| CPC C07K 16/2809 (2013.01) [A61K 39/3955 (2013.01); A61P 35/00 (2018.01); C07K 16/2803 (2013.01); C07K 16/2878 (2013.01); C07K 16/468 (2013.01); C12N 15/62 (2013.01); C12N 15/85 (2013.01); A61K 2039/505 (2013.01); C07K 2317/24 (2013.01); C07K 2317/31 (2013.01); C07K 2317/33 (2013.01); C07K 2317/35 (2013.01); C07K 2317/52 (2013.01); C07K 2317/524 (2013.01); C07K 2317/526 (2013.01); C07K 2317/53 (2013.01); C07K 2317/565 (2013.01); C07K 2317/622 (2013.01); C07K 2317/73 (2013.01)] | 1 Claim |

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1. A method of treating or improving a plasma cell disorder, a B cell disorder associated with a B cell maturation antigen (BCMA) expression, or an autoimmune disease, comprising a step of administering to a subject in need thereof with an effective amount of a bispecific antibody,
wherein the plasma cell disorder is selected from a group consists of multiple myeloma, plasmacytoma, plasma cell leukemia, macroglobulinaemia, amyloidosis, Waldenstrom's macroglobulinaemia, solitary bone plasmacytoma, extramedullary plasmacytoma, osteosclerotic myeloma, a heavy chain disease, monoclonal gammopathy of undetermined significance and smoldering multiple myeloma;
wherein the bispecific antibody is composed of two identical polypeptide chains bonded covalently to form a tetravalent homodimer, wherein each of the polypeptide chains has an amino acid sequence as set forth in SEQ ID NO: 20, wherein each of the polypeptide chains consists of an anti-BCMA (B cell maturation antigen) scFv, a linker peptide L2, an anti-CD3 scFv, and an Fc fragment in order, wherein VH (heavy chain variable region) and VL (light chain variable region) within the anti-BCMA scFv and the anti-CD3 scFv are connected by a linker sequence respectively, and wherein the amino acid sequence of the linker sequence is amino acids 3-17 of SEQ ID NO: 10, wherein the amino acid sequences of the VH and the VL of the anti-BCMA scFv are SEQ ID NO: 7 and SEQ ID NO: 8, respectively, wherein the amino acid sequences of the VH and the VL of the anti-CD3 scFv are SEQ ID NO: 17 and SEQ ID NO: 18, respectively, wherein the linker peptide L2 consists of a flexible peptide and a rigid peptide, wherein the amino acid sequence of the flexible peptide is SEQ ID NO: 29, and wherein the amino acid sequence of the rigid peptide is SEQ ID NO: 24.
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