Fusion proteins of flagellin and the major birch pollen allergen Bet v 1 show enhanced immunogenicity, reduced allergenicity, and intrinsic adjuvanticity

Recombinant African swine fever virus p30-flagellin fusion protein promotes p30-specific humoral and cellular immune responses in mice

African swine fever (ASF) is a transmissible and deadly viral disease caused by the African swine fever virus (ASFV) that has considerably affected the global pig industry. Vaccination is considered a potentially effective method to control ASF. However, live attenuated vaccines can't protect against all circulating virus isolates. Subunit vaccines can induce both cellular and humoral immune responses, but often require the addition of adjuvants. Flagellin, a stimulator of Toll-like receptor 5 (TLR5), functions as a potent adjuvant by enhancing cellular and humoral immune responses. However, its high antigenicity may cause severe systemic inflammation. In this study, an Escherichia coli expression system was used to express ASFV p30 protein (p30) fused with Salmonella Typhimurium FliCΔD2D3 (without the D2 and D3 domains of FliC). The immunological effect of p30-FlicΔD2D3 protein in mice was evaluated. Results revealed that the ASFV p30 protein and the p30-FlicΔD2D3 fusion protein were effectively expressed by the E. coli expression system. In vitro activity analysis showed that the p30-FlicΔD2D3 fusion protein could be recognized by ASFV-positive serum, had good immunoreactivity, and remarkably promoted IL-8 secretion related to TLR5 activity in HEK293-mTLR5 cells. However, p30-FlicΔD2D3 induced significantly lower levels of inflammatory factor IL-8 than that induced by wild-type flagellin. Immunization with the p30-FlicΔD2D3 fusion protein considerably promoted cellular and humoral immune responses in mice. Therefore, the p30-FlicΔD2D3 protein retained good immune reactivity and TLR5 agonist efficacy. It also enhanced humoral and cellular immune responses in mice. This work offered valuable information that will be helpful to develop ASF subunit vaccines.

Flagellin conjugated Per a 10 and its T cell peptides attenuate airway inflammation and restore cellular function

Adjuvants were used to modulate response towards relevant immune cells. The present study aims to investigate FlaA-conjugated Per a 10 and T cell peptides in amelioration of allergic airway disease in mice. Mice given Per a 10 showed allergic features with higher cellular infiltration, IgE, Th-2 cytokines and alarmins. Fusion protein treatment reduced lung inflammation (p < 0.0001) and cellular infiltrates (p < 0.001) with higher IgG2a/IgE indicating resolution of disease. Immunotherapy with FPT1 and FPT3 reduces IL-4, IL-5 and IL-13 levels (p < 0.0001) with a fourfold increase in IFN-γ secretion in BALF. FPT1- and FPT3-treated mice have increased IL-10 and TGF-β levels (p < 0.001) with CD4+Foxp3+ T cells (p < 0.01) indicating Treg response. There was enhanced expression of claudin-1 (1.7-fold) and occludin (fourfold) in lungs of FPT1- and FPT3-treated mice with reduced TSLP (p < 0.01) and IL-33 (p < 0.0001) secretion in BALF indicating recovery of epithelial function. Peptide-conjugated FlaA proteins showed protective immunity in mice and have potential for immunotherapy with restoration of cellular function.

Hot topics in allergen immunotherapy, 2023: Current status and future perspective

The importance of allergen immunotherapy (AIT) is multifaceted, encompassing both clinical and quality-of-life improvements and cost-effectiveness in the long term. Key mechanisms of allergen tolerance induced by AIT include changes in memory type allergen-specific T- and B-cell responses towards a regulatory phenotype with decreased Type 2 responses, suppression of allergen-specific IgE and increased IgG1 and IgG4, decreased mast cell and eosinophil numbers in allergic tissues and increased activation thresholds. The potential of novel patient enrolment strategies for AIT is taking into account recent advances in biomarkers discoveries, molecular allergy diagnostics and mobile health applications contributing to a personalized approach enhancement that can increase AIT efficacy and compliance. Artificial intelligence can help manage and interpret complex and heterogeneous data, including big data from omics and non-omics research, potentially predict disease subtypes, identify biomarkers and monitor patient responses to AIT. Novel AIT preparations, such as synthetic compounds, innovative carrier systems and adjuvants, are also of great promise. Advances in clinical trial models, including adaptive, complex and hybrid designs as well as real-world evidence, allow more flexibility and cost reduction. The analyses of AIT cost-effectiveness show a clear long-term advantage compared to pharmacotherapy. Important research questions, such as defining clinical endpoints, biomarkers of patient selection and efficacy, mechanisms and the modulation of the placebo effect and alternatives to conventional field trials, including allergen exposure chamber studies are still to be elucidated. This review demonstrates that AIT is still in its growth phase and shows immense development prospects.

