METHODS AND COMPOSITIONS FOR DIAGNOSING CARCINOMAS

Abstract: The invention is directed to compositions and methods for the detection of a malignant condition, and relates to the discovery of soluble forms of mesothelin polypeptides, including mesothelin related antigen (MRA). In particular the invention provides a nucleic acid sequence encoding MRA and an MRA variant. The invention also provides a method of screening for the presence of a malignant condition in a subject by detecting reactivity of an antibody specific for a mesothelin polypeptide with a molecule naturally occurring in soluble form in a sample from such a subject, and by hybridization screening using an MRA nucleotide sequence, as well as other related advantages.

Description: METHODS AND COMPOSITIONS FOR DIAGNOSING CARCINOMAS TECHNICAL FIELD The present invention relates generally to malignant conditions such as cancer, and in particular to methods and compositions for diagnosing certain carcinomas such as ovarian carcinoma. BACKGROUND OF THE INVENTION Cancer includes a broad range of diseases, affecting approximately one in four individuals worldwide. The severity of the adverse impact of cancer cannot be understated, influencing medical policy and procedure as well as society generally. Because a hallmark of many types of cancer is rapid and unregulated proliferation of malignant cells, an overarching problem in improving approaches to cancer is the need for early detection and diagnosis. Numerous attempts have been made to develop accurate and reliable criteria for diagnosing the presence of a malignant condition. In particular, efforts have been directed to the use of serologically defined antigenic markers known as tumor associated antigens, which are either uniquely expressed by cancer cells or are present at markedly higher levels in subjects having a malignant condition. However, due to the high heterogeneity of tumor associated antigen expression, for example the extreme diversity of carcinoma antigens, there is a need for additional tumor markers that are useful in cancer diagnosis. Many monoclonal antibodies reactive with carcinoma associated antigens are known (see, e.g., Papsidero, 1985 Semin. Surg. Oncol. 1 :171, Allum et al., 1986 Surg. Ann. 18:41). These and other described monoclonal antibodies bind to a variety of different carcinoma associated antigens including glycoproteins, glycolipids and mucins (see, e.g., Fink et al., 1984 Prog. Clin. Pathol. 9:121; U.S. Patent No. 4,737,579; U.S. Patent No. 4,753,894; U.S. Patent No. 4,579,827; U.S. Patent No. 4,713,352). Many such monoclonal antibodies recognize tumor associated antigens that exhibit restricted expression on some but not other tumors originating in a given cell lineage or tissue type. There are only relatively few examples of tumor associated antigens that appear to be useful for identifying a particular type of malignancy. Monoclonal antibody B72.3, for example, specifically binds to a high molecular mass (>10 6 Da) tumor-associated mucin antigen that is selectively expressed on a number of different carcinomas, including most if not all ovarian carcinomas and an overwhelming majority of non- small cell lung carcinomas, colon carcinomas and breast carcinomas (see, e.g., Johnston, 1987 Ada Cytol. 1 :537; U.S. 4,612,282). Nevertheless, detection of cell-associated tumor markers such as the mucin antigen recognized by B72.3 following surgical resection of a tumor may be of limited usefulness for diagnostic screening, in which early detection of a malignant condition prior to accumulation of substantial tumor mass is preferred. An alternative to the diagnosis of a particular type of cancer by screening surgically resected specimens for tumor associated antigens, where invasive surgery is usually indicated only after detection of an accumulated tumor mass, would be to provide compositions and methods for detecting such antigens in samples obtained from subjects by non-invasive or minimally invasive procedures. In ovarian and other carcinomas, for example, there are currently a number of soluble tumor associated antigens that are detectable in samples of readily obtained biological fluids such as serum or mucosal secretions. One such marker is CA125, a carcinoma associated antigen that is also shed into the bloodstream, where it is detectable in serum (e.g., Bast et al., 1983 N Eng. J. Med. 309:883; Lloyd et al., 1997 Int. J. Cane. 71 :842). CA125 levels in serum and other biological fluids have been measured along with levels of other markers, for example, carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCC), tissue polypeptide specific antigen (TPS), sialyl TΝ mucin (STΝ) and placental alkaline phosphatase (PLAP), in efforts to provide diagnostic and/or prognostic profiles of ovarian and other carcinomas (e.g., Sarandakou et al., 1997 Ada Oncol. 36:755; Sarandakou et al., 1998 Eur. J. Gynaecol. Oncol. 19:73; Meier et al, 1997 Anticanc. Res. 17(4B):2945; Kudoh et al., 1999 Gynecol. Obstet. Invest. 47:52; Ind et al., 1997 Br. J. Obstet. Gynaecol. 104:1024; Bell et al. 1998 Br. J. Obstet. Gynaecol. 105:1136; Cioffi et al., 1997 Tumori 83:594; Meier et al. 1997 Anticanc. Res. 17(4B):2949; Meier et al., 1997 Anticanc. Res. 17(4B):3019). Elevated levels of serum CA125 alone or in combination with other known indicators, however, do not provide a definitive diagnosis of malignancy, or of a particular malignancy such as ovarian carcinoma. For example, elevated CA125, CEA and SCC in vaginal fluid and serum correlate most strongly with inflammation in benign gynecological diseases, relative to cervical cancer and genital tract cancers (e.g., Moore et al., 1998 Infect. Dis. Obstet. Gynecol. 6:182; Sarandakou et al., 1997 Ada Oncol. 36:755). As another example, elevated serum CA125 may also accompany neuroblastoma (e.g., Hirokawa et al., 1998 Surg. Today 28:349), while elevated CEA and SCC, among others, may accompany colorectal cancer (Gebauer et al., 1997 Anticanc. Res. 17(4B):2939). Thus the compelling need for additional markers to be used, including markers useful in multi-factor diagnostic screening, is apparent. (See, e.g., Sarandakou et al., 1998; Kudoh et al., 1999; Ind et al., 1997.) The differentiation antigen mesothelin is expressed on the surfaces of normal mesothelial cells and also on certain cancer cells, including epithelial ovarian tumors and mesotheliomas. Also known as CAK1, mesothelin is identified by its reactivity with the monoclonal antibody K-l (MAb K-l), which was generated following immunization with the OVCAR-3 ovarian carcinoma cell line (Chang et al., 1992 Cane. Res. 52:181 ; Chang et al., 1992 Int. J. Can . 50:373; Chang et al., 1992 Int. J. Cane. 51 :548; Chang et al., 1996 Proc. Nat. Acad. Sci. USA 93:136; Chowdhury et al., 1998 Proc. Nat. Acad. Sci. USA 95:669). Mesothelin is synthesized as an approximately 70 kDa glycoprotein precursor having a C-terminal glycosylphosphatidylinositol (GPI) linkage site for cell membrane attachment. This precursor is processed by, inter alia, proteolytic cleavage into at least two components: (i) a shed N-terminal -31 kDa polypeptide (Chowdhury et al., 1998 Proc. Nat. Acad. Sci. USA 95:669) having extraordinarily high homology to a soluble 31 kDa polypeptide known as megakaryocyte potentiating factor (MPF) that is similarly derived by proteolysis of an approximately 70 kDa GPI-linked glycoprotein precursor belonging to the mesothelin polypeptide family (Yamaguchi et al., 1994 J. Biol. Chem. 269:805; Kojima et al., 1995 J. Biol. Chem. 270:21984; and (ii) a mature 40 kDa GPI-linked, cell surface-bound C-terminal mesothelin glycosylated polypeptide, which bears the K-l (MAb K-l) recognition epitope (Chang et al., 1996). As defined by reactivity with MAb K-l, mesothelin is present on a majority of squamous cell carcinomas including epithelial ovarian, cervical and esophageal tumors, and on mesotheliomas (Chang et al., 1992 Cane. Res. 52:181; Chang et al., 1992 Int. J. Cane. 50:373; Chang et al, 1992 Int. J. Cane. 51 :548; Chang et al., 1996 Proc. Nat. Acad. Sci. USA 93:136; Chowdhury et al., 1998 Proc. Nat. Acad. Sci. USA 95:669). Using MAb K-l, mesothelin is detectable only as a cell-associated tumor marker and has not been found in serum from ovarian cancer patients, or in medium conditioned by OVCAR-3 cells (Chang et al., 1992 Int. J. Cancer 50:373). Thus mesothelin, despite an expression pattern that correlates with specific malignant conditions, does not appear to offer a useful marker for early diagnostic screening, because only cell-associated and not soluble forms of mesothelin may be detectable by known methods. The compositions and methods of the present invention overcome these limitations of the prior art by providing a method of screening for the presence of a malignant condition using antibodies specific for mesothelin/MPF and/or mesothelin/MPF- related antigens to detect polypeptides that naturally occur in soluble form, and offer other related advantages. SUMMARY OF THE INVENTION The present invention is directed to compositions and methods useful in screening for the presence of a malignant condition in a subject. In particular, the invention relates to the unexpected finding that soluble mesothelin polypeptides, or molecules naturally occurring in soluble form and having an antigenic determinant reactive with at least one antibody that is specific for a mesothelin polypeptide, can be detected in a biological sample from a subject. It is one aspect of the invention to provide a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one antibody specific for a mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample and having an antigenic determinant that is reactive with the at least one antibody, under conditions and for a time sufficient to detect binding of the antibody to the antigenic determinant, and therefrom detecting the presence of a malignant condition. In some embodiments the biological sample is blood, serum, serosal fluid, plasma, lymph, urine, cerebrospinal fluid, saliva, a mucosal secretion, a vaginal secretion, ascites fluid, pleural fluid, pericardial fluid, peritoneal fluid, abdominal fluid, culture medium, conditioned culture medium or lavage fluid. In certain other embodiments, the mesothelin related antigen polypeptide comprises a polypeptide having the amino acid sequence set forth in SEQ ID NO:l or in SEQ ID NO:2 or a fragment or derivative thereof. In another embodiment the mesothelin related antigen polypeptide variant is a splice variant. In certain embodiments of the invention, the antibody comprises a polyclonal antibody, and in other embodiments the antibody comprises an affinity purified antibody. In particularly preferred embodiments the antibody comprises a monoclonal antibody. In another embodiment the antibody comprises a recombinant antibody and in another embodiment the antibody comprises a chimeric antibody. In another embodiment, the antibody comprises a humanized antibody. In another embodiment, the antibody comprises a single chain antibody. In some embodiments of the invention, detection of binding of the antibody to an antigenic determinant comprises detection of a radionuclide. In other embodiments, detection of binding of the antibody to an antigenic determinant comprises detection of a fluorophore. In another embodiment, detection of binding of the antibody to an antigenic determinant comprises detection of a binding event between an avidin molecule and a biotin molecule and in another embodiment detection of binding of the antibody to an antigenic determinant comprises detection of a binding event between a streptavidin molecule and a biotin molecule. In certain embodiments detection of binding of the antibody to an antigenic determinant comprises spectrophotometric detection of a product of an enzyme reaction. In some embodiments of the invention, the at least one antibody is detectably labeled, while in certain other embodiments the at least one antibody is not detectably labeled and detection of binding of the antibody to an antigenic determinant is indirect. According to certain embodiments of the invention, the malignant condition may be adenocarcinoma, mesothelioma, ovarian carcinoma, pancreatic carcinoma or non- small cell lung carcinoma. It is another aspect of the invention to provide a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one antibody to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample and having an antigenic determinant that is reactive with the at least one antibody, the antigen combining site of which competitively inhibits the immunospecific binding of a monoclonal antibody that is OV569, MAb K-l, 4H3, 3G3 or 1A6, under conditions and for a time sufficient to detect binding of the antibody to the antigenic determinant, and therefrom detecting the presence of a malignant condition. Another aspect of the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one antibody to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample and having an antigenic determinant that is reactive with the antibody, the antigen combining site of which competitively inhibits the immunospecific binding of monoclonal antibody OV569, under conditions and for a time sufficient to detect binding of the antibody to the antigenic determinant, and therefrom detecting the presence of a malignant condition. Still another aspect of the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one antibody specific for a human mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample and having an antigenic determinant that is reactive with the antibody, under conditions and for a time sufficient to detect binding of the at least one antibody to the antigenic determinant, wherein the at least one antibody immunospecifically binds to mesothelin related antigen, and therefrom detecting the presence of a malignant condition. In certain embodiments, the mesothelin related antigen is also immunospecifically reactive with monoclonal antibody MAb K-l . Turning to another aspect, the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one antibody specific for a human mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample and having an antigenic determinant that is reactive with the at least one antibody, the antigen combining site of which competitively inhibits the immunospecific binding of a monoclonal antibody that is OV569, MAb K-l, 4H3, 3G3 or 1A6, under conditions and for a time sufficient to detect binding of the antibody to the antigenic determinant, wherein the at least one antibody immunospecifically binds to mesothelin related antigen, and therefrom detecting the presence of a malignant condition. In certain embodiments the mesothelin related antigen is also immunospecifically reactive with monoclonal antibody MAb K-l . Turning to another aspect, the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one immobilized first antibody specific for a mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample, under conditions and for a time sufficient to specifically bind the at least one immobilized first antibody to the mesothelin related antigen polypeptide and thereby form an immune complex; removing constituents of the sample that do not specifically bind to the at least one immobilized first antibody; and contacting the immune complex with at least one second antibody specific for a mesothelin related antigen polypeptide, wherein the antigen combining site of the at least one second antibody does not competitively inhibit the antigen combining site of the at least one immobilized first antibody, under conditions and for a time sufficient to detect specific binding of the at least one second antibody to the mesothelin related antigen polypeptide, and therefrom detecting the presence of a malignant condition. In yet another aspect the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one immobilized first antibody specific for a mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample, wherein the antigen combining site of the at least one first antibody competitively inhibits the immunospecific binding of monoclonal antibody OV569 under conditions and for a time sufficient to specifically bind the at least one immobilized first antibody to the mesothelin related antigen polypeptide and thereby form an immune complex; removing constituents of the sample that do not specifically bind to the at least one immobilized first antibody; and contacting the immune complex with at least one second antibody specific for a mesothelin related antigen polypeptide, wherein the antigen combining site of the at least one second antibody does not competitively inhibit the immunospecific binding of monoclonal antibody OV569 , under conditions and for a time sufficient to detect specific binding of the at least one second antibody to the mesothelin related antigen polypeptide, and therefrom detecting the presence of a malignant condition. In another aspect, the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with at least one immobilized first antibody specific for a mesothelin related antigen polypeptide to determine the presence in the biological sample of a molecule naturally occurring in soluble form in the sample, wherein the antigen combining site of the at least one first antibody competitively inhibits the immunospecific binding of monoclonal antibody MAb K-l under conditions and for a time sufficient to specifically bind the at least one immobilized first antibody to the mesothelin related antigen polypeptide and thereby form an immune complex; removing constituents of the sample that do not specifically bind to the at least one immobilized first antibody; and contacting the immune complex with at least one second antibody specific for a mesothelin related antigen polypeptide, wherein the antigen combining site of the at least one second antibody does not competitively inhibit the immunospecific binding of monoclonal antibody MAb K-l, under conditions and for a time sufficient to detect specific binding of the at least one second antibody to the mesothelin related antigen polypeptide, and therefrom detecting the presence of a malignant condition. In certain embodiments the subject invention method further comprises determining the presence in the sample of at least one soluble marker of a malignant condition, wherein the marker is carcinoembryonic antigen, CA125, sialyl TN, squamous cell carcinoma antigen, tissue polypeptide antigen, or placental alkaline phosphatase. It is another aspect of the invention to provide a method of screening for the presence of a malignant condition in a subject comprising contacting each of (i) a first biological sample from a first subject suspected of having a malignant condition, and (ii) a second biological sample from a second subject known to be free of a malignant condition, with at least one antibody specific for a mesothelin related antigen polypeptide to determine the presence in each of the first and second biological samples of a molecule naturally occurring in soluble form in the samples and having an antigenic determinant that is reactive with the at least one antibody, under conditions and for a time sufficient to detect binding of the antibody to the antigenic determinant, and comparing a level of detectable binding of the antibody to the antigenic determinant in the first biological sample to a level of detectable binding of the antibody to the antigenic determinant in the second biological sample, and therefrom detecting the presence of a malignant condition. In another aspect, the invention provides a method of screening for the presence of a malignant condition in a subject comprising detecting in a biological sample from the subject the presence of an antibody that immunospecifically binds to a mesothelin related antigen polypeptide. In certain embodiments the mesothelin related antigen polypeptide comprises a polypeptide having the amino acid sequence of SEQ ID NO:l or SEQ ID NO:2 or SEQ ID NO:13. Turning to another aspect, the invention provides an antibody specific for a human mesothelin related antigen polypeptide, comprising a monoclonal immunoglobulin variable region that does not competitively inhibit the immunospecific binding of monoclonal antibody Mab K-l to a mesothelin polypeptide and that specifically binds to a mesothelin related antigen polypeptide comprising the amino acid sequence set forth in SEQ ID NO:l or in SEQ ID NO:2 or in SEQ ID NO:13. In certain embodiments the antibody is a fusion protein, while in certain other embodiments the antibody is a single chain antibody. In certain other embodiments, the mesothelin related antigen polypeptide further comprises a glycosylated mesothelin polypeptide. In another embodiment, the mesothelin related antigen polypeptide has an apparent molecular