Abstract:
The present invention relates to a bicistronic expression vector for antibody expression, an animal cell transfected with the expression vector, and a method for producing an antibody including culturing the animal cell, in which the expression vector includes a first expression cassette including ‘promoter-UTR-intron-antibody light chain gene-polyA’ and a second expression cassette including ‘promoter-UTR-intron-antibody heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. An expression vector capable of expressing a desired antibody with high efficiency can be constructed using the bicistronic expression vector including an intron for antibody expression according to the present invention, and the expression vector can produce the antibody by culturing the transfected animal cell with stability and high efficiency.

Description:
[0001]    This application is a U.S. National Phase of PCT/KR2014/009398, filed Oct. 7, 2014, which claims the benefit of priority to Korean Patent Application No. 10-2014-0085934, filed Jul. 9, 2014, Korean Patent Application No. 10-2014-0085933, filed Jul. 9, 2014, and Korean Patent Application No. 10-2014-0085932, filed Jul. 9, 2014, Korean Patent Application No. 10-2014-0019782, filed Feb. 20, 2014, Korean Patent Application No. 10-2014-0019781, filed Feb. 20, 2014, Korean Patent Application No. 10-2014-0019780, filed Feb. 20, 2014, and Korean Patent Application No. 10-2013-0119511, filed Oct. 7, 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a bicistronic expression vector for antibody expression, an animal cell transfected with the expression vector, and a method for producing an antibody including culturing the animal cell, in which the expression vector includes a first expression cassette including ‘promoter-untranslated region (UTR)-intron-antibody light chain gene-polyA’ and a second expression cassette including ‘promoter-UTR-intron-antibody heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
       BACKGROUND OF THE INVENTION 
       [0003]    Various human proteins have been produced by genetic recombination. However, more often than not, proteins with normal biological activities appear to be synthesized only when mammalian cells are used, due to a series of processes specific to eukaryotic cells, such as glycosylation and phosphorylation. An immunoglobulin G (IgG) gene, often used as a therapeutic antibody, consists of a heavy chain gene and a light chain gene. The heavy and light chains produced by the respective genes are linked during a folding process within a cell and discharged from the cell. Chinese hamster ovary (CHO) cells as mammalian cells are frequently used for the production of recombinant antibodies (Kaufman, et al.,  Mol. Cell. Biol.  (1985) 5, 1750). 
         [0004]    Among the various methods used for the construction of a recombinant expression vector capable of inducing a more powerful and stable gene expression in mammalian cells, the representative method is to increase the gene expression efficiency by selecting a strong promoter. A promoter is a site on DNA, in which RNA polymerase can bind and initiate mRNA synthesis due to the presence of binding sites for various transcription factors and TATA box, and the level of gene expression level varies a lot depending on the performance of the promoter. For the improvement of expression of an antibody, it is suitable to induce a high constitutive expression, and examples of representative strong promoters may include simian virus 40 (SV40) promoter, cytomegalovirus (CMV) promoter, elongation factor 1-α (EF1-α) promoter, etc. 
         [0005]    In addition to the method of increasing the capability of a vector itself for mRNA synthesis using a strong promoter, a gene amplification system may be employed for increasing therapeutic protein productivity. A brief overview of this method is as follows. Cells are transfected with a foreign gene and only the cells, which are incorporated with the foreign gene into the chromosome, are selectively cultured by adding a chemical. Then, the selectively cultured cells are separated and an increased amount of the chemical is added to a cell culture to induce the amplification of the foreign gene incorporated into the chromosome of the selectively cultured cells. The representative genes used in gene amplification include dihydrofolate reductase (hereinafter, DHFR) and glutamine synthetase (hereinafter, GS). The type of chemicals used for amplifying the amplification genes includes methotrexate (hereinafter, MTX) for DHFR and methionine sulfoximine (hereinafter, MSX) for GS. The cell lines with more than 1,000 copies of the amplified foreign gene can be prepared by the gene amplification process. 
         [0006]    The conventional methods for the construction of cell lines capable of constitutive expression of an antibody gene include a method, in which a plasmid vector DNA including the gene for a desired heavy chain and light chain and a vector DNA having an amplification gene are co-transfected into a cell, and the cell line incorporated with both of the two vector DNAs in the chromosome is separated (Kaufman,  Methods in Enz . (1990) 185, 487), or a method, in which a vector for expressing an amplification gene is constructed using SV40 promoter and then the cell line with the vector incorporated into the chromosome is separated. 
         [0007]    As another method for expressing an amplification gene, a bicistronic vector may be used. Unlike prokaryotic cells, eukaryotic cells in principle produce a single mRNA by one promoter and only the corresponding gene is translated to synthesize a protein. However, some viruses have a sequence for ribosome-binding in the middle of their mRNA sequences, and thus multiple proteins can be synthesized from a single mRNA. When an antibody gene and an amplification gene are expressed by different promoters, only the amplification gene, but not the antibody gene, may be amplified during gene amplification. However, this problem can be solved using the internal ribosome entry site (IRES) thereby expressing the genes using the same promoter. Nevertheless, the method of using the bicistronic vector also has a disadvantage in that a desired protein cannot be prepared in large-scale thus requiring a more powerful method. 
         [0008]    Meanwhile, bevacizumab (also called Avastin) is a humanized antibody for VEGF developed by Genentech (USA) and plays a role of an angiogenesis inhibitor, and has been highlighted as an antibody therapeutic mainly used for the treatment of colorectal cancer, lung cancer, kidney cancer, brain cancer, etc. Tocilizumab (also called Actemra®) is a human monoclonal antibody for IL-6 receptors developed by Roche, a Swiss pharmaceutical company, and has been approved in USA, Europe, and Japan as a treatment for rheumatoid arthritis under the product name of Actemra. Denosumab (also called Prolia®) is a human monoclonal antibody for the receptor activator of NF-kB ligand (RANKL) developed by Amgen (USA) and has been approved in USA, Canada, and Europe as a treatment for osteoporosis under the product name of Prolia, and has also been approved in Europe as a drug for the prevention of fracture in patients with bone metastasis from solid cancer under the product name of Xgeva. 
         [0009]    Meanwhile, belimumab (also called Benlysta®) is a human monoclonal antibody for B lymphocyte stimulator (BLyS) developed by GlaxoSmithKline (GSK), a multinational pharmaceutical company, and has been approved in USA, Canada, and Europe as a treatment for lupus (systemic lupus erythematosus, SLE). Golimumab (also called Simponi®) is a human monoclonal antibody for TNFα developed by Janssen Biotech, Inc., (formerly Centocor), a subsidiary of Johnson &amp; Johnson, a global pharmaceutical company, and has been approved in USA, Canada, and Korea as a treatment for rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis under the product name of Simponi. 
         [0010]    Meanwhile, ustekinumab (also called Stelara®) is a human monoclonal antibody for interleukin-12 (IL-12) and interleukin-23 (IL-23) developed by Janssen Pharmaceuticals, Inc., a multinational pharmaceutical company, and has been approved by the U.S. Food and Drug Administration (FDA) as a treatment for psoriatic arthritis, and the drug is in clinical trials for the treatment of severe psoriasis, moderate-to-severe plaque psoriasis, multiple sclerosis, sarcoidosis, etc. Ipilimumab (also called Yervoy®) is a human monoclonal antibody for cytotoxic T-lymphocyte antigen (CTLA-4) developed by Bristol-Myers Squibb Co. (BMS), a U.S. pharmaceutical company, and has been approved by the U.S. Food and Drug Administration (FDA) as a treatment for melanoma and skin cancer under the product name of Yervoy, and the drug is in clinical trials for the treatment of non-small cell lung carcinoma (NSCLC), small cell lung cancer (SCLC), bladder cancer, and metastatic hormone-refractory prostate cancer. 
         [0011]    There is a need for the development of a method for large-scale production of these blockbuster antibody therapeutics. 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0012]    The present inventors have endeavored to find a method for inducing a more powerful and stable gene expression in various mammalian cells, and as a result, they have constructed a bicistronic expression vector, which includes an untranslated region (UTR) and an intron to a conventional expression vector, and they have confirmed that the bicistronic expression vector can co-express in high yield the light and heavy chains of various antibody therapeutics along with the amplification gene, thereby completing the present invention. 
       Technical Solution 
       [0013]    An object of the present invention is to provide a bicistronic expression vector for antibody expression, which includes a first expression cassette including ‘promoter-untranslated region (UTR)-intron-antibody light chain gene-polyA’, and a second expression cassette including ‘promoter-UTR-intron-antibody heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0014]    Another object of the present invention is to provide an animal cell transfected with the expression vector. 
         [0015]    A further object of the present invention is to provide a method for producing an antibody including culturing the animal cell. 
       Advantageous Effects of the Invention 
       [0016]    An expression vector capable of expressing a desired antibody with high expression efficiency can be constructed using the bicistronic expression vector including an intron for antibody expression according to the present invention, and the expression vector can produce the antibody with stability and high efficiency by culturing the transfected animal cell. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows schematic diagrams illustrating the constructed constitutions of gene fragments, the Gln-LC and the Gln-HC, according to the present invention. 
           [0018]      FIG. 2  shows a schematic diagram illustrating the process of constructing the GS-Gln-LC according to the present invention. 
           [0019]      FIG. 3  shows a schematic diagram illustrating the process of constructing the pCYBIG vector containing the GS gene according to the present invention by inserting the Gln-HC to the GS-Gln-LC of the present invention. 
           [0020]      FIG. 4  shows a schematic diagram illustrating the process of constructing the pCYBID vector containing the DHFR gene according to the present invention from the pCYBIG vector of the present invention. 
           [0021]      FIG. 5  shows a schematic diagram illustrating the process of constructing the pCYB204IG vector, which is an expression vector for the light chain/heavy chains of bevacizumab containing the GS gene according to the present invention. 
           [0022]      FIG. 6  shows a schematic diagram illustrating the process of constructing the pCYB204ID vector, which is an expression vector for the light chain/heavy chains of bevacizumab containing the DHFR gene according to the present invention. 
           [0023]      FIG. 7A  shows the result of the amount of antibody expression in a cell line transfected with the pCYB204IG at 500 μM MSX. 
           [0024]      FIG. 7B  shows the result of the amount of antibody expression in a cell line transfected with the pCYB204ID at 800 nM MTX. 
           [0025]      FIG. 8  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS001 used in the present invention. 
           [0026]      FIG. 9  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS002 used in the present invention. 
           [0027]      FIG. 10  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS003 used in the present invention. 
           [0028]      FIG. 11  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS004 used in the present invention. 
           [0029]      FIG. 12  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS005 used in the present invention. 
           [0030]      FIG. 13  shows a schematic diagram illustrating the restriction map of the expression vector pCYBBSS006 used in the present invention. 
       
