Abstract:
The present invention is related to the obtaining of modified antibodies by means of DNA recombinant technology from the murine monoclonal antibody P3 (MAb P3), produced by the hybridoma cell line deposited under Budapest Treaty with accession number ECACC 94113026, and from its anti-idiotype murine monoclonal antibody 1E10(MAbai 1E10), produced by the hybridoma cell line with deposit number ECACC 97112901, with the objective of achieving monoclonal antibodies which preserve the biological function of specifically binding the antigen of the original antibodies, but being at the same time less immunogenic. The chimeric antibodies of the invention contain the variable domains of the murine immunoglobulin and the constant regions of the human immunoglobulin; and those humanized, besides containing the constant regions of the human immunoglobulins, are modified in the murine framework regions (FRs), in particular, in those zones that could be in a T cell antigenic site, so that several positions of the FRS are human as well. These antibodies can be used in the diagnosis and therapy of different types of tumors. The present invention is also related to the use of the antibodies for therapeutic and diagnostic purposes.

Description:
PRIOR RELATED APPLICATIONS 
     This patent application is a divisional patent application of U.S. patent application Ser. No. 10/473,977, filed Nov. 17, 2003 now abandoned, which claims priority to PCT Patent Application PCT/CU2002/00003, filed Apr. 8, 2002 and Cuban Patent Application CU 84/2001, filed Apr. 6, 2001 and incorporates these applications in their entireties by reference thereto. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention is related to the biotechnology field, in particular with new recombinant antibodies obtained by genetic engineering, specifically with chimeric and humanized antibodies obtained from the murine monoclonal antibody P3 (MAb P3) and its anti-idiotype murine monoclonal antibody 1E10 (MAbai 1E10). 
     More specifically, the invention is related with antibodies that bind to gangliosides containing N-glycolylated sialic acid, but not with the acetylated forms of the gangliosides or with neuter glycolipids. Gangliosides containing N-glycolylated sialic acid are antigens widely expressed in breast cancer and melanomas. On the other hand, the anti-tumor effect of the MAbai 1E10 has also been demonstrated in experimental models. 
     The present invention is also related with the pharmaceutical compositions that contain the previously described recombinant antibodies useful in the diagnosis and therapy of cancer, particularly breast cancer and melanomas. 
     2. Discussion of the Prior Art 
     Gangliosides are glycosphingolipids that contain sialic acid and they are present in the plasmatic membrane of cells in vertebrates (StuIts et al. (1989): 
     Glycosphingolipids: structure, biological source and properties, Methods Enzymology, 179:167-214). Some of these molecules have been reported in the literature as tumor-associated antigens or tumor markers (Hakomori et al. (1991): Possible functions of tumor associated carbohydrate antigens, Curr. Opin. Immunol., 3: 646-653). For that reason the use of anti-ganglioside antibodies has been described as useful in the diagnosis and therapy of cancer (Hougton et al. (1985): Mouse monoclonal antibody IgG3 antibody detecting GD3 ganglioside: to phase I trial in patients with malignant melanoma, PNAS USA, 82:1242-1246; Zhang et al. (1997): Selection of carbohydrate tumor antigens as targets for immune attack using immunohistochemistry. I. Focus on gangliosides, Int. J. Cancer, 73: 42-49). 
     The sialic acids more frequently expressed in animals are N-acetyl (NeuAc) and N-glycolyl (NeuGc) (Corfield et al. (1982): Occurrence of sialic acids, Cell. Biol. Monogr., 10: 5-50). Generally, NeuGc is not expressed in normal human and chickens tissues, but it is broadly distributed in other vertebrates (Leeden and Yu, (1976): Chemistry and analysis of sialic acid. In: Biological Role of Sialic Acid. Rosemberg A and Shengtrund C L (Eds). Plenum Press, New York, 1-48; Kawai et al. (1991): Quantitative determination of N-glycolylneuraminic acid expression in human cancerous tissues and avian lymphoma cell lines as a tumor associated sialic acid by gas chromatography-mass spectrometry, Cancer Research, 51: 1242-1246). However, there are reports that show that anti-NeuGc antibodies recognize some human tumors and tumor cell lines (Higashi et al. (1988): Detection of gangliosides as N-glycolylneuraminic acid specific tumor-associated Hanganutziu-Deicher antigen in human retinoblastoma cells, Jpn. J. Cancer Res., 79: 952-956; Fukui et al. (1989): Detection of glycoproteins as tumor associated Hanganutziu-Deicher antigen in human gastric cancer cell line, NUGC4, Biochem. Biophys. Res. Commun., 160: 1149-1154). Increased levels of GM3 (NeuGc) gangliosides have been found in human breast cancer (Marquina et al. (1996): Gangliosides expressed in human breast cancer, Cancer Research, 1996; 56: 5165-5171), and this result makes attractive the use of this molecule as a target for cancer therapy. 
     The monoclonal antibody (Mab) P3, produced by the cell line deposited with accession number ECACC 94113026 (European Patent EP 0 657 471 B1), is a murine monoclonal antibody with IgM isotype. Mab P3 was obtained when fusing murine splenocytes from a BALB/c mouse immunized with liposomes containing GM3(NeuGc) and tetanic toxoid with the cell line P3-X63-Ag8.653, which is a murine myeloma. This Mab P3 reacts strongly with N-glycolylated sialic acid-containing gangliosides but not with the acetylated forms of the gangliosides, nor with the neuter glycolipids. It was demonstrated by immunocytochemical and immunohistochemical studies carried out with cell lines and tissues from benign and neoplasic tumors that the Mab P3 recognizes breast cancer (Vzquez et al. (1995): Generation of a murine monoclonal antibody specific for N-glycolylneuraminic acid-containing gangliosides that also recognizes sulfated glycolipids, Hybridoma, 14: 551-556) and melanoma. 
     The Mab P3 induced an anti-idiotypic immune response (Ab2) in BALB/c mice (syngeneic model), even without adjuvant and carrier protein (Vazquez et al. (1998): Syngeneic anti-idiotypic monoclonal antibodies to an anti-NeuGc-containing ganglioside monoclonal antibody, Hybridoma, 17: 527-534). A role for the electronegative groups, sialic acid (for gangliosides) or SO 3 — (for sulfatides), in the recognition properties of this antibody was suggested by immunochemical analysis (Moreno et al. (1998): Delineation of epitope recognized by an antibody specific for N-glycolylneuraminic acid-containing gangliosides, Glycobiology, 8: 695-705). 
