Intranasal influenza vaccination using a new synthetic mucosal adjuvant SF-10: induction of potent local and systemic immunity with balanced Th1 and Th2 responses

Induction of systemic, mucosal, and cellular immunity against SARS-CoV-2 in mice vaccinated by trans-airway with a S1 protein combined with a pulmonary surfactant-derived adjuvant SF-10

Background

There is a need for vaccines that can induce effective systemic, respiratory mucosal, and cellular immunity to control the COVID-19 pandemic. We reported previously that a synthetic mucosal adjuvant SF-10 derived from human pulmonary surfactant works as an efficient antigen delivery vehicle to antigen presenting cells in the respiratory and gastrointestinal tracts and promotes induction of influenza virus antigen-specific serum IgG, mucosal IgA, and cellular immunity.

Methods

The aim of the present study was to determine the effectiveness of a new administration route of trans-airway (TA) vaccine comprising recombinant SARS-CoV-2 spike protein 1 (S1) combined with SF-10 (S1-SF-10 vaccine) on systemic, local, and cellular immunity in mice, compared with intramuscular injection (IM) of S1 with a potent adjuvant AddaS03™ (S1-AddaS03™ vaccine).

Results

S1-SF-10-TA vaccine induced S1-specific IgG and IgA in serum and lung mucosae. These IgG and IgA induced by S1-SF-10-TA showed significant protective immunity in a receptor binding inhibition test of S1 and angiotensin converting enzyme 2, a receptor of SARS-CoV-2, which were more potent and faster achievement than S1-AddaS03™-IM. Enzyme-linked immunospot assay showed high numbers of S1-specific IgA and IgG secreting cells (ASCs) and S1-responsive IFN-γ, IL-4, IL-17A cytokine secreting cells (CSCs) in the spleen and lungs. S1-AddaS03™-IM induced IgG ASCs and IL-4 CSCs in spleen higher than S1-SF-10-TA, but the numbers of ASCs and CSCs in lungs were low and hardly detected.

Conclusions

Based on the need for effective systemic, respiratory, and cellular immunity, the S1-SF-10-TA vaccine seems promising mucosal vaccine against respiratory infection of SARS-CoV-2.

Development of a safe and effective novel synthetic mucosal adjuvant SF-10 derived from physiological metabolic pathways and function of human pulmonary surfactant

A safe and effective mucosal adjuvant is required for vaccination against influenza A virus (IAV) infection. Previously, we described that intranasally administration of surfacten®, a medicine derived from bovine pulmonary surfactant (PS), with IAV vaccine can induce IAV-specific IgA in the respiratory tract mucosa and IgG in serum. PS is secreted by alveolar type II cells and Clara cells and serves to reduce lung surface tension. PS finished its rules is incorporated by antigen presenting cells (APCs), such as alveolar macrophages and dendritic cells, and alveolar type II cells and rapidly metabolized. We focused on the metabolic pathways and rapid metabolic turnover of PS and developed a PS-based mucosal adjuvant. First, we determined the essential components of PS adjuvanticity and found that the complex of three PS lipids and surfactant protein-C can enhance to deliver the vaccine antigen and activate APCs. Later, we improved the safety, efficacy and ease of manufacture and finally succeeded in developing SF-10. The use of SF-10 with influenza split vaccine (HAv) (HAv-SF-10) enhances HAv incorporation into APCs both in vitro and in vivo, and intranasal instillation of HAv-SF-10 induced systemic and mucosal HAv-specific immunities in not only mice but also cynomolgus monkeys. The report that PS has physiological effects on the gastrointestinal mucosa prompted us develop a new SF-10-based vaccine that can be administered orally. In this review, We summarize our work on the development of clinically effective PS-based nasal and oral mucosal adjuvants for influenza vaccine.

A lung-on-chip model of early Mycobacterium tuberculosis infection reveals an essential role for alveolar epithelial cells in controlling bacterial growth

We establish a murine lung-on-chip infection model and use time-lapse imaging to reveal the dynamics of host-Mycobacterium tuberculosis interactions at an air-liquid interface with a spatiotemporal resolution unattainable in animal models and to probe the direct role of pulmonary surfactant in early infection. Surfactant deficiency results in rapid and uncontrolled bacterial growth in both macrophages and alveolar epithelial cells. In contrast, under normal surfactant levels, a significant fraction of intracellular bacteria are non-growing. The surfactant-deficient phenotype is rescued by exogenous addition of surfactant replacement formulations, which have no effect on bacterial viability in the absence of host cells. Surfactant partially removes virulence-associated lipids and proteins from the bacterial cell surface. Consistent with this mechanism, the attenuation of bacteria lacking the ESX-1 secretion system is independent of surfactant levels. These findings may partly explain why smokers and elderly persons with compromised surfactant function are at increased risk of developing active tuberculosis.

