Novel vaccine development strategies for inducing mucosal immunity

Chitosan-alginate/R8 ternary polyelectrolyte complex as an oral protein-based vaccine candidate induce effective mucosal immune responses

Vaccination is the most effective method for preventing infectious diseases. Oral vaccinations have attracted much attention due to the ability to boost intestinal and systemic immunity. The focus of this study was to develop a poly (lactide-co-glycolide) acid (PLGA)-based ternary polyelectrolyte complex (PEC) with chitosan, sodium alginate, and transmembrane peptides R8 for the delivery of antigen proteins. In this study, the antigen protein (HBf), consisting of the Mycobacterium avium subspecies paratuberculosis (MAP) antigens HBHA, Ag85B, and Bfra, was combined with R8 to generate self-assembled conjugates. The results showed that PEC presented a cross-linked reticular structure to protect the encapsulated proteins in the simulated gastric fluid. Then, the nanocomposite separated into individual nanoparticles after entering the simulated intestinal fluid. The ternary PEC with R8 promoted the in vivo uptake of antigens by intestinal lymphoid tissue. Moreover, the ternary PEC administered orally to mice promoted the secretion of specific antibodies and intestinal mucosal IgA. In addition, in the mouse models of MAP infection, the ternary PEC enhanced splenic T cell responses, thus reducing bacterial load and liver pathology score. These results suggested that this ternary electrolyte complex could be a promising delivery platform for oral subunit vaccine candidates, not limited to MAP infection.

Commensal microbiome and gastrointestinal mucosal immunity: Harmony and conflict with our closest neighbor

BACKGROUND

The gastrointestinal tract contains a wide range of microorganisms that have evolved alongside the immune system of the host. The intestinal mucosa maintains balance within the intestines by utilizing the mucosal immune system, which is controlled by the complex gut mucosal immune network.

OBJECTIVE

This review aims to comprehensively introduce current knowledge of the gut mucosal immune system, focusing on its interaction with commensal bacteria.

RESULTS

The gut mucosal immune network includes gut-associated lymphoid tissue, mucosal immune cells, cytokines, and chemokines. The connection between microbiota and the immune system occurs through the engagement of bacterial components with pattern recognition receptors found in the intestinal epithelium and antigen-presenting cells. This interaction leads to the activation of both innate and adaptive immune responses. The interaction between the microbial community and the host is vital for maintaining the balance and health of the host's mucosal system.

CONCLUSION

The gut mucosal immune network maintains a delicate equilibrium between active immunity, which defends against infections and damaging non-self antigens, and immunological tolerance, which allows for the presence of commensal microbiota and dietary antigens. This balance is crucial for the maintenance of intestinal health and homeostasis. Disturbance of gut homeostasis leads to enduring or severe gastrointestinal ailments, such as colorectal cancer and inflammatory bowel disease. Utilizing these factors can aid in the development of cutting-edge mucosal vaccines that have the ability to elicit strong protective immune responses at the primary sites of pathogen invasion.

Multicomponent Pathogen-Mimicking Nanoparticles Induce Intestinal Immune Responses against Paratuberculosis

Given the worldwide problem posed by enteric pathogens, the discovery of safe and efficient intestinal adjuvants combined with novel antigen delivery techniques is essential to the design of mucosal vaccines. In this work, we designed poly (lactic-co-glycolic acid) (PLGA)-based nanoparticles (NPs) to codeliver all-trans retinoic acid (atRA), novel antigens, and CpG. To address the insolubility of the intestinal adjuvant atRA, we utilized PLGA to encapsulate atRA and form a "nanocapsid" with polydopamine. By leveraging polydopamine, we adsorbed the water-soluble antigens and the TLR9 agonist CpG onto the NPs' surface, resulting in the pathogen-mimicking PLPCa NPs. In this study, the novel fusion protein (HBf), consisting of the Mycobacterium avium subspecies paratuberculosis antigens HBHA, Ag85B, and Bfra, was coloaded onto the NPs. In vitro, PLPCa NPs were shown to promote the activation and maturation of bone marrow-derived dendritic cells. Additionally, we found that PLPCa NPs created an immune-rich microenvironment at the injection site following intramuscular administration. From the results, the PLPCa NPs induced strong IgA levels in the gut in addition to enhancing powerful systemic immune responses. Consequently, significant declines in the bacterial burden and inflammatory score were noted in PLPCa NPs-treated mice. In summary, PLPCa can serve as a novel and safe vaccine delivery platform against gut pathogens, such as paratuberculosis, capable of activating both systemic and intestinal immunity.

Mucosal Administration of Lactobacillus casei Surface-Displayed HA1 Induces Protective Immune Responses against Avian Influenza A Virus in Mice

Avian influenza is a serious threat to both public health and the poultry industry worldwide. This respiratory virus can be combated by eliciting robust immune responses at the site of infection through mucosal immunization. Recombinant probiotics, specifically lactic acid bacteria, are safe and effective carriers for mucosal vaccines. In this study, we engineered recombinant fusion protein by fusing the hemagglutinin 1 (HA1) subunit of the A/Aquatic bird/Korea/W81/2005 (H5N2) with the Bacillus subtilis poly γ-glutamic acid synthetase A (pgsA) at the surface of Lactobacillus casei (pgsA-HA1/L. casei). Using subcellular fractionation and flow cytometry we confirmed the surface localization of this fusion protein. Mucosal administration of pgsA-HA1/L. casei in mice resulted in significant levels of HA1-specific serum IgG, mucosal IgA and neutralizing antibodies against the H5N2 virus. Additionally, pgsA-HA1/L. casei-induced systemic and local cell-mediated immune responses specific to HA1, as evidenced by an increased number of IFN-γ and IL-4 secreting cells in the spleens and higher levels of IL-4 in the local lymphocyte supernatants. Finally, mice inoculated with pgsA-HA1/L. casei were protected against a 10LD50 dose of the homologous mouse-adapted H5N2 virus. These results suggest that mucosal immunization with L. casei displaying HA1 on its surface could be a potential strategy for developing a mucosal vaccine against other H5 subtype viruses.

16S rRNA and transcriptome analysis of the FOS-mediated alleviation of Aeromonas hydrophila-induced intestinal damage in Megalobrama amblycephala

This study was conducted to elucidate the effects of FOS that alleviate Aeromonas hydrophila-induced intestinal damage. The results showed that A. hydrophila disrupted the intestinal structure and increased intestinal permeability, causing abnormalities in mucosal pathology. Additionally, A. hydrophila induced an imbalance in the intestinal flora and disturbed its stability. Dietary FOS ameliorated the injury to the intestinal structure of fish, but also in part improved the condition of the intestinal tight junction complex. Transcriptomic analysis showed that 120 genes were up-regulated and 320 genes were down-regulated. The intestinal immune network for the IgA production signalling pathway was enriched following A. hydrophila infection, and the change in the FOS group was mainly in the Tight junction signalling pathway. Similarly, dietary FOS reduced the disruption of the intestinal microbiota induced by A. hydrophila and improved the intestinal microbiota's stability; FOS was also partially implicated in the upregulation of Tight junction and Adhesion junction pathways by transcriptomic analysis. After further analysis, it was found that fish fed FOS had upregulated expression of genes related to apoptosis, antigen presentation, and the T-cell-mediated immune response in the intestine compared with those in the A. hydrophila group, which may be related to changes in the intestinal microbiome.

Suitability of Polymyxin B as a Mucosal Adjuvant for Intranasal Influenza and COVID-19 Vaccines

Polymyxin B (PMB) is an antibiotic that exhibits mucosal adjuvanticity for ovalbumin (OVA), which enhances the immune response in the mucosal compartments of mice. Frequent breakthrough infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants indicate that the IgA antibody levels elicited by the mRNA vaccines in the mucosal tissues were insufficient for the prophylaxis of this infection. It remains unknown whether PMB exhibits mucosal adjuvanticity for antigens other than OVA. This study investigated the adjuvanticity of PMB for the virus proteins, hemagglutinin (HA) of influenza A virus, and the S1 subunit and S protein of SARS-CoV-2. BALB/c mice immunized either intranasally or subcutaneously with these antigens alone or in combination with PMB were examined, and the antigen-specific antibodies were quantified. PMB substantially increased the production of antigen-specific IgA antibodies in mucosal secretions and IgG antibodies in plasma, indicating its adjuvanticity for both HA and S proteins. This study also revealed that the PMB-virus antigen complex diameter is crucial for the induction of mucosal immunity. No detrimental effects were observed on the nasal mucosa or olfactory bulb. These findings highlight the potential of PMB as a safe candidate for intranasal vaccination to induce mucosal IgA antibodies for prophylaxis against mucosally transmitted infections.

