CpG Oligodeoxynucleotides Facilitate Delivery of Whole Inactivated H9N2 Influenza Virus via Transepithelial Dendrites of Dendritic Cells in Nasal Mucosa

Pathogen-Mimicking Nanoparticles Based on Rigid Nanomaterials as an Efficient Subunit Vaccine Delivery System for Intranasal Immunization

Despite the safety profile of subunit vaccines, the inferior immunogenicity hinders their application in the nasal cavity. This study introduces a novel antigen delivery and adjuvant system utilizing mucoadhesive chitosan-catechol (Chic) on silica spiky nanoparticles (Ssp) to enhance immunity through multiple mechanisms. The Chic functionalizes the Ssp surface and incorporates with SARS-CoV-2 spike protein receptor-binding domain (RBD) and toll-like receptor (TLR)9 agonist unmethylated cytosine-guanine (CpG) motif, forming uniform virus-like nanoparticles (Ssp-Chic-RBD-CpG) via electrostatic and covalent interactions. Ssp-Chic-RBD-CpG, mimicking the morphology and function of inactive virions, effectively prolongs the retention time of RBD in the nasal mucosa by 3.92-fold compared to RBD alone, enhances the maturation of dendritic cells (DCs), and facilitates the antigen trafficking to the draining lymph nodes, which subsequently induces a stronger mucosal immunity. Mechanistically, the enhanced chemokine chemokine (C-C motif) ligand 20 (CCL20)-driven DCs recruitment and maturation by Ssp-Chic-RBD-CpG are evidenced by a cell co-culture model. In addition, the overexpression of TLR4/9 and activation of MYD88/NF-κB signaling pathway in activation of DCs are observed. Proof of principle is obtained for RBD, but similar delivery mechanisms can be applied in other protein-based subunit vaccines as well when intranasal administration is needed.

Advax-SM™-Adjuvanted COBRA (H1/H3) Hemagglutinin Influenza Vaccines

Adjuvants enhance immune responses stimulated by vaccines. To date, many seasonal influenza vaccines are not formulated with an adjuvant. In the present study, the adjuvant Advax-SM™ was combined with next generation, broadly reactive influenza hemagglutinin (HA) vaccines that were designed using a computationally optimized broadly reactive antigen (COBRA) methodology. Advax-SM™ is a novel adjuvant comprising inulin polysaccharide and CpG55.2, a TLR9 agonist. COBRA HA vaccines were combined with Advax-SM™ or a comparator squalene emulsion (SE) adjuvant and administered to mice intramuscularly. Mice vaccinated with Advax-SM™ adjuvanted COBRA HA vaccines had increased serum levels of anti-influenza IgG and IgA, high hemagglutination inhibition activity against a panel of H1N1 and H3N2 influenza viruses, and increased anti-influenza antibody secreting cells isolated from spleens. COBRA HA plus Advax-SM™ immunized mice were protected against both morbidity and mortality following viral challenge and, at postmortem, had no detectable lung viral titers or lung inflammation. Overall, the Advax-SM™-adjuvanted COBRA HA formulation provided effective protection against drifted H1N1 and H3N2 influenza viruses.

Low-Temperature Adaptive Single-Atom Iron Nanozymes against Viruses in the Cold Chain

Outbreaks of viral infectious diseases, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV), pose a great threat to human health. Viral spread is accelerated worldwide by the development of cold chain logistics; Therefore, an effective antiviral approach is required. In this study, it is aimed to develop a distinct antiviral strategy using nanozymes with low-temperature adaptability, suitable for cold chain logistics. Phosphorus (P) atoms are added to the remote counter position of Fe-N-C center to prepare FeN4P2-single-atom nanozymes (SAzymes), exhibiting lipid oxidase (OXD)-like activity at cold chain temperatures (-20, and 4 °C). This feature enables FeN4P2-SAzymes to disrupt multiple enveloped viruses (human, swine, and avian coronaviruses, and H1-H11 subtypes of IAV) by catalyzing lipid peroxidation of the viral lipid envelope. Under the simulated conditions of cold chain logistics, FeN4P2-SAzymes are successfully applied as antiviral coatings on outer packaging and personal protective equipment; Therefore, FeN4P2-SAzymes with low-temperature adaptability and broad-spectrum antiviral properties may serve as key materials for developing specific antiviral approaches to interrupt viral transmission through the cold chain.

