Abstract:
A humanized antibody of the present invention shows similar antigen-binding affinity to a mouse monoclonal antibody and significantly low immunogenecity. Therefore, the humanized antibody of the present invention can be effectively used for treating chronic hepatitis B and preventing HBV infection of a patient received liver transplantation and vertical transmission from a mother infected with HBV to a fetus.

Description:
This is a Non-provisional application which claims priority under 35 U.S.C. § U.S.C. § 119 from Korean Patent Application No. 10-2004-0025573 filed Apr. 14, 2004. 
     FIELD OF THE INVENTION 
     The present invention relates to a humanized antibody against S-surface antigen of hepatitis B virus (hereinafter, referred to as “HBV”), a method for the preparation thereof, and a pharmaceutical composition for treating HBV-relating diseases comprising the humanized antibody. 
     BACKGROUND OF THE INVENTION 
     HBV well-known as a Dane particle is a spherical particle having a diameter of about 42 nm and composed of an outer envelope and a nucleocapsid. The outer envelope surrounding the nucleocapsid contains a large quantity of hepatitis B surface antigens, and the nucleocapsid comprising about 180 subunits of hepatitis B core protein includes several kinds of genes encoding HBV structural proteins, polymerase and so on (Summers et al.,  Proc. Nat. Acad. Sci.  72: 4579, 1975; Pierre Tiollais et al.,  Science  213: 406-411, 1981). 
     The gene coding region of HBV surface antigens contains three in-frame initiation sites, and all these sites share a termination codon of S-domain terminal. Therefore, the HBV surface antigens can be divided into three groups: (i) a small hepatitis B virus surface antigen (hereinafter, referred to as “S-surface antigen”) containing only the S-domain; (ii) a middle hepatitis B virus surface antigen (hereinafter, referred to as “M-surface antigen”) containing the S-domain and Pre-S2 consisting of 55 amino acids; and (iii) a large hepatitis B virus surface antigen (hereinafter, referred to as “L-surface antigen”) containing the S-domain, Pre-S2 and Pre-S1. The S-surface antigen accounts for about 80% or more of the total expressed surface antigen. 
     Interferon α and Lamivudin have been widely used for treating chronic hepatitis (C. L. Lai and P. C. Wu,  H.K.M.J.  3: 289-296, 1997). However, interferon α shows high toxicity in spite of its immune response against in vivo virus. On the other hand, Lamivudin acting as a nucleic acid derivative shows anti-viral activity by way of inhibiting DNA polymerase. A lamivudin formulation for oral administration exhibits high therapeutic effect, but when it is taken for a long time, there is a high risk of inducing a mutant resistant to Lamivudin (Daryl T. Y. Lau et al,  Hepatology  32: 828-834, 2000). Further, an anti-HBV polyclonal antibody isolated from human serum has been used for preventing HBV infection from liver transplantation and vertical transmission. However, this antibody also has problems in that it shows low antigen specificity and must be isolated from human blood. 
     A method employing a mouse monoclonal antibody against HBV surface antigen has been recently developed so as to solve the problems mentioned above, but a human antibody is formed against the mouse monoclonal antibody when used for a long time (Dimaggio J. J., et al.,  Cancer Chemother. Biol. Response Modif  11: 177-203, 1990). 
     To overcome the undesirable properties of mouse monoclonal antibodies, a humanized antibody has been developed by replacing the framework regions except for the antigen-binding site with regions of a human antibody. A method currently used for preparing such a humanized antibody comprises the steps of selecting a gene encoding the human antibody showing the closest sequence similarity to the mouse antibody and replacing only the complementarity determining region (CDR) of the mouse antibody with that of the human antibody by way of a CDR grafting method. The humanized antibody has the advantage of reducing the in vivo immune response (Riechmann et al.,  Nature  332: 323, 1988; Nakatani et al.,  Protein Engineering  7: 435, 1994). However, when only the CDR is grafted on the human antibody, its selectivity and reactivity are often compromised (Carter P., et al.,  Proc. Natl. Acad. Sci. USA  89: 4285-4289, 1992). 
     The present inventors have endeavored to overcome such problems of the conventional humanized antibody, and developed a novel humanized antibody against S-surface antigen of HBV which maintains antibody specificity of a mouse monoclonal antibody against HBV S-surface antigen while minimizing the immune response to the mouse monoclonal antibody. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a humanized antibody against S-surface antigen of HBV and a method for the preparation thereof. 
     It is another object of the present invention to provide a pharmaceutical composition for treating diseases relating to HBV comprising the humanized antibody as an effective ingredient. 
     In accordance with one aspect of the present invention, there is provided a humanized antibody against S-surface antigen of HBV which comprises 
     a) a heavy chain variable region having the amino acid sequences of SEQ ID NOs: 38 to 40 at a complementarity determining region (CDR); 