Novel adjuvants in allergen-specific immunotherapy: where do we stand?

Type I hypersensitivity, or so-called type I allergy, is caused by Th2-mediated immune responses directed against otherwise harmless environmental antigens. Currently, allergen-specific immunotherapy (AIT) is the only disease-modifying treatment with the potential to re-establish clinical tolerance towards the corresponding allergen(s). However, conventional AIT has certain drawbacks, including long treatment durations, the risk of inducing allergic side effects, and the fact that allergens by themselves have a rather low immunogenicity. To improve AIT, adjuvants can be a powerful tool not only to increase the immunogenicity of co-applied allergens but also to induce the desired immune activation, such as promoting allergen-specific Th1- or regulatory responses. This review summarizes the knowledge on adjuvants currently approved for use in human AIT: aluminum hydroxide, calcium phosphate, microcrystalline tyrosine, and MPLA, as well as novel adjuvants that have been studied in recent years: oil-in-water emulsions, virus-like particles, viral components, carbohydrate-based adjuvants (QS-21, glucans, and mannan) and TLR-ligands (flagellin and CpG-ODN). The investigated adjuvants show distinct properties, such as prolonging allergen release at the injection site, inducing allergen-specific IgG production while also reducing IgE levels, as well as promoting differentiation and activation of different immune cells. In the future, better understanding of the immunological mechanisms underlying the effects of these adjuvants in clinical settings may help us to improve AIT.

Stimulation of naïve B cells with a fusion protein consisting of FlaA and Bet v 1 induces regulatory B cells ex vivo

BACKGROUND

The experimental fusion protein rFlaA:Betv1 was shown to efficiently suppress allergen-specific sensitization in mice. However, the detailed mechanism of rFlaA:Betv1-mediated immune modulation is not fully understood. In this study, we investigated the effect of rFlaA:Betv1 on naïve murine B cells.

METHODS

Immune modulating capacity of rFlaA:Betv1 was screened in IL-10 reporter mice. B cells were isolated from spleens of naïve C57Bl/6, TLR5^-/- , or MyD88^-/- mice, stimulated with rFlaA:Betv1 and controls, and monitored for the expression of the regulatory B cell markers CD1d, CD24, CD38, and surface IgM by flow cytometry. Secreted cytokines, antibodies, and reactivity of the induced antibodies were investigated by ELISA and intracellular flow cytometry. Suppressive capacity of rFlaA:Betv1-stimulated B cells was tested in mDC:CD4⁺ T cell:B cell triple cultures.

RESULTS

Upon in vivo application of rFlaA:Betv1 into IL-10-GFP reporter mice, CD19⁺ B cells were shown to produce anti-inflammatory IL-10, suggesting B cells to contribute to the immune-modulatory properties of rFlaA:Betv1. rFlaA:Betv1-induced IL-10 secretion was confirmed in human B cells isolated from buffy coats. In vitro stimulation of naïve murine B cells with rFlaA:Betv1 resulted in an mTOR- and MyD88-dependent production of IL-10 and rFlaA:Betv1 induced Bet v 1-reactive IgG production, which was not observed for IgA. rFlaA:Betv1-stimulated B cells formed a CD19⁺ CD24⁺ CD1d⁺ IgM⁺ CD38⁺ Breg subpopulation capable of suppressing Bet v 1-induced TH2 cytokine secretion in vitro.

CONCLUSION

rFlaA:Betv1 can act as a thymus-independent B cell antigen, stimulating the mTOR- and MyD88-dependent differentiation of B cells displaying a regulatory phenotype, IL-10 secretion, antigen-binding antibody production, and a suppressive capacity in vitro.

