The present invention provides: a modified FcRn-binding domain having an enhanced affinity for the Fc Receptor neonatal (FcRn) at neutral pH； an antigen-binding molecule comprising said FcRn-binding domain, which has low immunogenicity, high stability and form only a few aggregates； a modified antigen-binding molecule having an increased FcRn-binding activity at neutral or acidic pH without an increased binding activity at neutral pH for a pre-existing anti-drug antibody； use of the antigen-binding molecules for improving antigen-binding molecule-mediated antigen uptake into cells； use of the antigen-binding molecules for reducing the plasma concentration of a specific antigen； use of the modified FcRn-binding domain for increasing the total number of antigens to which a single antigen-binding molecule can bind before its degradation； use of the modified FcRn-binding domain for improving pharmacokinetics of an antigen-binding molecule； methods for decreasing the binding activity for a pre-existing anti-drug antibody； and methods for producing said antigen-binding molecules.