     b) a light chain variable region having the amino acid sequences of SEQ ID NOs: 41 to 43 at the CDR; 
     c) a heavy chain constant region identical to that of a human antibody; and 
     d) a light chain constant region identical to that of a human antibody. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, which respectively show: 
         FIG. 1 : the heavy chain amino acid sequences of the mouse monoclonal antibody A9-11-5 against HBV S-surface antigen, humanized antibody HFW141 and human antibody subgroup 2 (Hh2); 
         FIG. 2 : the light chain amino acid sequences of the mouse monoclonal antibody A9-11-5 against HBV S-surface antigen, humanized antibodies LFW22-31 and LFW22-312 and human antibody subgroup 7 (hV7); 
         FIG. 3 : the procedure for constructing humanized antibody heavy chain expression vector pHAB-HFW141 HF; 
         FIG. 4 : the procedure for constructing humanized antibody light chain expression vectors pHAB-LFW22-31 LF and pHAB-LFW22-312 LF; 
         FIG. 5 : the expression patterns of humanized antibodies YH1110-13 and YHB-1110-15 determined by SDS-PAGE analysis; and
         Lane 1: mouse antibody, Lane 2: YHB-1110-13   Lane 3: YHB-1110-15       
         FIG. 6 : antigen-binding affinities of humanized antibodies YH1110-13 and YHB1110-15 against HBV S-surface antigen. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses a humanized antibody whose antigen-binding site, a complementarity determining region (CDR) in the heavy chain variable region or the light chain variable region is derived from a mouse monoclonal antibody, and the framework regions of the antibody molecule are derived from a human antibody. Preferably, the humanized antibody exhibits an antigen-binding affinity (Ka) ranging from 7×10 7  M −1  to 1×10 8  M −1 . 
     The humanized antibody of the present invention can be prepared from the mouse monoclonal antibody A9-11-5 (Accession NOs: KCTC 18020P and KCTC 18021P) according to a CDR grafting method, wherein the heavy chain variable region of the mouse monoclonal antibody A9-11-5 comprises three CDR regions of SEQ ID NOs: 38 to 40, and the light chain variable region, three CDR regions of SEQ ID NOs: 41 to 43. 
     First, the amino acid sequences of the light chain and heavy chain variable regions of mouse monoclonal antibody A9-11-5 are compared with human sequences in the GenBank database, and selected are the human heavy chain variable region subgroup 2 (Hh2) as defined by Kabat having the greatest sequence similarity to the mouse antibody A9-11-5 heavy chain and the human light chain variable region subgroup 7 (hV7) or V3 of human Ig lambda germline V genes of GenBank Ig blast that has the most similarity to the mouse antibody A9-11-5 light chain (Kawasaki K., et al.,  Genome Res.,  7: 250-261, 1997). 
     The genes encoding the humanized antibody heavy chain and light chain can be amplified by using the so-selected human genes as templates. In this procedure, each of the nucleotide sequences encoding the humanized antibody heavy chain and light chain may be modified based on the information of well-known genetic studies and antibody structural analyses. Further, if certain nucleotide sequences of the mouse monoclonal antibody encode amino acid residues affect the antigen-binding affinity or are important for the antibody structure, they are preserved without replacing with sequences (Kabat E. A., et al.,  D.H.H.S.  91: 3242, 1991; Chothia C., et al.,  Nature  342: 877-883, 1989; Gary M., et al.,  Protein Engineering  7: 805-814, 1994; Linda Harris and Bajorath, J.,  Protein Science  4: 306-310, 1995). 
     A gene encoding the heavy chain variable region of the humanized antibody may be prepared by replacing the framework regions except for the antigen-binding site in the heavy chain variable region of the mouse monoclonal antibody A9-11-5 specifically recognizing HBV S-surface antigen with the heavy chain subgroup 2 (Hh2) of a human antibody. Such a gene encoding the heavy chain variable region of the humanized antibody can be prepared by the steps of: designing primers for humanizing the mouse monoclonal antibody using the gene encoding the mouse monoclonal antibody A9-11-5 heavy chain as a template; performing PCR (polymerase chain reaction) using the corresponding primers; and ligating the so-amplified PCR products to each other using restriction enzymes and DNA ligase. The gene encoding the heavy chain variable region of the humanized antibody thus prepared has been designated HFW141 (SEQ ID NO: 32) which encodes the polypeptide having the amino acid sequence of SEQ ID NO: 35 (see  FIG. 1 ). 
     In order to prepare a gene encoding the full-length heavy chain of the humanized antibody including the gene encoding the humanized heavy chain variable region, gene HFW141 is inserted into a PCR vector to prepare expression vector pCR-HFW141. At this time, it is preferred to insert the Kozak sequence (Kozak, M.  Nuc. Acids Res.  15: 8125-8148, 1987) in front of the heavy chain leader sequence of the humanized antibody, and replace some codons of the heavy chain leader sequence by other codons showing high frequency of use in animal cells, which results in increasing the expression efficiency of the heavy chain variable region of the humanized antibody (SEQ ID NO: 1). The gene fragment encoding the heavy chain variable region of the humanized antibody is isolated from expression vector pCR-HFW141, and inserted into expression vector pHAB-HC (Accession NO: KCTC 10229BP; Korean Patent Laid-Open NO: 2004-12266) containing the gene encoding the heavy chain constant region of the human antibody, to obtain expression vector of the humanized antibody heavy chain. Expression vector thus prepared has been designated pHAB-HFW141 HF (Accession NO: KCTC 10533BP). The gene encoding the full-length heavy chain of the humanized antibody can be isolated from the heavy chain expression vector pHAB-HFW141 HF and has been designated HFW141 HF. 