Tuberculosis is a contagious respiratory disease caused by the bacterium Mycobacterium tuberculosis. Droplets in the air carry these bacteria deep into the lungs, where they cling onto and infect lung cells. Only small droplets, holding one or two bacteria, can reach the right cells, which means that just a couple of bacterial cells can trigger an infection. But people respond differently to the bacteria: some develop active and fatal forms of tuberculosis, while many show no signs of infection. With no effective tuberculosis vaccine for adults, understanding why individuals respond differently to Mycobacterium tuberculosis may help develop treatments.

Different responses to Mycobacterium tuberculosis may stem from the earliest stages of infection, but these stages are difficult to study. For one thing, tracking the movements of the few bacterial cells that initiate infection is tricky. For another, studying the molecules, called ‘surfactants’, that the lungs produce to protect themselves from tuberculosis can prove difficult because these molecules are necessary for the lungs to inflate and deflate normally. Normally, the role of a molecule can be studied by genetically modifying an animal so it does not produce the molecule in question, which provides information as to its potential roles. Unfortunately, due to the role of surfactants in normal breathing, animals lacking them die. Therefore, to reveal the role of some of surfactants in tuberculosis, Thacker et al. used ‘lung-on-chip’ technology. The ‘chip’ (a transparent device made of a polymer compatible with biological tissues) is coated with layers of cells and has channels to simulate air and blood flow.

To see what effects surfactants have on M. tuberculosis bacteria, Thacker et al. altered the levels of surfactants produced by the cells on the lung-on-chip device. Two types of mouse cells were grown on the chip: lung cells and immune cells. When cells lacked surfactants, bacteria grew rapidly on both lung and immune cells, but when surfactants were present bacteria grew much slower on both cell types, or did not grow at all. Further probing showed that the surfactants pulled out proteins and fats on the surface of M. tuberculosis that help the bacteria to infect their host, highlighting the protective role of surfactants in tuberculosis.

These findings lay the foundations for a system to study respiratory infections without using animals. This will allow scientists to study the early stages of Mycobacterium tuberculosis infection, which is crucial for finding ways to manage tuberculosis.

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.

Influenza A in Bovine Species: A Narrative Literature Review

It is quite intriguing that bovines were largely unaffected by influenza A, even though most of the domesticated and wild animals/birds at the human-animal interface succumbed to infection over the past few decades. Influenza A occurs on a very infrequent basis in bovine species and hence bovines were not considered to be susceptible hosts for influenza until the emergence of influenza D. This review describes a multifaceted chronological review of literature on influenza in cattle which comprises mainly of the natural infections/outbreaks, experimental studies, and pathological and seroepidemiological aspects of influenza A that have occurred in the past. The review also sheds light on the bovine models used in vitro and in vivo for influenza-related studies over recent years. Despite a few natural cases in the mid-twentieth century and seroprevalence of human, swine, and avian influenza viruses in bovines, the evolution and host adaptation of influenza A virus (IAV) in this species suffered a serious hindrance until the novel influenza D virus (IDV) emerged recently in cattle across the world. Supposedly, certain bovine host factors, particularly some serum components and secretory proteins, were reported to have anti-influenza properties, which could be an attributing factor for the resilient nature of bovines to IAV. Further studies are needed to identify the host-specific factors contributing to the differential pathogenetic mechanisms and disease progression of IAV in bovines compared to other susceptible mammalian hosts.

Oral vaccination with influenza hemagglutinin combined with human pulmonary surfactant-mimicking synthetic adjuvant SF-10 induces efficient local and systemic immunity compared with nasal and subcutaneous vaccination and provides protective immunity in mice