Novel perspective on the regulation of food allergy by probiotic: The potential of its structural components

Food allergy (FA) is a global public health issue with growing prevalence. Increasing evidence supports the strong correlation between intestinal microbiota dysbiosis and food allergies. Probiotic intervention as a microbiota-based therapy could alleviate FA effectively. In addition to improving the intestinal microbiota disturbance and affecting microbial metabolites to regulate immune system, immune responses induced by the recognition of pattern recognition receptors to probiotic components may also be one of the mechanisms of probiotics protecting against FA. In this review, it is highlighted in detail about the regulatory effects on the immune system and anti-allergic potential of probiotic components including the flagellin, pili, peptidoglycan, lipoteichoic acid, exopolysaccharides, surface (S)-layer proteins and DNA. Probiotic components could enhance the function of intestinal epithelial barrier as well as regulate the balance of cytokines and T helper (Th) 1/Th2/regulatory T cell (Treg) responses. These evidences suggest that probiotic components could be used as nutritional or therapeutic agents for maintaining immune homeostasis to prevent FA, which will contribute to providing new insights into the resolution of FA and better guidance for the development of probiotic products.

The secretome of irradiated peripheral blood mononuclear cells attenuates activation of mast cells and basophils

BACKGROUND

IgE-mediated hypersensitivity is becoming increasingly prevalent and activation of mast cells and basophils represent key events in the pathophysiology of allergy. We have previously reported that the secretome of γ-irradiated peripheral blood mononuclear cells (PBMCsec) exerts beneficial anti-inflammatory effects. Yet, its ability to alleviate allergic symptoms has not been investigated so far.

METHODS

Several experimental in vitro and in vivo models have been used in this basic research study. A murine ear swelling model was used to study the effects of PBMCsec on 48/80-induced mast cell degranulation in vivo. The transcriptional profile of murine mast cells was analysed by single cell RNA sequencing (scRNAseq). Mast cell activation was studied in vitro using primary skin mast cells. Basophils from individuals allergic to birch pollens were used to investigate basophile activation by allergens. Transcriptomic and lipidomic analyses were used to identify mRNA expression and lipid species present in PBMCsec, respectively.

FINDINGS

Topical application of PBMCsec on mouse ears (C57BL/6) significantly reduced tissue swelling following intradermal injection of compound 48/80, an inducer of mast cell degranulation. Single cell RNA sequencing of PBMCsec-treated murine dermal mast cells (Balb/c) revealed a downregulation of genes involved in immune cell degranulation and Fc-receptor signalling. In addition, treatment of primary human dermal mast cells with PBMCsec strongly inhibited compound 48/80- and α-IgE-induced mediator release in vitro. Furthermore, PBMCsec remarkably attenuated allergen driven activation of basophils from allergic individuals. Transcriptomic analysis of these basophils showed that PBMCsec downregulated a distinct gene battery involved in immune cell degranulation and Fc-receptor signalling, corroborating results obtained from dermal mast cells. Finally, we identified the lipid fraction of PBMCsec as the major active ingredient involved in effector cell inhibition.

INTERPRETATION

Collectively, our data demonstrate that PBMCsec is able to reduce activation of mast cells and basophils, encouraging further studies on the potential use of PBMCsec for treating allergy.

FUNDING

Austrian Research Promotion Agency (852748 and 862068, 2015-2019), Vienna Business Agency (2343727, 2018-2020), Aposcience AG, Austrian Federal Ministry of Education, Science and Research (SPA06/055), Danube Allergy Research Cluster, Austrian Science Fund (I4437 and P32953).

Innate Immunomodulatory Nanodevices for Cancer Therapy: A Review

The newly emerged cancer immunotherapy has shown a great potential in clinical trials. However, most immunotherapeutic strategies focus on restoring and/or enhancing the effector T cell responses, and only a small portion of malignancies respond favorably due to the lacking of T cell infiltration. Recently, the modulation of innate immune system has been applied as an alternative or combined strategy to improve host anti-tumor immunity. In this review, we summarize recent progress in nanotechnology-based innate immunomodulation for cancer therapy. Firstly, we present various types of nanodevices that serve to deliver or mimic the reactions of pathogen-associated molecular patterns (PAMPs), such as bacterial components, viral DNA or viral RNA, for the stimulation of type I interferons (IFNs) and pro-inflammatory cytokines. We also introduce nanodevice-mediated immunogenic cell death (ICD) for the generation of endogenous danger-associated molecular patterns (DAMPs) and improvement of immune responses. Moreover, targeted manipulation of specific types of innate immune cells by nanodevices are discussed. Lastly, we describe typical strategies of combining innate immunomodulatory nanodevices with immune checkpoint blockade to amplify the anti-tumor efficacy.