     The  E. coli  TOP10F′ transformant transformed with humanized heavy chain expression vector pHAB-HFW141 HF was deposited on Oct. 29, 2003 with the Korean Collection for Type Cultures (KCTC)(Address: Korea Research Institute of Bioscience and Biotechnology (KRIBB), #52, Oun-dong, Yusong-ku, Taejon, 305-333, Republic of Korea) under the accession number KCTC 10533BP, in accordance with the terms of Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure. 
     A gene encoding the light chain variable region of the humanized antibody may be prepared by replacing the framework regions except for the antigen-binding site in the light chain variable region of mouse monoclonal antibody A9-11-5 specifically recognizing HBV S-surface antigen with the light chain subgroup 7 (hV7) or the light chain lambda germline V3 of a human antibody. Such a gene encoding the light chain variable region of the humanized antibody can be prepared by the steps of: designing primers for humanizing the mouse monoclonal antibody using the gene encoding the mouse monoclonal antibody A9-11-5 light chain as a template; performing PCR using the corresponding primers; and ligating the so-amplified PCR products to each other using restriction enzymes and DNA ligase. Each of the genes encoding the light chain variable region of the humanized antibody thus prepared has been designated LFW22-31 (SEQ ID NO: 33) and LFW22-312 (SEQ ID NO: 34) that encode the polypeptides having the nucleotide sequences of SEQ ID NOs: 36 and 37, respectively (see  FIG. 2 ). 
     In order to prepare a gene encoding the full-length light chain of the humanized antibody including the gene encoding the humanized light chain variable region, gene LFW22-31 or LFW22-312 is inserted into a PCR vector to prepare expression vectors pCR-LFW22-31 or pCR-LFW22-312. At this time, it is preferred to insert the Kozak sequence (Kozak, M.  Nuc. Acids Res.  15: 8125-8148, 1987) in front of the light chain leader sequence of the humanized antibody, and replace some codons of the light chain leader sequence by other codons showing high frequency of use in animal cells, which results in increasing the expression efficiency of the light chain variable region of the humanized antibody (SEQ ID NO: 13). The gene fragment encoding the light chain variable region of the humanized antibody is isolated from expression vector pCR-LFW22-31 or pCR-LFW22-312, and inserted into expression vector pHAB-LC (Accession NO: KCTC 10231BP; Korean Patent Laid-Open NO: 2004-12267) containing the gene encoding the light chain constant region of the human antibody, to obtain an expression vector of the humanized antibody light chain. Each of the so-constructed expression vectors has been designated pHAB-LFW22-31 LF (Accession NO: KCTC 10532BP) and pHAB-LFW22-312 LF (Accession NO: KCTC 10553BP). The genes encoding the full-length humanized light chain can be isolated from the light chain expression vectors pHAB-LFW22-31 LF and pHAB-LFW22-312 LF, and have been designated LFW22-31 LF and LFW22-312 LF, respectively. 
       E. coli  TOP10F′ transformants transformed with each of the humanized light chain expression vectors pHAB LFW22-31 LF and pHAB LFW22-312 LF were deposited on Oct. 29, 2003 and Nov. 25, 2003 with the Korean Collection for Type Cultures (KCTC)(Address: Korea Research Institute of Bioscience and Biotechnology (KRIBB), #52, Oun-dong, Yusong-ku, Taejon, 305-333, Republic of Korea) under the accession numbers KCTC 10532BP and 10553BP, respectively, in accordance with the terms of Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure. 
     CHO cell lines may be transformed with humanized heavy chain expression vector pHAB-HFW141 HF and humanized light chain expression vector pHAB-LFW22-31 LF by using an appropriate transformation solution such as GenePORTER, to obtain a trasnformant producing the humanized antibody specifically recognizing HBV S-surface antigen, and the transformant has been designated CHO-YHB1110-13. Further, another transformant may be prepared by using humanized heavy chain expression vector pHAB-HFW141 HF and humanized light chain expression vector pHAB-LFW22-312 LF according to the same method as described above, and has been designated CHO-YHB1110-15. 
     To purify the humanized antibody of the present invention from the transformant cell lines, the transformant CHO-YHB1110-13 or CHO-YHB 1110-15 may be cultured in an appropriate culture medium, and the culture supernatant may be subjected to column chromatography using Protein-A (Amersham Bioscience, Sweden) or goat anti-human immunoglobulin G (Zymed Laboratories Inc., USA). The humanized antibodies thus purified have been designated YHB1110-13 and YHB1110-15, respectively. 
