Hybrid constant regions

Abstract

The invention provides hybrid constant regions and antibodies or fusion proteins incorporating the same. The hybrid constant regions include at least CH2 and CH3 regions of an IgG or IgA constant region and Cμ3 and Cμ4 regions of a Cμ constant region. The hybrids retain properties of both component constant regions. The hybrids retain the ability of a Cμ constant region to form multivalent complexes, e.g., pentameric or hexameric structures. IgG hybrids also retain IgG properties including pH-dependent FcRn binding, which is associated with a relatively long in vivo half-life, and specific binding to protein G, which facilitates purification. Depending on the isotype and subtype, the nature of the antigen and presence of additional IgG CH1 and hinge domains, IgG hybrids may also retain properties of specific binding to protein A, and effector functions ADCC, CDC and opsonization. IgA hybrids retain the property of IgA of binding to an Fc-alpha receptor CD89.

1 . A fusion protein comprising an immunoglobulin heavy chain constant region and a heterologous polypeptide, the immunoglobulin heavy chain region comprising in order from N- to C-terminus CH2 and CH3 regions, each of which is of IgG or IgA isotype, and Cμ3 and Cμ4 regions. 
     
     
         2 . The fusion protein of  claim 1 , wherein the immunoglobulin heavy chain further comprises a hinge region N-terminal to the CH2 region. 
     
     
         3 - 5 . (canceled) 
     
     
         6 . The fusion protein of  claim 1 , wherein the hinge region, if present, and the CH2 and CH3 regions are IgG1 regions. 
     
     
         7 . The fusion protein of  claim 1 , wherein the hinge region, if present, and the CH2 and CH3 regions are IgG2 regions. 
     
     
         8 . The fusion protein of  claim 1 , wherein the hinge region, if present, and the CH2 and CH3 regions are IgG3 regions. 
     
     
         9 . The fusion protein of  claim 1 , wherein the hinge region, if present, and the CH2 and CH3 regions are IgG4 regions. 
     
     
         10 . The fusion protein of  claim 1 , wherein the the CH2 and CH3 regions are IgA regions. 
     
     
         11 . The fusion protein of any preceding  claim 1 , the hinge region, if present, and the CH2 and CH3 regions are human CH1, hinge, CH2 and CH3 regions and the Cμ3 and Cμ4 regions are human Cμ3 and Cμ4 regions. 
     
     
         12 - 15 . (canceled) 
     
     
         16 . The fusion protein of  claim 2 , wherein the hinge region and CH2 and CH3 regions are IgG and the fusion protein which shows pH-dependent FcRn binding, specifically binds protein G, specifically binds protein A, exhibits ADCC, CDC and/or opsonization. 
     
     
         17 . The fusion protein of  claim 2 , wherein the hinge region, and CH2 and CH3 regions are human IgG1 regions and the antibody shows pH-dependent FcRn binding, specifically binds protein G, and specifically binds protein A. 
     
     
         18 . The antibody of  claim 17  that exhibits ADCC, CDC and opsonizaton. 
     
     
         19 . The fusion protein of  claim 2 , wherein the hinge, CH2 and CH3 regions are human IgG2 or IgG4 regions and the antibody or fusion protein shows pH-dependent FcRn binding, specifically binds protein G and specifically binds protein A. 
     
     
         20 . The fusion protein of  claim 2 , wherein the hinge region, and CH2 and CH3 regions are human IgG3 and the antibody shows pH-dependent FcRn binding, and specifically binds protein G. 
     
     
         21 . The antibody of  claim 20  that exhibits ADCC, CDC and opsonization. 
     
     
         22 . The fusion protein of  claim 1 , wherein the CH1, if present, and the CH2 and CH3 regions are human IgA and the antibody binds an Fc alpha receptor. 
     
     
         23 . (canceled) 
     
     
         24 . The fusion protein of  claim 1 , wherein the heterologous protein is linked to the hinge of the constant region via a flexible linker, such as Gly-Gly-Ala-Ala. 
     
     
         25 . The fusion protein of  claim 1 , wherein the heterologous polypeptide is a receptor extracellular domain or a protein that specifically binds to a receptor extracellular domain. 
     
     
         26 . The fusion protein of  claim 1  as a component of a multi-specific complex comprising a plurality of fusion proteins, the fusion proteins including different heterologous polypeptides. 
     
     
         27 . The fusion protein of  claim 1  that is a component of a multispecific complex further comprising an antibody comprising an immunoglobulin heavy chain region comprising in order from N- to C-terminus CH2 and CH3 regions, each of which is of IgG or IgA isotype, and Cμ3 and Cμ4 regions, the antibody and the fusion protein complexed via the Cμ3 and Cμ4 regions. 
     
     
         28 . (canceled) 
     
     
         29 . The fusion protein of  claim 1  that specifically binds the extracellular domain of a receptor. 
     
     
         30 . (canceled) 
     
     
         31 . The fusion protein of  claim 1 , wherein the heterologous polypeptide comprises an extracellular domain of a TNF-alpha receptor, LFA-3 or an IL-1 receptor. 
     
     
         32 . The fusion protein of  claim 1 , wherein the heterologous polypeptide comprises a TRAIL protein. 
     
     
         33 . The fusion protein of  claim 1  that is conjugated to a cytotoxic moiety. 
     
     
         34 - 40 . (canceled)