The Fusion Protein rFlaA:Betv1 Modulates DC Responses by a p38-MAPK and COX2-Dependent Secretion of PGE2 from Epithelial Cells

Developing new adjuvants/vaccines and better understanding their mode-of-action is an important task. To specifically improve birch pollen allergy treatment, we designed a fusion protein consisting of major birch pollen allergen Betv1 conjugated to the TLR5-ligand flagellin (rFlaA:Betv1). This study investigates the immune-modulatory effects of rFlaA:Betv1 on airway epithelial cells. LA-4 mouse lung epithelial cells were stimulated with rFlaA:Betv1 in the presence/absence of various inhibitors with cytokine- and chemokine secretion quantified by ELISA and activation of intracellular signaling cascades demonstrated by Western blot (WB). Either LA-4 cells or LA-4-derived supernatants were co-cultured with BALB/c bone marrow-derived myeloid dendritic cells (mDCs). Compared to equimolar amounts of flagellin and Betv1 provided as a mixture, rFlaA:Betv1 induced higher secretion of IL-6 and the chemokines CCL2 and CCL20 from LA-4 cells and a pronounced MAPK- and NFκB-activation. Mechanistically, rFlaA:Betv1 was taken up more strongly and the induced cytokine production was inhibited by NFκB-inhibitors, while ERK- and p38-MAPK-inhibitors only suppressed IL-6 and CCL2 secretion. In co-cultures of LA-4 cells with mDCs, rFlaA:Betv1-stimulated LA-4 cells p38-MAPK- and COX2-dependently secreted PGE2, which modulated DC responses by suppressing pro-inflammatory IL-12 and TNF-α secretion. Taken together, these results contribute to our understanding of the mechanisms underlying the strong immune-modulatory effects of flagellin-containing fusion proteins.

The Flagellin:Allergen Fusion Protein rFlaA:Betv1 Induces a MyD88- and MAPK-Dependent Activation of Glucose Metabolism in Macrophages

TLR5 ligand flagellin-containing fusion proteins are potential vaccine candidates for many diseases. A recombinant fusion protein of flagellin A and the major birch pollen allergen Bet v 1 (rFlaA:Betv1) modulates immune responses in vitro and in vivo. We studied the effects of rFlaA:Betv1 on bone marrow-derived macrophages (BMDMs). BMDMs differentiated from BALB/c, C57BL/6, TLR5^-/-, or MyD88^-/- mice were pre-treated with inhibitors, stimulated with rFlaA:Betv1 or respective controls, and analyzed for activation, cytokine secretion, metabolic state, RNA transcriptome, and modulation of allergen-specific Th2 responses. Stimulation of BMDMs with rFlaA:Betv1 resulted in MyD88-dependent production of IL-1β, IL-6, TNF-α, IL-10, CD69 upregulation, and a pronounced shift towards glycolysis paralleled by activation of MAPK, NFκB, and mTOR signaling. Inhibition of either mTOR (rapamycin) or SAP/JNK-MAPK signaling (SP600125) resulted in dose-dependent metabolic suppression. In BMDM and T cell co-cultures, rFlaA:Betv1 stimulation suppressed rBet v 1-induced IL-5 and IL-13 secretion while inducing IFN-γ production. mRNA-Seq analyses showed HIF-1a, JAK, STAT, phagosome, NLR, NFκB, TNF, TLR, and chemokine signaling to participate in the interplay of cell activation, glycolysis, and immune response. rFlaA:Betv1 strongly activated BMDMs, resulting in MyD88-, MAPK-, and mTOR-dependent enhancement of glucose metabolism. Our results suggest macrophages are important target cells to consider during restauration of allergen tolerance during AIT.