weight of approximately 42 to 45 kilodaltons. In certain embodiments the antibody is monoclonal antibody OV569, 4H3, 3G3 or 1A6. In still another aspect, the invention provides a method of screening for the presence of a malignant condition in a subject comprising contacting a biological sample from a subject with a detectably labeled mesothelin related antigen polypeptide, under conditions and for a time sufficient to detect binding to the mesothelin related antigen polypeptide of an antibody naturally occurring in soluble form in the sample, and therefrom detecting the presence of a malignant condition. Turning to another aspect, the invention provides an isolated nucleic acid molecule that is a nucleic acid molecule encoding a mesothelin related antigen polypeptide, the polypeptide comprising an amino acid sequence set forth in SEQ ID NO:l or in SEQ ID NO:2 or in SEQ ID NO:13; or that is a nucleic acid molecule that encodes a mesothelin related antigen polypeptide and that is capable of hybridizing to such a nucleic acid molecule encoding a mesothelin related antigen under moderately stringent conditions, wherein the isolated nucleic acid molecule is not a nucleic acid molecule consisting of the nucleotide sequence set forth in SEQ ID NO: 15, the nucleotide sequence set forth in SEQ ID NO: 16, the nucleotide sequence set forth in SEQ ID NO: 17 or the nucleotide sequence set forth in SEQ ID NO: 18. In certain embodiments the invention provides an antisense oligonucleotide comprising at least 15 consecutive nucleotides complementary to the nucleic acid molecule encoding a mesothelin related antigen polypeptide. In other embodiments, the present invention provides a fusion protein comprising a polypeptide sequence fused to a mesothelin related antigen polypeptide. In certain further embodiments, the polypeptide is an enzyme or a variant or fragment thereof. In certain further embodiments, the polypeptide sequence fused to a mesothelin related antigen polypeptide is cleavable by a protease. In another embodiment, the polypeptide sequence is an affinity tag polypeptide having affinity for a ligand. In other embodiments, the invention provides a recombinant expression construct comprising at least one promoter operably linked to a nucleic acid molecule encoding a mesothelin related antigen polypeptide as described above. In certain embodiments the promoter is a regulated promoter and in certain other embodiments the mesothelin related antigen polypeptide is expressed as a fusion protein with a polypeptide product of a second nucleic acid sequence. In a further embodiment the polypeptide product of the second nucleic acid sequence is an enzyme. In another embodiment the expression construct is a recombinant viral expression construct. According to other embodiments, the invention provides a host cell comprising a recombinant expression construct as provided herein. In one embodiment the host cell is a prokaryotic cell and in another embodiment the host cell is a eukaryotic cell. In another aspect, the invention provides a method of producing a recombinant mesothelin related antigen polypeptide by culturing a host cell comprising a recombinant expression construct comprising at least one promoter operably linked to a nucleic acid molecule encoding a mesothelin related antigen polypeptide as provided herein. In certain embodiments the promoter is a regulated promoter. In another embodiment the invention provides a method of producing a recombinant mesothelin related antigen polypeptide, by culturing a host cell infected with the recombinant viral expression construct as provided herein for expression of recombinant mesothelin related antigen polypeptide. The present invention also provides, in another embodiment, a method for detecting mesothelin related antigen expression in a sample by contacting an antisense oligonucleotide as described above with a sample comprising a nucleic acid sequence encoding a mesothelin related antigen polypeptide having the amino acid sequence set forth in SEQ ID NO: 13, or a fragment or variant thereof; and detecting in the sample an amount of mesothelin related antigen polypeptide-encoding nucleic acid that hybridizes to the antisense oligonucleotide, and therefrom detecting mesothelin related antigen expression in the sample. In another embodiment the amount of mesothelin related antigen polypeptide- encoding nucleic acid that hybridizes to the antisense oligonucleotide is determined using polymerase chain reaction. In another embodiment the amount of mesothelin related antigen polypeptide-encoding nucleic acid that hybridizes to the antisense oligonucleotide is determined using a hybridization assay. In another embodiment the sample comprises an RNA or cDNA preparation. These and other aspects of the present invention will become evident upon reference to the following detailed description and attached drawings. In addition, various references are set forth herein which describe in more detail certain aspects of this invention, and are therefore incorporated by reference in their entireties. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows Western immunoblot characterization of the carcinoma associated antigen detected by monoclonal antibody OV569. Figure 2 shows monoclonal antibody OV569 binding to human immunoglobulin constant region fusion proteins containing soluble (Dlhlg) or membrane- associated (D2hlg) domains of MPF in ELI S A. Figure 3 depicts detection of soluble mesothelin polypeptides in sera from carcinoma patients by sandwich ELISA. Figure 4 illustrates detection using sandwich ELISA of soluble mesothelin polypeptides in sera from normal subjects and from patients diagnosed with malignant conditions. Figure 5A-B shows a mesothelin related antigen (MRA-1) amino acid sequence (SEQ ID NO:l) and a nucleic acid sequence (SEQ ID NO:3) encoding the MRA- 1 mesothelin related antigen. Amino acid and nucleotide positions are numbered according to the MRA-2 sequence (Figure 6A-B) which begins with three additional N-terminal amino acids (nine additional 5' nucleotides). Highlighted in bold type is the 82 base insertion relative to the related mesothelin/ MPF sequences. Figure 5C shows amino acid sequence using single letter code. Figure 6A-B shows a mesothelin related antigen (MRA-2) amino acid sequence (SEQ ID NO:2) and a nucleic acid sequence (SEQ ID NO:4) encoding the MRA- 2 mesothelin related antigen, which begins with three additional N-terminal amino acids (nine additional 5' nucleotides). Highlighted in bold type are 80 nucleotides of the 82 base insertion relative to the related mesothelin/ MPF sequences. Figure 6A-B shows amino acid sequence using single letter code. Figure 7A-B shows a soluble mesothelin related (SMR) antigen amino acid sequence (SEQ ID NO: 13) and a nucleic acid sequence (SEQ ID NO: 14) encoding this SMR. Highlighted in bold type is the 82 base insertion relative to the related mesothelin/ MPF sequences. Figure 7C shows amino acid sequence using single letter code. DETAILED DESCRIPTION OF THE INVENTION The present invention pertains in part to the unexpected discovery that soluble forms of certain gene products referred to herein as mesothelin polypeptides occur naturally in subjects, including elevated levels of such soluble mesothelin polypeptides in subjects having certain carcinomas. The invention therefore provides useful compositions and methods for the detection and diagnosis of a malignant condition in a subject by specific detection of such soluble mesothelin polypeptides. As described in detail below, certain embodiments of the invention relate to human mesothelin polypeptides, which include polypeptides such as the novel soluble mesothelin related antigen (MRA) polypeptide described herein, and also include the cell surface-associated portion of mesothelin (Chang εt al., 1996 Proc. Nat. Acad. Sci. USA 93:136) and the membrane bound portion of the megakaryocyte potentiating factor (MPF) precursor (Kojima et al., 1995 J. Biol Chem. 270:21984). In certain other embodiments, the invention relates to fragments, derivatives and/or analogs of MRA polypeptides. Briefly, according to certain embodiments of the present invention, there is provided a method of screening for the presence of a malignant condition in a subject by contacting a biological sample from the subject with an antibody specific for a human mesothelin polypeptide. The complete amino acid and nucleic acid coding sequences of MRA are disclosed herein, including the surprising observation that a nucleic acid molecule derived from polyA+ RNA and which encodes MRA lacks a stop codon. The complete amino acid and nucleic acid coding sequences for mesothelin (Chang et al., 1996) and MPF (Kojima et al., 1995) are known, including the portions of those sequences corresponding to mesothelin polypeptides as used herein, including MRA. Expression of mesothelin polypeptides in the cytoplasm as well as on the surfaces of a variety of human tumor cell lines is known (see e.g., Chang et al., 1996; Kojima et al., 1995; and references cited therein), which permits the use of such cells as immunogens for generating antibodies specific for a mesothelin polypeptide, as described herein. A monoclonal antibody that specifically recognizes a human mesothelin polypeptide has been reported and is available (Chang et al., 1996; Chang et al., 1992 Int. J. Cancer 50:373). Alternatively, those having ordinary skill in the art may routinely and without undue experimentation immunize a host and screen for mesothelin polypeptide specific antibody production using the present teachings along with methodologies well known in the art. For example, certain tumor cells that may be used as immunogens are known to express mesothelin polypeptides (see e.g., Chang et al., 1996; Kojima et al., 1995; and references cited therein), and determination of mesothelin polypeptide expression in a candidate immunogenic cell line can be accomplished based upon characterization of mesothelin polypeptides provided herein and/or upon detectable expression of the nucleotide sequences encoding mesothelin polypeptides as reported, for example, in Chang et al. (1996) and Kojima et al. (1995). From the physicochemical and immunochemical properties of soluble mesothelin polypeptides disclosed herein, and using the presently disclosed nucleic acid sequences encoding members of the mesothelin polypeptide family that are mesothelin related antigens (MRAs), or optionally using the reported properties of nucleotide sequences encoding other mesothelin polypeptides (e.g., mesothelin or MPF), a person having ordinary skill in the art may also prepare a recombinant mesothelin polypeptide that can be used to produce and characterize specific antibodies according to well known methodologies. Mesothelin polypeptides can be expressed in mammalian cells, yeast, bacteria, or other cells under the control of appropriate promoters. Cell-free translation systems can also be employed to produce such proteins using RNAs derived from the mesothelin polypeptide DNA coding regions of the cited references (Chang et al., 1996; Kojima et al., 1995) or from the MRA-encoding nucleic acid sequences disclosed herein, or that can be deduced from MRA amino acid sequences provided herein. Appropriate cloning and expression vectors for use with prokaryotic and eukaryotic hosts are described by Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, NY, (1989). In preferred embodiments of the invention, mesothelin polypeptides are expressed in mammalian cells. The nucleic acids of the present invention may be in the form of RNA or in the form of DNA, which DNA includes cDNA, genomic DNA, and synthetic DNA. The DNA may be double-stranded or single-stranded, and if single stranded may be the coding strand or non-coding (anti-sense) strand. A coding sequence which encodes an MRA polypeptide for use according to the invention may be identical to the coding sequence provided in SEQ ID NO: 3 or in SEQ ID NO:4 or may be a different coding sequence, which, as a result of the redundancy or degeneracy of the genetic code, encodes the same MRA polypeptide as, for example, the cDNAs SEQ ID NOS:3 and 4. The present invention therefore provides an isolated nucleic acid molecule that encodes a mesothelin related antigen polypeptide having the amino acid sequence of SEQ ID NOS:l or 2, or a nucleic acid molecule capable of hybridizing to such an MRA polypeptide-encoding nucleic acid, or a nucleic acid molecule having a sequence complementary thereto. Variants preferably exhibit at least about 70% identity, more preferably at least about 80% identity and most preferably at least about 90% identity to a polynucleotide sequence that encodes a native mesothelin related antigen polypeptide or a portion thereof, such as, for example, the nucleic acid sequences set forth in SEQ ID NOS:3 and 4. The percent identity may be readily determined by comparing sequences using computer algorithms well known to those of ordinary skill in the art, such as Align or the BLAST algorithm (Altschul, J Mol. Biol. 219:555-565, 1991; Henikoff and Henikoff, Proc. Natl. Acad. Sci. USA 59:10915-10919, 1992), which is available at the NCBI website (http://www/ncbi.nlm.nih.gov/cgi-bin/BLAST). Default parameters may be used. Certain variants are substantially homologous to a native gene. Such polynucleotide variants are capable of hybridizing under moderately stringent conditions to a naturally occurring DNA or RNA sequence encoding a native mesothelin related antigen (or a complementary sequence). Suitable moderately stringent conditions include, for example, the following steps or their equivalent: prewashing in a solution of 5 X SSC, 0.5% SDS, 1.0 mM EDTA (pH 8.0); hybridizing at 50°C-65°C, 5 X SSC, overnight; followed by washing twice at 65°C for 20 minutes with each of 2X, 0.5X and 0.2X SSC containing 0.1% SDS. For additional stringency, conditions may include, for example, a wash in 0.1X SSC and 0.1% SDS at 60 °C for 15 minutes, or the equivalent. A person having ordinary skill in the art will readily appreciate the parameters that may be varied as a routine matter to create appropriately stringent hybridization conditions that are in some way selective for a particular nucleic acid of interest, and will further appreciate that such conditions may be a function, inter alia, of the particular nucleic acid sequences involved in the hybridization, such as, for example, those disclosed herein as SEQ ID NOS:3 and 4, which encode mesothelin related antigen polypeptides MRA-1 and MRA-2, respectively. See also, e.g., Ausubel et al., Current Protocols in Molecular Biology, Greene Publishing, 1995, regarding selection of nucleic acid hybridization conditions. The nucleic acids which encode MRA polypeptides, for example the human MRA polypeptides having the amino acid sequences of SEQ ID NOS: 1-2 or any other MRA polypeptides for use according to the invention, may include, but are not limited to: only the coding sequence for the MRA polypeptide; the coding sequence for the MRA polypeptide and additional coding sequence; the coding sequence for the MRA polypeptide (and optionally additional coding sequence) and non-coding sequence, such as introns or non-coding sequences 5' and/or 3' of the coding sequence for the MRA polypeptide, which for example may further include but need not be limited to one or more regulatory nucleic acid sequences that may be a regulated or regulatable promoter, enhancer, other transcription regulatory sequence, repressor binding sequence, translation regulatory sequence or any other regulatory nucleic acid sequence. Thus, the term "nucleic acid encoding an MRA polypeptide" encompasses a nucleic acid which includes only coding sequence for the polypeptide as well as a nucleic acid which includes additional coding and/or non-coding sequence(s). The present invention further relates to variants of the herein described nucleic acids which encode for fragments, analogs and derivatives of an MRA polypeptide, for example the human MRA polypeptides having the deduced amino acid sequences of SEQ ID NOS:l and 2. The variants of the nucleic acids encoding MRAs may be naturally occurring allelic variants of the nucleic acids or non-naturally occurring variants. As is known in the art, an allelic variant is an alternate form of a nucleic acid sequence which may have at least one of a substitution, a deletion or an addition of one or more nucleotides, any of which does not substantially alter the function of the encoded MRA polypeptide. Thus, for example, the present invention includes nucleic acids encoding the same MRA polypeptides as shown in SEQ ID NOS:l and 2, as well as variants of such nucleic acids, which variants may encode a fragment, derivative or analog of any of the polypeptides of SEQ ID NOS: 1 or 2. Variants and derivatives of MRA may be obtained by mutations of nucleotide sequences encoding MRA polypeptides. Alterations of the native amino acid sequence may be accomplished by any of a number of conventional methods. Mutations can be introduced at particular loci by synthesizing oligonucleotides containing a mutant sequence, flanked by restriction sites enabling ligation to fragments of the native sequence. Following ligation, the resulting reconstructed sequence encodes an analog having the desired amino acid insertion, substitution, or deletion. Alternatively, oligonucleotide-directed site-specific mutagenesis procedures can be employed to provide an altered gene wherein predetermined codons can be altered by substitution, deletion or insertion. Exemplary methods of making such alterations are disclosed by Walder εt al. (Gene 42:133, 1986); Bauer εt al. (Gene 37:13, 1985); Craik (BioTechniques, January 1985, 12-19); Smith εt al. (Genetic Engineering: Principles and Methods, Plεnum Prεss, 1981); Kunkεl (Proc. Natl. Acad. Sci. USA 52:488, 1985); Kunkεl et al. (Methods in Enzymol. 154:361, 1987); and U.S. Patent Nos. 4,518,584 and 4,737,462. Identification of nucleic acid molecules for use as antisensε agεnts, which includes antisensε oligonucleotides and ribozymes specific for nucleic acid sequences encoding MRA polypeptidεs or variants or fragments therεof; and of DNA oligonuclεotidεs encoding MRA genes for targeted delivery for genεtic thεrapy, involve mεthods wεll known in thε art. For εxamplε, thε desirable propertiεs, lengths and other characteristics of such oligonucleotidεs are well known. In certain preferred embodimεnts such an antisense oligonucleotidε comprises at least 15 consecutive nuclεotidεs complementary to an isolated nucleic acid molecule encoding an MRA polypeptide as provided herein. Antisensε oligonucleotides are typically designed to resist degradation by endogenous nucleolytic enzymes by using such linkages as: phosphorothioate, methylphosphonatε, sulfonε, sulfate, ketyl, phosphorodithioate, phosphoramidate, phosphate estεrs, and othεr such linkages (see, e.g., Agrwal et al., Tetrehedron Lett. 25:3539-3542 (1987); Miller et al., J. Am. Chem. Soc. 93:6651-6665 (1971); Stec εt al., Tetrehedron Lett. 2(5:2191-2194 (1985); Moody et al., Nucl. Acids Res. 72:4769-4782 (1989); Uznanski et al, Nucl. Acids Res. (1989); Letsinger εt al., Tetrahedron 40:131-143 (1984); Eckstεin, Annu. Rev. Biochem. 