    
    
     BEST MODE 
       [0031]    In order to achieve the above objects, in an aspect, the present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-antibody light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-antibody heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0032]    The present invention is directed to providing a bicistronic expression vector, which is designed to express an antibody gene for the heavy and light chains and an amplification gene as if they were a single gene, by including a UTR and an intron to enable a more powerful and stable gene expression in various mammalian cells. In particular, the present invention provides a novel expression cassette which includes a UTR and an intron. 
         [0033]    Specifically, the present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-bevacizumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-bevacizumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-tocilizumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-tocilizumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-denosumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-denosumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-belimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-belimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-golimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-golimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-ustekinumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-ustekinumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. The present invention provides a bicistronic expression vector for antibody expression, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-ipilimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-ipilimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0034]    As used herein, the term “bicistronic” refers to a system, in which a ribosome can synthesize a polypeptide within mRNA in a eukaryotic cell, thus enabling the synthesis of multiple proteins from a single mRNA. In the present invention, a vector was designed so that an antibody gene and an amplification gene can be expressed simultaneously. 
         [0035]    Unlike the prokaryotic cells such as  E. coli  having a polycistronic system, in which multiple proteins can be synthesized simultaneously from a single mRNA by the multiple binding of ribosome to various site of the mRNA, in eukaryotic cells, ribosome binds to the 5′ end of an mRNA and looks for a start codon AUG via scanning during the protein translation from the mRNA. Since protein synthesis starts only from this AUG codon, eukaryotic cells have a monocistronic system in which only a single polypeptide can be synthesized from a single mRNA, and Kozac sequence is known to play an important role in the recognition of ATG and initiation of protein synthesis. However, in the case of encephalomyocarditis virus (hereinafter, EMCV), which has an RNA sequence with a specialized structure called internal ribosome entry site (hereinafter, IRES), multiple proteins can be translated from a single mRNA in a eukaryotic cell (Jang, et al.,  J. Virol . (1989) 63, 1651). In the present invention, for the simultaneous expression of an antibody gene and an amplification gene, a vector was designed so that IRES can be positioned downstream of a heavy chain gene of an antibody, followed by the amplification gene. 
         [0036]    As used herein, the term “vector” refers to a gene construct including essential regulatory factors such as a promoter for expressing a target gene in an appropriate host cell, and preferably, for the purpose of the present invention, the vector refers to one for expressing an antibody, and it may be a bicistronic expression vector. 
         [0037]    In an exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing bevacizumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-bevacizumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-bevacizumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0038]    In another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing tocilizumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-tocilizumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-tocilizumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0039]    In still another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing denosumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-denosumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-denosumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0040]    In still another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing golimumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-golimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-golimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0041]    In still another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing belimumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-belimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-belimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0042]    In still another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing ustekinumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-ustekinumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-ustekinumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0043]    In still another exemplary embodiment, the vector of the present invention may be a bicistronic expression vector for expressing ipilimumab, including: (i) a first expression cassette including ‘promoter-untranslated region (UTR)-intron-ipilimumab light chain gene-polyA’; and (ii) a second expression cassette including ‘promoter-UTR-intron-ipilimumab heavy chain gene-internal ribosome entry site (IRES)-amplification gene-polyA’. 
         [0044]    As used herein, the term “promoter” refers to an area of DNA nucleotide sequence to which transcription regulatory factors bind, and for the purpose of the present invention, a promoter capable of inducing a powerful and stable gene expression may be used to increase the efficiency of gene expression. 
         [0045]    The promoter may preferably be one selected from the group consisting of simian virus 40 (SV40) early promoter, cytomegalovirus (CMV) promoter, and elongation factor1-α (EF1-α) promoter, although not limited thereto. In particular, the EF1-α may be human elongation factor1-α (hEF1-α). More preferably, the promoter may be a CMV promoter, and most preferably, the promoter of cytomegalovirus strain AD169. In an exemplary embodiment of the present invention, an expression vector was constructed by inserting the CMV promoter, which is one of the strongest promoters known so far on the sequence of the cytomegalovirus strain AD169 genome (GenBank: X17403.1), for inducing high antibody expression. 
         [0046]    As used herein, the term “untranslated region (UTR)”, which is an untranslated region of mRNA, generally refers to both ends of a coding region. Specifically, the 5′ end portion is called 5′ UTR and the 3′ end is called 3′UTR. More specifically, as used herein, the UTR is included in the bicistronic vector of the present invention and is not particularly limited as long as it has the effect of increasing the amount of gene expression. Even more specifically, the UTR may be a UTR derived from CMV. The present inventors first verified that the bicistronic expression vector, which includes an expression cassette containing both the UTR and an intron simultaneously, can increase the expression level of a gene incorporated into the vector, and thus the present invention is directed to providing a novel antibody expression vector. 
         [0047]    The UTR of the present invention may preferably be the UTR of the cytomegalovirus strain AD169 of SEQ ID NO: 2, although not limited thereto. In an exemplary embodiment of the present invention, an expression vector was constructed using the UTR on the sequence of the cytomegalovirus strain AD169 genome (GenBank: X17403.1) for stronger gene expression, by inserting the UTR between the promoter and the antibody gene for light and heavy chains, respectively. 
         [0048]    As used herein, the term “intron” refers to a characteristic sequence in a DNA region found in eukaryotic cells which does not encode a protein due to lack of genetic information. Intron is transcribed during mRNA synthesis by RNA polymerase in a nucleus and excised from the mRNA sequence via splicing while being transported out of the nucleus. More and more study results have been accumulated to support that a plasmid can have a higher gene expression level when it includes an intron and an untranslated exon. As a result, more improved vectors capable of stable and constitutive gene expression have been developed for use by introducing a heterologous intron into a recombinant expression vector. However, the intron insertion had been applied to monocistronic vectors, and thus only one gene could be expressed by the vector. In order to overcome the limitation, the present inventors have endeavored to insert a foreign intron gene into a bicistronic vector system in a position downstream of a promoter for inducing gene expression with high efficiency. In particular, the intron of the present invention may be an intron derived from CMV. 
         [0049]    The intron of the present invention may preferably be the UTR of cytomegalovirus strain AD169 of SEQ ID NO: 3, although not limited thereto. In an exemplary embodiment of the present invention, an expression vector was constructed using the UTR on the sequence of the cytomegalovirus strain AD169 genome (GenBank: X17403.1) for stronger gene expression, by inserting the UTR between the promoter and the antibody gene for light and heavy chains, respectively. 
         [0050]    The promoter, the UTR, and the intron included in the expression vector of the present invention may have the same or different origin. For example, the promoter may be SV40 early promoter and the UTR and the intron may be derived from SV40; the promoter may be CMV promoter and the UTR and the intron may be derived from CMV; and the promoter may be hEF1-α promoter and the UTR and the intron may be derived from hEF1-α. 
         [0051]    As used herein, the term “amplification gene” refers to a gene that is amplified for inducing the gene to be co-expressed along with a desired antibody gene, which is to be expressed with stability and high efficiency, in the present invention. An amplification gene can be amplified using a chemical based on the principle that cells without the incorporated amplification gene cannot grow in the presence of the chemical, thereby allowing the growth of only those having both the amplification gene and the antibody gene incorporated into their chromosomes. The bicistronic expression vector of the present invention can induce the amplification gene and the antibody gene to be co-expressed as if they were a single gene, thereby allowing high expression of the target antibody gene. 
