Method for improving antibody

1. A method for improving the expression level and/or stability of a human antibody or a humanized antibody, said method comprising:

modifying a human antibody or a humanized antibody by substituting proline at position 12 (according to Kabat numbering) in a light chain variable region (hereinafter referred to as “VL chain”) of the human antibody or the humanized antibody with a different amino acid other than proline selected from any one of the amino acid substitutions: Ser, His, Val, Gly, Leu, Arg, Phe, Met or Glu, wherein said VL chain belongs to human Vκ2 family and has a framework FR1, which prior to substitution, has the FR1 sequence encoded by SEQ ID:32 from DPK18 (GeneBank Accession No. X63403), to thereby obtain a modified human antibody or a modified humanized antibody having improved expression level and/or stability as compared to a control, which is identical to the human antibody or the humanized antibody but without said substitution.

2. The method according to claim 1 , wherein the FR1 of the VL chain belonging to human Vx2 family after substitution has the amino acid sequence selected from the amino acid sequences as depicted in SEQ ID NO: 9 to 17.

3. The method according to claim 1 , wherein said antibody is an intact antibody, or an antibody fragment such as Fab, Fab′, F(ab′)2, scAb, scFv, diabody [a recombinant dimer antibody consisting of homologous or heterologous heavy chain variable region (VH chain) and VL chain connected by a short linker peptide] or scFv-Fc; or a fused antibody or a fused antibody fragment with other proteins; or an antibody or an antibody fragment labeled with a low molecular weight compound; or an antibody or an antibody fragment modified with a high molecular weight compound.

4. The method according to claim 1 , wherein the amino acid substitution is done by a genetic recombination technique.

5. A method for preparing an antibody with an improved expression level and/or stability according to claim 1 , comprising:

preparing a gene coding for an amino acid sequence of said human antibody or said humanized antibody or a fragment of said human or humanized antibody, each comprising the amino acid sequence of the VL chain after substitution;

transforming a host of eukaryotic or prokaryotic organisms with said gene;

expressing said human antibody or said humanized antibody or said human antibody fragment or said humanized antibody fragment from said host; and

recovering said human antibody or said humanized antibody or said human antibody fragment or said humanized antibody fragment.