54:361-402 (1985); Eckstein, Trends Biol. Sci. 14:91-100 (1989); Stein In: Oligodeoxynucleotides. Antisense Inhibitors of Gene Expression, Cohen, Ed, Macmillan Prεss, London, pp. 97-117 (1989); Jagεr εt al., Biochemistry 27:7237-7246 (1988)). Antisεnsε nucleotides are oligonucleotidεs that bind in a sεquεnce-specific manner to nucleic acids, such as mRNA or DNA. When bound to mRNA that has complemεntary sεquencεs, antisense prevεnts translation of thε mRNA (see, e.g., U.S. Patεnt No. 5,168,053 to Altman et al.; U.S. Patent No. 5,190,931 to Inouyε, U.S. Patεnt No. 5,135,917 to Burch; U.S. Patεnt No. 5,087,617 to Smith and Clusεl εt al. (1993) Nucl. Acids Res. 27:3405-3411, which dεscribεs dumbbell antisense oligonucleotides). Triplex molecules refer to single DNA strands that bind duplex DNA forming a colinεar triplεx molεculε, thεrεby preventing transcription (see, e.g., U.S. Patent No. 5,176,996 to Hogan εt al., which dεscribεs mεthods for making synthεtic oligonuclεotidεs that bind to targεt sitεs on duplex DNA). According to this embodiment of the invention, particularly useful antisensε nuclεotidεs and triplex molecules are molecules that are complementary to or bind the sεnsε strand of DNA or mRNA that εncodεs an MRA polypεptidε such that inhibition of translation of mRNA encoding the MRA polypeptidε is εffεctεd. A ribozymε is an RNA molεculε that spεcifically clεavεs RNA substrates, such as mRNA, resulting in specific inhibition or interfεrεncε with cεllular gεnε expression. There ar at lεast fivε known classes of ribozymes involved in thε clεavagε and/or ligation of RNA chains. Ribozymεs can be targetεd to any RNA transcript and can catalytically clεavε such transcripts (see, e.g., U.S. Patεnt No. 5,272,262; U.S. Patent No. 5,144,019; and U.S. Patent Nos. 5,168,053, 5,180,818, 5,116,742 and 5,093,246 to Cech et al.). According to certain embodiments of the invention, any such MRA mRNA-specific ribozymε, or a nucleic acid encoding such a ribozyme, may be dεlivered to a host cell to effεct inhibition of MRA gεnε εxprεssion. Ribozymes, and the likε may thεrεforε be delivεred to the host cells by DNA encoding the ribozyme linked to a εukaryotic promoter, such as a eukaryotic viral promoter, such that upon introduction into the nucleus, the ribozymε will be directly transcribed. Equivalent DNA constructs that encode various additions or substitutions of amino acid residues or sequences, or delεtions of tεrminal or intεrnal residues or sequεncεs not nεεdεd for biological activity are also εncompassεd by thε invεntion. For εxamplε, sequences encoding Cys residuεs that are not εssential for biological activity can be altered to cause the Cys residuεs to bε dεlεtεd or rεplacεd with other amino acids, prevεnting formation of incorrect intramolecular disulfide bridges upon renaturation. Other equivalεnts can be prepared by modification of adjacent dibasic amino acid residues to enhance exprεssion in yεast systεms in which KEX2 protease activity is present. EP 212,914 discloses the usε of site-specific mutagenesis to inactivate KEX2 protεasε procεssing sitεs in a protein. KEX2 protease processing sites are inactivated by delεting, adding or substituting residues to alter Arg-Arg, Arg-Lys, and Lys-Arg pairs to eliminatε thε occurrence of thesε adjacent basic residuεs. Lys-Lys pairings are considerably less susceptible to KEX2 cleavagε, and conversion of Arg-Lys or Lys-Arg to Lys-Lys reprεsεnts a conservative and prefεrrεd approach to inactivating KEX2 sites. The appropriate DNA sequence(s) may bε insεrtεd into any of a numbεr of wεll known voctors appropriate for the selεcted host cell by a variety of procedures. In genεral, the DNA sequence is insertεd into an appropriate restriction endonucleasε site(s) by procedures known in the art. Standard techniques for cloning, DNA isolation, amplification and purification, for enzymatic reactions involving DNA ligasε, DNA polymerase, rεstriction εndonucleases and the like, and various separation techniques are those known and commonly εmployεd by those skilled in the art. A numbεr of standard tεchniquεs are dεscribεd, for εxamplε, in Ausubel et al. (1993 Current Protocols in Molecular Biology, Greene Publ. Assoc. Inc. & John Wiley & Sons, Inc., Boston, MA); Sambrook et al. (1989 Molecular Cloning, Second Ed., Cold Spring Harbor Laboratory, Plainview, NY); and εlsewhere. Examples of mammalian expression systems include the COS-7 lines of monkey kidney fibroblasts, described by Gluzman, Cell 23:115 (1981), and other cell lines capable of expressing a compatible vector, for example, thε C127, 3T3, CHO, HeLa and BHK cell lines. Mammalian expression vectors will comprise an origin of replication, a suitable promoter and enhancer, and also any necessary ribosome binding sitεs, polyadenylation site, splice donor and acceptor sites, transcriptional termination sequεncεs, and 5' flanking nontranscribεd sεquεnces. DNA sequences derivεd, for example, from SV40 splice and polyadenylation sites may bε usεd to providε thε required nontranscribed gεnεtic εlεments. Introduction of the construct into the host cell can be effected by a variety of mεthods with which those skilled in thε art will bε familiar, including but not limited to, for examplε, calcium phosphate transfection, DEAE-Dextran mεdiated transfection, or εlectroporation (Davis et al., 1986 Basic Methods in Molecular Biology). The prεsεnt invεntion furthεr rεlatεs to MRAs, to mεsothεlin rεlatεd antigεn polypeptides and in particular to methods for detεcting a malignant condition. In a prεfεrrεd embodiment, malignancy is detεcted by determining the presence in a biological sample of a naturally occurring soluble molecule having an antigenic determinant rεactivε with at lεast ono antibody spεcific for a human mεsothεlin polypεptide. In another prεfεrrεd εmbodimεnt, malignancy is dεtεctεd by dεtεrmining thε prεsεncε in a biological sample of at least one naturally occurring MRA polypεptidε. As providεd herein, a "mesothεlin rεlatεd antigεn polypoptidε" or "MRA polypεptide" includes any polypεptidε having an amino acid sequence of SEQ ID NO:l or 2, including any fragment, derivative or analog thereof, and also includes any polypeptidε encodεd by a nuclεic acid molεculε comprising SEQ ID NO: 3 or 4, or by a nuclεic acid molecule capable of hybridizing to a nucleic acid molεculε of SEQ ID NO:3 or 4, or a fragment, derivativε or analog thereof. Therefore, depεnding on thε portion of a presently disclosed MRA amino acid or nuclεic acid sequence that is selεctεd, an MRA polypεptidε may, but need not, be a mesothelin polypeptidε. As providεd hεrεin, a "mεsothelin polypeptide" is a soluble polypeptidε having an amino acid sεquεncε that includes the peptide: EVEKTACPSGKKAREIDES SEQ ID NO:5 and further having at least one antigenic dεtεrminant reactive with at least one antibody having an antigen combining site that compεtitivεly inhibits thε immunospεcific binding of MAb K-l (Chang et al, 1996 Proc. Nat. Acad. Sci. USA 93:136; MAb K-l is available from, e.g., Signet Laboratories, Inc., Dεdham, MA) or of monoclonal antibodies OV569, 4H3, 3G3 or 1A6 as provided hεrein. A mesothelin polypeptidε may include, for example, a mesothεlin rεlatεd antigεn (MRA) polypeptide as provided herein, or may be derived from the cεll surface associated portion of mesothelin itsεlf (Chang et al., 1996), the membrane bound portion of thε MPF precursor protein (Kojima et al., 1995 J. Biol Chem. 270:21984), or any fragments, analogs and dεrivativεs of such polypeptides. The MRA polypeptide or the mεsothεlin polypεptidε of thε invεntion may bε an unmodified polypeptidε or may bε a polypεptidε that has bεεn posttranslationally modifiod, for εxamplε by glycosylation, phosphorylation, fatty acylation including glycosylphosphatidylinositol anchor modification or thε likε, phospholipase cleavagε such as phosphatidylinositol-spεcific phospholipasε c mediated hydrolysis or the likε, protεasε cleavage, dephosphorylation or any other type of protein posttranslational modification such as a modification involving formation or clεavagε of a covalεnt chemical bond. The tεrms "fragmεnt," "dεrivativε" and "analog" whεn referring to mesothεlin related antigen polypeptidεs or fusion protεins, rεfεrs to any mεsothεlin rεlatεd antigεn polypεptidε that retains εssεntially thε samε biological function and/or activity as such polypeptide. Thus, an analog may include a mesothεlin rεlatεd antigen polypeptidε isoform such as a differentially posttranslationally modified mεsothεlin rεlatεd antigεn polypeptidε or a variant such as a splicε variant. As is wεll known in thε art, a "splicε variant" includεs variant or altεrnativε forms of a polypεptide that arise from the differential intracellular processing of an RNA transcript. For example, two distinct mRNA speciεs may be splice variants of one another wherε they differ only by the inclusion of all or a portion of a sequence corresponding to a particular εxon in onε mRNA species and its absence from the othεr spεciεs. As thosε familiar with thε art will appreciate, other structural relationships can exist bεtwεεn mRNA species that would be genεrally regarded as splicε variants. A mesothelin polypeptidε furthεr includεs a proprotein which can bε activated by cleavage of the proprotein portion to produce an active mesothelin polypeptide. Biological functions and/or activities of fragments, dεrivativεs and analogs of MRA polypeptides or of mesothelin polypeptidεs include, but neεd not bε limitεd to, thε usε of such polypeptides as markers in a mεthod of scrεεning for thε prεsεnce of a malignant condition in a subject as disclosed herein. For εxamplε, by detecting in a sample from the subjεct a molεculε naturally occurring in soluble form and having an antigenic determinant that is reactivε with at lεast onε antibody specific for a mesothelin polypeptidε, onε skilled in the art may be monitoring a biological function and/or activity of an MRA polypeptidε and/or of a mεsothεlin polypεptidε. Furthεr, it should be noted that in certain embodimεnts thε subjεct invention method of scrεεning is directed to comparing relativε quantitiεs, lεvεls and/or amounts of a detectable molecule naturally occurring in soluble form and having an antigenic determinant that is reactivε with at least one antibody specific for a mesothelin polypeptide in each of (i) a first biological sample from a. first subjεct suspected of having a malignant condition, and (ii) a second biological sample from a second subject known to be frεε of a malignant condition. Accordingly, thε rεlativε quantitativε presence of a mesothelin polypeptide in a biological sample may be a biological function and/or activity of a mesothelin polypeptidε, although such function and/or activity should not bε so limitεd. A fragment, derivative or analog of a MRA polypeptidε or a mεsothεlin polypεptidε may bε (i) onε in which onε or more of thε amino acid rεsiduεs are substitutεd with a consεrvεd or non-consεrved amino acid residue (prefεrably a conserved amino acid residuε); (ii) onε in which additional amino acids are fused to the mεsothelin polypeptide, including amino acids that may be employεd for purification of thε mεsothelin polypeptide or a proprotein sequεnce; or (iii) a truncated mesothεlin polypεptidε. Such fragments, dεrivatives and analogs are dεεmεd to be within the scope of thosε skilled in the art from the teachings hεrein. A truncatεd mεsothεlin polypεptidε may bε any mεsothεlin polypeptide molecule that comprises less than a full lεngth version of the mesothεlin polypεptidε. Truncatεd molecules provided by thε present invention may include truncated biological polymers, and in prefεrrεd εmbodimεnts of thε invεntion such truncatεd molεcules may be truncated nuclεic acid molεculεs or truncated polypeptidεs. Truncatεd nuclεic acid molecules have lεss than thε full lεngth nucleotide sequεncε of a known or dεscribεd nucleic acid molecule, where such a known or described nucleic acid molecule may be a naturally occurring, a synthetic or a recombinant nuclεic acid molεculε, so long as onε skilled in the art would rεgard it as a full lεngth molecule. Thus, for examplε, truncatεd nucleic acid molecules that correspond to a gεne sequence contain less than thε full length genε wherε the genε comprises coding and non-coding sequences, promoters, εnhancεrs and othεr regulatory sequencεs, flanking sεquεncεs and the like, and other functional and non- functional sequεncεs that are recognized as part of the gεne. In another εxamplε, truncatεd nuclεic acid molecules that correspond to a mRNA sequεncε contain lεss than the full length mRNA transcript, which may include various translated and non-translatεd rεgions as well as other functional and non-functional sequences. In other preferred embodimεnts, truncated molecules are polypeptidεs that comprise less than thε full length amino acid sequεnce of a particular protein. As usεd herein "delεtion" has its common meaning as understood by those familiar with thε art, and may refer to molecules that lack one or more of a portion of a sεquεncε from εither terminus or from a non-terminal region, relative to a corresponding full length molecule, for example, as in the case of truncatεd molεculεs provided herεin. Truncatεd molεcules that are linεar biological polymers such as nucleic acid molεculεs or polypεptidεs may havε onε or more of a dεlεtion from εithεr terminus of the molecule or a delεtion from a non-tεrminal region of thε molεculε, where such delεtions may be delεtions of 1-1500 contiguous nuclεotidε or amino acid residues, prefεrably 1-500 contiguous nucleotide or amino acid residuεs and more prεfεrably 1-300 contiguous nuclεotidε or amino acid rεsiduεs. As known in thε art "similarity" bεtwεεn two polypeptides is determinεd by comparing thε amino acid sequence and conserved amino acid substitutes thereto of thε polypεptidε to the sequεncε of a second polypeptidε. Similarity betwεεn two polypεptide or nucleotide sequencεs, or evεn the percent identity, may be readily dεtεrminεd by comparing sεquεncεs using computer algorithms well known to those of ordinary skill in the art, such as thε BLAST algorithm (Altschul, J. Mol. Biol. 219:555-565, 1991; Henikoff and Henikoff, Proc. Natl. Acad. Sci. USA 59:10915-10919, 1992), which is available at the NCBI websitε (http://www/ncbi.nlm.nih.gov/cgi-bin/BLAST). Default parameters may be used. Examples of other useful computer algorithms are those used in programs such as Align and FASTA, which may be accessεd, for εxamplε, at thε Gεnεstrεam intεrnet website of the Institut de Genεtique Humaine, Montpelliεr, France (www2.igh.cnrs.fr/home.εng.html) and used with default parameters. Fragments or portions of tho polypεptidεs of thε prεsεnt invεntion may bε εmployεd for producing thε corresponding full-length polypeptidε by peptidε synthεsis; thεrεforε, thε fragmεnts may bε employεd as intεrmεdiates for producing the full-lεngth polypεptidεs. The term "isolated" mεans that thε matεrial is rεmovεd from its original onvironmεnt (e.g., thε natural environment if it is naturally occurring). For examplε, a naturally occurring polypeptidε or polynuclεotidε prεsεnt in a living animal is not isolatεd, but the same polypeptidε or polynuclεotidε, separated from some or all of the co-existing matεrials in the natural system, is isolatεd. Such polypεptidεs or polynuclεotidεs could bε part of a composition, and still bε isolated in that such composition is not part of its natural environment. Affinity tεchniquεs are particularly usεful in thε context of isolating MRA polypeptidεs and/or mesothelin polypeptides for use according to the methods of thε prεsent invention, and may include any method that exploits a spεcific binding interaction with a MRA polypeptide or mεsothelin polypeptide to effεct a separation. For example, because mesothεlin polypεptides may contain covalently attachεd oligosaccharidε moiεtiεs (sεε, e.g., Chang εt al., 1996 Proc. Nat. Acad. Sci. USA 93:136; Chang εt al., 1992 Cancer Res. 52:181; Kojima εt al., 1995 J. Biol Chem. 270:21984; Yamaguchi εt al, 1994 J. Biol. Chem. 269:805), an affinity tεchniquε such as binding of a mεsothεlin polypεptide to a suitable immobilized lectin under conditions that permit carbohydrate binding by the lεctin may be a particularly useful affinity tεchniquε. Othεr usεful affinity tεchniquεs include immunological techniques for isolating a mesothelin polypeptide, which techniques rely on spεcific binding interaction betweεn antibody combining sitεs for antigεn and antigεnic dεtεrminants present in the complexεs. Immunological tεchniquεs include, but neεd not be limited to, immunoaffinity chromatography, immunoprecipitation, solid phase immunoadsorption or other immunoaffinity methods. For these and other useful affinity techniques, seε, for example, Scopes, R.K., Protein Purification: Principles and Practice, 1987, Springer- Verlag, NY; Weir, D.M., Handbook of Experimental Immunology, 1986, Blackwell Scientific, Boston; and Hermanson, G.T. εt al., Immobilized Affinity Ligand Techniques, 1992, Acadεmic Prεss, Inc., California; which arc hεrεby incorporated by refεr nce in their εntireties, for details regarding techniques for isolating and characterizing complεxεs, including affinity tεchniques. As described herein, the invention providεs a fusion protein comprising a polypeptidε fusεd to a MRA. Such MRA fusion proteins are encoded by nucleic acids that have the MRA coding sεquεncε fusεd in frame to an additional coding sequεncε to providε for εxprεssion of a MRA polypεptide sequεncε fusεd to an additional functional or nonfunctional polypεptidε sεquεncε that permits, for example by way of illustration and not limitation, dεtection, isolation and/or purification of the MRA fusion protεin. Such MRA fusion proteins may permit detection, isolation and/or purification of the MRA fusion protein by protεin-protein affinity, metal affinity or charge affinity-based polypeptidε purification, or by specific protease cleavage of a fusion protein containing a fusion sequence that is cleavablε by a protεasε such that thε MRA polypeptide is separable from the fusion protein. Thus, MRA fusion proteins may comprise affinity tag polypeptidε sεquεncεs, which refers to polypeptidεs or pεptides added to MRA to facilitate detεction and isolation of thε MRA via a spεcific affinity interaction with a ligand. The ligand may be any molecule, receptor, counterrecεptor, antibody or thε likε with which thε affinity tag may intεract through a spεcific binding intεraction as provided herεin. Such pεptides include, for examplε, poly-His or thε antigenic identification pεptidεs described in U.S. Patent No. 5,011,912 and in Hopp et al., (1988 Bio/Technology 6:1204), or the XPRESS™ εpitopε tag (Invitrogen, Carlsbad, CA). The affinity sequεncε may bε a hεxa-histidinε tag as suppliεd, for example, by a pBAD/His (Invitrogen) or a pQE-9 vector to provide for purification of thε mature polypeptidε fusεd to thε markεr in thε case of a bacterial host, or, for example, the affinity sεquεncε may be a hemagglutinin (HA) tag when a mammalian host, e.g., COS-7 cells, is usεd. Thε HA tag corresponds to an antibody definεd εpitopε dεrived from the influenza hemagglutinin protein (Wilson et al., 1984 Cell 37:161). MRA fusion proteins may further comprise immunoglobulin constant region polypeptides added to MRA to facilitatε dεtεction, isolation and/or localization of MRA. Thε immunoglobulin constant region polypεptidε preferably is fused to the C-terminus of a MRA polypeptide. Gεnεral preparation of fusion protεins comprising hεtεrologous polypεptides fused to various portions of antibody-derived polypeptidεs (including thε Fc domain) has been described, e.g., by Ashkenazi εt al. (RN4S USA 55. 