     Humanized antibodies YHB1110-13 and YHB1110-15 specifically recognizing HBV S-surface antigen show antigen-binding affinities ranging from 6×10 7  to 5×10 8  M −1 , which demonstrates that the humanized antibodies of the present invention maintain an antigen-binding activity similar to the previous reported mouse monoclonal antibody, but show significantly decreased immunogenecity, and therefore, can be effectively used for treating HBV-relating diseases without encountering adverse side-effects. 
     For this purpose, the humanized antibody of the present invention can be used as an effective ingredient in a pharmaceutical composition to treat HBV-relating diseases. The pharmaceutical composition can be formulated as an oral or non-oral dosage form, for immediate or extended release. The composition can comprise inactive ingredients ordinarily used in pharmaceutical preparation such as diluents, fillers, disintegrants, sweeteners, lubricants and flavors. The pharmaceutical composition is preferably formulated for intravenous administration, either by bolus injection or sustained drip, or for release from an implanted capsule. A typical formulation for intravenous administration utilizes physiological saline as a diluent. 
     Formulation of antibodies for therapeutic administration is considered known in the art. 
     The dose for a patient population depends upon the specific antibody used, body weight, age, gender, state of health, diet, administration time and formulation of the composition, route of administration, and the disease to be treated. A typical dose is from 0.01 mg/kg/day to 1,000 mg/kg/day. More typically the dose is from 0.1 mg/kg/day to 10 mg/kg/day. 
     The composition of the present invention can also include printed matter that describes clinical indications for which the antibodies can be administered as a therapeutic agent, dosage amounts and schedules, and/or contraindications for administration of the antibodies of the invention to a patient. 
     The following Examples are intended to further illustrate the present invention without limiting its scope. 
     EXAMPLE 1 
     Construction of a Gene Encoding a Heavy Chain Variable Region of a Humanized Antibody 
     PCR was conducted using a gene encoding the heavy chain variable region of the mouse monoclonal antibody A9-11-5 (Accession NOs: KCTC 18020P and KCTC 18021P) against HBV S-surface antigen as a template and a primer pair of SEQ ID NOs: 1 and 12, to amplify gene A encoding the heavy chain variable region of the humanized antibody carrying a leader sequence. The amplified PCR product was electrophoresed on an agarose gel and recovered from the gel using a QIAgel extraction kit (Qiagen, USA). 
     Gene A thus purified was subjected to PCR with a primer pair of SEQ ID NOs: 1 and 3 or SEQ ID NOs: 2 and 12. Each of the amplified PCR products was digested with StuI (BioLabs Inc., USA) at 37° C. for 2 hrs, and then, treated with T4 DNA ligase (BioLabs Inc, USA) at room temperature for 1 hr, to prepare gene B encoding the heavy chain variable region. 
     PCR was conducted using gene B as a template and a primer pair of SEQ ID NOs: 4 and 12 or SEQ ID NOs: 1 and 5. Each of the amplified PCR products was digested with PstI (BioLabs Inc., USA) at 37° C. for 2 hrs, and then, treated with T4 DNA ligase (BioLabs Inc., USA) at room temperature for 1 hr, to prepare gene C encoding the heavy chain variable region. 
     In the same manner as described above, gene C was subjected to PCR with a primer pair of SEQ ID NOs: 6 and 12 or SEQ ID NOs: 1 and 7, and the PCR products thus amplified were treated with SalI (BioLabs Inc., USA), to obtain gene D encoding the heavy chain variable region. Gene D was subjected to PCR with a primer pair of SEQ ID NOs: 8 and 12 or SEQ ID NOs: 1 and 9, and the PCR products thus amplified were treated with DraI (BioLabs Inc., USA), to obtain Gene E encoding the heavy chain variable region. PCR was conducted using Gene E as a template and a primer pair of SEQ ID NOs: 10 and 12 or SEQ ID NOs: 1 and 11. Each of the PCR products was digested with XbaI (BioLabs Inc., USA) at 37° C. for 2 hrs, and then, treated with T4 DNA ligase (BioLabs Inc., USA) at room temperature for 1 hr, to obtain gene A9V7FW42HV encoding the heavy chain variable region. 
     PCR was conducted using gene A9V7FW42HV as a template and a primer pair of SEQ ID NOs: 23 and 25 or SEQ ID NO: 1 and 24 according to the condition described in Table 1. Two PCR products were mixed at an equal molar ratio, and the mixture was subjected to overlapping PCR with a primer pair of SEQ ID NOs: 1 and 25. The PCR thermal cycle was repeated 30 times, each cycle being composed of: 95° C. for 2 min, 58° C. for 2 min and 72° C. for 2 min. The final gene encoding the heavy chain variable region of the humanized antibody thus amplified has been designated HFW141. 
     The nucleotide sequences of the primers and reaction conditions employed in each PCR reaction are shown in Table 1. 
     Each PCR reaction was conducted under the following conditions of 30 cycles as shown in Table 1 after initial denaturation of 5 min at 95° C., and final extension of 10 min at 72° C. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 PCR condition 
               