Perspectives in Allergen-Specific Immunotherapy: Molecular Evolution of Peptide- and Protein-Based Strategies

Allergen-specific Immunotherapy (AIT), through repetitive subcutaneous or sublingual administrations of allergen extracts, represents up to now the unique treatment against allergic sensitizations. However, the clinical efficacy of AIT can be largely dependent on the quality of natural allergen extracts. Moreover, the long duration and adverse side effects associated with AIT negatively impact patient adherence. Tremendous progress in the field of molecular allergology has made possible the design of safer, shorter and more effective new immunotherapeutic approaches based on purified and characterized natural or recombinant allergen derivatives and peptides. This review will summarize the characteristics of these different innovative vaccines including their effects in preclinical studies and clinical trials.

Toll-Like Receptor Agonists as Adjuvants for Allergen Immunotherapy

Toll-like receptors (TLRs) are essential components of innate immunity and provide defensive inflammatory responses to invading pathogens. Located within the plasma membranes of cells and also intracellular endosomes, TLRs can detect a range of pathogen associated molecular patterns from bacteria, viruses and fungi. TLR activation on dendritic cells can propagate to an adaptive immune response, making them attractive targets for the development of both prophylactic and therapeutic vaccines. In contrast to conventional adjuvants such as aluminium salts, TLR agonists have a clear immunomodulatory profile that favours anti-allergic T lymphocyte responses. Consequently, the potential use of TLRs as adjuvants in Allergen Immunotherapy (AIT) for allergic rhinitis and asthma remains of great interest. Allergic Rhinitis is a Th2-driven, IgE-mediated disease that occurs in atopic individuals in response to exposure to otherwise harmless aeroallergens such as pollens, house dust mite and animal dander. AIT is indicated in subjects with allergic rhinitis whose symptoms are inadequately controlled by antihistamines and nasal corticosteroids. Unlike anti-allergic drugs, AIT is disease-modifying and may induce long-term disease remission through mechanisms involving upregulation of IgG and IgG4 antibodies, induction of regulatory T and B cells, and immune deviation in favour of Th1 responses that are maintained after treatment discontinuation. This process takes up to three years however, highlighting an unmet need for a more efficacious therapy with faster onset. Agonists targeting different TLRs to treat allergy are at different stages of development. Synthetic TLR4, and TLR9 agonists have progressed to clinical trials, while TLR2, TLR5 and TLR7 agonists been shown to have potent anti-allergic effects in human in vitro experiments and in vivo in animal studies. The anti-allergic properties of TLRs are broadly characterised by a combination of enhanced Th1 deviation, regulatory responses, and induction of blocking antibodies. While promising, a durable effect in larger clinical trials is yet to be observed and further long-term studies and comparative trials with conventional AIT are required before TLR adjuvants can be considered for inclusion in AIT. Here we critically evaluate experimental and clinical studies investigating TLRs and discuss their potential role in the future of AIT.

IgE-blocking antibodies following SLIT with recombinant Mal d 1 accord with improved apple allergy

BACKGROUND

We recently reported that 16 weeks of sublingual immunotherapy (SLIT) with recombinant (r) Mal d 1, but not rBet v 1, significantly improved birch pollen-related apple allergy. Allergen-specific IgE-blocking IgG antibodies have been associated with clinical efficacy.

OBJECTIVE

We compared the quantity, quality, and IgE-blocking bioactivity of SLIT-induced Mal d 1-specific IgG antibodies in both treatment groups.

METHODS

Pre- and post-SLIT sera were assessed for rMal d 1-specific IgG antibodies in ELISA and for their ability to inhibit apple allergen-induced upregulation of CD63 on basophils from nontreated individuals with birch pollen-related apple allergy. Post-SLIT sera depleted of IgG1 or IgG4 were compared for their IgE-blocking activity. IgG1 binding to rMal d 1 was competed with rMal d 1 and rBet v 1 in ELISA.

RESULTS

SLIT with rMal d 1 and rBet v 1 induced comparable levels of rMal d 1-specific IgG1, IgG2, IgG3, and IgG4 antibodies. Only post-rMal d 1 SLIT sera displayed IgE-blocking activity, which was significantly reduced by depletion of IgG1 and less so by IgG4 depletion. In competition ELISA, IgG1 binding to Mal d 1 in post-rMal d 1 SLIT sera was fully inhibited with rMal d 1 but not with rBet v 1. Correspondingly, Bet v 1 was the more potent competitor for IgG1 binding to Mal d 1 in post-rBet v 1 SLIT sera.