A SARS-CoV-2 RBD vaccine fused to the chemokine MIP-3α elicits sustained murine antibody responses over 12 months and enhanced lung T-cell responses

Background

Previous studies have demonstrated enhanced efficacy of vaccine formulations that incorporate the chemokine macrophage inflammatory protein 3α (MIP-3α) to direct vaccine antigens to immature dendritic cells. To address the reduction in vaccine efficacy associated with a mutation in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants, we have examined the ability of receptor-binding domain vaccines incorporating MIP-3α to sustain higher concentrations of antibody when administered intramuscularly (IM) and to more effectively elicit lung T-cell responses when administered intranasally (IN).

Methods

BALB/c mice aged 6-8 weeks were immunized intramuscularly or intranasally with DNA vaccine constructs consisting of the SARS-CoV-2 receptor-binding domain alone or fused to the chemokine MIP-3α. In a small-scale (n = 3/group) experiment, mice immunized IM with electroporation were followed up for serum antibody concentrations over a period of 1 year and for bronchoalveolar antibody levels at the termination of the study. Following IN immunization with unencapsulated plasmid DNA (n = 6/group), mice were evaluated at 11 weeks for serum antibody concentrations, quantities of T cells in the lungs, and IFN-γ- and TNF-α-expressing antigen-specific T cells in the lungs and spleen.

Results

At 12 months postprimary vaccination, recipients of the IM vaccine incorporating MIP-3α had significantly, approximately threefold, higher serum antibody concentrations than recipients of the vaccine not incorporating MIP-3α. The area-under-the-curve analyses of the 12-month observation interval demonstrated significantly greater antibody concentrations over time in recipients of the MIP-3α vaccine formulation. At 12 months postprimary immunization, only recipients of the fusion vaccine had concentrations of serum-neutralizing activity deemed to be effective. After intranasal immunization, only recipients of the MIP-3α vaccine formulations developed T-cell responses in the lungs significantly above those of PBS controls. Low levels of serum antibody responses were obtained following IN immunization.

Conclusion

Although requiring separate IM and IN immunizations for optimal immunization, incorporating MIP-3α in a SARS-CoV-2 vaccine construct demonstrated the potential of a stable and easily produced vaccine formulation to provide the extended antibody and T-cell responses that may be required for protection in the setting of emerging SARS-CoV-2 variants. Without electroporation, simple, uncoated plasmid DNA incorporating MIP-3α administered intranasally elicited lung T-cell responses.

Self-Assembled Virus-Like Particle Vaccines via Fluorophilic Interactions Enable Infection Mimicry and Immune Protection

Influenza epidemics persistently threaten global health. Vaccines based on virus-like particles (VLPs), which resemble the native conformation of viruses, have emerged as vaccine candidates. However, the production of VLPs via genetic engineering remains constrained by challenges such as low yields, high costs, and being time consuming. In this study, a novel VLP platform is developed that could mimic infection and confer influenza protection through fluorination-driven self-assembly. The VLPs closely mimick the key steps in viral infection including dendritic cell (DC) attachment and pH-responsive endo-lysosomal escape, which enhances DC maturation and antigen cross-presentation. It is also observed that the VLPs migrate from the injection site to the draining lymph nodes efficiently. Immunization with VLPs triggers both Th1 and Th2 cellular responses, thereby inducing an improved CD8+ T cell response along with strong antigen-specific antibody responses. In several infected mouse models, VLP vaccines ameliorate weight loss, lung virus titers, pulmonary pathologies, and confer full protection against H1N1, H6N2, H9N2, and mixed influenza viruses. Therefore, the results support the potential of VLPs as an effective influenza vaccine with improved immune potency against infection. A methodology to generate VLPs based on fluorophilic interactions, which can be a general approach for development of pathogenic VLPs, is reported.