             
          
           
               
                 Primer pair 
                 Gene 
                 Denature 
                 Annealing 
                 Extension 
               
               
                   
               
               
                 SEQ ID NOs: 1 
                 A 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 12 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 1 
                 B 
                 94° C., 1.5 min 
                 50° C., 
                 72° C., 
               
               
                 and 3 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 2 
                   
                 94° C., 1.5 min 
                 50° C., 
                 72° C., 
               
               
                 and 12 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 4 
                 C 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 12 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 1 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 5 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 6 
                 D 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 12 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 1 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 7 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 8 
                 E 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 12 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 1 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 9 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 
                 A9V7FW42HV 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 10 and 12 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs: 1 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 11 
                   
                   
                   2 min 
                 2.5 min 
               
               
                 SEQ ID NOs:  
                 HFW141 
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 23 and 25 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 1 
                   
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 24 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 2 
     Construction of a Full-Length Heavy Chain Gene of a Humanized Antibody and an Expression Vector Thereof 
     In order to improve the expression efficiency of the gene encoding the heavy chain variable region of the humanized antibody, primers were so designed as to insert the Kozak sequence (Kozak, M.  Nuc. Acids Res.  15: 8125-8148, 1987) in front of the heavy chain leader sequence of the humanized antibody and replace the codon TTA encoding the 4 th  amino acid, leucine, of the heavy chain leader sequence with CTG preferable used in animal cells. The modified heavy chain leader sequence of the humanized antibody is shown in Table 2. 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Primer 
                 Sequence 
               
               
                   
               
             
             
               
                 Humanized heavy 
                 C ACC  ATG GCT GTC CTG TTC CTG CTC CTC TGC CTG 
               
               
                 chain leader 
               
               
                 sequence 
               
               
                 (SEQ ID NO:1) 
               
               
                   
               
             
          
         
       
     
