Effect of neonatal sublingual vaccination with native or denatured ovalbumin and adjuvant CpG or cholera toxin on systemic and mucosal immunity in mice

Towards the future exploration of mucosal mRNA vaccines against emerging viral diseases; lessons from existing next-generation mucosal vaccine strategies

The mRNA vaccine platform has offered the greatest potential in fighting the COVID-19 pandemic owing to rapid development, effectiveness, and scalability to meet the global demand. There are many other mRNA vaccines currently being developed against different emerging viral diseases. As with the current COVID-19 vaccines, these mRNA-based vaccine candidates are being developed for parenteral administration via injections. However, most of the emerging viruses colonize the mucosal surfaces prior to systemic infection making it very crucial to target mucosal immunity. Although parenterally administered vaccines would induce a robust systemic immunity, they often provoke a weak mucosal immunity which may not be effective in preventing mucosal infection. In contrast, mucosal administration potentially offers the dual benefit of inducing potent mucosal and systemic immunity which would be more effective in offering protection against mucosal viral infection. There are however many challenges posed by the mucosal environment which impede successful mucosal vaccination. The development of an effective delivery system remains a major challenge to the successful exploitation of mucosal mRNA vaccination. Nonetheless, a number of delivery vehicles have been experimentally harnessed with different degrees of success in the mucosal delivery of mRNA vaccines. In this review, we provide a comprehensive overview of mRNA vaccines and summarise their application in the fight against emerging viral diseases with particular emphasis on COVID-19 mRNA platforms. Furthermore, we discuss the prospects and challenges of mucosal administration of mRNA-based vaccines, and we explore the existing experimental studies on mucosal mRNA vaccine delivery.

Current possibilities and future perspectives for improving efficacy of allergen-specific sublingual immunotherapy

Allergen-specific sublingual immunotherapy (SLIT), a safe and efficient route for treating type I hypersensitivity disorders, requires high doses of allergens. SLIT is generally performed without adjuvants and delivery systems. Therefore, allergen formulation with appropriate presentation platforms results in improved allergen availability, targeting the immune cells, inducing regulatory immune responses, and enhancing immunotherapy's efficacy while decreasing the dose of the allergen. In this review, we discuss the adjuvants and delivery systems that have been applied as allergen-presentation platforms for SLIT. These adjuvants include TLRs ligands, 1α, 25-dihydroxy vitamin D3, galectin-9, probiotic and bacterial components that provoke allergen-specific helper type-1 T lymphocytes (TH1), and regulatory T cells (Tregs). Another approach is encapsulation or adsorption of the allergens into a particulate vector system to facilitate allergen capture by tolerogenic dendritic cells. Also, we proposed strategies to increasing the efficacy of SLIT via new immunopotentiators and carrier systems in the future.

Suppression of Hippo Pathway by Food Allergen Exacerbates Intestinal Epithelia Instability and Facilitates Hypersensitivity

SCOPE

Hippo signaling is a crucial pathway in innate immune responses, but the relationship between food allergy and Hippo pathway is unknown. The aim of this work is to investigate the regulation of food allergy by Hippo pathway and reveal the molecular mechanisms.

METHODS AND RESULTS

Two food allergens tropomyosin and ovalbumin are used to challenge a mouse model and CMT93 intestinal epithelia cell model. The allergic responses and the activation of Hippo pathway are tested in these models. In the mouse model, both allergens trigged significant allergic responses, and Hippo pathway is suppressed after allergen challenge. In CMT93, both allergens upregulate the expression of allergic cytokines thymic stromal lymphopoietin, interleukin (IL)-25, and IL-33. In TAZ KD CMT93, the Hippo pathway is blocked, and the expression of allergenic cytokines are also suppressed.

CONCLUSIONS

Both in vivo and in vitro data demonstrate that the two food allergens suppressed Hippo pathway by downregulating TAZ expression, resulting in intestinal epithelia instability, and finally leading to hypersensitivity reactions. These findings provide potential therapeutic targets and molecular markers for food allergy, and provide dietary guidelines for allergenic individuals.

