Patent Publication Number: US-9416191-B2

Title: Pharmaceutical composition for treatment and/or prevention of cancer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of copending application Ser. No. 13/576,953, filed on Aug. 3, 2012, which is a National Phase of PCT International Application No. PCT/JP2011/052413 filed on Feb. 4, 2011, which claims priority under 35 U.S.C. §119(a) to Patent Application Nos. 2010-023454 and 2010-183162 filed in Japan on Feb. 4, 2010 and Aug. 18, 2010 respectively. All of the above applications are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a novel pharmaceutical use of an antibody against CAPRIN-1 or a fragment thereof, as an agent, for treating and/or preventing a cancer. 
     BACKGROUND ART 
     Cancer is the leading cause of death. Currently conducted therapy comprises mainly surgical therapy in combination with radiation therapy and chemotherapy. In spite of the development of new operative procedures and the discovery of new anticancer agents in recent years, cancer treatment results have not been much improved recently, excluding that for some types of cancer. Recent advances in molecular biology or cancer immunology lead to identification of antibodies specifically reacting with cancer, cancer antigens to be recognized by cytotoxic T cells, genes encoding cancer antigens, and the like. Demands on specific cancer therapies targeting cancer antigens are increasing (Non-patent Literature 1). 
     In cancer therapy, it is desirable that peptides, polypeptides, or proteins recognized as antigens be almost absent in normal cells, but they be present specifically in cancer cells, in order to alleviate side effects. In 1991, Boon et al., (Ludwig Institute for Cancer Research, Belgium) isolated a human melanoma antigen MAGE1 recognized by CD8-positive T cells by the cDNA expression cloning method using autologous cancer cell lines and cancer-reactive T cells (Non-patent Literature 2). Thereafter, the SEREX (serological identification of antigens by recombinant expression cloning) method that comprises identifying tumor antigens recognized by antibodies that are produced in vivo in response to autologous cancer of a cancer patient by gene expression cloning techniques was reported (Non-patent Literature 3 and Patent Literature 1). With the use of this method, some cancer antigens, which are almost never expressed in normal cells but are specifically expressed in cancer cells, were isolated (Non-patent Literatures 4-9). Furthermore, clinical trials were conducted with cell therapies targeting some cancer antigens using immunocytes specifically reactive with cancer antigens, or cancer-specific immunotherapies using vaccines or the like containing cancer antigens. 
     Meanwhile, in recent years, various antibody medicines which target antigenic proteins on cancer cells for cancer treatment have appeared throughout the world. Antibody medicines exhibit some pharmacological effects as cancer specific therapeutic agents and are thus attracting attention. However, most antigen proteins to be targeted are also expressed in normal cells, so that not only cancer cells, but also normal cells expressing antigens are also damaged as a result of antibody administration. The resulting side effects cause for concern. Therefore, it is expected that identification of cancer antigens that are specifically expressed on the surface of a cancer cell and use of antibodies targeting the cancer antigens as pharmaceuticals will realize treatment with antibody medicines with lower side effects. 
     Cytoplasmic- and proliferation-associated protein 1 (CAPRIN-1) is expressed when normal cells at the resting phase are activated or undergo cell division, and it is an intracellular protein known to form intracellular stress granules with RNA within cells, so as to be involved in mRNA transport and translational regulation. Meanwhile, many other names that represent CAPRIN-1 exist, such as GPI-anchored membrane protein 1 or membrane component surface marker 1 protein (M11S1), as if such proteins had been known to be cell membrane proteins. These names originated from a report that the gene sequence of CAPRIN-1 is a membrane protein having a GPI-binding region and expressed in colorectal cancer cells (Non-patent Literature 10). However, the gene sequence of CAPRIN-1 provided in this report was later revealed to be wrong. The following has recently been reported; i.e., deletion of a single nucleotide in the gene sequence of CAPRIN-1 registered at GenBank or the like causes a frame shift, so that 80 amino acids are lost from the C-terminus, resulting in generation of an artifact (74 amino acids) which corresponds to the GPI-binding portion in the previous report, and additionally, another error is also present 5′ of the gene sequence, so that 53 amino acids were lost from the N-terminus (Non-patent Literature 11). It has been also recently reported that the protein encoded by the gene sequence of CAPRIN-1 registered at GenBank or the like is not a cell membrane protein (Non-patent Literature 11). 
     In addition, on the basis of the report of Non-patent Literature 10 that CAPRIN-1 is a cell membrane protein, Patent Literatures 2 and 3 describe that CAPRIN-1 (as a cell membrane protein) under the name of M11S1 can be used as a target of an antibody medicine in cancer therapy, although working examples do not describe treatment using an antibody against the protein. However, as reported in Non-patent Literature 11, it has been commonly believed from the time of the filing of Patent Literature 2 to date that CAPRIN-1 is not expressed on the surface of a cell. The contents of Patent Literatures 2 and 3 based only on incorrect information that CAPRIN-1 is a cell membrane protein should not clearly be understood as common general knowledge for persons skilled in the art. 
     PRIOR ART LITERATURE 
     Patent Literature 
     
         
         Patent Literature 1: U.S. Pat. No. 5,698,396 
         Patent Literature 2: US2008/0075722 
         Patent Literature 3: WO2005/100998 
       