Utilizing nanozymes for combating COVID-19: advancements in diagnostics, treatments, and preventative measures

The emergence of human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses significant challenges to global public health. Despite the extensive efforts of researchers worldwide, there remains considerable opportunities for improvement in timely diagnosis, specific treatment, and effective vaccines for SARS-CoV-2. This is due, in part, to the large number of asymptomatic carriers, rapid virus mutations, inconsistent confinement policies, untimely diagnosis and limited clear treatment plans. The emerging of nanozymes offers a promising approach for combating SARS-CoV-2 due to their stable physicochemical properties and high surface areas, which enable easier and multiple nano-bio interactions in vivo. Nanozymes inspire the development of sensitive and economic nanosensors for rapid detection, facilitate the development of specific medicines with minimal side effects for targeted therapy, trigger defensive mechanisms in the form of vaccines, and eliminate SARS-CoV-2 in the environment for prevention. In this review, we briefly present the limitations of existing countermeasures against coronavirus disease 2019 (COVID-19). We then reviewed the applications of nanozyme-based platforms in the fields of diagnostics, therapeutics and the prevention in COVID-19. Finally, we propose opportunities and challenges for the further development of nanozyme-based platforms for COVID-19. We expect that our review will provide valuable insights into the new emerging and re-emerging infectious pandemic from the perspective of nanozymes.

Bidirectionally Regulating Viral and Cellular Ferroptosis with Metastable Iron Sulfide Against Influenza Virus

Influenza virus with numerous subtypes and frequent variation limits the development of high-efficacy and broad-spectrum antiviral strategy. Here, a novel multi-antiviral metastable iron sulfides (mFeS) against various influenza A/B subtype viruses is developed. This work finds that mFeS induces high levels of lipid peroxidation and •OH free radicals in the conservative viral envelope, which depends on Fe2+ . This phenomenon, termed as a viral ferroptosis, results in the loss of viral infectibility and pathogenicity in vitro and in vivo, respectively. Furthermore, the decoction of mFeS (Dc(mFeS)) inhibits cellular ferroptosis-dependent intracellular viral replication by correcting the virus-induced reprogrammed sulfur metabolism, a conserved cellular metabolism. Notably, personal protective equipment (PPE) that is loaded with mFeS provides good antiviral protection. Aerosol administration of mFeS combined with the decoction (mFeS&Dc) has a potential therapeutic effect against H1N1 lethal infection in mice. Collectively, mFeS represents an antiviral alternative with broad-spectrum activity against intracellular and extracellular influenza virus.

Pulmonary Application of Novel Antigen-Loaded Chitosan Nano-Particles Co-Administered with the Mucosal Adjuvant C-Di-AMP Resulted in Enhanced Immune Stimulation and Dose Sparing Capacity

The most successful medical intervention for preventing infectious diseases is still vaccination. This effective strategy has resulted in decreased mortality and extended life expectancy. However, there is still a critical need for novel vaccination strategies and vaccines. Antigen cargo delivery by nanoparticle-based carriers could promote superior protection against constantly emerging viruses and subsequent diseases. This should be sustained by the induction of vigorous cellular and humoral immunity, capable of acting both at the systemic and mucosal levels. Induction of antigen-specific responses at the portal of entry of pathogens is considered an important scientific challenge. Chitosan, which is widely regarded as a biodegradable, biocompatible and non-toxic material for functionalized nanocarriers, as well as having adjuvant activity, enables antigen administration via less-invasive mucosal routes such as sublingual or pulmonic application route. In this proof of principle study, we evaluate the efficacy of chitosan nanocarriers loaded with the model antigen Ovalbumin (OVA) co-administrated with the STING agonist bis-(3',5')-cyclic dimeric adenosine monophosphate (c-di-AMP) given by pulmonary route. Here, BALB/c mice were immunized with four doses of the formulation that stimulates enhanced antigen-specific IgG titers in sera. In addition, this vaccine formulation also promotes a strong Th1/Th17 response characterized by high secretion of IFN-γ, IL-2 and IL-17, as well as induction of CD8⁺ T cells. Furthermore, the novel formulation exhibited strong dose-sparing capacity, enabling a 90% reduction of the antigen concentration. Altogether, our results suggest that chitosan nanocarriers, in combination with the mucosal adjuvant c-di-AMP, are a promising technology platform for the development of innovative mucosal vaccines against respiratory pathogens (e.g., Influenza or RSV) or for therapeutic vaccines.