Murine models for mucosal tolerance in allergy

Immunity is established by a fine balance to discriminate between self and non-self. In addition, mucosal surfaces have the unique ability to establish and maintain a state of tolerance also against non-self constituents such as those represented by the large numbers of commensals populating mucosal surfaces and food-derived or air-borne antigens. Recent years have seen a dramatic expansion in our understanding of the basic mechanisms and the involved cellular and molecular players orchestrating mucosal tolerance. As a direct outgrowth, promising prophylactic and therapeutic models for mucosal tolerance induction against usually innocuous antigens (derived from food and aeroallergen sources) have been developed. A major theme in the past years was the introduction of improved formulations and novel adjuvants into such allergy vaccines. This review article describes basic mechanisms of mucosal tolerance induction and contrasts the peculiarities but also the interdependence of the gut and respiratory tract associated lymphoid tissues in that context. Particular emphasis is put on delineating the current prophylactic and therapeutic strategies to study and improve mucosal tolerance induction in allergy.

Respiratory syncytial virus: an overview of infection biology and vaccination strategies

Respiratory syncytial virus (RSV) is the foremost cause of lower respiratory tract infections, especially in infants and young children. To date, there is no licensed vaccine available for RSV. Only option to restrain RSV is a prophylactic treatment in the form of monoclonal antibody (palivizumab). However, it is quite expensive and used in few patients with co-morbidities. In ongoing research, virologists contemplate about various vaccine candidates to control RSV infection. This review will help in understating the RSV pathobiology and encompass the advancement on various vaccine candidates that would lead to reduce the incidence, mortality and morbidity. Furthermore, it will lighten up the different avenues which might be useful for the development of novel vaccination approaches.

Mucosal vaccines: novel strategies and applications for the control of pathogens and tumors at mucosal sites

The mucosal immune system displays several adaptations reflecting the exposure to the external environment. The efficient induction of mucosal immune responses also requires specific approaches, such as the use of appropriate administration routes and specific adjuvants and/or delivery systems. In contrast to vaccines delivered via parenteral routes, experimental, and clinical evidences demonstrated that mucosal vaccines can efficiently induce local immune responses to pathogens or tumors located at mucosal sites as well as systemic response. At least in part, such features can be explained by the compartmentalization of mucosal B and T cell populations that play important roles in the modulation of local immune responses. In the present review, we discuss molecular and cellular features of the mucosal immune system as well as novel immunization approaches that may lead to the development of innovative and efficient vaccines targeting pathogens and tumors at different mucosal sites.

Buccal and sublingual vaccine delivery

Because of their large surface area and immunological competence, mucosal tissues are attractive administration and target sites for vaccination. An important characteristic of mucosal vaccination is its ability to elicit local immune responses, which act against infection at the site of pathogen entry. However, mucosal surfaces are endowed with potent and sophisticated tolerance mechanisms to prevent the immune system from overreacting to the many environmental antigens. Hence, mucosal vaccination may suppress the immune system instead of induce a protective immune response. Therefore, mucosal adjuvants and/or special antigen delivery systems as well as appropriate dosage forms are required in order to develop potent mucosal vaccines.

Whereas oral, nasal and pulmonary vaccine delivery strategies have been described extensively, the sublingual and buccal routes have received considerably less attention. In this review, the characteristics of and approaches for sublingual and buccal vaccine delivery are described and compared with other mucosal vaccine delivery sites. We discuss recent progress and highlight promising developments in the search for vaccine formulations, including adjuvants and suitable dosage forms, which are likely critical for designing a successful sublingual or buccal vaccine. Finally, we outline the challenges, hurdles to overcome and formulation issues relevant for sublingual or buccal vaccine delivery.