10535, 1991) and Byrn εt al. (Nature 344:611, 1990). A gεnε fusion εncoding thε MRA:Fc fusion protεin is insεrtεd into an appropriate expression vector. In certain εmbodimεnts of the invention, MRA:Fc fusion proteins may be allowed to assεmblε much likε antibody molεcules, whereupon interchain disulfidε bonds form bεtwεεn Fc polypεptides, yiεlding dimεric MRA fusion protεins. MRA fusion proteins having specific binding affinities for pre-selectεd antigεns by virtuε of fusion polypεptidεs comprising immunoglobulin V-rεgion domains εncodεd by DΝA sεquεnces linked in-frame to sεquences encoding MRA are also within the scope of the invεntion, including variants and fragmεnts thεrεof as providεd hεrεin. Gεnεral stratεgiεs for thε construction of fusion protεins having immunoglobulin V-region fusion polypeptidεs are disclosed, for examplε, in EP 0318554; U.S. 5,132,405; U.S. 5,091,513; and U.S. 5,476,786. The nucleic acid of the present invention may also εncodε a fusion protein comprising a MRA polypeptidε fusεd to othεr polypeptides having dεsirablε affinity propεrties, for examplε an enzyme such as glutathione-S-transferase. As anothεr example, MRA fusion protεins may also comprise a MRA polypeptide fused to a Staphylococcus aureus protεin A polypεptidε; protεin A encoding nucleic acids and their usε in constructing fusion protεins having affinity for immunoglobulin constant rεgions are disclosed genεrally, for εxamplε, in U.S. Patent 5,100,788. Other useful affinity polypεtidεs for construction of MRA fusion protεins may include streptavidin fusion proteins, as disclosed, for εxamplε, in WO 89/03422; U.S. 5,489,528; U.S. 5,672,691; WO 93/24631 ; U.S. 5,168,049; U.S. 5,272,254 and εlsεwhεrε, and avidin fusion protεins (sεε, e.g., EP 51 1,747). As provided herεin and in the cited refεr ncεs, MRA polypεptidε sεquεnces, including substrate trapping mutant MRAs, may be fused to fusion polypεptidε sequencεs that may bε full lεngth fusion polypεptides and that may alternatively be variants or fragmεnts thεrεof. Thε prεsεnt invεntion also contεmplatεs MRA fusion protoins that contain polypεptidε sεquεnces that direct thε fusion protεin to the cell nucleus, to residε in thε lumεn of the endoplasmic reticulum (ER), to bε sεcrεtεd from a cεll via thε classical ER- Golgi secretory pathway (see, e.g., von Heijnε, J. Membrane Biol. 775:195-201, 1990), to bε incorporated into the plasma membranε, to associate with a specific cytoplasmic component including the cytoplasmic domain of a transmεmbranε cεll surface rεcεptor or to bε directed to a particular subcellular location by any of a variety of known intracellular protein sorting mechanisms with which those skilled in the art will bε familiar (See, e.g., Rothman, Nature 372:55-63, 1994, Adrani εt al., 1998 J. Biol. Chem. 273:10317, and rεfεrεncεs citεd thεrein.). Accordingly, these and relatεd εmbodiments are encompassed by the instant compositions and methods directed to targeting a polypeptide of interεst to a predefinεd intracellular, membranε or εxtracεllular localization. Thε prεsεnt invεntion also rεlatεs to vεctors and to constructs that include nucleic acids of the presεnt invention, and in particular to "recombinant expression constructs" that include any nucleic acids encoding MRA polypeptidεs according to thε invεntion as providεd abovε; to host cεlls which arε gεnetically engineεrεd with vεctors and/or constructs of thε invεntion and to thε production of MRA polypεptidεs and fusion protεins of thε invention, or fragments or variants thereof, by recombinant tεchniquεs. MRA proteins can be exprεssεd in mammalian cεlls, yeast, bacteria, or other cells under the control of appropriate promoters. Cell-frεε translation systems can also be employεd to produce such proteins using RNAs derived from the DNA constructs of the presεnt invention. Appropriate cloning and exprεssion vεctors for usε with prokaryotic and εukaryotic hosts arε dεscribεd, for example, by Sambrook, et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, New York, (1989). Gεnerally, recombinant expression vectors will include origins of replication and sεlεctablε markers permitting transformation of the host cell, e.g., thε ampicillin resistance gene of E coli and S. cerevisiae TRP1 genε, and a promotεr dεrivεd from a highly-expressed genε to direct transcription of a downstream structural sεquεncε. Such promoters can be derivεd from opεrons encoding glycolytic enzymεs such as 3- phosphoglycεratε kinasε (PGK), -factor, acid phosphatasε, or hεat shock protεins, among othεrs. The hetεrologous structural sεquεncε is assεmblεd in appropriate phase with translation initiation and termination sequεncεs. Optionally, thε hεtεrologous sεquεncε can encode a fusion protein including an N-terminal identification peptide imparting desired characteristics, e.g., stabilization or simplified purification of expr ssεd recombinant product. Usεful εxpr ssion constructs for bacterial use are constructed by inserting into an εxprεssion voctor a structural DNA sεquεnce encoding a desired protein togεthεr with suitablε translation initiation and termination signals in operablε reading phasε with a functional promoter. The construct may comprise one or morε phεnotypic sεlεctable markers and an origin of replication to εnsurε maintεnance of the vεctor construct and, if dεsirablε, to provide amplification within the host. Suitable prokaryotic hosts for transformation include E coli, Bacillus subtilis, Salmonella typhimurium and various speciεs within thε gεnεra Psεudomonas, Streptomyces, and Staphylococcus, although othεrs may also bε εmployed as a matter of choice. Any othεr plasmid or vεctor may bε usεd as long as they are rεplicablε and viablε in the host. As a reprεsentative but non-limiting examplε, useful expression vectors for bacterial use can comprise a sεlεctablε marker and bacterial origin of replication derived from commercially available plasmids comprising genεtic εlεments of the well known cloning vector pBR322 (ATCC 37017). Such commercial vectors include, for examplε, pKK223-3 (Pharmacia Fine Chemicals, Uppsala, Swedεn) and GΕM1 (Promεga Biotεc, Madison, Wisconsin, USA). Thεsε pBR322 "backbone" sections arε combined with an appropriate promotεr and thε structural sεquεnce to be expressed. Following transformation of a suitable host strain and growth of the host strain to an appropriate cεll dεnsity, the selεcted promoter, if it is a regulatεd promotεr as provided herεin, is induced by appropriate means (e.g., temperature shift or chemical induction) and cells arε culturεd for an additional period. Cells arε typically harvεstεd by centrifugation, disruptεd by physical or chemical means, and the resulting crudε εxtract rεtainεd for furthεr purification. Microbial cεlls εmployεd in εxprεssion of protεins can bε disruptεd by any convεniεnt mεthod, including frεεzε-thaw cycling, sonication, mechanical disruption, or use of cεll lysing agεnts; such mεthods arε wεll know to those skilled in the art. Thus, for εxamplε, the nucleic acids of the invεntion as provided herein may be included in any one of a variεty of εxprεssion vεctor constructs as a recombinant expression construct for exprεssing a MRA polypεptide. Such vεctors and constructs include chromosomal, nonchromosomal and synthetic DNA sequεncεs, e.g., derivatives of SV40; bacterial plasmids; phagε DNA; baculovirus; yεast plasmids; vεctors derived from combinations of plasmids and phage DNA, viral DNA, such as vaccinia, adεnovirus, fowl pox virus, and psoudorabiεs. Howover, any other vector may be used for preparation of a recombinant εxprεssion construct as long as it is rεplicable and viable in thε host. Thε appropriate DNA sequεnce(s) may bε insεrtεd into thε vector by a variety of procedures. In genεral, thε DNA sεquεncc is insεrtεd into an appropriato rεstriction εndonuclεasε sitε(s) by procεdurεs known in thε art. Standard techniques for cloning, DNA isolation, amplification and purification, for enzymatic reactions involving DNA ligase, DNA polymεrase, restriction endonucleasεs and thε likε, and various sεparation tεchniquεs arε thosε known and commonly εmployεd by thosε skilled in the art. A numbεr of standard techniques are described, for examplε, in Ausubel et al. (1993 Current Protocols in Molecular Biology, Greεnε Publ. Assoc. Inc. & John Wilεy & Sons, Inc., Boston, MA); Sambrook εt al. (1989 Molecular Cloning, Sεcond Ed., Cold Spring Harbor Laboratory, Plainview, NY); Maniatis et al. (1982 Molεcular Cloning, Cold Spring Harbor Laboratory, Plainviεw, NY); and εlsewherε. Thε DNA sεquence in thε expression vector is opεratively linked to at lεast one appropriate expression control sequencεs (e.g., a promoter or a rεgulatεd promoter) to direct mRNA synthesis. Representativε εxamples of such expression control sequences include LTR or SV40 promotεr, thε E. coli lac or trp, the phage lambda P L promoter and other promotεrs known to control εxprεssion of gεnes in prokaryotic or eukaryotic cεlls or thεir virusεs. Promotor rεgions can bε sεlεctεd from any dεsirεd gεnε using CAT (chloramphenicol transferasε) vεctors or other vectors with selεctablε markεrs. Two appropriatε vεctors are pKK232-8 and pCM7. Particular named bacterial promotεrs include lad, lacZ, T3, T7, gpt, lambda P R , P L and trp. Eukaryotic promoters include CMV immεdiatε εarly, HSV thymidinε kinase, early and late SV40, LTRs from retrovirus, and mousε metallothionein-I. Sεlεction of thε appropriate vector and promoter is well within thε lεvεl of ordinary skill in tho art, and preparation of certain particularly prefεrrεd rεcombinant εxprεssion constructs comprising at lεast onε promotεr or rεgulatεd promotεr opεrably linked to a nucleic acid encoding a MRA polypeptide is described herεin. As notεd abovε, in certain embodiments the vector may be a viral vector such as a retro viral vector. For example, retro viruses from which the retro viral plasmid vectors may bε derived include, but arε not limitεd to, Molonεy Murinε Leukemia Virus, spleen necrosis virus, retrovirusεs such as Rous Sarcoma Virus, Harvεy Sarcoma virus, avian lεukosis virus, gibbon apo lεukεmia virus, human immunodεficiency virus, adenovirus, Myεloprolifεrativε Sarcoma Virus, and mammary tumor virus. Thε viral vεctor includεs onε or more promotεrs. Suitablε promotεrs which may bε εmployed include, but arε not limitεd to, thε retroviral LTR; the SV40 promotεr; and thε human cytomεgalovirus (CMV) promotεr dεscribεd in Millεr, εt al., Biotechniques 7:980-990 (1989), or any othεr promotεr (e.g., cεllular promoters such as eukaryotic cellular promoters including, but not limitεd to, thε histonε, pol III, and β-actin promotεrs). Othεr viral promoters which may be εmployed include, but are not limitεd to, adεnovirus promotεrs, thymidinε kinasε (TK) promoters, and B19 parvovirus promotεrs. Thε sεlεction of a suitablε promotεr will bε apparent to thosε skilled in the art from the tεachings contained herεin, and may bε from among either regulatεd promotεrs or promotεrs as dεscribed above. The retroviral plasmid vεctor is εmployεd to transducε packaging cεll linεs to form producer cell lines. Examplεs of packaging cells which may be transfected include, but arε not limitεd to, the PE501, PA317, ψ-2, ψ-AM, PA12, T19-14X, VT-19-17-H2, ψCRE, ψCRIP, GP+E-86, GP+envAml2, and DAN cell lines as described in Miller, Human Gene Therapy, 7:5-14 (1990), which is incorporated herein by refεrence in its εntirety. The vector may transduce the packaging cells through any means known in the art. Such mεans include, but are not limited to, electroporation, the usε of liposomes, and calcium phosphate precipitation. In onε altεrnative, the retroviral plasmid vεctor may bε εncapsulatεd into a liposome, or coupled to a lipid, and then administered to a host. Tho producer cell line gεnεratεs infεctious retroviral vector particles which include the nucleic acid sequence(s) encoding the MRA polypeptidεs or fusion protεins. Such rεtroviral vector particles then may be employod, to transducε εukaryotic cεlls, εithεr in vitro or in vivo. The transduced eukaryotic cells will express the nucleic acid sequεncε(s) εncoding thε MRA polypeptide or fusion protein. Eukaryotic cells which may be transduced include, but are not limitεd to, embryonic stem cεlls, εmbryonic carcinoma cεlls, as wεll as hematopoietic stem cεlls, hepatocytes, fibroblasts, myoblasts, koratinocytεs, endothelial cεlls, bronchial epithelial cells and various other culturε-adaptεd cεll linεs. As anothor εxamplε of an εmbodimont of thε invεntion in which a viral vεctor is usεd to prepare thε rεcombinant MRA εxprεssion construct, in onε prεfεrrεd embodimεnt, host cεlls transduced by a recombinant viral construct directing the expression of MRA polypeptidεs or fusion proteins may produce viral particles containing expressed MRA polypeptides or fusion proteins that are dεrivεd from portions of a host cεll membrane incorporated by thε viral particles during viral budding. In another preferred embodiment, MRA encoding nuclεic acid sequences are clonεd into a baculovirus shuttlε vector, which is then rεcombinεd with a baculovirus to generate a recombinant baculovirus expression construct that is used to infect, for εxamplε, Sf9 host cεlls, as dεscribεd in Baculovirus Expression Protocols, Methods in Molecular Biology Vol. 39, C. D. Richardson, Editor, Human Prεss, Totowa, NJ, 1995; Pi wnica- Worms, "Expression of Protεins in Insect Cells Using Baculoviral Vεctors," Sεction II in Chapter 16 in: Short Protocols in Molecular Biology, 2nd Ed., Ausubel et al., eds., John Wiley & Sons, New York, New York, 1992, pages 16-32 to 16-48. In another aspect, the present invention relates to host cells containing the above dεscribεd rεcombinant MRA εxprεssion constructs. Host cεlls are gεnεtically enginεεrεd (transduced, transformed or transfected) with the vectors and/or expression constructs of this invention which may bε, for example, a cloning vector, a shuttlε vεctor or an εxpression construct. The vector or construct may be, for example, in the form of a plasmid, a viral particle, a phagε, εtc. Thε εnginεεrεd host cεlls can bε cultured in conventional nutrient media modified as appropriatε for activating promotεrs, sεlεcting transformants or amplifying particular gεnεs such as gεnεs εncoding MRA polypεptidεs or MRA fusion protεins. Thε culture conditions for particular host cεlls sεlεctεd for expression, such as temperature, pH and the like, will be rεadily apparεnt to thε ordinarily skilled artisan. The host cεll can bε a highεr εukaryotic cεll, such as a mammalian cεll, or a lowεr εukaryotic cεll, such as a yeast cεll, or thε host cεll can be a prokaryotic cell, such as a bacterial cell. Reprεsεntativε εxamplεs of appropriatε host cεlls according to thε prεsεnt invεntion include, but neεd not be limitεd to, bacterial cells, such as E coli, Streptomyces, Salmonella typhimurium; fungal cεlls, such as yεast; insεct cεlls, such as Drosophila S2 and Spodoptera Sf9; animal cεlls, such as CHO, COS or 293 cells; adenovirusεs; plant cεlls, or any suitablε cεll alrεady adaptεd to in vitro propagation or so εstablishεd de novo. Thε sεlεction of an appropriate host is deemed to be within the scope of those skilled in thε art from thε tεachings hεrein. Various mammalian cell culture systems can also be εmployεd to εxprεss recombinant protein. Thε invεntion is thεrεforε directed in part to a method of producing a recombinant MRA polypeptide, by culturing a host cell comprising a rεcombinant εxprεssion construct that comprises at least one promoter operably linked to a nuclεic acid sequence encoding a MRA. In certain εmbodimεnts, thε promotεr may bε a regulated promoter as provided herein, for example a tetracylcinε-rεprεssiblε promotεr. In certain embodiments the recombinant expression construct is a rεcombinant viral εxprεssion construct as providεd hεrεin. Εxamplεs of mammalian expression systems include the COS-7 lines of monkey kidnεy fibroblasts, dεscribεd by Gluzman, Cell 25:175 (1981), and othεr cell lines capable of expressing a compatible vεctor, for example, the C127, 3T3, CHO, HεLa and BHK cεll linεs. Mammalian εxprεssion vεctors will comprise an origin of replication, a suitable promoter and enhancer, and also any necessary ribosome binding sitεs, polyadεnylation site, splice donor and accεptor sitεs, transcriptional termination sequεncεs, and 5' flanking nontranscribed sequεncεs, for εxamplε as dεscribed herεin regarding the preparation of MRA expression constructs. DNA sεquεnces derivεd from thε SV40 splicε, and polyadεnylation sitεs may bε usεd to providε the required nontranscribed genεtic εlεmεnts. Introduction of thε construct into thε host cell can be effεctεd by a variεty of mεthods with which those skilled in thε art will bε familiar, including but not limitεd to, for example, calcium phosphate transfεction, DEAE-Dextran mediatεd transfection, or elεctroporation (Davis et al., 1986 Basic Methods in Molecular Biology). The expressεd rεcombinant mεsothεlin rεlatεd antigεn polypεptidεs (or mεsothεlin polypεptides), or fusion proteins derived therefrom, may bε usεful as immunogεns in thε form of intact host cεlls; intact organεllεs such as cell membranεs, intracellular vesicles or other cεllular organεllεs; or disrupted cell preparations including but not limited to cell homogenates or lysates, uni- and multilamellar membranε vεsiclεs or othεr preparations. Alternativεly, expressεd rεcombinant mεsothelin relatεd antigen polypeptides (or mesothεlin polypεptidεs) or fusion protεins can bε recovered and purified from recombinant cell cultures by methods including ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulosε chromatography, hydrophobic interaction chromatography, affinity chromatography including immunoaffinity chromatography, hydroxylapatite chromatography and lectin chromatography. Protεin refolding steps can be usεd, as necessary, in completing configuration of the mature protein. Finally, high performance liquid chromatography (HPLC) can be εmployed for final purification steps. Expressed recombinant mesothelin relatεd antigεn polypεptidεs (or mεsothεlin polypεptidεs) or fusion protεins may also be useful as targεt antigεns in any of a numbεr of assay configurations for routine antibody screening, which can be readily performed by those having ordinary skill in the art. The mesothelin relatεd antigεn polypeptide (or mesothεlin polypeptide) that is an immunogen for the production of a specific antibody to be used in the method of the presεnt invention may thus be a naturally purified product, or a product of chemical synthetic procedures, or produced by recombinant techniques from a prokaryotic or, preferably, a eukaryotic host. Depending upon the host εmployod in a rεcombinant production procεdurε, thε polypeptidεs of thε prεsεnt invεntion may bε glycosylatεd or othεrwisε posttranslationally modifiεd as known in the art and as provided herein. According to thε prεsεnt invεntion, a solublε human mεsothεlin rεlatεd antigεn polypεptidε (or mεsothεlin polypeptide) may be dεtεctεd in a biological sample from a subject or biological source. Biological samples may be provided by obtaining a blood sample, biopsy specimen, tissue εxplant, organ culture, biological fluid or any other tissue or cell preparation from a subject or a biological source. Thε subjεct or biological source may be a human or non-human animal, a primary cell culture or culture adapted cell line including but not limited to genεtically εnginεεred cell lines that may contain chromosomally integratεd or εpisomal rεcombinant nuclεic acid sεquεncεs, immortalizεd or immortalizablε cεll linεs, somatic cεll hybrid cεll lines, differεntiatεd or differentiatable cell lines, transformed cell lines and the like. In certain prefεrrεd εmbodimεnts of the invεntion, thε subjεct or biological source may be suspεctεd of having or being at risk for having a malignant condition, and in certain prefεrrεd embodimεnts of thε invεntion thε subjεct or biological source may be known to be free of a risk or presεnce of such diseasε. In prεfεrrεd εmbodimεnts thε biological sample is a biological fluid containing a soluble human mesothεlin rεlatεd antigεn polypeptide. Biological fluids are typically liquids at physiological tεmpεraturεs and may include naturally occurring fluids presεnt in, withdrawn from, expressed or otherwise extracted from a subject or biological source. Certain biological fluids derivε from particular tissues, organs or localized rεgions and certain other biological fluids may be more globally or systemically situated in a subject or biological source. Examples of biological fluids include blood, serum and sεrosal fluids, plasma, lymph, urine, cerebrospinal fluid, saliva, mucosal secretions of the sεcrεtory tissuεs and organs, vaginal sεcrεtions, ascitεs fluids such as thosε associated with non-solid tumors, fluids of the plεural, pεricardial, peritoneal, abdominal and other body cavities, and the likε. Biological fluids may also include liquid solutions contacted with a subject or biological source, for εxamplε, cεll and organ culture medium including cell or organ conditioned medium, lavage fluids and thε likε. In certain highly prefεrrεd εmbodimεnts thε biological sample is serum, and in certain other highly prefεrrεd εmbodimεnts thε biological samplε is plasma. In othεr preferred embodiments the biological sample is a cell-frεε liquid solution. In certain other preferred embodiments the biological samplε comprises an intact cell, and in certain other preferred embodimεnts thε biological sample comprises a cell extract containing a nucleic acid sequence encoding a mεsothεlin related antigen polypεptidε having thε amino acid sequence set forth in SEQ ID NOS: l or 2, or a fragmεnt or variant thεrεof. A "molεculε naturally occurring in solublε form" in a sample may be a solublε protεin, polypεptidε, pεptidε, amino acid, or dεrivativε thεrεof; a lipid, fatty acid or the like, or derivativε thεr of; a carbohydrate, saccharide or thε likε or dεrivative therεof, a nuclεic acid, nucleotide, nucleoside, purine, pyrimidine or relatεd molεculε, or dεrivativε thεrεof, or thε likε; or any combination thereof such as, for example, a glycoprotein, a glycolipid, a lipoprotein, a proteolipid, or any other biological molecule that is a soluble or cell-frεε constituent of a biological sample as provided herεin. A "molεculε naturally occurring in solublε form" furthεr refers to a molecule that is in solution or present in a biological sample, including a biological fluid as provided hεrεin, and that is not bound to tho surfacε of an intact cell. For examplε, a molεculε naturally occurring in solublε form may includε but nεεd not be limited to a solute; a component of a macromolecular complex; a material that is shed, sεcrεtεd or εxportεd from a cell; a colloid; a microparticle or nanoparticle or other fine suspεnsion particle; or the like. Thε prεsεncε of a malignant condition in a subject refers to the presεncε of dysplastic, cancerous and/or transformed cells in the subject, including, for example neoplastic, tumor, non-contact inhibited or oncogenically transformεd cells, or the likε. By way of illustration and not limitation, in thε context of the present invention a malignant condition may refer further to the presεnce in a subject of cancer cεlls that arε capablε of sεcrεting, shedding, exporting or releasing a mesothelin relatεd antigεn polypεptidε (or a mεsothεlin polypeptide) in such a manner that εlεvatεd lεvεls of such a polypεptidε arε dεtεctablε in a biological sample from the subject. In prεfεrrεd εmbodiments, for examplε, such cancεr cεlls arε malignant εpithεlial cεlls such as carcinoma cεlls, and in particularly preferred embodiments such cancεr cεlls are malignant mesothelioma cells, which arε transformεd variants of squamous cεll εpithεlial or mεsothεlial cεlls that arε found, for εxamplε, lining plεural, pεricardial, pεritonεal, abdominal and othεr body cavities. In thε most prεfεrrεd εmbodiments of the invention, tumor cells, the presence of which signifies the presence of a malignant condition, are ovarian carcinoma cells, including primary and metastatic ovarian carcinoma cells. Criteria for classifying a malignancy as ovarian carcinoma arε well known in the art (see, e.g., Bell et al., 1998 Br. J. Obstet. Gynaecol. 