Systemically inoculated adjuvants stimulate pDC-dependent IgA response in local site

The stimulation of local immunity by vaccination is desirable for controlling virus replication in the respiratory tract. However, the local immune stimulatory effects of adjuvanted vaccines administered through the non-mucosal route are poorly understood. Here, we clarify the mechanisms by which non-mucosal inoculation of adjuvants stimulates the plasmacytoid dendritic cell (pDC)-dependent immunoglobulin (Ig)A response in the lungs. After systemic inoculation with type 1 interferon (IFN)-inducing adjuvants, type 1 IFN promotes CXCL9/10/11 release from alveolar endothelial and epithelial cells and recruits CXCR3-expressing pDCs into the lungs. Because adjuvant-activated pulmonary pDCs highly express major histocompatibility complex II, cluster of differentiation 80, and cluster of differentiation 86, transplantation of such cells into the lungs successfully enhances antigen-specific IgA production by the intranasally sensitized vaccine. In contrast, pDC accumulation in the lungs and subsequent IgA production are impaired in pDC-depleted mice and Ifnar1-/- mice. Notably, the combination of systemic inoculation with type 1 IFN-inducing adjuvants and intranasal antigen sensitization protects mice against influenza virus infection due to the pDC-dependent IgA response and type I IFN response. Our results provide insights into the novel mucosal vaccine strategies using non-mucosal inoculated adjuvants.

Shouhui Tongbian Capsules induce regression of inflammation to improve intestinal barrier in mice with constipation by targeted binding to Prkaa1: With no obvious toxicity

Constipation arising from the poor bowel movement is a rife enteric health problem. Shouhui Tongbian Capsule (SHTB) is a traditional Chinese medicine (TCM) which effectively improve the symptoms of constipation. However, the mechanism has not been fully evaluated. The purpose of this study was to evaluate the effect of SHTB on the symptoms and intestinal barrier of mice with constipation. Our data showed that SHTB effectively improved the constipation induced by diphenoxylate, which was confirmed by shorter first defecation time, higher internal propulsion rate and fecal water content. Additionally, SHTB improved the intestinal barrier function, which was manifested by inhibiting the leakage of Evans blue in intestinal tissues and increasing the expression of occludin and ZO-1. SHTB inhibited NLRP3 inflammasome signaling pathway and TLR4/NF-κB signaling pathway, reduced the number of proinflammatory cell subsets and increased the number of immunosuppressive cell subsets to relieve inflammation. The photochemically induced reaction coupling system combined with cellular thermal shift assay and central carbon metabolomics technology confirmed that SHTB activated AMPKα through targeted binding to Prkaa1 to regulate Glycolysis/Gluconeogenesis and Pentose Phosphate Pathway, and finally inhibited intestinal inflammation. Finally, no obvious toxicity related to SHTB was found in a repeated drug administration toxicity test for consecutive 13 weeks. Collectively, we reported SHTB as a TCM targeting Prkaa1 for anti-inflammation to improve intestinal barrier in mice with constipation. These findings broaden our knowledge of Prkaa1 as a druggable target protein for inflammation inhibition, and open a new avenue to novel therapy strategy for constipation injury.

Mucosal vaccination: onward and upward

INTRODUCTION

The unique mucosal immune system allows the generation of robust protective immune responses at the front line of pathogen encounters. The needle-free delivery route and cold chain-free logistic requirements also provide additional advantages in ease and economy. However, the development of mucosal vaccines faces several challenges, and only a handful of mucosal vaccines are currently licensed. These vaccines are all in the form of live attenuated or inactivated whole organisms, whereas no subunit-based mucosal vaccine is available.

AREAS COVERED

The selection of antigen, delivery vehicle, route and adjuvants for mucosal vaccination are highly important. This is particularly crucial for subunit vaccines, as they often fail to elicit strong immune responses. Emerging research is providing new insights into the biological and immunological uniqueness of mucosal tissues. However, many aspects of the mucosal immunology still await to be investigated.

EXPERT OPINION

This article provides an overview of the current understanding of mucosal vaccination and discusses the remaining knowledge gaps. We emphasize that because of the potential benefits mucosal vaccines can bring from the biomedical, social and economic standpoints, the unmet goal to achieve mucosal vaccine success is worth the effort.

Vaccine Design: An Introduction

Vaccines are the most successful and cost-effective medical interventions available to fight infectious diseases. They consist of biological preparations that are capable of stimulating the immune system to confer protective immunity against a particular harmful pathogen/agent. Vaccine design and development have evolved through the years. Early vaccines were obtained with little implementation of technology and in the absence of fundamental knowledge, representing a pure feat of human ingenuity. In contrast, modern vaccine development takes advantage of advances in technology and in our enhanced understanding of the immune system and host-pathogen interactions. Moreover, vaccine design has found novel applications beyond the prophylactic arena and there is an increasing interest in designing vaccines to treat human ailments like cancer and chronic inflammatory diseases. In this chapter, we focus on prophylactic vaccines against infectious diseases, providing an overview on immunology principles underlying immunization and on how vaccines work and are designed.

Characterization of Systemic and Mucosal Humoral Immune Responses to an Adjuvanted Intranasal SARS-CoV-2 Protein Subunit Vaccine Candidate in Mice

Continuous viral evolution of SARS-CoV-2 has resulted in variants capable of immune evasion, vaccine breakthrough infections and increased transmissibility. New vaccines that invoke mucosal immunity may provide a solution to reducing virus transmission. Here, we evaluated the immunogenicity of intranasally administered subunit protein vaccines composed of a stabilized SARS-CoV-2 spike trimer or the receptor binding domain (RBD) adjuvanted with either cholera toxin (CT) or an archaeal lipid mucosal adjuvant (AMVAD). We show robust induction of immunoglobulin (Ig) G and IgA responses in plasma, nasal wash and bronchoalveolar lavage in mice only when adjuvant is used in the vaccine formulation. While the AMVAD adjuvant was more effective at inducing systemic antibodies against the RBD antigen than CT, CT was generally more effective at inducing overall higher IgA and IgG titers against the spike antigen in both systemic and mucosal compartments. Furthermore, vaccination with adjuvanted spike led to superior mucosal IgA responses than with the RBD antigen and produced broadly targeting neutralizing plasma antibodies against ancestral, Delta and Omicron variants in vitro; whereas adjuvanted RBD elicited a narrower antibody response with neutralizing activity only against ancestral and Delta variants. Our study demonstrates that intranasal administration of an adjuvanted protein subunit vaccine in immunologically naïve mice induced both systemic and mucosal neutralizing antibody responses that were most effective at neutralizing SARS-CoV-2 variants when the trimeric spike was used as an antigen compared to RBD.

Rapid and Highly Efficient Genetic Transformation and Application of Interleukin-17B Expressed in Duckweed as Mucosal Vaccine Adjuvant

Molecular farming utilizes plants as a platform for producing recombinant biopharmaceuticals. Duckweed, the smallest and fastest growing aquatic plant, is a promising candidate for molecular farming. However, the efficiency of current transformation methods is generally not high in duckweed. Here, we developed a fast and efficient transformation procedure in Lemna minor ZH0403, requiring 7-8 weeks from screening calluses to transgenic plants with a stable transformation efficiency of 88% at the DNA level and 86% at the protein level. We then used this transformation system to produce chicken interleukin-17B (chIL-17B). The plant-produced chIL-17B activated the NF-κB pathway, JAK-STAT pathway, and their downstream cytokines in DF-1 cells. Furthermore, we administrated chIL-17B transgenic duckweed orally as an immunoadjuvant with mucosal vaccine against infectious bronchitis virus (IBV) in chickens. Both IBV-specific antibody titer and the concentration of secretory immunoglobulin A (sIgA) were significantly higher in the group fed with chIL-17B transgenic plant. This indicates that the duckweed-produced chIL-17B enhanced the humoral and mucosal immune responses. Moreover, chickens fed with chIL-17B transgenic plant demonstrated the lowest viral loads in different tissues among all groups. Our work suggests that cytokines are a promising adjuvant for mucosal vaccination through the oral route. Our work also demonstrates the potential of duckweed in molecular farming.