We reported previously that a synthetic mucosal adjuvant SF-10, which mimics human pulmonary surfactant, delivers antigen to mucosal dendritic cells in the nasal cavity and promotes induction of humoral and cellular immunity. The aim of the present study was to determine the effects of oral administration of antigen combined with SF-10 (antigen-SF-10) on systemic and local immunity. Oral administration of ovalbumin, a model antigen, combined with SF-10 enhanced ovalbumin uptake into intestinal antigen presenting MHC II⁺CD11c⁺ cells and their CD11b⁺CD103⁺ and CD11b⁺CD103^- subtype dendritic cells, which are the major antigen presenting subsets of the intestinal tract, more efficiently compared to without SF-10. Oral vaccination with influenza hemagglutinin vaccine (HAv)-SF-10 induced HAv-specific IgA and IgG in the serum, and HAv-specific secretory IgA and IgG in bronchoalveolar lavage fluid, nasal washes, gastric extracts and fecal material; their levels were significantly higher than those induced by subcutaneous HAv or intranasal HAv and HAv-SF-10 vaccinations. Enzyme-linked immunospot assay showed high numbers of HAv-specific IgA and IgG antibody secreting cells in the gastrointestinal and respiratory mucosal lymphoid tissues after oral vaccination with HAv-SF-10, but no or very low induction following oral vaccination with HAv alone. Oral vaccination with HAv-SF-10 provided protective immunity against severe influenza A virus infection, which was significantly higher than that induced by HAv combined with cholera toxin. Oral vaccination with HAv-SF-10 was associated with unique cytokine production patterns in the spleen after HAv stimulation; including marked induction of HAv-responsive Th17 cytokines (e.g., IL-17A and IL-22), high induction of Th1 cytokines (e.g., IL-2 and IFN-γ) and moderate induction of Th2 cytokines (e.g., IL-4 and IL-5). These results indicate that oral vaccination with HAv-SF-10 induces more efficient systemic and local immunity than nasal or subcutaneous vaccination with characteristically high levels of secretory HAv-specific IgA in various mucosal organs and protective immunity.

Immunization with attenuated non-transformable pneumococcal pep27 and comD mutant provides serotype-independent protection against pneumococcal infection

Streptococcus pneumoniae is a well-known pathogenic bacterium with a high mortality rate. Currently, a 23-valent pneumococcal polysaccharide vaccine (PPV23) and protein-conjugate vaccines (PCVs) are available on the market. However, both of these vaccines have limitations; specifically, PPV23 produces weak antibody responses in children younger than 2 years and PCVs only partially protect against secondary infection. Previously, we showed serotype-nonspecific protection by Δpep27 vaccine, but the reversion of Δpep27 to the wild type serotype during immunization cannot be excluded. To ensure the safety of the Δpep27 vaccine, comD, an important protein that activates competence, was inactivated, and the transformability of the double mutant (Δpep27ΔcomD) was determined. The transformation ability of this double mutant was successfully abolished. Δpep27ΔcomD immunization significantly increased the survival time after heterologous challenge(s), and diminished colonization levels independent of serotype, including a non-typeable strain (NCC1). Moreover, the double mutant was found to be highly safe in both normal and immunocompromised mice. In conclusion, this pneumococcal Δpep27ΔcomD vaccine appears to be a highly feasible and safe vaccine to prevent various types of pneumococcal infections.

Polymeric Caffeic Acid Is a Safer Mucosal Adjuvant That Augments Antigen-Specific Mucosal and Systemic Immune Responses in Mice

Infections remain a major threat to human lives. To overcome the threat caused by pathogens, mucosal vaccines are considered a promising strategy. However, no inactivated and/or subunit mucosal vaccine has been approved for human use, largely because of the lack of a safe and effective mucosal adjuvant. Here, we show that enzymatically synthesized polymeric caffeic acid (pCA) can act as a potent mucosal adjuvant in mice. Intranasal administration of ovalbumin (OVA) in combination with pCA resulted in the induction of OVA-specific mucosal IgA and serum IgG, especially IgG1. Importantly, pCA was synthesized from caffeic acid and horseradish peroxidase from coffee beans and horseradish, respectively, which are commonly consumed. Therefore, pCA is believed to be a highly safe material. In fact, administration of pCA did not show distinct toxicity in mice. These data indicate that pCA has merit for use as a mucosal adjuvant for nasal vaccine formulations.

Adjuvanting influenza hemagglutinin vaccine with a human pulmonary surfactant-mimicking synthetic compound SF-10 induces local and systemic cell-mediated immunity in mice

