Aline Zimmer

A regulatory dendritic cell signature correlates with the clinical efficacy of allergen-specific sublingual immunotherapy.

BACKGROUND Given their pivotal role in the polarization of T-cell responses, molecular changes at the level of dendritic cells (DCs) could represent an early signature indicative of the subsequent orientation of adaptive immune responses during immunotherapy. OBJECTIVE We sought to investigate whether markers of effector and regulatory DCs are affected during allergen immunotherapy in relationship with clinical benefit. METHODS Differential gel electrophoresis and label-free mass spectrometry approaches were used to compare whole proteomes from human monocyte-derived DCs differentiated toward either regulatory or effector functions. The expression of those markers was assessed by using quantitative PCR in PBMCs from 79 patients with grass pollen allergy enrolled in a double-blind, placebo-controlled clinical study evaluating the efficacy of sublingual tablets in an allergen exposure chamber over a 4-month period. RESULTS We identified several markers associated with DC1 and/or DC17 effector DCs, including CD71, FSCN1, IRF4, NMES1, MX1, TRAF1. A substantial phenotypic heterogeneity was observed among various types of tolerogenic DCs, with ANXA1, Complement component 1 (C1Q), CATC, GILZ, F13A, FKBP5, Stabilin-1 (STAB1), and TPP1 molecules established as shared or restricted regulatory DC markers. The expression of 2 of those DCs markers, C1Q and STAB1, was increased in PBMCs from clinical responders in contrast to that seen in nonresponders or placebo-treated patients. CONCLUSION C1Q and STAB1 represent candidate biomarkers of early efficacy of allergen immunotherapy as the hallmark of a regulatory innate immune response predictive of clinical tolerance.

Oral macrophage-like cells play a key role in tolerance induction following sublingual immunotherapy of asthmatic mice

Sublingual allergen-specific immunotherapy (SLIT) is a safe and efficacious treatment for type 1 respiratory allergies. Herein, we investigated the key subset(s) of antigen-presenting cells (APCs) involved in antigen/allergen capture and tolerance induction during SLIT. Following sublingual administration, fluorochrome-labeled ovalbumin (OVA) is predominantly captured by oral CD11b+CD11c− cells that migrate to cervical lymph nodes (CLNs) and present the antigen to naive CD4+ T cells. Conditional depletion with diphtheria toxin of CD11b+, but not CD11c+ cells, in oral tissues impairs CD4+ T-cell priming in CLNs. In mice with established asthma to OVA, specific targeting of the antigen to oral CD11b+ cells using the adenylate cyclase vector system reduces airway hyperresponsiveness (AHR), eosinophil recruitment in bronchoalveolar lavages (BALs), and specific Th2 responses in CLNs and lungs. Oral CD11b+CD11c− cells resemble tolerogenic macrophages found in the lamina propria (LP) of the small intestine in that they express the mannose receptor CD206, as well as class-2 retinaldehyde dehydrogenase (RALDH2), and they support the differentiation of interferon-γ/interleukin-10 (IFNγ/IL-10)-producing Foxp3+ CD4+ regulatory T cells. Thus, among the various APC subsets present in oral tissues of mice, macrophage-like cells play a key role in tolerance induction following SLIT.

Identification of a New Phenotype of Tolerogenic Human Dendritic Cells Induced by Fungal Proteases from Aspergillus oryzae

We characterized a new pathway to induce tolerogenic dendritic cells (DCs) following treatment of human monocyte-derived DCs with proteases from the fungus Aspergillus oryzae (ASP). ASP-treated DCs (ASP-DCs) exhibit a CD80−CD83−CD86−Ig-like transcript (ILT)2−ILT3−ILT4+ phenotype, do not secrete cytokines or chemokines, and express tolerogenic markers such as glucocorticoid-induced leucine zipper, NO synthetase-2, retinaldehyde dehydrogenase-1 or retinaldehyde dehydrogenase-2. When cocultured with naive CD4+ T cells, ASP-DCs induce an anergic state that can be reversed by IL-2. Generated T cells mediate a suppressive activity in third-party experiments that is not mediated by soluble factors. A comparison between dexamethasone-treated DCs used as a reference for regulatory T cell-inducing DCs and ASP-DCs reveals two distinct phenotypes. In contrast to dexamethasone, ASP treatment induces glucocorticoid-induced leucine zipper independently of glucocorticoid receptor engagement and leads to NF-κB p65 degradation. Abrogation of protease activities in ASP using specific inhibitors reveals that aspartic acid-containing proteases are key inducers of regulatory genes, whereas serine, cysteine, and metalloproteases contribute to NF-κB p65 degradation. Collectively, those features correspond to a previously unreported anergizing phenotype for human DCs. Such regulatory mechanisms may allow fungi to downregulate host immune responses and provide clues for new approaches to treat proinflammatory disorders.

Induction of Allergen-Specific Tolerance via Mucosal Routes

Allergen-specific immunotherapy is the only curative treatment of allergies against insect venom, house dust mites, tree/grass pollens, or cat dander. Subcutaneous immunotherapy is successful to reorient the immune system and re-establish long-term tolerance. However, major drawbacks for using this route include: repeated injections, as well as the risk of anaphylaxis. In this context, alternative mucosal routes of administration are being considered together with the combined use of adjuvants/vector systems and recombinant allergens or peptide fragments. Herein, we review the current status in the use of mucosal routes (i.e., sublingual, oral, intranasal) for allergen-specific immunotherapy, as well as the latest understanding with respect to underlying mechanisms of action.