     The anti-idiotypic Mab 1E10 (Mabai 1E10) of IgG1 subtype was obtained from a BALB/c mouse immunized with the Mab P3 coupled to KLH (U.S. Pat. No. 6,063,379, cell line deposited under accession number ECACC 97112901). Mabai 1E10 specifically recognized MAb P3 and did not bind other IgM anti-ganglioside antibodies. Moreover, Mabai 1E10 inhibited the specific binding of Mab P3 to GM3(NeuGc) and to the ductal breast carcinoma-derived cell line MDA-MB-435, which is positive for Mab P3 binding. The MAbai 1E10 induced a strong immune response of Ab3 antibodies when mice from syngeneic or alogenic models were immunized. These Ab3 antibodies did not exhibit the same specificity as the Mab P3 even though they carry idiotopes similar to those carried by the Ab1 antibody (Vazquez et al. (1998): Syngeneic anti-idiotypic monoclonal antibodies to an anti-NeuGc-containing ganglioside monoclonal antibody, Hybridoma, 17: 527-534). MAbai 1E10 induced a strong antitumor effect in syngeneic as well as alogenic mice. The growth of the mammary carcinoma cell line F311 was significantly reduced by repeated doses of KLH-coupled MAbai 1E10 in Freund&#39;s adjuvant when BALB/c mice were vaccinated. Also the number of spontaneous lung metastasis was reduced after the vaccination. Intravenous administration of the MAbai 1E10 to C57BLU6 mice, 10 to 14 days after the intravenous inoculation of B16 melanoma cells, caused a dramatic reduction of the number of lung metastases when compared with mice treated with an irrelevant IgG. These results suggest that more than one anti tumor effect mechanism is triggered (Vazquez et al. (2000): Anti tumor properties of an anti-idiotypic monoclonal antibody in relation to N-glycolyl-containing gangliosides, Oncol. Rep., 7: 751-756, 2000). 
     Even though hybridoma technology has been developed for 15 years (Koehler y Milstein (1975): Continuous cultures of fused cells secreting antibody of predefined specificity, Nature, 256: 495497) and monoclonal antibodies are still very useful in diagnosis as well as research, they have not demonstrated their therapeutic effectiveness in humans. This has been mainly due to their short half-life in blood, to the human anti-mouse antibody immune response (HAMA response), and also because murine effector functions fail for the human immune system. 
     Genetic engineering technology has revolutionized MAb potential, since by manipulating immunoglobulin genes it is possible to obtain modified antibodies with reduced antigenicity, as well as to improve their effector functions when used in the treatment or diagnosis of certain pathologies. Methods for reducing immunoglobulin immunogenicity have as essential object to diminish the differences between the murine antibody and a human immunoglobulin, without altering the antigen recognition specificity (Morrison y Oi (1989): Genetically engineered antibody molecules, Adv Immunol., 44: 65-92). 
     Recently, several methods have been developed to humanize murine or rat antibodies, thus reducing the xenogenic immune response against foreign proteins when they are injected into humans. One of the first approaches to reduce the antigenicity were chimeric antibodies, in which the variable domains of the murine protein are inserted in constant domains of human molecules that exhibit the same specificity but reduced immunogenicity compared to their murine counterparts. Additionally, human effector functions are preserved by chimeric antibodies (Morrison et al. (1984): Chimeric human antibody molecules: Mouse antigen-binding domains with human constant region domains, PNAS USA, 81: 6851-6855). Even when chimeric antibodies have the same specificity as their murine counterpart, an immune response to the rodent variable regions is frequently observed. 
     In an attempt to further reduce the immunogenicity of chimeric antibodies, only the CDRs from the rodent monoclonal antibody have been grafted onto human framework regions and this hybrid variable region has been expressed with human constant regions (Jones et al. (1986): Replacing the complementary-determining regions in a human antibody with those from a mouse, Nature 321: 522-524; Verhoeyen et al. (1988): Reshaping human antibodies: grafting an antilysozyme activity, Science 239, 1534-1536). However, this approach has several shortcomings: frequently the resulting antibody has decreased affinity and a number of framework residues must be mutated back to the corresponding murine ones to restore binding (Rietchmann et al. (1988): Reshaping human antibodies for therapy, Nature, 332: 323-327; Queen et al. (1989): A humanized antibody that binds to the interleukin 2 receptor, PNAS USA, 86: 10029-10033; Tempest et al. (1991): Reshaping a human monoclonal antibody to inhibit human respiratory syncytial virus infection in vivo, Biotechnology, 9: 266-272). In addition, persisting immunogenicity is frequently observed in the CDR-grafted antibodies. 
     Mateo and collaborators (U.S. Pat. No. 5,712,120) have described a procedure for reducing immunogenicity of murine antibodies. According to the method, the modifications are restricted to the variable domains and specifically to the murine FRs of chimeric antibodies. Moreover, the replacements are only carried out in those regions of the FRs that have amphipatic sequences and therefore they are potential epitopes recognized by T cells. 
     The method comprises judicious replacement of a few amino acid residues, located in the potential immunogenic epitopes by the corresponding residues from the most homologous human sequence. Those amino acids that are mainly responsible for canonical structures, as well as the residues in the immediate neighborhood of the CDRs or in the Vernier zone must be retained. 
     The resulting antibody retains its antigen binding specificity and is less immunogenic than either its murine or chimeric predecessor (Mateo et al. (2000): Removal of T cell epitopes from genetically engineered antibodies: Production of modified immunoglobulins with reduced immunogenicity, Hybridoma 19: 463-71). These properties increase its therapeutic usefulness. Using this new procedure, only few mutations, and of course less genetic manipulations, have to be done. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is related to recombinant antibodies, obtained by genetic engineering technology. Specifically, the invention is related to a chimeric antibody derived from the murine monoclonal antibody P3, produced by hybridoma cell line with deposit number ECACC 94113026. MAB P3 recognizes an antigen expressed in breast tumor cells and melanomas. The MAb P3 is characterized by the following sequences of the hypervariable regions (CDRs) of the heavy and light chains: 
                             Heavy Chain           (SEQ ID NO: 1)           CDR1: RYSVH                   (SEQ ID NO: 2)           CDR2: MIWGGGSTDYNSALKS                   (SEQ ID NO: 3)           CDR3: SGVREGRAQAWFAY                   Light Chain           (SEQ ID NO: 4)           CDR1: KASQDVSTAVA                   (SEQ ID NO: 5)           CDR2: SASYRYT                   (SEQ ID NO: 6)           CDR3: QQHYSTPWT            
Preferably, the FRs sequences of the heavy and light chain are the following:
 
