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

• Published in: Allergy (Copenhagen) Vol. 75; no. 3; pp. 648 - 659
• Main Authors: Benito‐Villalvilla, Cristina, Soria, Irene, Pérez‐Diego, Mario, Fernández‐Caldas, Enrique, Subiza, José Luis, Palomares, Oscar
• Format: Journal Article
• Language: English
• Published: Denmark Blackwell Publishing Ltd 01-03-2020; John Wiley and Sons Inc
• Subjects: Adjuvanticity; Allergens; allergen‐specific immunotherapy; Allergoids; alum; Alum Compounds; Animals; Blocking antibodies; Cytokines; Dendritic Cells; Flow cytometry; Forkhead protein; Foxp3 protein; Glycolysis; Helper cells; Humans; Immunotherapy; Inflammation; Lymphocytes T; Mannan; Mannans; Metabolic rate; Metabolism; Mice; Mice, Inbred BALB C; Original; ORIGINAL ARTICLES; PD-L1 protein; polymerized allergoids conjugated to mannan; Reactive oxygen species; regulatory T cells; Spleen; T-Lymphocytes, Regulatory; TOR protein; TOR Serine-Threonine Kinases; Vaccines; regulatory T cells; polymerized allergoids conjugated to mannan; dendritic cells; alum; allergen-specific immunotherapy
• ISSN: 0105-4538; 1398-9995
• DOI: 10.1111/all.14036

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.
This study investigated the potential influence of alum in the tolerogenic properties imprinted by PM. Alum decreased expression of PD‐L1 and production of IL‐10, IL‐6 and lactate, increased IL‐23 release and inhibited mTOR activation in PM‐activated DCs. Alum suppressed PM‐induced functional FOXP3+ Treg cells and promoted Th1/Th2/Th17 responses.