Allergen alters IL-2/αIL-2-based Treg expansion but not tolerance induction in an allergen-specific mouse model

Background: Regulatory T lymphocytes (Treg) play an important role in preventing allergic diseases. We characterized Treg expansion kinetics, marker profiles, and recirculation behavior in allergen-challenged mice, which had been pretreated with IL-2/αIL-2 complexes in the presence or absence of allergen. Moreover, the ability of induced Treg to control airway hyperreactivity and effector functions of lung T cells was determined.

Methods: Humanized TCR/HLA-transgenic allergy mice were treated in vivo with recombinant IL-2 complexed to the anti-IL-2 mAb JES6-1 in the presence or absence of mugwort pollen extract (MPE) on days 0-2. Afterward, they were intranasally challenged with MPE (days 13-15) followed by determination of airway hyperreactivity and lung T cell effector functions. Multiparametric flow cytometry on peripheral blood T cells was performed on a daily basis.

Results: IL-2/αIL-2 complexes highly efficiently expanded peripheral Treg cells, while concomitant allergen exposure altered the phenotype of expanded Treg cells. Notably, application of allergen together with IL-2/αIL-2 complexes induced expression of Treg marker molecules CTLA4, NRP1, Helios, and GITR on conventional T cells. Apart from CD25, GARP was identified as the most reliable surface-expressed lineage discrimination marker of Treg expanded in the presence of IL-2/αIL-2 complexes and allergen. Finally, IL-2/αIL-2 complex-expanded Treg cells could be recalled upon allergen challenge, which was associated with suppression of lung-specific Th2 responses long after initial treatment.

Conclusion: The characterization of reliable surface and transcription markers of IL-2/αIL-2 complex-expanded Treg along with their expansion kinetics and function will help to identify protocols for their long-term expansion in vivo.