     
       
         
               
               
             
           
               
                   
                 Heavy Chain 
               
               
                   
                 (SEQ ID NO: 7) 
               
               
                   
                 FR1: QVQLKESGPGLVAPSQSLSITCTVSGFSLS 
               
               
                   
               
               
                   
                 (SEQ ID NO: 8) 
               
               
                   
                 FR2: WVRQPPGKGLEWLG 
               
               
                   
               
               
                   
                 (SEQ ID NO: 9) 
               
               
                   
                 FR3: RLSISKDNSKSQVFLKMNSLQTDDTAMYYCAR 
               
               
                   
               
               
                   
                 (SEQ ID NO: 10) 
               
               
                   
                 FR4: WGQGTLV 
               
               
                   
               
               
                   
                 Light Chain 
               
               
                   
                 (SEQ ID NO: 11) 
               
               
                   
                 FR1: DIVMTQSHKFMSTSVGDRVSITC 
               
               
                   
               
               
                   
                 (SEQ ID NO: 12) 
               
               
                   
                 FR2: WYQQKPGQSPKLLIY 
               
               
                   
               
               
                   
                 (SEQ ID NO: 13) 
               
               
                   
                 FR3: GVPDRFTGSGSGTDFTFTISSVQAEDLAVYYC 
               
               
                   
               
               
                   
                 (SEQ ID NO: 14) 
               
               
                   
                 FR4: FGGGTKL 
               
             
          
         
       
     
     In a preferred embodiment, the chimeric antibody of the present invention contains the constant region of human IgG1 heavy chain and the constant region of human Ck light chain. In another aspect, the present invention is related with a humanized antibody derived from the Mab P3 produced by the hybridoma cell line with deposit number ECACC 94113026, characterized in that it contains the constant region of human IgG1 heavy chain and the constant region of human Ck light chain and the FRs regions of the light chain contain any of the following point mutations: 
     
       
         
               
               
             
           
               
                   
                 Light Chain: 
               
               
                   
                 Position 8 in SEQ ID NO: 11: His by Pro 
               
               
                   
               
               
                   
                 Position 9 in SEQ ID NO: 11: Lys by Ser 
               
               
                   
               
               
                   
                 Position 10 in SEQ ID NO: 11: Phe by Ser 
               
               
                   
               
               
                   
                 Position 11 in SEQ ID NO: 11: Met by Leu 
               
               
                   
               
               
                   
                 Position 13 in SEQ ID NO: 11: Thr by Ala 
               
             
          
         
       
     
     In another aspect, the invention is related with a chimeric antibody derived from the murine monoclonal antibody 1E10 produced by the hybridoma cell line with deposit number ECACC 97112901 and it is an antidiotype antibody which recognizes the MAb P3. The MAbai 1E10 is characterized by the following sequences of the hypervariable regions (CDRs) of the heavy and light chains: 
     
       
         
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                   
                 Heavy chain 
               
             
          
           
               
                 (SEQ ID NO: 15) 
               
             
          
           
               
                   
                 CDR1: SYDIN 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 16) 
               
             
          
           
               
                   
                 CDR2: WIFPGDGSTKYNEKFKG 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 17) 
               
             
          
           
               
                   
                 CDR3: EDYYDNSYYFDY 
               
               
                   
               
               
                   
                 Light chain 
               
             
          
           
               
                 (SEQ ID NO: 18) 
               
             
          
           
               
                   
                 CDR1: RASQDISNYLN 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 19) 
               
             
          
           
               
                   
                 CDR2: YTSRLHSG 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 20) 
               
             
          
           
               
                   
                 CDR3: QQGNTLPWT 
               
             
          
         
       
     
     Preferably, the FRs sequences of the heavy and light chains are the following: 
     
       
         
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                   
                 Heavy chain 
               
             
          
           
               
                 (SEQ ID NO: 21) 
               
             
          
           
               
                   
                 FR1: QVQLQQSGAELVKPGASVKLSCKASGYTFT 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 22) 
               
             
          
           
               
                   
                 FR2: WVRQRPEQGLEWIG 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 23) 
               
             
          
           
               
                   
                 FR3: KATLTTDKSSSTAYMQLSRLTSEDSAVYFCAR 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 24) 
               
             
          
           
               
                   
                 FR4: WGQGTTLTV 
               
               
                   
               
               
                   
                 Light chain 
               
             
          
           
               
                 (SEQ ID NO: 25) 
               
             
          
           
               
                   
                 FR1: DIQMTQTTSSLSASLGDRVTISC 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 26) 
               
             
          
           
               
                   
                 FR2: WYQQKPDGTVKLLIY 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 27) 
               
             
          
           
               
                   
                 FR3: VPSRFSGSGSGTDYSLTISNLEQEDIATYFC 
               
               
                   
               
             
          
           
               
                 (SEQ ID NO: 28) 
               
             
          
           
               
                   
                 FR4: FGGGTKLESK 
               
             
          
         
       
     
     In a preferred embodiment, the chimeric antibody of the present invention contains the constant region of human IgG1 heavy chain and the constant region of human Ck light chain. 
     In another aspect, the present invention is related with a humanized antibody derived from the Mab 1E10 produced by the hybridoma cell line with deposit number ECACC 97112901, characterized in that it contains the constant region of human IgG1 heavy chain and the constant region of human Ck light chain and the FRs regions of the heavy and light chains contain any of the following point mutations: 
                             Light Chain:           Position 7 in SEQ ID NO: 25: Thr by Ser                   Position 8 in SEQ ID NO: 25: Thr by Pro                   Position 15 in SEQ ID NO: 25: Leu by Val                   Heavy Chain:           Position 5 in SEQ ID NO: 21: Gln by Val                   Position 5 in SEQ ID NO: 22: Arg by Ala                   Position 7 in SEQ ID NO: 22: Glu by Gly                   Position 21 in SEQ ID NO: 23: Thr by Arg            
Position 21 in SEQ ID NO: 23: Thr by Arg
 