    
     Non-Patent Literature 
     
         
         Non-patent Literature 1: Tsuyoshi Akiyoshi, “Gan To Kagaku-Ryoho (Cancer and Chemotherapy),” 1997, Vol. 24, p 551-519 (Cancer and Chemotherapy Publishers, Inc., Japan) 
         Non-patent Literature 2 Bruggen P. et al., Science, 254: 1643-1647 (1991) 
         Non-patent Literature 3: Proc. Natl. Acad. Sci. U.S.A, 92: 11810-11813 (1995) 
         Non-patent Literature 4: Int. J. Cancer, 72: 965-971 (1997) 
         Non-patent Literature 5: Cancer Res., 58: 1034-1041 (1998) 
         Non-patent Literature 6: Int. J. Cancer, 29: 652-658 (1998) 
         Non-patent Literature 7: Int. J. Oncol., 14: 703-708 (1999) 
         Non-patent Literature 8: Cancer Res., 56: 4766-4772 (1996) 
         Non-patent Literature 9: Hum. Mol. Genet6: 33-39, 1997 
         Non-patent Literature 10: J. Biol. Chem., 270: 20717-20723, 1995 
         Non-patent Literature 11: J. Immunol., 172: 2389-2400, 2004 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     Objects of the present invention are to identify a cancer antigen protein specifically expressed on the surface of a cancer cell and to provide the use of an antibody targeting the cancer antigen protein as an agent for treating and/or preventing a cancer. 
     Means for Solving the Problem 
     As a result of intensive studies, the present inventors have now obtained a cDNA encoding a protein that binds to an antibody existing in sera from dogs with breast cancer by the SEREX method using both cDNA libraries prepared from dog testis tissues and sera of dogs with breast cancer. The present inventors have now further prepared CAPRIN-1 proteins having the even-numbered amino acid sequences of SEQ ID NOS: 2 to 30 and antibodies against such CAPRIN-1 proteins based on the obtained dog gene and the corresponding human, cattle, horse, mouse, and chicken homologous genes. Thus, the present inventors have now found that CAPRIN-1 is specifically expressed in breast cancer, brain tumor, leukemia, lymphoma, lung cancer, uterine cervix cancer, bladder cancer, esophageal cancer, colorectal cancer, gastric cancer, renal cancer, ovarian cancer, prostate cancer, and fibrosarcoma, and that a portion of the CAPRIN-1 protein is specifically expressed on the surface of each cancer cell. The present inventors have thus now found that an antibody or antibodies against the portion of CAPRIN-1 expressed on the surface of each cancer cell is/are cytotoxic to the CAPRIN-1-expressing cancer cells. On the basis of these findings, the present invention as described below was completed. 
     The present invention has the following characteristics. 
     The present invention provides a pharmaceutical composition for treating and/or preventing a cancer, comprising an antibody or a fragment thereof as an active ingredient having immunological reactivity with a partial polypeptide of CAPRIN-1, wherein CAPRIN-1 is represented by any of the even-numbered sequences of SEQ ID NOS: 2 to 30, and wherein the partial polypeptide comprises the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more sequence identity with the amino acid sequence of SEQ ID NO: 37. 
     In an embodiment, the above cancer is breast cancer, brain tumor, leukemia, lymphoma, lung cancer, uterine cervix cancer, bladder cancer, esophageal cancer, colorectal cancer, gastric cancer, renal cancer, ovarian cancer, prostate cancer, or fibrosarcoma. 
     In another embodiment, the antibody is a monoclonal antibody or a polyclonal antibody. 
     In another embodiment, the antibody is a human antibody, humanized antibody, chimeric antibody, single chain antibody, or bispecific antibody. 
     This description includes all or part of the contents as disclosed in the descriptions and/or drawings of Japanese Patent Application Nos. 2010-023454 and 2010-183162, from which the present application claims the priority. 
     Effects of the Invention 
     The antibody against CAPRIN-1 used in the present invention is cytotoxic to cancer cells. As such, the antibody against CAPRIN-1 is useful for treating or preventing cancers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the expression patterns of genes encoding CAPRIN-1 proteins in normal tissues and tumor cell lines. Reference No. 1 indicates the expression patterns of genes encoding CAPRIN-1 proteins, and Reference No. 2 indicates the expression patterns of GAPDH genes. 
         FIG. 2  shows the cytotoxicity to the MDA-MB-157 breast cancer cell line expressing CAPRIN-1 by anti-CAPRIN-1 polyclonal antibodies that are reactive with the surfaces of the cancer cells. Reference No. 3 indicates the activity exhibited when the anti-CAPRIN-1 polyclonal antibody #1 was added. Reference No. 4 indicates the activity exhibited when a control antibody from a rabbit not immunized with an antigen was added. Reference No. 5 indicates the activity exhibited when PBS was added instead of the antibodies. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     The anti-tumor activity of an antibody against a polypeptide represented by any of the even-numbered sequences of SEQ ID NOS: 2 to 30 used in the present invention can be evaluated by examining in vivo suppression of tumor growth in animals with cancer, or, examining whether or not the antibody exhibits cytotoxicity via immunocytes or complements to tumor cells expressing the polypeptide in vitro, as described later. 
     In the context, the nucleotide sequences of polynucleotides encoding proteins comprising the even-numbered amino acid sequences (i.e., SEQ ID NOS: 2, 4, 6, . . . , 28, 30) of SEQ ID NOS: 2 to 30 are represented by the odd-numbered sequences (i.e., SEQ ID NOS: 1, 3, 5, . . . , 27, 29) of SEQ ID NOS: 1 to 29. 
     The amino acid sequences that are represented by SEQ ID NOS: 6, 8, 10, 12, and 14 in the Sequence Listing disclosed herein are the amino acid sequences of CAPRIN-1 isolated as polypeptides, which bind to antibodies specifically existing in serum from a dog with cancer, through the SEREX method using a cDNA library from dog testis tissue and the serum of a dog with breast cancer. The amino acid sequences represented by SEQ ID NOS: 2 and 4 are the amino acid sequences of CAPRIN-1 isolated as human homologues. The amino acid sequence represented by SEQ ID NO: 16 is the amino acid sequence of CAPRIN-1 isolated as a cattle homologue. The amino acid sequence represented by SEQ ID NO: 18 is the amino acid sequence of CAPRIN-1 isolated as a horse homologue. The amino acid sequences represented by SEQ ID NOS: 20 to 28 are the amino acid sequences of CAPRIN-1 isolated as mouse homologues. The amino acid sequence represented by SEQ ID NO: 30 is the amino acid sequence of CAPRIN-1 isolated as a chicken homologue (see Example 1 described later). CAPRIN-1 is known to be expressed when normal cells in the resting phase are activated or give rise to cell division. 
     It was known that CAPRIN-1 was not expressed on cell surfaces. However, as a result of the examination by the present inventors, it has now revealed that a portion of the CAPRIN-1 protein is expressed on the surfaces of various cancer cells. It has thus been now revealed that an antibody recognizing a partial polypeptide of the CAPRIN-1 protein, which comprises the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more, preferably 85% or more, more preferably 90% or more, further preferably 95% or more sequence identity with the amino acid sequence of SEQ ID NO: 37, exhibits anti-tumor activity. Examples of the antibody of the present invention include all antibodies which bind to a fragment of the above CAPRIN-1 protein and exhibit anti-tumor activity. 
     The above-described anti-CAPRIN-1 antibody used in the present invention may be any type of antibody as long as it can exhibit anti-tumor activity. Examples of such antibodies include monoclonal antibodies, polyclonal antibodies, recombinant antibodies, such as synthetic antibodies, multispecific antibodies, humanized antibodies, chimeric antibodies, and single chain antibodies (scFv), human antibodies, and fragments thereof, such as Fab, F(ab′) 2 , and Fv. These antibodies and fragments thereof can be prepared by methods known by persons skilled in the art. In the present invention, antibodies having immunological reactivity with CAPRIN-1 proteins or partial (poly)peptides thereof (that is, binding to CAPRIN-1 proteins via antigen-antibody reaction) and preferably antibodies capable of specifically binding to CAPRIN-1 proteins are desired. Preferably, they are monoclonal antibodies. Polyclonal antibodies may also be used as long as homogenous antibodies can be stably produced. Also, when a subject is a human, human antibodies or humanized antibodies are desired in order to avoid or suppress rejection. The term “specifically binding to a CAPRIN-1 protein” as used herein means that the antibody specifically binds to a CAPRIN-1 protein, but does not substantially bind to proteins other than the CAPRIN-1 protein.” 
     The anti-tumor activity of an antibody that can be used in the present invention can be evaluated as described below by examining in vivo the suppression of the tumor growth in animals with cancer, or, by examining whether or not it exhibits in vitro an activity of cytotoxicity, which is mediated by immunocytes or complements, to tumor cells expressing the polypeptide. 
     Furthermore, examples of the subject for cancer treatment and/or prevention in the present invention include mammals, such as humans, pet animals, domestic animals, and animals for competition. A preferable subject is a human. 
     Preparation of antigens and antibodies and pharmaceutical compositions relating to the present invention are described below. 
     &lt;Preparation of Antigens for Antibody Preparation&gt; 
     Proteins or fragments thereof to be used as sensitizing antigens for obtaining anti-CAPRIN-1 antibodies used in the present invention may be derived from any animal species without particular limitation, such as humans, dogs, cattle, horses, mice, rats, and chickens. However, proteins or fragments thereof are preferably selected in consideration of compatibility with parent cells used for cell fusion. In general, mammal-derived proteins are preferred and, in particular, human-derived protein is preferred. For example, when CAPRIN-1 is human CAPRIN-1, the human CAPRIN-1 protein, a partial peptide thereof, or cells expressing human CAPRIN-1 can be used. 
     The nucleotide sequences and the amino acid sequences of human CAPRIN-1 and homologues thereof can be obtained by accessing GenBank (NCBI, U.S.A.) and using an algorithm such as BLAST or FASTA (Karlin and Altschul, Proc. Natl. Acad. Sci. U.S.A., 90: 5873-5877, 1993; Altschul et al., Nucleic Acids Res. 25: 3389-3402, 1997). 
     In the present invention, on the basis of the nucleotide sequence (SEQ ID NO: 1 or 3) or the amino acid sequence (SEQ ID NO: 2 or 4) of human CAPRIN-1, a target nucleic acid or a target protein comprises a sequence having 70% to 100%, preferably 80% to 100%, more preferably 90% to 100%, even more preferably 95% to 100% (e.g., 97% to 100%, 98% to 100%, 99% to 100%, or 99.5% to 100%) sequence identity with the nucleotide sequence or the amino acid sequence of the ORF or the mature portion of human CAPRIN-1. As use herein, the term “% sequence identity” refers to a percentage (%) of identical amino acids (or nucleotides) relative to the total number of amino acids (or nucleotides), when two sequences are aligned to achieve the highest similarity with or without introduction of gaps. 
     The length of a fragment of CAPRIN-1 protein ranges from the amino acid length of an epitope (antigenic determinant), which is the minimum unit recognized by an antibody, to a length less than the full length of the protein. The term “epitope” refers to a polypeptide fragment having antigenicity or immunogenicity in mammals, preferably in humans, and the minimum unit of the epitope consists of about 7 to 12 amino acids, for example 8 to 11 amino acids. Therefore, the antibody of the present invention is characterized by recognizing a fragment consisting of about 7 to 12 amino acids (e.g., 8 to 11 amino acids) in the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more, preferably 85% or more, more preferably 90% or more, further preferably 95% or more sequence identity with the amino acid sequence of SEQ ID NO: 37. 
     The polypeptides comprising the above-mentioned human CAPRIN-1 protein or partial peptides of the protein, can be synthesized by a chemical synthesis method, such as the Fmoc method (fluorenylmethyloxycarbonyl method) or the tBoc method (t-butyloxycarbonyl method) (Edited by The Japanese Biochemical Society, Seikagaku Jikken Koza (Biochemical Experimental Lecture Series) 1, Protein Chemistry IV, Chemical Modification and Peptide Synthesis, TOKYO KAGAKU DOZIN (Japan), 1981). Alternatively, the above-mentioned polypeptides may also be synthesized by conventional methods using various commercially available peptide synthesizers. Furthermore, with the use of known genetic engineering techniques (e.g., Sambrook et al., Molecular Cloning, 2 nd  Edition, Current Protocols in Molecular Biology (1989), Cold Spring Harbor Laboratory Press, Ausubel et al., Short Protocols in Molecular Biology, 3 rd  Edition, A compendium of Methods from Current Protocols in Molecular Biology (1995), John Wiley &amp; Sons), a polynucleotide encoding the above polypeptide is prepared and then incorporated into an expression vector, which is subsequently introduced into a host cell in order to produce a polypeptide of interest in the host cell, and then recover it. 
     The polynucleotides encoding the above polypeptides can be easily prepared by known genetic engineering techniques or conventional techniques using a commercially available nucleic acid synthesizer. For example, DNA comprising the nucleotide sequence of SEQ ID NO: 1 can be prepared by PCR using a human chromosomal DNA or cDNA library, as a template, and a pair of primers designed to be able to amplify the nucleotide sequence represented by SEQ ID NO: 1. PCR conditions can be appropriately determined. For example, PCR conditions comprise conducting 30 cycles of the reaction cycle of: denaturation at 94° C. for 30 seconds; annealing at 55° C. for 30 seconds to 1 minute; and extension at 72° C. for 2 minutes, using a thermostable DNA polymerase (e.g., Taq polymerase or Pfu polymerase) and PCR buffer containing Mg 2+ , followed by reacting at 72° C. for 7 minutes. However, the PCR conditions are not limited to the above example. PCR techniques, conditions, and the like are described in Ausubel et al., Short Protocols in Molecular Biology, 3 rd  Edition, A compendium of Methods from Current Protocols in Molecular Biology (1995), John Wiley &amp; Sons (particularly Chapter 15). 
     Also, on the basis of the nucleotide sequence and amino acid sequence information represented by SEQ ID NOS: 1 to 30 in the Sequence Listing described herein, appropriate probes or primers are prepared, and then a cDNA library of a human or the like is screened using them, so that desired DNA can be isolated. A cDNA library is preferably constructed from cells, organs or tissues, which express proteins having even-numbered sequences of SEQ ID NOS: 2 to 30. Examples of such cells or tissues include cells or tissues derived from testis, and cancers or tumors, such as leukemia, breast cancer, lymphoma, brain tumor, lung cancer, colorectal cancer, and the like. Procedures such as the preparation of probes or primers, construction of a cDNA library, screening of a cDNA library, and cloning of target genes are known by a person skilled in the art and can be carried out by the methods described in Sambrook et al., Molecular Cloning, 2 nd  Edition, Current Protocols in Molecular Biology (1989), Ausbel et al., (above), and the like. DNA encoding a human CAPRIN-1 protein or a partial peptide thereof can be obtained from the thus obtained DNA. 
     The host cells may be any cells, as long as they can express the above-mentioned polypeptide. Examples of prokaryotic cells include, but are not limited to,  Escherichia coli  and the like. Examples of eukaryotic cells include, but are not limited to, mammalian cells, such as monkey kidney cells (COS1) and Chinese hamster ovary cells (CHO), human fetal kidney cell line (HEK293), fetal mouse skin cell line (NIH3T3), yeast cells such as budding yeast and fission yeast, silkworm cells, and  Xenopus  oocyte. 
     When prokaryotic cells are used as host cells, an expression vector used herein contains an origin replicable within prokaryotic cells, a promoter, a ribosome-binding site, a multiple cloning site, a terminator, a drug resistance gene, an auxotrophic complementary gene, and the like. Examples of  Escherichia coli  expression vector include a pUC-based vector, pBluescript II, a pET expression system, and a pGEX expression system. DNA encoding the above polypeptide is incorporated into such an expression vector, prokaryotic host cells are transformed with the vector, the thus obtained transformed cells are cultured, and thus the polypeptide encoded by the DNA can be expressed in prokaryotic host cells. At this time, the polypeptide can also be expressed as a fusion protein with another protein. 
     When eukaryotic cells are used as host cells, an expression vector used herein is an expression vector for eukaryotic cells, which contains a promoter, a splicing region, a poly(A) addition site, and the like. Examples of such an expression vector include pKA1, pCDM8, pSVK3, pMSG, pSVL, pBK-CMV, pBK-RSV, EBV vector, pRS, pcDNA3, and pYES2. In a manner similar to the above, DNA encoding the above polypeptide is incorporated into such an expression vector, eukaryotic host cells are transformed with the vector, the thus obtained transformed cells are cultured, and thus the polypeptide encoded by the DNA can be expressed in eukaryotic host cells. When pIND/V5-His, pFLAG-CMV-2, pEGFP-N1, pEGFP-C1, or the like is used as an expression vector, the above polypeptide can be expressed as a fusion protein to which a tag from among various tags such as a His tag (e.g., (His) 6 -(His) 10 ), a FLAG tag, a myc tag, an HA tag, and GFP has been added. 
     For introduction of an expression vector into host cells, a known method can be employed, such as electroporation, a calcium phosphate method, a liposome method, a DEAE dextran method, microinjection, viral infection, lipofection, and binding to a cell membrane-permeable peptide. 
     The polypeptide of interest can be isolated and purified from host cells by a combination of known separation procedures. Examples of such procedures include, but are not limited to, treatment with a denaturing agent such as urea or a surfactant, ultrasonication, enzymatic digestion, salting-out or solvent fractionation and precipitation, dialysis, centrifugation, ultrafiltration, gel filtration, SDS-PAGE, isoelectric focusing, ion exchange chromatography, hydrophobic chromatography, affinity chromatography, and reverse phase chromatography. 
     &lt;Antibody Structure&gt; 
     An antibody is a heteromultimeric glycoprotein that generally contains at least two heavy chains and two light chains. Antibodies other than IgM is an antibody is an about 150-kDa heterotetramer glycoprotein composed of two identical light (L) chains and two identical heavy (H) chains. Typically, each light chain is connected to a heavy chain via one disulfide covalent bond, however, the number of disulfide bonds between heavy chains of various immunoglobulin isotypes is varied. Each heavy chain or each light chain also has an intrachain disulfide bond. Each heavy chain has a variable domain (VH region) on one end followed by several constant regions. Each light chain has a variable domain (VL region) and has one constant region on an end opposite to the other end. The constant region of a light chain is aligned with the first constant region of a heavy chain, and a light chain variable domain is aligned with a heavy chain variable domain. A specific region of an antibody variable domain exhibits specific variability that is referred to as a complementarity determining region (CDR), so that it imparts binding specificity to the antibody. A portion of a variable region, which is relatively conserved, is referred to as a framework region (FR). Complete heavy chain and light chain variable domains separately contains four FRs ligated via three CDRs. The three CDRs in a heavy chain are referred to as CDRH1, CDRH2, and CDRH3 in this order from the N-terminus. Similarly, in the case of a light chain, CDRLs are referred to as CDRL1, CDRL2, and CDRL3. CDRH3 is most important for the binding specificity of an antibody to an antigen. Also, the CDRs of each chain are retained together in a state of being adjacent to each other due to the FR regions, contributing to the formation of the antigen binding site of the antibody together with CDRs from the other chain. A constant region does not directly contribute to the binding of an antibody to an antigen, but exhibits various effector functions, such as involvement in antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis via binding to an Fcγ receptor, the rate of half-life/clearance via a neonate Fc receptor (FcRn), and complement-dependent cytotoxicity (CDC) via a C1q constituent of the complement cascade. 
     &lt;Preparation of Antibody&gt; 
     The term “anti-CAPRIN-1 antibody” as used herein refers to an antibody having immunological reactivity with a full-length CAPRIN-1 protein or a fragment thereof. 
     As used herein, the term “immunological reactivity” refers to the property of in vivo binding of an antibody to a CAPRIN-1 antigen. Through such an in vivo binding, the function of damaging tumor (e.g., death, suppression, or degeneration) is exhibited. Specifically, an antibody used in the present invention may be any type of antibody, as long as it binds to a CAPRIN-1 protein so as to be able to damage tumor, such as leukemia, lymphoma, breast cancer, brain tumor, lung cancer, esophageal cancer, gastric cancer, renal cancer, colorectal cancer, ovarian cancer, prostate cancer, or fibrosarcoma. 
     Examples of an antibody include a monoclonal antibody, a polyclonal antibody, a synthetic antibody, a multispecific antibody, a human antibody, a humanized antibody, a chimeric antibody, a single chain antibody, and an antibody fragment (e.g., Fab and F(ab′) 2 ). Also, an antibody may be an immunoglobulin molecule of any class such as IgG, IgE, IgM, IgA, IgD, or IgY, or any subclass such as IgG1, IgG2, IgG3, IgG4, IgA1, or IgA2. 
     The antibody may further be modified by, in addition to glycosylation, acetylation, formylation, amidation, phosphorylation, pegylation (PEG), or the like. 
     Various antibody preparation examples are as described below. 
     When the antibody is a monoclonal antibody, for example, the breast cancer cell line SK-BR-3 expressing CAPRIN-1 is administered to a mouse for immunization, the spleen is removed from the mouse, cells are separated, and then the cells and mouse myeloma cells are fused. From among the thus obtained fusion cells (hybridomas), a clone producing an antibody having the effect of suppressing cancer cell proliferation is selected. A hybridoma producing a monoclonal antibody that has the effect of suppressing cancer cell proliferation is isolated, the hybridoma is cultured, and then an antibody is purified from the culture supernatant by general affinity purification, so that the antibody can be prepared. 
     The hybridoma producing a monoclonal antibody can also be prepared as described below, for example. First, an animal is immunized with a sensitizing antigen according to a known method. A general method is carried out by injecting a sensitizing antigen to a mammal intraperitoneally or subcutaneously. Specifically, a sensitizing antigen is diluted with PBS (Phosphate-Buffered Saline), saline, or the like to an appropriate amount, followed by suspension. The resultant is then mixed with an appropriate amount of a general adjuvant as necessary, such as Freund&#39;s complete adjuvant. After emulsification, the solution was administered to a mammal several times every 4 to 21 days. Furthermore, an appropriate carrier can also be used upon immunization with a sensitizing antigen. 
     A mammal is immunized as described above. After confirmation of a rise in a desired serum antibody level, immunized cells are collected from the mammal and then subjected to cell fusion. Preferable immunized cells are particularly splenocytes. 
     Mammalian myeloma cells are used as the other parent cells to be fused with the immunized cells. As the myeloma cells, various known cell lines are preferably used, such as P3U1 (P3-X63Ag8U1), P3 (P3x63Ag8. 653) (J. Immunol. (1979) 123, 1548-1550), P3x63Ag8U.1 (Current Topics in Microbiology and Immunology (1978) 81, 1-7), NS-1 (Kohler. G. and Milstein, C. Eur. J. Immunol. (1976) 6, 511-519), MPC-11 (Margulies. D. H. et al., Cell (1976) 8, 405-415), SP2/0 (Shulman, M. et al., Nature (1978) 276, 269-270), FO (deSt. Groth, S. F. et al., J. Immunol. Methods (1980) 35, 1-21), S194 (Trowbridge, I. S. J. Exp. Med. (1978) 148, 313-323), and R210 (Galfre, G. et al., Nature (1979) 277, 131-133). 
     Fusion of the immunized cell and the myeloma cell can be carried out according to basically a known method such as Kohler and Milstein&#39;s technique (Kohler, G. and Milstein, C. Methods Enzymol. (1981) 73, 3-46), for example. 
     More specifically, the above cell fusion is carried out, for example, in the presence of a cell fusion accelerator in a usual nutrient culture medium. As this fusion accelerator, polyethyleneglycol (PEG), Sendai virus (HVJ), or the like is used. If desired, an auxiliary agent such as dimethylsulfoxide may be added and used in order to enhance fusion efficiency. 
     The ratio of the immunized cells to the myeloma cells to be used herein can be arbitrarily set. For example, the number of immunized cells that are preferably used is one to ten times the number of myeloma cells. As a culture medium to be used for the above-mentioned cell fusion, an RPMI1640 culture medium suitable for proliferation of the above-mentioned myeloma cell line, an MEM culture medium, and other culture media usually used for culturing this kind of cell can be used. Further, liquid that is supplemental to serum such as fetal bovine serum (FCS) can be used together therewith. 
