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.