A hypoallergenic variant of the major birch pollen allergen shows distinct characteristics in antigen processing and T-cell activation

Background BM4 is a novel genetically engineered variant of the major birch pollen allergen Bet v 1 that lacks the typical Bet v 1‐like fold and displays negligible IgE‐binding but strong T cell–activating capacity. The aim of this study was to elucidate possible differences between BM4 and Bet v 1 in internalization, antigen processing, and presentation. Methods Proliferative responses to BM4 and Bet v 1 of peripheral blood mononuclear cells and Bet v 1‐specific T‐cell clones were compared. Fluorescently labeled BM4 and Bet v 1 were used to study surface binding, endocytosis, and intracellular degradation by monocyte‐derived DC (mdDC). Both proteins were digested by endolysosomal extracts of mdDC. BM4‐ and Bet v 1‐pulsed mdDC were employed to assess the kinetics of activation of Bet v 1‐specific T‐cell clones and the polarization of naïve T cells. Results BM4 displayed a significantly stronger T cell–activating capacity than Bet v 1. Furthermore, BM4 showed increased surface binding and internalization as well as faster endolysosomal degradation compared with Bet v 1. BM4‐pulsed mdDC induced enhanced proliferative responses at earlier time‐points in Bet v 1‐specific T‐cell clones and promoted less IL‐5 production in T cells than Bet v 1‐pulsed mdDC. Conclusion The loss of the Bet v 1‐fold changes the protein's interaction with the human immune system at the level of antigen‐presenting cells resulting in altered T‐cell responses. By combining low IgE‐binding with strong and modulating T cell–activating capacity, BM4 represents a highly interesting candidate for specific immunotherapy of birch pollen allergy.