CONCLUSION

rMal d 1 SLIT for 16 weeks induced functional, primarily Mal d 1-specific IgE-blocking antibodies, whereas rBet v 1 SLIT induced Bet v 1-specific, Mal d 1-cross-reactive IgG antibodies with limited cross-blocking activity. These results provide a possible explanation for the limited effectiveness of birch pollen immunotherapy in birch pollen-related food allergy and indicate a dominant protective role of functional IgE-blocking IgG1 antibodies in the early phase of allergy treatment.

Molecular approaches to allergen-specific immunotherapy: Are we so far from clinical implementation?

Conventional allergen-specific immunotherapy (AIT), based on administrations of allergen extracts, represents up to now the unique protocol for the desensitization of allergic patients. Whereas the effectiveness of AIT was evidenced for the treatment of allergic rhinitis and allergic asthma, such strategy remains experimental for food allergies up to now. However, important issues are commonly associated with AIT as the quality of natural allergen extracts, the long duration and adverse side-effects which negatively affect successful desensitization together with the patient compliance. The rapid progression of molecular allergology made possible the quest of safer, shorter and more effective immunotherapeutic approaches. The aim of this review was to provide an update on these different innovative recombinant derivatives including their efficacy but also their limitations. Despite promising preclinical and early clinical studies, the absence of convincing data in large phase III trials precludes so far the translation of these immunotherapeutic candidates into the clinic.

Designs of Antigen Structure and Composition for Improved Protein-Based Vaccine Efficacy

Today, vaccinologists have come to understand that the hallmark of any protective immune response is the antigen. However, it is not the whole antigen that dictates the immune response, but rather the various parts comprising the whole that are capable of influencing immunogenicity. Protein-based antigens hold particular importance within this structural approach to understanding immunity because, though different molecules can serve as antigens, only proteins are capable of inducing both cellular and humoral immunity. This fact, coupled with the versatility and customizability of proteins when considering vaccine design applications, makes protein-based vaccines (PBVs) one of today's most promising technologies for artificially inducing immunity. In this review, we follow the development of PBV technologies through time and discuss the antigen-specific receptors that are most critical to any immune response: pattern recognition receptors, B cell receptors, and T cell receptors. Knowledge of these receptors and their ligands has become exceptionally valuable in the field of vaccinology, where today it is possible to make drastic modifications to PBV structure, from primary to quaternary, in order to promote recognition of target epitopes, potentiate vaccine immunogenicity, and prevent antigen-associated complications. Additionally, these modifications have made it possible to control immune responses by modulating stability and targeting PBV to key immune cells. Consequently, careful consideration should be given to protein structure when designing PBVs in the future in order to potentiate PBV efficacy.

NFκB- and MAP-Kinase Signaling Contribute to the Activation of Murine Myeloid Dendritic Cells by a Flagellin A:Allergen Fusion Protein

Fusion proteins incorporating the TLR5-ligand flagellin are currently undergoing clinical trials as vaccine candidates for many diseases. We recently reported a flagellin:allergen fusion protein containing the TLR5-ligand flagellin A (FlaA) from Listeria monocytogenes and the major birch pollen allergen Bet v 1 (rFlaA:Betv1) to prevent allergic sensitization in an experimental mouse model. This study analyzes the signaling pathways contributing to rFlaA:Betv1-mediated pro- and anti-inflammatory cytokine secretion and cell metabolism in myeloid dendritic cells (mDCs) in vitro. The influence of mammalian target of rapamycin (mTOR)-, NFκB-, and MAP kinase (MAPK)-signaling on cytokine secretion and metabolic activity of bone marrow (BM)-derived mDCs stimulated with rFlaA:Betv1 were investigated by pre-treatment with either mTOR- (rapamycin), NFκB- (dexamethason, BMS-345541, TPCA-1, triptolide, or BAY-11) or MAPK- (SP600125, U0126, or SB202190) inhibitors, respectively. rFlaA:Betv1-mediated IL-10 secretion as well as activation of mDC metabolism, rather than pro-inflammatory cytokine secretion, were inhibited by rapamycin. Inhibition of NFκB-signaling suppressed rFlaA:Betv1-induced IL-12, while inhibition of MAPK-signaling dose-dependently suppressed rFlaA:Betv1-induced IL-10 as well as pro-inflammatory IL-6 and TNF-α production. Notably, with the exception of a partial JNK-dependency, rFlaA:Betv1-mediated effects on mDC metabolism were mostly NFκB- and MAPK-independent. Therefore, MAPK-mediated activation of both NFκB- and mTOR-signaling likely is a key pathway for the production of pro- and anti-inflammatory cytokines by flagellin fusion protein vaccines.