Biomimetic Neutrophil Nanotoxoids Elicit Potent Immunity against Acinetobacter baumannii in Multiple Models of Infection

Acinetobacter baumannii is a leading cause of antibiotic-resistant nosocomial infections with high mortality rates, yet there is currently no clinically approved vaccine formulation. During the onset of A. baumannii infection, neutrophils are the primary responders and play a major role in resisting the pathogen. Here, we design a biomimetic nanotoxoid for antivirulence vaccination by using neutrophil membrane-coated nanoparticles to safely capture secreted A. baumannii factors. Vaccination with the nanotoxoid formulation rapidly mobilizes innate immune cells and promotes pathogen-specific adaptive immunity. In murine models of pneumonia, septicemia, and superficial wound infection, immunization with the nanovaccine offers significant protection, improving survival and reducing signs of acute inflammation. Lower bacterial burdens are observed in vaccinated animals regardless of the infection route. Altogether, neutrophil nanotoxoids represent an effective platform for eliciting multivalent immunity to protect against multidrug-resistant A. baumannii in a wide range of disease conditions.

Factors Limiting the Translatability of Rodent Model-Based Intranasal Vaccine Research to Humans

The intranasal route of vaccination presents an attractive alternative to parenteral routes and offers numerous advantages, such as the induction of both mucosal and systemic immunity, needle-free delivery, and increased patient compliance. Despite demonstrating promising results in preclinical studies, however, few intranasal vaccine candidates progress beyond early clinical trials. This discrepancy likely stems in part from the limited predictive value of rodent models, which are used frequently in intranasal vaccine research. In this review, we explored the factors that limit the translatability of rodent-based intranasal vaccine research to humans, focusing on the differences in anatomy, immunology, and disease pathology between rodents and humans. We also discussed approaches that minimize these differences and examined alternative animal models that would produce more clinically relevant research.

Mucosal Vaccination: A Promising Alternative Against Flaviviruses

The Flaviviridae are a family of positive-sense, single-stranded RNA enveloped viruses, and their members belong to a single genus, Flavivirus. Flaviviruses are found in mosquitoes and ticks; they are etiological agents of: dengue fever, Japanese encephalitis, West Nile virus infection, Zika virus infection, tick-borne encephalitis, and yellow fever, among others. Only a few flavivirus vaccines have been licensed for use in humans: yellow fever, dengue fever, Japanese encephalitis, tick-borne encephalitis, and Kyasanur forest disease. However, improvement is necessary in vaccination strategies and in understanding of the immunological mechanisms involved either in the infection or after vaccination. This is especially important in dengue, due to the immunological complexity of its four serotypes, cross-reactive responses, antibody-dependent enhancement, and immunological interference. In this context, mucosal vaccines represent a promising alternative against flaviviruses. Mucosal vaccination has several advantages, as inducing long-term protective immunity in both mucosal and parenteral tissues. It constitutes a friendly route of antigen administration because it is needle-free and allows for a variety of antigen delivery systems. This has promoted the development of several ways to stimulate immunity through the direct administration of antigens (e.g., inactivated virus, attenuated virus, subunits, and DNA), non-replicating vectors (e.g., nanoparticles, liposomes, bacterial ghosts, and defective-replication viral vectors), and replicating vectors (e.g., Salmonella enterica, Lactococcus lactis, Saccharomyces cerevisiae, and viral vectors). Because of these characteristics, mucosal vaccination has been explored for immunoprophylaxis against pathogens that enter the host through mucosae or parenteral areas. It is suitable against flaviviruses because this type of immunization can stimulate the parenteral responses required after bites from flavivirus-infected insects. This review focuses on the advantages of mucosal vaccine candidates against the most relevant flaviviruses in either humans or animals, providing supporting data on the feasibility of this administration route for future clinical trials.

Intranasal immunization with a proteosome-adjuvanted SARS-CoV-2 spike protein-based vaccine is immunogenic and efficacious in mice and hamsters

With the persistence of the SARS-CoV-2 pandemic and the emergence of novel variants, the development of novel vaccine formulations with enhanced immunogenicity profiles could help reduce disease burden in the future. Intranasally delivered vaccines offer a new modality to prevent SARS-CoV-2 infections through the induction of protective immune responses at the mucosal surface where viral entry occurs. Herein, we evaluated a novel protein subunit vaccine formulation containing a resistin-trimerized prefusion Spike antigen (SmT1v3) and a proteosome-based mucosal adjuvant (BDX301) formulated to enable intranasal immunization. In mice, the formulation induced robust antigen-specific IgG and IgA titers, in the blood and lungs, respectively. In addition, the formulations were highly efficacious in a hamster challenge model, reducing viral load and body weight loss. In both models, the serum antibodies had strong neutralizing activity, preventing the cellular binding of the viral Spike protein based on the ancestral reference strain, the Beta (B.1.351) and Delta (B.1.617.2) variants of concern. As such, this intranasal vaccine formulation warrants further development as a novel SARS-CoV-2 vaccine.

STxB as an Antigen Delivery Tool for Mucosal Vaccination

Immunotherapy against cancer and infectious disease holds the promise of high efficacy with minor side effects. Mucosal vaccines to protect against tumors or infections disease agents that affect the upper airways or the lung are still lacking, however. One mucosal vaccine candidate is the B-subunit of Shiga toxin, STxB. In this review, we compare STxB to other immunotherapy vectors. STxB is a non-toxic protein that binds to a glycosylated lipid, termed globotriaosylceramide (Gb3), which is preferentially expressed by dendritic cells. We review the use of STxB for the cross-presentation of tumor or viral antigens in a MHC class I-restricted manner to induce humoral immunity against these antigens in addition to polyfunctional and persistent CD4⁺ and CD8⁺ T lymphocytes capable of protecting against viral infection or tumor growth. Other literature will be summarized that documents a powerful induction of mucosal IgA and resident memory CD8⁺ T cells against mucosal tumors specifically when STxB-antigen conjugates are administered via the nasal route. It will also be pointed out how STxB-based vaccines have been shown in preclinical cancer models to synergize with other therapeutic modalities (immune checkpoint inhibitors, anti-angiogenic therapy, radiotherapy). Finally, we will discuss how molecular aspects such as low immunogenicity, cross-species conservation of Gb3 expression, and lack of toxicity contribute to the competitive positioning of STxB among the different DC targeting approaches. STxB thereby appears as an original and innovative tool for the development of mucosal vaccines in infectious diseases and cancer.

Nanotechnologies in Delivery of DNA and mRNA Vaccines to the Nasal and Pulmonary Mucosa

Recent advancements in the field of in vitro transcribed mRNA (IVT-mRNA) vaccination have attracted considerable attention to such vaccination as a cutting-edge technique against infectious diseases including COVID-19 caused by SARS-CoV-2. While numerous pathogens infect the host through the respiratory mucosa, conventional parenterally administered vaccines are unable to induce protective immunity at mucosal surfaces. Mucosal immunization enables the induction of both mucosal and systemic immunity, efficiently removing pathogens from the mucosa before an infection occurs. Although respiratory mucosal vaccination is highly appealing, successful nasal or pulmonary delivery of nucleic acid-based vaccines is challenging because of several physical and biological barriers at the airway mucosal site, such as a variety of protective enzymes and mucociliary clearance, which remove exogenously inhaled substances. Hence, advanced nanotechnologies enabling delivery of DNA and IVT-mRNA to the nasal and pulmonary mucosa are urgently needed. Ideal nanocarriers for nucleic acid vaccines should be able to efficiently load and protect genetic payloads, overcome physical and biological barriers at the airway mucosal site, facilitate transfection in targeted epithelial or antigen-presenting cells, and incorporate adjuvants. In this review, we discuss recent developments in nucleic acid delivery systems that target airway mucosa for vaccination purposes.

