Abstract:
The invention relates to purinergic (P2X) receptors, to detection of protein in extra-cellular body fluids and to anti-bodies for the diagnosis or condition, especially cancer.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 12/677,795, filed Mar. 11, 2010, which is national stage of PCT/AU2008/001365, filed Sep. 12, 2008, (incorporated by reference in its entirety for all purposes), which claims priority to Australian patent application number 2007905017, filed Sep. 14, 2007. 
     FIELD OF THE INVENTION 
     The invention relates to purinergic (P2X) receptors, to detection of protein in extra-cellular body fluids and to antibodies for the diagnosis of a disease or condition, especially cancer. 
     BACKGROUND OF THE INVENTION 
     Purinergic (P2X) receptors are ATP-gated cation-selective channels. Each receptor is made up of three protein subunits or monomers. To date seven separate genes encoding P2X monomers have been identified: P2X1, P2X2, P2X3, P2X4, P2X5, P2X5, ( FIGS. 2 to 7  respectively, herein), P2X7 ( FIG. 1 ). 
     P2X7 receptors are of particular interest as the expression of these receptors is understood to be limited to cells having potential to undergo programmed cell death, such as thymocytes, dendritic cells, lymphocytes, macrophages and monocytes. Further, a P2X7 receptor containing one or more monomers having a cis isomerisation at Pro210 (according to  FIG. 1 ), and which is devoid of ATP binding function is found on cells that are understood to be unable to undergo programmed cell death, such as preneoplastic cells and neoplastic cells in the form of many carcinomas and blood cancers. 
     At least 9 splice variants of P2X7 monomers are known to exist ( FIGS. 8 to 15 ). These include variants having cytoplasmic N and C termini, 2 transmembrane spanning domains and an extra-cellular domain, and variants that have a cytoplasmic N terminus, transmembrane domain and a truncated extra-cellular domain of various lengths. 
     To date, P2X7 receptors have only been detected in the cytoplasm, the nucleus and anchored to the lipid bilayer of the cell surface membrane by one or more transmembrane spanning domains as discussed above. 
     SUMMARY OF THE INVENTION 
     In certain embodiments there is provided an isolated purinergic receptor, monomer or fragment thereof obtainable from an extra-cellular body fluid. 
     In another embodiment there is provided an immune complex formed from the binding of an anti purinergic receptor antibody or fragment thereof to a purinergic receptor, monomer or fragment thereof as described above. 
     In a further embodiment there is provided a complex formed from the binding of a purine to a purinergic receptor, monomer or fragment thereof as described above. 
     In still further embodiments there is provided an antibody or fragment thereof for binding to an epitope on an extra-cellular purinergic receptor, monomer or fragment thereof, the epitope not being found on a purinergic receptor, monomer or fragment thereof that is expressed on a cell surface membrane. 
     In certain embodiments there is provided a method for determining whether an extra-cellular body fluid contains a purinergic receptor, monomer or fragment thereof including:
         contacting an extra-cellular body fluid with an anti purinergic receptor antibody or fragment thereof in conditions for forming an immune complex, and   detecting whether an immune complex has been formed,
 
wherein the detection of an immune complex indicates that the fluid contains a purinergic receptor, monomer or fragment thereof.
       

     In other embodiments there is provided a method for determining whether an individual has cancer, or is predisposed to cancer including the steps of:
         providing a sample of extra-cellular body fluid obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   contacting the sample with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex between a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid in the sample and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, thereby determining whether the individual has a cancer or predisposition thereto.       

     In yet further embodiments there is provided a method for determining whether an individual has cancer, or is predisposed to cancer including the steps of:
         providing a sample in the form of a tissue biopsy including an extra-cellular body fluid, the sample being obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   contacting the sample with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex between a purinergic (P2X) receptor, monomer or fragment thereof, in or derived from, the extra-cellular body fluid in the sample and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, to determine whether the individual has or is predisposed to a cancer.       