Allergen content in German cockroach extracts and sensitization profiles to a new expanded set of cockroach allergens determine in vitro extract potency for IgE reactivity

BACKGROUND

Cockroach allergens are an important cause of IgE-mediated sensitization in inner-city asthmatic patients. However, cockroach extracts used for diagnosis and immunotherapy are not standardized.

OBJECTIVE

We sought to determine the allergen content of nonstandardized German cockroach extracts and the levels of sensitization to an expanded set of cockroach allergens as determinants of in vitro extract potency for IgE reactivity.

METHODS

Twelve German cockroach extracts were compared for allergen content and potency of IgE reactivity. Bla g 1, Bla g 2, and Bla g 5 were measured by using immunoassays. IgE antibody levels to 8 purified recombinant allergens from groups 1, 2, 4, 5, 6, 7, 9, and 11 were measured by using ImmunoCAP. IgE antibody binding inhibition assays were performed to assess extract in vitro potencies (concentration inhibiting 30% of the total IgE antibody-binding inhibition) relative to an arbitrarily selected reference extract in 5 patients with cockroach allergy.

RESULTS

Allergen levels were highly variable. Three new major allergens (groups 6, 9, and 11), were identified among highly cockroach-sensitized subjects (CAP class ≥ 3). Sensitization profiles were unique per subject without immunodominant allergens. The sum of IgE to 8 allergen components showed a good correlation with cockroach-specific IgE levels (r = 0.88, P < .001). In vitro potencies varied among different extracts per subject and among subjects for each extract.

CONCLUSIONS

The in vitro potency of German cockroach extracts for IgE reactivity depends on allergen content and allergen-specific IgE titers of patients with cockroach allergy. These factors are relevant for selection of potent extracts to be used for immunotherapy and for the design and interpretation of data from immunotherapy trials.

The optimized fusion protein HA1-2-FliCΔD2D3 promotes mixed Th1/Th2 immune responses to influenza H7N9 with low induction of systemic proinflammatory cytokines in mice

H7N9 influenza virus has an unusually high fatality rate of approximately 40%, and a safe and effective vaccine against this subtype is urgently needed. Flagellin, a Toll-like receptor (TLR) 5 agonist, has been deemed as a potent adjuvant candidate. However, its high antigenicity and potential for causing inflammatory injury might restrict its clinical application. Previously, we demonstrated that a fusion protein, HA1-2-FliC, comprising the hemagglutinin globular head protein (HA1-2) of H7N9 influenza virus and the full-length Salmonella typhimurium flagellin protein (FliC), had high efficiency against H7N9 in mouse and chicken models. Here, we constructed an improved fusion protein, HA1-2-FliCΔD2D3, with HA1-2 fused to the FliCΔD2D3 (lacking the hypervariable-region domains D2 and D3 of FliC). HA1-2-FliCΔD2D3 exhibited efficient immunoreactivity and TLR5 agonist efficacy, and promoted innate immune-response activation in mouse macrophages, peripheral blood mononuclear cells, and splenocytes, based on cytokine- and chemokine-expression profiles. Mice immunized with HA1-2-FliCΔD2D3 showed significantly lower systemic inflammatory responses (compared with HA1-2-FliC) and highly reduced flagellin-specific antibody production, without affecting HA1-2-specific antibody production and cellular immune responses. Enhanced IFN-γ/IL-4 generation suggested that HA1-2-FliCΔD2D3 maintained balanced Th1/Th2 immune responses. Furthermore, virus challenge was performed in a chicken model. The results showed that chickens receiving FliCΔD2D3 adjuvant vaccine induced high levels of serum neutralizing antibodies, and exhibited a significant reduction of viral loads in throat and cloaca compared to chickens receiving only HA1-2. In conclusion, we constructed the H7N9 influenza subunit vaccine candidate HA1-2-FliCΔD2D3, with reduced immunogenicity against FliC and lower adverse events. The improved adjuvant FliCΔD2D3 can potentially help in developing safe and effective universal protein-based influenza vaccines for humans.