         [0052]    The amplification gene may preferably be glutamine synthetase (GS) or dihydrofolate reductase (DHFR), but is not limited thereto. In an exemplary embodiment of the present invention, the pCYB204IG expression vector including GS as an amplification gene and the pCYB204IG expression vector including DHFR as an amplification gene, ( FIGS. 5 and 6 ) were constructed, and it was confirmed that the expression vectors pCYBBSS001 ( FIG. 8 ), pCYBBSS002 ( FIG. 9 ), pCYBBSS003 ( FIG. 10 ), pCYBBSS004 ( FIG. 11 ), pCYBBSS005 ( FIG. 12 ), and pCYBBSS006 ( FIG. 13 ) are useful for high-level expression of an antibody gene. 
         [0053]    As used herein, the term “antibody” refers to a material, which is produced by an antigenic stimulus in an immune system and specifically binds to a particular antigen and circulates freely in the bloodstream and the lymph thereby causing antigen-antibody interactions. For the purpose of the present invention, the antibody is to be constitutively expressed at high level. The expression vector of the present invention can induce a strong and stable expression of the antibody gene, and the antibody can be efficiently produced using an animal cell transfected with the expression vector. 
         [0054]    The antibody is a protein consisting of amino acids and a sugar chain, and forms a Y-shaped protein by disulfide bonds between two light chains and two heavy chains. In an exemplary embodiment of the present invention, an expression vector capable of producing an antibody having both light and heavy chains were constructed, by constructing a vector, which includes an antibody light chain-expressing cassette with a UTR and an intron, and an antibody heavy chain-expressing cassette with a UTR and an intron. 
         [0055]    The antibody of the present invention may preferably be any therapeutic antibody conventionally used in the art, although not limited thereto. For example, the antibody may be one selected from the group consisting of bevacizumab, an antibody targeting vascular endothelial Growth Factor-A (VEGF-A); tocilizumab, an antibody targeting IL-6 receptors; denosumab, an antibody targeting receptor activator of NF-kB ligand (RANKL); belimumab, an antibody targeting B lymphocyte stimulator (BLyS); golimumab, an antibody targeting TNFα; ustekinumab, an antibody targeting interleukin-12 (IL-12) and interleukin-23 (IL-23); and ipilimumab, an antibody targeting cytotoxic T lymphocyte Antigen-4. 
         [0056]    Bevacizumab, also called Avastin, is a humanized antibody which is known as a antibody therapeutic for the treatment of colorectal cancer, lung cancer, kidney cancer, and brain cancer, developed by Genentech (USA). In an exemplary embodiment of the present invention, it was confirmed that the introduction of bevacizumab, the representative antibody therapeutic, into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. 
         [0057]    Tocilizumab is a human monoclonal antibody developed by Chugai, which is a Japanese subsidiary of Roche (a Swiss pharmaceutical company), and has been approved as a treatment for rheumatoid arthritis in USA, Europe, and Japan under the product name of Actemra. In an exemplary embodiment of the present invention, it was confirmed that the introduction of tocilizumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, tocilizumab. 
         [0058]    Denosumab is a human monoclonal antibody developed by Amgen (USA), which has been approved as a treatment for osteoporosis in USA, Canada, and Europe, under the product name of Prolia, and has also been approved in Europe as a drug for the prevention of fracture in patients with bone metastasis from solid cancer under the product name of Xgeva. In an exemplary embodiment of the present invention, it was confirmed that the introduction of denosumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, denosumab. 
         [0059]    Belimumab is a human monoclonal antibody developed by for B lymphocyte stimulator (BLyS) developed by GlaxoSmithKline (GSK), a multinational pharmaceutical company, and has been approved in USA, Canada, and Europe as a treatment for lupus (systemic lupus erythematosus, SLE). In an exemplary embodiment of the present invention, it was confirmed that the introduction of belimumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, belimumab. 
         [0060]    Golimumab is a human monoclonal antibody developed by Janssen Biotech, Inc., (formerly Centocor), a subsidiary of Johnson &amp; Johnson, a global pharmaceutical company, and has been approved in USA, Canada, and Korea as a treatment for rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis under the product name of Simponi. In an exemplary embodiment of the present invention, it was confirmed that the introduction of golimumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, golimumab. 
         [0061]    Uustekinumab is a human monoclonal antibody for interleukin-12 (IL-12) and interleukin-23 (IL-23) developed by Janssen Pharmaceuticals, Inc., a multinational pharmaceutical company, and has been approved by the U.S. Food and Drug Administration (FDA) as a treatment for psoriatic arthritis, and the drug is in clinical trials for the treatment of severe psoriasis, moderate-to-severe plaque psoriasis, multiple sclerosis, sarcoidosis, etc. In an exemplary embodiment of the present invention, it was confirmed that the introduction of ustekinumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, ustekinumab. 
         [0062]    Ipilimumab is a human monoclonal antibody for cytotoxic T-lymphocyte antigen (CTLA-4) developed by Bristol-Myers Squibb Co. (BMS), a U.S. pharmaceutical company, and has been approved by the U.S. Food and Drug Administration (FDA) as a treatment for melanoma and skin cancer under the product name of Yervoy, and the drug is in clinical trials for the treatment of non-small cell lung carcinoma (NSCLC), small cell lung cancer (SCLC), bladder cancer, and metastatic hormone-refractory prostate cancer. In particular, Yervoy, approved as a treatment for melanoma by the FDA, is administered in the form of an intravenous injection, and it exhibits pharmaceutical efficacies by assisting the human immune system to attack the melanoma-forming tumor cells by recognizing them as targets. In an exemplary embodiment of the present invention, it was confirmed that the introduction of ipilimumab into the bicistronic expression vector for antibody expression of the present invention effectively produced the antibody. As a result, it was confirmed that the bicistronic expression vector of the present invention is a system capable of high-level expression of the antibody, ipilimumab. 
         [0063]    As used herein, the term “antibody light chain gene” refers to a gene encoding the light chain region in an antibody, which is a Y-shaped protein linked by amino acids and sugar chains between two light chains and two heavy chains. In the present invention, the antibody light chain gene may include without limitation any light chain gene for any antibody, in which the expression level can be increased using the bicistronic vector of the present invention, and for example, the light chain gene may be a nucleotide sequence encoding the light chain region of antibody therapeutics, i.e., bevacizumab, tocilizumab, denosumab, belimumab, golimumab, ustekinumab, or ipilimumab. 
         [0064]    Specifically, the antibody light chain gene may be one consisting of a nucleotide sequence encoding an amino acid selected from the group consisting of SEQ ID NO: 13 for the light chain region of bevacizumab; SEQ ID NO: 17 for the light chain region of tocilizumab; SEQ ID NO: 21 for the light chain region of denosumab; SEQ ID NO: 25 for the light chain region of belimumab; SEQ ID NO: 29 for the light chain region of golimumab; SEQ ID NO: 33 for the light chain region of ustekinumab; and SEQ ID NO: 37 for the light chain region of ipilimumab. More specifically, the antibody light chain gene may be one consisting of a nucleotide sequence selected from the group consisting of SEQ ID NO: 11 encoding the light chain region of bevacizumab; SEQ ID NO: 15 encoding the light chain region of tocilizumab; SEQ ID NO: 19 encoding the light chain region of denosumab; SEQ ID NO: 23 encoding the light chain region of belimumab; SEQ ID NO: 27 encoding the light chain region of golimumab; SEQ ID NO: 31 encoding the light chain region of ustekinumab; and SEQ ID NO: 35 encoding the light chain region of ipilimumab. 
         [0065]    As used herein, the term “antibody heavy chain gene” refers to a gene encoding the heavy chain region in an antibody, which is a Y-shaped protein linked by amino acids and sugar chains between two light chains and two heavy chains. In the present invention, the antibody heavy chain gene may include without limitation any heavy chain gene for any antibody, in which the expression level can be increased using the bicistronic vector of the present invention, and for example, the heavy chain gene may be a nucleotide sequence encoding the heavy chain region of antibody therapeutics, i.e., bevacizumab, tocilizumab, denosumab, belimumab, golimumab, ustekinumab, or ipilimumab. 
         [0066]    Specifically, the antibody light chain gene may be one consisting of a nucleotide sequence encoding an amino acid selected from the group consisting of SEQ ID NO: 14 for the heavy chain region of bevacizumab; SEQ ID NO: 18 for the heavy chain region of tocilizumab; SEQ ID NO: 22 for the heavy chain region of denosumab; SEQ ID NO: 26 for the heavy chain region of belimumab; SEQ ID NO: 30 for the heavy chain region of golimumab; SEQ ID NO: 34 for the heavy chain region of ustekinumab; and SEQ ID NO: 38 for the heavy chain region of ipilimumab. More specifically, the antibody heavy chain gene may be one consisting of a nucleotide sequence selected from the group consisting of SEQ ID NO: 12 encoding the heavy chain region of bevacizumab; SEQ ID NO: 16 encoding the heavy chain region of tocilizumab; SEQ ID NO: 20 encoding the heavy chain region of denosumab; SEQ ID NO: 24 encoding the heavy chain region of belimumab; SEQ ID NO: 28 encoding the heavy chain region of golimumab; SEQ ID NO: 32 encoding the heavy chain region of ustekinumab; and SEQ ID NO: 36 encoding the heavy chain region of ipilimumab. 
         [0067]    As used herein, the term “internal ribosome entry site (IRES), SEQ ID NO: 4)” refers to a particular region present inside of mRNA of a eukaryotic cell, to which ribosome directly binds, thereby capable of synthesizing multiple proteins from a single mRNA. In the present invention, IRES serves to prepare the expression vector of the present invention to be a bicistronic expression vector. 
         [0068]    Translation of mRNA in eukaryotic cells is normally dependent on the cap structure at the 5′ end of mRNA. However, when translation is independent of the cap structure, ribosome may directly bind to a particular region inside of mRNA and start translation therefrom, which is called an internal initiation site. In the internal initiation site, the ribosome-binding site on mRNA is called IRES, which is found in mRNAs of viruses such as poliovirus and encephalomyocarditis (EMC) virus, and also in cellular mRNAs such as binding immunoglobulin protein (BiP) mRNA and  Drosophila antennapedia  homeobox gene (Antp) mRNA. 
