated in HeLa cells transfected with the plasmids pVAX1-H9 or pCR-H9 using western blot and Immunofluorescent assay (IFA). The efficacy of pVAX-H9 and pCR- H9, naked or saponin-adjuvanted, was evaluated in turkey poults at 3 weeks and challenged with A/CK/Egypt/SCU8/2014 (10⁶ EID₅₀/bird at 3 weeks post-vaccination. The efficacy was assesses based on virus shedding, oropharyngeal and cloacal, as well as seroconversion using haemagglutination inhibition (HI) test. All immunized birds showed high HI antibody titers (7-8 log₂) at 3 weeks post-vaccination. None of the birds vaccinated with naked or saponin-adjuvanted pVAX-H9 or pCR-H9 showed any clinical signs. The pVAX-H9 and pCR-H9 alone did not prevent cloacal and oropharyngeal virus shedding, however, saponin-adjuvanted pVAX1-H9 and pCR-H9 prevented cloacal and oropharyngeal virus shedding at 3 and 5 days post challenge, respectively. In conclusion, DNA vaccination with pVAX1-H9 and pCR-H9 could protect turkey from the H9N2 virus, but vaccination regimes need to be improved.

Protective immunity against influenza virus challenge by norovirus P particle-M2e and HA2-AtCYN vaccines in chickens

Development of a broadly reactive influenza vaccine that can provide protection against emerging type A influenza viruses is a big challenge. We previously demonstrated that a vaccine displaying the extracellular domain of the matrix protein 2 (M2e) on the surface loops of norovirus P-particle (M2eP) can partially protect chickens against several subtypes of avian influenza viruses. In the current study, a chimeric vaccine containing a conserved peptide from the subunit 2 of hemagglutinin (HA) glycoprotein (HA2) and Arabidopsis thaliana cyanase protein (AtCYN) (HA2-AtCYN vaccine) was evaluated in 2-weeks-old chickens. Depending on the route of administration, the HA2-AtCYN vaccine was shown to induce various levels of HA2-specific IgA in tears as well as serum IgG, which were associated with partial protection of chickens against tracheal shedding of a low pathogenicity H5N2 challenge virus. Furthermore, intranasal administration with a combination of HA2-AtCYN and M2eP vaccines resulted in enhanced protection compared to each vaccine alone. Simultaneous intranasal administration of the vaccines did not interfere with secretory IgA induction by each vaccine. Additionally, significantly higher M2eP-specific proliferative responses were observed in peripheral blood mononuclear cells of all M2eP-vaccinated groups when compared with the mock-vaccinated group. Although tripling the number of M2e copies did not enhance the protective efficacy of the chimeric vaccine, it significantly reduced immunodominance of P-particle epitopes without affecting the robustness of M2e-specific immune responses. Taken together, our data suggests that mucosal immunization of chickens with combinations of mechanistically different cross-subtype-conserved vaccines has the potential to enhance the protective efficacy against influenza virus challenge.

Influenza A Virus Subpopulations and Their Implication in Pathogenesis and Vaccine Development

The concept of influenza A virus (IAV) subpopulations emerged approximately 75 years ago, when Preben von Magnus described "incomplete" virus particles that interfere with the replication of infectious virus. It is now widely accepted that infectious particles constitute only a minor portion of biologically active IAV subpopulations. The IAV quasispecies is an extremely diverse swarm of biologically and genetically heterogeneous particle subpopulations that collectively influence the evolutionary fitness of the virus. This review summarizes the current knowledge of IAV subpopulations, focusing on their biologic and genomic diversity. It also discusses the potential roles IAV subpopulations play in virus pathogenesis and live attenuated influenza vaccine development.