Innate mechanisms can predict successful allergy immunotherapy Liam O’Mahony, PhD,a Cezmi A. Akdis, MD,a and Thomas Eiwegger, MDb Key words: Dendritic cells, allergen immunotherapy, biomarker, type 2 dendritic cell, regulatory dendritic cells
Cellular mechanisms associated with successful allergy immunotherapy (AIT) have mainly focused on modulation of adaptive immune responses, such as downregulation of allergen-specific TH2 cells concomitant with the induction of regulatory T cells and sometimes TH1 cells and upregulation of blocking IgG4 antibodies associated ultimately with a decrease in specific IgE levels.1-4 Although AIT is now commonly used throughout the world5 and data for its efficacy, prevention of asthma development,6 and use in primary and secondary prevention are accumulating,7,8 biomarkers are needed for patient selection to start AIT and early predictors of responders to decide when to stop.9 Sublingual immunotherapy (SLIT) and subcutaneous immunotherapy have an apparent concordance of mechanisms. However, the list of proved mechanisms and, consequently, biomarkers is shorter for SLIT compared with subcutaneous AIT.3 Recently, the question was posed whether innate cells, such as dendritic cells (DCs), drive the appropriate adaptive responses required for successful AIT. In this issue of the Journal, Gueguen et al10 provide new clues to the innate mechanisms induced by AIT. DC subsets, such as regulatory DC (DCreg) cells and type 2 dendritic cells (DC2s), are already implicated in the pathomechanisms of allergic rhinitis (Fig 1, A). However, innate events related to AIT have mainly been considered to be of limited relevance to delineate successful AIT because of their general and redundant nature. The authors proceed from the assumption that upstream events of the adaptive immune response driven by the key regulators of cellular immune From athe Swiss Institute of Allergy and Asthma Research (SIAF), University of Z€urich, Davos, and bthe Division of Immunology and Allergy, Food Allergy and Anaphylaxis Program, Department of Paediatrics, Hospital for Sick Children, University of Toronto. Disclosure of potential conflict of interest: L. O’Mahony has consultant arrangements with Alimentary Health and has received a grant from GlaxoSmithKline. C. A. Akdis has consultant arrangements with Actellion, Aventis, Stallergenes, Allergopharma, and Circacia; is employed by the Swiss Institute of Allergy and Asthma Research, University of Zurich; has received grants from Novartis, PREDICTA: European Commission’s Seventh Framework programme no. 260895, the Swiss National Science Foundation, MeDALL: European Commission’s Seventh Framework Programme No. 261357, and the Christine K€uhne Center for Allergy Research and Education. T. Eiwegger declares that he has no relevant conflicts of interest. Received for publication October 21, 2015; revised October 30, 2015; accepted for publication October 30, 2015. Corresponding author: Thomas Eiwegger, MD, Division of Immunology and Allergy, Food Allergy and Anaphylaxis Program, Department of Paediatrics, Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, Ontario, M5G 1X8 Canada. E-mail: [email protected]
J Allergy Clin Immunol 2016;137:559-61. 0091-6749/$36.00 Ó 2015 American Academy of Allergy, Asthma & Immunology http://dx.doi.org/10.1016/j.jaci.2015.10.047
Davos, Switzerland, and Toronto, Ontario, Canada
responses, namely DCs, might be more appropriate to serve as early markers of successful immunotherapy (Fig 1, B). Through use of in vitro–generated functional prototypic DC subsets (DC2s and DCreg cells), they identify genetic signatures predictive for innate immune mechanisms associated with subsequent regulatory or TH2 adaptive responses. Taking advantage of these innate signatures, the authors are able to distinguish clinical responders from nonresponders in the first few months of allergen-specific immunotherapy. Innate antigen-presenting cells, such as DCs, play a major role in the polarization of adaptive lymphocyte responses.11 DCs integrate multiple danger and tissue signals to present antigen in the appropriate context. This is achieved through expression of costimulatory molecules, inhibitory molecules, cytokines, and metabolites. Thus, within the mucosa, immature DCs become polarized as either type 1 DCs, DC2s, type 17 DCs, or DCreg cells, which subsequently support the differentiation of effector (proinflammatory) TH1, TH2, TH17, or regulatory (tolerogenic) T cells, respectively. Considerable effort has been invested in the identification of specific DC markers, which drive lymphocyte polarization. For example, IL-10 secretion by DCs promotes polarization of regulatory lymphocytes, whereas activation of the histamine 2 receptor on DCs blocks LPS-induced TH1 polarization. Gueguen et al10 have progressed this field by performing transcriptomic and proteomic analysis of DCs polarized in vitro. DCs, which promote TH2-type responses, were induced by a ‘‘DC2 cocktail’’ containing IL-25, IL-33, LPS, prostaglandin E2, thymic stromal lymphopoietin, and histamine. By using a similar strategy, DCs, which promote suppressor or regulatory lymphocytes, were induced by using dexamethasone. Comparison of these DC phenotypes identified ADAM8, CD141, CREM, CYTIP, FMOD, GATA3, HCRTR1, ILDR2, ITK, NRP2, PADI2, PDE4D, OX40L, RGS9, RIPK4, SEMA7A, SIX2, TBC1D13, THBS1, and TRIM9 as being overexpressed in DC2s, whereas C1QA, FCER1G, FCGR3A, MCTP1, and SIGLEC5 were underexpressed. In contrast, DCreg cells overexpressed C1QA, C1QB, C1QC, C3AR1, CD163, CD300LF, CFH, CSGALNACT1, CYP1B1, DAB2, DPYD, FCER1G, FCGR2A, FCGR2B, FCGR3A, FKBP5, FTL, GCLC, IVNS1ABP, LRRC25, MCTP1, NUDT16, P2RY14, PDCD4, PECAM1, RNASE6, RNASET2, SIGLEC5, SLCO2B1, STAB1, and ZBTB16. Some of these markers have been previously described to be expressed by DC2s (eg, GATA3, CD141, and OX40 ligand) or DCreg cells (eg, C1Q), but many novel markers have been identified by using this analysis. After an initial verification, the authors selected 5 markers (C1QA, FCGR3A, CD141, GATA3, and RIPK4) and applied quantitative RT-PCR in PBMCs of patients who underwent a double-blind placebo-controlled trial with grass pollen SLIT and linked them to clinical outcome. Given the need for biomarkers to select positive responders, this approach might 559