     Gene HFW141 encoding the heavy chain variable region of the humanized antibody prepared in Example 1 was cloned into a PCR vector, to obtain expression vector pCR-HFW141. 
     Further, in order to construct the gene encoding the humanized full-length heavy chain, expression vector pHAB-HC (KCTC 10229BP, Korean Patent Laid-Open NO: 2004-12266) containing the gene encoding the heavy chain constant region of the human antibody was employed. First, in order to insert gene HFW141 encoding the heavy chain variable region of the humanized antibody into expression vector pHAB-HC, expression vector pCR-HFW141 was treated with HindIII/ApaI (BioLabs, Inc., USA) at 37° C. for 2 hrs, electrophoresed on a 1.5% agarose gel and stained with etidium bromide (EtBr), to obtain an about 450 bp fragment of the gene. 
     In the same manner as described above, expression vector pHAB-HC was treated with HindIII/ApaI, to obtain an about 6.5 kb fragment of the vector. After then, each of the gene fragments was recovered from the gels using a QIAgel extraction kit (Qiagen, USA), treated with T4 DNA ligase (BioLabs, Inc., USA) at 16° C. overnight, and transformed into  E. coli  TOP10F′, to obtain a transformant. The transformant was cultured in an LB medium supplemented with 100 μg/ml of ampicillin overnight, and plasmids were isolated from the culture medium. The isolated plasmids were treated with HindIII/ApaI and subjected to agarose gel electrophoresis, to obtain an about 1.4 kb full-length heavy chain of the humanized antibody. 
     The full-length heavy chain of the humanized antibody thus prepared was designated HFW141 HF. Further, the heavy chain expression vector of the humanized antibody inserted with the full-length heavy chain HFW141 HF of the humanized antibody was designated pHAB-HFW141 HF ( FIG. 3 ), and transformed into  E. coli  TOP10F′, to obtain a transformant, which was deposited on Oct. 29, 2003 with the Korean Collection for Type Cultures (KCTC)(Address: Korea Research Institute of Bioscience and Biotechnology (KRIBB), #52, Oun-dong, Yusong-ku, Taejon, 305-333, Republic of Korea) under the accession number KCTC 10533BP. 
     EXAMPLE 3 
     Construction of a Gene Encoding a Light Chain Variable Region of a Humanized Antibody 
     PCR was conducted using the gene encoding the light chain variable region of mouse monoclonal antibody A9-11-5 specifically recognizing HBV S-surface antigen as a template and a primer pair of SEQ ID NOs: 13 and 22, to amplify gene A′ encoding the light chain variable region containing a leader sequence. Gene A′ was subjected to agarose gel electrophoresis and EtBr staining, and then, recovered from the gel using a QIAgel extraction kit. 
     Purified gene A′ was subjected to PCR with a primer pair of SEQ ID NOs: 14 and 22 or a primer pair of SEQ ID NOs: 13 and 15. The amplified PCR product was digested with KpnI (BioLabs, Inc., USA) at 37° C. for 2 hrs, and treated with T4 DNA ligase (BioLabs, Inc., USA) at room temperature for 1 hr, to obtain gene B′ encoding the light chain variable region. 
     PCR was carried out using gene B′ as a template and a primer pair of SEQ ID NOs: 16 and 22 or a primer pair of SEQ ID NOs: 13 and 17. The amplified PCR product was digested with MscI (BioLabs, Inc., USA) at 37° C. for 2 hrs, and treated with T4 DNA ligase (BioLabs, Inc., USA) at room temperature for 1 hr, to obtain gene C′ encoding the light chain variable region. 
     In the same manner as described above, gene C′ was subjected to PCR with a primer pair of SEQ ID NOs: 18 and 22 or a primer pair of SEQ ID NOs: 13 and 19, and PCR products thus amplified were digested with ApaLI (BioLabs, Inc., USA), to obtain gene D′ encoding the light chain variable region. 
     Further, after PCR was conducted using gene D′ as a template and a primer pair of SEQ ID NOs: 20 and 22 or a primer pair of SEQ ID NOs: 13 and 21, the PCR products thus amplified were digested with SmaI (BioLabs, Inc., USA) and treated with T4 DNA ligase (BioLabs, Inc., USA) at room temperature for 1 hr, to obtain gene A9V7LV encoding the light chain variable region. 
     PCR was conducted using gene A9V7LV as a template and a primer pair of SEQ ID NOs: 26 and 22 or SEQ ID NO: 13 and 27 according to the condition described in Table 3. Two PCR products were mixed at an equal molar ratio, and the mixture was subjected to overlapping PCR with a primer pair of SEQ ID NOs: 13 and 22. The PCR thermal cycle was repeated 30 times, each cycle being composed of: 95° C. for 2 min, 58° C. for 2 min and 72° C. for 2 min. The gene encoding the light chain variable region of the humanized antibody thus amplified has been designated LFW22. 
     In the same manner as described above, PCR was conducted using gene LFW22 as a template and a primer pair of SEQ ID NOs: 28 and 22 or SEQ ID NO: 13 and 29 according to the condition described in Table 3. Two PCR products were mixed at an equal molar ratio, and the mixture was subjected to overlapping PCR with a primer pair of SEQ ID NOs: 13 and 22. The PCR thermal cycle was repeated 30 times, each cycle being composed of: 95° C. for 2 min, 58° C. for 2 min and 72° C. for 2 min. The final gene encoding the light chain variable region of the humanized antibody thus amplified has been designated LFW22-31. 
     In the same manner as described above, PCR was conducted using gene LFW22-31 as a template and a primer pair of SEQ ID NOs: 30 and 22 or SEQ ID NO: 13 and 31 according to the condition described in Table 3. Two PCR products were mixed at an equal molar ratio, and the mixture was subjected to overlapping PCR with a primer pair of SEQ ID NOs: 13 and 22. The PCR thermal cycle was repeated 30 times, each cycle being composed of: 95° C. for 2 min, 58° C. for 2 min and 72° C. for 2 min. The final gene encoding the light chain variable region of the humanized antibody thus amplified has been designated LFW22-312. 
     The nucleotide sequences of the primers and PCR conditions employed in the above PCR reactions are described in the following Table 3. 
     Each of the PCR reactions was conducted under the conditions of 30 cycles as shown in Table 3 after initial denaturation of 5 min at 95° C., and final extension of 10 minutes at 72° C. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 PCR conditions 
               
             
          
           
               
                 Primer pair 
                 Gene 
                 Denature 
                 Annealing 
                 Extension 
               
               
                   
               
               
                 SEQ ID NOs: 13 
                 A′ 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 14 
                 B′ 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 13 
                   
                 94° C., 1.5 min 
                 55° C,, 
                 72° C., 
               
               
                 and 15 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 16 
                 C′ 
                 94° C., 1.5 min 
                 49° C,, 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 13 
                   
                 94° C., 1.5 min 
                 50° C., 
                 72° C., 
               
               
                 and 17 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 18 
                 D′ 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 13 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 19 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 20 
                 A9V7LV 
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 13 
                   
                 94° C., 1.5 min 
                 55° C., 
                 72° C., 
               
               
                 and 21 
                   
                   
                   2 min 
                   3 min 
               
               
                 SEQ ID NOs: 26 
                 LFW22 
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                   2 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 13 
                   
                 95° C.,   1 min 
                 50° C., 
                 72° C., 
               
               
                 and 27 
                   
                   
                   2 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 28 
                 LFW22-31 
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 13 
                   
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 29 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 30 
                 LFW22-312 
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 22 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                 SEQ ID NOs: 13 
                   
                 95° C.,   1 min 
                 55° C., 
                 72° C., 
               
               
                 and 31 
                   
                   
                 1.5 min 
                 1.5 min 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 4 
     Construction of a Full-Length Light Chain Gene of a Humanized Antibody and an Expression Vector Thereof 
     In order to enhance the expression of the gene encoding the light chain variable region of the humanized antibody, primers were so designed as to insert the Kozak sequence in front of the light chain leader sequence of the humanized antibody (Kozak, M.  Nuc. Acids Res.,  15: 8125-8148, 1987), and replace the 8 th  amino acid, phenylalanine, in the nucleotide sequence of the gene encoding the light chain leader sequence was replaced with leucine preferable used in animal cells. Further, CTT encoding the 6 th  leucine was replaced with CTG and ATA encoding the 7 th  isoleucine, with ATC. The modified light chain leader sequence of the humanized antibody is shown in Table 4. 
     