     In yet further embodiments there is provided a method for determining whether an individual has cancer or is predisposed to cancer including the steps of:
         administering an anti purinergic (P2X) receptor antibody or fragment thereof to an individual in whom the presence or absence of cancer or predisposition thereto is to be determined in conditions for forming an immune complex between the antibody or fragment thereof and a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid of the individual; and   detecting whether the immune complex has been formed to determine whether the individual has a cancer or predisposition thereto.       

     In yet further embodiments there is provided a method for determining whether an individual has cancer or is predisposed to cancer including the steps of:
         providing a sample of extra-cellular body fluid obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   applying the sample to a solid phase in conditions for fixing a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid of the individual to the solid phase;   contacting the solid phase with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex between a purinergic (P2X) receptor, monomer or fragment thereof fixed to the solid phase and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, thereby determining whether the individual has cancer or predisposition thereto.       

     In yet further embodiments there is provided a kit or composition for determining whether an individual has cancer, or predisposed to cancer including:
         an anti purinergic (P2X) receptor antibody or fragment thereof, and/or   a purinergic receptor, monomer or fragment thereof as described above; and optionally   a further antibody for binding to the antibody or fragment thereof or the purinergic receptor, monomer or fragment thereof;   written instructions for use of the kit in a method described above.       

     Examples of purinergic receptors are P2X receptors, especially those comprising a P2X1, P2X2, P2X3, P2X4, P2X5, P2X6, P2X7 monomer. In certain embodiments, the purinergic receptor is a P2X7 receptor, examples of which are discussed further below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 : Human P2X7 (SEQ ID NO:8). 
         FIG. 2 : Human P2X1 (SEQ ID NO:9). 
         FIG. 3 : Human P2X2 (SEQ ID NO:10). 
         FIG. 4 : Human P2X3 (SEQ ID NO:11). 
         FIG. 5 : Human P2X4 (SEQ ID NO:12). 
         FIG. 6 : Human P2X5 (SEQ ID NO:13). 
         FIG. 7 : Human P2X6 (SEQ ID NO:14). 
         FIG. 8 : Human isoform H (SEQ ID NO:15). 
         FIG. 9 : Human isoform D (SEQ ID NO:16). 
         FIG. 10 : Human isoform B receptor (SEQ ID NO:17). 
         FIG. 11 : Human isoform F receptor (SEQ ID NO:18). 
         FIG. 12 : Human isoform E receptor (SEQ ID NO:19). 
         FIG. 13 : Human isoform G receptor (SEQ ID NO:20). 
         FIG. 14 : Human isoform J receptor (SEQ ID NO:21). 
         FIG. 15 : Human isoform C receptor (SEQ ID NO:22). 
         FIG. 16 : Detection of (P2X) purinergic receptors in extra-cellular body fluid by direct ELISA. 
         FIG. 17 : Detection of (P2X) purinergic receptors in extra-cellular body fluid by indirect ELISA. 
         FIG. 18 : Dot blot obtained with urine from ovarian and bladder cancer patients as well as controls. 
         FIG. 19A : Immunohistochemistry for non-functional P2X7 receptor in sentinel lymph nodes from prostate cancer. 
         FIG. 19B : Immunohistochemistry for non-functional P2X7 receptor in sentinel lymph nodes from breast cancer. 
         FIG. 19C : Immunohistochemistry for non-functional P2X7 receptor in lymph nodes. 
         FIG. 20 : Western Blot of faecal samples. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The inventors have found purinergic (P2X) receptors in extracellular body fluids of individuals having various forms of cancer. This is a surprising finding as all P2X7 receptors to date have been found to be anchored into the cell surface lipid bilayer by one or two transmembrane spanning domains. Hence the teaching in the art to date has been that purinergic (P2X) receptors are expressed predominantly on the cell membrane. 
     The finding that certain purinergic (P2X) receptors are found in the extra-cellular body fluids of individuals having various disease and conditions, or predisposed to same is significant because in certain embodiments individuals may be screened on the basis of an extra-cellular body fluid sample, which is generally much more simple to isolate than a tissue biopsy. The latter has been required to determine cell membrane expression of purinergic P2X receptors to date. 
     In certain embodiments there is provided an isolated purinergic (P2X) receptor, P2X monomer or fragment thereof obtainable from an extra-cellular body fluid. Typically the receptor is a P2X7 receptor, monomer or fragment thereof. 
     In certain embodiments, a P2X7 receptor includes all receptors including at least one P2X7 monomer sequence, whether or not the P2X7 receptor is functional in the sense of capable of binding to ATP and or forming a pore for ingress of cations into a cell leading to programmed cell death. An example of a P2X7 receptor that has impaired ATP binding function is a receptor having a cis isomerisation at proline 210 of the sequence shown in SEQ ID NO: 1. 
     The fluid may be selected from the group consisting of blood, plasma, serum, lymph, urine, semen, saliva, sputum, ascites, faeces, uterine and vaginal secretions, bile, amniotic fluid, cerebrospinal fluid and organ and tissue flushings. The extra-cellular body fluid is typically cell-free although in some circumstances it may contain residual cells or fragments thereof. 
     The receptor, monomer or fragment thereof may include an amino acid sequence as shown in Table 1 below. 
     The receptor, monomer or fragment thereof may have an amino acid sequence consisting of part of any one of the sequences listed in Table 1. Typically a fragment is part of a monomer of at least about 10 amino acid residues length and no more than about 595 amino acids in length. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Name (SEQ ID NO:) 
                 Accession no 
                 Length (aa) 
               