105:1136; Meier εt al., 1997 Anticancer Res. 17(4B):3019; Mεiεr εt al. 1997 Anticancer Res. 17(4B):2949; Cioffi εt al., 1997 Tumori 83:594; and rεfεrences citεd thεrεin) as are the establishmεnt and characterization of human ovarian carcinoma cell linεs from primary and mεtastatic tumors (e.g., OVCAR-3, Amεr. Typε Culture Collection, Manassas, VA; Yuan et al., 1997 Gynecol. Oncol. 66:378). In othεr εmbodimεnts, thε malignant condition may bε mesothelioma, pancreatic carcinoma, non-small cell lung carcinoma or another form of cancer, including any of the various carcinomas such as squamous cell carcinomas and adenocarcinomas, and also including sarcomas and hεmatologic malignancies (e.g., leukεmias, lymphomas, myεlomas, etc.). Classification of these and other malignant conditions is known to thosε having familiarity with the art, and the present disclosure provides dεtermination of the presεncε of a mεsothelin polypεptidε, including determination of the presεncε of a MRA polypεptidε, in such a malignant condition without undue experimentation. As provided herεin, the method of screening for thε prεsεncε of a malignant condition in a subjεct may feature the usε of an antibody spεcific for a human mεsothεlin rεlatεd antigεn polypεptidε or an antibody spεcific for a human mεsothεlin polypεptide. Antibodies that are specific for a mεsothelin relatεd antigεn polypεptidε (or a mεsothεlin polypεptidε) arε rεadily gεnεratεd as monoclonal antibodies or as polyclonal antisera, or may bε produced as genetically engineεrεd immunoglobulins (Ig) that arε dεsignεd to havε dεsirablε propεrtiεs using mεthods wεll known in thε art. For εxamplε, by way of illustration and not limitation, antibodiεs may includε recombinant IgGs, chimeric fusion protεins having immunoglobulin dεrived sequεnces or "humanized" antibodies (see, e.g., U.S. Patent Nos. 5,693,762; 5,585,089; 4,816,567; 5,225,539; 5,530,101; and rεfεrεncεs citεd thεrein) that may all be usεd for dεtection of a human mesothεlin polypεptidε according to thε invεntion. Many such antibodies have beεn disclosεd and arε availablε from specific sources or may be preparεd as provided herεin, including by immunization with mesothelin polypeptidεs as described below. For εxamplε, as providεd herein, nucleic acid sequences encoding mesothεlin polypεptidεs arε known for thε cεll surface associated portion of mesothelin itsεlf (Chang et al., 1996) and for the membrane bound portion of the megakaryocyte potentiating factor (MPF) precursor protεin (Kojima ot al., 1995), and thε present disclosure furthεr providεs nuclεic acid sεquεncεs encoding mesothεlin related antigen (MRA) polypeptidεs, such that thosε skilled in the art may routinely prεparε thεsε polypεptidεs for use as immunogens. For instance, monoclonal antibodies such as 4H3, 3G3 and 1A6, which are described in greater detail bεlow, may bε usεd to practice certain methods according to the present invention. As also discussed above, another useful antibody is MAb K-l, a monoclonal antibody reactive with a mesothelin polypeptide (Chang et al., 1996 Proc. Nat. Acad. Sci. USA 93:136; Chang et al., 1992 Int. J. Cancer 50:373; MAb K-l is available from, e.g., Signet Laboratories, Inc., Dedham, MA). Thε tεrm "antibodiεs" includεs polyclonal antibodies, monoclonal antibodies, fragments thereof such as F(ab') 2 , and Fab fragments, as well as any naturally occurring or recombinantly produced binding partners, which are molecules that specifically bind a mεsothεlin polypεptidε, for εxamplε mεsothεlin, mεsothelin relatεd antigεn (MRA) or MPF. Antibodiεs are definεd to bε "immunospεcific" or specifically binding if they bind a mesothεlin polypεptide with a K of grεatεr than or εqual to about 10 4 M" 1 , prefεrably of grεatεr than or εqual to about 10 5 M" 1 , more profεrably of greater than or equal to about 10 6 M" 1 and still more prefεrably of grεatεr than or εqual to about 10 7 M" 1 . Affinities of binding partners or antibodies can be readily dεtermined using conventional techniques, for example those dεscribεd by Scatchard et al., Ann. N. Y. Acad. Sci. 51:660 (1949). Detεrmination of othεr protεins as binding partnεrs of a mεsotholin polypεptide can be performεd using any of a numbεr of known mothods for identifying and obtaining proteins that specifically interact with other protεins or polypεptidεs, for example, a yeast two-hybrid screening system such as that describεd in U.S. Patεnt No. 5,283,173 and U.S. Patεnt No. 5,468,614, or thε εquivalεnt. Thε prεsεnt invεntion also includεs thε usε of a mesothelin polypeptide, and peptidεs basεd on thε amino acid sequence of a mesothelin polypeptide, to preparε binding partnεrs and antibodies that specifically bind to a mεsothεlin polypεptidε. Antibodiεs may gεnεrally bε prepared by any of a variety of techniques known to those of ordinary skill in the art (see, e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988). In onε such tεchniquε, an immunogεn comprising a mεsothεlin polypεptidε, for example a cεll having a mεsothεlin polypεptidε on its surfacε or an isolatεd mosothεlin polypeptide such as mesothelin, MRA or MPF, is initially injected into a suitable animal (e.g., micε, rats, rabbits, shεεp and goats), preferably according to a predεtεrmined schedulε incorporating onε or morε boostεr immunizations, and the animals are blεd pεriodically. Polyclonal antibodiεs spεcific for thε mεsotholin polypεptidε may then be purified from such antisεra by, for example, affinity chromatography using the polypeptidε couplεd to a suitablε solid support. Monoclonal antibodiεs spεcific for mεsothεlin polypεptides or variants thereof may bε preparεd, for εxamplε, using thε tεchniquε of Kohlεr and Milstεin (1976 Eur. J. Immunol. (5:51 1-519), and improvomεnts thεreto. Briefly, thεsε methods involve the preparation of immortal cell lines capable of producing antibodiεs having thε dεsirεd spεcificity (i.e., reactivity with the mesothεlin polypεptidε of intεrεst). Such cεll linεs may bε produced, for examplε, from sploεn cells obtained from an animal immunized as described above. The spleen cells are then immortalizεd by, for εxamplε, fusion with a myεloma cell fusion partner, preferably one that is syngeneic with the immunized animal. For example, the spleεn cεlls and myεloma cεlls may bε combined with a membrane fusion promoting agent such as polyethylene glycol or a nonionic detergent for a few minutes, and then plated at low density on a selective medium that supports the growth of hybrid cells, but not myeloma cells. A prefεrrεd selection tεchniquε usεs HAT (hypoxanthinε, aminoptεrin, thymidinε) sεlεction. After a sufficient time, usually about 1 to 2 weeks, colonies of hybrids are observed. Single colonies are selεctεd and tεstεd for binding activity against thε polypεptidε. Hybridomas having high reactivity and specificity are prεfεrrεd. Hybridomas that generate monoclonal antibodies that specifically bind to mesothεlin polypeptides are contemplated by the presεnt invεntion. Monoclonal antibodiεs may bε isolated from the supernatants of growing hybridoma colonies. In addition, various techniques may be employεd to εnhance the yield, such as injection of thε hybridoma cεll linε into thε pεritonεal cavity of a suitablε vεrtεbratε host, such as a mouse. Monoclonal antibodies may then bε harvested from thε ascitεs fluid or thε blood. Contaminants may bε rεmovεd from the antibodies by conventional techniques, such as chromatography, gel filtration, precipitation, and extraction. For example, antibodies may be purified by chromatography on immobilized Protein G or Protein A using standard techniques. Within certain embodimεnts, the usε of antigεn-binding fragments of antibodies may be prefεrrεd. Such fragments include Fab fragments, which may be prepared using standard tεchniquεs (e.g., by digεstion with papain to yiεld Fab and Fc fragments). The Fab and Fc fragments may be sεparated by affinity chromatography (e.g., on immobilized protein A columns), using standard tεchniquεs. See, e.g., Weir, D.M., Handbook of Experimental Immunology, 1986. Blackwεll Scientific, Boston. Multifunctional fusion proteins having spεcific binding affinities for pre- selεcted antigens by virtue of immunoglobulin V-region domains encoded by DNA sequences linked in-framε to sεquεncεs εncoding various effector proteins are known in thε art, for εxamplε, as disclosed in EP-B 1-0318554, U.S. Patent No. 5,132,405, U.S. Patent No. 5,091,513 and U.S. Patent No. 5,476,786. Such effector proteins include polypεptidε domains that may be used to detect binding of the fusion protεin by any of a variety of techniques with which those skilled in thε art will bε familiar, including but not limitεd to a biotin mimetic sequencε (see, e.g., Luo et al., 1998 J. Biotechnol. 65:225 and references cited therεin), direct covalεnt modification with a dεtεctablε labεling moiety, non-covalεnt binding to a specific labelεd reporter molecule, enzymatic modification of a detectable substrate or immobilization (covalεnt or non-covalεnt) on a solid-phase support. Single chain antibodies for use in the present invention may also be generated and selectεd by a method such as phage display (see, e.g., U.S. Patent No. 5,223,409; Schlebusch et al., 1997 Hybridoma 16:47; and refεrεncεs cited therεin). Briεfly, in this mεthod, DNA sεquεncεs are insεrtεd into thε gene III or genε VIII gεnε of a filamεntous phagε, such as Ml 3. Sεvεral vεctors with multicloning sites have beεn dεvεlopεd for insεrtion (McLafferty et al., Gene 725:29-36, 1993; Scott and Smith, Science 249:386-390, 1990; Smith and Scott, Methods Enzymol. 277:228-257, 1993). Thε insεrtεd DNA sequencεs may bε randomly gonerated or may be variants of a known binding domain for binding to a mεsothεlin polypeptide. Single chain antibodiεs may readily bε generated using this method. Gεnεrally, the inserts encode from 6 to 20 amino acids. The peptide encoded by the insertεd sεquεncε is displayed on the surface of thε bactεriophage. Bacteriophage expressing a binding domain for a mesothelin polypeptidε are selected by binding to an immobilized mesothelin polypeptide, for example a recombinant polypεptidε prεparεd using mεthods wεll known in thε art and nuclεic acid coding sequencεs as disclosed by Chang et al. (1996 Proc. Nat. Acad. Sci. USA 93:136) or by Kojima et al. (1995 J Biol. Chem. 270:21984). Unbound phage are removεd by a wash, typically containing 10 mM Tris, 1 mM EDTA, and without salt or with a low salt concentration. Bound phage arε εlutεd with a salt containing buffer, for example. The NaCl concentration is increasεd in a stεp-wisε fashion until all thε phagε are eluted. Typically, phage binding with higher affinity will be released by higher salt concentrations. Eluted phagε arε propagated in the bacteria host. Further rounds of selection may be pεrformεd to select for a few phage binding with high affinity. The DNA sequεncε of thε insεrt in the binding phage is thεn dεtεrminεd. Oncε thε predicted amino acid sequence of the binding peptidε is known, sufficiεnt pεptide for use hεrεin as an antibody spεcific for a human mosothelin polypeptidε may bε madε εithεr by recombinant means or synthetically. Recombinant means are usεd whεn thε antibody is produced as a fusion protein. Thε pεptide may also be genεratεd as a tandεm array of two or more similar or dissimilar pεptidεs, in ordεr to maximizε affinity or binding. To dεtεct an antigεnic determinant reactive with an antibody specific for a human mesothεlin polypεptidε, thε dεtection reagεnt is typically an antibody, which may be preparεd as dεscribed herein. There arε a variεty of assay formats known to thosε of ordinary skill in thε art for using an antibody to dεtεct a polypεptidε in a samplε, including but not limited to enzyme linked immunosorbent assay (ELISA), radioimmunoassay (RIA), immunofluorimεtry, immunoprecipitation, equilibrium dialysis, immunodiffusion and other techniques. See, e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988; Weir, D.M., Handbook of Experimental Immunology, 1986, Blackwell Scientific, Boston. For examplε, thε assay may bε performed in a Westεrn blot format, whεrεin a protein preparation from thε biological samplε is submittεd to gεl electrophoresis, transferred to a suitable membrane and allowed to react with the antibody. The prεsεnce of the antibody on thε membrane may then bε detected using a suitable dεtεction reagent, as is well known in the art and described below. In another embodimεnt, thε assay involvεs thε usε of an antibody immobilizεd on a solid support to bind to thε target mesothεlin polypeptide and remove it from the rεmaindεr of thε samplε. The bound mesothεlin polypεptidε may thεn bε dεtεctεd using a second antibody reactive with a distinct mesothεlin polypεptide antigenic detεrminant, for εxamplε, a rεagεnt that contains a detectable reportor moioty. As a non- limiting εxamplε, according to this εmbodimεnt thε immobilized antibody and the second antibody which recognize distinct antigenic detεrminants may be any two of the monoclonal antibodies described herein selεctεd from the monoclonal antibodies OV569, 4H3, 3G3 and 1A6. Alternatively, a competitive assay may be utilized, in which a mesothεlin polypεptidε is labεlεd with a dεtεctablε rεportεr moiεty and allowed to bind to the immobilized mesothεlin polypeptidε specific antibody after incubation of thε immobilized antibody with the sample. The εxtεnt to which components of the sample inhibit thε binding of thε labεlεd polypεptidε to thε antibody is indicativε of thε rεactivity of thε samplε with the immobilized antibody, and as a result, indicative of the levεl of mεsothεlin in thε samplε. The solid support may be any matεrial known to thosε of ordinary skill in the art to which the antibody may be attached, such as a tεst wεll in a microtitεr platε, a nitrocellulose filter or anothεr suitablε membrane. Alternativεly, thε support may bε a bead or disc, such as glass, fiberglass, latex or a plastic such as polystyrenε or polyvinylchloride. The antibody may be immobilizεd on thε solid support using a variεty of techniques known to those in the art, which are amply described in the patent and scientific litεraturε. In cεrtain prεfεrrεd εmbodimεnts, thε assay for dεtεction of mεsothεlin rεlatεd antigεn polypεptidε in a sample is a two-antibody sandwich assay. This assay may be performed by first contacting a mesothεlin rεlatεd antigεn polypeptide-spεcific antibody (e.g., a monoclonal antibody such as OV569, 1A6, 3G3 or 4H3) that has boεn immobilizεd on a solid support, commonly thε well of a microtiter platε, with the biological sample, such that a soluble molecule naturally occurring in the samplε and having an antigenic detεrminant that is rεactive with the antibody is allowed to bind to thε immobilizεd antibody (e.g., a 30 minutε incubation time at room tempεraturε is gεnerally sufficient) to form an antigεn-antibody complεx or an immunε complex. Unbound constituents of the sample arε thεn removed from the immobilized immune complexεs. Next, a second antibody spεcific for a mεsothεlin rεlatεd antigen polypeptide is added, whεrεin the antigεn combining sitε of thε sεcond antibody doεs not compεtitivεly inhibit binding of thε antigεn combining sitε of thε immobilizεd first antibody to a mεsothεlin rεlated antigen polypeptidε (e.g., a monoclonal antibody such as OV569, 1A6, 3G3 or 4H3 that is not thε samε as the monoclonal antibody immobilized on thε solid support). Thε sεcond antibody may be detεctably labεlεd as provided herεin, such that it may bε dirεctly dεtected. Altεrnativεly, thε sεcond antibody may bε indirεctly dεtεcted through the use of a detεctably labεlεd sεcondary (or "sεcond stagε") anti-antibody, or by using a specific detection reagεnt as providεd hεrεin. The subject invεntion mεthod is not limitεd to any particular dεtεction procedure, as those having familiarity with immunoassays will appreciate that therε are numerous rεagεnts and configurations for immunologically detecting a particular antigen (e.g., a mesothεlin polypeptidε) in a two-antibody sandwich immunoassay. In cεrtain preferred embodiments of the invεntion using the two-antibody sandwich assay described above, thε first, immobilizεd antibody spεcific for a mεsothεlin rεlatεd antigεn polypεptidε is a polyclonal antibody and thε sεcond antibody spεcific for a mεsothεlin rεlatεd antigεn polypεptide is a polyclonal antibody. In certain othεr εmbodimεnts of thε invεntion thε first, immobilizεd antibody specific for a mesothεlin rεlatεd antigεn polypeptide is a monoclonal antibody and the second antibody specific for a mesothelin related antigen polypeptidε is a polyclonal antibody. In cεrtain othεr εmbodimεnts of thε invεntion thε first, immobilizεd antibody specific for a mesothεlin related antigen polypeptidε is a polyclonal antibody and thε second antibody specific for a mεsothεlin rεlatεd antigεn polypεptidε is a monoclonal antibody. In cεrtain othεr highly prεfεrred embodimεnts of the invention thε first, immobilizεd antibody specific for a mesothelin relatεd antigen polypeptidε is a monoclonal antibody and thε sεcond antibody spεcific for a mεsothelin relatεd antigεn polypeptide is a monoclonal antibody. For example, in thesε εmbodimεnts it should bε notod that monoclonal antibodies 4H3, 3G3, 1A6 and OV569 as provided hεrein recognize distinct and non-competitivε antigεnic dεtεrminants (e.g., εpitopεs) on mεsothεlin polypεptidεs such as MRA polypεptides, such that any pairwise combination of these monoclonal antibodies may bε employed. In other preferred embodiments of the invention the first, immobilized antibody spεcific for a mεsothεlin rεlatεd antigεn polypeptide and/or the second antibody spεcific for a mεsothεlin rεlatεd antigεn polypεptidε may bε any of thε kinds of antibodiεs known in thε art and referred to herein, for examplε by way of illustration and not limitation, Fab fragments, F(ab') 2 fragments, immunoglobulin V-rεgion fusion protεins or singlε chain antibodiεs. Thosε familiar with the art will appreciate that the presεnt invεntion εncompassεs thε usε of othεr antibody forms, fragmεnts, dεrivativεs and the like in the methods disclosed and claimed herein. In certain particularly preferred embodiments, the second antibody may contain a detεctablε reporter moiety or label such as an enzymε, dye, radionuclide, luminεscεnt group, fluorescent group or biotin, or the like. The amount of the second antibody that rεmains bound to thε solid support is thεn dεtεrmined using a method appropriate for the specific detectable reportεr moiεty or labεl. For radioactive groups, scintillation counting or autoradiographic methods are generally appropriate. Antibody- enzyme conjugates may be preparεd using a variety of coupling techniques (for reviεw sεε, e.g., Scoutεn, W.H., Methods in Enzymology 135:30-65, 1987). Spectroscopic methods may be used to detect dyes (including, for example, colorimetric products of enzymε reactions), luminescent groups and fluorescent groups. Biotin may be detected using avidin or streptavidin, coupled to a different reporter group (commonly a radioactive or fluorescent group or an enzymε). Enzyme rεportεr groups may gεnεrally bε dεtεctεd by the addition of substrate (gεnεrally for a spεcific period of time), followed by spectroscopic, spectrophotometric or other analysis of the rεaction products. Standards and standard additions may bε usεd to dεtεrminε thε lεvεl of mεsothεlin polypeptide in a sample, using well known techniques. In another εmbodimεnt, thε invention contemplatεs thε usε of a mεsothεlin rεlated antigen polypeptidε as provided herεin to scrεεn for thε prεsεncε of a malignant condition by detection of immunospecifically reactive antibodies in a biological samplε from a biological source or subject. According to this embodimεnt, a mεsothεlin rεlated antigen polypeptide (or a fragment or variant thereof including a truncated mesothelin related antigen polypeptide as provided herein) is detεctably labεlεd and contacted with a biological sample to detεct binding to thε mesothelin rεlated antigεn polypεptide of an antibody naturally occurring in soluble form in thε sample. For examplε, thε mεsothεlin rεlatεd antigεn polypεptide may be labelεd biosynthεtically by using thε sεquεnces disclosed herεin in concεrt with wεll known mεthods such as incorporation during in vitro translation of a rεadily dεtεctable (e.g., radioactively labelεd) amino acid, or by using othεr dεtεctable reportεr moiεties such as those doscribεd abovε. Without wishing to bε bound by thoory, this embodiment of the invεntion contεmplatεs that cεrtain mεsothεlin polypεptidεs such as thε MRA polypεptides disclosed herεin, which feature frame-shifted sequences that result from in-framε insεrtions of coding sequences at the nucleic acid lεvεl, may providε pεptidεs that are particularly immunogenic and so givε rise to specific and detεctablε antibodiεs. For εxamplε, according to this theory certain MRA polypeptides may reprεsεnt "non-self antigens that provoke an avid immune response, while mesothelin polypeptides that lack in-frame insertions (e.g., MPF or mesothelin) may be viewεd by thε immunε system as "self antigens that do not readily elicit humoral or cell-mεdiated immunity. As noted above, the presεnt invεntion pεrtains in part to the surprising finding that soluble forms of human mesothεlin rεlatεd antigεn polypeptides occur naturally in subjects, including elεvatεd lεvεls of such solublε mεsothelin polypeptides in subjects having cεrtain carcinomas. A mothod of screening for the presεncε of a malignant condition according to the presεnt invention may bε further enhancεd by thε dεtεction of more than onε tumor associated marker in a biological sample from a subject. Accordingly, in cεrtain εmbodimεnts thε present invention provides a method of screεning that, in addition to detecting reactivity of a naturally occurring solublε samplε component with an antibody specific for a mesothelin relatεd antigen polypεptidε, also includεs dεtεction of at lεast onε additional soluble marker of a malignant condition using established methods as known in the art and providεd herein. As noted above, therε arε currently a number of solublε tumor associated antigens that are detεctablε in samples of readily obtainεd biological fluids. Thεsε includε, but nεed not be limited to, CEA, CA125, sialyl TN, SCC, TPS and PLAP, (seε e.g., Bast εt al., 1983 N. Eng. J. Med. 309:883; Lloyd εt al., 1997 Int. J. Cane. 71 :842; Sarandakou εt al., 1997 Ada Oncol. 