D1.195 - Fc-Engagers as a targeted approach for antigen-specific immune inhibition in HDM allergy

Allergic diseases are a growing global health challenge, with house dust mite (HDM) allergy being the most prevalent perennial allergic trigger, affecting hundreds of millions of patients worldwide. HDM sensitization occurs in up to 50- 80% of allergic asthma patients and is strongly associated with moderate-to-severe disease and frequent exacerbations, underscoring the urgent need for disease-modifying therapies. Allergen-specific B cells, particularly those class-switched to IgE, play a central role in allergic responses. Secreted allergen-specific IgE antibodies bind to high-affinity Fc-epsilon receptors (FcεRI) on mast cells and basophils, which release bioactive mediators upon subsequent allergen exposure causing symptoms like itching, swelling, bronchoconstriction, mucus secretion, or anaphylaxis. Targeting inhibitory pathways offers a promising strategy to suppress allergen-specific responses. CD32B (FcγRIIB), a potent inhibitory receptor expressed on B cells and other key immune effector cells such as basophils and dendritic-cells (DCs), can induce potent suppressive signaling when crosslinked with activating receptors such as the B cell receptor (BCR) or IgE-sensitized FcεRI.

We engineered Fc-Engager molecules combining defined antigens with Fc-domains biased towards CD32B binding. Fc-Engagers are Fc-fusion proteins consisting of antigen(s) or allergen(s) and an engineered Fc-domain which specifically binds to the inhibitory Fc-receptor FcγRIIB while exhibiting abrogated affinity to activating FcγRs. This design enables simultaneous engagement of FcγRIIB and allergen-specific receptors (BCR or FcεRI), aiming to inhibit allergen-specific, pathogenic cells and promote antigen-specific inhibitory signaling. Binding and functional activity were assessed using mast cell and basophil activation assays, including whole-blood assays with primary human basophils sensitized with allergen-specific IgE or allergic donor sera.

Using ovalbumin-specific model systems for mechanistic validation, we show that: (1) Fc-Engager molecules were able to inhibit B-cell activation via B-cell receptor signaling in an antigen-specific and FcγRIIB-dependent manner. (2) Activation of sensitized mast cells, as well as primary human basophils was strongly inhibited by Fc-Engager molecules. In contrast, control molecules (non-relevant antigens and/or wild-type Fc-domains) could not mediate inhibition. In addition, ex vivo experiments in primary human basophils using HDM-specific Fc-Engagers demonstrate that Fc-Engagers can be engineered to target multiple allergens simultaneously, as shown by a single molecule incorporating three HDM allergens with retained functional activity.

These findings show that CD32B-biased Fc-Engagers selectively suppress allergic effector cell activation via the induction of antigen-specific inhibitory signaling and support their continued development towards clinical evaluation for HDM allergy.