ANTI-HUMAN MESOTHELIAL CELL MONOCLONAL ANTIBODY

Abstract: A monoclonal antibody is disclosed capable of specifically reacting with the human mesothelial cell but not with other normal cells and human tumor cells, and therefore applicable in diagnosis of cancers.

Description: The present invention relates to monoclonal antibodies capable of specifically reacting with the human mesothelial cells and to a method of producing such antibodies. It is known that in lung cancer, cancer cells desquamate into sputum and/or pleural effusion, and that in various abdominal cancers, cancer cells desquamate into ascitic fluid. Therefore it is important in the diagnosis of cancer to detect cancer cells desquamating into sputum and/or pleural effusion, or ascitic fluid. Diagnosis and differentiation of cancer cells are generally carried out by pathologists. Sputum, pleural effusion and ascitic fluid contain many kinds of normal cells, and above all it is difficult to distinguish cancer cells from mesothelial cells and macrophages. Recently, many monoclonal antibodies having specificity for cancer cells have been produced using hybridoma technology, and the application of such monoclonal antibodies to cytodiagnosis is known. However, since some of the monoclonal antibodies produced react with macrophages and/or mesothelial cells, or some of them react only with particular cancer cells, it is not easy to carry out cytodiagnosis of cancer using those monoclonal antibodies. It is especially difficult to distinguish between cancer cells and mesothelial cells. As prior art in this field, there may he acknowledged: Lancet, Vol.2 pp 512-515 (1982) which discloses a monoclonal antibody which binds to malignant tumour cells, including malignant mesothelial cells, but not with non-malignant cells. The specificity of that antibody is therefore the opposite of that of the antibody of the present invention. Fed. Proc. 38, (3 part 1), P912, Nr. 3605 (1979) which discloses an anti-mesothelial antiserum which is absorbed by red blood cells, liver and MOLT-4 cell line lymphocytes. The absorbed antiserum reacts with the mesothelial lining of the pleura and peritoneum. It did not react with various normal or malignant non-mesothelial cells, but did react with malignant mesothelial cells. Again the specificity and reactivity appears to be different from that of the antibody of this invention. The same disclosure is contained in Biol. Abs. 69, Nr. 4147, (1979). Am. Rev. Respir. Dis. 123 (4 part 2), p61 (1981) discloses an anti-mesothelial antiserum which reacts with both mesothelial cells and macrophages. Accordingly, an improved monoclonal antibody which specifically reacts with normal human mesothelial cells but not with other normal human cells or tumour cells would be useful. In accordance with the present invention, an improved monoclonal antibody of the IgG class has been produced which is capable of specifically reacting with normal human mesothelial cells but not with other normal human cells or human tumour cells, that monoclonal antibody being obtainable from hybridoma cell line KM-277, ECACC No. 86102303). Further, successful cytological diagnoses of expectoration, pleural effusion and ascitic fluid from patients with cancer have been made using the monoclonal antibody, thus indicating that the monoclonal antibody of the present invention has a great significance in clinical pathology. The monoclonal antibody according to the present invention was obtained by fusing spleen cells of a mouse immunized with human mesothelial cells according to the following procedure. (1) Immunization of animal and preparation of antibody-producing cells Mice between 3 - 10 weeks of age, preferably 8-week-old mice, are immunized with human mesothelial cells, to cause such mice to prepare antibody-producing cells in the spleen, lymph node and peripheral blood. The immunization is performed generally by administering human mesothelial cells (5 x 10⁵ to 5 x 10⁶ cells per animal), together with an appropriate adjuvant (e.g. Freund's complete adjuvant, or aluminium hydroxide gel plus B .pertussis vaccine) to the mice subcutaneously, intravenously or interperitoneally. Thereafter, the same antigen administration is repeated 2 to 5 times at 1 to 2 week intervals. Three to seven days after each immunization, the blood is sampled from the eyeground venous plexus and the serum of each sample is tested to determine whether it reacts with human mesothelial cells by the immunocytochemical staining technique described hereinafter: Immunocytochemical staining : A mesothelial cell suspension (1 x 10⁷ cells/ml) in PBS