     In another aspect, the present invention is related to the cell lines that express the described chimeric and humanized antibodies; additionally the invention is related to pharmaceutical compositions comprising the described antibodies. 
     Preferably it is related with pharmaceutical compositions for the treatment of breast, lung, digestive system, urogenital system, melanomas, sarcomas and neuroectodermic tumors, their metastases and relapses, comprising the described antibodies and an appropriate exicipient. 
     In another representation of the present invention, the pharmaceutical compositions can be used for the in vivo localization and diagnosis of breast, lung, digestive system, urogenital system, melanomas, sarcomas and neuroectodrmico tumors, their metastases and relapses, comprising the described antibodies. 
     cDNA Synthesis and Gene Amplification by PCR (Polymerase chain reaction) of the Variable Region of MAb P3 and Mabai 1E10. 
     Cytoplasmic RNA was extracted from about 10 6  P3 hybridoma cells (murine IgM MAb that recognizes GM3 N-glycolylated gangliosides) or 1E10 (antidiotype anti-P3 antibody). The RNA was extracted using the reagent TRIZOL® (GIBCO® BRL, Grand Island, N.Y.), according to the manufacturer&#39;s instructions. 
     The cDNA synthesis reaction was carried out mixing 5 μg of the RNA, 25 pmoles of Vh (complementary to the constant region of murine IgM for VHP3, and with the constant region of murine IgG1 for VH 1E10) or Vk (complementary to constant murine kappa region for both antibodies), 2.5 mM of each dNTP, 50 mM Tris-Hcl pH 7.5, 75 mM KCl, 10 mM DTT, 8 mM MgCl2 and 15 units of RNAse inhibitor in a 50 μl reaction mixture. It was heated at 70° C. for 10 minutes and slowly cooled up to 37° C. Then, 100 units of MLV reverse transcriptase enzyme were added and incubation at 42° C. continued for one hour. 
     The VK and VH variable region cDNAs were amplified by PCR. Briefly, 5 μl cDNA of VH or VK were mixed with 25 pmoles of specific primers, 2.5 mM of each dNTP, 5 μl constituents of 10× buffer Taq DNA polymerase and 1 unit of this enzyme. The samples were subjected to 25 thermal cycles at 94° C., 30 sec; 50° C., 30 sec; 72° C., 1 min, and a last incubation for 5 minutes at 72° C. 
     Cloning and Sequencing of Amplified cDNA 
     The PCR products of VH and VK (of the P3 and of the 1E10, respectively) were cloned into TA vector (TA Cloning kit. Promega, USA). The resulting clones were sequenced by the dideoxy method using T7 DNA Polymerase (T7 sequencing kit, Pharmacia, Sweden). 
     Construction of Chimeric Genes 
     The VH and VK genes were excised from TA vectors by enzymatic digestion and were cloned into the respective expression vectors (Coloma et al. (1992): Novel vectors for the expression of antibody molecules using variable regions generated by polymerase chain reaction, J. Immunol. Meth., 152: 89-104). 
     The VH genes were excised from the TA vector by enzymatic digestion with EcoRV and NheI and cloned into an expression vector (PAH 4604) that includes a human IgG1 variable region and the histidinol resistance gene. The resultant constructions were P3VH-PAH4604 and 1E10VH-PAH4604. The VK genes were excised from TA vector by enzymatic digestion with EcoRV and SalI and cloned into an expression vector (PAG4622). This vector included mycophenolic acid resistance gene and the human kappa constant region. The resultant constructions were P3VK-PAG4622 and 1E10VK-PAG4622. 
     Expression of Chimeric Antibodies Obtained from Mab P3 and MAbai 1E10. 
     NS-0 cells were electroporated with 10 μg of P3VK-PAG4622 or 1E10VK-PAG4622, and clones expressing human kappa light chains were transfected with 10 μg of P3VH-PAH4604 or 1E10VH-PAH4604. 
     The DNAs were linearized by digestion with Pvul enzyme, precipitated with ethanol and dissolved in 50 μl of PBS. Approximately 10 7  cells were harvested by centrifugation and re-suspended in 0.5 ml of PBS together with the digested DNA in an electroporation cuvette. After 10 minutes on ice, the cells were given a pulse of 200 volts and 960 μF and left in ice for further 10 minutes. The cells were distributed into a 96 well plate with D′MEM F12 supplemented with 10% fetal calf serum. Two or four days later, selective medium (D′MEM F12 with mycophenolic acid 0.45 μg/mL or histidinol 10 mM, respectively) is added. Transfected clones were visible to the naked eye 14 days later. 
     The presence of human antibody in the medium of the wells containing transfected clones was measured by ELISA. Microtiter plate wells were coated with goat anti-human kappa light chain antibodies (for human kappa chain producing clones) or anti-human IgG antibodies (gamma chain specific) (for the complete antibody producing clones). After washing with PBST (saline phosphate buffered solution containing 0.05% Tween 20), diluted culture medium of the wells containing transfectants was added to each microtiter well for one hour at 37° C. The wells were washed with PBS-T, spicy radish peroxidase-conjugated goat anti-human kappa light chain or alkaline phosphatase-conjugated goat anti-human IgG (gamma chain specific) was added and incubation took place at 37° C. for one hour. The wells were washed with PBS-T and substrate buffer was added containing o-phenylendiamine or p-nitrophenylphosphate, respectively. After half an hour, the absorbance was measured at 492 or 405 nm, respectively. 
     Construction of the Humanized Antibodies P3hu and 1E10 hu by Humanization of T Cell Epitopes. Prediction of T Cell Epitopes 