Induced pluripotent stem cells without c-Myc reduce airway responsiveness and allergic reaction in sensitized mice

BACKGROUND

Allergic disorders have increased substantially in recent years. Asthma is characterized by airway damage and remodeling. Reprogramming induced pluripotent stem cells (iPSCs) from adult somatic cells transfected by Oct-4/Sox-2/Klf-4, but not c-Myc, has shown the potential of embryonic-like cells. These cells have potential for multilineage differentiation and provide a resource for stem cell-based utility. However, the therapeutic potential of iPSCs without c-Myc (iPSC-w/o-c-Myc) in allergic diseases and airway hyperresponsiveness has not been investigated. The aim of this study was to evaluate the therapeutic effect of iPSC-w/o-c-Myc transplantation in a murine asthma model.

METHODS

BALB/c mice were sensitized with alum-adsorbed ovalbumin (OVA) and then challenged with aerosolized OVA. Phosphate-buffered saline or iPSC-w/o-c-Myc was then intravenously injected after inhalation. Serum allergen-specific antibody levels, airway hyperresponsiveness, cytokine levels in spleen cells and bronchoalveolar lavage fluid (BALF), and cellular distribution in BALF were then examined.

RESULTS

Treatment with iPSC-w/o-c-Myc effectively suppressed both Th1 and Th2 antibody responses, which was characterized by reduction in serum allergen-specific IgE, IgG, IgG1, and IgG2a levels as well as in interleukin-5 and interferon-γ levels in BALF and in OVA-incubated splenocytes. Meanwhile, regulatory cytokine, interleukin-10, was enhanced. Transplantation of iPSC-w/o-c-Myc also significantly attenuated cellular infiltration in BALF and allergic airway hyperresponsiveness. However, no tumor formation was observed 6 months after transplantation.

CONCLUSIONS

Administration of iPSC-w/o-c-Myc not only inhibited Th1 inflammatory responses but also had therapeutic effects on systemic allergic responses and airway hyperresponsiveness. iPSC-w/o-c-Myc transplantation may be a potential modality for treating allergic reactions and bronchial asthma.

Effect of oral administration with pravastatin and atorvastatin on airway hyperresponsiveness and allergic reactions in asthmatic mice

BACKGROUND

Asthma is characterized by airway hyperresponsiveness and remodeling. Pravastatin and atorvastatin are used clinically as cholesterol-lowering agents but also exhibit anti-inflammatory and immunomodulating properties.

OBJECTIVE

To investigate the therapeutic effect of oral statins on airway hyperresponsiveness and allergic reaction.

METHODS

BALB/c mice received intraperitoneal sensitization and aerosol inhalation with ovalbumin consequently. One week after ovalbumin aerosol challenge, pravastatin, atorvastatin, or phosphate-buffered saline were given by intragastric gavage daily for 2 weeks. Airway hyperresponsiveness, serum allergen specific antibody levels, cytokine production by splenocytes, and bronchoalveolar lavage fluid were examined.

RESULTS

Both pravastatin and atorvastatin effectively reduced airway hyperresponsiveness. Pravastatin effectively suppressed both T(H)1- and T(H)2-mediated antibody responses, reducing serum specific IgE, IgG, IgG1, and IgG2a levels. Pravastatin also effectively reduced interleukin (IL) 4, IL-5, and interferon γ production but significantly enhanced IL-10 levels in splenocytes and BALF. Similarly, atorvastatin effectively attenuated production of specific IgE, IgG1, and IgG2a antibodies. It also significantly attenuated IL-4, interferon γ, and increased IL-10 concentration in bronchoalveolar lavage fluid and splenocytes.

CONCLUSION

Oral administration of pravastatin or atorvastatin not only was able to inhibit T(H)1 inflammatory responses but also had therapeutic effects on airway hyperresponsiveness and T(H)2 allergic responses. These results seem to suggest that these drugs have potential as a nonimmunosuppressive therapy for asthma and allergic diseases.