Nanocarriers-Assisted Needle-Free Vaccine Delivery Through Oral and Intranasal Transmucosal Routes: A Novel Therapeutic Conduit

Drug delivery using oral route is the most popular, convenient, safest and least expensive approach. It includes oral transmucosal delivery of bioactive compounds as the mucosal cavity offers an intriguing approach for systemic drug distribution. Owing to the dense vascular architecture and high blood flow, oral mucosal layers are easily permeable and can be an ideal site for drug administration. Recently, the transmucosal route is being investigated for other therapeutic candidates such as vaccines for their efficient delivery. Vaccines have the potential to trigger immune reactions and can act as both prophylactic and therapeutic conduit to a variety of diseases. Administration of vaccines using transmucosal route offers multiple advantages, the most important one being the needle-free (non-invasive) delivery. Development of needle-free devices are the most recent and pioneering breakthrough in the delivery of drugs and vaccines, enabling patients to avoid needles, reducing anxiety, pain and fear as well as improving compliance. Oral, nasal and aerosol vaccination is a novel immunization approach that utilizes a nanocarrier to administer the vaccine. Nanocarriers improve the bioavailability and serve as adjuvants to elicit a stronger immune response, resulting in increased effectiveness of vaccination. Drugs and vaccines with lower penetration abilities can also be delivered transmucosally while maintaining their biological function. The development of micro/nanocarriers for transmucosal delivery of macromolecules, vaccines and other substances is currently drawing much attention and a number of studies were performed recently. This comprehensive review is aimed to summarize the most recent investigations on needle-free and non-invasive approaches for the delivery of vaccines using oral transmucosal route, their strengths and associated challenges. The oral transmucosal vaccine delivery by nanocarriers is the most upcoming advancement in efficient vaccine delivery and this review would help further research and trials in this field.

Oral nanomedicine for modulating immunity, intestinal barrier functions, and gut microbiome

The gastrointestinal tract (GIT) affects not only local diseases in the GIT but also various systemic diseases. Factors that can affect the health and disease of both GIT and the human body include 1) the mucosal immune system composed of the gut-associated lymphoid tissues and the lamina propria, 2) the intestinal barrier composed of mucus and intestinal epithelium, and 3) the gut microbiota. Selective delivery of drugs, including antigens, immune-modulators, intestinal barrier enhancers, and gut-microbiome manipulators, has shown promising results for oral vaccines, immune tolerance, treatment of inflammatory bowel diseases, and other systemic diseases, including cancer. However, physicochemical and biological barriers of the GIT present significant challenges for successful translation. With the advances of novel nanomaterials, oral nanomedicine has emerged as an attractive option to not only overcome these barriers but also to selectively deliver drugs to the target sites in GIT. In this review, we discuss the GIT factors and physicochemical and biological barriers in the GIT. Furthermore, we present the recent progress of oral nanomedicine for oral vaccines, immune tolerance, and anti-inflammation therapies. We also discuss recent advances in oral nanomedicine designed to fortify the intestinal barrier functions and modulate the gut microbiota and microbial metabolites. Finally, we opine about the future directions of oral nano-immunotherapy.

Eyedrop vaccination: an immunization route with promises for effective responses to pandemics

INTRODUCTION

Mucosal vaccines have several advantages over parenteral vaccines. They induce both systemic and mucosal antigen-specific immune responses, allow easy administration, and bypass the need for trained medical personnel.

AREAS COVERED

Eye mucosa is a novel route of mucosal vaccine administration. Eyedrop vaccination induces systemic and mucosal immune responses similar to other forms of mucosal vaccines such as oral and intranasal vaccines.

EXPERT OPINION

Eyedrop vaccines are free of serious adverse side effects like the infiltration of CNS by pathogens. Studies over the years have shown promising results for eye drop vaccines against infectious agents like the influenza virus, Salmonella typhi, and Escherichia coli in animal models. Such efficacy and safety of eyedrop vaccination enable the application of eyedrop vaccines against other infectious diseases as well as chronic diseases. In this review of published literature, we examine the mechanism, efficacy, and safety of eyedrop vaccines and contemplate their role in times of a pandemic.

Mucosal vaccines: wisdom from now and then

The oral and nasal cavities are covered by the mucosal epithelium that starts at the beginning of the aero-digestive tract. These mucosal surfaces are continuously exposed to environmental antigens including pathogens and allergens and are thus equipped with a mucosal immune system that mediates initial recognition of pathogenicity and initiates pathogen-specific immune responses. At the dawn of our scientific effort to explore the mucosal immune system, dental science was one of the major driving forces as it provided insights into the importance of mucosal immunity and its application for the control of oral infectious diseases. The development of mucosal vaccines for the prevention of dental caries was thus part of a novel approach that contributed to building the scientific foundations of the mucosal immune system. Since then, mucosal immunology and vaccines have gone on a scientific journey to become one of the major entities within the discipline of immunology. Here, we introduce our past and current efforts and future directions for the development of mucosal vaccines, specifically a rice-based oral vaccine (MucoRice) and a nanogel-based nasal vaccine, with the aim of preventing and controlling gastrointestinal and respiratory infectious diseases using the interdisciplinary fusion of mucosal immunology with agricultural science and biomaterial engineering, respectively.

Cellular Immunotherapy and the Lung

The new era of cellular immunotherapies has provided state-of-the-art and efficient strategies for the prevention and treatment of cancer and infectious diseases. Cellular immunotherapies are at the forefront of innovative medical care, including adoptive T cell therapies, cancer vaccines, NK cell therapies, and immune checkpoint inhibitors. The focus of this review is on cellular immunotherapies and their application in the lung, as respiratory diseases remain one of the main causes of death worldwide. The ongoing global pandemic has shed a new light on respiratory viruses, with a key area of concern being how to combat and control their infections. The focus of cellular immunotherapies has largely been on treating cancer and has had major successes in the past few years. However, recent preclinical and clinical studies using these immunotherapies for respiratory viral infections demonstrate promising potential. Therefore, in this review we explore the use of multiple cellular immunotherapies in treating viral respiratory infections, along with investigating several routes of administration with an emphasis on inhaled immunotherapies.

Adjuvants: friends in vaccine formulations against infectious diseases

Infectious diseases represent a major cause of deaths worldwide. No vaccine or effective treatment exists nowadays, especially against intracellular pathogens. The increase in multiple drug and superbug antibiotic resistance strains, excessive medication, or misuse of drugs has prompted the search for other safe and effective alternatives. Consistent with this, adjuvants (Latin word "adjuvare": "help or aid") co-administered (Exo) in vaccines have emerged as a promising alternative to initiate and boost an innate, downstream signal that led to adaptative immune response. Nowadays, a promising model of strong immunogens and adjuvants at mucosal sites are the microbial bacterial toxins. Other adjuvants that are also used and might successfully replace aluminum salts in combination with nanotechnology are CpG-ODN, poly IC, type I IFNs, mRNA platforms. Therefore, in the present review, we focused to revisit the old to the new adjuvants compounds, the properties that make them friends in vaccine formulations against infectious diseases.

Fusion-expressed CtxB-TcpA-C-CPE improves both systemic and mucosal humoral and T-cell responses against cholera in mice

BACKGROUND

Development of an effective oral vaccine against Cholera, a life-threatening dehydrating diarrheal disease, proved to be a challenging task. To improve oral subunit vaccine immunogenicity and to prevent the state of oral tolerance, application of mucosal adjuvants might be a promising approach. In the present study, the CtxB-TcpA-C-CPE fusion was constructed in which CtxB and C-CPE were used as mucosal adjuvants and vaccine delivery system, respectively, to induce mucosal immune responses, and to improve the anti-toxin and anti-colonizing immunity against V. cholerae.

MATERIALS & METHODS

The fusion construct was synthesized, sub-cloned in pQE30 and expressed in E. coli. The three antigen, making the fusion protein, were also separately expressed in E. coli. The recombinant proteins were purified by affinity chromatography using Ni-NTA agarose. Western blot analysis using anti-His antibody was applied to confirm identity of the purified proteins. BALB/c mice were subcutaneously immunized with CtxB, TcpA, C-CPE and the fusion protein CtxB-TcpA-C-CPE separately. The mice were orally immunized (in 3 boosts) by the same vaccine. Mucosal immune response stimulation was evaluated by measuring the levels of intestinal IgA. Systemic immune response was evaluated by measuring total serum IgG, IgG1, IgG2a, IgG2b subclasses, and also IL-4, IL-5, IL-10 and IFN-γ cytokines in spleen cell culture.

