Fel d 1 (major cat allergen protein)

Class

anti-allergen monoclonal antibody combination

Pathway

REGN1908 + REGN1909 bind and neutralize cat allergen Fel d 1, blocking IgE-mediated allergic/asthmatic response to cat exposure

Fel d 1 is the major protein allergen produced by cats, secreted from sebaceous and salivary glands and shed on dander, hair, and saliva. In sensitized individuals, the immune system has generated allergen-specific immunoglobulin E (IgE) antibodies that coat mast cells and basophils. When airborne Fel d 1 encounters this IgE, it cross-links the antibodies on the cell surface, triggering release of histamine and other inflammatory mediators. This cascade produces the familiar symptoms of allergic rhinitis, conjunctivitis, and, in more severe cases, asthma exacerbation upon cat exposure. Rather than modulating the immune system broadly, this mechanism works by directly neutralizing the allergen protein itself before it can engage IgE. A combination of two monoclonal antibodies is used because Fel d 1 presents multiple distinct binding surfaces; targeting more than one simultaneously improves the likelihood of fully blocking the protein's capacity to cross-link IgE, rather than leaving alternate faces available for immune recognition. This allergen-neutralization strategy is relevant wherever a single, well-characterized protein is responsible for the bulk of an allergic response, offering a targeted alternative to therapies that act more generally on IgE or downstream inflammatory pathways.