Mucosal vaccine adjuvants update

Mucosal vaccination, capable of inducing protective immune responses both in the mucosal and systemic immune compartments, has many advantages and is regarded as a blue ocean in the vaccine industry. Mucosal vaccines can offer lower costs, better accessability, needle-free delivery, and higher capacity of mass immunizations during pandemics. However, only very limited number of mucosal vaccines was approved for human use in the market yet. Generally, induction of immune responses following mucosal immunization requires the co-administration of appropriate adjuvants that can initiate and support the effective collaboration between innate and adaptive immunity. Classically, adjuvant researches were rather empirical than keenly scientific. However, during last several years, fundamental scientific achievements in innate immunity have been translated into the development of new mucosal adjuvants. This review focuses on recent developments in the concepts of adjuvants and innate immunity, mucosal immunity with special interest of vaccine development, and basic and applied researches in mucosal adjuvant.

The circadian clock controls toll-like receptor 9-mediated innate and adaptive immunity

Circadian rhythms refer to biologic processes that oscillate with a period of ~24 hr. These rhythms are sustained by a molecular clock and provide a temporal matrix that ensures the coordination of homeostatic processes with the periodicity of environmental challenges. We demonstrate the circadian molecular clock controls the expression and function of Toll-like receptor 9 (TLR9). In a vaccination model using TLR9 ligand as adjuvant, mice immunized at the time of enhanced TLR9 responsiveness presented weeks later with an improved adaptive immune response. In a TLR9-dependent mouse model of sepsis, we found that disease severity was dependent on the timing of sepsis induction, coinciding with the daily changes in TLR9 expression and function. These findings unveil a direct molecular link between the circadian and innate immune systems with important implications for immunoprophylaxis and immunotherapy.

Robust antigen-specific humoral immune responses to sublingually delivered adenoviral vectors encoding HIV-1 Env: association with mucoadhesion and efficient penetration of the sublingual barrier

The efficient induction of virus-specific mucosal antibodies is an important unmet objective in Human Immunodeficiency Virus Type-1 (HIV-1) vaccine research. One promising approach is sublingual (SL) immunization. We examined the effectiveness of SL delivery of two different viral vectors: (i) a recombinant adenovirus (rAd5), and (ii) a Herpes Simplex Virus Type-1 amplicon vector (HSV-1). Initial in vitro videomicroscopy experiments showed that rAd5 particles were trapped in saliva (i.e., that Ad5 was mucoadhesive) - unlike HSV-1 virions, which migrated freely in both saliva and water. In vivo imaging studies in mice revealed that only the rAd5 vector efficiently transduced the SL epithelium. Consistent with this, SL delivery of an rAd5 encoding HIV-1 envelope glycoprotein (Env) resulted in robust antigen-specific antibody responses in plasma and in vaginal washes, whereas SL delivery of a HSV-1 amplicon vector encoding HIV-1 Env failed to elicit Env-specific antibodies. In contrast, both vectors elicited equivalent humoral responses following intramuscular (IM) delivery. Finally, SL delivery of the rAd5:Env vector resulted in elevated levels of Env-specific serum IgA, and vaginal IgA and IgG, when compared to IM delivery of the same vector. These results findings shed light on vector properties (mucoadhesion, penetration of the sublingual barrier) which may be important for the induction of potent humoral immune responses following sublingual vector administration. Our data also show that SL delivery of an Env-encoding rAd5 vector can elicit a potent antigen-specific mucosal antibody response in the absence of adjuvant. Overall, these findings support the further exploration of the SL delivery route for HIV-1 vaccine delivery.

Sublingual therapeutic immunization with a polyvalent bacterial preparation in patients with recurrent respiratory infections: immunomodulatory effect on antigen-specific memory CD4+ T cells and impact on clinical outcome

