Abstract: The present invention provides antigen-binding molecules containing (i) an antigen-binding domain whose antigen-binding activity varies depending on ion concentration conditions, (ii) an Fc?R-binding domain having Fc? RIIb-selective binding activity, and (iii) an FcRn-binding domain having FcRn-binding activity under an acidic pH range condition, and methods of decreasing plasma antigen concentration as compared to before administering the molecule, which include the step of administering the molecule.

Abstract: The present inventors created antigen-binding molecules containing an antigen-binding domain and an Fc?-receptor-binding domain, wherein the molecules have human-FcRn-binding activity in an acidic pH range condition, the antigen-binding domain changes the antigen-binding activity of the antigen-binding molecules depending on the ion-concentration condition, and the Fc? receptor-binding domain has higher binding activity to the Fc? receptor in a neutral pH range condition than an Fc region of a native human IgG in which the sugar chain bound at position 297 (EU numbering) is a fucose-containing sugar chain.

Abstract: The present inventors have discovered that in living organisms that have received an antigen-binding molecule containing an antigen-binding domain whose binding activity to an antigen changes depending on ion concentration conditions and containing an FcRn-binding domain having FcRn-binding activity in a neutral pH range, immune responses to the antigen are induced. Furthermore, the present inventors have discovered that in living organisms that have received an antigen-binding molecule containing an antigen-binding domain whose binding activity to an antigen changes depending on ion concentration conditions and containing an FcRn-binding domain having FcRn-binding activity in a neutral pH range, immune responses to the antigen are induced, and also the antigen-binding molecule has cytotoxicity or antiproliferative action against cancer cells, foreign biological species, or such that express the antigen to which the antigen-binding molecule binds.

Abstract: The present invention demonstrated that the modification of the Fc region of an antigen-binding molecule into an Fc region that does not form in a neutral pH range a heterotetramer complex containing two molecules of FcRn and an active Fc? receptor improved the pharmacokinetics of the antigen-binding molecule and reduced the immune response to the antigen-binding molecule. The present invention also revealed methods for producing antigen-binding molecules having the properties described above, and successfully demonstrated that pharmaceutical compositions containing as an active ingredient such an antigen-binding molecule or an antigen-binding molecule produced by a production method of the present invention have excellent features over conventional antigen-binding molecules in that when administered, they exhibit improved pharmacokinetics and reduced in vivo immune response.