               
                   
               
             
             
               
                   
                 Human P2X7 isoform H 
                 AAX82093 
                 505aa 
               
               
                   
                 (SEQ ID NO: 15) 
                   
                   
               
               
                   
                 Human P2X7 isoform D 
                 AAX82089 
                 425aa 
               
               
                   
                 (SEQ ID NO: 16) 
                   
                   
               
               
                   
                 Human P2X7 isoform B 
                 AAX82087 
                 364aa 
               
               
                   
                 (SEQ ID NO: 17) 
                   
                   
               
               
                   
                 Human P2X7 isoform F 
                 AAX82091 
                 306aa 
               
               
                   
                 (SEQ ID NO: 18) 
                   
                   
               
               
                   
                 Human P2X7 isoform J 
                 ABD59798 
                 258aa 
               
               
                   
                 (SEQ ID NO: 21) 
                   
                   
               
               
                   
                 Human P2X7 isoform E 
                 AAX82090 
                 275aa 
               
               
                   
                 split splice (SEQ ID NO: 19) 
                   
                   
               
               
                   
                 Human P2X7 isoform C 
                 Q4VK13 
                 128aa 
               
               
                   
                 (SEQ ID NO: 22) 
                   
                   
               
               
                   
                 Human P2X7 isoform G 
                 AAX82092 
                 274aa 
               
               
                   
                 (SEQ ID NO: 20) 
               
               
                   
               
             
          
         
       
     
