The neonatal Fc receptor ((FcRn) is a protein and Fc receptor found in several types of tissues and cells in the body. It plays a role at two different phases during life: in early development, FcRn is responsible for passing immunity from mother to child; during lifetime, FcRn helps maintain the number of antibodies present in the circulation. FcRn recycles IgGs which have binding sites that fit with FcRn receptors, allowing them to avoid degradation. When an IgG antibody connects to an FcRn receptor, it gets recycled back into the bloodstream and stays in circulation. Unfortunately, the IgG recycling functionality of FcRn may also play a major role in many autoimmune diseases.
Severe autoimmune diseases can be associated with high levels of pathogenic immunoglobulin G, or IgG, antibodies for which few innovative biologic treatments have been approved and severe unmet medical need exists. A number of monoclonal antibodies have been created to block the interaction of FcRn and IgG, accelerating the catabolism of antibodies and reducing the concentration of pathogenic IgG autoantibodies. Such treatments have potential in many large and orphan indications, such as multiple sclerosis, immune thrombocytopenia, systemic lupus erythematosus, myasthenia gravis and pemphigus vulgaris.
At present, three FcRn blocking antibodies have reached the commercial stage. Two of them (Vyvgart and Rystiggo) posted combined 2024 global sales of US$ 2.5 bln making FcRn a commercially attractive and clinically validated target for treatment of antibody-mediated autoimmune diseases.