         [0069]    As used herein, the term “polyA”, which is also called polyadenylic acid or polyadenylic acid fragment, refers to a continuous sequence of adenylic acids that are normally present at the 3′ end of mRNA in eukaryotic cells. The length thereof is from 10- to 200 nucleotides and may be controlled variously depending on the allowable size of the backbone of the expression vector. PolyA is known to be involved in stabilization, translation, and transport of mRNA from nucleus to cytoplasm. 
         [0070]    The bicistronic expression vector for antibody production of the present invention may preferably be pCYB204IG illustrated in  FIG. 5 , pCYB204ID illustrated in  FIG. 6 , pCYBBSS001 illustrated in  FIG. 8 , pCYBBSS002 illustrated in  FIG. 9 , pCYBBSS003 illustrated in  FIG. 10 , pCYBBSS004 illustrated in  FIG. 11 , pCYBBSS005 illustrated in  FIG. 12 , or pCYBBSS006 illustrated in  FIG. 13 , although not limited thereto. 
         [0071]    The pCYB204IG expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-bevacizumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-bevacizumab heavy chain gene-IRES-GS-polyA’. The pCYB204ID expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-bevacizumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-bevacizumab heavy chain gene-IRES-DHFR-polyA’. The pCYBBSS001 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-tocilizumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-tocilizumab heavy chain gene-IRES-DHFR-polyA’. The pCYBBSS002 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-denosumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-denosumab heavy chain gene-IRES-DHFR-polyA’. The pCYBBSS003 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-belimumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-belimumab heavy chain gene-IRES-DHFR-polyA’. The pCYBBSS004 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-golimumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-golimumab heavy chain gene-IRES-DHFR-polyA’. The pCYBBSS005 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-ustekinumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-ustekinumab heavy chain gene-IRES-DHFR-polyA’. Additionally, the pCYBBSS006 expression vector is an expression vector, which includes a first expression cassette including ‘CMV promoter-UTR-intron-ipilimumab light chain gene-polyA’, and a second expression cassette including ‘CMV promoter-UTR-intron-ipilimumab heavy chain gene-IRES-DHFR-polyA’. 
         [0072]    In an exemplary embodiment of the present invention, the pCYBIG expression vector was constructed using GS as the amplification gene along with a light chain an expression cassette and a heavy chain expression cassette, and the pCYBID expression vector, which includes DHFR instead of GS as the amplification gene, was constructed from the pCYBIG expression vector. 
         [0073]    The bicistronic expression vector of the present invention is designed so that the antibody gene for the heavy chain and the light chain can be expressed along with the amplification gene as if they were a single gene, as described above, and thus the expression vector can be used for expressing the antibody with stability and high efficiency. 
         [0074]    In an exemplary embodiment, the present invention provides an animal cell transfected with the expression vector. 
         [0075]    In the present invention, the expression vector transfected into the animal cell is a bicistronic expression vector for antibody expression, as explained above. 
         [0076]    As used herein, the term “transfection” refers to genetic alteration of a cell by direct insertion of DNA into a cultured animal cell, and generally the target gene is inserted into a carrier such as a plasmid to be introduced into the cell. The transfection may be performed according to a conventional method known in the art. Preferably, examples of the transfection method may include calcium phosphate co-precipitation, DEAE-dextran, electroporation, and redistribution (a method for fusing an artificial membrane called ribosome with a cell for preparing a DNA complex). In an exemplary embodiment of the present invention, animal cells were transfected with a light chain/heavy chain expression vector using lipofectamine. 
         [0077]    The animal cell may be any type of animal cells used in the art without limitation as long as they are capable of producing an antibody, and preferably the animal cell may be a Chinese hamster ovary (CHO) cell. 
         [0078]    In an exemplary embodiment of the present invention, pCYB204IG and pCYB204GS bicistronic vectors for the expression of antibody bevacizumab were constructed by inserting the light and heavy chain genes of bevacizumab into a vector, in which the amplification gene varied to be either GS or DHFR. Upon examining the amount of the expression of antibody bevacizumab in each cell line transfected with the above two vectors, the cell line transfected with the pCYB204ID vector showed at least a 2-fold higher expression of bevacizumab than the cell line transfected with the pCYB204IG vector. 
         [0079]    Additionally, in an exemplary embodiment of the present invention, pCYBBSS001 bicistronic vector for the expression of antibody tocilizumab was constructed by inserting the light and heavy chain genes of tocilizumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody tocilizumab in the cell line transfected with the pCYBBSS001 bicistronic vector, high expression of 50.8 μg/mL and 51.7 μg/mL were confirmed under the gene amplification condition with 800 nM methotrexate (MTX). 
         [0080]    In an exemplary embodiment of the present invention, pCYBBSS002 bicistronic vector for the expression of antibody denosumab was constructed by inserting the light and heavy chain genes of denosumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody denosumab in the cell line transfected with the pCYBBSS002 bicistronic vector, high expression of 81.4 μg/mL was confirmed under the gene amplification condition with 800 nM MTX. 
         [0081]    In an exemplary embodiment of the present invention, pCYBBSS003 bicistronic vector for the expression of antibody belimumab was constructed by inserting the light and heavy chain genes of belimumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody belimumab in the cell line transfected with the pCYBBSS003 bicistronic vector, high expression of 4 μg/mL was confirmed. 
         [0082]    In an exemplary embodiment of the present invention, pCYBBSS004 bicistronic vector for the expression of antibody golimumab was constructed by inserting the light and heavy chain genes of golimumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody golimumab in the cell line transfected with the pCYBBSS004 bicistronic vector, high expression of 120.3 μg/mL was confirmed under the gene amplification condition with 500 nM MTX. 
         [0083]    In an exemplary embodiment of the present invention, pCYBBSS005 bicistronic vector for the expression of antibody ustekinumab was constructed by inserting the light and heavy chain genes of ustekinumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody ustekinumab in the cell line transfected with the pCYBBSS005 bicistronic vector, high expression of 2.5 μg/mL was confirmed. 
         [0084]    Additionally, in an exemplary embodiment of the present invention, pCYBBSS006 bicistronic vector for the expression of antibody ipilimumab was constructed by inserting the light and heavy chain genes of ipilimumab into a vector, which includes DHFR as the amplification gene. Upon examination of the amount of the expression of antibody ipilimumab in the cell line transfected with the pCYBBSS006 bicistronic vector, high expression of 8 μg/mL was confirmed under the gene amplification condition with 500 nM MTX. 
         [0085]    In summary, as explained above, the amount of antibody expression was measured by applying the bicistronic expression vector for antibody expression of the present invention to various antibody therapeutics, and as a result, it was confirmed that the expression vector of the present invention improved the expression capability of various antibodies. 
         [0086]    In another aspect, the present invention provides a method for producing an antibody, including culturing the animal cell. 
         [0087]    The animal cell of the present invention is the one transfected with a bicistronic expression vector including an intron according to the present invention, as described above. 
         [0088]    The method for producing antibody of the present invention can produce an antibody with stability and high efficiency. The method may further include purifying the antibody from the culture product in which the animal cell was cultured. 
         [0089]    The antibodies that can be produced according to the present invention are the same as described above, and they may be bevacizumab, tocilizumab, denosumab, belimumab, golimumab, ustekinumab, or ipilimumab, although not limited thereto. 
       DETAILED DESCRIPTION 
       [0090]    Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, these Examples are for illustrative purposes only, and the invention is not intended to be limited by these Examples. 
       Example 1 
     Construction of Gln-LC, a Gene Set for the Expression of Light Chain 
       [0091]    The DNA sequence of a CMV promoter, which includes the UTR and an intron, was obtained based on the nucleotide sequence of the complete genome (GenBank: X17403.1) of human cytomegalovirus strain AD169. Since a promoter, a cloning site, and a poly A element are required at least for the expression of the target protein, the DNAs for the CMV promoter, the UTR, the intron, the cloning site, and the SV40 poly A were synthesized by requesting to Genotech (Korea). 
         [0092]    Additionally, XbaI and NotI restriction sites were inserted between the intron and the poly A for the cloning of the light chain of the antibody protein, respectively; an AscI restriction site was inserted at the 5′ end of the CMV promoter; and BamHI and XhoI restriction sites were inserted at the 3′ end to be used for the subsequent cloning process. 
         [0093]    Through the process described above, a gene set Gln-LC having the constitution of [AscI]-CMVpromoter-UTR-intron-[XbaI/NotI]-polyA-[BamHI/XhoI] for the expression of the light chain was constructed ( FIG. 1 ). 
       Example 2 
     Construction of Gln-HC, a Gene Set for the Expression of Heavy Chain 
       [0094]    PCR was performed using the Gln-LC gene set constructed in Example 1 as a template along with the BamHI Gln-F primer (SEQ ID NO: 7) and the NheI Gln-R primer (SEQ ID NO: 8) summarized in Table 1 below. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 SEQ 
               