PA-X protein of H9N2 subtype avian influenza virus suppresses the innate immunity of chicken bone marrow-derived dendritic cells

H9N2 subtype avian influenza (AI) is an infectious disease associated with immunosuppression in poultry. Here, the regulation function of PA-X protein was determined on the host innate immune response of H9N2-infected chicken bone marrow-derived DCs (chBM-DCs). Based on 2 mutated viruses expressing PA-X protein (rTX) or deficient PA-X protein (rTX-FS), and the established culture system of chBM-DCs, results showed PA-X protein inhibited viral replication in chBM-DCs but not in non-immune chicken cells (DF-1). Moreover, PA-X protein downregulated the expression of phenotypic markers (CD40, CD86, and MHCII) and proinflammatory cytokine (IL-12 and IL-1β) of chBM-DCs. The mixed lymphocyte reaction between chBM-DCs and chicken T cells showed PA-X protein significantly decreased H9N2-infected chBM-DCs to induce T cell proliferation, implying a suppression of the DC-induced downstream T cell response. Taken together, these findings indicated that PA-X protein is a key viral protein to help H9N2 subtype AIVs escape the innate immunity of chBM-DCs.

PA-X Protein of H1N1 Subtype Influenza Virus Disables the Nasal Mucosal Dendritic Cells for Strengthening Virulence

PA-X protein arises from a ribosomal frameshift in the PA of influenza A virus (IAV). However, the immune regulatory effect of the PA-X protein of H1N1 viruses on the nasal mucosal system remains unclear. Here, a PA-X deficient H1N1 rPR8 viral strain (rPR8-△PAX) was generated and its pathogenicity was determined. The results showed that PA-X was a pro-virulence factor in mice. Furthermore, it reduced the ability of H1N1 viruses to infect dendritic cells (DCs), the regulator of the mucosal immune system, but not non-immune cells (DF-1 and Calu-3). Following intranasal infection of mice, CCL20, a chemokine that monitors the recruitment of submucosal DCs, was downregulated by PA-X, resulting in an inhibition of the recruitment of CD11b+ DCs to submucosa. It also attenuated the migration of CCR7+ DCs to cervical lymph nodes and inhibited DC maturation with low MHC II and CD40 expression. Moreover, PA-X suppressed the maturation of phenotypic markers (CD80, CD86, CD40, and MHC II) and the levels of secreted pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) while enhancing endocytosis and levels of anti-inflammatory IL-10 in vitro, suggesting an impaired maturation of DCs that the key step for the activation of downstream immune responses. These findings suggested the PA-X protein played a critical role in escaping the immune response of nasal mucosal DCs for increasing the virulence of H1N1 viruses.

Status and Challenges for Vaccination against Avian H9N2 Influenza Virus in China

In China, H9N2 avian influenza virus (AIV) has become widely prevalent in poultry, causing huge economic losses after secondary infection with other pathogens. Importantly, H9N2 AIV continuously infects humans, and its six internal genes frequently reassort with other influenza viruses to generate novel influenza viruses that infect humans, threatening public health. Inactivated whole-virus vaccines have been used to control H9N2 AIV in China for more than 20 years, and they can alleviate clinical symptoms after immunization, greatly reducing economic losses. However, H9N2 AIVs can still be isolated from immunized chickens and have recently become the main epidemic subtype. A more effective vaccine prevention strategy might be able to address the current situation. Herein, we analyze the current status and vaccination strategy against H9N2 AIV and summarize the progress in vaccine development to provide insight for better H9N2 prevention and control.

