Abstract:
Monoclonal antibodies, which can be produced in vitro, against cardiac epitopes of the human My-C are produced by generating myeloma cell clones that produce such specific antibodies having epitope specificity. These monoclonal antibodies allow, among other things, the creation of an enzyme-linked immunosorbent assay (ELISA) for the specific, cross-reactivity-free quantitative determination of My-C in serum, plasma, whole blood or other body fluid. Specifically, a hybridoma cell clone producing a monoclonal antibody that detects and binds a cardiac epitope in the My-C is provided, which has no cross-reactivity with respect to the myosin-binding proteins of the skeletal muscles. The hybridoma cell line can be obtained by fusing myeloma cells with spleen cells of a test animal, in particular a mouse, immunized against recombinant My-C. The invention furthermore relates to epitope-specific antibodies produced by the hybridoma cell line, and to the use thereof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a mouse hybridoma clone producing a monoclonal antibody (anti-My-C-cC0C2-259-1A4; IgG1, kappa), which is directed against the cardiac myosin-binding protein C (C-protein, MYBPC3, cMyBP-C or My-C) and detects the same, and which does not react with the closely related isomers of My-C from the skeletal muscles. This monoclonal antibody is suitable as a catcher antibody or as a detection antibody for creating an enzyme-linked immunosorbent assay (ELISA) for quantitatively determining My-C in serum, plasma, whole blood or other body fluids for the early diagnosis of cardiac infarctions. Within the scope of this diagnostic procedure, this can allow a considerably early treatment of myocardial infarctions. 
         [0002]    Due to the acute life-threatening hazard, myocardial infarctions must be diagnosed quickly and distinguished from other causes of chest pain. [1] 
         [0003]    Determining biomarkers of myocardial necroses has meanwhile become an essential component in the diagnosis of infarctions with suspected non-ST-elevation acute coronary syndromes (NSTE-ACSs) and is imperative for making a diagnosis in the corresponding clinical context. At present, cardiac troponins (cTn) are considered the crucial biomarker. They are an integral component of the general infarction definition. [2] Cardiac troponins (cTn), however, have disadvantages, and new biomarkers could prove to be very valuable. [3] 
         [0004]    The cTn concentration in the serum reaches a maximum only 16 to 18 hours after the onset of symptoms, and one disadvantage of the existing cTn tests is the lack of analytical sensitivity for detecting low cTn concentrations in the first hours after symptoms begin to manifest. [4; 5] 
         [0005]    More recent cTn tests strive for a reliable determination of low cTn values; however, the reduced specificity thereof with respect to infarctions lowers the value thereof, since cTn concentrations in the vicinity of the 99th percentile of healthy test subjects can be observed. 
         [0006]    However, even then the cTn concentrations are below this threshold in as many as 25% of the infarction patients. [6] 
         [0007]    In view of the limited sensitivity and specificity of the cTn tests, corresponding guidelines (NICE) recommend determining the cTn 10 to 12 hours after the onset of symptoms (pain in the thoracic region) so as to confirm the diagnosis. [1] 
         [0008]    While a number of biomarkers exist that are released more quickly after an infarction, none of these have prevailed, since these are not expressed in a cardioselective manner. [7] For this reason, current efforts are focused on analyzing the extent of the changes in the cTn concentrations over time so as to improve the validity of the cTn tests. It remains unclear how large the absolute difference in concentration would have to be to render differences in the analytical and biological variations of the cTn concentrations irrelevant for making the intended diagnosis. 
         [0009]    The ideal biomarker would have to be released quickly from the myocardium after an infarction, but, contrary to comparable existing markers, would have to be a cardiac marker. The cardiac myosin-binding protein C (C-protein, MYBPC3, cMyBP-C or My-C) is a protein that meets these criteria. It was identified in the course of the proteomic analysis of coronary effluent from ischemic mouse hearts. [8] It is one of the most highly expressed proteins in the myocardium (19th out of 2,300 proteins), and the concentration is at least double that of cTnI and cTnT (92nd and 118th, respectively, out of 2,300 proteins). [9] 
         [0010]    Three different My-C isomers exist, which are encoded by different genes. In contrast with the My-C of the fast skeletal muscles and the My-C of the slow skeletal muscles, the cardiac isoform has a unique N-terminal domain ( FIG. 1 ) and other cardiac regions that could serve as specific epitopes. [10] 
         [0011]    The release of My-C after myocardial infarctions or damage has been demonstrated [8; 11; 12; 13; 14] and the progression of the increases in the concentration over time was compared to that of cTn. 
       SUMMARY OF THE INVENTION 
       [0012]    It was the object of the invention to create monoclonal antibodies, which can be produced in vitro, against cardiac epitopes of the human My-C by generating myeloma cell clones that produce such specific antibodies having epitope specificity. These monoclonal antibodies were to allow, among other things, the creation of an enzyme-linked immunosorbent assay (ELISA) for the specific, cross-reactivity-free quantitative determination of My-C in serum, plasma, or whole blood or other body fluid. 