36:755; Sarandakou et al., 1998 Eur. J. Gynaecol. Oncol. 19:73; Meiεr εt al., 1997 Anticanc. Res. 17(4B):2945; Kudoh et al., 1999 Gynecol. Obstet. Invest. 47:52; Ind et al, 1997 Br. J Obstet. Gynaecol. 104:1024; Bεll εt al. 1998 Rr. J. Obstet. Gynaecol. 105:1136; Cioffi εt al., 1997 Tumori 83:594; Mεiεr εt al. 1997 Anticanc. Res. 17(4B):2949; Mεiεr εt al., 1997 Anticanc. Res. 17(4B):3019) and may furthεr includε any known markεr thε presεncε of which in a biological samplε may bε correlated with the presεncε of at least one malignant condition, as provided herεin. Altεrnativεly, nucleic acid sequεncεs encoding mesothεlin rεlatεd antigεn polypεptidεs may bε detected, using standard hybridization and/or polymerasε chain rεaction (PCR) tεchniques. Suitable probes and primers may bε dεsignεd by thosε of ordinary skill in thε art basεd on thε mεsothεlin rεlated antigen cDNA sεquεncεs providεd hεrεin. Assays may gεnerally bε performed using any of a variety of samplεs obtainεd from a biological source, such as eukaryotic cells, bacteria, virusεs, εxtracts prepared from such organisms and fluids found within living organisms. The following Examples are offεrεd by way of illustration and not by way of limitation. EXAMPLES EXAMPLE 1 MONOCLONAL ANTIBODY OV569 SPECIFIC FOR MESOTHELIN POLYPEPTIDE This examplε describes generation of a murine monoclonal antibody (Mab), OV569, following immunization with human malignant ascites cells from ovarian carcinoma. Cells for usε as immunogεns wεrε unfractionatεd cells recovεrεd from pεritonεal ascites fluids of a patient with malignant ovarian cancer by centrifugation, washεd and stored in liquid nitrogon until usε. BALB/c micε (approximatεly 3 months old) wεrε immunizεd a total of seven times at 14-day intervals with 1 x 10 7 thawed ovarian carcinoma cεlls pεr immunization; no adjuvant was used. For the initial immunization, mice were injected both intraperitonεally (i.p.) and subcutaneously (s.c), while for the remaining six immunizations, injεctions of thawεd cεlls wεre administered only i.p. Four days after the last immunization, the spleen was removed from one mouse, teasεd apart to form a single cell suspension in IMDM culture medium (Gibco BRL, Grand Island, NY) and the splenocytes subsequently fused to myeloma cεlls P3x63Ag8.653 (CRL 1580, ATCC, Rockvillε, MD) as previously described using 40% polyethylεnε glycol (PEG) as tho fusing agεnt (Yεh εt al., 1979 Proc. Nat. Acad. Sci. USA 76:2927). Following hybridization, thε fusεd cεll suspεnsions wεrε dilutεd to form low dεnsity cultures prefεrably originating from single cells, and seeded into 96 well platεs (Falcon, Linden Park, NY) in selεctivε mεdium containing 10% hybridoma growth factor (Igεn Inc, Gaithεrsburg, MO), 10% fεtal bovinε sεrum, 2% HAT and 0.25% Geneticin (Yεh et al, 1979). Supernatants from each well were scrεεnεd for thε presence of antibodies capable of binding to the ovarian carcinoma ascites cells used for immunizations, to cultured ovarian carcinoma cells from other patients, and to culturεd human fibroblasts, using an εnzyme linked immunosorbent assay (ELISA) as dεscribεd by Douillard, εt al. (1983 Met/?. Enzymol. 92:168). Hybridoma cεlls that produced antibodies that bound to the human ovarian cancer cεlls but not to thε cultured human fibroblasts were clonεd twicε by limiting dilution, re-tested for specific reactivity of supernatant antibody with the ovarian cancer cells (and for non-rεactivity with cεlls from a variεty of normal human tissuεs) and εxpandεd in vitro. Antibodiεs wεre purified from hybridoma supernatants by affinity chromatography on immobilizεd protεin A (RεpliGεn, Cambridge, MA), using phosphate buffεrεd saline (PBS) as buffer and low pH elution followed by neutralization as recommended by the suppliεr, after which they werε filtεr stεrilizεd and stored at -70°C until usε. One such monoclonal hybridoma antibody that bound ovarian carcinoma cells but not normal fibroblasts was named OV569. Monoclonal antibody (MAb) OV569 was dεtεrmined to bε of thε murine IgGl isotype by ELISA. Briεfly, wεlls of an Immunolon 96 wεll platε (Dynatεch, Chantilly, VA) wεrε coated overnight at 4°C with goat antibodies (1 μg/ml in PBS) specific for the diffεrεnt mousε IgG subclasses (Southern Biotεch, Birmingham, AL), blockεd and usεd to test various dilutions of OV569 hybridoma supernatant according to a dεscribεd procedure (Yeh et al., 1979 Proc. Nat. Acad. Sci. USA 76:2927). EXAMPLE 2 SECOND GENERATION MONOCLONAL ANTIBODIES SPECIFIC FOR OVARIAN CARCINOMA ANTIGEN RECOGNIZED BY OV569 A second sot of hybridomas was gεnεratεd and sεlεctεd for production of antibodiεs that bind to the antigen molεculε rεcognizεd by MAb OV569, but via recognition of antigεnic εpitopεs distinct from that usεd by OV569. For usε as an immunogεn to εlicit thε sεcond gεnεration MAbs, the OV569-binding antigen was affinity purified from supernatants of human ovarian and lung carcinoma cell cultures establishεd from surgically rεmovεd tumors (as dεscribεd, for εxamplε, by Hεllstrom εt al., 1990 Cancer Res. 50:2183) or following collection of ascites or pleural fluids using a column of immobilized MAb OV569. Briefly, to 1.5 g cyanogen bromide activated Sepharose 4B (Sigma, St. Louis, MO) 9.2 mg of OV569 was added and thε column washed and equilibrated for use according to the supplier's protocol. Starting material from which antigen was to be purified (e.g., culture supernatant clarified by centrifugation) was passed through the column, after which the column was washed with 0.01 M 0.02% NaN 3 in PBS- pH 7.2, until no material having absorbance at 280 nm was detεctablε in thε column offluent. Soluble antigen spεcifically bound to thε MAb OV569 column was thεn eluted using a pH 2.6 elution buffer (0.1 M glycinε-HCl- pH 2.6, 0.15 M NaCl). Thε εluatε was collected in a volume of 2 ml, nεutralizεd with 2.5 M Tris-HCl buffεr, pH 8.8, and quantifiεd by spectrophotometric detεrmination of absorbance at 280 nm and 260 nm. Affinity purified OV569 antigεn (30 μg protεin in 0.1 ml) was mixεd with 0.1 ml of Ribi adjuvant (Ribi Immunochεm. Rεsεarch, Inc., Hamilton, MT) and thε mixture was injεctεd into 3 month old BALB/c mice at two s.c. sites, followed 14 days later by a first booster immunization, which was administered i.p. For booster immunizations, the Ribi adjuvant was mixed with antigen purified by OV569 affinity chromatography from the supernatant of cultured H4013 lung carcinoma cells (a carcinoma cell linε εstablishεd using the methods as dεscribεd, for εxample, by Hellstrom εt al., 1990 Cancer Res. 50:2183). Fourtεεn days aftεr administration of thε third in a sεriεs of thrεε booster immunizations (each given at 14 day intεrvals), thε micε were given a final boost by injecting the antigen intravenously (i.v.) without adjuvant. Thrεε days after the final boost, spleεns wεre rεmovεd and cεll fusions wεrε pεrformεd as dεscribed above in Example 1 for MAb OV569. The supernatants of thε resultant hybridoma cεlls wεrε tεstεd for thε prεsεncε of antibodiεs capable of binding to target antigen immobilized on plastic 96 wεll plates using conventional ELISA methods (Current Protocols in Immunology, J.E. Coligan εt al., (Eds.) 1998 John Wilεy & Sons, NY). Targεt antigεn was (i) affinity purifiεd OV569 antigεn (thε immunizing antigεn) prepared as described above; or (ii) D2hlg, an immunoglobulin fusion protein consisting of amino acids 294-628 of the mesothεlin mεmbranε-bound portion (Chang εt al, 1996 Proc. Nat. Acad. Sci. USA 93:136) fusεd to an immunoglobulin constant region using a dεscribεd vεctor encoding a human Ig sequence (Hollenbaugh εt al., 1995 J. Immunol. Meth. 188:1-7) and purified by protein A/G affinity chromatography (ImmunoPure A/G, Piercε Chεmicals, Rockford, IL) according to thε suppliεr' s instructions. Positivε supεrnatants wεrε rε-tested by ELISA to confirm reactivity and subsequently screεned in a modifiod ELISA binding competition immunoassay. Briefly, in this assay, OV569-binding antigεn, affinity purifiεd as dεscribεd abovε, was immobilizεd in wεlls of 96 wεll platεs. Wεlls received of each positivε hybridoma supεrnatant and 50 μl (400 ng) of biotinylatεd MAb OV569 prεparεd by biotinylation according to Wεir, D.M., Handbook of Experimental Immunology (1986, Blackwεll Scientific, Boston), for a binding competition incubation stεp (1 hr at room tεmpεraturε) followεd by washing with PBS and a dεtεction stεp using 50 μl HRP-strεptavidin (PharMingεn, San Diεgo, CA) diluted according to the supplier's recommendations. This assay selεctεd for MAbs that recognized epitopεs diffεrent from the onε recognized by OV569, by virtue of their inability to inhibit biotinyl-MAb OV569 binding. Supernatants testεd in this competition assay were also testεd using a parallεl set of control plates coatεd with thε affinity purified OV569 binding antigen to confirm hybridoma antibody binding to the OV569 antigen. Three hybridomas, designatεd 4H3, 3G3 and 1 A6, were idεntifiεd that produced antibodies capable of binding to D2hlg and to OV569 affinity -purified antigen from cultured OV569- positivo carcinoma culture supernatants, and that did not compete with the OV569 MAb. Thesε thrεε hybridomas wεrε cloned, expanded and transplanted in syngεnεic mice to εstablish antibody -producing ascitεs tumors. Thε IgGl MAb referred to as 4H3 was used with OV569 in a double determinant ("sandwich ELISA") assay described below. EXAMPLE 3 EXPRESSION OF OV569 OVARIAN CARCINOMA ANTIGEN ON HUMAN TUMOR CELL SURFACES This examplε dεscribεs immunohistologic characterization of the exprεssion of thε antigen definεd by MAb OV569. A modification of thε immunopεroxidase technique (Sternbεrger, In: Immunocytochemistry, pp.104- 169, John Wilεy & Sons, Inc., Nεw York, 1979) was εmployed, using the Vεctastain ABC immunostaining reagent system (Vεctor Laboratories, Burlingame, CA) according to thε manufacturer's instructions. Briεfly, various normal human tissuεs or human tumor samplεs were obtainεd by standard surgical rεsεction or biopsy procedures and immediatεly frozεn. Thε frozen samples wεre sεctionεd using a chilled microtome, air-driεd on glass microscope slides, fixed with cold acetonε (5 min, -20°C), washεd twice in PBS, blocked with normal mouse serum (20 min, room temperaturε), and then treatεd with avidin/biotin blocking reagents. The slides wεrε nεxt incubatεd with primary antibodiεs dilutεd in Vεctastain blocking solution (Vεctor Laboratories) for 90 min at room temperaturε and washεd with PBS. Slidεs wεrε thεn incubatεd with biotinylated goat anti-mouse IgG (Southern Biotechnology Assoc, Birmingham, AL) diluted 1 :150 in Vεctastain blocking solution for 30 min at room temperaturε, and again washεd with PBS. A Vεctastain ABC ("Vector Elite") horseradish peroxidasε (HRP) working solution was prεpared and kept at room tεmpεraturε. The slides were incubated with this HRP solution for 30 min at room temperature, washed 3 times with PBS, and rinsed in Tris buffer (0.05M Tris-HCl-pH 7.5, 150 mM NaCl). A diaminobenzamidinε (DAB, Bio-Tek Instruments, Inc., Winooski, VT) chromogεn rεagεnt solution was prεparεd daily according to thε Vεctastain ABC instructions, and thε slidεs were incubated with this rεagεnt for 7 min. at room temperaturε in subduεd light. Thε rεaction was stopped by adding PBS and washing twicε with double distilled water. Slides wεrε countεrstained with hematoxylin (Bio-Tεk Hεmatoxylin solution dilutεd 1 :10 with distilled water) for 10-45 seconds, rinsed threε times with water and dεhydratεd through a gradεd ethanol sεriεs prior to mounting for microscopy. Thε slidεs wεrε coded and examinεd by an indεpεndεnt invεstigator, who photographεd representativε microscope fields using diffεr ntial intεrfεrence contrast (Nomarski) optics under bright-field illumination with a Zeiss upright microscope (Carl Zeiss, Inc., Thornwood, NY). As presεntεd here, samples were scored as "positive" whεn at least one third of the cells examinεd showεd DAB staining; samplεs referred to as "negative" exhibited no significant staining (<5% of cells) using the samε MAb dilutions. Tablε 1 shows thε ratio of positivεly staining cancεr ("Ca.") spεcimεns relative to the number of cancεr spεcimεns tεstεd. The staining was seεn in thε cytoplasm of thε tumor cεlls and, in some cases, also at the cell surface. No staining of normal (i.e., non- cancerous) cells was observεd with MAb OV569. Both nεoplastic colls and stromal cεlls wεre obsεrvεd in tumor samples, and only the formor wεrε stainεd by MAb OV569. Rεsults using normal human tissuε samplεs are shown in Table 2. Table 1. IMMUNOHISTOLOGICAL STAINING OF HUMAN TUMORS WITH MAB OV569 Table 2. IMMUNOHISTOLOGICAL STAINING OF NORMAL HUMAN TISSUES WITH MAB OV569 * *Wεak staining of a subpopulation (<10%) of cells EXAMPLE 4 EXPRESSION OF OV569 OVARIAN CARCINOMA ANTIGEN ON CULTURED HUMAN CARCINOMA CELL SURFACES In this example, MAb OV569 binding to carcinoma cell surface antigεns was evaluated by flow immunocytofluorimetry using a Coulter Epics C FACS cytofluorimetεr (Coultεr Corp., Miami, FL) εssεntially as previously dεscribεd (Hεllstrom εt al., 1986 Cane. Res. 46:3917). Cultured adherent human carcinoma cells generated as described above (e.g., Hollstrom εt al., 1990 Cancer Res. 50:2183) wεre removεd from culture flasks with trypsin/EDTA, washed two times by centrifugation (200 x g, 10 min) and resuspension in IMDM medium (GibcoBRL, Grand Island, NY) containing 15% FBS and equilibrated for at least 1 h at room tεmpεrature in the same medium. Aliquots of the cells (0.5-1.0 x 10 6 cells/0.1 ml for each group) were then held on ice for 15 min and resuspended for 1 h at 4°C in 100 μl OV569 hybridoma cεll culture supernatant. Thε cεlls wεre washed threε timεs in staining buffεr (IMDM mεdium containing 5% fεtal calf serum) and resuspεndεd for 30 min. at 4°C in 0.1 mL pεr group of fluor scεin-conjugatεd goat anti-mouse immunoglobulin (FITC-GaMIg, BioSource International, Inc., Camarillo, CA) diluted in staining buffer according to the supplier's recommendations. Cells were again washed threε timεs, rεsuspεndεd in 0.5 mL chilled staining buffεr and maintainεd at 4°C in the dark until analysis. Flow immunocytofluorimetry was performεd using thε Coultεr Epics C FACS cytofluorimotεr (Coultεr Corp., Miami, FL) according to thε manufacturer's instructions, with forward and side-scattεr paramεtεrs gatεd to record singlε-cεll events. The mean fluorescεncε intεnsity was dεtεrminεd for εach sample and used to calculate the linear fluorescence equivalence (LFE) using the software with which the Coulter Epics C FACS was equipped. The LFE of εach tεst samplε dividεd by the LFE of a negativε control sample (incubated with a MAb of irrelεvant spεcificity during the first antibody incubation step) providεd a ratio for comparing the relativε brightness of specifically immunofluorescεntly stainεd cεlls to that of cεlls stainεd with thε nεgativε control antibody. The results are shown in Tablε 3. Table 3. FLOW IMMUNOCYTOFLUORIMETRIC ANALYSIS OF OV569 EXPRESSION BY CULTURED HUMAN CARCINOMA CELLS CARCINOMA TYPE CELL LINE LFE(sample)/LFE(control Ovarian H3538 2.55 Ovarian H3907 3.85 Ovarian H3909 3.84 Ovarian H4004 2.43 Ovarian H3633 1.0 Ovarian H3750 2.57 Ovarian H3759 6.74 Ovarian H3659.5 5.63 Ovarian H4002 8.48 Ovarian H4014 1.0 Ovarian H4006 2.53 Ovarian H4007 8.72 Ovarian H4010-1 1.12 Ovarian H4012 1.0 Lung H4013 7.0 Lung H2981 1.3 Lung H2987 1.25 Lung H3963 1.1 1 Lung H3776 1.33 Lung H3754 1.59 EXAMPLE 5 HUMAN CARCINOMA CELLS FAIL TO INTERNALIZE OV569 OVARIAN CARCINOMA ANTIGEN To determine whethεr the antigen dεfinεd by MAb OV569 can bε internalized by antigen positive carcinoma cells, immunofluorescεncε antibody localization assays wεrε pεrformεd using lasεr scanning confocal microscopy. Human lung carcinoma cεlls (H4013), or ovarian carcinoma cεlls (H4007) adapted to culture following surgical resεction as dεscribεd abovε (e.g., Hellstrom et al., 1990 Cancer Res. 50:2183) were cultured in IMDM culture mεdium (Gibco BRL, Grand Island, NY) containing 10% fetal calf serum and allowed to adherε onto glass slidos (NUNC chamber coverslips, NUNC, Rochεstεr, NY) for 48 hrs at 37°C, 5% CO 2 in a humidifiεd atmosphεrε. For immunofluorescent antibody labeling, thε cells were equilibratεd for 15 min at 4°C, a tεmperature that is non-pεrmissivε for intεrnalization of cεll surface antigens. FITC- conjugated OV569 was preparεd by incubation of fluorεscεin isothiocyanatε (Sigma. St. Louis, MO) under described conditions (Weir, D.M., Handbook of Experimental Immunology, 1986, Blackwell Scientific, Boston) with MAb OV569 affinity purified on immobilizεd protein A (RepliGen, Cambridge, MA) according to the manufacturer's recommendations. Either FITC-OV569, or, as a negativε control, FITC conjugated goat anti-mouse IgG (Tago, Burlingame, CA), was addεd to thε cεlls at a concentration of 10 μg/ml for 1 hr. at 4°C, in a volume sufficient to cover each coverslip. Unbound antibody was removed by extεnsivεly rinsing thε coverslips with cold culture mεdium. The cells were thεn incubatεd for different periods of time at 37°C, a tεmpεraturε that is permissive for intemalization of certain cell surface antigεns (Hεllstrom ot al., 1990 Cane. Res. 50:2183). Thε 37°C incubation pεriod was terminated by adding cold PBS to the cultures and post-fixing the cells with 2% formaldehydε in PBS for 15 min. at room tεmpεrature. Each coverslip was then treatεd with thε anti-fading reagent dithioerythritol (Sigma, St. Louis, MO) or with the VectaStain anti-fading reagent (Vector Laboratories, Burlingame, CA) according to thε supplier's instructions. Laser scanning confocal microscope images were obtained using a Leica confocal microscope (Leica, Inc., Deerfiεld, IL) equippεd with a fluorεscεin detection filter set according to the manufacturer's instructions. Confocal images demonstratεd exclusive localization of FITC-MAb OV569 to the surfaces of human ovarian carcinoma and lung carcinoma cells exposed to the antibody at 4°C, washεd and immεdiately fixed. When cells stained with FITC-MAb OV569 at 4°C wεrε shiftεd to 37°C for pεriods of 8 h or longεr, detectable FITC-MAb OV569 remained exclusivεly localized to cell surfaces and no cytoplasmic fluorescent staining