An influenza virus vector candidate vaccine stably expressing SARS-CoV-2 receptor-binding domain produces high and long-lasting neutralizing antibodies in mice

Viral infectious pathogens, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus, can cause extremely high infection rates and mortality in humans. Therefore, it is urgent to develop an effective vaccine against coronavirus and influenza virus infection. Herein, we used the influenza virus as a vector to express the SARS-CoV-2 spike receptor-binding domain (RBD) and hemagglutinin-esterase-fusion (HEF) protein of the influenza C virus. We then evaluated the feasibility and effectiveness of this design strategy through experiments in vitro and in vivo. The results showed that the chimeric viruses could stably express the HEF protein and the SARS-CoV-2 spike RBD at a high level. BALB/c mice, infected with the chimeric virus, exhibited mild clinical symptoms, yet produced high specific antibody levels against RBD and HEF, including neutralizing antibodies. Importantly, high neutralizing antibodies could be retained in the sera of mice for at least 20 weeks. Altogether, our data provided a new strategy for developing safe and effective COVID-19 and influenza virus vaccines.

Riboflavin as a Mucosal Adjuvant for Nasal Influenza Vaccine

Intranasal immunization with whole inactivated virus (WIV) is an important strategy used for influenza prevention and control. However, a powerful mucosal adjuvant is required to improve nasal vaccine efficacy. Riboflavin, as a food additive with the advantages of being safe and low-cost, widely exists in living organisms. In this paper, the mucosal adjuvant function of riboflavin was studied. After intranasal immunization with H1N1 WIV plus riboflavin in mice, we found that the mucosal immunity based on the secretory IgA (sIgA) levels in the nasal cavity, trachea, and lung were strongly enhanced compared with H1N1 WIV alone. Meanwhile, the IgG, IgG1, and IgG2a levels in serum also showed a high upregulation and a decreased ratio of IgG1/IgG2a, which implied a bias in the cellular immune response. Moreover, riboflavin strongly improved the protection level of H1N1 inactivated vaccine from a lethal influenza challenge. Furthermore, riboflavin was found to possess the capacity to induce dendritic cell (DC) phenotypic (MHCII, CD40, CD80, and CD86) and functional maturation, including cytokine secretion (TNF-α, IL-1β, IL-12p70, and IL-10) and the proliferation of allogeneic T cells. Lastly, we found that the DC maturation induced by riboflavin was dependent on the activation of the mitogen-activated protein kinase (MAPK) signaling pathway, which plays an important role in immune regulation. Therefore, riboflavin is expected to be developed as an alternative mucosal adjuvant for influenza nasal vaccine application.

Bacillus subtilis Spore-Trained Dendritic Cells Enhance the Generation of Memory T Cells via ICAM1

Immunological memory is a cardinal feature of the immune system. The intestinal mucosa is the primary exposure and entry site of infectious organisms. For an effective and long-lasting safeguard, a robust immune memory system is required, especially by the mucosal immunity. It is well known that tissue-resident memory T cells (Trms) provide a first response against infections reencountered at mucosal tissues surfaces, where they accelerate pathogen clearance. However, their function in intestinal immunization remains to be investigated. Here, we report enhanced local mucosal and systemic immune responses through oral administration of H9N2 influenza whole inactivated virus (H9N2 WIV) plus Bacillus subtilis spores. Subsequently, H9N2 WIV plus spores led to the generation of CD103⁺ CD69⁺ Trms, which were independent of circulating T cells during the immune period. Meanwhile, we also found that Bacillus subtilis spores could stimulate Acrp30 expression in 3T3-L1 adipocytes. Moreover, spore-stimulated adipocyte supernatant also upregulated the expression of intercellular adhesion molecule-1 (ICAM1) in dendritic cells (DCs). Furthermore, the proportion of HA-tetramer⁺ cells was severely curtailed upon suppressed ICAM1 expression, which also depended on HA-loaded DCs. Taken together, our data demonstrated that spore-promoted H9N2 WIV induced an immune response by enhancing Trms populations, which were associated with the activation of ICAM1 in DCs.

