The aim of this project is to develop a systems biology strategy to quantitatively predict the response potential of activated Th2 (T-helper type 2) cells from resting Th2 cells of allergic patients undergoing allergen desensitization treatment. The investigators plan to analyze the transcriptome of their cells at different timepoints throughout the course of AIT and to infer networks of gene expression that will allow us to determine key prognostic factors for AIT responsiveness and immune tolerance induction. In parallel to Th2 cells, the investigators will study the roles and subpopulations of NK cells, as the role of these subsets in allergy is still largely unknown. Additionally, as the gut microbiota is known to be associated and interacting with the immune system, the investigators will seize the opportunity to collect microbiota samples of patients undergoing AIT to assess changes that might occur during desensitization. The completion of this study will allow us i) to identify potential biomarkers that might ultimately be used to predict therapy outcome or to refine and adapt therapy to a patient's features ii) to monitor the changes occurring in NK cells from patients exposed to desensitization procedures, iii) to study the gut microbiota of allergic patients and explore potential microbiota predictive biomarkers (part of the study performed at IBBL). This study stands as a proof-of-concept study to start a future larger cohort, since the discovery of new biomarkers/features could open up new avenues to understand other disorders linked to immune dysregulation and in which tolerance induction is required, such as autoimmune diseases, transplant rejection and others.