RESULTS

The recombinant proteins CtxB, TcpA, C-CPE and the fusion protein CtxB-TcpA-C-CPE were expressed in E. coli and highly purified in a single step of chromatography. BALB/c mice immunized with the fusion protein had highest levels of intestinal IgA, serum IgG and IgG subclasses, compared to each of the three proteins making the fusion. Moreover, stimulated splenocytes of mice immunized with the fusion protein displayed significantly higher amounts of IL-5 and IFN-ɣ cytokines. Th2 dominance of the immune response was more evident in mice receiving the fusion protein.

CONCLUSION

Inclusion of CtxB, as the mucosal adjuvant, and C-CPE, as the vaccine delivery system, in the fusion protein CtxB-TcpA-C-CPE significantly enhanced the elicited mucosal and systemic immune responses, compared to TcpA alone. Of note, significant production of intestinal IgA in mice immunized with the fusion protein is presumably capable of neutralizing TcpA, CtxB and C-CPE antigens, preventing V. cholera colonization, and toxic function of CtxB and C-CPE. Challenge infection of the immunized mice is required to evaluate protective potential of the fusion protein against V. cholera.

A systematic assessment of the relationship between synthetic surfactants and mucosal adjuvanticity

Intranasal immunization with surfactants as vaccine adjuvants enhances protective immunity against invasive mucosal pathogens. However, the effects of surfactants and their adjuvanticity on mucosal immune responses remain unclear. Comparison of the mucosal adjuvanticity of 20 water-soluble surfactants from the four classes based upon the polarity composition of the hydrophilic headgroup revealed that the order of mucosal adjuvanticity was as follows: amphoteric > nonionic > cationic > anionic. Within the same class, each surfactant displayed different adjuvanticity values. Analysis of the diameter and ζ-potential of amphoteric surfactant-OVA complexes and their surface physicochemical properties revealed that the diameter was approximately 100 nm, which is considered suitable for immune induction, and that the ζ-potential of the anionic surfactant-OVA complexes was exceedingly negative. The increase in the number of carbon atoms in the hydrophobic tailgroups of the amphoteric surfactant resulted in an increase in the OVA-specific Ab titers. Our findings demonstrate that amphoteric surfactants exhibit potent mucosal adjuvanticity and highlight the importance of the number of carbon atoms in the tailgroups and the diameter and ζ-potential of the complexes when designing mucosal adjuvants.

Chitosan Nanoparticles Loaded with Truncated ORF2 Protein as an Oral Vaccine Candidate against Hepatitis E

In a continuous effort to develop effective vaccines against hepatitis E (HE), oral vaccine nanoparticles using the truncated capsid protein p146 (aa460-605) are formulated and characterized. To improve the immunogenicity of p146, chitosan nanoparticles (CSNPs) are used as a mucosal delivery system. Next, the physical-chemical properties, cytotoxic effects in vitro, and immunogenicity in mice of the produced NPs are analyzed. The results show that the produced CS/p146 NPs are stable and well dispersive and display a near-spherical shape with a mean size of 200-300 nm. The findings also demonstrate high encapsulation efficiency (65-73.9%) and loading capacity (27.7-67.5%) of the formulated nanoparticles. Further, the CS/p146 NPs exhibit low cytotoxicity and an obvious sustained-release effect in vitro. Immunogenicity experiments in mice indicate that CS/p146 NPs can induce antigen-specific systemic and mucosal immune responses higher than the purified p146 do. Besides, the expression levels and mRNA transcription of Interleukin (IL)-4 in spleen cells of CS/p146 NPs-immunized mice are higher than those of p146, indicating that a Th2-mediated cellular immune response is activated by the CS/p146 NPs. Overall, the synthesized CS/p146 NPs display promising properties as a potential HE oral vaccine candidate.

Characterization and Specification of a Trivalent Protein-Based Pneumococcal Vaccine Formulation Using an Adjuvant-Free Nanogel Nasal Delivery System

We previously developed a safe and effective nasal vaccine delivery system using a self-assembled nanosized hydrogel (nanogel) made from a cationic cholesteryl pullulan. Here, we generated three pneumococcal surface protein A (PspA) fusion antigens as a universal pneumococcal nasal vaccine and then encapsulated each PspA into a nanogel and mixed the three resulting monovalent formulations into a trivalent nanogel-PspA formulation. First, to characterize the nanogel-PspA formulations, we used native polyacrylamide gel electrophoresis (PAGE) to determine the average number of PspA molecules encapsulated per nanogel molecule. Second, we adopted two methods-a densitometric method based on lithium dodecyl sulfate (LDS)-PAGE and a biologic method involving sandwich enzyme-linked immunosorbent assay (ELISA)-to determine the PspA content in the nanogel formulations. Third, treatment of nanogel-PspA formulations by adding methyl-β-cyclodextrin released each PspA in its native form, as confirmed through circular dichroism (CD) spectroscopy. However, when nanogel-PspA formulations were heat-treated at 80 °C for 16 h, CD spectroscopy showed that each PspA was released in a denatured form. Fourth, we confirmed that the nanogel-PspA formulations were internalized into nasal mucosa effectively and that each PspA was gradually released from the nanogel in epithelial cells in mice. Fifth, LDS-PAGE densitometry and ELISA both indicated that the amount of trivalent PspA was dramatically decreased in the heat-treated nanogel compared with that before heating. When mice were immunized nasally using the heat-treated formulation, the immunologic activity of each PspA was dramatically reduced compared with that of the untreated formulation; in both cases, the immunologic activity correlated well with the content of each PspA as determined by LDS-PAGE densitometry and ELISA. Finally, we confirmed that the trivalent nanogel-PspA formulation induced equivalent titers of PspA-specific serum IgG and mucosal IgA Abs in immunized mice. These results show that the specification methods we developed effectively characterized our nanogel-based trivalent PspA nasal vaccine formulation.

Systemic and Mucosal B and T Cell Responses Upon Mucosal Vaccination of Teleost Fish

The development of mucosal vaccines against pathogens is currently a highly explored area of research in both humans and animals. This is due to the fact that mucosal vaccines have the potential to best elicit protective responses at these mucosal surfaces, which represent the frontline of host defense, thus blocking the pathogen at its initial replication sites. However, in order to provide an efficient long-lasting protection, these mucosal vaccines have to be capable of eliciting an adequate systemic immune response in addition to local responses. In aquaculture, the need for mucosal vaccines has further practical implications, as these vaccines would avoid the individual manipulation of fish out of the water, being beneficial from both an economic and animal welfare point of view. However, how B and T cells are organized in teleost fish within these mucosal sites and how they respond to mucosally delivered antigens varies greatly when compared to mammals. For this reason, it is important to establish which mucosally delivered antigens have the capacity to induce strong and long-lasting B and T cell responses. Hence, in this review, we have summarized what is currently known regarding the adaptive immune mechanisms that are induced both locally and systemically in fish after mucosal immunization through different routes of administration including oral and nasal vaccination, anal intubation and immersion vaccination. Finally, based on the data presented, we discuss how mucosal vaccination strategies could be improved to reach significant protection levels in these species.