comprising 1.83 g of disodium phosphate, 0.21 g of monopotassium phosphate and 7.65 g of sodium chloride in 1 l of distilled water (pH 7.2) is distributed into the wells of a 12-well microtitre slide glass (Flow Laboratories, CAT No. 60-412-05) coated with egg white albumin in an amount of 5 µl per well and dried over cooled air for 5 to 10 minutes. Then, acetone cooled at -20 to-30°C is added to each well and the slide glass is allowed to stand for 10 minutes. After drying for 2 to 3 minutes, endogenous peroxidase is inactivated by immersion in 3% hydrogen peroxide in methanol solution for 30 minutes. After washing well with PBS, 20 µl of antiserum or monoclonal antibody solution (1 to 20 µg/mℓ) is distributed into each well as the first antibody, and the slide glass is allowed to stand for 30 minutes to 2 hours at room temperature and washed well with PBS. Then, 20 µℓ of a biotin-labeled rabbit anti-mouse immunoglobulin (10 µg/mℓ) is distributed into each well as the second antibody, and the glass is allowed to stand at room temperature for 30 minutes and then washed well with PBS. Avidin-biotin-peroxidase complex (ABC reagent, product of Vector) is added to the wells, and the glass is allowed to stand at room temperature for 30 minutes and then washed well with PBS. Color is developed by the addition of diaminobenzidine as the substrate solution for peroxidase, and the glass is observed with a microscope. The procedure subsequent to ABC reagent addition is made by the method recommended by Vector. When the target cells are various tumor cells or normal cells instead of mesothelial cells, the immunocytochemical staining is conducted in the same manner except for changing the cells fixed on a slide glass as the first step. In preparation for cell fusion, human mesothelial cells are intraperitoneally administered to the immunized mice in a dose of 5x10⁵ to 5x10⁶ cells per animal 3 to 4 days prior to the fusion treatment. The spleens are then extirpated and the spleen cells are prepared for fusion. That is, the spleen is cut into fragments in MEM (product of Nissui Pharmaceutical), loosened up with forceps, and centrifuged at 1,200 rpm for 5 minutes. The supernatant is discarded, and the sediment is deprived of erythrocytes by treatment with Tris-ammonium chloride buffer (pH 7.6,) for 1-2 minutes, washed three times with MEM, and used as the spleen cells for fusion. Mesothelial cells are obtained from the lining of the thorax and of the abdominal cavity at autopsy. Cells are collected from the surface of the lining and washed with PBS two or three times. Alternatively, mesothelial cells may be obtained from the homogenates of the cardiac vesicle. Cells thus obtained are washed with PBS, centrifuged at 1,200 rpm for 5 minutes, and the resultant pellet re-suspended in PBS. (2) Preparation of myeloma cells A mouse-derived established myeloma cell line is used. Suitable examples are the 8-azaguanine resistant mouse (BALB/c-derived) myeloma cell lines P3-X63Ag8-U1 (P3-U1) [Current Topics in Microbiology and Immunology 81 , 1-7 (1987)], P3-NSI/1-Ag41 (NS-1) [European J. Immunology, 6 , 511-519 (1976)], SP2/0-Ag14 (SP-2) [Nature, 276 , 269-270 (1978)], P3-X63-Ag8 653 (653) [J. Immunology, 123 , 1548-1550 (1979)] and P3-X63-Ag8 (X63) [Nature, 256 , 495-497 (1975)], all of which are commercially available. The screening of these cell lines is performed in 8-azaguanine medium [normal medium prepared by adding, to RPMI-1640 medium, glutamine (1.5 mM), 2-mercaptoethanol (5x10⁻⁵ M), gentamicin (10 µg/mℓ) and fetal calf serum (FCS; product of CSL) (10%), with further supplementation with 8-azaguanine (15 µg/mℓ)]. The cell line selected for cell fusion should be transferred to normal medium 3 to 4 days before fusion to ensure the cell count of not less than 2x10⁷ on the day of fusion. (3) Cell fusion The antibody-producing cells obtained in (1) and the myeloma cells obtained in (2) are washed well with MEM or PBS and mixed in a cell number ratio of antibody-producing cells : myeloma cells in the range of 5:1 to 10:1 and then subjected to centrifugation (1,200 rpm, 5 minutes). The supernatant is discarded and the cell sediment is loosened up. With stirring at 37°C, a mixture of 2 g of polyethylene glycol 1,000 (PEG-1,000), 2 mℓ of MEM and 0.7 mℓ of dimethylsulfoxide is added in an amount of 0.2-1 mℓ per 10³ antibody-producing cells, and MEM is added until the whole volume is made 50 mℓ after several additions of 1-2 mℓ of MEM at 1 to 2 minute intervals. After centrifugation (900 rpm, 5 minutes), the supernatant is discarded and the cell sediment is loosened gently. To the cells is