     The receptor, monomer or fragment thereof may have a molecular weight in the range of from 20 to 80 kDa. 
     The receptor, monomer or fragment thereof may lack a transmembrane domain. 
     The receptor, monomer or fragment thereof may be linked to a fragment of a cell membrane. The cell membrane fragment may be the result of cell lysis or membrane blebbing. The cell membrane fragment may be provided in the form of a liposome-like or micelle-like structure with purinergic (P2X) receptors located thereon. 
     In certain embodiments the receptor is linked to a solid phase, such as an assay plate, bead or tissue culture vessel. These forms of the receptor are particularly useful for preparation of antibodies to the receptor described further below which may be used in the diagnostic and therapeutic applications described further below. 
     In another embodiment there is provided an immune complex formed from the binding of an anti purinergic (P2X) receptor antibody or fragment thereof to a purinergic (P2X) receptor, monomer or fragment thereof as described above. 
     Generally an immune complex otherwise known as an antigen-antibody complex is a product that is formed from the binding of an antibody via an antibody binding site to an epitope on a antigen against which the antibody was raised. The complex may or may not consist of more than one antibody. 
     Typically the receptor is a P2X7 receptor and the antibody is an anti P2X7 antibody or fragment thereof. 
     The immune complex is particularly important as detection of this in vitro or in vivo is indicative of presence of, or predisposition to a disease or condition including preneoplasia and neoplasia. These detection methods are described in more detail below. 
     As is generally understood in the art, neoplasia is literally new growth and usually refers to abnormal new growth or proliferation generally persisting in the absence of an original growth stimulus. Neoplasia may be benign or malignant. 
     Pre-neoplasia is generally a form of cellular growth or transformation preceding neoplasia. It may be characterised by hyperplasia and/or appearance of mitotic figures histologically without marked anaplasia or loss of cell differentiation. Pre-neoplastic tissue is sometimes found in regions adjacent to a tumour lesion. 
     The extra-cellular body fluid is typically cell-free although in some circumstances it may contain residual cells or fragments thereof. However, the immune complexes are predominantly formed from antibody binding to receptors, monomers or fragments thereof that are not located on a cell surface of an intact or whole cell, but rather to receptors, monomers or fragments thereof that are suspended or dissolved in the body fluid. 
     The antibody may be a whole antibody of any isoform. The antibody may be one obtained from monoclonal or polyclonal antisera. The antibody may be produced by hybridoma, or by recombinant expression. The antibody may be human or one formed by grafting CDRs onto a xenogeneic or allogeneic framework. 
     Where the antibody is an antibody fragment, the antibody fragment is selected from the group consisting of a dAb, Fab, Fd, Fv, F(ab′)2, scFv and CDR. 
     The antibody may bind to an extra-cellular domain of a purinergic (P2X) receptor. In one embodiment, the purinergic (P2X) receptor is a P2X7 receptor. As discussed herein, there are a number of isoforms of the P2X7 receptor. The antibody may bind to any one of the domains of these isoforms. A full length isoform includes an intra-cellular N-terminal domain, a transmembrane domain, an extra-cellular domain, a further transmembrane domain and a C-terminal intra-cellular domain. 
     Examples of epitopes located on an extra-cellular domain of a P2X7 receptor are set forth in Table 2. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Antibody name 
                 Epitope 
                 Epitope amino acid sequence 
                 SEQ ID NO: 
               
               
                   
               
             
             
               
                 E80-P2X7 
                 71-87 
                 VKEEIVENGVKKLVHSVGSGC 
                 SEQ ID NO: 1 
               
               
                   
                 inclusive + GSG 
                   
                   
               
               
                   
               
               
                 E200-P2X7 
                 200-216 
                 GHNYTTRNILPGLNITC 
                 SEQ ID NO: 2 
               
               
                   
                 inclusive 
                   
                   
               
               
                   
               
               
                 E200L 
                 197-216 
                 DFPGHNYTTRNILPGLNITC 
                 SEQ ID NO: 3 
               
               
                   
                 inclusive 
                   
                   
               
               
                   
               
               
                 E200T-P2X7 
                 197-207C 
                 DFPGHNYTTRNC 
                 SEQ ID NO: 4 
               
               
                   
                 inclusive 
                   
                   
               
               
                   
               
               
                 mP2X7 
                 200-216 
                 GHNYTTRNILPTMNGSC 
                 SEQ ID NO: 5 
               
               
                   
                 inclusive 
                   
                   
               
               
                   
               
               
                 E140P2X7 
                 137-152 
                 KGWMDPQSKGIQTGRC 
                 SEQ ID NO: 6 
               
               
                   
               
               
                 E300 
                 297-314 
                 KYYKENNVEKRTLIKVFC 
                 SEQ ID NO: 7 
               
               
                   