We reported previously that intranasal instillation of a synthetic human pulmonary surfactant with a carboxy vinyl polymer as a viscosity improver, named SF-10, shows potent adjuvanticity for humoral immunity in mice and cynomolgus monkeys. SF-10 effectively induces influenza hemagglutinin vaccine (HAv)-specific IgA in nasal and lung washes and IgG in sera with their neutralizing activities. Since CD8⁺ T cell-mediated protection is an important requirement for adaptive immunity, we investigated in this study the effects of SF-10 with antigen on local and systemic cell-mediated immunity. Nasal instillation of ovalbumin, a model antigen, combined with SF-10 efficiently delivered antigen to mucosal dendritic and epithelial cells and promoted cross-presentation in antigen presenting cells, yielding a high percentage of ovalbumin-specific cytotoxic T lymphocytes in the nasal mucosa, compared with ovalbumin alone. Nasal immunization of HAv-SF-10 also induced HAv-specific cytotoxic T lymphocytes and upregulated granzyme B expression in splenic CD8⁺ T cells with their high cytotoxicity against target cells pulsed with HA peptide. Furthermore, nasal vaccination of HAv-SF-10 significantly induced higher cytotoxic T lymphocytes-mediated cytotoxicity in the lungs and cervical lymph nodes in the early phase of influenza virus infection compared with HAv alone. Protective immunity induced by HAv-SF-10 against lethal influenza virus infection was partially and predominantly suppressed after depletion of CD8⁺ and CD4⁺ T cells (induced by intraperitoneal injection of the corresponding antibodies), respectively, suggesting that CD4⁺ T cells predominantly and CD8⁺ T cells partially contribute to the protective immunity in the advanced stage of influenza virus infection. These results suggest that SF-10 promotes effective antigen delivery to antigen presenting cells, activates CD8⁺ T cells via cross-presentation, and induces cell-mediated immune responses against antigen.

A small-molecule IRF3 agonist functions as an influenza vaccine adjuvant by modulating the antiviral immune response

Vaccine adjuvants are essential to drive a protective immune response in cases where vaccine antigens are weakly immunogenic, where vaccine antigen is limited, or where an increase in potency is needed for a specific population, such as the elderly. To discover novel vaccine adjuvants, we used a high-throughput screen (HTS) designed to identify small-molecule agonists of the RIG-I-like receptor (RLR) pathway leading to interferon regulatory factor 3 (IRF3) activation. RLRs are a group of cytosolic pattern-recognition receptors that are essential for the recognition of viral nucleic acids during infection. Upon binding of viral nucleic acid ligands, the RLRs become activated and signal to transcription factors, including IRF3, to initiate an innate immune transcriptional program to control virus infection. Among our HTS hits were a series of benzothiazole compounds from which we designed the lead analog, KIN1148. KIN1148 induced dose-dependent IRF3 nuclear translocation and specific activation of IRF3-responsive promoters. Prime-boost immunization of mice with a suboptimal dose of a monovalent pandemic influenza split virus H1N1 A/California/07/2009 vaccine plus KIN1148 protected against a lethal challenge with mouse-adapted influenza virus (A/California/04/2009) and induced an influenza virus-specific IL-10 and Th2 response by T cells derived from lung and lung-draining lymph nodes. Prime-boost immunization with vaccine plus KIN1148, but not prime immunization alone, induced antibodies capable of inhibiting influenza virus hemagglutinin and neutralizing viral infectivity. Nevertheless, a single immunization with vaccine plus KIN1148 provided increased protection over vaccine alone and reduced viral load in the lungs after challenge. These findings suggest that protection was at least partially mediated by a cellular immune component and that the induction of Th2 and immunoregulatory cytokines by a KIN1148-adjuvanted vaccine may be particularly beneficial for ameliorating the immunopathogenesis that is associated with influenza viruses.

Intranasal hydroxypropyl-β-cyclodextrin-adjuvanted influenza vaccine protects against sub-heterologous virus infection

Intranasal vaccination with inactivated influenza viral antigens is an attractive and valid alternative to currently available influenza (flu) vaccines; many of which seem to need efficient and safe adjuvant, however. In this study, we examined whether hydroxypropyl-β-cyclodextrin (HP-β-CD), a widely used pharmaceutical excipient to improve solubility and drug delivery, can act as a mucosal adjuvant for intranasal flu vaccines. We found that intranasal immunization of mice with hemagglutinin split- as well as inactivated whole-virion influenza vaccine with HP-β-CD resulted in secretion of antigen-specific IgA and IgGs in the airway mucosa and the serum as well. As a result, both HP-β-CD adjuvanted-flu intranasal vaccine protected mice against lethal challenge with influenza virus, equivalent to those induced by experimental cholera toxin-adjuvanted ones. Of note, intranasal use of HP-β-CD as an adjuvant induced significantly lower antigen-specific IgE responses than that induced by aluminum salt adjuvant. These results suggest that HP-β-CD may be a potent mucosal adjuvant for seasonal and pandemic influenza vaccine.