added 100 mℓ of normal medium (RPMI-1640 with 10% FCS). The cells are gently suspended in the medium with a measuring pipette. The suspension obtained is distributed, in 1 mℓ-portions, into the wells of a 24-well incubation plate. Incubation is carried out in a 5% CO₂ incubator at 37°C for 24 hours. HAT medium [normal medium supplemented with hypoxanthine (10⁻⁴ M), thymidine (1.5x20⁻⁵ M) and aminopterine (4x10⁻⁷ M)] is added to the incubation plate (1 mℓ per well) and incubation is conducted for a further 24 hours. Thereafter, 1 mℓ of the culture supernatant is discarded and the same volume of fresh HAT medium is added at 24-hour intervals for 2 days. The incubation in the CO₂ incubator at 37°C is continued for 10-14 days. In those wells in which grown fused colony-forming cells are found, 1 mℓ of the supernatant is discarded and the same volume of HT medium (HAT medium minus aminopterine) is added, followed by medium replacement with fresh portions of HT medium at 24-hour intervals for 2 days. After 3 to 4 days of cultivation in HT medium, a portion of the culture supernatant is collected and assayed for antibody titer against human mesothelial cells by the above-mentioned immunocytochemical staining. In like manner, the reactivities with normal human cells or tumor cells are also determined, and those wells in which selective reactivity with human mesothelial cells is found, are selected. Cloning is repeated twice by limiting dilution technique and those clones for which stable high antibody titer value against human mesothelial cells are obtained, are selected as anti-human mesothelial cell monoclonal antibody-producing hybridoma cell lines. (4) Preparation of monoclonal antibody Eight- to ten-week-old female BALB/c mice treated with pristane [intraperitioneally administered with 0.5 mℓ of 2, 6, 10, 14-tetramethylpentadecane (pristane) and fed for 2-weeks] are intraperitioneally injected with the anti-human mesothelial cell monoclonal antibody-producing hybridoma cells obtained in procedure (3) above at a dose of 2-4x10⁶ cells per animal. In 10-21 days, the hybridoma cells produce ascites carcinoma in the mice. The ascitic fluid is collected from such mice, centrifuge (3,000 rpm, 5 minutes) to remove solids, subjected to salting out with 50% ammonium sulfate, dialyzed against 0.04 M phosphate buffer (pH 8.0) supplemented with 0.03 M NaCl, and passed through DE52® (product of Whatman) column. An IgG fraction is collected and used as a purified monoclonal antibody. The isotype of the antibody is determined by Ouchterlony's method (double immunodiffusion) [Seibutsukagaku Jikkenho (Methods in Experimental Biochemistry), vol. 15, Introduction to Experimental Immunology, p. 74, Gakkai Shuppan Center, 1981]. The quantity of protein is estimated by the Folin's method, followed by calculation based on the absorbance at 280 nm [1.4 (OD₂₈₀) approximately corresponds to 1 mg of immunoglobulin per mℓ]. The monoclonal antibody thus obtained is effective in cytological diagnosis of expectoration for lung cancer and cytological diagnosis of pleural effusion for lung cancer and cytological diagnosis of ascitic fluid for various abdominal cancers by the above-mentioned immunocytochemical staining. Certain specific embodiments of the present invention are illustrated by the following examples. Example 1 (1) Preparation of antibody-producing cells Eight-week old female BALB/c mice (Shizuoke Agricultural Cooperative Association for Laboratory Animals) were intraperitoneally administered and Immunisation with human mesothelial cells (2x10⁶ cells per animal) as an antigen, together with aluminium hydroxide gel (2 mg per animal) and killed B . pertussis vaccine (Chiba Serum Institute; 1x10⁹ cells per animal) as an adjuvant. The same antigen administration was repeated 3-5 times at a dose of 2x10⁶ cells per animal at 1 to 2 week intervals without an adjuvant. From among these immunized mice, those mice whose antisera intensely reacted with human mesothelial cells were selected, and spleen cells were prepared from such mice and submitted to cell fusion. (2) Preparation of myeloma cells The 8-azaguanine-resistant murine myeloma cell line P3-U1 was cultivated in normal medium to thereby secure not less than 2x10⁷ cells at the time of cell fusion and submitted to cell fusion as a parent strain. (3) Hybridoma production The spleen cells and meyloma cells obtained in (1) and (2), respectively, were used in a ratio of 5:1 and subjected to fusion according to the procedure previously described. After cultivation in HAT medium at 37°C in 5% CO₂ incubator for 14 days, fused cells were