     Cell fusion can be performed by thoroughly mixing the predetermined amounts of the above immunized cells and the myeloma cells in the above culture medium, and a PEG solution (for example, having an average molecular weight ranging from about 1000 to 6000) prewarmed at about 37° C. is added usually at a concentration of 30%-60% (w/v) and mixed, thereby forming a culture containing hybridomas of interest. Next, a suitable culture medium is successively added to the thus-obtained culture, which is then centrifuged to remove the supernatant, and this procedure is repeated to remove the cell fusion agent or the like which is not preferable for the growth of hybridomas. 
     The thus obtained hybridomas are cultured for selection in a usual selection culture medium (e.g., a HAT culture medium containing hypoxanthine, aminopterin and thymidine). Culturing in this HAT culture medium is continued for a sufficient period of time (usually several days to several weeks) so that the cells (non-fused cells) other than the target hybridomas die. Subsequently, screening and single cloning of the hybridoma which produces an antibody of interest are performed using the general limiting dilution method. 
     The above hybridomas are obtained by an immunizing non-human animal with an antigen. In addition to this method, hybridomas that produce a human antibody having desired activity (e.g., activity of suppressing cell proliferation) can also be obtained by in vitro sensitizing human lymphocytes, such as human lymphocytes that have been infected with the EB virus, with a protein, a protein-expressing cell, or a lysate thereof, followed by fusing of the thus sensitized lymphocytes with human-derived myeloma cells having an ability to permanently divide, such as U266 (registration no. TIB 196). 
     The thus prepared hybridoma that produces a monoclonal antibody of interest can be passaged in a general culture medium and can be stored in liquid nitrogen over a long period of time. 
     Specifically, a hybridoma can be prepared by immunizing by a general immunization method using, as a sensitizing antigen, a desired antigen or a cell that expresses the desired antigen, fusing the thus obtained immunized cell with a known parent cell by a general cell fusion method, and then screening for a monoclonal antibody-producing cell (i.e., a hybridoma) by a general screening method. 
     Another example of an antibody that can be used in the present invention is a polyclonal antibody. A polyclonal antibody can be obtained as described below, for example. 
     A small animal, such as a mouse, a human antibody-producing mouse, or a rabbit, is immunized with a natural CAPRIN-1 protein, a recombinant CAPRIN-1 protein expressed in a microorganism such as  Escherichia coli  in the form of a fusion protein with GST or the like, or a partial peptide thereof, and then serum is obtained. The serum is purified by ammonium sulfate precipitation, protein A column, protein G column, DEAE ion exchange chromatography, affinity column to which a CAPRIN-1 protein or a synthetic peptide has been coupled, or the like, so that a polyclonal antibody can be prepared. 
     As a human antibody-producing mouse, a KM mouse (Kirin Pharma/Medarex) and a Xeno mouse (Amgen) are known (e.g., International Patent Publications WO02/43478 and WO02/092812), for example. When such a mouse is immunized with a CAPRIN-1 protein or a fragment thereof, a complete human polyclonal antibody can be obtained from blood. Also, splenocytes are collected from the immunized mouse and then a human-type monoclonal antibody can be prepared by a method for fusion with myeloma cells. 
     An antigen can be prepared according to a method using animal cells (JP Patent Publication (Kohyo) No. 2007-530068) or baculovirus (e.g., International Patent Publication WO98/46777), for example. When an antigen has low immunogenicity, the antigen may be bound to a macromolecule having immunogenicity, such as albumin, and then immunization is carried out. 
     Furthermore, an antibody gene is cloned from said hybridoma and then incorporated into an appropriate vector. The vector is then introduced into a host, and then the genetically recombined antibody produced using gene recombination techniques can be used (e.g., see Carl, A. K. Borrebaeck, James, W. Larrick, THERAPEUTIC MONOCLONAL ANTIBODIES, Published in the United Kingdom by MACMILLAN PUBLISHERS LTD, 1990). Specifically, the cDNA of a variable region (V region) of an antibody is synthesized from the mRNA of the hybridoma using reverse transcriptase. When DNA encoding the V region of an antibody of interest can be obtained, this DNA is ligated to DNA encoding the constant region (C region) of a desired antibody, and then the resultant fusion product is incorporated into an expression vector. Alternatively, DNA encoding the V region of an antibody may be incorporated into an expression vector containing the DNA for the C region of an antibody. At this time, the DNA can be incorporated into an expression vector so that it is expressed under the control of expression control regions, such as enhancer and promoter. Next, host cells are transformed with the expression vector, so that the antibody can be expressed. 
     The anti-CAPRIN-1 antibody of the present invention is preferably a monoclonal antibody. However, the anti-CAPRIN-1 antibody may also be a polyclonal antibody or a genetically-modified antibody (e.g., a chimeric antibody or a humanized antibody), for example. 
     Examples of a monoclonal antibody include human monoclonal antibodies, non-human animal monoclonal antibodies (e.g., a mouse monoclonal antibody, a rat monoclonal antibody, a rabbit monoclonal antibody, and a chicken monoclonal antibody), and chimeric monoclonal antibodies. A monoclonal antibody can be prepared by culturing a hybridoma obtained by cell fusion of a splenocyte from a non-human mammal (e.g., a mouse, a human antibody-producing mouse, a chicken, or a rabbit) immunized with a CAPRIN-1 protein, with a myeloma cell. A chimeric antibody is prepared by combining sequences from different animals, such as an antibody comprising heavy chain and light chain variable regions of a mouse antibody and heavy chain and light chain constant regions of a human antibody. A chimeric antibody can be prepared using a known method. For example, a chimeric antibody can be obtained by ligating DNA encoding an antibody V region to DNA encoding a human antibody C region, incorporating the resultant fusion product into an expression vector, and then introducing the vector into a host for production of the chimeric antibody. 
     In Examples described later, monoclonal antibodies having immunological reactivity with a partial polypeptide of CAPRIN-1 were prepared, wherein CAPRIN-1 is represented by any of the even-numbered sequences of SEQ ID NOS: 2 to 30, and wherein the partial polypeptide comprises the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more sequence identity with the amino acid sequence of SEQ ID NO: 37. The anti-tumor effects of the monoclonal antibodies were confirmed. These monoclonal antibodies comprise a heavy chain variable (VH) region comprising the amino acid sequence of SEQ ID NO: 43 or 63 and a light chain variable (VL) region comprising the amino acid sequence of SEQ ID NO: 47, 51, or 67, wherein: the VH region comprises CDR1 represented by the amino acid sequence of SEQ ID NO: 40 or 60, CDR2 represented by the amino acid sequence of SEQ ID NO: 41 or 61, and CDR3 represented by the amino acid sequence of SEQ ID NO: 42 or 62; and the VL region comprises CDR1 represented by the amino acid sequence of SEQ ID NO: 44, 48, or 64, CDR2 represented by the amino acid sequence of SEQ ID NO: 45, 49, or 65, and CDR3 represented by the amino acid sequence of SEQ ID NO: 46, 50, or 66. 
     Examples of a polyclonal antibody include an antibody obtained by immunizing a human antibody-producing animal (e.g., a mouse) with a CAPRIN-1 protein. 
     A humanized antibody is a modified antibody that is also referred to as a reshaped human antibody. A humanized antibody can be constructed by transplanting CDRs of an antibody from an immunized animal into the complementarity determining regions of a human antibody. General gene recombination techniques therefor are also known. 
     Specifically, DNA sequences designed to have each of the CDRs of a mouse or chicken antibody ligated to each of the framework regions (FRs) of a human antibody are synthesized by the PCR method from several oligonucleotides, which are prepared so as to have overlap portions at their terminal portions, for example. A humanized antibody can be obtained by ligating the thus obtained DNA to DNA encoding the constant region of a human antibody, incorporating the resultant fusion product into an expression vector, introducing the vector into a host, and thus causing the host to produce the gene product (see European Patent Publication No. 239400 and International Patent Publication WO96/02576). As the FRs of a human antibody, which is ligated via CDRs, FRs that allow the formation of an antigen-binding site with good complementarity determining regions are selected. If necessary, for the formation of an antigen-binding site having the appropriate complementarity determining regions of a reshaped human antibody, the amino acids of the framework regions of an antibody variable region may be substituted (Sato, K. et al., Cancer Research, 1993, 53: 851-856). Also, the amino acids of FRs may be substituted with those of framework regions from various human antibodies (see International Patent Publication WO99/51743). 
     As the framework regions (FRs) of a human antibody, which are ligated via CDRs, FRs that allows the formation of an antigen-binding site with good complementarity determining regions are selected. If necessary, for the formation of an antigen-binding site having the appropriate complementarity determining regions of a reshaped human antibody, the amino acids of the framework regions of an antibody variable region may be substituted (Sato K. et al., Cancer Research 1993, 53: 851-856). 
     After preparation of a chimeric antibody or a humanized antibody, amino acids in a variable region (e.g., FR) or a constant region may be substituted with other amino acids. 
     Amino acid substitution is a substitution of, for example, less than 15, less than 10, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less amino acids and is preferably a substitution of 1 to 5 amino acids, and more preferably 1 or 2 amino acids. A substituted antibody should be functionally equivalent to an unsubstituted antibody. Substitution is desirably a substitution of a conservative amino acid(s) between amino acids having analogous properties such as electric charge, side chain, polarity, and aromaticity. Amino acids having analogous properties can be classified into basic amino acids (arginine, lysine, and histidine), acidic amino acids (aspartic acid and glutamic acid), uncharged polar amino acids (glycine, asparagine, glutamine, serine, threonine, cysteine, and tyrosine), nonpolar amino acids (leucine, isoleucine, alanine, valine, proline, phenylalanine, tryptophan, and methionine), branched-chain amino acids (threonine, valine, and isoleucine), and aromatic amino acids (phenylalanine, tyrosine, tryptophan, and histidine), for example. 
     Examples of a modified antibody product include antibodies bound to various molecules such as polyethylene glycol (PEG). Substances to be bound in the modified antibody product of the present invention are not limited. Such a modified antibody product can be obtained by subjecting the thus obtained antibody to chemical modification. Methods therefor have already been established in the art. 
     As used herein, the term “functionally equivalent” refers to that a subject antibody has biological or biochemical activity similar to that of the antibody of the present invention, and specifically refers to that a subject antibody has the function of impairing tumor without essentially causing rejection upon its application to a human, for example. An example of such activity includes an activity to suppress cell proliferation or a binding activity. 
     As a method well known by persons skilled in the art for preparation of a polypeptide functionally equivalent to a polypeptide, a method for introducing a mutation into a polypeptide is known. For example, persons skilled in the art can prepare an antibody functionally equivalent to the antibody of the present invention by appropriately introducing a mutation into the antibody using site-directed mutagenesis (Hashimoto-Gotoh, T. et al., (1995) Gene 152, 271-275; Zoller, M J., and Smith, M. (1983) Methods Enzymol. 100, 468-500; Kramer, W. et al., (1984) Nucleic Acids Res. 12, 9441-9456; Kramer, W. and Fritz, H J., (1987) Methods Enzymol. 154, 350-367; Kunkel, T A., (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 488-492; Kunkel (1988) Methods Enzymol. 85, 2763-2766), for example. 
     An antibody that recognizes an epitope of a CAPRIN-1 protein recognized by the above anti-CAPRIN-1 antibody can be obtained by a method known by persons skilled in the art. For example, such an antibody can be obtained by a method that involves determining an epitope of a CAPRIN-1 protein recognized by an anti-CAPRIN-1 antibody, by a general method (e.g., epitope mapping) and then preparing an antibody using a polypeptide having an amino acid sequence contained in the epitope as an immunogen, or a method that involves determining an epitope of such an antibody prepared by a general method, and then selecting an antibody having the epitope identical with that of an anti-CAPRIN-1 antibody. As used herein, the term “epitope” refers to, in a mammal and preferably a human, a polypeptide fragment having antigenicity or immunogenicity. The minimum size unit thereof consists of about 7 to 12 amino acids, and preferably 8 to 11 amino acids. 
     The affinity constant Ka (k on /k off ) of the antibody of the present invention is preferably at least 10 7  M −1 , at least 10 8  M −1 , at least 5×10 8  M −1 , at least 10 9  M −1 , at least 5×10 9  M −1 , at least 10 10  M −1 , at least 5×10 10  M −1 , at least 10 11  M −1 , at least 5×10 11  M −1 , at least 10 12  M −1 , or at least 10 13  M −1 . 
     The antibody of the present invention can be conjugated with an antitumor agent. Conjugation of the antibody with an antitumor agent can be carried out via a spacer having a group reactive to an amino group, a carboxyl group, a hydroxy group, a thiol group or the like (e.g., a succinimidyl succinate group, a formyl group, a 2-pyridyldithio group, a maleimidyl group, an alkoxy carbonyl group, and a hydroxy group). 
     Examples of the antitumor agent include the following known antitumor agents as in prior art literatures and the like, such as paclitaxel, doxorubicin, daunorubicin, cyclophosphamide, methotrexate, 5-fluorouracil, thiotepa, busulfan, improsulfan, piposulfan, benzodopa, carboquone, meturedopa, uredopa, altretamine, triethylenemelamine, triethylenephosphoramide, triethilenethiophosphoramide, trimethylolomelamine, bullatacin, bullatacinone, camptothecin, bryostatin, callystatin, cryptophycin1, cryptophycin8, dolastatin, duocarmycin, eleutherobin, pancratistatin, sarcodictyin, spongistatin, chlorambucil, chlornaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard, carmustine, chlorozotocin, fotemustine, lomustine, nimustine, ranimustine, calicheamicin, dynemicin, clodronate, esperamicin, aclacinomycin, actinomycin, authramycin, azaserine, bleomycin, cactinomycin, carabicin, carminomycin, carzinophilin, chromomycin, dactinomycin, detorbicin, 6-diazo-5-oxo-L-norleucine, adriamycin, epirubicin, esorubicin, idarubicin, marcellomycin, mitomycinC, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin, denopterin, pteropterin, trimetrexate, fludarabine, 6-mercaptopurine, thiamiprine, thioguanine, ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine, androgens (e.g., calusterone, dromostanolone propionate, epitiostanol, mepitiostane, and testolactone), aminoglutethimide, mitotane, trilostane, frolinic acid, aceglatone, aldophosphamideglycoside, aminolaevulinic acid, eniluracil, amsacrine, bestrabucil, bisantrene, edatraxate, defofamine, demecolcine, diaziquone, elfornithine, elliptinium acetate, epothilone, etoglucid, lenthinan, lonidamine, maytansine, ansamitocine, mitoguazone, mitoxantrone, mopidanmol, nitraerine, pentostatin, phenamet, pirarubicin, losoxantrone, podophyllinic acid, 2-ethyl hydrazide, procarbazine, razoxane, rhizoxin, schizophyllan, spirogermanium, tenuazonic acid, triaziquone, roridine A, anguidine, urethane, vindesine, dacarbazine, mannomustine, mitobronitol, mitolactol, pipobroman, gacytosine, docetaxel, chlorambucil, gemcitabine, 6-thioguanine, mercaptopurine, cisplatin, oxaliplatin, carboplatin, vinblastine, etoposide, ifosfamide, mitoxanthrone, vincristine, vinorelbine, novantrone, teniposide, edatrexate, daunomycin, aminopterin, xeloda, ibandronate, irinotecan, topoisomerase inhibitor, difluoromethylolnitine (DMFO), retinoic acid, capecitabine, and pharmaceutically acceptable salts or derivatives thereof. 
     Through administration of the antibody of the present invention in combination with an antitumor agent, even higher therapeutic effects can be obtained. This technique is applicable to both before and after surgery of a cancer patient with the expression of CAPRIN-1. Particularly after surgery, more effective prevention of cancer recurrences or prolonged survival period can be obtained against cancer with the expression of CAPRIN-1, which has been conventionally treated with an antitumor agent alone. 
     Examples of the antitumor agent to be administered in combination with the antibody of the present invention include the following known antitumor agents as in prior art literatures or the like, such as paclitaxel, doxorubicin, daunorubicin, cyclophosphamide, methotrexate, 5-fluorouracil, thiotepa, busulfan, improsulfan, piposulfan, benzodopa, carboquone, meturedopa, uredopa, altretamine, triethylenemelamine, triethylenephosphoramide, triethilenethiophosphoramide, trimethylolomelamine, bullatacin, bullatacinone, camptothecin, bryostatin, callystatin, cryptophycin1, cryptophycin8, dolastatin, duocarmycin, eleutherobin, pancratistatin, sarcodictyin, spongistatin, chlorambucil, chlornaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard, carmustine, chlorozotocin, fotemustine, lomustine, nimustine, ranimustine, calicheamicin, dynemicin, clodronate, esperamicin, aclacinomycin, actinomycin, authramycin, azaserine, bleomycin, cactinomycin, carabicin, carminomycin, carzinophilin, chromomycin, dactinomycin, detorbicin, 6-diazo-5-oxo-L-norleucine, adriamycin, epirubicin, esorubicin, idarubicin, marcellomycin, mitomycinC, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin, denopterin, pteropterin, trimetrexate, fludarabine, 6-mercaptopurine, thiamiprine, thioguanine, ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine, calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone, aminoglutethimide, mitotane, trilostane, frolinic acid, aceglatone, aldophosphamideglycoside, aminolaevulinic acid, eniluracil, amsacrine, bestrabucil, bisantrene, edatraxate, defofamine, demecolcine, diaziquone, elfornithine, elliptinium acetate, epothilone, etoglucid, lenthinan, lonidamine, maytansine, ansamitocine, mitoguazone, mitoxantrone, mopidanmol, nitraerine, pentostatin, phenamet, pirarubicin, losoxantrone, podophyllinic acid, 2-ethyl hydrazide, procarbazine, razoxane, rhizoxin, schizophyllan, spirogermanium, tenuazonic acid, triaziquone, roridine A, anguidine, urethane, vindesine, dacarbazine, mannomustine, mitobronitol, mitolactol, pipobroman, gacytosine, docetaxel, chlorambucil, gemcitabine, 6-thioguanine, mercaptopurine, cisplatin, oxaliplatin, carboplatin, vinblastine, etoposide, ifosfamide, mitoxanthrone, vincristine, vinorelbine, novantrone, teniposide, edatrexate, daunomycin, aminopterin, xeloda, ibandronate, irinotecan, topoisomerase inhibitor, difluoromethylolnitine (DMFO), retinoic acid, capecitabine, and pharmaceutically acceptable (known) salts or (known) derivatives thereof. Of the above examples, particularly cyclophosphamide, paclitaxel, docetaxel, and vinorelbine are preferably used. 
     Alternatively, a known radio isotope as in prior art literatures or the like, such as  211 At,  131 I,  125 I,  90 Y,  186 Re,  188 Re,  153 Sm,  212 Bi,  32 P,  175 Lu, or  176 Lu can be bound to the antibody of the present invention. A desired radio isotope is effective for treatment or diagnosis of tumor. 
     The antibody of the present invention is an antibody having immunological reactivity with CAPRIN-1, an antibody specifically recognizing CAPRIN-1, or an antibody specifically binding to CAPRIN-1, which exhibits cytotoxic activity against cancer or the effect of suppressing tumor growth. The antibody should have a structure such that rejection is almost or completely avoided in a subject animal to which the antibody is administered. Examples of such an antibody include, when a subject animal is human, human antibody, humanized antibody, chimeric antibody (e.g., human-mouse chimeric antibody), single chain antibody, and bispecific antibody. These antibodies are: recombinant antibodies having heavy chain and light chain variable regions from a human antibody; recombinant antibodies having heavy chain and light chain variable regions composed of complementarity determining regions (CDRs) (CDR1, CDR2, and CDR3) from a non-human animal antibody and framework regions from a human antibody; or recombinant antibodies having heavy chain and light chain variable regions from a non-human animal antibody; said recombinant antibodies also having heavy chain and light chain constant regions from a human antibody. Preferable antibodies are the former two antibodies. 
     These recombinant antibodies can be prepared as follows by cloning DNA encoding an anti-human CAPRIN-1 monoclonal antibody (e.g., a human monoclonal antibody, a mouse monoclonal antibody, a rat monoclonal antibody, a rabbit monoclonal antibody, or a chicken monoclonal antibody) from an antibody-producing cell such as a hybridoma, preparing DNA encoding a light chain variable region and a heavy chain variable region of the antibody by an RT-PCR method using it as a template, and then determining the sequence of each variable region of light chain and heavy chain or each sequence of CDR1, CDR2, and CDR3 based on a Kabat EU numbering system (Kabat et al., Sequences of Proteins of Immunological Interest, 5 th  Ed. Public Health Service, National Institute of Health, Bethesda, Md. (1991)). 
     Furthermore, DNA encoding each of these variable regions or DNA encoding each CDR is prepared using gene recombination techniques (Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press (1989)) or a DNA synthesizer. Here, the above human monoclonal antibody-producing hybridoma can be prepared by immunizing a human antibody-producing animal (e.g., a mouse) with human CAPRIN-1 and then fusing splenocytes excised from the immunized animal to myeloma cells. Alternatively, DNAs encoding a light chain or heavy chain variable region and a constant region from a human antibody are prepared as necessary using gene recombination techniques or a DNA synthesizer. 
     In the case of humanized antibody, DNA is prepared by substituting a CDR coding sequence in DNA encoding a variable region of light chain or heavy chain derived from a human antibody, with a CDR coding sequence corresponding thereto of an antibody derived from a non-human animal (e.g., a mouse, a rat, or a chicken) and then ligating the DNA thus obtained to DNA encoding a constant region of light chain or heavy chain derived from a human antibody. Thus, DNA encoding humanized antibody can be prepared. 
     In the case of chimeric antibody, DNA encoding a chimeric antibody can be prepared by ligating DNA encoding a light chain or heavy chain variable region of an antibody from a non-human animal (e.g., a mouse, a rat, and a chicken) to DNA encoding a light chain or heavy chain constant region from a human antibody. 
     In the case of single chain antibody, this antibody is an antibody prepared by linearly ligating a heavy chain variable region to a light chain variable region via a linker. Thus, DNA encoding a single chain antibody can be prepared by binding DNA encoding a heavy chain variable region, DNA encoding a linker, and DNA encoding a light chain variable region. Herein, a heavy chain variable region and a light chain variable region are both from a human antibody, or, only CDRs are substituted with CDRs of an antibody from a non-human animal (e.g., a mouse, a rat, and a chicken) although the other regions are from a human antibody. Also, a linker comprises 12 to 19 amino acids, such as (G 4 S) 3  of 15 amino acids (G.-B. Kim et al., Protein Engineering Design and Selection 2007, 20 (9): 425-432). 
     In the case of bispecific antibody (diabody), this antibody is capable of specifically binding to two different epitopes. For example, DNA encoding a bispecific antibody can be prepared by linking DNA encoding a heavy chain variable region A, DNA encoding a light chain variable region B, DNA encoding a heavy chain variable region B, and DNA encoding a light chain variable region A in this order (here, DNA encoding a light chain variable region B is bound to DNA encoding a heavy chain variable region B via DNA encoding the above linker). Here, a heavy chain variable region and a light chain variable region are both from a human antibody, or, a human antibody in which only CDRs have been substituted with CDRs of an antibody from a non-human animal (e.g., a mouse, a rat, or a chicken). 
     The above-prepared recombinant DNA is incorporated into one or a plurality of appropriate vectors, they are introduced into host cells (e.g., mammalian cells, yeast cells, or insect cells), and then (co)expression is caused, so that a recombinant antibody can be prepared (P. J. Delves., ANTIBODY PRODUCTION ESSENTIAL TECHNIQUES., 1997 WILEY, P. Shepherd and C. Dean., Monoclonal Antibodies., 2000 OXFORD UNIVERSITY PRESS; J. W. Goding., Monoclonal Antibodies: principles and practice., 1993 ACADEMIC PRESS). 
     Examples of the antibody of the present invention prepared by the above method include the following antibody (a), (b), or (c) obtained in Examples below: 
     (a) an antibody (e.g., the antibody composed of the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 47) comprising a heavy chain variable region comprising SEQ ID NOS: 40, 41, and 42 and a light chain variable region comprising SEQ ID NOS: 44, 45, and 46; and
 
