Basophil sensitivity reflects long-term clinical outcome of subcutaneous immunotherapy in grass pollen-allergic patients

Background: Allergic rhinoconjunctivitis is a public health problem. Allergen Immunotherapy is an effective and safe treatment, that modifies the natural course of allergic disease and induces long-term tolerance. Objective: To correlate basophil and antibody biomarkers of subcutaneous immunotherapy to clinical outcomes and cellular changes in target tissue. Methods: Adults suffering from allergic rhinoconjunctivitis due to grass pollen allergy were randomized to receive subcutaneous immunotherapy (n = 18) or to an open control group (n = 6). Patients reported daily symptom and medication scores and weekly rhinitis related quality of life scores during four pollen seasons. Biomarkers were measured every 3 months for three years treatment and every 6 months in the follow-up year. Nasal and cutaneous allergen challenge tests were performed annually. Leukocyte subsets were assessed in nasal mucosa biopsies at baseline and after treatment. Results: Subcutaneous immunotherapy led to a 447-fold decrease in basophil sensitivity during the first treatment year. This remained 100-fold lower than baseline during the 3 year-treatment period and 10-fold lower during the follow-up year (n = 18, P =.03). Decrease in basophil sensitivity after three weeks of treatment predicted long-term improvement in seasonal combined symptom and medication scores (ῥ=−0.69, P =.0027) during three years of treatment. AUC of IgE-blocking factor correlated to nasal allergen challenge (ῥ = 0.63, P =.0012) and SPT (ῥ = 0.45, P =.03). Plasma cell numbers in the nasal mucosa increased during treatment (P =.02). Conclusion: Decrease in basophil sensitivity after three weeks of subcutaneous allergen immunotherapy predicted the clinical outcome of this treatment.