The Protective HIV-1 Envelope gp41 Antigen P1 Acts as a Mucosal Adjuvant Stimulating the Innate Immunity

Mucosal nasal vaccine development, although ideal to protect from pathogens invading mucosally, is limited by the lack of specific adjuvant. We recently used P1, a conserved region of HIV-1 gp41-envelope glycoprotein, as efficient antigen in a prophylactic HIV-1 mucosal vaccine applied nasally. Herein, P1 immunomodulation properties were assessed on human nasal mucosal models by measuring induction of cytokine and chemokine production, intracellular signaling pathways, mucosal dendritic cell (DC) activation, and T cell proliferation. P1 adjuvant properties were evaluated by quantification of antigen-specific B cell responses against a model antigen in an in vitro immunization model. We now demonstrated that P1 has additional immunological properties. P1 initiates immune responses by inducing nasal epithelial cells to secrete the Th2-cytokine thymic stromal lymphopoietin (TSLP), a described mucosal adjuvant. Secreted TSLP activates, in turn, intracellular calcium flux and PAR-2-associated NFAT signaling pathway regulated by microRNA-4485. Thereafter, P1 induces mucosal dendritic cell maturation, secretion of TSLP in a TSLP-receptor (R)-dependent autocrine loop, but also IL-6, IL-10, IL-8, CCL20, CCL22, and MMP-9, and proliferation of CD4+ T cells. Finally, P1 acts as an adjuvant to stimulate antigen-specific B cell responses in vitro. Overall, P1 is a multi-functional domain with various immuno-modulatory properties. In addition to being a protective vaccine antigen for HIV prevention, P1 acts as adjuvant for other mucosal vaccines able to stimulate humoral and cellular antigen-specific responses.

Cord Blood-Based Approach to Assess Candidate Vaccine Adjuvants Designed for Neonates and Infants

Neonates and infants are particularly susceptible to infections, for which outcomes tend to be severe. Vaccination is a key strategy for preventing infectious diseases, but the protective immunity achieved through vaccination typically is weaker in infants than in healthy adults. One possible explanation for the poor acquisition of vaccine-induced immunity in infants is that their innate immune response, represented by toll-like receptors, is immature. The current system for developing pediatric vaccines relies on the confirmation of their safety and effectiveness in studies involving the use of mature animals or adult humans. However, creating vaccines for neonates and infants requires an understanding of their uniquely immature innate immunity. Here we review current knowledge regarding the innate immune system of neonates and infants and challenges in developing vaccine adjuvants for those children through analyses of cord blood.

Non-Reflex Defense Mechanisms of Upper Airway Mucosa: Possible Clinical Application

The sinonasal mucosa has an essential role in defense mechanisms of the upper respiratory tract. The innate immune system presents the primary defense against noxious microorganisms followed by induction of the adaptive immune mechanisms as a consequence of the presence of pathogens. This well-known activation of adaptive immune system in response to presence of the antigen on mucosal surfaces is now broadly applicated in vaccinology research. Prevention of infectious diseases belongs to substantial challenges in maintaining the population health. Non-invasive, easily applicable mucosal vaccination purposes various research opportunities that could be usable in daily practice. However, the existence of multiple limitations such as rapid clearance of vaccine from nasal mucosa by means of mucociliary transport represents a great challenge in development of safe and efficient vaccines. Here we give an updated view on nasal functions with focus on nasal mucosal immunity and its potential application in vaccination in nearly future.

Mucosal IL-4R antagonist HIV vaccination with SOSIP-gp140 booster can induce high-quality cytotoxic CD4+/CD8+ T cells and humoral responses in macaques

Inducing humoral, cellular and mucosal immunity is likely to improve the effectiveness of HIV-1 vaccine strategies. Here, we tested a vaccine regimen in pigtail macaques using an intranasal (i.n.) recombinant Fowl Pox Virus (FPV)-gag pol env-IL-4R antagonist prime, intramuscular (i.m.) recombinant Modified Vaccinia Ankara Virus (MVA)-gag pol-IL-4R antagonist boost followed by an i.m SOSIP-gp140 boost. The viral vector-expressed IL-4R antagonist transiently inhibited IL-4/IL-13 signalling at the vaccination site. The SOSIP booster not only induced gp140-specific IgG, ADCC (antibody-dependent cellular cytotoxicity) and some neutralisation activity, but also bolstered the HIV-specific cellular and humoral responses. Specifically, superior sustained systemic and mucosal HIV Gag-specific poly-functional/cytotoxic CD4⁺ and CD8⁺ T cells were detected with the IL-4R antagonist adjuvanted strategy compared to the unadjuvanted control. In the systemic compartment elevated Granzyme K expression was linked to CD4⁺ T cells, whilst Granzyme B/TIA-1 to CD8⁺ T cells. In contrast, the cytotoxic marker expression by mucosal CD4⁺ and CD8⁺ T cells differed according to the mucosal compartment. This vector-based mucosal IL-4R antagonist/SOSIP booster strategy, which promotes cytotoxic mucosal CD4⁺ T cells at the first line of defence, and cytotoxic CD4⁺ and CD8⁺ T cells plus functional antibodies in the blood, may prove valuable in combating mucosal infection with HIV-1 and warrants further investigation.

Chitosan Nanoparticle Based Mucosal Vaccines Delivered Against Infectious Diseases of Poultry and Pigs

Infectious disease of poultry and pig are major threat to health and cause severe economic loss to the food industry and a global food safety issue. Poultry and pig act as a mixing vessel of zoonotic transmission of disease to humans. Effective mucosal vaccines used in animals could reduce the impact of diseases in food animals. Chitosan is a biocompatible polymer, and its positive charge makes it a natural mucoadhesive agent. Therefore, since last one-decade chitosan derived nanoparticles (CS NPs) have been in use widely to deliver vaccine antigens in animals through mucosal route. Primary route of entry of most infectious disease pathogen is through oral and nasal routes, and the CS NPs based vaccines delivered through that routes enhance the immunogenicity of encapsulated vaccine antigens by targeting the cargo to mucosal microfold cells, dendritic cells and macrophages. Resulting in induction of robust secretory and systemic antibodies and/or cell mediated immune response which provides protection against infections. To date, CS NPs is being widely used for mucosal vaccine delivery in poultry and pigs to control bacterial and viral infections, and tested in several preclinical trials for vaccine delivery in humans. In this review, we highlighted the progress so far made in using CS NPs as a vehicle for mucosal vaccine delivery against infectious and zoonotic diseases of poultry and pigs. Discussed about the need of CS NPs modifications, CS NPs based vaccines induced immune responses and its role in protection, and challenges in vaccination and future directions.

The immune response to a recombinant Lactococcus lactis oral vaccine against foot-and-mouth disease virus in mice

Objective

Development of an effective mucosal vaccine to induce specific immune responses against Foot-and-mouth disease virus (FMDV).

Results

For this purpose, the FMDV VP1 gene (SPVP1) was optimized and synthesized based on the codon bias of Lactococcus lactis (L. lactis), and then incorporated in the plasmid pNZ8148. L. lactis NZ9000 containing the pNZ8148-SPVP1 recombinant plasmid was used as an oral delivery vehicle to induce anti-FMDV mucosal and systemic immune responses in mice. After confirmation that the SPVP1 protein was expressed successfully in the recombinant L. latic, the mice were orally challenged with NZ9000-pNZ8148, NZ9000-pNZ8148-SPVP1, phosphate-buffered saline as a mock infection group, or with inactivated vaccine as a positive group. Mice immunized with NZ9000-pNZ8148-SPVP1 produced high levels of mucosal secretory IgA (sIgA), antigen-specific serum IgG, IgA, and neutralizing antibodies, and developed stronger cell-mediated immune reactions and significant T spleen lymphocyte proliferation. Furthermore, the recombinant group generated much higher levels of IFN-γ, IL-2, IL-4, IL-5, and IL-10 than the other groups.

Conclusions

Potent immune responses were successfully elicited in mice with FMDV VP1 delivered through L. lactis.

Rational application of nanoadjuvant for mucosal vaccine delivery system

The surface of the mucosa is the biggest path through which pathogens enter the human body. We need an understanding of mucosal immune systems to use vaccines that generate protective mucosal and systemic immunity to regulate the outbreak of various infectious diseases. The better impact of the mucosal vaccine over traditional injectable vaccines are that not only do they induce efficient immune reactions to the mucosa but they are also comfortable in physical aspect & psychological aspect. The material of the vaccine includes pathogens antigens and adjuvants, which enable vaccination to be effective. Vaccines are classified into different criteria, including the used vaccine material and method of administration. Vaccines have traditionally been injected through a needle. However, as most of the pathogens first infect the mucosal surfaces, and growing interest is expressed in establishing protective immunity from the mucosa, which is accomplished through mucosal paths through vaccinosis. To improve the existing vaccines further, innovative strategies derived from interdisciplinary scientific research will need to develop new vaccine production, storage, and delivery systems. A distinctive & vast research and development platform has been set up for the growth of the next generation of mucosal vaccinations. The latest science and technological advancement in the areas of molecular biology, bio and chemical engineering, genome and system biology has provided accumulated understanding of the inborn and acquired multi-dimensional immune system. This review summarizes recent developments in the use of mucosal vaccines and their associated nanoadjuvants for the control of infectious diseases.

