Blocking peanut allergy through protective IgG antibodies

Project Information

AllergyBLOCK

Grant agreement ID: 656086

DOI

10.3030/656086

Project closed

EC signature date 4 May 2015

Start date 1 October 2015

End date 30 September 2017

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 185 076,00

EU contribution

€ 185 076,00

Coordinated by

INSTITUT NATIONAL DE LA SANTE ET DE LA RECHERCHE MEDICALE
France

Periodic Reporting for period 1 - AllergyBLOCK (Blocking peanut allergy through protective IgG antibodies)

Reporting period: 2015-10-01 to 2017-09-30

Summary of the context and overall objectives of the project

Food allergies are chronic and potentially fatal diseases for which there is no approved treatment other than food allergen avoidance. Such avoidance is difficult since many foods contain traces of allergens sufficient to trigger important allergic reactions. The European Commission has therefore created a Labelling Directive (2000/13/EC) obliging manufacturers to list major allergens present in pre-packaged foods sold in the EU. However, despite this directive, the prevalence of food allergies has recently increased, now affecting ~6% of people in Europe3.
Among all food allergies, peanut allergy (PA) is a particularly important public health problem since PA tends to persist throughout life and is more likely than other types of food allergies to cause severe shock (i.e. “anaphylaxis”) and death. The current paradigm states that PA is mostly triggered by IgE antibodies. Evidence derived from mouse models indicates that some IgG isotypes can also mediate allergic reactions, but the roles of human IgG in PA remain unknown. Among the potential treatments for PA under investigation, oral immunotherapy (OIT) appears very promising since subjects completing OIT tolerate food challenges despite persistent high-titers of IgE in the blood. OIT consists of the administration of slowly increasing doses of the allergenic food over several months/years and is associated with the production of large levels of IgG, but a direct link between these antibodies and the beneficial effects of OIT has not been demonstrated.
We hypothesize that PA patients produce both pro-allergic and protective IgG, and that successful OIT is associated with an increased production of protective IgG that are particularly potent at blocking the allergic reaction. Our main objective are to:
• Determine which IgG isotypes produced by PA patients are pro-allergic.
• Determine which IgG isotypes produced during peanut OIT are protective.
• Demonstrate that protective IgG can be used to treat PA and/or improve OIT protocols.
We propose to demonstrate this by developing and exploiting ‘humanized’ mouse models of PA, combined with the use of clinical samples and purified IgG from PA patients completing a phase 2 OIT clinical trial.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

This project was mainly focused on the mechanisms of allergic shock reactions (also known as anaphylaxis), and the role of IgG antibodies and myeloid cells in these reactions. Conflicting results have been obtained regarding the roles of antibody receptors and effector cells in models of anaphylaxis. In part, this might reflect the choice of adjuvant used during sensitization because various adjuvants might differentially influence the production of particular antibody isotypes. We thus decided to develop an "adjuvant-free" mouse model of anaphylaxis and assess the pathways of anaphylaxis in this model. We found that anaphylaxis is reduced in mice lacking the IgE receptor FcεRI, the IgG receptor FcγRIII or the common γ-chain FcRγ. Depletion of monocytes/macrophages also reduced anaphylaxis. By contrast, depletion of neutrophils or basophils had no significant effects in this model. Anaphylaxis was dependent on platelet-activating factor and histamine and was reduced in two types of mast cell (MC)-deficient mice. Finally, engraftment of MC-deficient mice with bone marrow-derived cultured MCs significantly exacerbated the hypothermia response and restored inflammation to levels similar to those observed in wild-type mice. We thus demonstrated that MCs, monocytes/macrophages and IgG antibodies play key roles in this model of anaphylaxis. These results were published in the Journal of Allergy and Clinical Immunology (Balbino et al. 2017).

We then demonstrated that each subclass of mouse IgG (IgG1, IgG2a, or IgG2b) can induce anaphylaxis using passive models. We then sought to determine which pathways control the induction of IgG1-, IgG2a-, and IgG2b-dependent anaphylaxis.
We found that the activating FcγRIII is the receptor primarily responsible for all 3 models of anaphylaxis, and subsequent downregulation of this receptor was observed. These models differentially relied on histamine release and the contribution of mast cells, basophils, macrophages, and neutrophils. Strikingly, basophil contribution and histamine predominance in mice with IgG1- and IgG2b-induced anaphylaxis correlated with the ability of inhibitory FcγRIIB to negatively regulate these models of anaphylaxis.
In conclusion, we demonstrated that the differential expression of inhibitory FcγRIIB on myeloid cells and its differential binding of IgG subclasses controls the contributions of mast cells, basophils, neutrophils, and macrophages to IgG subclass-dependent anaphylaxis. Collectively, our results unravel novel complexities in the involvement and regulation of cell populations in IgG-dependent reactions in vivo. These results were published in the Journal of Allergy and Clinical Immunology (Beutier et al. 2017).

We then established and characterized mice humanized for IgG receptors, in order to study the role of human IgG antibodies in food-induced anaphylaxis. We confirmed that the expression profile of these receptors is similar of that observed in human cells. We also showed that these receptors are functional since human IgG can activate these receptors in vivo. We have now also demonstrated that anaphylaxis can be induced in these humanized mice upon sensitization with purified IgG from peanut allergic patients and challenge with peanut extract, thus demonstrating that human IgG can induce anaphylaxis. We are now preparing a manuscript to report these findings, and are assessing the role of IgG produced during oral immunotherapy.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The scientific results of this project should have a major impact in the food allergy and immunotherapy fields. The contribution of human IgG to food allergy and anaphylaxis has not been assessed in vivo due to technical limitations. We will provide a definitive evaluation of the contribution of each human IgG subclass (and human IgE) to peanut anaphylaxis and oral immunotherapy (OIT). Although in vitro work indicates that some IgG, and in particular IgG4, produced during OIT might be protective, this also has never been proven in vivo. Notably, since several protection mechanisms have been proposed for OIT (e.g. suppression of mast cell activation by regulatory T cells, suppression of effector T-cell migration to tissues), it will be interesting to assess whether generation of ‘protective’ IgG is sufficient to reduce allergic responses.
This work will also introduce and characterize mice expressing multiple human antibody receptors (FcRs), and which can therefore respond to human antibodies. We anticipate that these ‘humanized’ mice will represent an attractive research tool for the scientific community, to assess the role of human antibodies and their receptors in many disease models.

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