selected, and after change of the medium to HT medium, cultivation was continued. Based on the results of anti-human mesothelial cell antibody titer determination, active wells were selected, and after change of the medium to normal medium, cloning was repeated twice by the limiting dilution technique. The clone for which stable antibody titer values against human mesothelial cells were obtained, was selected as anti-human mesothelial cell-producing hybridoma cell line KM-277. The hybridoma cell line KM-277 has been deposited under the terms of the Budapest Treaty with the European Collection of Animal Cell Cultures, Great Britain, as of October 23, 1986 under the deposit number ECACC No. 86102303. (4) Monclonal antibody purification Eight-week-old female BALB/c mice treated with pristane were intraperitoneally injected with the hybridoma cell line KM-277 obtained in (3) at a dose of 4x10⁶ cells per animal. In 10-21 days, the hybridoma produced ascites carcinoma. The ascitic fluid was collected from ascitic fluid-bearing mice (5 to 10 mℓ per animal), centrifuged to remove solids (3,000 rpm, 5 minutes), subjected to salting out with 40% ammonium sulfate, dialyzed against 0.04 M phosphate buffer supplemented with NaCl (0.03 M), and passed through a DE52® (product of Whatman) column (bed volume: 50 mℓ) at a flow rate of 20 to 30 mℓ/hr. An IgG fraction was collected and used as the purified antibody. (5) Antigenic specificity of KM-277 The specificity of the thus-obtained monoclonal antibody KM-277 for three human mesothelial cell samples, two human peripheral lymphocyte cell (PBL) samples and various cancer cell lines was investigated using immunocytochemical staining. The results are shown in Table 1. As shown in Table 1, KM-277 was very specifically reactive with the human mesothelial cell but not with PBL and the various cancer cell lines. Example 2 In this example, cells in sputum samples and pleural effusion samples derived from three patients with lung cancer, and cells in ascitic fluid samples derived from four patients with gastric cancer were stained by immunocytochemical staining using KM-277. The mesothelial cells in smeared preparations (smear) were stained and cancer cells in all the preparations were not stained. Therefore, cancer cells can be distinguished from mesothelial cells in smears. Whilst the invention has been described in terms of a particular monoclonal antibody, and a particular cell line capable of expressing that antibody, present day technology is such that it is now feasible to recover cDNA sequences encoding for a particular protein and to insert such cDNA sequences by recombinant DNA technology into a host thereby transforming that host into a transformant capable of expressing that protein. Thus the present invention extends to cDNA sequences encoding for the monoclonal antibody obtainable from hybridoma cell line KM-277, ECACC No. 86102303, and to transformants transformed with such cDNA and which are capable of expressing that antibody.

Claims: A monoclonal antibody of the IgG class obtainable from the hybridoma cell line KM-277, ECACC No. 86102303, and capable of specifically reacting with normal human mesothelial cells but not with other normal human cells or human tumour cells. The hybridoma cell line KM-277, ECACC No. 86102303. A method of producing an antibody according to claim 1, which comprises cultivating hybridoma cells of or derived from the hybridoma cell line KM-277, ECACC No. 86102303, and capable of producing the said antibody, and recovering the product antibody from the culture. An immunocytochemical staining method for distinguishing human tumour cells from human mesothelial cells in samples from patients suspected of having tumours, which comprises applying to the samples the monoclonal antibody according to claim 1 obtainable from the hybridoma cell line KM-277, ECACC No. 86102303 to determine the selective reaction of the antibody with human mesotheliai cells and the absence of a reaction with human tumour cells, and observing the stained sample. A method according to claim 4, wherein the sample tested is an expectoration, pleural effusion or ascitic fluid sample. A cDNA sequence encoding for the monoclonal antibody according to claim 1. A transformant transformed with a cDNA sequence according to claim 6 and capable of expressing the monoclonal antibody according to claim 1.

Inventors: HANAI, NOBUO C/O PATENT DEPARTMENT, YOSHIDA, HAJIME C/O PATENT DEPARTMENT
Applicants: KYOWA HAKKO KOGYO CO., LTD.
Application year: 1987
Main classification: A61K39
IPC codes: C12N15, C12R1, C12P21, G01N33, C07K14, C12N5, C07K16