               
                   
                 Primer 
                 Nucleotide Sequence 
                 ID NO 
               
               
                   
               
             
             
               
                   
                 BamHI Gln-F 
                 GGC CGG ATC CGG CGC 
                 7 
               
               
                   
                   
                 GCC TGC AGT GAA T 
                   
               
               
                   
               
               
                   
                 NheI Gln-R 
                 GGC CCT CGA GAA AGA 
                 8 
               
               
                   
                   
                 TCT GGG CTA GCC GTG 
                   
               
               
                   
                   
                 TCA AGG ACG GTG ACT 
                   
               
               
                   
                   
                 GCA G 
               
               
                   
               
             
          
         
       
     
         [0095]    In the gene set Gln-HC for the expression of a heavy chain, a BamHI restriction site was inserted at the 3′ end of the CMV promoter, and NheI and XhoI restriction sites were inserted downstream of the CMV promoter for the cloning of the UTR, the intron, and the heavy chain region of the antibody protein to be used for the subsequent cloning process. 
         [0096]    PCR was performed by denaturation at 94° C. for 5 min; 30 cycles consisting of denaturation at 94° C. for 50 s, annealing at 50° C. for 30 s, and extension at 72° C. for 2 m; and polymerization at 72° C. for 7 m. The PCR reaction solution contained 25 μL of Premix Taq (Ex Taq version) (TAKARA Co., Ltd.), 2 μL each of SEQ ID NOS: 7 and 8 (10 μmole/μL), and added with distilled water to a final volume of 50 μL. 
         [0097]    Through the process described above, a gene set Gln-HC having the constitution of [BamHI]-CMV promoter-UTR-intron-[NheI/XhoI]-[NheI] for the expression of the heavy chain was prepared ( FIG. 1 ). 
         [0098]    The Gln-HC gene amplified by PCR was inserted into the pGEM T-easy vector (Promega Corporation) according to the manufacturer&#39;s manual. 
       Example 3 
     Construction of GS-Gln-LC Plasmid Via GS Vector of a Gene Set for the Expression of a Light Chain 
       [0099]    For the construction of an expression vector containing a glutamine synthetase (GS) as an amplification gene, the IRES-GS vector developed by the company of the present inventors was used. The IRES-GS vector containing the IRES, the GS gene, and poly A was treated with MluI and XhoI at 37° C. for 4 hours, and the DNA fragment containing the IRES-GS gene-fl origin-Kanamycin/neomycin resistant gene resistant gene-Poly A-pUC origin was recovered. 
         [0100]    Meanwhile, the gene set for the expression of a light chain, Gln-LC, constructed in Example 1 was cleaved by digesting with AscI and XhoI. 
         [0101]    The cleaved IRES-GS vector fragment and the Gln-LC gene set fragment were respectively subjected to 1% agarose gel electrophoresis and recovered by gel extraction. The recovered DNA fragments were linked to construct a GS-Gln-LC plasmid ( FIG. 2 ). 
       Example 4 
     Construction of pCYBIG, a Plasmid for the Expression of Light Chain and Heavy Chain 
       [0102]    To obtain the DNA of the Gln-HC, a gene set for the expression of a light chain inserted into the T-easy vector constructed in Example 2, the constructed vector was cleaved by treating with BamHI and XhoI at 37° C. for 4 hours. The treated DNA was subjected to 1% agaroge gel electrophoresis and the DNA fragment corresponding to the size of the Gln-HC was recovered. 
         [0103]    Meanwhile, the GS-Gln-LC plasmid constructed in Example 3 was cleaved by treating with BamHI and XhoI at 37° C. for 4 hours. The DNA treated with the restriction enzymes was subjected to 1% agaroge gel electrophoresis and the DNA fragment corresponding to the size of the GS-Gln-LC plasmid was recovered. 
         [0104]    The Gln-HC gene set fragment and the GS-Gln-LC plasmid fragment recovered above were linked to construct the pCYBIG vector ( FIG. 3 ). 
       Example 5 
     Construction of pCYBID, a Plasmid for the Expression of Light Chain and Heavy Chain 
       [0105]    The construction of pCYBID vector, in which the GS amplification gene in the pCYBIG vector constructed in Example 4 was substituted with the DHFR gene, was attempted. 
         [0106]    Specifically, PCR was performed using the DHFR gene as a template along with the sail DHFR-F primer (SEQ ID NO: 9) and the NheI DHFR-R primer (SEQ ID NO: 10) summarized in Table 2 below. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 SEQ 
               
               
                   
                 Primer 
                 Nucleotide Sequence 
                 ID NO 
               
               
                   
               
             
             
               
                   
                 SalI DHFR-F 
                 GGC CGT CGA CAT GGT 
                  9 
               
               
                   
                   
                 TCG ACC GCT G 
                   
               
               
                   
               
               
                   
                 NheI DHFR-R 
                 GGC CGC TAG CTT AGC 
                 10 
               
               
                   
                   
                 CTT TCT TCT CAT AGA 
                   
               
               
                   
                   
                 C 
               
               
                   
               
             
          
         
       
     