         [0013]    The object is achieved by generating a hybridoma cell clone producing a monoclonal antibody that detects and binds a cardiac epitope in the My-C, and that has no cross-reactivity with respect to the myosin-binding proteins of the skeletal muscles. The hybridoma cell line can be obtained by fusing myeloma cells with spleen cells of a test animal, in particular a mouse, immunized against recombinant My-C. The hybridoma cell line was deposited on Dec. 10, 2013 with the DSMZ with accession number DSM ACC3224 in accordance with the requirements of the Budapest Treaty. The antibody produced by this hybridoma cell clone, in combination with one or more other monoclonal antibodies in an ELISA, is suitable for sensitively determining the concentration of My-C in the serum, and thus for the early diagnosis of cardiac infarctions. 
         [0014]    The invention furthermore relates to epitope-specific antibodies produced by the hybridoma cell line, and to the use thereof. 
         [0015]    So as to generate hybridoma clones producing monoclonal antibodies against human cardiac My-C, BALB/c mice were immunized in the known manner at intervals of six to eight weeks with the recombinant domains cC0C2 of the My-C ( FIG. 2 ). The mice received booster immunizations prior to having the spleen removed. The isolated spleen cells were fused in the known manner with cells from the mouse myeloma cell line P3X63Ag8.653 (ATCC CPL 1580) and were cultivated in suitable media. [15] 
         [0016]    The hybridomas that exclusively produce antibodies against the human My-C are selected, cloned multiple times, and propagated. The primary selection of these specific hybridomas was carried out using an ELISA in which the COC2 peptide of the My-C was adsorbed on the surface of microtiter plates. 
         [0017]    The epitope specificity of the monoclonal antibody of the clone according to the invention selected from the clones based on these criteria was ascertained by way of peptide scanning (Pepscan) (16, 17, 18). For this purpose, peptides (having sequences identical to the cC0C2 domain of the My-C used for the immunization) having a length of 15 amino acid esters were synthesized as individual spots on a membrane. The sequences of the 15-mer peptides of neighboring spots overlap, so that the entire amino acid sequence of the cC0C2 domain of the 
         [0018]    My-C was synthesized so as to overlap in a total of 111 spots. These peptides were incubated on the mapping membrane using the monoclonal antibody according to the invention. The bound antibody was detected by way of the ECL™ (enhanced chemiluminescence) system on film. 
         [0019]    This method allowed an ascertainment as to which of the 15-mer peptides are identified by the monoclonal antibody produced according to the invention. Using the known sequence of the peptides in the detected individual spots (see  FIG. 3 ), it was possible to infer the amino acid sequence of the epitope of the human My-C identified by the monoclonal antibody of the hybridoma clone ( FIG. 4 ). 
         [0020]    The monoclonal antibody 1A4 produced by the hybridoma clone generated according to the invention binds in the human My-C to the epitope having the sequence 
         [0000]      -A124-A-E-L-G-E-S-A-P-S-P-K- 
         [0021]    The proof that the monoclonal antibody produced according to the invention detects not only peptides on this PepSpot membrane, but also the entire molecule of the cC0C2 domain of the human My-C that includes this epitope was provided by the use thereof in the ELISA. Such an exemplary ELISA using the monoclonal antibody 1A4 is shown in  FIG. 5 . 
         [0022]    The above-described, epitope-characterized monoclonal antibody (IgG 1 , kappa) can be modified or labeled in the native form thereof, or in the form of a fragment. This antibody, or the modified forms thereof, can be used to clarify the processing of the human My-C, the kinetics of the release thereof and of the clearance thereof from the serum or other body fluid, for the qualitative detection thereof, and the quantitative determination thereof (such as ELISA and Western Blot), in immunohistology or as a diagnostic agent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows the primary structure of cardiac My-C in the region of the epitope detected by the monoclonal antibody anti-My-C-cC0C2-259-1A4 compared to the primary structures of My-C of skeletal muscles and smooth muscles; 
           [0024]      FIG. 2  shows the amino acid sequence of the cC0C2 domains of cardiac My-C; 
           [0025]      FIG. 3  shows epitope mapping of anti-My-C-cC02-259-1A4; 
           [0026]      FIG. 4  shows epitope mapping, namely, a list of the peptides present in the overlapping 15-mer peptides present in the PepSpots 1 to 41 of the mapping membrane; and 
           [0027]      FIG. 5  shows proof of binding of the monoclonal antibody anti-My-C-c0002-259-1A4 to recombinant c0002 in the ELISA. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The invention will be described in more detail hereafter by way of exemplary embodiments. 