H5N1 avian influenza virus without 80-84 amino acid deletion at the NS1 protein hijacks the innate immune system of dendritic cells for an enhanced mammalian pathogenicity

NS gene is generally considered to be related to the virulence of highly pathogenic avian influenza virus (AIV). In recent years, the strains with five amino acids added to the 80-84 positions of the NS1 protein have become prevalent in H5N1 subtype AIVs isolated from mammals. However, the pathogenicity and mechanism of this pattern in mammals remain unclear. In this study, H5N1 subtype AIVs without 80-84 amino acids of the NS1 protein (rNS_Δ5aa ) and a mutant virus (rNS_5aa-R ) with no deletion of 80-84 amino acids of the NS1 protein were used to determine the pathogenicity in mice. Our results showed that rNS_5aa-R possessed an enhanced pathogenicity compared with rNS_Δ5aa in vivo and in vitro, which was accompanied by high expression of IL-6, MX1 and CXCL10 in murine lungs. Furthermore, we found that rNS_5aa-R increased the infection ability to dendritic cells (DCs). Besides, rNS_5aa-R enhanced the expression of phenotypic markers (CD80, CD86, CD40 and MHCII), activation marker CD69, inflammatory cytokines (IL-6, TNF-α and IL-10) and antagonized interferon (IFN-α) of DCs, in comparison to rNS_Δ5aa . Moreover, rNS_5aa-R induced DCs to quickly migrate into nearby cervical lymph nodes by highly upregulating CCR7, and CD86 showed a high expression on the migrated DCs. We also found that rNS_5aa-R -infected DCs significantly promoted the allogeneic CD4⁺ T-cell proliferation. These findings suggested that rNS_5aa-R strongly induced the innate immune response compared with the rNS_Δ5aa , which is conducive to activate a wide immune response, resulting in a strong cytokine storm and causing an enhanced pathogenicity of H5N1 subtype AIVs in mammals.

Mucosal Vaccination for Influenza Protection Enhanced by Catalytic Immune-Adjuvant

Influenza poses a severe threat to global health. Despite the whole inactivated virus (WIV)-based nasal vaccine being a promising strategy for influenza protection, the mucosal barrier is still a bottleneck of the nasal vaccine. Here, a catalytic mucosal adjuvant strategy for an influenza WIV nasal vaccine based on chitosan (CS) functionalized iron oxide nanozyme (IONzyme) is developed. The results reveal that CS-IONzyme increases antigen adhesion to nasal mucosa by 30-fold compared to H1N1 WIV alone. Next, CS-IONzyme facilitates H1N1 WIV to enhance CCL20-driven submucosal dendritic cell (DC) recruitment and transepithelial dendrite(TED) formation for viral uptake via the toll-like receptor(TLR) 2/4-dependent pathway. Moreover, IONzyme with enhanced peroxidase (POD)-like activity by CS modification catalyzes a reactive oxygen species (ROS)-dependent DC maturation, which further enhances the migration of H1N1 WIV-loaded DCs into the draining lymph nodes for antigen presentation. Finally, CS-IONzyme-based nasal vaccine triggers an 8.9-fold increase of IgA-mucosal adaptive immunity in mice, which provides a 100% protection against influenza, while only a 30% protection by H1N1 WIV alone. This work provides an antiviral alternative for designing nasal vaccines based on IONzyme to combat influenza infection.

Catalytic inactivation of influenza virus by iron oxide nanozyme

Influenza poses a severe threat to human health in the world. However, developing a universal anti-viral strategy has remained challenging due to the presence of diverse subtypes as well as its high mutation rate, resulting in antigenic shift and drift. Here we developed an antiviral strategy using iron oxide nanozymes (IONzymes) to target the lipid envelope of the influenza virus. Methods: We evaluated the antiviral activities of our IONzymes using a hemagglutination assay, together with a 50% tissue culture infectious doses (TCID₅₀) method. Lipid peroxidation of the viral envelope was analyzed using a maleic dialdehyde (MDA) assay and transmission electron microscopy (TEM). The neighboring viral proteins were detected by western blotting. Results: We show that IONzymes induce envelope lipid peroxidation and destroy the integrity of neighboring proteins, including hemagglutinin, neuraminidase, and matrix protein 1, causing the inactivation of influenza A viruses (IAVs). Furthermore, we show that our IONzymes possess a broad-spectrum antiviral activity on 12 subtypes of IAVs (H1~H12). Lastly, we demonstrate that applying IONzymes to a facemask improves the ability of virus protection against 3 important subtypes that pose a threat to human, including H1N1, H5N1, and H7N9 subtype. Conclusion: Together, our results clearly demonstrate that IONzymes can catalyze lipid peroxidation of the viral lipid envelope to inactivate enveloped viruses and provide protection from viral transmission and infection.