Induction of systemic and mucosal immunity and maintenance of its memory against influenza A virus by nasal vaccination using a new mucosal adjuvant SF-10 derived from pulmonary surfactant in young cynomolgus monkeys

Induction of systemic and mucosal immunity and maintenance of its memory was investigated in 12 young male cynomolgus monkeys after intranasal instillation of flu vaccine using a new mucosal adjuvant SF-10 derived from pulmonary surfactant constituents. Split-product of influenza virus A/California/7/2009(H1N1)pdm hemagglutinin vaccine (HAv) at 15 μg with or without SF-10 and the adjuvant alone were instilled intranasally three times every 2 weeks. SF-10-adjuvanted HAv (SF-10-HAv) elicited significantly higher HAv-specific IgG and hemagglutinin inhibition (HI) titers in serum and HAv-specific secretory IgA and its neutralizing activities in nasal washes compared with HAv antigen and SF-10 alone. Significant cross-neutralizing activities of nasal washes after the third vaccination to several other H1N1 and H3N2 strains were observed. HI titers in serum and neutralizing activities in nasal washes reached peak levels at 6 weeks after initial vaccination, then gradually decreased after 10 weeks and returned to the baseline levels at 36 weeks. A single intranasal revaccination of SF-10-HAv at 36 weeks rapidly and significantly increased both immunity in serum and nasal washes compared with naïve monkeys. Revaccination by one or two doses achieved almost maximal immunity at 2 or 4 weeks after instillation. Statistically significant adverse effects (e.g., body weight loss, elevated body temperature, nasal discharge, change in peripheral blood leukocyte and platelet counts) were not observed for 2 weeks after vaccination of SF-10-HAv, HAv or SF-10 and also during the experimental period. These results in young monkey model suggest the potential of clinical use SF-10 for intranasal flu vaccine.

A mucosal adjuvant for the inactivated poliovirus vaccine

The eradication of poliovirus from the majority of the world has been achieved through the use of two vaccines: the inactivated poliovirus vaccine (IPV) and the live-attenuated oral poliovirus vaccine (OPV). Both vaccines are effective at preventing paralytic poliomyelitis, however, they also have significant differences. Most importantly for this work is the risk of revertant virus from OPV, the greater cost of IPV, and the low mucosal immunity induced by IPV. We and others have previously described the use of an alphavirus-based adjuvant that can induce a mucosal immune response to a co-administered antigen even when delivered at a non-mucosal site. In this report, we describe the use of an alphavirus-based adjuvant (GVI3000) with IPV. The IPV-GVI3000 vaccine significantly increased systemic IgG, mucosal IgG and mucosal IgA antibody responses to all three poliovirus serotypes in mice even when administered intramuscularly. Furthermore, GVI3000 significantly increased the potency of IPV in rat potency tests as measured by poliovirus neutralizing antibodies in serum. Thus, an IPV-GVI3000 vaccine would reduce the dose of IPV needed and provide significantly improved mucosal immunity. This vaccine could be an effective tool to use in the poliovirus eradication campaign without risking the re-introduction of revertant poliovirus derived from OPV.

Intranasal influenza vaccination using a new synthetic mucosal adjuvant SF-10: induction of potent local and systemic immunity with balanced Th1 and Th2 responses

BACKGROUND

We found previously that bovine pulmonary Surfacten® used in newborns with acute respiratory distress syndrome is a safe and efficacious antigen vehicle for intranasal vaccination.

OBJECTIVES

The objective of this study was to industrially produce a synthetic adjuvant mimicking Surfacten® for clinical use without risk of bovine spongiform encephalopathy.

METHODS

We selected three Surfacten lipids and surfactant protein (SP)-C as essential constituents for adjuvanticity. For replacement of the hydrophobic SP-C, we synthesized SP-related peptides and analyzed their adjuvanticity. We evaluated lyophilization to replace sonication for the binding of influenza virus hemagglutinin (HA) to the synthetic adjuvant. We also added a carboxy vinyl polymer (CVP) to the synthetic adjuvant and named the mixture as SF-10 adjuvant. HA combined with SF-10 was administered intranasally to mice, and induction of nasal-wash HA-specific secretory IgA (s-IgA) and serum IgG with Th1-/Th2-type cytokine responses in nasal cavity and virus challenge test were assessed.

RESULTS AND CONCLUSIONS

Intranasal immunization with HA-SF-10 induced significantly higher levels of anti-HA-specific nasal-wash s-IgA and serum IgG than those induced by HA-poly(I:C), a reported potent mucosal vaccine, and provided highly efficient protection against lethal doses of virus challenge in mice. Anti-HA-specific serum IgG levels induced by HA-SF-10 were almost equivalent to those induced by subcutaneous immunization of HA twice. Intranasal administration of HA-SF-10 induced balanced anti-HA-specific IgG1 and IgG2a in sera and IFN-γ- and IL-4-producing lymphocytes in nasal cavity without any induction of anti-HA IgE. The results suggest that HA-SF-10 is a promising nasal influenza vaccine and that SF-10 can be supplied in large quantities commercially.