     The sequences of P3 and 1E10 variable domains were analyzed with the algorithm AMPHI (Margalit et al. (1987): Prediction of immunodominant helper T cell antigenic sites from the primary sequence, J. Immunol., 138: 2213-2229). It searched helical amphipatic segments, with 7 or 11 amino acid residues, which have been associated with T immunogenicity. The program SOHHA also predicted helical hydrophobic segments (Elliot et al. (1987). An hypothesis on the binding of an amphipatic, alpha helical sequence in li to the desotope of class II antigen, J. Immunol., 138: 2949-2952). Both algorithms predicted which segments from variable region sequences of antibodies P3 and 1E10 could be presented to T-helper cells in the context of MHC class 11 molecules. 
     Homology Analysis with Human Immunoglobulins. 
     The amino acid sequences of murine variable regions were compared with the immunoglobulin sequences included in the GeneBank and EMBL database (available in Internet). The most homologous human variable region sequence was determined for each antibody. Software PC-TWO HIBIO PROSIS 06-00 (Hitachi) was used for sequence homology searching. 
     Analysis for the Immunogenicity Reduction. 
     The aim of the method is to reduce immunogenicity, breaking or humanizing potential immunogenic T epitopes with a minimum of changes. The method comprises judicious replacement of few amino acid residues, located into helical amphipatic segments. The amino acids which are mainly responsible for canonical structures, as well as the residues in the immediate neighborhood of the CDRs or into the Vernier zone, must be retained. 
     According to the method, murine variable region sequences were compared with the most homologous human sequence and amino acid residues that differ between the murine MAb and the most homologous human sequence were identified, only taking into account those residues inside the FRs (Kabat (1991), Sequences of proteins of immunological interest, Fifth Edition, National Institute of Health). The previously defined residues were replaced by those residues present in the most homologous human sequence. Replacements were made by directed mutagenesis techniques. 
     Residues involved in three-dimensional structure of the binding site were not mutated; it could affect antigen recognition. Additional information about the influence of the replacements in the tertiary structure can be obtained by molecular modeling of the antigen binding site. 
     The presence of proline residues in the helical amphipatic segment and the fact that a certain murine residue does not appear in the same position in the most homologous human sequence but is frequent in other human immunoglobulins must be kept in mind. For that reason, there is not a unique ensemble of murine amino acids to be replaced in the frameworks. It is possible to obtain different versions of the modified antibody with different number of replacements. The mutations were carried out by overlapping PCRs. 
     Cloning and Expressing Humanized Antibodies P3hu and 1E10hu. 
     The genetic constructions corresponding to the P3hu and 1E10hu, were cloned in expression vectors following the method described for the chimeric antibodies. The resultant constructions were P3VKhu-PAG4622 or 1E10Vkhu-PAG4622 and P3VHhu-PAH4604 and 1E10VHhu-PAH4604. They were transfected into NS-0 cells following the protocol described previously for chimeric antibodies. 
     Purification of the Recombinant Antibodies. 
     The recombinant antibodies were purified by affinity chromatography using protein A (Pharmacia, Upsala, Sweden). 
     Biological Activity. 
     The biological activity of the recombinant antibodies was tested by their specific binding to antigen as measured by ELISA. 
     For recombinant MAb P3, microtiter plates were coated with GM3(NeuGc) ganglioside in methanol. After drying for one hour, unspecific binding was blocked by incubating for one hour at 37° C. with bovine sera albumin (BSA) 1% in Tris-HCl buffer. The wells were washed with PBS and incubated for 1 hour at 37° C. with purified recombinant Mab P3. The wells were washed with tris-HCl and incubated at 37° C. for one hour with goat anti-human antibody conjugated with alkaline phosphatase. Finally, the wells were washed and substrate buffer containing p-nitrophenylphosphate was added. After half an hour, absorbance was measured at 405 or 492 nm, respectively. 
     For recombinant MAbai 1E10, the ELISA assay was similar, except that wells were coated with Mab P3 and washing steps were made with PBS-0.05% Tween 20. 
     EXAMPLES 
     In the following examples all the enzymes used, as well as reagents and materials, were obtained from commercial sources unless otherwise specified. 
     Example 1 
     Obtaining of Chimeric MAb P3 
     The cDNA synthesis was obtained by a reaction with reverse transcriptase enzyme, starting with RNA from the hybridoma producing Mab P3, as described previously. The sequence of the specific primers used in this reaction is shown: 
                     For VH:       (SEQ ID NO: 29)       5′ AGGTCTAGAA(CT)CTCCACACAC AGG(AG)(AG)CCAGTGGATA       GAC 3′               For VK:       (SEQ ID NO: 30)       5′ GCGTCTAGAACTGGATGGTGGGAAGATGG 3′            
cDNA VHP3 and cDNA VKP3 were amplified by PCR using Taq Polymerase and specific primers. The restriction sites included in the primers were ECORV/NHEI, for VH and ECORV/SALI for VK. The primer sequences used were the following:
 