was observεd. EXAMPLE 6 IMMUNOBLOT CHARACTERIZATION OF OV569 OVARIAN CARCINOMA ANTIGEN This εxamplε describes characterization of the human carcinoma cεll surface antigen recognized by MAb OV569 using Western immunoblot analysis. Samples for immunoblot analysis included lysates wεre preparεd from the following human cell linεs: H4013 lung carcinoma (Fig. 1, lanε 5), OVCAR-3 ovarian carcinoma (Amer. Type Culture Collεction, Manassas, VA) (Fig. 1 , lanε 7), and 6K kidnεy carcinoma (Fig. 1, lanε 8) cεll lysates werε prεpared according to standard procedures (Current Protocols in Immunology, J.E. Coligan et al., (Eds.) 1998 John Wiley & Sons, NY). Protεin was quantifiεd using thε Bradford Commassiε protεin assay rεagεnt (Piεrcε Chemicals, Inc., Rockford, IL) according to the manufacturer's instructions. Other samples for immunoblot analysis included material dεrivεd from human patiεnts and affinity purifiεd on a column of immobilizεd MAb OV569 as dεscribεd abovε in Examplε 2. Thεsε samples included OV569 affinity-purifiεd fractions of ovarian cancεr ascitεs fluid from a patient having ovarian carcinoma (Fig. 1, lane 2), and of plεural effusion fluid collected from the fluid-filled interpleural mεmbranε cavity of a patiεnt diagnosεd as having lung carcinoma (Fig. 1, lanε 3). Fluid sample preparation and affinity chromatography, rεspεctivεly, wεrε as dεscribεd bεlow in Example 7 and above in Example 2. Other samplεs for immunoblot analysis included material derivεd from human carcinoma cell lines and affinity purified on a column of immobilized MAb OV569 as dεscribεd abovε in Examplε 2. Thεsε samplεs included OV569 affinity-purified fractions of H4013 lung carcinoma (Figure 1, lane 4), OVCAR-3 ovarian carcinoma (ATCC, Manassas, VA) (Figure 1, lanε 6). Thε D2hlg fusion protεin dεscribεd in Examplε 2 was also analyzed (Figure 1, lane 1). Each samplε standardizεd by protεin content was diluted 1 : 1 with SDS sample buffer (Novex, San Diego, CA), 20 μl (300 ng/lanε) was loadεd onto a 14% Tris- glycinε gel (Novex, San Diego, CA) and the gel was subject to electrophoresis using SDS running buffεr at 125 V for about 1.5 hours according to thε manufacturer's instructions. Following gεl εlεctrophorεsis, sεparatεd protεins wεre electroblottεd onto PVDF mεmbrane (Novex, San Diego, CA) using Tris-glycine SDS transfεr buffεr and εlεctrophorεtic transfεr conditions as rεcommεndεd by thε manufacturer. Prior to antibody probing, the PVDF membrane was blocked with 5% nonfat milk in washing buffer (0.2% Twεεn 20-PBS) at room tεmperature for 1 hr, followεd by washing with washing buffεr, oncε for 10 minutεs and twice for 5 minutes. Nεxt, thε mεmbranε was bathed in a solution of protein A affinity purified MAb OV569 (4.6 mg/ml) diluted to 3 μg/ mL in washing buffer containing 1% nonfat milk at room tempεraturε for 1 hour, followεd by a sεquεnce of 3 washes as described above. Detεction of specifically bound MAb OV569 was achieved using chemiluminescent detεction of horseradish peroxidasε (HRP) conjugated secondary antibodies. Briefly, the mεmbranε was incubatεd for 1 hr at room temperature in a 1 :5000 dilution of HRP-labelεd goat anti- mousε IgG antibody (Zymεd Laboratories, South San Francisco, California) in washing buffer containing 1% nonfat milk, and then unbound antibodies werε removεd by bathing thε blot in washing buffεr oncε for 10 minutεs, and thεn 4 timεs for 5 minutos εach. Thε ECL chemoluminescence substratε (ECL-Amεrsham, Buckinghamshire, England) was applied onto the membranε for 1 minutε in a dark room according to tho suppliεr' s instructions, followεd by briεf exposure to X-omat radiology film (Kodak, Rochester, NY). Figure 1 shows the pattern of εlectrophoretically rεsolvεd species that were detεctεd by binding MAb OV569, which identifies a component having an apparent relative molecular mass of 42-45 kDa in samples derived from various human carcinomas. EXAMPLE 7 MESOTHELIN RELATED ANTIGEN (MRA), A CARCINOMA ANTIGEN RECOGNIZED BY MONOCLONAL ANTIBODY OV569 Is A MESOTHELIN POLYPEPTIDE This example describes identification of a molecule that naturally occurs in soluble form in a biological sample from a carcinoma patient, and that is recognized by MAb OV569, as a mesothεlin polypeptide. This naturally soluble mesothelin polypeptidε is rεfεrrεd to hεrεin as "mεsothεlin related antigen" (MRA). Pleural effusion fluid (2 liters) collectεd into hεparinized tubes by a single drawing from a patient diagnosed as having lung carcinoma was clarified by centrifugation to remove cells, diluted 1 :1 (v/v) with PBS and filtεrεd through 3MM filtεr paper (Whatman, Clifton, NJ) prior to immunoaffinity chromatography. Thε diluted pleural fluid was applied to a column of immobilized MAb OV569, the column was washed to remove non-binding components and specifically bound material was elutεd and collected as described in Example 2. Bound and elutεd fractions wεre neutralized by addition of 3 mM glycine-0.2 N NaOH nεutralization buffεr. The pooled, εlutεd OV569-binding matεrial was alkylatεd by addition of sεvεral grains of crystalline iodoacetamidε (Sigma, St. Louis, MO) to block artifactual disulfide bond formation through potεntially prεsent cysteinε residuεs, and thε matεrial was rεsolvεd by SDS-polyacrylamidε gεl electrophoresis and blot transferred to a PVDF membranε as dεscribεd in Example 6, except that the resolving gel contained 7.5% polyacrylamide. A lanε of thε PVDF mεmbranε was immunostainεd with MAb OV569 as also dεscribεd in Examplε 6 to localize a diffuse band of approximately 40 kDa for N-terminal sequεncε analysis. Thε amino acid sεquεncε of thε approximately 40 kDa band was analyzed by sequεntial Edman degradation on an ABI Model 473 solid-phasε sεquεncεr (Applied Biosystεms Inc., Foster City, CA). Partial sequεnce analysis revealed the following N- tεrminal amino acid sεquεncε for thε OV569 affinity-isolatεd 40 kDa polypεptidε: EVEKTACPSGKKAREIDES SEQ ID NO:5 This amino acid sequence reprεsεnts a partial amino acid sεquεncε of a novel, naturally solublε mεmbεr of the mesothelin polypeptide family. Because the amino acid sequence of SEQ ID NO:5 is also presεnt at positions 294-312 of mesothelin, a cell surface differentiation antigen expressed on mesothεlium, mεsothεliomas and ovarian cancers that is not detectable as a naturally soluble molecule as provided hεrein (Chang εt al., 1992 Int. J. Cane. 50:373; Chang et al., 1996 Proc. Nat. Acad. Sci. USA 93:136), the soluble OV569- binding polypeptidε dεscribεd here has beεn termed "mesothelin related antigen" (MRA). As noted abovε, thε amino acid sεquεncε of SEQ ID NO:5 is also present in the cεll surface membrane-bound (i.e., not soluble as provided herein) portion of thε MPF precursor protein (Kojima et al., 1995 J Biol. Chem. 270:21984). As notεd abovε, mεsothεlin and MPF arε synthesized as approximately 70 kDa precursors that are protεolytically procεssεd into soluble and cell surface-bound products (Chang et al., 1996 Proc. Nat. Acad. Sci. USA 93: 136; Chowdhury et al., 1998 Proc. Nat. Acad. Sci. USA 95:669; Kojima et al., 1995 J. Biol. Chem. 270:21984; Yamaguchi εt al., 1994 J Biol. Chem. 269:805). To idεntify thε domain (solublε or mεmbranε associated) in which the OV569 εpitopε rεsidεd, two human immunoglobulin constant region fusion protεins were constructed. Dlhlg contained the 33 kDa MPF soluble domain (Chang et al., 1996; Kojima et al., 1995), whilε D2hlg contained the 44 kDa membrane-bound domain of MPF (Chang et al., 1996; seε Examplε 2). OV569 spεcificity was tεstεd by conventional ELISA methods as described above. As shown in Figure 2, OV569 bound to D2hlg but failed to recognize Dlhlg. EXAMPLE 8 ASSAY FOR DETECTION OF OVARIAN CARCINOMA ANTIGEN DEFINED BY MONOCLONAL ANTIBODY OV569 IN MALIGNANT EFFUSION AND SERA OF PATIENTS This examplε dεscribεs a sandwich ELISA immunoassay for thε dεtεction of MRA, a novel, naturally soluble member of the mεsothεlin polypeptide family. The assay εmploys MAb OV569 and MAb 4H3, which bind to distinct εpitopεs present on MRA. The wεlls of Maxisorp Immuno™ platεs (Nalgε Nunc Intεrnational, Napεvillε, IL) platεs wεrε coated overnight at 4°C with 50 ng of protein A immunoaffinity (ImmunoPurε A/G IgG Purification Kit, Pierce Chemicals, Rockford, Illinois) purified MAb 4H3 immunoglobulin in 50 μl/well of carbonate-bicarbonatε buffεr (C-3041, Sigma). Thε nεxt day, wεlls wεre drained and blocked for 2 h at room tempεraturε with 200 μl/ wεll of GSC blocking buffεr (Genetic Systems Corp., Redmond, WA). Wεlls wεrε thεn washεd four timεs with 200 μl/ wεll of PBS containing 0.1% Twεεn 20 (Fischer Chemicals, Fairlawn, New Jersey). To initiate the assay, 100 μl pεr wεll of serial doubling dilutions (1 :40 to 1 :1280) of patient sera diluted in blocking buffer werε addεd, and platεs hεld at room temperaturε for 1 h. Wεlls were washed four times with PBS-0.1% Tweεn-20, aftεr which 50 μl/ wεll of biotinylatεd MAb OV569 (prεpared as described in Example 2), 200 ng/ml in conjugate diluεnt (Gεnetic Systems) was added and allowed to incubate for 1 h at room temperature. Wells wεrε again washεd four timεs with PBS-Twεεn. Nεxt, 50 μl/ wεll HRP-strεptavidin (PharMingen, San Diego, CA) diluted 1 :1000 in conjugatε diluent was added and the plates held at room tempεrature for 45 min. Wells wεre washed four times with PBS-Twεεn and dεvεlopεd by adding buffered 3,3',5,5'-tetramεthylbεnzidine (TMB, Genεtic Systems) plus 1% (v/v) of thε HRP-strεptavidin conjugatε for 15 min. Thε reaction was stopped by addition of 2M H2SO4, and the plates wεrε rεad at 460 nm using a Spεctracount microplatε spεctrophotomεtεr (Packard Instrument Co., Meriden, CT). Positivε and negative control serum samples from two patients were included in all assays. The negative control serum camε from a hεalthy voluntεεr and gavε no dεtεctable signal when presεnt at a 1 :40 dilution. Thε positivε control ("c+") camε from a patiεnt diagnosed with ovarian carcinoma and provided a rεadily dεtεctable signal under the described assay conditions when presεnt at a 1 : 1280 dilution or lεss. Figure 3 illustrates reprεsεntativε results using thε sandwich ELISA immunoassay for the detection of MRA. Soluble molecules recognized by the two MAbs, 4H3 and OV569, were readily detected in sera from two ovarian carcinoma patients (#2896 and #2897) and in serum from a lung carcinoma patient (#3L), and could bε rεlativεly quantifiεd as titratable reactivities. The positivε control sεrum (c+) also εxhibitεd reactivity with thε MRA-binding MAbs, which decreased as the dilution factor increasεd. Sεra from additional patients diagnosed as having ovarian carcinoma, and also from patients with various other tumors were assayed using the sandwich ELISA immunoassay for thε detection of MRA. Additional patient sera having non-neoplastic disεases and sera from healthy patients were also compared using this assay. A summary of the results is graphically depicted in Figure 4. At a sεrum dilution of 1 :160, 23 of 30 sera from patients who had ovarian carcinoma in stage 3 or stage 4 exhibited circulating MRA levels that werε significantly εlεvated, compared to 0 of 68 sera from healthy volunteers. Using the same criteria, 25 of 75 sera from patients with tumors other than ovarian carcinoma exhibitεd detectable reactivity in the MRA sandwich ELISA, with the highest frequency of positive sεra (66%) bεing obsεrvεd in patients with lung carcinoma (Table 4). Sera from three patients with non-neoplastic diseasεs were negative in the MRA sandwich ELISA. Table 4 EXAMPLE 9 MOLECULAR CLONING AND SEQUENCING OF NUCLEIC ACID SEQUENCE ENCODING A MESOTHELIN RELATED ANTIGEN (MRA-!) Bεcausε monoclonal antibody OV569 recognized the membrane bound (D2hlg) but not the soluble (Dlhlg) domain of MPF, but also could be used to affinity isolate a soluble polypeptidε from plεural εffusion fluid (Example 7), the identity of a novel mesothεlin rεlatεd antigεn (MRA) was dεtεrminεd. This εxamplε describes the cloning and sequεncing of a cDNA molεculε εncoding an MRA, MRA-1, from a human prostatic carcinoma cεll linε, using sequence information from the antigen defined by monoclonal antibody OV569. Plasmid isolation, production of competεnt cεlls, transformation and Ml 3 manipulations were carried out according to published procedures (Sambrook et al., Molecular Cloning, a Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989). Total RNA was isolatεd from a human prostatic carcinoma cεll line (HE1P generated as described above, seε. e.g., Hεllstrom εt al., 1990 Cancer Res. 50:2183) using an RNAgεnts™ kit (Promεga, Inc., Madison, WI) and polyA+ RNA was purified from the total RNA with an mRNA Separator™ (Cloncech, Inc., Palo Alto, CA), both according to the manufacturer's recommendations. A Marathon™ cDNA amplification kit (Clontech, Palo Alto, CA) was used to revεrsε transcribe the RNA and make double-strandεd cDNA, which was ligatεd to an adaptor providεd with the Marathon™ kit and amplified using the EXPAND™ high fidelity PCR systεm (Rochε Molecular Biochemicals, Indianapolis, IN) according to the supplier's instructions. For this amplification, the first oligonuclεotidε primεr was spεcific for thε Marathon™ adaptor sεquεncε and thε sεcond primεr corrεspondεd to thε coding region for the N-terminal sεquεncε of thε OV569 antigεn [SEQ ID NO:5] and had thε following sεquence dεrivεd from thε MPF cDNA sεquεncε (Kojima εt al., 1995): GSP1: 5'-GGA AGT GGA GAA GAC AGC CTG TCC TTC-3' SEQ ID NO:6 Thε PCR product was ligated into pGEM-T vector (Promega, Madison, WI) and the ligation mixture was transformεd into DH5α competent cells (Lifε Tεchnologiεs, Gathεrsburg, MD), both according to thε manufacturers' instructions. Plasmids wεre isolatεd from individual coloniεs of transformed DH5α cells using a QIAprεp™ spin minipr p kit (Qiagεn, Valεncia, CA) and sεquεncεd using a BigDyε™ tεrminator cycle sequencing kit (PE Applied Biosystεms, Fostεr City, CA). Tεn clones werε isolatεd, including eight that possessεd a nuclεic acid sεquεnce identical to thε MPF cDNA sequεncε (Kojima et al., 1995), one that had a sεquence identical to mesothelin (Chang εt al., 1996), and one that upon sequencing revεalεd a nucleic acid sequence (Figure 5A-B and SEQ ID NO:3) related to MPF and mesothεlin sεquεnces but also containing an 82 bp insert at a nucleotidε position corresponding to nucleotide 1874 of the MPF coding sequεncε (Kojima et al., 1995), which induced a frame shift of 212 bp. Sequence analysis indicated that this frame shift r sultεd in a coding sequεncε for a new polypeptide refεrrεd to hεrεin as mεsothεlin related antigen- 1 (MRA-1) which, unlike both MPF and mesotholin, contains a hydrophilic C-tεrminal tail and is thεrεfore likely to be solublo in aquεous physiological εnvironmεnts. The C-terminal 98 amino acids of MRA-1 werε distinct from any amino acid sεquεnces found in the C- terminal regions of either MPF or mεsothεlin. Surprisingly, this novεl protεin-encoding nucleic acid sequεncε (SEQ ID NO:3) included no stop codon, but instead continued directly to thε polyadenylation site for the polyA tail.. This lack of a stop codon may be related to the origin of this sequence in neoplastic cells. The MRA-1 sequence was more closely rεlatεd to MPF than to mεsothεlin in that it lacked a 24 bp insertion that was presεnt in thε mεsothelin DNA sequεnce but not the MPF sequεnce, and in that it was identical to MPF at two nuclεotidε positions whεre single base differences were found betweεn MPF and mεsothelin. Thε MRA-1 polypeptide sequεncε (SEQ ID NO:l) is shown in Figure 5A-B. EXAMPLE 10 INVERSE PCR CLONING OF A MESOTHELIN RELATED ANTIGEN (MRA-2) This εxamplε dεscribεs thε cloning and sequencing of a cDNA molεculε εncoding an MRA variant, MRA-2, from a human colon carcinoma cεll linε. MRA-2 diffεrs from MRA-1 by thε prεsεncε of thrεε additional amino acids (FRR) at thε N- tεrminus (SEQ ID NO:2) and, by virtuε of the manner in which it was identified as described below, lacks the completε C-terminal region of MRA-1, instead terminating at the amino acid position corresponding to residue 325 of MRA-1. Plasmid isolation, production of competεnt cεlls, transformation and rεlatεd manipulations worε carried out according to published procedurεs (Sambrook ot al., Molecular Cloning, a Laboratory Manual, Cold Spring Harbor Laboratory Prεss, Cold Spring Harbor, NY, 1989). Inverse PCR (Zeiner et al., 1994 Biotechniques 17:1051) was used to clone a nucleic acid molecule encoding a MRA from 3719 colon carcinoma, a cell line genεratεd as dεscribεd abovε (sεε, e.g., Hεllstrom εt al., 1990 Cancer Res. 50:2183). Briεfly, total RNA (5 mg) was εxtractεd from bulk cultures of 3719 cεlls using Trizol™ reagεnt (GIBCO-BRL, Grand Island, NY) and polyA + mRNA was purifiεd using PolyATtract™ oligo-dT-coatεd magnεtic beads (Promega, Inc., Madison, WI) as instructed by the supplier. First strand cDNA synthesis was initiatεd by rεvεrsε transcription using an oligonuclεotidε primεr spεcific for a portion comprising nucleotides at positions 56-80 of the 82 bp insert identified in the MRA nucleotidε sεquεncε in Examplε 9: op56-80: 5'-GCG CTC TGA GTC ACC CCT CTC TCTG-3' SEQ ID NO:7 The cDNA second strand was generated using the Marathon™ adaptor primεr as dεscribεd in Examplε 9 (Clontech, Palo Alto, CA). The cDNA was permitted to circularize by rεligating to itsεlf for 24 hours at 15°C using thε Marathon™ kit protocol (Clontech) in a reaction volume of 200 μl. From this ligation mixture, an aliquot of 5 μl was used as tεmplatε in a PCR rεaction with the following primers: mpf f735: AGA AAC TTC TGG GAC CCC AC SEQ ID NO:8 mpf r290: GGG ACG TCA CAT TCC ACT TG SEQ ID NO:9 and thε following nested primers: GSP-25'— GAA GGA CAG GCT GTC TTC TCC ACT TCC C— 3' SEQ ID NO: 10 r80-54 5'— CAG AGA GAG GGG TGA CTC AGA GC— 3' SEQ ID NO:l l The PCR product was sequεncεd using a BigDyε™ tεrminator cyclε sεquεncing kit (PE Appliεd Biosystεms, Fostεr City, CA). Thε rεsulting DNA sεquεncε (SEQ ID NO:4, Figure 6A-B) was idεntical to nuclεotidεs at positions 1-978 of thε MRA-1 DNA sequence (SEQ ID NO:3) described in Example 9, except for the presence of nine additional bp situated 5' to the nuclεotidε at position numbεr 1 of SEQ ID NO:3. These nine nucleotidεs εncodε thε N-tεrminal tripεptidε FRR which comprise amino acids 1-3 of SEQ ID NO:2, refεrrεd to hεrein as MRA-2. Thesε thrεε nuclεotidε codons arε idεntical to thε thrεε codons found in thε coding sεquεncεs upstream of thε cleavage site bεtwεεn mεsothεlin and its precursor (Chang et al., 1996) and betwεεn MPF and its precursor (Kojima εt al., 1995). Accordingly, thε dεducεd soluble mesothelin related (SMR) antigen polypoptidε sεquεncε (SEQ ID NO: 13) is shown in Figure 7Λ-B, as is a nucleic acid sequεncε (SEQ ID NO: 14) encoding such SMR polypεptidε. SMR comprises the FRR N- tεrminal tripεptidε idεntifiεd in MRA-2 plus thε εntire polypeptide sequεncε (SEQ ID NO:l) of MRA-1 (SEQ ID NO:l) as dεscribεd abovε, thε C-tεrminus of which is εncodεd by a nuclεotidε sεquεncε that extεnds into a polyadεnylation sitε but lacks a stop codon. EXAMPLE 11 EXPRESSION OF MRA IN AN OVARIAN CARCINOMA CELL LINE In this example, detεction of MRA-encoding nucleic acid sεquεncεs in a cDNA library derived from a human ovarian carcinoma cell line is described. RNA is extracted from cultured 3997 ovarian carcinoma cells (genεratεd as dεscribεd abovo, sεε. e.g., Hεllstrom εt al., 1990 Cancer Res. 50:2183) and usεd to produce a cDNA library by revεrsε transcription using thε Marathon™ cDNA amplification kit (Clontεch, Palo Alto, CA) according to thε manufacturer's instructions. Thε library is clonεd in pCDNA3-Zεo (InVitrogen, Inc., San Diego, CA) and scrεεned by oligonucleotide probe hybridization to northern blots. The following oligonucleotide is synthεsizεd corresponding to a region of the MRA 82 nucleotidε insert described in Example 9: 135: 5' -CCA GGG CTG GGG GC A GAG CTG GGG GGG CGT GGA GGT G-3 ' SEQ ID NO: 12 End-labeling of 135 with [ 32 P] is performεd using the Primer Extension System (Promεga, Madison, WI) according to thε supplier's instructions, and the labeled oligonucleotidε is usεd to probε a northεrn blot containing εlεctrophorεtically separated RNA samples from various human tissues (MTN™ Mutitple Tissuε Northεrn Blot, Cat. No. 7760-1, Clontεch, Palo Alto, CA), according to wεll known procedures. Individual clones identified by the screεning assay arε selected, amplified and sequεncεd as described in Examplε 10, to dεtεrminε an MRA sεquεncε from thε ovarian carcinoma cell line. From the foregoing, it will bo apprεciatεd that, although specific embodimεnts of thε invention have been described herein for purposes of illustration, various modifications may be made without dεviating from thε spirit and scope of the invention. Accordingly, the invention is not limitεd except as by the appendεd claims.