Recurrent respiratory tract infections (RRTIs) are common clinical conditions in individuals with alterations of the immune function. A prospective open pilot study in a cohort of patients with RRTIs has been performed to assess whether sublingual immunization with a polyvalent bacterial vaccine could exert an immunomodulatory effect on the antigen-specific immunological responses and have an impact on the clinical outcome. Seventeen patients with RRTIs were recruited. An oral polyvalent bacterial preparation (Bactek®) was administered to all patients daily for 6 months. Immunological assessment was performed at baseline and at the end of immunization. Immunological measurements included: T cell-specific proliferations of CD3+CD4+ and CD3+CD8+ to Bactek® antigens, total immunoglobulin levels, antibodies to pneumococcal polysaccharide and tetanus toxoid and B, T and natural killer (NK) cell subsets. There was a significant increase in the proliferative capacity of CD3+CD4+ T cells specific to Bactek® antigens at month 6 in comparison to baseline (P < 0·0001). A significant increase in total CD3+ T cells was also observed (P < 0·05). No significant differences were observed between baseline and month 6 in levels of total immunoglobulins, specific antibodies and B, T or NK cell subsets. A significant reduction in the patient's rate of RRTIs was observed compared with 1 year prior to initiation of therapy (P < 0·0001). The results demonstrate that long-term administration of a sublingual polyvalent bacterial preparation in patients with RRTIs exerts an immune stimulating effect on CD4+ T helper cell responses to bacterial antigens which could be associated with clinical benefit.

Defending the mucosa: adjuvant and carrier formulations for mucosal immunity

A majority of infectious microorganisms either colonize or cross mucosal surfaces to enter the host. A major goal in vaccine design is to induce a protective, lasting immune response against potential pathogens at mucosal surfaces. In addition, mucosal vaccines can offer needle-free delivery, thereby improving accessibility, safety, and cost-effectiveness. Challenges to successful mucosal vaccination include poor induction of mucosal immunity, limited understanding of protective mechanisms and crosstalk between mucosal compartments, and the availability of safe, effective mucosal adjuvants and delivery systems. This review focuses on some key advances in the field of mucosal vaccinology within the past 2-3 years, including reports on promising new formulations and investigations into the mechanisms of established mucosal adjuvants and/or particulate carrier systems.

Dendritic cell-targeting DNA-based mucosal adjuvants for the development of mucosal vaccines

In order to establish effective mucosal immunity against various mucosal pathogens, vaccines must be delivered via the mucosal route and contain effective adjuvant(s). Since mucosal adjuvants can simply mix with the antigen, it is relatively easy to adapt them for different types of vaccine development. Even in simple admixture vaccines, the adjuvant itself must be prepared without any complications. Thus, CpG oligodeoxynucleotides or plasmids encoding certain cDNA(s) would be potent mucosal adjuvant candidates when compared with other substances that can be used as mucosal adjuvants. The strategy of a DNA-based mucosal adjuvant facilitates the targeting of mucosal dendritic cells, and thus is an effective and safe approach. It would also provide great flexibility for the development of effective vaccines for various mucosal pathogens.

Mucosal and systemic immunization with targeted fusion anti-caries DNA plasmid in young rats

Early life vaccination is necessary to protect young children from dental caries. Our group had previously reported that a plasmid DNA vaccine pGJA-P/VAX against the glucosyltransferase (GTF) enzyme and cell surface antigen AgI/II (PAc) of Streptococcus mutans (S. mutans) elicited a specific and protective immunity in adult experimental animal models. In this report, early life immunization with the same plasmid was studied following intranasal (i.n.) and intramuscular (i.m.) delivery in murine models. The potential of inducing mucosal and systemic immune responses to special antigens was measured by ELISA. In addition, cytokine production and protection effectiveness against dental caries formation were also investigated. In the i.n. route, rats were primed when they were 5 days old, and boosted after 10 and 20 days with either plasmid pGJA-P/VAX-bupivacaine complexes, or pGJA-P/VAX alone, or empty vector. The pGJA-P/VAX-bupivacaine combination was able to mount the immune responses characterized by increased antibody levels of specific salivary IgA and serum IgG, preferential IFN-gamma production and significant reduction in the dental caries lesions. In the i.m. route, rats were vaccinated with either pGJA-P/VAX alone or empty vector with the same immunization schedule as the i.n. route. Plasmid pGJA-P/VAX alone induced a significant increase in the serum IgG and IFN-gamma production. However, it was not effective in eliciting specific salivary IgA and in decreasing the dental caries formation. All these findings indicate the feasibility of immunity with a targeted fusion DNA vaccine to a young immune system.