TLR Activation and Allergic Disease: Early Life Microbiome and Treatment

PURPOSE OF REVIEW

Allergy and asthma are growing problems in the developed world. The accelerated increase of these diseases may be related to microbiome modification that leads to aberrant activation of Toll-like receptors (TLRs). Current research supports the concept that changes in microbial communities in early life impact TLR activation, resulting in an altered risk for the development of asthma and allergies.

RECENT FINDINGS

Prenatal and early childhood events that generate microbiome modification are closely related with TLR activation. Early childhood exposure to a rich array of TLR agonists, particularly lipopolysaccharide, strongly predicts protection against allergic disease later in life even when other lifestyle factors are accounted for. Genetic deletion of TLR signaling components in mice results in reduced function of tolerogenic cell populations in the gut. In contrast, weak TLR signaling can promote allergic sensitization later in life. This review summarizes the role of TLR signaling in microbiome-mediated protection against allergy.

Flagellin as a vaccine adjuvant

INTRODUCTION

Bacterial flagellin, as a pathogen-associated molecular pattern (PAMP), can activate both innate and adaptive immunity. Its unique structural characteristics endow an effective and flexible adjuvant activity, which allow the design of different types of vaccine strategies to prevent various diseases. This review will discuss recent progress in the mechanism of action of flagellin and its prospects for use as a vaccine adjuvant.

AREAS COVERED

Herein we summarize various types of information related to flagellin adjuvants from PubMed, including structures, signaling pathways, natural immunity, and extensive applications in vaccines, and it discusses the immunogenicity, safety, and efficacy of flagellin-adjuvanted vaccines in clinical trials.

EXPERT COMMENTARY

It is widely accepted that as an adjuvant, flagellin can induce an enhanced antigen-specific immune response. Flagellin adjuvants will allow more effective flagellin-based vaccines to enter clinical trials. Furthermore, vaccine formulations containing PAMPs are crucial to exert the maximum potential of vaccine antigens. Therefore, combinations of flagellin-adjuvanted vaccines with other adjuvants that act in a synergistic manner, particularly TLR ligands, represent a promising method for tailoring targeted vaccines to meet specific requirements.

Critical role of mammalian target of rapamycin for IL-10 dendritic cell induction by a flagellin A conjugate in preventing allergic sensitization

BACKGROUND

Fusion proteins incorporating the Toll-like receptor 5 ligand flagellin are currently undergoing clinical trials as vaccine candidates for many diseases.

OBJECTIVE

We studied the mechanisms of immune modulation by a flagellin:allergen fusion protein containing the Toll-like receptor 5 ligand flagellin A from Listeria monocytogenes and the birch pollen allergen Bet v 1 (recombinant flagellin A [rFlaA]:Betv1).

METHODS

BALB/c mice were vaccinated with rFlaA:Betv1 in an experimental Bet v 1 sensitization model. Myeloid dendritic cells (mDCs) were differentiated from mouse bone marrow, and PBMCs were isolated from subjects with birch pollen allergy. Cells were stimulated with equimolar amounts of rFlaA, rBet v 1, rFlaA plus rBet v 1, or the rFlaA:Betv1 conjugate and analyzed for cell activation, cytokine secretion, and metabolic state.

RESULTS

rFlaA:Betv1 displayed strong immune-modulating properties both in vivo and in vitro, as characterized by secretion of both proinflammatory and anti-inflammatory cytokines from murine mDCs and PBMCs from patients with birch allergy. rFlaA:Betv1 suppressed T_H2 responses from Bet v 1-specific CD4⁺ T cells and prevented allergic sensitization in a mouse allergy model. Aggregation of rFlaA:Betv1 resulted in stronger protein uptake accompanied by an increased resistance to microsomal digestion. Remarkably, rFlaA:Betv1 induced activation of mammalian target of rapamycin, which increased the metabolic activity of the stimulated mDCs. rFlaA:Betv1-mediated IL-10 secretion, but not proinflammatory cytokine secretion, was inhibited by rapamycin in mDCs.

CONCLUSION

These results provide evidence that mammalian target of rapamycin is a key player involved in prevention of T_H2 responses by flagellin A conjugate vaccines.