         [0107]    PCR was performed by denaturation at 94° C. for 5 min; 30 cycles consisting of denaturation at 94° C. for 50 s, annealing at 50° C. for 30 s, and extension at 72° C. for 2 m; and polymerization at 72° C. for 7 m. The PCR reaction solution contained 25 μL of Premix Taq (Ex Taq version) (TAKARA Co., Ltd.), 2 μL each of SEQ ID NOS: 9 and 10 (10 pmole/μL), and added with distilled water to a final volume of 50 μL. The DHFR gene amplified by PCR as described above was inserted into the pGEM T-easy vector (Promega Corporation) according to the manufacturer&#39;s manual. 
         [0108]    Meanwhile, the DNA of the pCYBIG vector constructed in Example 4 was cleaved by treating with sail and XbaI and the DNA of the DHFR gene cloned into the T-easy vector was cleaved by treating with sail and NheI. 
         [0109]    Each of the cleaved DNAs was recovered via 1% agarose gel electrophoresis, and the two DNAs were linked to construct pCYBID vector, in which the GS gene was substituted with the DHFR gene ( FIG. 4 ). 
       Example 6 
     Construction of a Plasmid for the Expression of Bevacizumab 
     6-1. Insertion of a Gene for the Light Chain of Bevacizumab 
       [0110]    The pCYBIG vector and the pCYBID vector constructed in Examples 4 and 5, respectively, were inserted with the gene for the bevacizumab light chain to construct plasmids for the expression of the bevacizumab light chain. 
         [0111]    Specifically, the pCYBIG vector and the pCYBID vector were cleaved with XbaI and NotI. 
         [0112]    Regarding the gene for the bevacizumab light chain, the amino acid sequence (SEQ ID NO: 13) of bevacizumab was substituted with a DNA nucleotide sequence (SEQ ID NO: 11). 
         [0113]    The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. 
         [0114]    The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0115]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct the pCYBIG vector and the pCYBID vector respectively inserted with the gene for bevacizumab light chain. 
       6-2. Insertion of a Gene for the Heavy Chain of Bevacizumab 
       [0116]    The pCYBIG-bevacizumab light chain gene vector and the pCYBID-bevacizumab light chain gene vector, the vectors constructed in Example 6-1 for the expression of light chain, were cleaved with NheI and XhoI. The amino acid sequence (SEQ ID NO: 14) of bevacizumab was substituted with a DNA nucleotide sequence (SEQ ID NO: 12). Then, the vectors were designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 6-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct vectors in which the light chain and the heavy chain gene of bevacizumab were inserted, respectively ( FIGS. 5 and 6 ). 
         [0117]      FIGS. 5 and 6  are schematic diagrams illustrating the pCYB204IG vector and the pCYB204ID vector regarding the method of cloning the light chain and the heavy chain of bevacizumab. 
       Example 7 
     Measurement of the Efficiency of Antibody Expression by pCYB204IG Vector 
     7-1. Transfection 
       [0118]    For the development of a cell line capable of stably expressing an antibody protein, first, GS-deficient CHO-K1 cells were aliquoted into 6-well plates at a concentration of 4×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell viability of 98% or higher, the pCYB204IG vector was transfected into cells using lipofectamine (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 20 μg of the expression vector DNA and 10 μL of lipofectamine in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-K1 cells transfected with the pCYB204IG were selected therefrom. 
       7-2. Amplification of Antibody Gene 
       [0119]    The CHO-K1 cell line transfected with the pCYB204IG in Example 7-1 was treated with methionine sulfoximine (MSX) at the initial concentration of 25 μM, and the progress of the growth was observed until the cell growth recovered to normal. After the treatment with 25 μM MSX, the MSX concentration for treatment was increased to 250 μM in the subculture after the day 7. In the same manner, the MSX concentration for treatment was finally increased to 500 μM by increasing the MSX concentration at the time-point of subculturing, in which the growth was recovered by the external pressure due to MSX. The expression level of cell line pools (pool 1 and pool 2) prepared at 500 μM MSX were measured. The measurement of the expression level was confirmed via ELISA using anti-Fc ( FIG. 7A ). 
       Example 8 
     Measurement of the Efficiency of Antibody Expression by pCYB204ID Vector 
     8-1: Transfection 
       [0120]    For the comparison of expression levels of cell lines transfected with the pCYB204ID expression vector containing, as the amplification gene, the DHFR gene instead of the GS gene of the pCUB204IG vector, the CHO-DG44 cells (Gibco, 12609-012) were transfected with the pCYB204ID, and the transfected CHO-DG44 cells were selected. 
       8-2: Amplification of Antibody Gene 
       [0121]    The CHO-DG44 cell line transfected with the pCYB204ID in Example 8-1 was amplified by treating with methotrexate (MTX). In the same manner as in Example 7-2, the expression level was measured by the method of increasing the MTX concentration when the cell growth was recovered to normal. The MTX concentrations for treatment were 50 nM, 200 nM, and 800 nM. The measurement of the expression level was confirmed via ELISA using anti-Fc ( FIG. 7B ). 
         [0122]    Upon comparison of the expression levels of antibody measured per each vector in Examples 7-2 and 8-2, it was confirmed that the cell line transfected with the pCYB204ID vector had at least 2-fold higher expression than the cell line transfected with the pCYB204IG vector. 
       Example 9 
     Construction of a Plasmid for the Expression of Tocilizumab 
     9-1. Insertion of a Gene for the Light Chain of Tocilizumab 
       [0123]    The pCYBID vector constructed in Example 5 was inserted with the gene for the tocilizumab light chain to construct a plasmid for the expression of the tocilizumab light chain. 
         [0124]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0125]    The gene for the tocilizumab light chain was substituted with a DNA nucleotide sequence (SEQ ID NO: 15) which encodes the amino acid sequence (SEQ ID NO: 17) of tocilizumab. The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0126]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector inserted with the gene for tocilizumab light chain. 
       9-2. Insertion of a Gene for the Heavy Chain of Tocilizumab 
       [0127]    The pCYBID-tocilizumab light chain gene vector constructed in Example 9-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence (SEQ ID NO: 18) of tocilizumab was substituted with a DNA nucleotide sequence (SEQ ID NO: 16). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 9-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of tocilizumab ( FIG. 8 ). 
         [0128]      FIG. 8  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS001 of the present invention. 
       Example 10 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS001 Vector 
     10-1. Transfection 
       [0129]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS001 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS001 were selected therefrom. 
       10-2. Amplification of Antibody Gene 