       
         
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Primer 
                 Sequence 
               
               
                   
               
             
             
               
                 Humanized light 
                 C ACC  ATG GCC TGG ATT TCA CTG ATC CTC TCT 
               
               
                 chain leader 
                 CTC CTG 
               
               
                 sequence (SEQ ID NO:13) 
               
               
                   
               
             
          
         
       
     
     Gene LFW22-31 encoding the light chain variable region of the humanized antibody prepared in Example 3 was inserted into a PCR vector, to obtain expression vector pCR-LFW22-31. 
     Further, in order to prepare the full-length light chain of the humanized antibody, expression vector pHAB-LC (KCTC 10231BP, Korean Laid-Open NO: 2004-12267) containing the gene encoding the light chain constant region of the human antibody was employed. 
     First, in order to insert gene LFW22-31 encoding the light chain variable region of the humanized antibody into expression vector pHAB-LC, expression vector pCR-LFW22-31 was treated with HindIII/AvrII at 37° C. for 2 hrs, and electrophoresed on a 1.5% agarose gel and stained with EtBr, to obtain an about 400 bp fragment of the gene. 
     In the same manner as described above, expression vector pHAB-LC was treated with HindIII/AvrII to obtain an about 5.6 kb fragment of the vector. Each of the gene fragments was recovered from the gels using a QIAgel extraction kit (Qiagen, USA), treated with T4 DNA ligase (BioLabs, Inc., USA) at 16° C. overnight, and then, transformed into  E. coli  TOP10F′ to obtain a transformant. The transformant was cultured in an LB medium supplemented with 100 μg/ml of ampicillin overnight, and a plasmid was isolated from the culture solution. The plasmid was treated with HindIII/NotI (BioLabs, Inc., USA) and subjected to agarose gel electrophoresis, to obtain an about 0.7 kb full-length light chain of the humanized antibody. 
     The so-prepared gene encoding the full-length light chain of the humanized antibody was designated LFW22-31 LF. Further, the light chain expression vector of the humanized antibody containing the gene LFW22-31 LF was designated pHAB LFW22-31 LF ( FIG. 4 ), and transformed into  E. coli  TOP10F′ to obtain a transformant, which was deposited on Oct. 29, 2003 with the Korean Collection for Type Cultures (KCTC)(Address: Korea Research Institute of Bioscience and Biotechnology (KRIBB), #52, Oun-dong, Yusong-ku, Taejon, 305-333, Republic of Korea) under the accession number KCTC 10532BP. 
     Another full-length light chain of the humanized antibody was prepared by using gene LFW22-312 according to the same method as described above, and was designated LFW22-312 LF. Further, the light chain expression vector of the humanized antibody containing gene LFW22-312 LF was designated pHAB LFW22-312 LF ( FIG. 4 ), and transformed into  E. coli  TOP10F′ to obtain a transformant, which was deposited on Nov. 25, 2003 with the Korean Collection for Type Cultures (KCTC)(Address: Korea Research Institute of Bioscience and Biotechnology (KRIBB), #52, Oun-dong, Yusong-ku, Taejon, 305-333, Republic of Korea) under the accession number KCTC 10553BP. 
     EXAMPLE 5 
     Transformation of a Humanized Antibody into CHO Cell Lines 
     In order to measure the humanized antibody activity in animal cells, heavy chain expression vector pHAB-HFW141 HF prepared in Example 2 and light chain expression vector pHAB-LFW22-31 LF prepared in Example 4 were transformed into CHO cells (ATCC CRL-9096, USA). 
     First, CHO cells were cultured in a DMEM/F12 medium (JRH Inc., USA) supplemented with 1.5 g/l of sodium bicarbonate (Sigma, USA) and 10% heat inactivated FBS (Gibco BRL, USA) in a 37° C. humidified CO 2  incubator for 2 to 3 days. The culture solution was centrifuged at 1,200 rpm, room temperature (25° C.) for 5 min, to harvest a cell pellet. The cells were stained with 0.4% trypan blue (Gibco BRL, USA), and counted with a hematocytometer. The cells were transferred to a T-225 flask (or T-75 flask) in an amount of about 6×10 6  cells and subjected to sub-culture. 
     The sub-cultured CHO cells were allowed to proliferate until they occupied the flask&#39;s surface by as much as about 60 to 90%. 10 μg of the gene to be transformed and 40 μl of a GenePORTER solution (GTS, USA) for transformation were mixed with 5 ml of a DMEM/F12 (serum-free) medium. After the mixture was kept at room temperature for 10 to 45 min, the culture medium was removed therefrom, and the proliferated cells were cultured in a 37° C. humidified CO 2  incubator for about 3 to 5 hrs, to obtain a transformant, which was designated CHO-YHB1110-13. 
