Freneslerbart is an investigational, immunoglobulin G4 kappa (IgG4κ) monoclonal antibody developed for the treatment or prevention of allergic reactions to cats. It functions as a targeted allergen-neutralizing therapy. Freneslerbart is designed to specifically bind with high affinity to Fel d 1 (Felis domesticus allergen 1), the major allergenic protein found in cat saliva, dander, and sebaceous glands. By binding to and neutralizing Fel d 1 in the environment (e.g., on airborne particles) or potentially within the body, the antibody aims to prevent the allergen from interacting with allergen-specific immunoglobulin E (IgE) on mast cells and basophils. This blockade inhibits the subsequent degranulation and release of inflammatory mediators (like histamine) that cause allergic symptoms, such as rhinitis, conjunctivitis, and asthma.