An exhausted phenotype of TH2 cells is primed by allergen exposure, but not reinforced by allergen‐specific immunotherapy.

Background: Studies show that proallergic TH2 cells decrease after successful allergen‐specific immunotherapy (AIT). It is likely that iatrogenic administration of allergens drives these cells to exhaustion due to chronic T‐cell receptor stimulation. This study aimed to investigate the exhaustion of T cells in connection with allergen exposure during AIT in mice and two independent patient cohorts. Methods: OVA‐sensitized C57BL/6J mice were challenged and treated with OVA, and the development of exhaustion in local and systemic TH2 cells was analyzed. In patients, the expression of exhaustion‐associated surface markers on TH2 cells was evaluated using flow cytometry in a cross‐sectional grass pollen allergy cohort with and without AIT. The treatment effect was further studied in PBMC collected from a prospective long‐term AIT cohort. Results: The exhaustion‐associated surface markers CTLA‐4 and PD‐1 were significantly upregulated on TH2 cells upon OVA aerosol exposure in OVA‐allergic compared to non‐allergic mice. CTLA‐4 and PD‐1 decreased after AIT, in particular on the surface of local lung TH2 cells. Similarly, CTLA‐4 and PD‐1 expression was enhanced on TH2 cells from patients with allergic rhinitis with an even stronger effect in those with concomitant asthma. Using an unbiased Louvain clustering analysis, we discovered a late‐differentiated TH2 population expressing both markers that decreased during up‐dosing but persisted long term during the maintenance phase. Conclusions: This study shows that allergen exposure promotes CTLA‐4 and PD‐1 expression on TH2 cells and that the dynamic change in frequencies of exhausted TH2 cells exhibits a differential pattern during the up‐dosing versus the maintenance phases of AIT. [ABSTRACT FROM AUTHOR]