Innovative Mucosal Vaccine Formulations Against Influenza A Virus Infections

Despite efforts made to develop efficient preventive strategies, infections with influenza A viruses (IAV) continue to cause serious clinical and economic problems. Current licensed human vaccines are mainly inactivated whole virus particles or split-virion administered via the parenteral route. These vaccines provide incomplete protection against IAV in high-risk groups and are poorly/not effective against the constant antigenic drift/shift occurring in circulating strains. Advances in mucosal vaccinology and in the understanding of the protective anti-influenza immune mechanisms suggest that intranasal immunization is a promising strategy to fight against IAV. To date, human mucosal anti-influenza vaccines consist of live attenuated strains administered intranasally, which elicit higher local humoral and cellular immune responses than conventional parenteral vaccines. However, because of inconsistent protective efficacy and safety concerns regarding the use of live viral strains, new vaccine candidates are urgently needed. To prime and induce potent and long-lived protective immune responses, mucosal vaccine formulations need to ensure the immunoavailability and the immunostimulating capacity of the vaccine antigen(s) at the mucosal surfaces, while being minimally reactogenic/toxic. The purpose of this review is to compile innovative delivery/adjuvant systems tested for intranasal administration of inactivated influenza vaccines, including micro/nanosized particulate carriers such as lipid-based particles, virus-like particles and polymers associated or not with immunopotentiatory molecules including microorganism-derived toxins, Toll-like receptor ligands and cytokines. The capacity of these vaccines to trigger specific mucosal and systemic humoral and cellular responses against IAV and their (cross)-protective potential are considered.

Characterization of immunogenicity of avian influenza antigens encapsulated in PLGA nanoparticles following mucosal and subcutaneous delivery in chickens

Mucosal vaccine delivery systems have paramount importance for the induction of mucosal antibody responses. Two studies were conducted to evaluate immunogenicity of inactivated AIV antigens encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs). In the first study, seven groups of specific pathogen free (SPF) layer-type chickens were immunized subcutaneously at 7-days of age with different vaccine formulations followed by booster vaccinations two weeks later. Immune responses were profiled by measuring antibody (Ab) responses in sera and lachrymal secretions of vaccinated chickens. The results indicated that inactivated AIV and CpG ODN co-encapsulated in PLGA NPs (2x NanoAI+CpG) produced higher amounts of hemagglutination inhibiting antibodies compared to a group vaccinated with non-adjuvanted AIV encapsulated in PLGA NPs (NanoAI). The tested adjuvanted NPs-based vaccine (2x NanoAI+CpG) resulted in higher IgG responses in the sera and lachrymal secretions at weeks 3, 4 and 5 post-vaccination when immunized subcutaneously. The incorporation of CpG ODN led to an increase in Ab-mediated responses and was found useful to be included both in the prime and booster vaccinations. In the second study, the ability of chitosan and mannan coated PLGA NPs that encapsulated AIV and CpG ODN was evaluated for inducing antibody responses when delivered via nasal and ocular routes in one-week-old SPF layer-type chickens. These PLGA NPs-based and surface modified formulations induced robust AIV-specific antibody responses in sera and lachrymal secretions. Chitosan coated PLGA NPs resulted in the production of large quantities of lachrymal IgA and IgG compared to mannan coated NPs, which also induced detectable amounts of IgA in addition to the induction of IgG in lachrymal secretions. In both mucosal and subcutaneous vaccination approaches, although NPs delivery enhanced Ab-mediated immunity, one booster vaccination was required to generate significant amount of Abs. These results highlight the potential of NPs-based AIV antigens for promoting the induction of both systemic and mucosal immune responses against respiratory pathogens.