     Heavy chain expression vector pHAB-HFW141 HF prepared in Example 2 and light chain expression vector pHAB-LFW22-312 LF prepared in Example 4 were transformed into CHO cells to obtain another transformant according to the same method as described above, and the transformant was designated CHO-YHB1110-15. 
     EXAMPLE 6 
     Purification of a Humanized Antibody 
     The transformant CHO-YHB1110-13 cells obtained in Example 5 were inoculated into a T-75 flask containing a DMEM/F12 medium supplemented with 10% fetal bovine serum in an amount of 2×10 6  cells and incubated at 37° C. for 5 hrs. The culture solution was centrifuged to isolate a supernatant, and the supernatant was filtered, to obtain a cell-free culture solution. 
     In order to purify the humanized antibody from the culture solution, sepharose 4B columns conjugated with Protein-A (Pharmacia) and goat anti-human Immunoglobulin G (Zymed Laboratories Inc., USA) were employed. The culture supernatant was applied to Protein-A conjugated sepharose 4B column chromatography to bind the humanized antibody to Protein-A, and a glycine buffer (pH 2.5) was introduced into the column, to elute the humanized antibody. Then, the effluent was neutralized by mixing with 1 M Tris-Cl (pH 8.0) at a volume ratio of 1:10. The neutralized effluent was subjected to sepharose 4B column chromatography conjugated with goat anti-human IgG, to specifically capture the humanized antibody protein. 
     The humanized antibody was further purified according to the same method using the Protein-A column chromatography as described above and designated YHB1110-13. 
     Humanized antibody YHB1110-15 was purified by culturing the transformant CHO-YHB1110-15 prepared in Example 5 and purifying the antibody from the culture supernatant, according to the same method as described above. 
     As a result of analyzing the purified humanized antibodies with SDS-PAGE, bands of about 50 kDa and about 25 kDa were observed, which were identified as the heavy chain and light chain of the humanized antibody, respectively ( FIG. 5 ). 
     EXAMPLE 7 
     Measurement of Antigen-Binding Affinity of a Humanized Antibody Against HBV S-Surface Antigen 
     The humanized antibodies purified in Example 6 were quantified with sandwich ELISA, and their antigen-binding activities were analyzed by using an S-surface antigen (International Enzyme Inc., USA) adr type. For antibody quantification, 100 ng of goat anti-human immunoglobulin G. A. M (Zymed Laboratories Inc., USA) was distributed into each well of a microplate (Dynatech Laboratories Inc., USA) and the well plate was kept at 4° C. overnight to coat it with the immunoglobulin. At this time, mouse monoclonal antibody A9-11-5 was used as a control. 
     In order to measure an antigen-binding affinity of the humanized antibody against HBV S-surface antigen, antigen solutions (100 μl each) having different concentrations ranging from 10 −11  to 10 −6  M were mixed with 5 ng of the mouse monoclonal antibody A9-11-5, humanized antibodies YHB1110-13 and YHB1110-15, respectively, and reacted at 37° C. for 1 hr. Each of the reactants was added to the well plate coated with 0.5 μg of the antigen and the well plate was kept at 37° C. for about 2 hrs. A goat anti-human polyclonal antibody (BioRad, USA) conjugated with horseradish peroxidase was diluted at a ratio of 1:1000 and 100 μl of the diluted antibody solution was added to each well. The well plate was kept at 37° C. for 1 hr. After the reaction was completed, the optical density of each well was measured using a horseradish peroxidase substrate kit (BioRad, USA). 
     Concentrations of the antibody bound to the antigen and the unbound antibody were calculated from the measured optical density, and antigen-binding affinity of the humanized antibodies were determined therefrom (Friguet, et al.,  J. Immunol. Meth.  77: 305-319, 1985). The results are shown in Table 5. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                 Humanized 
                 Humanized 
               
               
                   
                 Mouse antibody 
                 antibody 
                 antibody 
               
               
                 Antigen 
                 mA9-11-5 
                 YHB1110-13 
                 YHB1110-15 
               
               
                   
               
             
             
               
                 Antigen-binding 
                 1 × 10 8  M −1   
                 1 × 10 8  M −1   
                 7 × 10 7  M −1   
               
               
                 affinity 
               
               
                 (Ka) 
               
               
                   
               
             
          
         
       
     
     As can be seen in Table 5, the antigen-binding affinities of humanized antibodies YHB1110-13 and YHB1110-15 were similar to that of mouse monoclonal antibody A9-11-5 ( FIG. 6 ). 
     While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.