Claims: CLAIMS What is claimed is: 1. A method of scrεεning for thε prεsεncε of a malignant condition in a subjεct comprising: contacting a biological sample from a subject with at least one antibody specific for a mesothεlin rεlatεd antigεn polypεptidε to dεtermine the presence in said biological sample of a molεculε naturally occurring in solublε form in said sample and having an antigenic detεrminant that is reactivε with said at least one antibody, under conditions and for a time sufficient to detect binding of said antibody to said antigenic determinant, and therefrom detecting the presence of a malignant condition. 2. The method of claim 1 wherein the biological samplε is sεlεctεd from thε group consisting of blood, serum, serosal fluid, plasma, lymph, urinε, cεrεbrospinal fluid, saliva, a mucosal secretion, a vaginal secretion, ascitεs fluid, plεural fluid, pεricardial fluid, peritoneal fluid, abdominal fluid, culture medium, conditioned culture medium and lavagε fluid. 3. Thε mεthod of claim 1 whεrεin thε biological sample is serum. 4. Thε mεthod of claim 1 whεrεin the biological sample is plasma. 5. The method of claim 1 wherein thε biological samplε is ascites fluid. 6. Thε mεthod of claim 1 whεrεin thε biological samplε is a vaginal sεcrεtion. 7. Thε mεthod of claim 1 whεrεin thε biological sample is pleural fluid. 8. The method of claim 1 whεrεin thε mεsothεlin rεlatεd antigen comprises a polypeptidε having the sequence set forth in SEQ ID NO:l, or a fragmεnt or dεrivativε thεrεof. 9. Thε method of claim 8 wherein the mεsothεlin relatεd antigεn polypεptidε is a splicε variant. 10. Thε mεthod of claim 1 whεrein the mesotholin relatεd antigεn comprises a polypeptide having the sequεncε set forth in SEQ ID NO:2, or a fragmεnt or dεrivativε thεrεof. 1 1. Tho mεthod of claim 10 whεrεin thε mεsothεlin rεlatεd antigεn polypεptidε is a splicε variant. 12. The method of claim 1 wherein thε mεsothεlin rεlatεd antigεn polypεptidε is a mεsothelin relatεd antigen variant or a fragment or derivative thereof. 13. The mεthod of claim 1 whεrεin thε antibody comprises a polyclonal antibody. 14. The method of claim 1 whεrεin thε antibody comprises an affinity purified antibody. 15. The method of claim 1 whεrεin thε antibody comprises a monoclonal antibody. 16. The mεthod of claim 1 wherein the antibody comprises a recombinant antibody. 17. Thε mεthod of claim 1 whεrεin thε antibody comprises a chimeric antibody. 18. The method of claim 1 wherein the antibody comprises a humanized antibody. 19. The mεthod of claim 1 wherein the antibody comprises a single chain antibody. 20. Thε method of claim 1 wherein dεtεction of binding of the antibody to an antigenic determinant comprises detεction of a radionuclido. 21. Thε method of claim 1 wherein detεction of binding of thε antibody to an antigenic detεrminant comprises detection of a fluorophore. 22. Thε method of claim 1 wherein detεction of binding of the antibody to an antigenic detεrminant comprises detεction of a binding εvεnt bεtwεen an avidin molecule and a biotin molecule. 23. The method of claim 1 wherein detεction of binding of thε antibody to an antigεnic dεtεrminant comprises detεction of a binding εvεnt bεtween a streptavidin moloculε and a biotin molεculε. 24. Thε method of claim 1 wherein detεction of binding of thε antibody to an antigεnic determinant comprises spectrophotometric detεction of a product of an εnzymε rεaction. 25. Thε mεthod of claim 1 whεrein said at least one antibody is detεctably labεled. 26. The method of claim 1 wherein said at least one antibody is not dεtεctably labeled and wherein detection of binding of the antibody to an antigenic detεrminant is indirect. 27. The method of claim 1 whεrεin thε malignant condition is sεlεcted from the group consisting of adεnocarcinoma, mεsothεlioma, ovarian carcinoma, pancreatic carcinoma and non-small cεll lung carcinoma. 28. A method of screεning for the presence of a malignant condition in a subject comprising: contacting a biological samplε from a subject with at least onε antibody to dεtεrminε the presence in said biological sample of a molecule naturally occurring in soluble form in said sample and having an antigenic detεrminant that is reactive with said at least one antibody, the antigen combining site of which compεtitivεly inhibits thε immunospecific binding of a monoclonal antibody selεctεd from the group consisting of OV569, MAb K-l, 4H3, 3G3 and 1A6, under conditions and for a time sufficient to detεct binding of said antibody to said antigεnic dεtεrminant, and thεrεfrom dεtεcting thε presence of a malignant condition. 29. A method of screεning for tho prεsεncε of a malignant condition in a subjεct comprising: contacting a biological samplε from a subjεct with at least one antibody to determine the presence in said biological sample of a moleculε naturally occurring in solublε form in said samplε and having an antigεnic determinant that is reactive with said antibody, the antigen combining site of which competitively inhibits the immunospecific binding of monoclonal antibody OV569, under conditions and for a timε sufficient to detεct binding of said antibody to said antigεnic dεtεrminant, and thεrεfrom dεtεcting thε presence of a malignant condition. 30. A method of screening for the presεncε of a malignant condition in a subjεct comprising: contacting a biological sample from a subject with at lεast onε antibody spεcific for a human mεsothelin relatεd antigεn polypεptidε to determine the presence in said biological sample of a molεcule naturally occurring in soluble form in said sample and having an antigenic determinant that is reactivε with said antibody, under conditions and for a time sufficient to detεct binding of said at least onε antibody to said antigεnic dεtεrminant, whεrεin said at lεast onε antibody immunospεcifically binds to mεsothεlin rεlatεd antigεn, and thεrεfrom detecting the presεnce of a malignant condition. 31. The method of claim 30 wherein thε mεsothelin relatεd antigεn is also immunospecifically reactivε with monoclonal antibody MAb K-l . 32. A mεthod of scrεεning for thε prεsence of a malignant condition in a subjεct comprising: contacting a biological samplε from a subjεct with at least one antibody specific for a human mesothεlin rεlatεd antigεn polypεptidε to determine the prεsence in said biological sample of a molεculε naturally occurring in solublε form in said samplε and having an antigenic detεrminant that is reactivε with said at lεast onε antibody, thε antigεn combining sitε of which compεtitivεly inhibits thε immunospεcific binding of a monoclonal antibody sεlεcted from the group consisting of OV569, MAb K-l, 4H3, 3G3 and 1A6, under conditions and for a time sufficient to detεct binding of said antibody to said antigεnic dεtεrminant, whεrεin said at lεast onε antibody immunospεcificaily binds to mεsothεlin rεlatεd antigεn, and therefrom detεcting thε prεsεncε of a malignant condition. 33. Thε mεthod of claim 32 whεrein thε mεsothεlin rεlated antigen is also immunospεcifically rεactivε with monoclonal antibody MAb K-l . 34. A mεthod of scrεεning for the presence of a malignant condition in a subject comprising: contacting a biological samplε from a subjεct with at lεast one immobilized first antibody specific for a mesothelin relatεd antigen polypeptide to determine the prεsence in said biological sample of a molecule naturally occurring in soluble form in said samplε, undεr conditions and for a timε sufficient to specifically bind said at lεast onε immobilizεd first antibody to said mεsothεlin rεlated antigen polypeptide and thereby form an immune complex; removing constituents of the sample that do not spεcifically bind to said at least one immobilized first antibody; and contacting said immune complex with at least one second antibody specific for a mesothelin related antigen polypeptide, wherein the antigen combining site of said at least one second antibody does not competitively inhibit the antigen combining site of said at least one immobilizεd first antibody, undεr conditions and for a timε sufficient to detect specific binding of said at lεast one second antibody to said mesothelin relatεd antigεn polypεptidε, and therefrom detecting the presence of a malignant condition. 35. A method of screening for the presencε of a malignant condition in a subjεct comprising: contacting a biological sample from a subject with at least one immobilized first antibody specific for a mesothelin related antigen polypeptide to determine the presence in said biological sample of a moleculε naturally occurring in solublε form in said sample, wherein the antigen combining site of said at least onε first antibody competitively inhibits the immunospecific binding of monoclonal antibody OV569 under conditions and for a time sufficient to specifically bind said at least one immobilized first antibody to said mesothεlin related antigen polypeptide and thereby form an immune complex; removing constituents of the sample that do not specifically bind to said at least one immobilized first antibody; and contacting said immune complex with at least one second antibody specific for a mesothelin related antigen polypeptide, wherein the antigen combining site of said at least one second antibody does not competitively inhibit the immunospecific binding of monoclonal antibody OV569 , under conditions and for a time sufficient to detect specific binding of said at least one second antibody to said mesothelin related antigen polypeptide, and therεfrom dεtεcting the presence of a malignant condition. 36. A method of screεning for the presence of a malignant condition in a subject comprising: contacting a biological sample from a subject with at least onε immobilizεd first antibody specific for a mesothεlin rεlatεd antigen polypeptidε to detεrmine the presεncε in said biological sample of a molecule naturally occurring in soluble form in said sample, wherein the antigen combining site of said at least one first antibody competitively inhibits the immunospecific binding of monoclonal antibody MAb K-l under conditions and for a time sufficient to specifically bind said at least one immobilized first antibody to said mesothelin rεlatεd antigen polypeptide and thεrεby form an immunε complex; removing constituεnts of thε samplε that do not specifically bind to said at least one immobilized first antibody; and contacting said immune complex with at least one second antibody spεcific for a mesothelin related antigen polypeptide, wherein the antigen combining sitε of said at least one second antibody does not competitively inhibit the immunospecific binding of monoclonal antibody MAb K-l. under conditions and for a time sufficient to detect specific binding of said at least one second antibody to said mesothelin related antigen polypeptide, and therefrom detecting the presence of a malignant condition. 37. The method of any one of claims 1-36 further comprising determining the presence in said sample of at least one soluble marker of a malignant condition selected from the group consisting of carcinoembryonic antigen, CA125, sialyl TN, squamous cell carcinoma antigen, tissue polypeptidε antigen, and placental alkaline phosphatasε. 38. A method of screening for the presence of a malignant condition in a subject comprising: contacting each of (i) a first biological sample from a first subject suspected of having a malignant condition, and (ii) a second biological sample from a second subject known to be free of a malignant condition, with at least one antibody specific for a mesothelin related antigen polypeptidε to determine the presence in each of said first and second biological samples of a molεcule naturally occurring in soluble form in said samples and having an antigenic determinant that is reactive with said at least one antibody, undεr conditions and for a time sufficient to dεtεct binding of said antibody to said antigεnic determinant, and comparing a level of detectable binding of said antibody to said antigenic detεrminant in thε first biological samplε to a lεvεl of dεtεctablε binding of said antibody to said antigεnic dεtεrminant in thε sεcond biological sample, and therefrom dεtecting the presεncε of a malignant condition. 39. A method of screening for the presence of a malignant condition in a subject comprising: detecting in a biological sample from the subject thε presence of an antibody that immunospecifically binds to a mesothelin related antigen polypεptide. 40. The method of claim 39 wherein the mesothεlin related antigen polypeptide comprises a polypeptide having an amino acid sequεncε selected from the group consisting of SEQ ID NO:l, SEQ ID NO:2 and SEQ ID NO: 13. 41. An antibody specific for a mesothelin related antigen polypeptide, comprising: a monoclonal immunoglobulin variable region that does not competitively inhibit the immunospecific binding of monoclonal antibody Mab K-l to a mesothelin polypeptide and that specifically binds to a mesothelin related antigen polypeptide, wherein said mesothelin related antigen polypeptide comprises a polypeptide having an amino acid sequence selected from the group consisting of SEQ ID NO:l, SEQ ID NO:2 and SEQ ID NO:13. 42. The antibody of claim 41 which is a fusion protein. 43. The antibody of claim 41 which is a single chain antibody. 44. The antibody of claim 41 wherein the mesothelin related antigen polypeptide is glycosylated. 45. The antibody of claim 41 wherein the mesothεlin rεlated antigen polypeptidε has an apparent molεcular mass of approximately 42 to 45 kilodaltons. 46. The antibody of claim 41 selected from the group consisting of monoclonal antibodies OV569, 4H3, 3G3 and 1 A6. 47. A method of screεning for thε presεnce of a malignant condition in a subject comprising: contacting a biological sample from a subject with a detεctably labεlεd mεsothεlin rεlatεd antigεn polypeptide, under conditions and for a timε sufficient to detect binding to said mesothelin relatεd antigen polypeptide of an antibody naturally occurring in soluble form in said sample, and therefrom detecting the presence of a malignant condition. 48. An isolated nucleic acid molecule selected from the group consisting of: (a) a nucleic acid molecule encoding a mesothelin related antigen polypeptide, the polypeptidε comprising an amino acid sequence selected from the group consisting of the amino acid sequence set forth in SEQ ID NO:l, thε amino acid sequence set forth in SEQ ID NO:2 and the amino acid sequence set forth in SEQ ID NO: 13; and (b) a nucleic acid moleculε capable of hybridizing to a nucleic acid molecule of (a) under moderately stringent conditions and encoding a mesothelin related antigen polypeptide, wherein the isolated nucleic acid molecule is not a nucleic acid molecule consisting of the nucleotide sequence selected from the group consisting of the nucleotide sequence set forth in SEQ ID NO: 15, the nucleotide sequence set forth in SEQ ID NO: 16, the nucleotidε sequence set forth in SEQ ID NO: 17 and the nucleotide sequence set forth in SEQ ID NO:18. 49. An antisense oligonucleotidε comprising at least 15 consecutive nucleotides complementary to the nuclεic acid molecule of claim 48. 50. A fusion protein comprising a polypeptidε sεquεnce fused to a mesothεlin rεlatεd antigεn polypεptidε. 51. Thε fusion protεin of claim 50 whεrein thε polypεptidε is an εnzyme or a variant or fragment thereof. 52. Thε fusion protein of claim 51 wherein the polypeptidε sequence fused to a mesothelin related antigen polypeptidε is clεavable by a protease. 53. The fusion protein of claim 50 wherein the polypeptide sequence is an affinity tag polypeptidε having affinity for a ligand. 54. A recombinant εxpression construct comprising at least one promoter operably linked to a nucleic acid of claim 48. 55. The expression construct of claim 54 wherein the promoter is a regulated promoter. 56. An expression construct according to claim 54 wherein the mesothelin related antigen polypeptide is expressed as a fusion protein with a polypeptide product of a sεcond nucleic acid sequence. 57. The expression construct of claim 56 wherein the polypeptide product of said second nucleic acid sequence is an enzyme. 58. A recombinant expression construct according to claim 54 wherein the expression construct is a recombinant viral expression construct. 59. A host cell comprising a recombinant expression construct according to any one of claims 54-58. 60. A host cell according to claim 59 wherein the host cell is a prokaryotic cell. 61. A host cell according to claim 59 wherein the host cell is a εukaryotic cell. 62. A method of producing a recombinant mesothelin related antigen polypeptide, comprising: culturing a host cell comprising a recombinant expression construct comprising at least onε promoter operably linked to a nucleic acid sequεncε of claim 48. 63. The method of claim 62 wherein thε promotεr is a rεgulatεd promotεr. 64. A method of producing a recombinant mesothelin related antigen polypeptide, comprising: culturing a host cell infected with the rεcombinant viral εxpression construct of claim 58. 65. A method for detecting mesothelin related antigen expression in a sample, comprising: (a) contacting an antisense oligonucleotidε according to claim 49 with a samplε comprising a nucleic acid sequence encoding a mesothelin related antigen polypeptide having the amino acid sequence set forth in SEQ ID NO: 13 or a fragment or variant thereof; and (b) detecting in the sample an amount of mesothelin related antigen polypeptide-encoding nucleic acid that hybridizes to the antisense oligonucleotide. and therefrom detecting mesothelin related antigen expression in the sample. 66. A method according to claim 65, wherein the amount of mesothelin related antigen polypeptide-encoding nucleic acid that hybridizes to the antisense oligonucleotide is determined using polymerase chain reaction. 67. A method according to claim 65. wherεin thε amount of mesothelin related antigen polypeptide-encoding nucleic acid that hybridizes to the antisεnse oligonucleotide is determined using a hybridization assay. 68. A method according to claim 65, wherein the sample comprises an RNA or cDNA preparation.

Inventors: HELLSTROM INGEGERD, HELLSTROM KARL ERIK, SCHOLLER NATHALIE B, HELLSTROM, INGEGERD, HELLSTROM, KARL, ERIK, SCHOLLER, NATHALIE, B.
Applicants: HELLSTROM INGEGERD, HELLSTROM KARL ERIK, PACIFIC NORTHWEST RESEARCH INS, SCHOLLER NATHALIE B, HELLSTROM, INGEGERD, HELLSTROM, KARL, ERIK, PACIFIC NORTHWEST RESEARCH INSTITUTE, SCHOLLER, NATHALIE, B.
Application year: 2000
Main classification: G01N33
IPC codes: C07K16, G01N33