A CpG-adjuvanted intranasal enterovirus 71 vaccine elicits mucosal and systemic immune responses and protects human SCARB2-transgenic mice against lethal challenge

Enterovirus 71 (EV71) is an aetiological agent responsible for seasonal epidemics of hand-foot-and-mouth disease, which causes considerable mortality among young children. Mucosal vaccines can efficiently induce secretory IgA at mucosal surfaces and thereby prevent or limit infection at the site of virus entry. CpG oligodeoxynucleotides (ODNs), which resemble bacterial DNA, can induce the innate immune response through activation of Toll-like receptor 9. Here, we used CpG ODNs as adjuvants to investigate an EV71 mucosal vaccine in mice. In the EV71 + CpG group, the EV71-specific IgG and IgA titres in the serum, nasal wash, bronchoalveolar lavage fluid, and faeces were substantially higher than those in the EV71- and phosphate-buffered saline-treated groups. Moreover, the number of EV71-specific IgG- and IgA-producing cells was also higher in the EV71 + CpG group. Furthermore, T-cell proliferative responses and interleukin-17 secretion were markedly increased when CpG-adjuvanted EV71 was delivered intranasally. More importantly, the induced antibodies neutralised infection by EV71 of the C2 genotype and crossneutralised infection by EV71 of the B4 and B5 genotypes. Lastly, human scavenger receptor class B, member 2-transgenic mice intranasally immunised with the CpG-adjuvanted EV71 vaccine resisted a subsequent lethal challenge with EV71, indicating that CpG was an effective intranasal adjuvant for EV71 mucosal-vaccine development.

Rapid, directed transport of DC-SIGN clusters in the plasma membrane

C-type lectins, including dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), are all-purpose pathogen receptors that exist in nanoclusters in plasma membranes of dendritic cells. A small fraction of these clusters, obvious from the videos, can undergo rapid, directed transport in the plane of the plasma membrane at average speeds of more than 1 μm/s in both dendritic cells and MX DC-SIGN murine fibroblasts ectopically expressing DC-SIGN. Surprisingly, instantaneous speeds can be considerably greater. In MX DC-SIGN cells, many cluster trajectories are colinear with microtubules that reside close to the ventral membrane, and the microtubule-depolymerizing drug, nocodazole, markedly reduced the areal density of directed movement trajectories, suggesting a microtubule motor-driven transport mechanism; by contrast, latrunculin A, which affects the actin network, did not depress this movement. Rapid, retrograde movement of DC-SIGN may be an efficient mechanism for bringing bound pathogen on the leading edge and projections of dendritic cells to the perinuclear region for internalization and processing. Dengue virus bound to DC-SIGN on dendritic projections was rapidly transported toward the cell center. The existence of this movement within the plasma membrane points to an unexpected lateral transport mechanism in mammalian cells and challenges our current concepts of cortex-membrane interactions.

Retinoic acid facilitates inactivated transmissible gastroenteritis virus induction of CD8(+) T-cell migration to the porcine gut

The digestive tract is the entry site for transmissible gastroenteritis virus (TGEV). TGEV transmission can be prevented if local immunity is established with increased lymphocytes. The current parenteral mode of vaccination stimulates systemic immunity well, but it does not induce sufficient mucosal immunity. Retinoic acid (RA) plays an important role in the induction of cells that imprint gut-homing molecules. We examined whether RA assist parenteral vaccination of pigs could improve mucosal immunity. We demonstrated that elevated numbers of gut-homing CD8⁺ T cells (which express α4β7 and CCR9 molecules) were presented in porcine inguinal lymph nodes and were recruited to the small intestine by RA. Intestinal mucosal immunity (IgA titre) and systemic immunity (serum IgG titre) were enhanced by RA. Therefore, we hypothesized that RA could induce DCs to form an immature mucosal phenotype and could recruit them to the small intestinal submucosa. Porcine T-cells expressed β7 integrin and CCR9 receptors and migrated to CCL25 by a mechanism that was dependent of activation by RA-pretreated DCs, rather than direct activation by RA. Together, our results provide powerful evidence that RA can assist whole inactivated TGEV (WI-TGEV) via subcutaneous (s.c.) immunization to generate intestinal immunity, and offer new vaccination strategies against TGEV.