Mevonlerbart is a human IgG4-kappa monoclonal antibody specifically designed to target and neutralize the major cat allergen Fel d 1. As an IgG4 isotype, it is engineered to minimize immune effector functions while focusing on allergen neutralization. By binding with high affinity to Fel d 1—the primary allergen shed by cats in saliva, skin, and fur—Mevonlerbart aims to prevent the allergen from interacting with IgE on mast cells and basophils. This blockade is intended to inhibit the initiation of the allergic cascade, thereby reducing or preventing allergic symptoms in sensitized individuals. It is being developed as a passive immunotherapy for the management of cat allergy.