               
             
          
         
       
     
     The antibody or antibody fragment may be attached to a solid phase, such as a bead or a plate, or blotting paper, for example nitrocellulose paper, so that the immune complex is attached to a solid phase when formed. In this embodiment the antibody may function as a “capture” antibody. 
     Alternatively, a receptor or fragment thereof is attached to a solid phase. 
     The anti P2X7 receptor antibody may be labelled for detection of formation of the immune complex. 
     The immune complex may further include a further antibody or fragment thereof, for example for capture of the immune complex. The further antibody or fragment thereof may be bound to the anti P2X7 receptor antibody. Also the further antibody or fragment thereof may be bound to the receptor or fragment thereof. 
     The further antibody or fragment thereof may be bound to a solid phase such as a phase described above. 
     The further antibody or fragment thereof may be labelled for detection of formation of the immune complex. Examples of labels include fluorophores, dyes, isotopes etc. 
     As an alternative, a complex may be provided by contacting a purinergic (P2X) receptor, such as a P2X7 receptor to a compound capable of binding to the receptor to form a detectable complex. 
     Thus in a further embodiment them is provided a complex formed from the binding of a purine or purine related compound to a P2X7 receptor, monomer, or fragment thereof as described above. An example is ATP or ATP analogue such as benzoyl-benzoyl ATP. The ATP may be bound or conjugated to a label to facilitate detection of formation of the complex. 
     In still further embodiments there is provided an antibody or fragment thereof for binding to an epitope on an extra-cellular purinergic receptor, monomer or fragment thereof, the epitope not being found on a purinergic receptor, monomer or fragment thereof that is expressed on a cell surface membrane. 
     Typically the antibody binds to an epitope on an extra-cellular P2X7 receptor, monomer or fragment thereof. 
     An example of an antibody fragment includes a dAb, Fab, Fd, Fv, F(ab′)2, scFv and CDR. 
     In certain embodiments there is provided a method for determining whether an extra-cellular body fluid contains a purinergic receptor, monomer or fragment thereof including:
         contacting an extra-cellular body fluid with an anti purinergic receptor antibody or fragment thereof in conditions for forming an immune complex, and   detecting whether an immune complex has been formed,
 
wherein the detection of an immune complex indicates that the fluid contains a purinergic receptor, monomer or fragment thereof.
       

     Typically the antibody is an anti purinergic (P2X) receptor antibody such as an anti P2X7 receptor antibody or, fragment thereof. 
     In other embodiments there is provided a use of an anti P2X7-receptor antibody or fragment thereof in the manufacture of means for determining whether an extra-cellular body fluid contains a P2X7 receptor, monomer or fragment thereof. 
     In other embodiments there is provided a method for determining whether an extra-cellular body fluid contains an antibody against an extra-cellular purinergic receptor, monomer or fragment thereof including:
         contacting extra-cellular body fluid with a purinergic receptor, monomer or fragment thereof in conditions for forming an immune complex between the purinergic receptor, monomer or fragment thereof and an antibody against an extra-cellular purinergic receptor, and   detecting whether an immune complex has been formed;
 
wherein the detection of an immune complex indicates that the fluid contains an antibody against an extra-cellular purinergic receptor, monomer or fragment thereof.
       

