Novel Bispecific Engagers Targeting the CεmX Domain of mIgE ‐Expressing Cells

Background IgE‐associated allergic diseases, affecting approximately 30% of the global population, are a major health burden. Standard treatments, including pharmacotherapy and allergen immunotherapy (AIT), have limitations such as adverse effects, insufficient symptom relief and long treatment durations. Methods In this study, we developed and evaluated a bispecific T‐cell engager (TCE) and a half‐life extended (HLE) bispecific natural killer (NK) cell engager (NKCE) targeting IgE‐producing cells, to offer novel, potentially curative therapeutic options. The TCE and HLE‐NKCE constructs were designed to target the CεmX domain of membrane‐bound IgE (mIgE) and engage T cells and NK cells, respectively. Their efficacy was assessed through in vitro luciferase‐based cytotoxicity assays using Ramos and U266 B‐cell lines expressing mIgE as target cells, and primary human immune effector cells and the NK‐cell line NK‐92 as effector cells. Additional characterisation of the constructs was performed using flow cytometry. Results Both TCE and HLE‐NKCE specifically mediated killing of CεmX‐expressing cells in a dose‐ and effector‐to‐target (E:T) ratio‐dependent manner. The TCE demonstrated robust activity even at low antigen densities and concentrations as low as 1 ng/mL (18 pM). The HLE‐NKCE effectively mediated killing in the presence of human serum albumin, suggesting functionality in physiological conditions. T‐ and NK‐cell activation was observed only in the presence of target cells and TCE. Conclusion Our novel anti‐CεmX TCE and HLE‐NKCE effectively target and eliminate mIgE‐expressing cells in vitro. Although further investigation is needed, our bispecific engagers are promising off‐the‐shelf therapeutics for the treatment of IgE‐associated allergic diseases.