Particulate carrier systems as adjuvants for cancer vaccines

To overcome the immunosuppressive milieu of malignancy and lack of well-defined antigens, potent adjuvants are needed for cancer immunotherapy. Numerous small molecular immunomodulators have the potential to fulfill this role. To enhance the immune response and decrease the toxicity, particulate systems including nanoparticles and macroparticles have been increasingly proposed as carriers for cancer antigen and adjuvant delivery. These systems have the potential to co-deliver the antigens and adjuvants simultaneously in the same particle. In addition, the particles can be engineered for localized and targeted delivery, whether it be to the cellular or sub-cellular level. These properties limit systemic side effects and improve delivery efficiency, and thus enhance the vaccine's immune response. In particular, the particles can be constructed to mimic the size and surface patterns of microbes, organisms to which we have evolved a strong immune response. The release characteristics of the particles can likewise be controlled to simulate the body's response to infections. Boosting the immune response of vaccines by virtue of their intrinsic immunostimulatory properties, these particles can be dosing-sparing and have the potential to reduce production cost of vaccines. As the interest in personalized cancer vaccines increases with their encouraging outcomes in clinical trials, particulate carrier systems have the potential to play an important role in optimizing cancer vaccines.

IL-33 Is Essential for Adjuvant Effect of Hydroxypropyl-β-Cyclodexrin on the Protective Intranasal Influenza Vaccination

Vaccine adjuvants are traditionally used to augment and modulate the immunogenicity of vaccines, although in many cases it is unclear which specific molecules contribute to their stimulatory activity. We previously reported that both subcutaneous and intranasal administration of hydroxypropyl-β-cyclodextrin (HP-β-CD), a pharmaceutical excipient widely used to improve solubility, can act as an effective adjuvant for an influenza vaccine. However, the mechanisms by which mucosal immune pathway is critical for the intranasal adjuvant activity of HP-β-CD have not been fully delineated. Here, we show that intranasally administered HP-β-CD elicits a temporary release of IL-33 from alveolar epithelial type 2 cells in the lung; notably, IL-33 expression in these cells is not stimulated following the use of other vaccine adjuvants. The experiments using gene deficient mice suggested that IL-33/ST2 signaling is solely responsible for the adjuvant effect of HP-β-CD when it is administered intranasally. In contrast, the subcutaneous injection of HP-β-CD and the intranasal administration of alum, as a damage-associated molecular patterns (DAMPs)-inducing adjuvant, or cholera toxin, as a mucosal adjuvant, enhanced humoral immunity in an IL-33-independent manner, suggesting that the IL-33/ST2 pathway is unique to the adjuvanticity of intranasally administered HP-β-CD. Furthermore, the release of IL-33 was involved in the protective immunity against influenza virus infection which is induced by the intranasal administration of HP-β-CD-adjuvanted influenza split vaccine. In conclusion, our results suggest that an understanding of administration route- and tissue-specific immune responses is crucial for the design of unique vaccine adjuvants.

Exosomal regulation of lymphocyte homing to the gut

Exosomes secreted from T cells have been shown to affect dendritic cells, cancer cells, and other T cells. However, little is known about how T-cell exosomes (T exosomes) modulate endothelial cell functions in the context of tissue-specific homing. Here, we study the roles of T exosomes in the regulation of gut-specific T-cell homing. The gut-tropic T cells induced by retinoic acid secrete the exosomes that upregulate integrin α4β7 binding to the MAdCAM-1 expressed on high endothelial venules in the gut. T exosomes were preferentially distributed to the villi of the small intestine in an α4β7-dependent manner. Exosomes from gut-tropic T cells suppressed the expression of MAdCAM-1 in the small intestine, thereby inhibiting T-cell homing to the gut. Moreover, microRNA (miRNA) profiling analysis has shown that exosomes from gut-tropic T cells were enriched with miRNAs targeting NKX2.3, a transcription factor critical to MAdCAM-1 expression. Taken together, our study proposes that α4β7-expressing T exosomes distribute themselves to the small intestine and modify the expression of microenvironmental tissues such that any subsequent lymphocyte homing is precluded. This may represent a novel mechanism by which excessive lymphocyte homing to the intestinal tissues is downsized.

Nanoparticles for mucosal vaccine delivery

Mucosal surfaces represent important routes of entry into the human body for the majority of pathogens, and they constitute unique sites for targeted vaccine delivery. Nanoparticle-based drug delivery systems are emerging technologies for delivering and improving the efficacy of mucosal vaccines. Recent studies have provided new insights into formulation and delivery aspects of importance for the design of safe and efficacious mucosal subunit vaccines based on nanoparticles. These include novel nanomaterials, their physicochemical properties and formulation approaches, nanoparticle interaction with immune cells in the mucosa, and mucosal immunization and delivery strategies. Here, we present recent progress in the application of nanoparticle-based approaches for mucosal vaccine delivery and discuss future research challenges and opportunities in the field.

Development of prime-boost-type next-generation mucosal vaccines

Our bodies are constantly exposed to a wide variety of pathogenic micro-organisms through mucosal sites. Therefore, effective vaccines that can protect at the mucosa are vital; however, only a few clinically established mucosal vaccines are available. Although conventional injectable vaccines can induce antigen-specific serum immunoglobulin G (IgG) and prevent severe infection, it is difficult to efficiently inhibit the invasion of pathogens at mucosal surfaces because of the inadequate ability to induce antigen-specific IgA. Recently, we have developed a parenteral vaccine with emulsified curdlan and CpG oligodeoxynucleotides and reported its application. Unlike other conventional injectable vaccines, this immunization contributes to the induction of antigen-specific mucosal and systemic immune responses. Even if antigen-specific IgA at the mucosa disappears, this immunization can induce high-titer IgA after boosting with a small amount of antigen on the target mucosal surface. Indeed, vaccination with Streptococcus pneumoniae antigen effectively prevented lung infection induced by this bacterium. In addition, vaccination with Clostridium ramosum, which is a representative pathobiont associated with obesity and diabetes in humans, reduced obesity in mice colonized with this microorganism. This immunization approach might be an effective treatment for intestinal bacteria-mediated diseases that have been difficult to regulate so far, as well as common infectious diseases.

Protein delivery by porous cationic maltodextrin-based nanoparticles into nasal mucosal cells: Comparison with cationic or anionic nanoparticles

Different types of biodegradable nanoparticles (NPs) have been studied as delivery systems for proteins into nasal mucosal cells, especially for vaccine applications. Such a nanocarrier must have the ability to be loaded with proteins and to transport this payload into mucosal cells. However, comparative data on nanoparticles' capacity for protein loading, efficiency of subsequent endocytosis and the quantity of nanocarriers used are either lacking or contradictory, making comparisons and the choice of a best candidate difficult. Here we compared 5 types of nanoparticles with different surface charge (anionic or cationic) and various inner compositions as potential vectors: the NPL (cationic maltodextrin NP with an anionic lipid core), cationic and anionic PLGA (Poly Lactic co-Glycolic Acid) NP, and cationic and anionic liposomes. We first quantified the protein association efficiency and NPL associated the largest amount of ovalbumin, used as a model protein. In vitro, the delivery of fluorescently-labeled ovalbumin into mucosal cells (airway epithelial cells, dendritic cells and macrophages) was assessed by flow cytometry and revealed that the NPL delivered protein to the greatest extent in all 3 different cell lines. Taken together, these data underlined the potential of the porous and cationic maltodextrin-based NPL as efficient protein delivery systems to mucosal cells.