     Typically the purinergic P2X receptor is a P2X7 receptor, monomer or fragment thereof. 
     In other embodiments there is provided a use of a P2X7 receptor, monomer or fragment thereof obtainable from an extra-cellular body fluid in the manufacture of means for determining whether an extra-cellular body fluid contains an anti-P2X7 receptor antibody. 
     The presence of a given protein, or level of expression of a given protein such as a purinergic (P2X) receptor or fragment thereof in an extra-cellular body fluid can be detected by any number of assays. Examples include immunoassays, chromatography and mass spectrometry. 
     Immunoassays, i.e. assays involving an element of the immune system are particularly preferred. These assays may generally be classified into one of:
     (i) assays in which purified antigen is used to detect an antibody In host serum. For example, purified antigen is bound to solid phase by adsorption or indirectly through another molecule and host serum or other body fluid is applied followed by another antibody for detecting presence or absence of host antibody;   (ii) assays in which purified antigen is used to detect immune cells, such as T and B lymphocytes. For example, peripheral white cells are purified from a host and cultured with purified antigen. The presence or absence of one or more factors indicating immunity are then detected. Other examples include assays that measure cell proliferation (lymphocyte proliferation or transformation assays) following exposure to purified antigen, and assays that measure cell death (including apoptosis) following exposure to purified antigen:   (iii) assays in which purified antibody specific for antigen is used to detect antigen in the host. For example, purified antibody is bound to solid phase, host extra-cellular body fluid is then applied followed by another antibody specific for the antigen to be detected. There are many examples of this approach including ELISA, RIA and the like;   (iv) assays in which a purified anti-idiotypic antibody is used to detect host antibody. For example, anti-idiotypic antibody is adsorbed to solid phase, host serum is added and anti-Fc antibody is added to bind to any host antibodies having been bound by the anti-idiotypic antibody.   (v) assays in which extra-cellular body fluid is separated from a protein component contained within it, the protein component is then fixed onto a solid phase and the probed with an antibody. Examples include dot blotting and Western blotting.   

     The immunoassays can be applied in vitro or in vivo. 
     A further assay format which does not require formation of an immune complex is one in which an assay output is the result of catalysis of a substrate and the output is observed for example by measuring a change in optical density. 
     The extra-cellular body fluid to be assessed in the above described embodiments of the invention may be selected from the group consisting of blood, plasma, serum, lymph, urine, semen, saliva, sputum, ascites, faeces, uterine and vaginal secretions, bile, amniotic fluid, cerebrospinal fluid, tear, and organ and tissue flushings. The extra-cellular body fluid is typically cell-free although in some circumstances it may contain residual cells or fragments thereof. 
     It will be appreciated that any disease where a purinergic (P2X) receptor is expressed in extra-cellular body fluid can be detected by these methods. The disease is typically a cancer such as carcinoma, sarcoma, lymphoma, leukaemia or other parenchymal cell growth abnormality. 
     Carcinomas that may be detected include, but not limited to, prostate, breast, skin, lung, cervix, uterus, stomach, esophagus, bladder, and colon cancers. As generally understood, a cancer or tumour is a neoplastic state and may be benign or malignant. In certain embodiments the cancer is metastatic disease. 
     Whilst any body fluid can be used to detect any of these diseases, in certain embodiments, some body fluids may be more appropriate than others to detect certain diseases, for example urine may be more appropriate to detect prostate cancer. Blood may be more appropriate for detecting blood cancers such as lymphoma. 
     In another embodiment there is provided a method for determining whether an individual has a cancer including the steps of:
         collecting a sample of extra-cellular body fluid from the individual and   contacting extra-Cellular body fluid with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex as described above, and   detecting whether an immune complex has been formed.       

     In a further embodiment there is provided use of anti purinergic (P2X) receptor antibody or fragment thereof for determining whether an individual has a cancer. 
     In yet further embodiments there is provided a method for determining whether an individual has cancer, or is predisposed to cancer including the steps of:
         providing a sample of extra-cellular body fluid obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   contacting the sample with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex (as described above) between a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid in the sample and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, thereby determining whether the individual has a cancer or predisposition thereto.       

     In one embodiment the method is implemented as a direct, indirect or sandwich ELISA, RIA or like assay involving the application of a liquid sample to an assay system. The sample may or may not be processed prior to contact with an antibody. 
     In yet further embodiments there is provided a method for determining whether an individual has cancer, or is predisposed to cancer including the steps of:
         providing a sample in the form of a tissue biopsy including an extra-cellular body fluid, the sample being obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   contacting the sample with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex between a purinergic (P2X) receptor, monomer or fragment thereof, in or derived from, the extra-cellular body fluid in the sample and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, to determine whether the individual has or is predisposed to a cancer.       