     
       
         
               
             
           
               
                 For VH: 
               
               
                 Primer 1 (signal peptide): 
               
               
                 (SEQ ID NO: 31) 
               
               
                 5′GGGGATATCCACCATGG(AG)ATG(CG) AGCTG(TG)GT(CA)AT 
               
               
                 (CG)CTCTT 3′ 
               
               
                   
               
               
                 Primer 2 (CH1): 
               
               
                 (SEQ ID NO: 32) 
               
               
                 5′ GGGGCTAGCTGCAGAGACAGTGACCAGAGT 3′ 
               
               
                   
               
               
                 For VK: 
               
               
                 Primer 1 (signal peptide): 
               
               
                 (SEQ ID NO: 33) 
               
               
                 5′ GGGGATATCCACCATGGAG(TA)CAC A(GT)(TA)CTCAGGTCTTT 
               
               
                 (GA)T 3′ 
               
               
                   
               
               
                 Primer 2 (Ck): 
               
               
                 (SEQ ID NO: 34) 
               
               
                 5′ AGCGTCGACTTACGTTT(TG)ATTTCCA(GA)CTT(GT)GTCCC 3′ 
               
             
          
         
       
     
     PCR products were cloned into TA vector (TA cloning kit, Invitrogen). Twelve independent clones were sequenced by the dideoxy method using T7 DNA Pol (Pharmacia). The most homologous sequence groups for VHP3 and VKP3 was determined by homology search analysis. VHP3 and VKP3 sequences ( FIGS. 1 and 2 ) have high homology with groups IB and V, respectively, according to Kabat&#39;s classification. 
     After digestion with the restriction enzymes ECORV and NHEI for VHP3 and with ECORV and SALI for VKP3, they were cloned in the expression vectors PAH4604 and PAG4622 (for VH and VK, respectively), both previously digested with the same enzymes. These expression vectors were donated by Sherie Morrison (UCLA, Calif., USA), and they are suitable for immunoglobulin expression in mammalian cells. Vector PAH 4604 includes the human IgG1 constant region and vector PAG 4622 the human Ck (Coloma et al. (1992): Novel vectors for the expression of antibody molecules using variable regions generated by polymerase chain reaction, J. Immunol. Meth., 152: 89-104). The resultant constructs were P3VH-PAH4604 and P3VK-PAG4622. 
     NS-0 cells were transfected with 10 μg of P3VK-PAG4622, and the clone expressing light chain was transfected with 10 μg P3VH-PAH4604. In both cases DNA was linearized with Pvul, ethanol precipitated and dissolved in 50 μl of PBS before transfection. 
     Approximately 10 7  cells were harvested by centrifugation and resupended in 0.5 ml of PBS together with the digested DNA in an electroporation cuvette. After 10 minutes on ice, the cells were given a pulse of 200 volts and 960 μF and left in ice for further 10 minutes. The cells were distributed into a 96 well plate with D′MEM F12 supplemented with 10% fetal calf serum. Two or four days later, selective medium (D′MEM F12 with mycophenolic acid 0.45 μg/mL or histidinol 10 mM, respectively) is added. Transfected clones were visible to the naked eye 14 days later. 
     The presence of human antibody in the medium of wells containing transfected clones was measured by ELISA. Microtiter plate wells were coated with goat anti-human kappa light chain antibody (for human kappa chain producing clones) or anti-human IgG antibody (gamma chain specific) (for the complete antibody producing clones). After washing with PBST (saline phosphate buffered solution containing 0.05% Tween 20), diluted culture medium of the wells containing transfectants was added to each Microtiter well for one hour at 37° C. The wells were washed with PBS-T, spicy radish peroxidase-conjugated goat anti-human kappa light chain or alkaline phosphatase-conjugated goat anti-human IgG (gamma chain specific) was added, and incubation took place at room temperature for one hour. The wells were washed with PBS-T and substrate buffer containing o-phenylendiamine or p-nitrophenylphosphate, respectively, was added. After half an hour, absorbance was measured at 492 or 405 nm, respectively. 
     Example 2 
     Obtaining Different Versions of the Humanized Antibody P3 
     Murine VHP3 and VKP3 sequences ( FIGS. 1 and 2 ) were compared with human sequences.  FIGS. 3 and 4  show the most homologous human sequences. Helical amphipatic regions or potential T cell epitopes were searched on murine P3 variable region sequences and, according to the method, a judicious strategy for amino acid replacements was established in order to break or humanize potential T cell epitopes inside the murine sequences. 
     The analysis on VHP3 rendered ( FIG. 3 ) 2 amphipatic segments; the first one embraces CDR1, FR2 and some residues of the CDR2, while the second one embraces the end of FR3 and CDR3. The main differences of the murine sequence in comparison with the most homologous human sequence were found in CDRs or in residues involved in the three dimensional structure of the binding site. For that reason it was decided not to replace any amino acids in murine VHP3. 
     The analysis for VKP3 also rendered 2 amphipatic segments ( FIG. 4 ); the first segment embraces FR1, while the second one embraces CDR2 and some residues of FR3. It was decided to replace residues at positions 8, 9, 10, 11 and 13 by residues at the same positions in the most homologous human sequence. The amino acids His, Lys, Phe, Met and Thr were replaced by Pro, Ser, Ser, Leu, and Ala, respectively. The replacements were made by overlapping PCR (Kammann et al. (1989) Rapid insertional mutagenesis of DNA by polymerase chain reaction (PCR), Nucleic Acids Res., 17: 5404) using primers 1, 2, 3 and 4, whose sequences are the following: 
     
       
         
               
             
           
               
                 (SEQ ID NO: 35) 
               
               
                 Primer 1: 5′ ATGACCCAGTCTCCTTCTTCTCTTTCCGCGTCAGTAG 
               
               
                 GAGAC 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 36) 
               
               
                 Primer 2: 5′ AGCGTCGACTTACGTTT(TG)ATTTCCA(GA)CT- 
               
               
                 T(GT)GTCCC 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 37) 
               
               
                 Primer 3: 5′ GTCTCCTACTGACGCGGAAAGAGA-AGAAGGAGACTG 
               
               
                 GGTCAT 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 38) 
               
               
                 Primer 4: 5′GGGGATATCCACCATGGAG(TA)CACA(GT)(TA)CTC 
               
               
                 AGGTCTTT (GA)T 3′ 
               
             
          
         
       
     
     The point mutations were verified by sequencing. The resulting construct was P3Vkhu and it was cloned in PAG 4622 expression vector. The resulting construct was P3VKhu-PAG4622. 
     To express the humanized antibody P3, NS-0 cells were transfected with P3VH-PAH4604 and P3VKhu-PAG4622. P3hu antibody was transfected following the same electroporation and detection procedure described previously for the chimeric antibodies. 
     Example 3 
     Biological Activity of Chimeric MAb P3 
     The biological activity of the chimeric Mab P3 was tested by its specific binding to antigen as measured by ELISA. 
     For recombinant MAb P3, microtiter plates were coated with GM3(NeuGc) ganglioside in methanol. After drying one hour at 37° C., unspecific binding was blocked by incubating with 1% bovine sera albumin (BSA) in Tris-HCl buffer for one hour at 37° C. The wells were washed with PBS and incubated for 1 hour at 37° C. with purified recombinant Mab P3. The wells were washed with tris-HCl and incubated with goat anti-human antibody conjugated with alkaline phosphatase at 37° C. for one hour. Finally, the wells were washed with Tris-HCl and substrate buffer containing p-nitrophenylphosphate was added. After half an hour, absorbance was measured at 405 nm. 
     Chimeric Mab Ti was used as negative control. 
       FIG. 5  shows the specific binding of chimeric Mab P3 to the antigen. 
     Example 4 
     Obtaining of Chimeric MAb 1E10 
     The cDNA synthesis was obtained by a reaction with reverse transcriptase enzyme, starting with RNA from the hybridoma producing Mab 1E10, as described previously. The sequence of the specific primers used in this reaction is shown below: 
                             For VH:           (SEQ ID NO: 39)           5′GGGGCTAGCTGAGGAGACTGTGAGAGTGGT 3′                   For VK:           (SEQ ID NO: 40)           5′GCGTCTAGAACTGGATGGTGGGAAGATGGA 3′            
cDNA VH1E10 and cDNA VK1E10 were amplified by PCR using Taq Pol and specific primers.
 