       [0130]    Gene amplification was performed by treating the CHO-DG44 cell line, which was transfected with the pCYBBSS001 in Example 10-1, with methotrexate (MTX). The expression level was measured by the method of increasing the concentration of MTX when the cell growth was recovered to normal. The MTX treatment was at the concentration of 50 nM, 200 nM, and 800 nM. As a result, the cell line transfected with the pCYBBSS001 vector showed the highest expression level when treated with 800 nM MTX. The expression level was measured via Octet titer assay, and Protein A Dip and Read biosensors (ForteBIO, Cat. No. 18-5010, Lot No. 120716) was equilibrated with 1×PBS for at least 10 minutes and reacted with the culture liquid. The regeneration/neutralization of the biosensor was performed for 3 cycles after the analysis of each sample, and the culture liquid was analyzed after diluting with 1×PBS to be analyzed within the standard range. The expression levels at the concentration of 800 nM MTX in the two pools were confirmed to be 50.8 μg/mL and 51.7 μg/mL, and the result indicates that the transfection of the expression vector inserted with an intron of the present invention enables a constitutive and high expression of a gene. 
       Example 11 
     Construction of a Plasmid for the Expression of Denosumab 
     11-1. Insertion of a Gene for the Light Chain of Denosumab 
       [0131]    The pCYBID vector constructed in Example 5 was inserted with the gene for the denosumab light chain to construct a plasmid for the expression of the denosumab light chain. 
         [0132]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0133]    Regarding the gene for the denosumab light chain, the amino acid sequence (SEQ ID NO: 21) of tocilizumab was substituted with a DNA nucleotide sequence (SEQ ID NO: 19). The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0134]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector inserted with the gene for denosumab light chain. 
       11-2. Insertion of a Gene for the Heavy Chain of Denosumab 
       [0135]    The pCYBID-denosumab light chain gene vector constructed in Example 11-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence of denosumab (SEQ ID NO: 22) was substituted with a DNA nucleotide sequence (SEQ ID NO: 20). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 11-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of denosumab ( FIG. 9 ). 
         [0136]      FIG. 9  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS002 of the present invention. 
       Example 12 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS002 Vector 
     12-1. Transfection 
       [0137]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS002 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS002 were selected therefrom. 
       12-2. Amplification of Antibody Gene 
       [0138]    Gene amplification was performed by treating the CHO-DG44 cell line, which was transfected with the pCYBBSS002 in Example 12-1, with methotrexate (MTX). The expression level was measured by the method of increasing the concentration of MTX when the cell growth was recovered to normal. The MTX treatment was at the concentration of 50 nM, 200 nM, and 800 nM. As a result, the cell line transfected with the pCYBBSS002 vector showed the highest expression level when treated with 800 nM MTX. The expression level was measured via Octet titer assay, and Protein A Dip and Read biosensors (ForteBIO, Cat. No. 18-5010, Lot No. 120716) was equilibrated with 1×PBS for at least 10 minutes and reacted with the culture liquid. The regeneration/neutralization of the biosensor was performed for 3 cycles after the analysis of each sample, and the culture liquid was analyzed after diluting with 1×PBS to be analyzed within the standard range. The expression level at the concentration of 800 nM MTX was confirmed to be 81.4 μg/mL, and the result indicates that the transfection of the expression vector inserted with an intron of the present invention enables a constitutive and high expression of a gene. 
       Example 13 
     Construction of a Plasmid for the Expression of Belimumab 
     13-1. Insertion of a Gene for the Light Chain of Belimumab 
       [0139]    The pCYBID vector constructed in Example 5 was inserted with the gene for the belimumab light chain to construct a plasmid for the expression of the belimumab light chain. 
         [0140]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0141]    The gene for the belimumab light chain was substituted with a DNA nucleotide sequence (SEQ ID NO: 23) which encodes the amino acid sequence (SEQ ID NO: 25). The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0142]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector was inserted with the gene for belimumab light chain. 
       13-2. Insertion of a Gene for the Heavy Chain of Belimumab 
       [0143]    The pCYBID-belimumab light chain gene vector constructed in Example 13-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence of belimumab (SEQ ID NO: 26) was substituted with a DNA nucleotide sequence (SEQ ID NO: 24). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 13-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of belimumab, respectively ( FIG. 10 ). 
         [0144]      FIG. 10  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS003 of the present invention. 
       Example 14 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS003 Vector 
     14-1. Transfection 
       [0145]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS003 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS003 were selected therefrom. 
       14-2. Measurement of Expression Level of Antibody Gene 
       [0146]    The expression level of belimumab in the CHO-DG44 cell line, which was transfected with the pCYBBSS003 in Example 14-1, was measured. The expression level was measured via ELISA using anti-Fc, and the expression level/cell was obtained by the calculation of picograms/cell/day (PCD). As a result, the cell line transfected with the pCYBBSS003 vector showed an expression level of 4 μg/mL, and the result indicates that the transfection of the expression vector inserted with an intron of the present invention enables a constitutive and high expression of a gene. 
       Example 15 
     Construction of a Plasmid for the Expression of Golimumab 
     15-1. Insertion of a Gene for the Light Chain of Golimumab 
       [0147]    The pCYBID vector constructed in Example 5 was inserted with the gene for the golimumab light chain to construct a plasmid for the expression of the golimumab light chain. 
         [0148]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0149]    The gene for the golimumab light chain was substituted with a DNA nucleotide sequence (SEQ ID NO: 27) which encodes the amino acid sequence (SEQ ID NO: 29) of golimumab. The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0150]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector inserted with the gene for golimumab light chain. 
       15-2. Insertion of a Gene for the Heavy Chain of Golimumab 
       [0151]    The pCYBID-golimumab light chain gene vector constructed in Example 15-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence of golimumab (SEQ ID NO: 30) was substituted with a DNA nucleotide sequence (SEQ ID NO: 28). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 15-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of golimumab ( FIG. 11 ). 
         [0152]      FIG. 11  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS004 of the present invention. 
       Example 16 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS004 Vector 
     16-1. Transfection 
       [0153]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS004 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS004 were selected therefrom. 
       16-2. Amplification of Antibody Gene 
