House Dust Mite Sublingual Immunotherapy : the Role for Transforming Growth Factor–β and Functional Regulatory T Cells

Rationale: Sublingual allergen-specific immunotherapy is gaining popularity for treatment of allergic diseases, but underlying immunological mechanisms are unresolved. Objectives: To perform detailed immunological investigation of sublingual house dust mite (HDM) immunotherapy. Methods: A 12-month randomized double-blind placebo-controlled study of sublingual HDM immunotherapy in 30 HDM-allergic subjects was performed, with 1-year open extension in 9 patients on active treatment. HDM-stimulated blood mononuclear cells were analyzed for proliferation, cytokines, and regulatory T cells (Tregs) by flow cytometry and ELISA. Effects of blocking transforming growth factor (TGF)-β and IL-10 on proliferation were determined. Treg suppressor function and allergen-specific antibody levels were measured. Clinical efficacy was assessed by symptom, medication, and Juniper quality-of-life scores. Measurements and Main Results: Allergen-induced CD4+ T-cell division and IL-5 production were significantly decreased after 6- and 12-months' active treatment but not placebo. sTGF-βRII blocked immunotherapy-induced suppression of allergen-specific T-cell proliferation, maximal at 6 months. Decreased allergen-specific CD4+ T-cell proliferation and increased IL-10 secretion and serum Der p 2–specific IgG4 were maximal at 24 months' active treatment. Treg (CD4+CD25+CD127lo/Foxp3+) function was demonstrated by suppression of allergen-specific effector T-cell (CD4+CD25–CD127hi) proliferation and cytokine production. Clinical efficacy of immunotherapy was supported by significantly decreased rhinitis symptom score, total asthma score, and Juniper quality-of-life score. Conclusions: This study establishes the novel finding that TGF-β mediates the immunological suppression seen early in clinically effective sublingual HDM immunotherapy in addition to an increase in Tregs with suppressor function.