(b) an antibody (e.g., the antibody composed of the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 51) comprising a heavy chain variable region comprising SEQ ID NOS: 40, 41, and 42 and a light chain variable region comprising SEQ ID NOS: 48, 49, and 50.
 
(c) an antibody (e.g., the antibody composed of the heavy chain variable region of SEQ ID NO: 63 and the light chain variable region of SEQ ID NO: 67) comprising a heavy chain variable region comprising SEQ ID NOS: 60, 61, and 62 and a light chain variable region comprising SEQ ID NOS: 64, 65, and 66.
 
     The amino acid sequences represented by SEQ ID NOS: 40, 41, and 42, and SEQ ID NOS: 60, 61, and 62 are CDR1, CDR2, and CDR3, respectively, of mouse antibody heavy chain variable regions. Also, the amino acid sequences represented by SEQ ID NOS: 44, 45, and 46, SEQ ID NOS: 48, 49, and 50, and SEQ ID NOS: 64, 65, and 66 are CDR1, CDR2, and CDR3, respectively, of mouse antibody light chain variable regions. 
     Also, the humanized antibody, the chimeric antibody, the single chain antibody, or the bispecific antibody of the present invention is the following antibody (exemplified as “antibody (a)”), for example: 
     (i) an antibody wherein the heavy chain variable region comprises the amino acid sequences of SEQ ID NOS: 40, 41, and 42 and the amino acid sequences of framework regions from a human antibody, and, a light chain variable region comprises the amino acid sequences of SEQ ID NOS: 44, 45, and 46 and the amino acid sequences of framework regions from a human antibody (preferably, the antibody wherein the heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 43, and, the light chain variable region comprises the amino acid sequence of SEQ ID NO: 47); and
 
(ii) an antibody wherein a heavy chain variable region comprises the amino acid sequences of SEQ ID NOS: 40, 41, and 42 and the amino acid sequences of framework regions from a human antibody, and, a heavy chain constant region comprises an amino acid sequence from a human antibody, and, a light chain variable region comprises the amino acid sequences of SEQ ID NOS: 44, 45, and 46 and the amino acid sequences of framework regions from a human antibody, and a light chain constant region comprises an amino acid sequence from a human antibody (preferably, the antibody wherein a heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 43, and, a heavy chain constant region comprises an amino acid sequence from a human antibody, as well as, a light chain variable region comprises the amino acid sequence of SEQ ID NO: 47, and, a light chain constant region comprises an amino acid sequence from a human antibody).
 
     In addition, the sequences of human antibody heavy chain and light chain constant regions and variable regions can be obtained from NCBI (e.g., U.S.A.: GenBank, UniGene), for example. For example, the sequence of Accession No. J00228 can be referred to for a human IgG1 heavy chain constant region, the sequence of Accession No. J00230 can be referred to for a human IgG2 heavy chain constant region, the sequence of Accession No. X03604 can be referred to for a human IgG3 heavy chain constant region, the sequence of Accession No. K01316 can be referred to for a human IgG4 heavy chain constant region, the sequences of Accession Nos. V00557, X64135, X64133, and the like can be referred to for human light chain κ constant regions, and the sequences of Accession Nos. X64132, X64134, and the like can be referred to for human light chain λ constant regions. 
     The above antibodies preferably have cytotoxic activity and thus can exhibit anti-tumor effects. 
     Also, the specific sequences of heavy chain and light chain variable regions or CDRs in the above antibodies are given simply for illustrative purposes, and thus are clearly not limited to such specific sequences. A hybridoma capable of producing another human antibody or non-human animal antibody (e.g., a mouse antibody) against human CAPRIN-1 is prepared, a monoclonal antibody that is produced by the hybridoma is collected, and then whether or not it is a target antibody is determined by immunological binding property with human CAPRIN-1 and cytotoxic activity as indicators. After identification of a hybridoma producing the target monoclonal antibody in this manner, DNA encoding heavy chain and light chain variable regions of the target antibody is prepared from the hybridoma as described above, sequencing is carried out, and then the DNA is used for preparation of another antibody. 
     Furthermore, regarding the above antibody, the sequence of the above antibodies (a) to (c), particularly the sequence of the framework region and/or the sequence of the constant region of each of the antibodies may have a substitution, a deletion, or an addition of one or several amino acids, as long as it has specificity for specific recognition of CAPRIN-1. Here the term “several” refers to preferably 2 to 5, and more preferably 2 or 3. 
     The present invention further provides DNA encoding the above antibody of the present invention, or, DNA encoding the above antibody heavy chain or light chain, or, DNA encoding the above antibody heavy chain or light chain variable region. Examples of such DNA include, in the case of antibody (a), DNA encoding a heavy chain variable region comprising the nucleotide sequences encoding the amino acid sequences of SEQ ID NOS: 40, 41, and 42 and DNA encoding a light chain variable region comprising the nucleotide sequences encoding the amino acid sequences of SEQ ID NOS: 44, 45, and 46. 
     Complementarity determining regions (CDRs) encoded by the sequences of DNA are regions for determining the specificity of an antibody. Thus, sequences encoding regions in an antibody other than CDRs (specifically, a constant region and a framework region) may be from other antibodies. Here, examples of such “other antibodies” include antibodies from non-human organisms, and are preferably from a human in view of reduction of side effects. Thus, in the case of the above DNA, regions encoding each framework region and each contact region of heavy chains and light chains preferably comprise nucleotide sequences encoding corresponding amino acid sequences from a human antibody. 
     Further alternative examples of DNA encoding the antibody of the present invention include, in the case of antibody (a), DNA encoding a heavy chain variable region comprising the nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 43 and DNA encoding a light chain variable region comprising the nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 47. Here, an example of the nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 43 is the nucleotide sequence of SEQ ID NO: 52. Also, an example of the nucleotide sequence encoding the amino acid sequence of SEQ ID NO: 47 is the nucleotide sequence of SEQ ID NO: 53. In these DNAs, regions encoding each constant region of heavy chains and light chains preferably comprise nucleotide sequences encoding the corresponding amino acid sequences from a human antibody. 
     The DNAs of these antibodies can be obtained by the above methods or the following method, for example. First, total RNA is prepared from a hybridoma relating to the antibody of the present invention using a commercially available RNA extraction kit, and then cDNA is synthesized with reverse transcriptase using random primers, and the like. Subsequently, cDNA encoding an antibody is amplified by a PCR method using as primers the oligonucleotides of sequences conserved in each variable region of known mouse antibody heavy chain and light chain genes. The sequence encoding a constant region can be obtained by amplifying a known sequence by a PCR method. The nucleotide sequence of DNA can be determined by a conventional method such as insertion of it into a plasmid or a phage for sequencing. 
     An anti-CAPRIN-1 antibody to be used in the present invention is considered to exhibit the anti-tumor effects against CAPRIN-1-expressing cancer cells through the following mechanism: 
     effector-cell antibody-dependent cytotoxicity (ADCC) of CAPRIN-1-expressing cells, and the complement-dependent cytotoxicity (CDC) of CAPRIN-1-expressing cells. 
     Therefore, the activity of an anti-CAPRIN-1 antibody to be used in the present invention can be evaluated by, as specifically described in Examples below, measuring ex vivo the above ADCC activity or CDC activity against CAPRIN-1-expressing cancer cells. 
     An anti-CAPRIN-1 antibody to be used in the present invention binds to a CAPRIN-1 protein on a cancer cell and exhibits anti-tumor effects due to the above activity, and thus it is useful for treating or preventing cancer. Specifically, the present invention provides a pharmaceutical composition for treating and/or preventing cancer, which comprises an anti-CAPRIN-1 antibody as an active ingredient. When the anti-CAPRIN-1 antibody is used for administration thereof to a human body (antibody therapy), it is preferably human antibody or humanized antibody in order to decrease immunogenicity. 
     In addition, the higher the binding affinity between an anti-CAPRIN-1 antibody and a CAPRIN-1 protein on the cancer cell surfaces, the stronger the anti-tumor activity of the anti-CAPRIN-1 antibody that can be obtained. Therefore, when an anti-CAPRIN-1 antibody having high binding affinity with a CAPRIN-1 protein can be acquired, stronger anti-tumor effects can be expected and such antibody&#39;s application as a pharmaceutical composition for the purpose of cancer treatment and/or prevention becomes possible. Such high binding affinity is desirably as follows. As described above, binding constant (affinity constant) Ka (k on /k off ) is preferably at least 10 7  M −1 , at least 10 8  M −1 , at least 5×10 8  M −1 , at least 10 9  M −1 , at least 5×10 9  M −1 , at least 10 10  M −1 , at least 5×10 10  M −1 , at least 10 11  M −1 , at least 5×10 11  M −1 , at least 10 12  M −1 , or, at least 10 13  M −1 . 
     &lt;Binding to Antigen-Expressing Cell&gt; 
     The capacity of an antibody to bind to CAPRIN-1 can be specified by binding assay using ELISA, a Western blot method, immuno-fluorescence and flow cytometric analysis, or the like as described in Examples. 
     &lt;Immunohistochemical Staining&gt; 
     An antibody that recognizes CAPRIN-1 can be tested for reactivity to CAPRIN-1 by a method for immunohistochemistry known by persons skilled in the art using paraformaldehyde- or acetone-fixed frozen sections or paraformaldehyde-fixed paraffin-embedded tissue sections, which is prepared from tissue samples obtained from a patient during surgery, or tissue samples obtained from an animal having heterotransplant tissue inoculated with a cell line expressing CAPRIN-1, naturally or after transfection. 
     An antibody reactive to CAPRIN-1 can be stained by various methods for immunohistochemical staining. For example, a horseradish peroxidase-conjugated goat anti-mouse antibody or goat anti-chicken antibody is caused to undergo reaction, a target antibody can be visualized. 
     &lt;Pharmaceutical Composition&gt; 
     The present invention further provides a pharmaceutical composition for treating and/or preventing cancer, which is characterized by containing the above antibody or a fragment thereof as an active ingredient that has immunological reactivity with partial polypeptides of CAPRIN-1 represented by even-numbered SEQ ID NOS: 2 to 30, wherein the polypeptide has the amino acid sequence represented by SEQ ID NO: 37, or an amino acid sequence having 80% or more sequence identity with the amino acid sequence of SEQ ID NO: 37. 
     A target of the pharmaceutical composition for treating and/or preventing cancer of the present invention is not particularly limited, as long as it is cancer (cell) expressing a CAPRIN-1 gene. 
     The term “tumor” and “cancer” as used herein refers to malignant neoplasm and is used interchangeably. 
     Cancer to be subjected to the present invention is cancer expressing genes encoding CAPRIN-1 proteins having amino acid sequences of even-numbered SEQ ID NOS: 2 to 30. Examples of such cancer include preferably breast cancer, brain tumor, leukemia, lung cancer, lymphoma, mastocytoma, renal cancer, uterine cervix cancer, bladder cancer, esophageal cancer, gastric cancer, colorectal cancer, ovarian cancer, prostate cancer, and fibrosarcoma. 
     Examples of such specific cancer include, but are not limited to, breast adenocarcinoma, composite type breast adenocarcinoma, mammary gland malignant mixed tumor, intraductal papillary adenocarcinoma, lung adenocarcinoma, squamous cell carcinoma, small cell carcinoma, large cell carcinoma, glioma that is neural epithelial tissue tumor, ependymoma, neurocytoma, fetal neuroectodermal tumor, schwannoma, neurofibroma, meningioma, chronic lymphocytic leukemia, lymphoma, gastrointestinal lymphoma, digestive lymphoma, small-cell to medium-cell lymphoma, cancer of cecum, ascending colon cancer, descending colon cancer, transverse colon cancer, sigmoid colon cancer, rectal cancer, epithelial ovarian cancer, germ cell tumor, and interstitial cell tumor. 
     Moreover, preferable subjects are mammals including primates, pet animals, domestic animals, animals for race, and the like and are particularly preferably humans, dogs, and cats. 
     When an antibody to be used in the present invention is used as a pharmaceutical composition, it can be formulated by a method known by persons skilled in the art. For example, the antibody can be used parenterally in the form of an injection preparation such as an aseptic solution or a suspension prepared with water or a pharmacologically acceptable solution other than water. For example, it can be formulated by mixing in a unit dosage form required by generally accepted pharmaceutical practice in appropriate combination with a pharmacologically acceptable carrier or medium, specifically, sterile water or saline, vegetable oil, an emulsifier, a suspension, a surfactant, a stabilizer, a flavoring compound, an excipient, a vehicle, an antiseptic, a binder, and the like. The amounts of active ingredients in these preparations are determined so that an appropriate dose within the indicated range can be obtained. 
     An aseptic composition for injection can be prescribed according to general pharmaceutical practice using a vehicle such as distilled water for injection. 
     Examples of an aqueous solution for injection include saline, an isotonic solution containing dextrose or other adjuvants, such as D-sorbitol, D-mannose, D-mannitol, and sodium chloride. These examples may be used in combination with an appropriate solubilizing agent such as alcohol, specifically ethanol and polyalcohol (e.g., propylene glycol and polyethylene glycol), and nonionic surfactant (e.g., polysorbate 80 (TM) and HCO-60). 
     Examples of the oil include sesame oil and soybean oil, which can be used in combination with a solubilizing agent such as benzyl benzoate or benzyl alcohol. Also, a buffering agent such as phosphate buffer or sodium acetate buffer, a soothing agent such as procaine hydrochloride, a stabilizer such as benzyl alcohol or phenol, and an antioxidant may be combined therewith. An appropriate amplus is generally filled with the thus prepared injection solution. 
     Administration is peroral or perenteral administration and is preferably perenteral administration. Specific examples of the route of administration include injection, transnasal administration, pulmonary administration, and transdermal administration. Examples of injection include intravenous injection, intramuscular injection, intraperitoneal injection, and subcutaneous injection, so that systemic or local administration is possible. 
     Also, administration methods can be appropriately selected depending on a patient&#39;s age, body weight, gender, symptoms, and the like. The dosage per administration of a pharmaceutical composition containing an antibody or a polynucleotide encoding the antibody can be selected from the range between 0.0001 mg and 1000 mg per kg of body weight, for example. Alternatively, for example, dosage can be selected from the range between 0.001 mg/body and 100000 mg/body per patient. However, the dosage range is not always limited to these numerical values. The dosage and administration method are varied depending on a patient&#39;s body weight, age, gender, symptoms, and the like, but can be appropriately selected by persons skilled in the art. 
     The above pharmaceutical composition containing the antibody or a fragment thereof of the present invention is administered to a subject, so that cancer, preferably, breast cancer, brain tumor, leukemia, lung cancer, lymphoma, mastocytoma, renal cancer, uterine cervix cancer, bladder cancer, esophageal cancer, gastric cancer, and colorectal cancer can be treated and/or prevented. 
     The present invention further encompasses a method for treating and/or preventing cancer, comprising administering to a subject the pharmaceutical composition of the present invention in combination with the above exemplified antitumor agent or pharmaceutical composition containing such antitumor agent. The antibody or a fragment thereof of the present invention and an antitumor agent may be administered simultaneously or separately to a subject. They can be separately administered regardless of the order of administration. The administration intervals, dosage, the route of administration, and the frequency of administration can be appropriately selected by a specialist. Examples of the other pharmaceutical formulation to be administered simultaneously include pharmaceutical compositions obtained by mixing the antibody or a fragment thereof of the present invention with an antitumor agent in a pharmacologically acceptable carrier (or a medium) followed by formulation. Furthermore, to either the above pharmaceutical composition containing an antitumor agent or formulation, explanations concerning prescription, formulation, the route of administration, dose, cancer, and the like for administration of a pharmaceutical composition containing the antibody of the present invention and formulation are applicable. 
     Therefore, the present invention also provides a pharmaceutical combination for treating and/or preventing cancer, comprising the pharmaceutical composition of the present invention, and the above exemplified pharmaceutical composition containing an antitumor agent. Also, the present invention provides a pharmaceutical composition for treating and/or preventing cancer, comprising the antibody or a fragment thereof of the present invention and an antitumor agent together with a pharmacologically acceptable carrier. 
     &lt;Polypeptide and DNA&gt; 
     The present invention further provides the following polypeptides and DNAs relating to the above antibody (a), (b), or (c). 
     (i) A polypeptide comprising the amino acid sequences of SEQ ID NOS: 43 and 63, and DNA encoding the polypeptide, wherein the DNA comprises the nucleotide sequences of SEQ ID NOS: 52 and 68. 
     (ii) A polypeptide comprising the amino acid sequences of SEQ ID NOS: 47, 51, and 67, and DNA encoding the polypeptide, wherein the DNA comprises the nucleotide sequences of SEQ ID NOS: 70, 53, and 69. 
     (iii) A heavy chain CDR polypeptide selected from the group consisting of the amino acid sequences represented by SEQ ID NOS: 40, 41, and 42 and SEQ ID NOS: 60, 61, and 62, and DNA encoding the polypeptide. 
     (iv) A light chain CDR polypeptide selected from the group consisting of the amino acid sequences represented by SEQ ID NOS: 44, 45, and 46, SEQ ID NOS: 48, 49, and 50, and SEQ ID NOS: 64, 65, and 66, and DNA encoding the polypeptide. 
     These polypeptides and DNAs can be prepared using gene recombination techniques as described above. 
     SUMMARY OF THE PRESENT INVENTION 
     The above-explained present invention is as summarized as follows. 
     (1) A pharmaceutical composition for treating and/or preventing a cancer, comprising an antibody or a fragment thereof as an active ingredient that has immunological reactivity with a partial polypeptide of CAPRIN-1, wherein CAPRIN-1 is represented by any of the even-numbered sequences of SEQ ID NOS: 2 to 30, and wherein the partial polypeptide comprises the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more sequence identity with the amino acid sequence of SEQ ID NO: 37.
 
