Targeting the neonatal Fc receptor (FcRn) to treat autoimmune diseases and maternal-fetal immune cytopenias.

FcRn, a non-classical Fc gamma (γ) receptor (FcγR) with near ubiquitous expression, plays key roles in disease pathogenesis and progression though immunoglobulin G (IgG) transport, IgG recycling, and IgG-immune complex clearance. FcRn function can be inhibited using IgG-based and non-IgG-based antagonists, by exploiting the pH-dependent binding affinity of FcRn for the IgG Fc region. FcRn therapeutics have shown promise in murine models and human clinical trials for autoimmune diseases and maternal-fetal immune cytopenias; they appear safe, well-tolerated, and reduce circulating IgG levels. Compared to traditional therapeutics, inhibiting FcRn has fewer adverse side effects and represents a new approach that is less invasive, time-consuming, and costly.