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A ILC2 Mast cell
IL33 IL25 TSLP PGE2 DC 2
IL5 IL13 IL4
Naive T-cell DC2
ILC2 DCreg DC2
C1QA FcγRIIIA F RIIIA C CD141 G GATA3 RIPK4 OX40L O
TH IgE IgG
adaptive FIG 1. DC signatures reveal upstream markers of successful immunotherapy. On exposure to environmental allergens, DCs act as key regulators that define effector cell properties based on their priming and functional commitment. A, Imbalance between DC subsets in favor of DC2 subsets drives generation of TH2 cells, production of IgE, and activation of tissue-resident effector cell populations that lead to clinical symptoms on exposure to the respective allergen. B, Successful SLIT modifies DC commitment by downregulation of the DC2 signature toward an increase in DCreg cell numbers, which ultimately contributes to downstream events that result in a reduction of clinical symptoms. aaM, Alternatively activated macrophage; ILC2, type 2 innate lymphoid cell; LN, lymph node; PGE2, prostaglandin E2; Treg, regulatory T cell; TSLP, thymic stromal lymphopoietin.
contribute as a set of indicators of clinical response that are easily accessible in clinical trials.12 However, a sensitivity of 90% and specificity of 60% do not meet the criteria required for clinical decision making at an individual level. An interesting aspect of this study is the delineation of responders in the placebo and treatment groups. Despite a clinical response, the DCreg markers C1QA and FCGR3A were not upregulated and the DC2 markers CD141, GATA3, and RIPK4 were not downregulated in responders from the placebo group. This supports a favorable innate mechanism that is related to the grass pollen extract and does not reflect nonallergic status.
Perhaps surprising is the upregulation of Fcg receptors on DCreg cells because some of these receptors bind IgG and can mediate anaphylactic responses in murine models. Moreover, FcgRIII has been reported to drive TH2 responses in combination with IL-33.13 Binding of antibody-antigen complexes is a process that occurs constantly in health. Recently, FCGR3A (CD16a) expression in human subjects has been reported on immature but not mature slanDCs, plasmacytoid DCs, or CD1c1 DCs. FCGR3A was crucial for IgG-dependent immune complex uptake and was lost on maturation. Upregulation or increase of FCGR3A expression in the periphery might represent a marker both for efficient allergen-IgG immune complex uptake and an immature/anti-inflammatory setting provided by the respective cytokine microenvironment that differs between responders and nonresponders. C1QA expression has been linked to successful grass pollen SLIT by the same group previously. In line with FCGR3, C1Q-expressing DCs have been reported to be relatively immature, with a lower expression of CD80, CD83, and CD86, and less responsive to CD40 ligand–related activation and reduced T-cell activation. Initial contact of mucosal DCs with the allergen extract or allergen-loaded complexes and transfer of these allergen-loaded protolerogenic DCs to sites of inflammation and immune education seems feasible. Although their characteristics remain unclear, this data set might provide new hints for novel DC markers. Although this study suggests that appropriate induction of innate responses by means of immunotherapy might lead to a successful outcome, there are some limitations to this interpretation. Quantification of these genes in whole blood or isolated PBMCs will quantify not only gene expression in innate cells but also lymphocytes that are present. Future studies are required to separate cell subsets and confirm cell type–specific expression. In addition, it would have been useful to compare these innate changes with more traditional adaptive measures (eg, allergenspecific lymphocyte polarization and IgG4 or IgE levels) to correlate the innate observations with adaptive outcomes. One major handicap for these whole blood approaches is that the frequency of allergen-specific T and B cells is less than 0.1% and that the changes in these cells are not visible. Moreover, there is a need to verify these findings in studies with long-term follow-up. An issue not addressed in this study is an assessment of cellular resources that are upstream of DCs and act as decisive promotors of protolerogenic DC populations in vivo. Novel study designs that allow a better chronologic resolution of events that take place during SLIT are required. Regardless of these limitations, the identification of novel cell subsets defined by their function and novel molecular pathways that support the induction of tolerance, particularly in vivo, are crucial to generate new therapeutic options for patients with a breakdown in tolerance to exogenous or self-antigens. REFERENCES 1. Subbarayal B, Schiller D, Mobs C, Pfutzner W, Jahn-Schmid B, Gepp B, et al. The diversity of Bet v 1-specific IgG antibodies remains mostly constant during the course of birch pollen immunotherapy. J Allergy Clin Immunol 2015;136:1680-2. 2. Wollmann E, Lupinek C, Kundi M, Selb R, Niederberger V, Valenta R. Reduction in allergen-specific IgE binding as measured by microarray: a possible surrogate marker for effects of specific immunotherapy. J Allergy Clin Immunol 2015;136:806-9.e7. 3. Akdis M, Akdis CA. Mechanisms of allergen-specific immunotherapy: multiple suppressor factors at work in immune tolerance to allergens. J Allergy Clin Immunol 2014;133:621-31. 4. Gepp B, Lengger N, M€obs C, Pf€utzner W, Radauer C, Bohle B, et al. Monitoring the epitope recognition profiles of IgE, IgG1 and IgG4 during birch pollen
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