(2) The pharmaceutical composition according to (1) above, wherein the cancer is breast cancer, brain tumor, leukemia, lymphoma, lung cancer, mastocytoma, renal cancer, uterine cervix cancer, bladder cancer, esophageal cancer, gastric cancer, or colorectal cancer.
 
(3) The pharmaceutical composition according to (1) or (2) above, wherein the antibody is a monoclonal antibody or a polyclonal antibody.
 
(4) The pharmaceutical composition according to any one of (1) to (3) above, wherein the antibody is a human antibody, humanized antibody, chimeric antibody, single chain antibody, or a bispecific antibody.
 
(5) An antibody having immunological reactivity with a polypeptide that comprise the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more sequence identity with the amino acid sequence of SEQ ID NO: 37.
 
(6) The antibody according to (5) above, which has a cytotoxic activity against a cancer cell expressing a CAPRIN-1 protein.
 
(7) An antibody, which comprises a heavy chain variable region comprising SEQ ID NOS: 40, 41, and 42 and a light chain variable region comprising SEQ ID NOS: 44, 45, and 46, and has immunological reactivity with a CAPRIN-1 protein.
 
(8) An antibody, which comprises a heavy chain variable region comprising SEQ ID NOS: 40, 41, and 42 and a light chain variable region comprising SEQ ID NOS: 48, 49, and 50, and has immunological reactivity with a CAPRIN-1 protein.
 
(9) An antibody, which comprises a heavy chain variable region comprising SEQ ID NOS: 60, 61, and 62 and a light chain variable region comprising SEQ ID NOS: 64, 65, and 66, and has immunological reactivity with a CAPRIN-1 protein.
 
(10) The antibody according to any one of (5) to (9) above, which is a human antibody, humanized antibody, chimeric antibody, single chain antibody, or bispecific antibody.
 
(11) A pharmaceutical composition for treating and/or preventing a cancer, comprising the antibody or a fragment thereof of any one of (5) to (10) above as an active ingredient.
 
(12) The pharmaceutical composition according to (11) above, wherein the cancer is breast cancer, brain tumor, leukemia, lymphoma, lung cancer, mastocytoma, renal cancer, uterine cervix cancer, bladder cancer, esophageal cancer, gastric cancer, or colorectal cancer.
 
(13) A pharmaceutical combination for treating and/or preventing a cancer, comprising the pharmaceutical composition of any one of (1) to (4) above or the pharmaceutical composition of (11) or (12) above, and a pharmaceutical composition containing an antitumor agent.
 
(14) A method for treating and/or preventing a cancer, comprising administering to a subject the antibody or a fragment thereof of any one of (5) to (10) above or the pharmaceutical composition of (11) or (12) above.
 
(15) A method for treating and/or preventing a cancer, comprising using pharmaceutical compositions of the pharmaceutical combination of (13) above in combination in a subject.
 
