Alum impairs tolerogenic properties induced by allergoid-mannan conjugates inhibiting mTOR and metabolic reprogramming in human DCs.

BACKGROUND: Polymerized allergoids conjugated to mannan (PM) are suitable vaccines for allergen-specific immunotherapy (AIT). Alum remains the most widely used adjuvant in AIT, but its way of action is not completely elucidated. The better understanding of the mechanisms underlying alum adjuvanticity could help to improve AIT vaccine formulations. OBJECTIVE: We sought to investigate the potential influence of alum in the tolerogenic properties imprinted by PM at the molecular level. METHODS: Flow cytometry, ELISAs, cocultures, intracellular staining and suppression assays were performed to assess alum and PM effects in human dendritic cells (DCs). BALB/c mice were immunized with PM alone or adsorbed to alum. Allergen-specific antibodies, splenocyte cytokine production and splenic forkhead box P3 (FOXP3)+ regulatory T (Treg) cells were quantified. Metabolic and immune pathways were also studied in human DCs. RESULTS: Alum decreases PD-L1 expression and IL-10 production induced by PM in human DCs and increases pro-inflammatory cytokine production. Alum impairs PM-induced functional FOXP3+ Treg cells and promotes Th1/Th2/Th17 responses. Subcutaneous immunization of mice with PM plus alum inhibits in vivo induction of Treg cells promoted by PM without altering the capacity to induce functional allergen-specific blocking antibodies. Alum inhibits mTOR activation and alters metabolic reprogramming by shifting glycolytic pathways and inhibiting reactive oxygen species (ROS) production in PM-activated DCs, impairing their capacity to generate functional Treg cells. CONCLUSION: We uncover novel mechanisms by which alum impairs the tolerogenic properties induced by PM, which might well contribute to improve the formulation of novel vaccines for AIT.

Novel vaccines targeting dendritic cells by coupling allergoids to mannan.

Allergen-specific immunotherapy (AIT) is the single disease-modifying treatment for allergy. Clinical trials show AIT to be safe and effective for many patients; however, it still faces problems related to efficacy, safety, long treatment duration and low patient adherence. There has been intensive research to develop alternative strategies, including novel administration routes, adjuvants or hypoallergenic molecules. Promising results are reported for some of them, but clinical progress is still moderate. Allergoids conjugated to nonoxidized mannan from Saccharomyces cerevisiae have emerged as a novel concept of vaccine targeting dendritic cells (DCs). Preclinical human and animal models demonstrated that allergoids conjugated to mannan enhance allergen uptake, promote healthy responses to allergens by inducing Th1 and T regulatory (Treg) cells, and show clinical efficacy in veterinary medicine. Dose-finding phase II clinical trials in humans are currently ongoing. We review the current stage of allergoids conjugated to mannan as next generation vaccines for AIT.

Tropomyosins in mosquito and house dust mite cross-react at the humoral and cellular level.

BACKGROUND: Aedes aegypti and Dermatophagoides pteronyssinus contain important allergens including cross-reactive tropomyosins. However, the functional and clinical relevance of their cross-reactivity is still debated. OBJECTIVE: To analyse the humoral and cellular cross-reactivity of recombinant Aed a 10.01, Aed a 10.02 and Der p 10. METHODS: Sera from 15 Austrian house dust mite-allergic, Der p 10-sensitized individuals were tested for IgE reactivity to recombinant tropomyosins in ELISA, inhibition ELISA and basophil activation tests. BALB/c mice were immunized with Aed a 10.01 or Aed a 10.02, and their sera were assessed for reactivity to all tropomyosins. Splenocytes were stimulated with all tropomyosins and synthetic peptides representing the amino acid sequence of Aed a 10.01. RESULTS: IgE antibodies of Der p 10-sensitized patients cross-reacted with both tropomyosins from A. aegypti. Aed a 10.01 was a more potent inhibitor of IgE binding to Der p 10 and a stronger activator of basophils sensitized with Der p 10-specific IgE than Aed a 10.02. Murine antibodies raised against Aed a 10.01 and Aed a 10.02 cross-reacted with Der p 10. Aed a 10.01-specific antibody showed stronger cross-reactivity with Der p 10 than Aed a 10.02-specific antibody. Splenocytes from both groups of mice proliferated similarly to all tropomyosins. Five cross-reactive T cell-activating regions were identified. CONCLUSION AND CLINICAL RELEVANCE: Tropomyosins from D. pteronyssinus and A. aegypti show humoral and cellular cross-reactivity, involving 5 potential T cell-activating regions. The more pronounced cross-reactivity of Aed a 10.01 and Der p 10 matched the higher sequence similarity of both proteins.

Mite allergoids coupled to nonoxidized mannan from Saccharomyces cerevisae efficiently target canine dendritic cells for novel allergy immunotherapy in veterinary medicine.

