CATNIP will be conducted at multiple sites in the US and enroll cat‐allergic adults who will be randomized to four possible treatment groups: immunotherapy plus MEDI9929/AMG 157, immunotherapy plus placebo, placebo plus MEDI9929/AMG 157, or two corresponding placebos. This study is specifically enrolling cat allergic individuals who do not live with cats in order to limit exposure to the allergen outside of the study. Treatment will be given for about one year, followed by one year off therapy.