     EXAMPLES 
     The present invention is described more specifically based on Examples, but the scope of the present invention is not limited by these specific examples. 
     Example 1 
     Identification of Novel Cancer Antigen Protein by SEREX Method 
     (1) Preparation of cDNA Library 
     Total RNA was extracted from a testis tissue of a healthy dog by an acid guanidium-phenol-chloroform method. PolyA RNA was purified according to protocols attached to an Oligotex-dT30 mRNA purification Kit (Takara Shuzo Co., Ltd.) using the kit. 
     A dog testis cDNA phage library was synthesized using the thus obtained mRNA (5 μg). For preparation of the cDNA phage library, a cDNA synthesis kit, a ZAP-cDNA synthesis kit, and a ZAP-cDNA gigapack III gold cloning kit (STRATAGENE) were used and the library was prepared according to protocols attached to the kit. The size of the thus prepared cDNA phage library was 7.73×10 5  pfu/ml. 
     (2) Screening of cDNA Library Using Serum 
     Immunoscreening was carried out using the above-prepared dog testis cDNA phage library. Specifically, host  Escherichia coli  (XL1-Blue MRF′) was infected with the phage so that 2210 clones were present on a φ90×15 mm NZY agarose plate. Cells were cultured at 42° C. for 3 to 4 hours, so as to cause plaque formation. The plate was covered with a nitrocellulose membrane (Hybond C Extra: GE HealthCare Bio-Sciences) impregnated with IPTG (isopropyl-β-D-thiogalactoside) at 37° C. for 4 hours. Proteins were induced, expressed, and then transferred to the membrane. Subsequently, the membrane was recovered, immersed, and shaken in TBS (10 mM Tris-HCl, 150 mM NaCl pH 7.5) containing 0.5% powdered skim milk at 4° C. overnight, so that nonspecific reaction was suppressed. The filter was caused to react with 500-fold diluted sera of dogs with cancer at room temperature for 2 to 3 hours. 
     As the above sera from dogs with cancer, sera collected from dogs with breast cancer were used. The sera were stored at −80° C. and then subjected to pretreatment immediately before use. Pretreatment for sera was performed by the following method. Specifically, host  Escherichia coli  (XL1-Blure MRF′) was infected with λ ZAP Express phage into which no foreign gene had been inserted, and then cultured on NZY plate medium at 37° C. overnight. Subsequently, a 0.2 M NaHCO 3  buffer (pH 8.3) containing 0.5 M NaCl was added to the plate and then the plate was left to stand at 4° C. for 15 hours. The supernatants were collected as  Escherichia coli /phage extracts. Next, the collected  Escherichia coli /phage extract was passed through a NHS-column (GE HealthCare Bio-Sciences), so as to immobilize the  Escherichia coli •phage-derived protein. The serum of a dog with cancer was passed through the column to which the protein had been immobilized for reaction, thereby removing  Escherichia coli  and antibodies adsorbed to the phage from the serum. Each serum fraction that had passed through the column was diluted 500-fold with TBS containing 0.5% powdered skim milk, and the resultant was used as an immunoscreening material. 
     A membrane, to which the thus treated serum and the fusion protein had been blotted, was washed 4 times with TBS-T (0.05% Tween20/TBS). The membrane was reacted with goat anti-dog IgG (Goat anti Dog IgG-h+I HRP conjugated: BETHYL Laboratories) diluted 5000-fold as a secondary antibody with TBS containing 0.5% powdered skim milk at room temperature for 1 hour. Detection was carried out by enzyme color reaction using an NBT/BCIP reaction solution (Roche). Colonies corresponding to the color reaction positive site were collected from the φ90×15 mm NZY agarose plate, and then dissolved in 500 μl of SM buffer (100 mM NaCl, 10 mM MgClSO 4 , 50 mM Tris-HCl, 0.01% gelatin, pH 7.5). Until unification of color reaction positive colonies, secondary screening and tertiary screening were repeated by a method similar to the above. Thus, 30940 phage clones that had reacted with serum IgG were screened so that 5 positive clones were isolated. 
     (3) Homology Search for Isolated Antigen Gene 
     A procedure for conversion of phage vectors to plasmid vectors was performed for the 5 positive clones isolated by the above method for the purpose of subjecting the clones to nucleotide sequence analysis. Specifically, 200 μl of a solution of host  Escherichia coli  (XL1-Blue MRF′) prepared to give an absorbance OD 600  of 1.0, 250 μl of a purified phage solution, and 1 μl of ExAssist helper phage (STRATAGENE) were mixed and allowed to react at 37° C. for 15 minutes. After that, 3 ml of LB medium was added, cells were cultured at 37° C. for 2.5 to 3 hours, and then the resultant was immediately put in water bath at 70° C. for incubation for 20 minutes. Centrifugation was carried out at 4° C., 1000×g for 15 minutes, and then the supernatant was collected as a phagemid solution. Subsequently, 200 μl of a solution prepared from phagemid host  Escherichia coli  SOLR to give an absorbance OD 600  of 1.0 and 10 μl of the purified phage solution were mixed, followed by 15 minutes of reaction at 37° C. 50 μl of the resultant was plated on LB agar medium containing ampicillin (at final concentration of 50 μg/ml) and then cultured overnight at 37° C. A single colony of transformed SOLR was collected and then cultured on LB medium containing ampicillin (at final concentration of 50 μg/ml) at 37° C. After culture, plasmid DNA carrying an insert of interest was purified using a QIAGEN plasmid Miniprep Kit (QIAGEN). 
     The purified plasmid was subjected to the analysis of the entire sequence of the insert by the primer walking method using the T3 primer of SEQ ID NO: 31 and the T7 primer of SEQ ID NO: 32. The gene sequences of SEQ ID NOS: 5, 7, 9, 11, and 13 were obtained by the sequence analysis. With the use of the nucleotide sequences of the genes and the amino acid sequences thereof (SEQ ID NOS: 6, 8, 10, 12, and 14), homology search program BLAST search (www.ncbi.nlm.nih.gov/BLAST/) was conducted for searching homology with known genes. As a result, it was revealed that all the five obtained genes were genes encoding CAPRIN-1. The sequence identities among the five genes were 100% at the nucleotide sequence level and 99% at the amino acid sequence level in the regions to be translated into proteins. The sequence identities of these genes and the human homologue-encoding gene were 94% at the nucleotide sequence level and 98% at the amino acid sequence level in the regions to be translated into proteins. The nucleotide sequences of the human homologues are represented by SEQ ID NOS: 1 and 3 and the amino acid sequences of the same are represented by SEQ ID NOS: 2 and 4. Also, the sequence identities of the obtained dog genes and the cattle homologue-encoding gene were 94% at the nucleotide sequence level and 97% at the amino acid sequence level in the regions to be translated into proteins. The nucleotide sequence of the cattle homologue is represented by SEQ ID NO: 15 and the amino acid sequence of the same is represented by SEQ ID NO: 16. In addition, the sequence identities of the human homologue-encoding genes and the cattle homologue-encoding gene were 94% at the nucleotide sequence level and 93% to 97% at the amino acid sequence level in the regions to be translated into proteins. Also, the sequence identities of the obtained dog genes and the horse homologue-encoding gene were 93% at the nucleotide sequence level and 97% at the amino acid sequence level in the regions to be translated into proteins. The nucleotide sequence of the horse homologue is represented by SEQ ID NO: 17 and the amino acid sequence of the same is represented by SEQ ID NO: 18. In addition, the sequence identities of the human homologue-encoding genes and the horse homologue-encoding gene were 93% at the nucleotide sequence level and 96% at the amino acid sequence level in the regions to be translated into proteins. Also, the sequence identities of the obtained dog genes and the mouse homologue-encoding genes were 87% to 89% at the nucleotide sequence level and 95% to 97% at the amino acid sequence level in the regions to be translated into proteins. The nucleotide sequences of the mouse homologues are represented by SEQ ID NOS: 19, 21, 23, 25, and 27 and the amino acid sequences of the same are represented by SEQ ID NOS: 20, 22, 24, 26, and 28. In addition, the sequence identities of the human homologue-encoding genes and the mouse homologue-encoding genes were 89% to 91% at the nucleotide sequence level and were 95% to 96% at the amino acid sequence level in the regions to be translated into proteins. Also, the sequence identities of the obtained dog genes and the chicken homologue-encoding gene were 82% at the nucleotide sequence level and 87% at the amino acid sequence level in the regions to be translated into proteins. The nucleotide sequence of the chicken homologue is represented by SEQ ID NO: 29 and the amino acid sequence of the same is represented by SEQ ID NO: 30. In addition, the sequence identities of the human homologue-encoding genes and the chicken homologue-encoding gene were 81% to 82% at the nucleotide sequence level and 86% at the amino acid sequence level in the regions to be translated into proteins. 
     (4) Gene Expression Analysis in Each Tissue 
     The expression of genes obtained by the above method was examined in dog and human normal tissues and various cell lines by an RT-PCR method. Reverse transcription reaction was performed as follows. Specifically, total RNA was extracted from 50 mg to 100 mg of the tissue or 5 to 10×10 6  cells of the cell line using a TRIZOL reagent (Invitrogen) according to the accompanying protocols. cDNA was synthesized with the total RNA using a Superscript First-Strand Synthesis System for RT-PCR (Invitrogen) according to the accompanying protocols. PCR was performed as follows using primers of SEQ ID NOS: 33 and 34 specific to the obtained genes. Specifically, reagents and an accompanying buffer were added to 0.25 μl of the sample prepared by the reverse transcription reaction to a total volume of 25 μl so that the resultant contained the above primers of 2 μM each, dNTPs of 0.2 mM each, and 0.65 U ExTaq polymerase (Takara Shuzo Co., Ltd.). PCR was carried out by repeating a cycle of 94° C. for 30 seconds, 60° C. for 30 seconds, and 72° C. for 30 seconds 30 times using a Thermal Cycler (BIO RAD). The above gene-specific primers are capable of amplifying the region ranging from nucleotides 206 to 632 in the nucleotide sequence of SEQ ID NO: 5 (dog CAPRIN-1 gene) and the region ranging from nucleotides 698 to 1124 in the nucleotide sequence of SEQ ID NO: 1 (human CAPRIN-1 gene). As a control for comparison, GAPDH-specific primers of SEQ ID NOS: 35 and 36 were also used concurrently. As a result, as shown in  FIG. 1 , strong expression was observed in testis among normal dog tissues, while expression was observed in dog breast cancer and adenocarcinoma tissues. Moreover, the observation of the expression of the human homologues from the obtained genes was also carried out. As a result, similarly to the case of the dog CAPRIN-1 gene, expression could be observed in only testis among normal tissues. However, in the case of cancer cells, expression was detected in many types of cancer cell lines, including breast cancer, brain tumor, leukemia, lung cancer, and esophageal cancer cell lines. Expression was observed particularly in many breast cancer cell lines. It was confirmed by the results that the expression of CAPRIN-1 is not observed in normal tissues other than testis, while CAPRIN-1 was expressed in many cancer cells and particularly in breast cancer cell lines. 
     In  FIG. 1 , reference number 1 on each vertical axis indicates the expression patterns of genes identified above and reference number 2 indicates the expression patterns of the GAPDH gene as a control. 
     (5) Preparation of Polyclonal Antibody Against CAPRIN-1-Derived Peptide 
     To obtain an antibody binding to CAPRIN-1, the CAPRIN-1-derived peptide represented by SEQ ID NO: 37 was synthesized. 1 mg of the peptide as an antigen was mixed with an equivalent volume of an incomplete Freund&#39;s adjuvant (IFA) solution. The mixture was subcutaneously administered to rabbits 4 times every 2 weeks. Blood was then collected and antiserum containing polyclonal antibodies was obtained. Furthermore, the antiserum was purified using a protein G carrier (GE HealthCare Bio-Sciences), so that polyclonal antibodies against the CAPRIN-1-derived peptide were obtained. Also, the serum of a rabbit to which no antigen had been administered was purified using a protein G carrier in a manner similar to the above, and the resultant was used as a control antibody. 
     (6) Analysis of Antigen Protein Expression on Cancer Cells 
     Next, 7 breast cancer cell lines (MDA-MB-157, T47D, MRK-nu-1, MDA-MB-231V, BT20, SK-BR-3, and MDA-MB-231T) for which CAPRIN-1 gene expression had been observed at high levels were examined for CAPRIN-1 protein expression on the cell surfaces. 10 6  cells of each human breast cancer cell line for which gene expression had been observed above were centrifuged in a 1.5-ml microcentrifuge tube. 2 μg (5 μl) of the polyclonal antibodies against the CAPRIN-1-derived peptide prepared in (5) above was added thereto. After suspension with 95 μl of PBS containing 0.1% fetal calf serum, it was left to stand on ice for 1 hour. After washing with PBS, the resultant was suspended in PBS containing 5 μl of FITC-labeled goat anti-rabbit IgG antibody (SantaCruz) and 95 μl of 0.1% fetal bovine serum (FBS), and then the resultant was left to stand on ice for 1 hour. After washing with PBS, fluorescence intensity was measured using a FACS Caliber (Becton, Dickinson and Company). Meanwhile, procedures similar to the above were performed using the control antibody prepared in (5) above instead of the polyclonal antibodies against the CAPRIN-1-derived peptide so that a control sample was obtained. As a result, all cells to which the anti-human CAPRIN-1 antibody had been added exhibited enhanced fluorescence intensity compared with the control. Specifically, fluorescence intensity was enhanced to 193% in the case of MDA-MB-231V and 169% in the case of SK-BR-3. It was revealed by these results that the CAPRIN-1 protein was expressed on the cell membrane surfaces of the above human cancer cell lines. The percentage of enhancement in the above fluorescence intensity was expressed as percentage of increase in mean fluorescence intensity (MFI level) in each type of cell and calculated by the following formula.
 
Percentage of increase in mean fluorescence intensity(percentage of enhancement in fluorescence intensity) (%)=((MFI level of cells having reacted with anti-human CAPRIN-1 antibody)−(MFI level of control))/(MFI level of the control)×100.
 