We have recently reported that grass pollen allergoids conjugated with nonoxidized mannan of Saccharomyces cerevisae using glutaraldehyde results in a novel hypoallergenic mannan-allergen complex with improved properties for allergen vaccination. Using this approach, human dendritic cells show a better allergen uptake and cytokine profile production (higher IL-10/IL-4 ratio) for therapeutic purposes. Here we aim to address whether a similar approach can be extended to dogs using canine dendritic cells. Six healthy Spanish Greyhound dogs were used as blood donors to obtain canine dendritic cells (DC) derived from peripheral blood monocytes. Allergens from Dermatophagoides farinae mite were polymerized and conjugated with nonoxidized mannan. Nuclear magnetic resonance (NMR), gel electrophoresis (SDS-PAGE), immunoblotting and IgE-ELISA inhibition studies were conducted to evaluate the main characteristics of the allergoid obtained. Mannan-allergen conjugate and controls were assayed in vitro for canine DC uptake and production of IL-4 and IL-10. The results indicate that the conjugation of D. farinae allergens with nonoxidized mannan was feasible using glutaraldehyde. The resulting product was a polymerized structure showing a high molecular weight as detected by NMR and SDS-PAGE analysis. The mannan-allergen conjugate was hypoallergenic with a reduced reactivity with specific dog IgE. An increase in both allergen uptake and IL-10/IL-4 ratio was obtained when canine DCs were incubated with the mannan-allergen conjugate, as compared with the control allergen preparations (unmodified D. farinae allergens and oxidized mannan-allergen conjugate). We conclude that hypoallergenic D. farinae allergens coupled to nonoxidized mannan is a novel allergen preparation suitable for canine allergy immunotherapy targeting dendritic cells.

Novel vaccines targeting dendritic cells by coupling allergoids to nonoxidized mannan enhance allergen uptake and induce functional regulatory T cells through programmed death ligand 1.

BACKGROUND: Allergen immunotherapy (AIT) is the only curative treatment for allergy. AIT faces pitfalls related to efficacy, security, duration, and patient compliance. Novel vaccines overcoming such inconveniences are in demand. OBJECTIVES: We sought to study the immunologic mechanisms of action for novel vaccines targeting dendritic cells (DCs) generated by coupling glutaraldehyde-polymerized grass pollen allergoids to nonoxidized mannan (PM) compared with glutaraldehyde-polymerized allergoids (P) or native grass pollen extracts (N). METHODS: Skin prick tests and basophil activation tests with N, P, or PM were performed in patients with grass pollen allergy. IgE-blocking experiments, flow cytometry, confocal microscopy, cocultures, suppression assays, real-time quantitative PCR, ELISAs, and ELISpot assays were performed to assess allergen capture by human DCs and T-cell responses. BALB/c mice were immunized with PM, N, or P. Antibody levels, cytokine production by splenocytes, and splenic forkhead box P3 (FOXP3)(+) regulatory T (Treg) cells were quantified. Experiments with oxidized PM were also performed. RESULTS: PM displays in vivo hypoallergenicity, induces potent blocking antibodies, and is captured by human DCs much more efficiently than N or P by mechanisms depending on mannose receptor- and dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin-mediated internalization. PM endorses human DCs to generate functional FOXP3(+) Treg cells through programmed death ligand 1. Immunization of mice with PM induces a shift to nonallergic responses and increases the frequency of splenic FOXP3(+) Treg cells. Mild oxidation impairs these effects in human subjects and mice, demonstrating the essential role of preserving the carbohydrate structure of mannan. CONCLUSIONS: Allergoids conjugated to nonoxidized mannan represent suitable vaccines for AIT. Our findings might also be of the utmost relevance to development of therapeutic interventions in other immune tolerance-related diseases.

Structural studies of novel glycoconjugates from polymerized allergens (allergoids) and mannans as allergy vaccines.

Immunotherapy for treating IgE-mediated allergies requires high doses of the corresponding allergen. This may result in undesired side effects and, to avoid them, hypoallergenic allergens (allergoids) polymerized with glutaraldehyde are commonly used. Targeting allergoids to dendritic cells to enhance cell uptake may result in a more effective immunotherapy. Allergoids coupled to yeast mannan, as source of polymannoses, would be suitable for this purpose, since mannose-binding receptors are expressed on these cells. Conventional conjugation procedures of mannan to proteins use oxidized mannan to release reactive aldehydes able to bind to free amino groups in the protein; yet, allergoids lack these latter because their previous treatment with glutaraldehyde. The aim of this study was to obtain allergoids conjugated to mannan by an alternative approach based on just glutaraldehyde treatment, taking advantage of the mannoprotein bound to the polymannose backbone. Allergoid-mannan glycoconjugates were produced in a single step by treating with glutaraldehyde a defined mixture of allergens derived from Phleum pratense grass pollen and native mannan (non-oxidized) from Saccharomyces cerevisae. Analytical and structural studies, including 2D-DOSY and (1)H-(13)C HSQC nuclear magnetic resonance spectra, demonstrated the feasibility of such an approach. The glycoconjugates obtained were polymers of high molecular weight showing a higher stability than the native allergen or the conventional allergoid without mannan. The allergoid-mannan glycoconjugates were hypoallergenic as detected by the IgE reactivity with sera from grass allergic patients, even with lower reactivity than conventional allergoid without mannan. Thus, stable hypoallergenic allergoids conjugated to mannan suitable for using in immunotherapy can be achieved using glutaraldehyde. In contrast to mannan oxidation, the glutaraldehyde approach allows to preserve mannoses with their native geometry, which may be functionally important for its receptor-mediated recognition.