This study will implement the concept referred to as "allergen-plus," which aims to enhance the disease-modifying mechanisms of allergen-specific immunotherapy by combining it with other anti-inflammatory or immune-modulating agents. Thymic stromal lymphopoietin (TSLP) is a cytokine which appears to be instrumental in both initiating and maintaining allergic sensitivity to antigens, and Immune Tolerance Network (ITN) investigators hypothesize that blocking TSLP during the administration of cat immunotherapy will induce durable immune changes that lead to tolerance.