     With a technique similar to the above, CAPRIN-1 expression was also analyzed for 3 renal cancer cell lines (Caki-1, Caki-2, and A498), ovary cancer cell line (SKOV3), lung cancer cell line (QG56), prostate cancer cell line (PC3), uterine cervix cancer cell line (Hela), fibrosarcoma cell line (HT1080), 2 brain tumor cell lines (T98G and U87MG), 2 mouse colorectal cancer cell lines (CT26 and colon 26), mouse breast cancer cell line (4T1), mouse melanoma cell line (B16), and 2 mouse neuroblastoma cell lines (N1E-115 and Neuro2a). As a result, CAPRIN-1 expression was confirmed in all cell lines. In addition, similar results were obtained in the case of using the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #1) comprising the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 47, or the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #2) comprising the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 51, or the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #3) comprising the heavy chain variable region of SEQ ID NO: 63 and the light chain variable region of SEQ ID NO: 67 (obtained in Example 3). 
     (7) Immunohistochemical Staining 
     (7)-1 CAPRIN-1 Expression in Mouse and Dog Normal Tissues 
     Mice (Balb/c, female) and dogs (beagles, female) were exsanguinated under ether anesthesia and ketamine/isoflurane anesthesia. After laparotomy, each organ (stomach, liver, eyeball, thymus gland, muscle, bone marrow, uterus, small bowel, esophagus, heart, kidney, salivary gland, large bowel, mammary gland, brain, lung, skin, adrenal gland, ovary, pancreas, spleen, and bladder) was transferred to a 10-cm dish containing PBS. Each organ was cut open in PBS and then subjected to perfusion fixation overnight in 0.1 M phosphate buffer (pH 7.4) containing 4% paraformaldehyde (PFA). The perfusion solution was discarded, the tissue surface of each organ was rinsed with PBS, a PBS solution containing 10% sucrose was added to a 50-ml centrifuge tube, each tissue was added to the tube, and then the tube was shaken using a rotor at 4° C. for 2 hours. The solution was replaced by a PBS solution containing 20% sucrose, and then left to stand at 4° C. until the tissue sank. The solution was replaced by a PBS solution containing 30% sucrose and then left to stand at 4° C. until the tissue sank. The tissue was removed and then needed portions were excised with a surgical scalpel. Next, an OCT compound (Tissue Tek) was added to the tissue so that it was thoroughly applied to the tissue surface, and then the tissue was placed in a cryomold. The cryomold was placed on dry ice for quick freezing. Thereafter, the tissue was sliced to 10 μm to 20 μM using a cryostat (LEICA). Slices were air-dried on slide glasses using a hair dryer for 30 minutes, to prepare the sliced tissue mounted on a slide glass. Next, each sample was placed in a staining bottle filled with PBS-T (saline containing 0.05% Tween20) and then subjected to replacement with PBS-T being repeated three times every 5 minutes. Excess water around the sections was removed with Kimwipes, and then the sections were circled using a DAKOPEN (DAKO). As blocking solutions, an MOM mouse Ig blocking reagent (VECTASTAIN) and a PBS-T solution containing 10% FBS were overlaid on mouse tissue and dog tissue, respectively, and then left to stand in a moist chamber at room temperature for 1 hour. Next, a solution of the polyclonal antibodies (reactive with the surfaces of cancer cells, prepared in (5) above) against the CAPRIN-1-derived peptide (SEQ ID NO: 37) of 10 μg/ml adjusted with a blocking solution was placed on and then left to stand overnight in a moist chamber at 4° C. 10 minutes of washing with PBS-T was performed 3 times, and then an MOM biotin-labeled anti-IgG antibody (VECTASTAIN) diluted 250-fold with the blocking solution was placed and then left to stand at room temperature for 1 hour in a moist chamber. After ten (10) minutes of washing with PBS-T was performed 3 times, an avidin-biotin ABC reagent (VECTASTAIN) was placed on, and then the sample was left to stand in a moist chamber at room temperature for 5 minutes. After ten (10) minutes of washing with PBS-T was performed 3 times, a DAB coloring solution (DAB 10 mg+30% H 2 O 2  10 μl/0.05 M Tris-HCl (pH 7.6) 50 ml) was placed on, and then the sample was left to stand in a moist chamber at room temperature for 30 minutes. After rinsing with distilled water, a hematoxylin reagent (DAKO) was placed on, the sample was left to stand at room temperature for 1 minute, and then rinsed with distilled water. The slide glass was immersed in 70%, 80%, 90%, 95%, and then 100% ethanol solutions in such order for 1 minute each and then left to stand overnight in xylene. The slide glass was removed, sealed in Glycergel Mounting Medium (DAKO), and then observed. As a result, the expression of CAPRIN-1 was slightly observed within cells of each tissue of salivary gland, kidney, colon, and stomach, but the expression of the same was not observed on cell surfaces. Furthermore, no expression was observed in tissues from other organs. In addition, similar results were obtained in the case of using the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #1) comprising the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 47, the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #2) comprising the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 51, or the anti-CAPRIN-1 monoclonal antibody (monoclonal antibody #3) comprising the heavy chain variable region of SEQ ID NO: 63 and the light chain variable region of SEQ ID NO: 67 (obtained in Example 3). 
     (7)-2 CAPRIN-1 Expression in Dog Breast Cancer Tissue 
     Frozen section slides were prepared by a method similar to the above using 108 frozen breast cancer tissue specimens of dogs pathologically diagnosed as having malignant breast cancer, and immunohistochemical staining was performed using the polyclonal antibody against the CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in (5) above. As a result, the expression of CAPRIN-1 was observed in 100 out of 108 specimens (92.5%) and CAPRIN-1 was strongly expressed on the surfaces of cancer cells with a particularly high grade of atypism. In addition, similar results were obtained in the case of using the monoclonal antibody #1, #2, or #3 obtained in Example 3. 
     (7)-3 CAPRIN-1 Expression in Human Breast Cancer Tissues 
     Immunohistochemical staining was performed using 188 breast cancer tissue specimens on a paraffin-embedded human breast cancer tissue array (BIOMAX). After 3 hours of treatment of the human breast cancer tissue array at 60° C., the array was placed in a staining bottle filled with xylene, followed by xylene replacement being repeated three times every 5 minutes. Next, a similar procedure was performed with ethanol and PBS-T instead of xylene. The human breast cancer tissue array was placed in a staining bottle filled with 10 mM citrate buffer (pH 6.0) containing 0.05% Tween20. After 5 minutes of treatment at 125° C., the array was left to stand at room temperature for 40 minutes or more. Excess water around the sections was removed with Kimwipes, the sections were circled with a DAKOPEN, and Peroxidase Block (DAKO) was added dropwise in appropriate amounts. After left to stand at room temperature for 5 minutes, the array was placed in a staining bottle filled with PBS-T, followed by PBS-T replacement being repeated three times every 5 minutes. As a blocking solution, a PBS-T solution containing 10% FBS was placed on the array, and then the array was left to stand in a moist chamber at room temperature for 1 hour. Next, a solution of the polyclonal antibody against the CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in (5) above having a concentration of 10 μg/ml adjusted with a PBS-T solution containing 5% FBS was placed on, and the array was left to stand overnight in a moist chamber at 4° C. After ten (10) minutes of washing with PBS-T was performed 3 times, Peroxidase Labeled Polymer Conjugated (DAKO) was added dropwise in appropriate amounts and then the array was left to stand in a moist chamber at room temperature for 30 minutes. After ten (10) minutes of washing with PBS-T was performed 3 times, a DAB coloring solution (DAKO) was placed on and then it was left to stand at room temperature for about 10 minutes. The coloring solution was discarded, 10 minutes of washing with PBS-T was performed 3 times, and then it was rinsed with distilled water. The array was immersed in 70%, 80%, 90%, 95%, and then 100% ethanol solutions in such order for 1 minute each, and then left to stand in xylene overnight. The slide glass was removed, sealed in Glycergel Mounting Medium (DAKO), and then observed. As a result, the strong expression of CAPRIN-1 was observed in 138 out of a total of 188 breast cancer tissue specimens (73%). In addition, similar results were obtained in the case of using the monoclonal antibody #1, #2, or #3 obtained in Example 3. 
     (7)-4 CAPRIN-1 Expression in Human Malignant Brain Tumor 
     Immunohistochemical staining was performed according to a method similar to that used in (7)-3 above with 247 malignant brain tumor tissue specimens on a paraffin-embedded human malignant brain tumor tissue array (BIOMAX), using the polyclonal antibodies against the CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in (5) above. As a result, the strong expression of CAPRIN-1 was observed in 227 out of a total of 247 malignant brain tumor tissue specimens (92%). In addition, similar results were obtained in the case of using the monoclonal antibody #1, #2, or #3 obtained in Example 3 
     (7)-5 CAPRIN-1 Expression in Human Breast Cancer Metastasized Lymph Node 
     Immunohistochemical staining was performed according to a method similar to that in (7)-3 above with 150 breast cancer metastasized lymph node tissue specimens on a paraffin-embedded human breast cancer metastasized lymph node tissue array (BIOMAX), using the polyclonal antibody against the CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in (5) above. As a result, the strong expression of CAPRIN-1 was observed in 136 out of a total of 150 breast cancer metastasized lymph node tissue specimens (90%). Specifically, it was revealed that CAPRIN-1 was strongly expressed also in cancer tissues that had metastasized from breast cancer. In addition, similar results were obtained in the case of using the monoclonal antibody #1, #2, or #3 obtained in Example 3. 
     (7)-6 CAPRIN-1 Expression in Various Human Cancer Tissues 
     Immunohistochemical staining was performed according to a method similar to the above with specimens on various paraffin-embedded human cancer tissue arrays (BIOMAX), using the polyclonal antibody against the CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in (5) above. As a result, the strong expression of CAPRIN-1 was observed in esophageal cancer, colon cancer, rectal cancer, lung cancer, renal cancer, bladder cancer, and uterine cervix cancer. In addition, similar results were obtained in the case of using the monoclonal antibody #1, #2, or #3 obtained in Example 3. 
     Example 2 
     Preparation of Human CAPRIN-1 
     (1) Preparation of Recombinant Protein 
     Based on the gene of SEQ ID NO: 1 obtained in Example 1, a recombinant human CAPRIN-1 protein was prepared by the following method. PCR was performed in a total volume of 50 μl with 1 μl of cDNA, two primers (SEQ ID NOS: 38 and 39 comprising Sac I and Xho I restriction enzyme cleavage sequences) of 0.4 μM each, 0.2 mM dNTP, and 1.25U PrimeSTAR HS polymerase (Takara Shuzo Co., Ltd.), prepared by adding the reagents and an accompanying buffer. The expression had been confirmed by an RT-PCR method for the cDNA used herein from among various human-derived tissue- or cell-derived cDNAs prepared in Example 1. PCR was preformed by repeating a cycle of 98° C. for 10 seconds and 68° C. for 2.5 minutes 30 times using a Thermal Cycler (BIO RAD). The above two primers are capable of amplifying a region encoding the entire amino acid sequence of SEQ ID NO: 2. After PCR, the thus amplified DNA was subjected to electrophoresis on 1% agarose gel, and then an about 2.1 kbp DNA fragment was purified using a QIAquick Gel Extraction Kit (QIAGEN). 
     The thus purified DNA fragment was ligated to a cloning vector PCR-Blunt (Invitrogen). After transformation of  Escherichia coli  with it, plasmid was collected. It was verified by sequencing that the thus amplified gene fragment has the sequence of interest. The plasmid having a matched sequence with the sequence of interest was treated with Sac I and Xho I restriction enzymes and then purified with a QIAquick Gel Extraction Kit. The gene sequence of interest was inserted into an  Escherichia coli  expression vector pET30a (Novagen) treated with Sac I and Xho I restriction enzymes. A His-tag fused recombinant protein can be produced using the vector. The plasmid was transformed into  Escherichia coli  for recombinant expression, BL21(DE3), and then expression was induced with 1 mM IPTG, so that the protein of interest was expressed in  Escherichia coli.    
     (2) Purification of Recombinant Protein 
     The above-obtained recombinant  Escherichia coli  expressing the gene of SEQ ID NO: 1 was cultured in LB medium containing 30 μg/ml kanamycin at 37° C. until absorbance at 600 nm reached around 0.7, isopropyl-β-D-1-thiogalactopyranoside was added at a final concentration of 1 mM, and then cells were cultured at 37° C. for 4 hours. Subsequently, centrifugation was performed at 4800 rpm for 10 minutes and then cells were collected. The resulting cell pellet was suspended in phosphate buffered saline and centrifuged at 4800 rpm for 10 minutes, and then cells were washed. 
     The cells were suspended in phosphate buffered saline and then disrupted by ultrasonication on ice. The resulting lysate of the ultrasonicated  Escherichia coli  was subjected to centrifugation at 6000 rpm for 20 minutes, and then the resulting supernatant was regarded as a soluble fraction and the precipitate was regarded as an insoluble fraction. 
     The soluble fraction was added to a nickel chelate column adjusted according to a conventional method (carrier: Chelating Sepharose™ Fast Flow (GE HealthCare); column capacity of 5 ml; and equilibration buffer: 50 mM hydrochloride buffer (pH 8.0)). Unadsorbed fractions were washed off with 50 mM hydrochloride buffer (pH 8.0) in an amount 10 times the column capacity and 20 mM phosphate buffer (pH 8.0) containing 20 mM imidazole. Immediately after washing, 6 beds were eluted with 20 mM phosphate buffer (pH 8.0) containing 100 mM imidazole. The elution of the protein of interest was confirmed by Coomassie staining on the elution fraction with 20 mM phosphate buffer (pH 8.0) containing 100 mM imidazole, and then the elution fraction was added to a strong anion exchange column (carrier: Q Sepharose™ Fast Flow (GE HealthCare); column capacity of 5 ml; and 20 mM phosphate buffer (pH 8.0) as an equilibration buffer). An unabsorbed fraction was washed off with 20 mM phosphate buffer (pH 7.0) in an amount 10 times the column capacity and 20 mM phosphate buffer (pH 7.0) containing 200 mM sodium chloride. Immediately after washing, 5 beds were eluted with 20 mM phosphate buffer (pH 7.0) containing 400 mM sodium chloride, and thus the purified fraction of the protein having the amino acid sequence represented by SEQ ID NO: 2 was obtained. 
     200 μl of each purified sample obtained by the above method was dispensed into 1 ml of reaction buffer (20 mM Tris-Hcl, 50 mM, NaCl, 2 mM CaCl 2′  pH 7.4), followed by addition of 2 μl of enterokinase (Novagen). After that, the resultant was left to stand overnight at room temperature for reaction so that His-tag was cleaved off, and then purification was performed using an Enterokinase Cleavage Capture Kit (Novagen) according to the accompanying protocols. Next, 1.2 ml of the purified sample obtained by the above method was subjected to the buffer replacement with physiological phosphate buffer (Nissui Pharmaceutical Co., Ltd.) using an ultrafiltration NANOSEP 10K OMEGA (PALL). Further, sterile filtration was performed using HT Tuffryn Acrodisc 0.22 μm (PALL) and then the resultant was used for the following experiment. 
     Example 3 
     Preparation of Mouse Monoclonal Antibody Against CAPRIN-1 
     100 μg of the antigen protein (human CAPRIN-1) comprising the amino acid sequence of SEQ ID NO: 2 prepared in Example 2 was mixed with an equivalent amount of MPL+TDM adjuvant (Sigma), and then this was used as an antigen solution per one mouse. The antigen solution was intraperitoneally administered to 6-week-old Balb/cc mice (Japan SLC Inc.), and then the administration was performed 7 times every week, and thus immunization was completed. Each spleen was excised 3 days after the final immunization, and sandwiched between two sterilized slide glasses and then crushed. The resultant was washed with PBS(−) (Nissui) and then centrifuged at 1500 rpm for 10 minutes to remove the supernatant. This procedure was repeated 3 times, so that splenocytes were obtained. The thus obtained splenocytes and mouse myeloma cells SP2/0 (purchased from ATCC) were mixed at a ratio of 10:1. A PEG solution prepared by mixing 200 μl of RPMI1640 medium containing 10% FBS heated at 37° C. and 800 μl of PEG1500 (Boehringer) was added to the mixture, left to stand for 5 minutes for cell fusion, and then subjected to centrifugation at 1700 rpm for 5 minutes. After removal of the supernatant, cells were suspended in 150 ml of RPMI1640 medium containing 15% FBS, supplemented with a HAT solution (Gibco) (2% equivalent) (HAT selective medium), and then the cell suspension was plated on fifteen 96-well plates (Nunc) at 100 μl per well. Cells were cultured for 7 days at 37° C. under conditions of 5% CO 2 , so that hybridomas prepared by fusion of splenocytes and myeloma cells were obtained. 
     Hybridomas were selected using as a marker the binding affinity of the antibody produced by the prepared hybridomas to human CAPRIN-1. The CAPRIN-1 protein solution (1 μg/ml) prepared in Example 2 was added to a 96-well plate at 100 μl per well and then left to stand at 4° C. for 18 hours. Each well was washed 3 times with PBS-T, 400 μl of a 0.5% Bovine Serum Albumin (BSA) solution (SIGMA) was added per well, and then the plate was left to stand at room temperature for 3 hours. The solution was removed, and then the wells were washed three times with 400 μl of PBS-T per well. The culture supernatant of the above-obtained hybridomas was added at 100 μl per well, and then left to stand at room temperature for 2 hours. After washing each well three times with PBS-T, an HRP-labeled anti-mouse IgG (H+L) antibody (Invitrogen) diluted 5000-fold with PBS was added at 100 μl per well and the resultant was then left to stand at room temperature for 1 hour. After washing the wells three times with PBS-T, 100 μl of a TMB substrate solution (Thermo) was added per well and then left to stand for 15 to 30 minutes for coloring reaction. After color development, 100 μl of 1N sulfuric acid was added per well to stop the reaction, and then absorbances at 450 nm and 595 nm were measured using an absorption spectrometer. As a result, several hybridomas producing antibodies with high absorbance values were selected. 
     The thus selected hybridomas were added to a 96-well plate at 0.5 cells per well and then cultured. After 1 week, hybridomas that had formed single colonies in wells were observed. These cells in the wells were further cultured, and then hybridomas were selected using as a marker the binding affinity of antibodies produced by the cloned hybridomas to the human CAPRIN-1. The CAPRIN-1 protein solution (1 μg/ml) prepared in Example 3 was added to a 96-well plate at 100 μl per well, and then left to stand at 4° C. for 18 hours. Each well was washed with PBS-T three times, 400 μl of a 0.5% BSA solution was added per well, and then the resultant was left to stand at room temperature for 3 hours. The solution was removed, and then the wells were washed three times with 400 μl of PBS-T per well. 100 μl of each culture supernatant of the above-obtained hybridomas was added per well, and then the plate was left to stand at room temperature for 2 hours. After washing each well three times with PBS-T, 100 μl of an HRP-labeled anti-mouse IgG (H+L) antibody (Invitrogen) diluted 5000-fold with PBS was added per well and then left to stand at room temperature for 1 hour. After washing the wells three times with PBS-T, 100 μl of a TMB substrate solution (Thermo) was added per well, and then left to stand for 15 to 30 minutes for coloring reaction. After color development, 100 μl of 1N sulfuric acid was added per well to stop the reaction and then absorbances at 450 nm and 595 nm were measured using an absorption spectrometer. As a result, 50 hybridoma cell lines producing monoclonal antibodies immunoreactive with the human CAPRIN-1 were obtained. 
     Next, of those monoclonal antibodies, antibodies reactive with the cell surfaces of breast cancer cells expressing human CAPRIN-1 were selected. Specifically, 10 6  cells of the MDA-MB-231V human breast cancer cell line were centrifuged in a 1.5-ml microcentrifuge tube, and 100 μl of the culture supernatant of each of the above hybridomas was added to the tube, and then the tube was left to stand on ice for 1 hour. After washing with PBS, an FITC-labeled goat anti-mouse IgG antibody (Invitrogen) diluted 500-fold with PBS containing 0.1% FBS was added, and then left to stand on ice for 1 hour. After washing with PBS, fluorescence intensity was measured using a FACS caliber (Becton, Dickinson and Company). Meanwhile, procedures similar to the above were performed using the serum of a 6-week-old Balb/c mouse that had not been treated with antibodies and had been diluted 500-fold with medium for culturing hybridomas, so that a control sample was obtained. As a result, three monoclonal antibodies (monoclonal antibodies #1, #2, and #3) that had exhibited fluorescence intensity stronger than that of the control, and that is, that reacted with the cell surfaces of breast cancer cells, were selected. 
     Example 4 
     Characterization of Selected Antibodies 
     (1) Cloning of Genes of Anti-Human CAPRIN-1 Mouse Monoclonal Antibody Variable Regions 
     mRNA was extracted from each hybridoma cell line producing one of the three monoclonal antibodies selected in Example 3. An RT-PCR method using primers specific to the mouse FR1-derived sequence and the mouse FR4-derived sequence was performed therefor, and the genes of the heavy chain variable (VH) regions and the genes of the light chain variable (VL) regions of all anti-CAPRIN-1 monoclonal antibodies were obtained. For sequence determination, these genes were cloned into a pCR2.1 vector (Invitrogen). 
     (2) RT-PCR 
     mRNA was prepared from 10 6  cells of each hybridoma cell line using a mRNA micro purification kit (GE HealthCare). The thus obtained mRNA was reverse-transcribed and then cDNA was synthesized using a SuperScriptII 1st strand Synthesis Kit (Invitrogen). These procedures were performed according to protocols attached to each kit. 
     Antibody gene amplification was performed by a PCR method using the thus obtained cDNA. 
     To obtain the gene of the VH region, a primer (SEQ ID NO: 54) specific to the mouse heavy chain FR1 sequence and a primer (SEQ ID NO: 55) specific to the mouse heavy chain FR4 sequence were used. Furthermore, to obtain the gene of the VL region, a primer (SEQ ID NO: 56) specific to the mouse light chain FR1 sequence and a primer (SEQ ID NO: 57) specific to the mouse light chain FR4 were used. These primers were designed in reference to Jones, S. T. and Bending, M. M. Bio/Technology 9, 88-89 (1991). Ex-taq (Takara Bio Inc.) was used for PCR. A cDNA sample was added to 5 μl of 10×EX Taq Buffer, 4 μl of dNTP Mixture (2.5 mM), primers (1.0 μM) (2 μl each), and 0.25 μl of Ex Taq (5 U/μl), and then the total amount thereof was adjusted with sterile water to 50 μl. PCR was performed under the conditions: 2 minutes of treatment at 94° C., followed by 30 cycles of 1 minute of denaturation at 94° C., 30 seconds of annealing at 58° C., and 1 minute of extension reaction at 72° C. 
     (3) Cloning 
     The thus obtained PCR products were each subjected to agarose gel electrophoresis, and DNA bands of the VH region and the VL region were excised. DNA fragments were purified using a QIAquick Gel purification kit (QIAGEN) according to the accompanying protocols. The purified DNA was cloned into a pCR2.1 vector using a TA cloning kit (Invitrogen). The ligated vector was transformed into DHSa competent cells (TOYOBO) according to a conventional method. 10 clones of each transformant were cultured overnight in medium (100 μg/ml ampicillin) at 37° C., and then plasmid DNA was purified using a Qiaspin Miniprep kit (QIAGEN). 
     (4) Sequence Determination 
     The gene sequences of the VH region and the VL region in each plasmid obtained above were analyzed with an M13 forward primer (SEQ ID NO: 58) and an M13 reverse primer (SEQ ID NO: 59) on a fluorescence sequencer (DNA sequencer 3130XL; ABI), using a Big Dye Terminator Ver3.1 Cycle Sequencing Kit (ABI) according to the accompanying protocols. As a result, each gene sequence was determined. The sequences were identical among the 10 clones. 
     The thus obtained gene sequences encoding the monoclonal antibody heavy chain variable regions are shown by SEQ ID NOS: 52 and 68, and the amino acid sequences thereof are shown by SEQ ID NOS: 43 and 63; and the gene sequences encoding the light chain variable regions are shown by SEQ ID NOS: 70, 53, and 69 and the amino acid sequences thereof are shown by SEQ ID NOS: 47, 51, and 67. Specifically, it was revealed that the monoclonal antibody #1 comprises the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 47, and #2 comprises the heavy chain variable region of SEQ ID NO: 43 and the light chain variable region of SEQ ID NO: 51, and #3 comprises the heavy chain variable region of SEQ ID NO: 63 and the light chain variable region of SEQ ID NO: 67. 
     Example 5 
     Identification of CAPRIN-1 Epitope to be Recognized by Anti-CAPRIN-1 Monoclonal Antibodies #1, #2 and #3 
     CAPRIN-1 epitope regions recognized by the anti-CAPRIN-1 monoclonal antibodies #1, #2, and #3 (obtained in Example 3) reactive with cancer cell surfaces were identified. 
     93 candidate peptides, each comprising 12 to 16 amino acids in the amino acid sequence of the human CAPRIN-1 protein, were synthesized, and then each peptide was dissolved in DMSO at a concentration of 1 mg/ml. Each peptide was dissolved in 0.1 M sodium carbonate buffer (pH 9.6) at a concentration of 30 μg/ml, added to a 96-well plate (Nunc, Product No. 436006) at 100 μl per well, and then left to stand overnight at 4° C. The solution was discarded, 10 mM ethanolamine/0.1 M sodium carbonate buffer (PH9.6) was added at 200 μl per well, and then the resultant was left to stand at room temperature for 1 hour. The solution was discarded and then the plate was washed twice with PBS containing 0.5% Tween 20 (PBST), so that a plate onto which each peptide had been immobilized was prepared. 
     The cell culture supernatant containing the mouse monoclonal antibodies (#1, #2, and #3) obtained in Example 3 was added at 50 μl per well, and then shaken at room temperature for 1 hour. The solution was removed, followed by three times of washing with PBST. Next, a secondary antibody solution prepared by diluting a HRP-labeled anti-mouse IgG (Invitrogen) antibody 3000- to 4000-fold with PBST was added (50 μl each) to the mouse monoclonal antibodies. The solution was removed, followed by six times of washing with PBST. 
     A TMB substrate solution (Thermo) was added at 100 μl per well and then left to stand for 15 to 30 minutes for coloring reaction. After color development, 1 N sulfuric acid was added at 100 μl per well to stop the reaction, and then absorbances at 450 nm and 595 nm were measured using an absorption spectrometer. As a result, a polypeptide comprising the amino acid sequence of SEQ ID NO: 37 was identified as a partial CAPRIN-1 sequence recognized by both anti-CAPRIN-1 monoclonal antibodies #1 and #2. 
     Therefore, it was revealed that the polypeptide of SEQ ID NO: 37, a partial sequence of human CAPRIN-1, contains the epitope regions for the anti-CAPRIN-1 monoclonal antibodies #1, #2, and #3. 
     Example 6 
     CAPRIN-1 Expression on Various Cancer Cell Surfaces Using Anti-CAPRIN-1 Antibodies #1, #2, and #3 
     Next, 7 breast cancer cell lines (MDA-MB-157, T47D, MRK-nu-1, MDA-MB-231V, BT20, SK-BR-3, and DA-MB-231T) for which CAPRIN-1 gene expression had been observed, and the other 3 breast cancer cell lines (MDA-MB-231C, MCF-7, and ZR75-1), 5 glioma cell lines (T98G, SNB19, U251, U87MG, and U373), 4 renal cancer cell lines (Caki-1, Caki-2, A498, and ACHN), 2 gastric cancer cell lines (MKN28 and MKN45), 5 colorectal cancer cell lines (HT29, LoVo, Caco2, SW480, and HCT116), 3 lung cancer cell lines (A549, QG56, and PC8), 4 leukemia cell lines (AML5, Namalwa, BDCM, RPI1788), 1 uterine cervix cancer cell line (SW756), 1 bladder cancer cell line (T24), 1 esophageal cancer cell line (KYSE180), and 1 lymphoma cell line (Ramos) were examined for CAPRIN-1 protein expression on the cell surfaces of each cell line using the culture supernatants containing #1, #2, and #3 obtained in Example 3. 10 6  cells of each cell line were centrifuged in a 1.5 ml microcentrifuge tube. Each cell culture supernatant (100 μl) containing #1, #2, or #3 was added and then left to stand on ice for 1 hour. After washing with PBS, a FITC-labeled goat-anti mouse IgG (H+L) antibody (SouthernBiotech) diluted 500-fold with PBS containing 0.1% FBS was added and then the resultant was left to stand on ice for 1 hour. After washing with PBS, fluorescence intensity was measured using a FACS Calibur (Becton, Dickinson and Company). Meanwhile, a sample subjected to a reaction with only a secondary antibody was used as a negative control. As a result, cells to which the antibodies #1, #2, and #3 had been added exhibited fluorescence intensity stronger by 20% or more than that of the negative control. It was revealed by these results that the CAPRIN-1 protein was expressed on the cell membrane surfaces of the above human cancer cell lines. The percentage of enhancement in the above fluorescence intensity was expressed as percentage of increase in mean fluorescence intensity (MFI level) in each type of cell and calculated by the following formula.
 