     
       
         
               
             
           
               
                 For VH: 
               
               
                 (SEQ ID NO: 41) 
               
               
                 Primer 1 (signal peptide): 5′GGGGATATCCACCATGG(AG) 
               
               
                 ATG-(CG)AGCTG(TG)GT(CA)AT(CG)CTCTT 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 42) 
               
               
                 Primer 2 (CH1): 5′ GGGGCTAGCTGAGGAGACTGTGAGAGTGG 
               
               
                 T 3′ 
               
               
                   
               
               
                 For VK: 
               
               
                 (SEQ ID NO: 43) 
               
               
                 Primer 1 (signal peptide): 5′GGGGTTAACCACCATGAGG 
               
               
                 (GT)C-CCC(AT)GCTCAG(CT)T(CT)CT(TG)GG(GA)3′ 
               
               
                   
               
               
                 (SEQ ID NO: 44) 
               
               
                 Primer 2 (Ck): 5′AGCGTCGACTTACGTTT(TG)ATTTCCA(GA)C 
               
               
                 TT(GT)GTCCC3′ 
               
             
          
         
       
     
     PCR products were cloned into TA vector (TA cloning kit, Invitrogen). Twelve independent clones were sequenced ( FIGS. 7 and 8 ) by the dideoxy method using T7 DNA Pol (Pharmacia). The most homologous sequence group for VHIE10 and VK1E10 was determined by homology search analysis. VH1E10 and VK1E10 sequences have high homology with groups miscellaneous and V, respectively, according to Kabat&#39;s classification. 
     After digestion with the restriction enzymes ECORV and NHEI for VH1E10 and with HincII I and SALI for VKIE10, they were cloned in the expression vectors PAH4604 and PAG4622 (for VH and VK, respectively), both previously digested with appropriate enzymes. These expression vectors were donated by Sherie Morrison (UCLA, Calif., USA), and they are suitable for immunoglobulin expression in mammalian cells. Vector PAH 4604 includes the human IgG1 constant region and vector PAG 4622 the human Ck (Coloma et al. (1992): Novel vectors for the expression of antibody molecules using variable regions generated by polymerase chain reaction, J. Immunol. Meth., 152: 89-104). The resultant constructs were 1E10VH-PAH4604 and 1E10VK-PAG4622. 
     NS-0 cells were transfected with 10 μg of 1E10VK-PAG4622, and a clone expressing light chain was transfected with 10 μg 1E10VH-PAH4604. In both cases DNA was linearized with Pvul, ethanol precipitated and dissolved in 50 μl of PBS before transfection. 
     Approximately 10 7  cells were harvested by centrifugation and re-suspended in 0.5 ml of PBS together with the digested DNA in an electroporation cuvette. After 10 minutes on ice, the cells were given a pulse of 200 volts and 960 .μF. and left in ice for further 10 minutes. The cells were distributed into a 96 well plate with D′MEM F12 supplemented with 10% fetal calf serum. Two or four days later, selective medium (D′MEM F12 with mycophenolic acid 0.45 μg/mL or histidinol 10 mM, respectively) is added. Transfected clones were visible to the naked eye 14 days later. 
     The presence of human antibody in the medium of wells containing transfected clones was measured by ELISA. Microtiter plate wells were coated with goat anti-human kappa light chain antibody (for human kappa chain producing clones) or anti-human IgG antibody (gamma chain specific) (for the complete antibody producing clones). After washing with PBST (phosphate buffered saline containing 0.05% Tween 20), diluted culture medium of the wells containing transfectants was added to each Microtiter well for one hour at 37° C. The wells were washed with PBS-T, spicy radish peroxidase-conjugated goat anti-human kappa light chain or alkaline phosphatase-conjugated goat anti-human IgG (gamma chain specific) was added, and incubation took place at room temperature for one hour. The wells were washed with PBS-T and substrate buffer containing o-phenylendiamine or p-nitrophenylphosphate, respectively, was added. After half an hour, absorbance was measured at 492 or 405 nm, respectively. 
     Example 5 
     Obtaining Different Versions of the Humanized Antibody 1E10 
     Murine VH1E10 VK1E10 sequences ( FIGS. 6 and 7 ) were compared with human sequences.  FIGS. 8 and 9  shown the most homologous human sequences. Helical amphipatic regions or potential T cell epitopes were searched on murine 1E10 variable region sequences and, according to the method, a judicious strategy for amino acid replacements was established in order to break or humanize potential T cell epitopes inside the murine sequences 
     The analysis on VH1E10 rendered ( FIG. 8 ) 3 amphipatic segments; the first one embraces FR1, the second one embraces FR2, and the third one embraces FR3. It was decided to replace residues at positions 5, 40, 42 and 87 (83 according to Kabat&#39;s numbering) by residues at the same position in the most homologous human sequence. The amino acids Gln, Arg, Glu were replaced by Val, Ala, Gly and Arg, respectively. 
     The replacements were made by overlapping PCR (Kammann et al. (1989) Rapid insertional mutagenesis of DNA by polymerase chain reaction (PCR), Nucleic Acids Res., 17: 5404) using different sets of primers. 
     Primers for mutation at position 5, of the heavy chain were 1, 2, 3 and 4 whose sequences are the following: 
     
       
         
               
               
             
           
               
                   
                 (SEQ ID NO: 45) 
               
               
                   
                 Primer 1: 5′ CAGGTTCAGCTGGTGCAGTCTGGAGCT 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 46) 
               
               
                   
                 Primer 2: 5′ GGGGCTAGCTGAGGAGACTGTGAGAGTGGT 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 47) 
               
               
                   
                 Primer 3: 5′ AGCTCCAGACTGCACCAGCTGAACCTG 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 48) 
               
               
                   
                 Primer 4: 5′GGGGATATCCACCATGG(AG)ATG(CG)AGCTG 
               
               
                   
                 (TG)GT(CA)AT(CG)CTCTT 3′ 
               
             
          
         
       
     
     After checking the point mutation at position 5 by sequencing, mutations at positions 40 and 42 were introduced. 
     Primer for mutations at positions 40 and 42 of the heavy chain: 
     
       
         
               
             
           
               
                 (SEQ ID NO: 49) 
               
               
                 Primer 1: 5′ TGGGTGAGGCAGGCGCCTGGGCAGGGACTTGAG 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 50) 
               
               
                 Primer 2: 5′ GGGGCTAGCTGAGGAGACTGTGAGAGTGGT 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 51) 
               
               
                 Primer 3: 5′ CTCAAGTCCCTGCCCAGGCGCCTGCCTCACCCA 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 52) 
               
               
                 Primer 4: 5′GGGGATATCCACCATGG(AG)ATG(CG)AGCTG(TG) 
               
               
                 GT(CA)AT(CG)CTCTT 3′ 
               
             
          
         
       
     
     After checking the point mutation at positions 40 and 42 by sequencing, mutations at positions 87 (83 according to Kabat&#39;s numbering) was introduced. 
     Primer for mutations at position 87 (83 according to Kabat&#39;s numbering) of the heavy chain: 
     