       [0154]    Gene amplification was performed by treating the CHO-DG44 cell line, which was transfected with the pCYBBSS004 in Example 16-1, with methotrexate (MTX). The expression level was measured by the method of increasing the concentration of MTX when the cell growth was recovered to normal. The MTX treatment was at the concentration of 50 nM, 200 nM, 500 nM, and 800 nM. As a result, the cell line transfected with the pCYBBSS004 vector showed the highest expression level when treated with 800 nM MTX. The expression level was measured via Octet titer assay, and Protein A Dip and Read biosensors (ForteBIO, Cat. No. 18-5010, Lot No. 120716) was equilibrated with 1×PBS for at least 10 minutes and reacted with the culture liquid. The regeneration/neutralization of the biosensor was performed for 3 cycles after the analysis of each sample, and the culture liquid was analyzed after diluting with 1×PBS to be analyzed within the standard range. The expression level at the concentration of 500 nM MTX was confirmed to be 120.3 μg/mL, and the result indicates that the transfection of the golimumab-expressing vector of the present invention enables a constitutive and high expression of a gene. 
       Example 17 
     Construction of a Plasmid for the Expression of Ustekinumab 
     17-1. Insertion of a Gene for the Light Chain of Ustekinumab 
       [0155]    The pCYBID vector constructed in Example 5 was inserted with the gene for the ustekinumab light chain to construct a plasmid for the expression of the ustekinumab light chain. 
         [0156]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0157]    The gene for the ustekinumab light chain was substituted with a DNA nucleotide sequence (SEQ ID NO: 31) which encodes the amino acid sequence (SEQ ID NO: 33) of ustekinumab. The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0158]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector inserted with the gene for ustekinumab light chain. 
       17-2. Insertion of a Gene for the Heavy Chain of Ustekinumab 
       [0159]    The pCYBID-ustekinumab light chain gene vector constructed in Example 17-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence of ustekinumab (SEQ ID NO: 34) was substituted with a DNA nucleotide sequence (SEQ ID NO: 32). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 17-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of ustekinumab ( FIG. 12 ). 
         [0160]      FIG. 12  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS005 of the present invention. 
       Example 18 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS005 Vector 
     18-1. Transfection 
       [0161]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS005 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS005 were selected therefrom. 
       18-2. Measurement of Expression Level of Antibody Gene 
       [0162]    The expression level of ustekinumab in the CHO-DG44 cell line, which was transfected with the pCYBBSS005 in Example 18-1, was measured. The expression level was measured via ELISA using anti-Fc, and the expression level/cell was obtained by the calculation of picograms/cell/day (PCD). As a result, the cell line transfected with the pCYBBSS005 vector showed an expression level of 2.5 μg/mL, and the result indicates that the transfection of the expression vector inserted with an intron of the present invention enables a constitutive and high expression of a gene. 
       Example 19 
     Construction of a Plasmid for the Expression of Ipilimumab 
     19-1. Insertion of a Gene for the Light Chain of Ipilimumab 
       [0163]    The pCYBID vector constructed in Example 5 was inserted with the gene for the ipilimumab light chain to construct a plasmid for the expression of the ipilimumab light chain. 
         [0164]    Specifically, the pCYBID vector was cleaved with XbaI and NotI. 
         [0165]    The gene for the ipilimumab light chain was substituted with a DNA nucleotide sequence (SEQ ID NO: 37) which encodes the amino acid sequence (SEQ ID NO: 35) of ipilimumab. The substitution of the DNA nucleotide sequence was performed using a DNA nucleotide sequence optimized for CHO cells, which is an antibody-expressing cell line, and NheI and NotI restriction sites were inserted at both 5′- and 3′ ends. The Kozak sequence (GCCACC) was inserted upstream of the start codon, ATG, for inducing the increase of expression level, and ‘MGWSCIILFLVATATGVHS’ was inserted as a signal sequence for gene synthesis. The thus-synthesized gene was cleaved by treating with NheI and NotI. 
         [0166]    Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYBID vector inserted with the gene for ipilimumab light chain. 
       19-2. Insertion of a Gene for the Heavy Chain of Ipilimumab 
       [0167]    The pCYBID-ipilimumab light chain gene vector constructed in Example 19-1 for the expression of light chain was cleaved with NheI and XhoI. The amino acid sequence of ipilimumab (SEQ ID NO: 38) was substituted with a DNA nucleotide sequence (SEQ ID NO: 36). Then, the vector was designed by inserting the Kozak sequence (GCCACC) upstream of the start codon, ATG, as in Example 19-1, and a gene was synthesized by inserting NheI and XhoI restriction sites at both ends, and cleaved by treating with NheI and XhoI. Each of the cleaved DNAs was recovered by subjecting to 1% agarose gel electrophoresis, and the two DNAs were linked to construct a vector, which is the pCYB vector inserted with the light chain and the heavy chain gene of ustekinumab ( FIG. 13 ). 
         [0168]      FIG. 13  is a schematic diagram illustrating the restriction map of the expression vector pCYBBSS006 of the present invention. 
       Example 20 
     Measurement of the Efficiency of Antibody Expression by pCYBBSS006 Vector 
     20-1. Transfection 
       [0169]    For the development of a cell line capable of stably expressing an antibody protein, first, DHFR-deficient CHO-DG44 cells (Dr. Chasin, Univ. Columbia. USA) were aliquoted into 6-well plates at a concentration of 8×10 5  cells the day before the transfection and cultured in a CO 2  incubator at 37° C. Upon confirmation of the cell growth to 70% to 80% confluency in the plates, the light chain/heavy chain expression vector pCYBBSS005 vector was transfected into the cells using lipofectamine LTX and PLUS reagent (Invitrogen Corporation). In particular, the transfection was performed using a medium, which contains 2.5 μg of the expression vector DNA and 10 μL of lipofectamine LTX in the Opti-MEM-1 (Invitrogen Corporation), and the CHO-DG44 cells transfected with the light chain/heavy chain expression vector pCYBBSS006 were selected therefrom. 
       20-2. Amplification of Antibody Gene 
       [0170]    Gene amplification was performed by treating the CHO-DG44 cell line, which was transfected with the pCYBBSS006 in Example 20-1, with methotrexate (MTX). The expression level was measured by the method of increasing the concentration of MTX when the cell growth was recovered to normal. The MTX treatment was at the concentration of 50 nM, 200 nM, 500 nM, and 800 nM. As a result, the cell line transfected with the pCYBBSS006 vector showed the highest expression level when treated with 500 nM MTX. The expression level was measured via Octet titer assay, and Protein A Dip and Read biosensors (ForteBIO, Cat. No. 18-5010, Lot No. 120716) was equilibrated with 1×PBS for at least 10 minutes and reacted with the culture liquid. The regeneration/neutralization of the biosensor was performed for 3 cycles after the analysis of each sample, and the culture liquid was analyzed after diluting with 1×PBS to be analyzed within the standard range. The expression level at the concentration of 500 nM MTX was confirmed to be 8 μg/mL, and the result indicates that the transfection of the expression vector inserted with an intron of the present invention enables a constitutive and high expression of a gene. 
         [0171]    Those of ordinary skill in the art will recognize that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within the scope of the present invention.