     In one embodiment the method is implemented in an immuno-histochemical format whereby a tissue section containing extra-cellular body fluid is applied to a slide leading to fixing of protein in the fluid to the slide and staining with an antibody. According to these embodiments, the method includes the step of assessing the sample, for example the tissue section, for the presence or absence of the immune complex in an extra-cellular space. Examples of these spaces include those in the form of a lumen of a gland, duct or vessel such as a blood vessel or lymphatic. Other extra-cellular spaces include those defined by an impermeable or semi-permeable layer of epithelial cells, one example of the former being the space defined by the blood brain barrier, an example of the latter being a convoluted tubule of a nephron. 
     In yet further embodiments there is provided a method for determining whether an individual has cancer or is predisposed to cancer including the steps of:
         administering an anti purinergic (P2X) receptor antibody or fragment thereof to an individual in whom the presence or absence of cancer or predisposition thereto is to be determined in conditions for forming an immune complex between the antibody or fragment thereof and a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid of the individual; and   detecting whether the immune complex has been formed to determine whether the individual has a cancer or predisposition thereto.       

     The method may include the step of obtaining a sample of extra-cellular body fluid from the individual and determining whether the sample contains the immune complex, to detect whether the immune complex has been formed. 
     Alternatively, the method may include the step of obtaining a sample in the form of a tissue biopsy including an extra-cellular body fluid from the individual and assessing the sample for the presence or absence of the immune complex in an extra-cellular space of the tissue biopsy, to detect whether the immune complex has been formed. 
     In yet further embodiments there is provided a method for determining whether an individual has cancer or is predisposed to cancer including the steps of:
         providing a sample of extra-cellular body fluid obtained from an individual in whom the presence or absence of cancer or predisposition thereto is to be determined;   applying the sample to a solid phase in conditions for fixing a purinergic (P2X) receptor, monomer or fragment thereof in the extra-cellular body fluid of the individual to the solid phase;   contacting the solid phase with an anti purinergic (P2X) receptor antibody or fragment thereof in conditions for forming an immune complex between a purinergic (P2X) receptor, monomer or fragment thereof fixed to the solid phase and the antibody or fragment thereof; and   detecting whether the immune complex has been formed, thereby determining whether the individual has cancer or predisposition thereto.       

     In yet further embodiments there is provided a kit or composition for determining whether an extra-cellular body fluid contains a purinergic (P2X) receptor, monomer of fragment thereof as described above, or an antibody against an extra-cellular P2X7 receptor or fragment thereof as described above including:
         an anti purinergic (P2X) receptor antibody or fragment thereof; and/or   a P2X7 receptor, monomer or fragment thereof obtainable from extra-cellular body fluid as described above; and optionally   a further antibody for binding to the antibody or fragment thereof or the P2X7 receptor, monomer or fragment thereof;   written instructions for use of the kit in a method described above.       