       
         
               
               
             
           
               
                   
                 (SEQ ID NO: 53) 
               
               
                   
                 Primer 1: 5′ CTCAGCAGGCTGCGGTCTGAGGACTCT 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 54) 
               
               
                   
                 Primer 2: 5′ GGGGCTAGCTGAGGAGACTGTGAGAGTGGT 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 55) 
               
               
                   
                 Primer 3: 5′ AGAGTCCTCAGACCGCAGCCTGCTGAG 3′ 
               
               
                   
               
               
                   
                 (SEQ ID NO: 56) 
               
               
                   
                 Primer 4: 5′GGGGATATCCACCATGG(AG)ATG(CG)AGCTG 
               
               
                   
                 (TG)GT(CA)AT(CG)CTCTT 3′ 
               
             
          
         
       
     
     Other replacements were not made because residues were involved in the three dimensional structure of the binding site. 
     The point mutations were verified by sequencing. The resulting construct was 1E10VHhu and it was cloned in PAH4604 expression vector. The resulting construct was 1E10 VH-PAH4604. 
     The analysis for VKIEI0 rendered also 3 amphipatic segments ( FIG. 9 ); the first segment embraces FR1, the second one embraces CDR1 and the third one embraces FR3. It was decided to replace residues at positions 7, 8 and 15 by residues at the same position in the most homologous human sequence. The amino acids Thr, Thr and Leu were replaced by Ser, Pro and Val, respectively. The replacements were made by overlapping PCR (Kammann et al. (1989) Rapid insertional mutagenesis of DNA by polymerase chain reaction (PCR), Nucleic Acids Res., 17: 5404) using primers 1, 2, 3 and 4, whose sequences are the following: 
     Primers for mutations at positions 7, 8 and 15 of the light chain: 
     
       
         
               
             
           
               
                 (SEQ ID NO: 57) 
               
               
                 Primer 1: 5′CAGATGACACAGTCTCCTTCCTCCCTGTCTGCCTCTGT 
               
               
                 GGGAGA-CAGAGTC 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 58) 
               
               
                 Primer 2: 5′AGCGTCGACTTACGTTT(TG)ATTTCCA(GA)CTT 
               
               
                 (GT)GTCCC 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 59) 
               
               
                 Primer 3: 5′GACTCTGTCTCCCACAGAGGCAGACAGGGAGGAAGGAG 
               
               
                 ACTGTGTCATCTG 3′ 
               
               
                   
               
               
                 (SEQ ID NO: 60) 
               
               
                 Primer 4: 5′GGGGTTAACCACCATGAGG(GT)CCCC(-AT)GCTCA 
               
               
                 G(CT)T(CT)CT(TG)GG(GA) 3′ 
               
             
          
         
       
     
     The point mutations were verified by sequencing. The resulting construct was 1E10 Vkhu and it was cloned in PAG 4622 expression vector. The resultant construct was 1E10 VKhu-PAG4622. 
     To express the humanized antibody 1E10, NS-0 cells were transfected with 1E10 VHhu-PAH4604 and 1E10 VKhu-PAG4622. 
     1E10 humanized antibody was transfected following the same electroporation and detection procedure described previously for the chimeric antibodies. 
     Example 6 
     Biological Activity of Chimeric MAbIE10 
     The biological activity of the chimeric Mab 1E10 was tested by its specific binding to antigen as measured by ELISA. 
     For recombinant MAb 1 E10, Microtiter plates were coated with Mab P3. After washing with PBST (saline phosphate buffered solution containing 0.05% Tween 20), unspecific binding was blocked by incubating with 1% bovine sera albumin (BSA) in PBST for one hour at 37° C. 
     The wells were washed and incubated for 1 hour at 37° C. with purified recombinant Mab 1E10. The wells were washed with PBST and incubated with goat anti-human antibody conjugated with alkaline phosphatase at 37° C. for one hour. Finally, the wells were washed with PBST and substrate buffer containing p-nitrophenylphosphate was added. After half an hour, the absorbance was measured at 405 nm. Chimeric Mab C5 was used as negative control. 
       FIG. 10  shows the specific binding of chimeric Mab 1E10 to Mab P3. 
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1 : VHP3 DNA and deduced amino acid sequences. Sequences are aligned according Kabat&#39;s numbering (Kabat et al. (1991), Sequences of proteins of immunological interest, Fifth Edition, National Institute of Health). CDRs are marked with dotted lines. 
       FIG. 2 : VKP3 DNA and deduced amino acid sequences. Sequences are aligned according Kabat&#39;s numbering (Kabat and collaborators (1991), Sequences of proteins of immunological interest, Fifth Edition, National Institute of Health). CDRs are marked with dotted lines. 
       FIG. 3 : VHP3 was aligned with the most homologous human sequence. Amphipatic segments are underlined and CDRs are in bold letters. 
       FIG. 4 : VKP3 was aligned with the most homologous human sequence. Amphipatic segments are underlined and CDRs are in bold letters. 
       FIG. 5 : Specific binding to GM3(NeuGc) by chimeric Mab P3. Different concentrations of Mab P3 and MAb TI (negative control) were tested by ELISA. Microtiter plates were coated with GM3(NeuGc) and GM3(NeuAc) (negative control) ganglioside in methanol and specific binding was measured. 
       FIG. 6 : VH1E10 DNA and deduced amino acid sequences. Sequences are aligned according Kabat&#39;s numbering (Kabat and collaborators (1991), Sequences of proteins of immunological interest, Fifth Edition, National Institute of Health). CDRs are marked with dotted lines. 
       FIG. 7 : VK1E10 DNA and deduced amino acid sequences. Sequences are aligned according Kabat&#39;s numbering (Kabat et al. (1991), Sequences of proteins of immunological interest, Fifth Edition, National Institute of Health). CDRs are marked with dotted lines. 
       FIG. 8 : VH1E10 was aligned with the most homologous human sequence. Amphipatic segments are underlined and CDRs are in bold letters. 
       FIG. 9 : VK1E10 was aligned with the most homologous human sequence. Amphipatic segments are underlined and CDRs are in bold letters. 
       FIG. 10 : Specific binding of murine Mab P3 by chimeric Mab 1E10. Different concentrations of Mab 1E10 and MAb C5 (negative control) were tested by ELISA. Microtiter plates were coated with Mab P3 and Mab A3 (negative control) and specific binding was measured.