A role for the CCR5-CCL5 interaction in the preferential migration of HSV-2-specific effector cells to the vaginal mucosa upon nasal immunization

Our current study focused on elucidating the role of specific chemokine-receptor interactions in antigen (Ag)-specific immune cell migration from nasal to genital mucosal tissues. This cellular migration is critical to induce effective Ag-specific immune responses against sexually transmitted genital infections. In this study, nasal immunization with live attenuated HSV-2 TK^- induced the upregulation of CCR5 expression in effector immune cells, including CD4⁺ T cells, in Ag-priming sites and vaginal tissue. The CCR5 ligands CCL3, CCL4, and CCL5 all showed upregulated expression in vaginal tissue; in particular, CCL5 expression was highly enhanced in the stromal cells of vaginal tissue after nasal immunization. Intravaginal blockade of CCL5 by using neutralizing antibody diminished the number of HSV-2-specific effector cells in the vagina. Furthermore, loss of CCR5, a receptor for CCL5, impaired the migration of nasally primed Ag-specific effector cells from the airway to vagina. Effector cells adoptively transferred from CCR5-deficient mice failed to migrate into vaginal tissue, consequently increasing recipient mice's susceptibility to HSV-2 vaginal infection. These results indicate that the CCR5-CCL5 chemokine pathway is required for the migration and retention of nasally primed Ag-specific effector cells in vagina for providing protective immunity against HSV-2 infection.

Nasal route for vaccine and drug delivery: Features and current opportunities

Mucosal administration, and specifically nasal route, constitutes an alternative and promising strategy for drug and vaccine delivery. Mucosal routes have several advantages supporting their selective use for different pathologies. Currently, many efforts are being made to develop effective drug formulations and novel devices for nasal delivery. This review described the structure and main characteristics of the nasal cavity. The advantages, achievements and challenges of the nasal route use for medical purposes are discussed, with particular focus on vaccine delivery. Compelling evidences support the potentialities and safety of the nasal delivery of vaccines and drugs. This alternative route could become a solution for many unmet medical issues and also may facilitate and cheapen massive immunization campaigns or long-lasting chronic treatments. Nowadays, in spite of certain remaining skepticism, the field of nasal delivery of drugs and vaccines is growing fast, bolstered by current developments in nanotechnology, imaging and administration devices. A notable increase in the number of approved drugs for nasal administration is envisaged.

Staphylococcus aureus-specific IgA antibody in milk suppresses the multiplication of S. aureus in infected bovine udder

Background

Bovine mastitis caused by Staphylococcus aureus (S. aureus) is extremely difficult to control and new methods for its prevention and management are required. Nasal vaccines may prevent initial bovine mastitis infection caused by S. aureus. However, limited information is available regarding induction of mucosal immune response through nasal immunization with antigen and its suppression of S. aureus multiplication during bovine mastitis. This study sought to investigate whether induction of immunoglobulin A (IgA) in milk by nasal immunization could suppress multiplication of S. aureus in the bovine udder.

Results

Nasal immunization with formalin-killed S. aureus conjugated with a cationic cholesteryl-group-bearing pullulan-nanogel was performed. Anti-S. aureus-specific IgA antibodies were significantly more abundant in the milk of immunized cows than in non-immunized animals (P < 0.05). S. aureus counts in the quarter were negative in both non-immunized and nasal-immunized cows 1 week after mock infusion. In S. aureus-infused quarters, S. aureus multiplication was significantly suppressed in immunized compared with non-immunized cows (P < 0.05). Furthermore, a significant negative correlation was found between S. aureus-specific IgA antibodies and S. aureus counts in infused quarters of both non-immunized and nasal-immunized cows (r = − 0.811, P < 0.01).

Conclusion

In conclusion, the present study demonstrates that S. aureus-specific IgA antibodies in milk successfully suppressed the multiplication of S. aureus in infected bovine udders. Although the exact mechanism explaining such suppressive effect remains to be elucidated, nasal vaccines that can induce humoral immunity may help prevent initial infection with S. aureus and the onset of bovine mastitis.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2025-3) contains supplementary material, which is available to authorized users.

Screening and Identification of a Chicken Dendritic Cell Binding Peptide by Using a Phage Display Library

Dendritic cells (DCs), as antigen-presenting cells, can initiate adaptive immune responses efficiently. Although the DC-targeting strategy has attracted more attention, relevant studies on chicken are rare. Here, specific chicken bone marrow DC-binding peptides were selected using a phage display peptide library and confirmed through ELISA, flow cytometry, fluorescence microscopy, and laser confocal microscopy. The peptide candidate SPHLHTSSPWER, named SP, was fused to the infectious bursal disease virus (IBDV) structural protein and protective antigen VP2. In vitro, the expression of DC markers (CD80, CD83, CD86, DEC205, and MHCII) and some cytokines (IFN-γ, IL-12, TNF-α, IL-1β, IL-6, and CXCLi1) by VP2-SP-stimulated DCs was significantly higher than that by DCs treated with the VP2-control peptide at 4 h (p < 0.001). In addition, an oral vaccine targeting DCs was generated using chicken-borne Lactobacillus saerimneri M11 (L. sae M11) to deliver VP2 fused with SP. Anti-IBDV mucosal and humoral immune responses were induced efficiently via oral administration, resulting in higher protective efficacy in the VP2-SP group than the VP2 group. Therefore, chicken DC targeting of IBDV protective antigen VP2 delivered by L. sae provides effective immune protection in chicken. Our study may promote research on the DC-targeting strategy to enhance the effectiveness of chicken vaccines.

Immunological association of inducible bronchus-associated lymphoid tissue organogenesis in Ag85B-rHPIV2 vaccine-induced anti-tuberculosis mucosal immune responses in mice

We previously reported that Ag85B-expressing human parainfluenza type 2 virus (Ag85B-rHPIV2) was effective as a nasal vaccine against tuberculosis in mice; however, the mechanism by which it induces an immune response remains to be investigated. In the present study, we found that organogenesis of inducible bronchus-associated lymphoid tissue (iBALT) played a role in the induction of antigen-specific T cells and IgA antibody responses in the lung of mice intra-nasally administered Ag85B-rHPIV2. We found that expression of Ag85B was dispensable for the development of iBALT, suggesting that HPIV2 acted as an iBALT-inducing vector. When iBALT organogenesis was disrupted in Ag85B-rHPIV2-immunized mice, either by neutralization of the lymphotoxin pathway or depletion of CD11b⁺ cells, Ag85B-specific immune responses (i.e. IFN γ-producing T cells and IgA antibody) were diminished in the lung. Furthermore, we found that immunization with Ag85B-rHPIV2 induced neutrophil and eosinophil infiltration temporally after the immunization in the lung. Thus, our results show that iBALT organogenesis contributes to the induction of antigen-specific immune responses by Ag85B-rHPIV2 and that Ag85B-rHPIV2 provokes its immune responses without inducing long-lasting inflammation.

Upregulation of CD4+CD8+ memory cells in the piglet intestine following oral administration of Bacillus subtilis spores combined with PEDV whole inactivated virus

Oral immunization is a commonly employed route for inducing local immunity. However, the application of oral immunization is limited by the short-term persistence of immunity, particularly for inactivated viruses. The ultimate goal for mucosal vaccination is to stimulate protective immunological memory. In the intestine, long-term persistence of immunity is related to CD4⁺CD8⁺ memory T-cells. In this study, piglets were orally immunized with Bacillus subtilis spores (B.s) plus whole inactivated porcine epidemic diarrhea virus (PEDV WIV), followed by booster oral immunization. Initially, the results showed that B.s plus PEDV WIV enhanced the anti-PEDV capability on mucosal surfaces, as evidenced by plaque reduction neutralization tests in serum and intestinal fluid. Elevated antigen-specific IgG titers in the serum and IgA titers in saliva, feces and nasal washing liquid were also observed. Meanwhile, B.s plus PEDV WIV increased the area of Peyer's patches and the number of intraepithelial lymphocytes in the ileum of piglets. Similarly, the percentage of CD4⁺CD8⁺ memory T-cells were upregulated and proliferation ability of antigen-specific memory T-cell was strengthened in intestinal mucosal-associated lymphocytes, which was accompanied with increased expression of CCR9 after oral immunization with B.s plus PEDV WIV. In addition, the activation of memory T-cells is correlated with the increased mRNA expression of Toll-like receptor 2 and 4, as well as interleukin-6 and induced by B.s. Collectively, the study provided further insight into the potential immunopotentiator ability of B.s to assist PEDV WIV in the potentiation of immunity by upregulating memory CD4⁺CD8⁺ T cells via oral immunization.