     EXAMPLES 
     The following protocols are provided as non-limiting examples of suitable methods for detecting P2X7R in a sample of extra-cellular fluid for the purpose of illustrating the invention. 
     Example 1 
     Detection of (P2X) purinergic receptors in extra-cellular body fluid by direct ELISA. Plasma samples (1 mL) obtained from 9 patients with Grade III ovarian adenocarcinoma were diluted 1:50 for direct ELISA in triplicate. Control plasma are the 3 samples at left ( FIG. 16 ). 
     Only low volumes of samples were required for reliable detection of shed receptor sourced from cancer cells in the patients&#39; plasma. 
     Example 2 
     Detection of (P2X) purinergic receptors in extra-cellular body fluid by indirect ELISA. Shed receptor from bladder cancer patients was detected in urine. Patients with extant disease and those in remission following treatment could be separated using a competition ELISA. Urine was diluted 1:10 and the spiked P2X7 antibody was used at 2.5 ug/mL ( FIG. 17 ). Test sample 1 was a patient in remission, close to the control level, while Test sample 2 had existing disease manifest by the presence of shed receptor. Urine samples (1 mL) were sufficient for detection (in triplicate). 
     Example 3 
     Detection of (P2X) Purinergic Receptors in Extra-Cellular Body Fluid by Dot Blotting. 
     Samples of urine from patients with ovarian and bladder cancer were examined using dot blots and a range of antibodies to P2X7 receptors. PVDF sheets were wet in PBS for 15 min then air dried. Sheets were then dotted with urine or sera (neat or diluted) and dried at 37 C. Sheets were then placed at 4 C (dry) until ready to test. 
     Sheets were wet in TBS before blocking in 3% BSA/TBS for 1 hr. 
     Antibodies were added into bags containing nitrocellulose sheets (1 sheet per bag) at 50 ug/mL in 3% BSA/TBS and incubated on rocker for 2 hrs. 
     Sheets were washed three times in TBS before conjugates were added at 1/1K concentration in 3% BSA/TBS and placed on rocker for 1.5 hrs. 
     Sheets were washed in TBS for 4 solution changes then developed using Chloro-1-Napthol. 
     Staining was neutralized in tap water before air drying and photographing with video camera. 
       FIG. 18  is an example of results obtained with ovarian and bladder cancer patients as well as controls. Urine from all cancer positive patients was observed to contain P2X7 while the control urine samples were devoid of detectable levels of receptor. 
     Example 4 
     Detection of (P2X) purinergic receptors in extra-cellular body fluid by immuno histochemistry. In one embodiment of the invention we have detected shed receptor in lymph nodes draining the area of identified tumours. In the absence of metastatic cells, lymph nodes considered sentinel nodes for breast and prostate cancers were removed in the course of surgery, fixed and embedded. Sections were stained for the presence of non-functional P2X7 receptor. Receptor was detected in the sentinel nodes whereas control nodes were devoid of shed receptor in the medulla. Examples, include prostate (A) and breast (B) where brown stain in the form of DAB reveals the presence of receptor, ( FIG. 19 ). 
     Example 5 
     Detection of Prostate Cancer by Detection of (P2X) Purinergic Receptors in Serum and Urine. 
     In one embodiment of the invention we have used a direct ELISA to detect the presence of P2X7 receptor in urine and serum from a patient with advanced prostate cancer. 
     The microtitre plate-based EIA kit consists of 12 strips of 8 wells each, pre-coated with E80, E140 or E200 antibodies to P2X7. The assay operates on the basis of competition between the shed receptor in the sample and the receptor-enzyme conjugate for the limited number of specific binding sites on the pre-coated microtitre plate. 
     After overnight incubation, unbound reagents were removed by rinsing wells with PBS. The enzyme conjugate utilised horseradish peroxidase (HRP) as a tracer. The amount of P2X7-HRP bound was measured by adding the chromogen substrate 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ARTS). Bound P2X7-HRP conjugate converted the colourless ABTS solution to a blue product. The ABTS reaction was stopped by the addition of the stopping solution, 5% oxalic acid, which converted the solution to a yellow-coloured product. The colour intensity was measured at 405 nm with reference at 490 nm using a microplate reader. The colour intensity was inversely proportional to the P2X7 epitope concentration in the calibrator or sample. 
     Example 6 
     Detection of Colon Cancer by Detection of (P2X) Purinergic Receptors in Faeces. 
     Faecal samples from two patients with established adenocarcinomas were collected and shed cells buffer extracted. The samples were run on polyacrylamide gels and major P2X7 protein bands identified in a Western blot. The figure shows two major bands at molecular weights of 75 kDa and 30 kDa respectively using an antibody to SEQ ID NO:2 corresponding with full length receptor and a truncated piece of receptor containing the epitope 200-216.