       EXEMPLARY EMBODIMENTS 
     Example 1 
     Production of the Hybridoma Cell Line 
       [0029]    The spleen of a mouse immunized in the known manner with cC0C2 of the My-C is removed under sterile conditions, and the spleen cells are flushed out of the spleen capsule using RPMI 1640 medium (Life Technologies™, Karlsruhe) with a syringe and isolated. The spleen cells are pelletized (10 minutes at 300×g), washed three times with RPMI 1640 medium, and resuspended in RPMI 1640 medium. They are then fused with myeloma cells of the line P3X63Ag8.653 (ATTC CPL 1580). For this purpose, cultivated myeloma cells, which are in the log phase of growth, are likewise pelletized and washed three times. 1×10 8  spleen cells and 5×10 7  myeloma cells are pipetted into a centrifuge tube, mixed intensively and centrifuged; 1.5 ml preheated 50% polyethylene glycol 1500 (Roche, Basel) is added dropwise to the cell sediment within one minute, while the tubule is continuously rotated at 37° C. The fusion batch is then incubated for another minute at 37° C. In the following three minutes, preheated medium (RPMI 1640) is added dropwise, 1 ml being added in the first minute, 3 ml in the second minute, and then 18 ml. Centrifuging is carried out immediately thereafter at 200×g for 10 minutes. The cell pellet is placed in RPMI 1640 medium comprising 10% FCS and HAT. A portion of the pellets are seeded in 96-well culture plates, and the remainder is frozen in liquid nitrogen at −196° C. Mouse peritoneal macrophages, which were cultivated 1 day prior to the fusion (1×10 4  macrophages per well in HAT medium), are used as feeder cells during cultivation. The cells are incubated in a CO 2  incubator at 37° C. The medium is replaced after 3 to 5 days, respectively, with fresh RPMI 1640 HAT medium, and, depending on the growth of the fused cells, the culture supernatants are tested after approximately 2 weeks for the reactivity thereof with respect to the antigen (My-C) using an ELISA. 
       Example 2 
     Selection of the Antibody-Producing Clones 
       [0030]    All growing clones or the antibodies thereof were tested for reactivity using an enzyme-linked immunosorbent assay (ELISA). The immunosorbent was the immunogen, this being the recombinant cC0C2 domain of the My-C (approximately 2 μg/ml). 
         [0031]    Carrying out the ELISA:
       1. Coat each of the microtiter plates (Costar, high binding) with 50 μl immunogen solution per well at 4° C. over night;   2. wash the microtiter plates (MTP) 3 times with Tris-buffered saline (TBS), pH 7.4;   3. block the MTP using 200 μl blocking reagent (Boehringer, Mannheim) per well, 1 hour at 37° C.;   4. wash the MTP 3 times with NaCl Tween 20;   5. incubate with culture supernatant of the hybridoma cultures; 50 μl per well, respectively, diluted approximately 1:2 with TBS Tween 20;   6. wash the MTP 3 times with NaCl Tween 20;   7. incubate with anti-mouse Ig antibodies, coupled to peroxidase, 50 μl per well, 1 hour at room temperature;   8. wash the MTP 3 times with NaCl Tween 20;   9. incubate with ABTS solution (100 mg ABTS per 100 ml substrate buffer [citrate, sodium perborate, pH 4.4]), 50 μl per well;   10. measure at 405 nm after an incubation time of 60 minutes at room temperature using a microplate reader (SLT).       
 
       Example 3 
     Epitope Mapping for the Monoclonal Antibody 1A4 in the Human Cardiac My-C 
       [0042]    The binding site of the monoclonal antibody 1A4 was identified by way of the peptide scanning method. For this purpose, the entire amino acid sequence of the human cC0C2 domain of the My-C that was used for the immunization is divided into a total of 111 overlapping amino acid sequences, each having a length of 15 amino acids. These sequences are synthesized as individual peptides in spots directly on a cellulose membrane. The membrane is incubated with the antibody-containing culture supernatants of the hybridomas, and the binding sites of the antibodies are rendered visible by way of incubation with a peroxidase-coupled anti-mouse Ig antibody. For this purpose, after washing three times with TBS Tween, the membrane is placed between copy film, and then incubated for 3 minutes with the ECL™ (enhanced chemiluminescent) detection reagent (Amersham, Braunschweig). An applied film (Hyperfilm ECL™ [RPN 2103H Amersham, Braunschweig]) is thereafter exposed to light, for between 30 seconds and 3 minutes. 
         [0043]    The identification of the sequences detected by the antibody takes place by assigning the spots 31 and 32 ( FIG. 4 ) exposed on the film to the 15-mer partial sequences of the immunogen (cC0C2 domain of the My-C) localized in the spots. 
       Spot 31 121 PAPAAELGESAPSPK 15 1A4 
     Spot 32 125 AELGESAPSPKGSSS 15 1A4 
       [0044]    The identified central sequence of the two partial sequences is the amino acid sequence -A 124  -A-E-L-G-E-S-A-P-S-P-K-. This sequence is the detected epitope to which the antibody 1A4 binds in the human My-C. 
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