Percentage of increase in mean fluorescence intensity(percentage of enhancement in fluorescence intensity)(%)=((MFI level in cells having reacted with anti-human CAPRIN-1 antibody)−(MFI level of control))/(MFI level of control)×100.
 
     Example 7 
     Anti-Tumor Effects (ADCC Activity and CDC Activity) of Anti-CAPRIN-1 Antibodies on Cancer Cells 
     Whether or not anti-CAPRIN-1 antibodies could damage cancer cells expressing CAPRIN-1 was examined by measuring ADCC activity first. Evaluation was performed using a polyclonal antibody against the human CAPRIN-1-derived peptide (SEQ ID NO: 37) prepared in Example 1. 10 6  cells of the MDA-MB-157 human breast cancer cell line for which CAPRIN-1 expression had been confirmed were collected in a 50-ml centrifugal tube, 100 μCi chromium-51 was added, and then incubation was performed at 37° C. for 2 hours. Subsequently, the resultant was washed three times with RPMI1640 medium containing 10% fetal calf serum. Cells were added to a 96-well V-bottom plate at 10 3  cells per well. 1 μg of the polyclonal antibody against the above human CAPRIN-1-derived peptide was added to the wells and then lymphocytes (2×10 5  each) separated from rabbit peripheral blood were added, followed by 4 hours of culture at 37° C. under conditions of 5% CO 2 . After culture, the amount of chromium (Cr)-51 released from damaged cancer cells in a culture supernatant was measured, so that the ADCC activity of the polyclonal antibodies against the human CAPRIN-1-derived peptide against cancer cells was calculated. As a result, 18.1% ADCC activity against MDA-MB-157 was observed (see  FIG. 2 ). On the other hand, when similar procedures were performed using a control antibody (Example 1 (5)) prepared from peripheral blood of a rabbit not immunized with the antigen, and when no antibody was added, almost no activity was observed (see  FIG. 2 ). Therefore, it was revealed that the anti-CAPRIN-1 antibody can damage cancer cells expressing CAPRIN-1 by ADCC activity. 
     Herein, the cytotoxic activity was determined as a cytotoxic activity against a cancer cell line. Specifically, as described above, the result was obtained by mixing an anti-CAPRIN-1 antibody to be used in the present invention, a rabbit lymphocyte, and 10 3  cells of each cancer cell line that had incorporated chromium-51, culturing cells for 4 hours, measuring the amount of chromium-51 released in medium after culture, and then calculating the cytotoxic activity against the cancer cell line by the following formula*. * Formula: cytotoxic activity (%)=(the amount of chromium-51 released from cancer cells upon addition of an anti-CAPRIN-1 antibody and a rabbit lymphocyte)/(the amount of chromium-51 released from target cells to which 1N hydrochloric acid had been added)×100. 
     Next, the anti-CAPRIN-1 mouse monoclonal antibodies #1, #2, and #3 (obtained in Example 3) were evaluated for their cytotoxic activity against cancer cells. Each cell culture supernatant producing #1, #2, or #3 was purified using Hitrap ProteinA Sepharose FF (GE HealthCare), subjected to buffer replacement with PBS(−), and then filtered with a 0.22 μm filter (Millipore). The resultants were used as antibodies for activity measurement. 10 6  cells of the MDA-MB-157 human breast cancer cell line were collected in a 50-ml centrifuge tube, 100 chromium-51 was added, and then incubation was performed at 37° C. for 2 hours. Subsequently, the resultant was washed three times with RPMI1640 medium containing 10% FBS. Cells were added to a 96-well V-bottom plate at 10 3  cells per well for use as target cells. The above purified antibodies (1 μg each) were added to the cells. 5×10 4  cells of mouse splenocytes isolated from the spleen of a 6-week-old BALB/C mouse (Japan SLC Inc.) according to a conventional method were further added and then cultured for 4 hours at 37° C. under conditions of 5% CO 2 . After culture, the amount of chromium-51 released from damaged tumor cells in a culture supernatant was measured, and the cytotoxic activity of each anti-CAPRIN-1 antibody against cancer cells was calculated. As negative control samples, a sample prepared by adding PBS instead of the antibodies and a sample prepared by adding an isotype control antibody instead of the antibodies were used. As a result, the antibodies #1, #2, and #3 exhibited more than 25% cytotoxic activity against MDA-MB-157. In contrast, the activity in the sample prepared by adding PBS as a negative control and the activity in the sample prepared by adding the isotype control antibody as a negative control were 1.7% and 3.0%, respectively. Similarly, the antibodies #1, #2, and #3 were examined for their cytotoxic activity against other cancer cells including glioma cell lines T98G and U373, lung cancer cell lines A549 and QG56, renal cancer cell lines Caki-1 and ACHN, a uterine cervix cancer cell line SW756, a bladder cancer cell line T24, an esophageal cancer cell line KYSE180, gastric cancer cell lines MKN28 and MKN45, a colorectal cancer cell line SW480, a leukemia cell line AML5, and a lymphoma cell line Ramos. As a result, the antibody #1 exhibited 13.2% against T98G (2.5% in the case of isotype control), 16.0% against U373 (4.3% in the case of isotype control), 12.0% against A549 (4.5% in the case of isotype control), 12.6% against QG56 (5.3% in the case of isotype control), 10.3% against Caki-1 (4.5% in the case of isotype control), 9.0% against ACHN (3.8% in the case of isotype control), 8.6% against SW756 (5.1% in the case of isotype control), 13.0% against T24 (3.8% in the case of isotype control), 8.9% against KYSE180 (5.7% in the case of isotype control), 16.2% against MKN28 (4.2% in the case of isotype control), 12.1% against MKN45 (4.6% in the case of isotype control), 13.4% against SW480 (6.4% in the case of isotype control), 8.9% against AML5 (4.7% in the case of isotype control), and 8.1% against Ramos (2.5% in the case of isotype control). Also the antibodies #2 and #3 exhibited similar results. It was demonstrated by the above results that the thus obtained anti-CAPRIN-1 antibodies #1, #2, and #3 damage cancer cells expressing CAPRIN-1 by ADCC activity. It was demonstrated by the above results that the thus obtained anti-CAPRIN-1 mouse monoclonal antibodies #1, #2, and #3 damage cancer cells expressing CAPRIN-1 by ADCC activity. 
     Herein, the cytotoxic activity was determined as a cytotoxic activity against a cancer cell line. Specifically, as described above, the result was obtained by mixing an anti-CAPRIN-1 antibody to be used in the present invention, a mouse splenocyte, and 10 3  cells of each cancer cell line that had incorporated chromium-51, culturing cells for 4 hours, measuring the amount of chromium-51 released in medium after culture, and then calculating the cytotoxic activity against the cancer cell line by the following formula*. * Formula: cytotoxic activity (%)=(the amount of chromium-51 released from cancer cells upon addition of an anti-CAPRIN-1 antibody and a mouse splenocyte)/(the amount of chromium-51 released from target cells to which 1N hydrochloric acid had been added)×100. 
     Next, the obtained anti-CAPRIN-1 mouse monoclonal antibodies #1 and #2 were evaluated for their cytotoxic activity (CDC activity) against cancer cells. Blood collected from a rabbit was added to an Eppendorf tube, left to stand at room temperature for 60 minutes, and then subjected to 5 minutes of centrifugation at 3000 rpm. Thus, serum for measurement of CDC activity was prepared. 10 5  cells of the MDA-MB-231V human breast cancer cell line were collected in a 50-ml centrifuge tube, 100 μCi chromium-51 was added, and then incubation was performed at 37° C. for 2 hours. The resultant was washed three times with RPMI medium containing 10% FBS. Subsequently, the cells were suspended in RPMI medium containing the above-prepared rabbit serum (50%), and then added to a 96-well V-bottom plate at 10 3  cells per well. 1 μg each of the mouse monoclonal antibodies #1 and #2 was added to the cells and then cells were cultured for 4 hours at 37° C. under conditions of 5% CO 2 . After culture, the amount of chromium-51 released from damaged tumor cells in a culture supernatant was measured, and then the CDC activity of each antibody against MDA-MB-231V was calculated. As a result, the antibodies #1 and #2 both exhibited more than 20% CDC activity. Also, no cytotoxic activity was observed in a negative control group to which no antibody had been added. Therefore, it was revealed that the antibodies #1 and #2 can damage tumor cells expressing CAPRIN-1 also by CDC activity. 
     Herein, the cytotoxic activity was determined as a cytotoxic activity against a cancer cell line. Specifically, as described above, the result was obtained by mixing an anti-CAPRIN-1 antibody to be used in the present invention, serum, and 10 3  cells of each cancer cell line that had incorporated chromium-51, culturing cells for 4 hours, measuring the amount of chromium-51 released in medium after culture, and then calculating the cytotoxic activity against the cancer cell line by the following formula*. * Formula: cytotoxic activity (%)=(the amount of chromium-51 released from cancer cells upon addition of an anti-CAPRIN-1 antibody and serum)/(the amount of chromium-51 released from target cells to which 1N hydrochloric acid had been added)×100. 
     Next, the thus obtained anti-CAPRIN-1 mouse monoclonal antibodies #1 and #2 were evaluated for their in vivo anti-tumor effects in tumor-bearing mice. Antibodies used herein were prepared by column purification of the culture supernatant of each cell producing #1 or #2 in the same manner as described above. 
     The anti-tumor effects of the antibodies #1 and #2 were examined using tumor-bearing mice into which a mouse-derived cancer cell line expressing CAPRIN-1 had been transplanted. 4T1 cells (purchased from ATCC) were transplanted subcutaneously to the dorsal region of 30 Balb/c mice (Japan SLC Inc.) at 5×10 5  cells/mouse. Tumors were allowed to grow to reach a size of about 5 mm in diameter. The antibodies #1 and #2 were each administered intraperitoneally to 20 tumor-bearing mice from among the 30 tumor-bearing mice in an amount of 200 μg (200 μl)/mouse (each antibody was administered to 10 mice). Subsequently, the same amount of the antibody was administered intraperitoneally to each tumor-bearing mouse 3 times in total within 2 days. Tumor sizes were measured every day and anti-tumor effects were examined by observation. Meanwhile, as a control group, PBS (−) was administered instead of the antibodies to the remaining 10 tumor-bearing mice. The tumor size was calculated as a volume using the formula: length of major axis×length of minor axis×length of minor axis×0.5. 
     As a result of observation of anti-tumor effects, in the examination group to which the anti-CAPRIN-1 mouse monoclonal antibodies #1 and #2 had been administered, tumors were found to have almost completely regressed up to day 16 after the administration of the antibodies. On the other hand, in the control group to which PBS(−) had been administered, tumors were found to have increased to about 820% on day 12. It was demonstrated by these results that the obtained anti-human CAPRIN-1 mouse monoclonal antibodies #1 and #2 exhibit strong in vivo anti-tumor effects on cancer cells expressing CAPRIN-1. 
     INDUSTRIAL APPLICABILITY 
     The antibodies of the present invention are useful for treating and/or preventing cancer. 
     All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety. 
     SEQUENCE LISTING FREE TEXT 
     SEQ ID NO: 31: T3 primer 
     SEQ ID NO: 32: T7 primer 
     SEQ ID NOS: 33, 34, 38, 39, and 54-59: primers 
     SEQ ID NOS: 35 and 36: GAPDH primers