The present invention relates to methods for detecting and measuring plasmacytoma cells in a sample.
Plasmacytoma, represented by multiple myeloma, is generally termed a myeloma, and is pathologically divided into multiple myeloma, plasma cell leukemia, solitary plasmacytoma, extramedullary plasmacytoma, smoldering multiple myeloma, or asymptomatic myeloma. All of them are B cell tumors and are characterized by abnormal growth of monoclonal plasma cells (antibody-producing cells). Many of these tumors accumulate in the bone marrow and are diseases of poor prognosis accompanied by systemic bone lesions.
In multiple myeloma, terminally differentiated B cells or plasma cells that produce and secrete immunoglobulins monoclonally increase predominantly in the bone marrow, and thereby monoclonal immunoglobulins (M proteins) or their constituent light chains and/or H chains are detected in the blood and urine. With the aging of the population in recent years, patients with multiple myeloma are growing in number, and the mortality rate has reached 2.1 in 100,000 people in Japan.
The diagnosis of multiple myeloma has been made based on the detection of M proteins and/or bone lesions. These methods, however, required that the number of myeloma cells to be detected amounted to 0.2 to 1.2xc3x971012, systemically, and even for the detection of M proteins, growth of myeloma cells to about 1.2xc3x971010 was required. This rendered the early detection thereof difficult.
Furthermore, since these methods of diagnosis do not always reflect the amount of tumor cells, it was inconveniently impossible to decide effective regimens for treatment. In addition, it was also difficult to differentiate from benign monoclonal immunoglobulinemia in which M proteins are similarly detected, or to diagnose the non-secretory type myeloma in which no M proteins are present.
On the other hand, there have been attempts to diagnose myeloma using antibodies that recognize antigen on the cell membrane of plasma cells. These antibodies include such monoclonal antibodies as anti-PCA-1 (Anderson, K. C. et al., J. Immunol. (1983) 130, 1132), anti-PC-1 (Anderson, K. C. et al., J. Immunol. (1983) 132, 3172), anti-MM4 (Tong, A. W. et al., Blood (1987) 69, 238), anti-CD38 (Epstein, J. et al., N. Eng. J. Med. (1990) 322, 664, Terstappen, L. W. M. M. et al., Blood (1990) 76, 1739, Leo, R. et al., Ann. Hematol. (1992) 64, 132, Shimazaki, C. et al., Am. J. Hematol. (1992) 39, 159, Hata, H. et al., Blood (1993) 81, 3357, Harada, H. et al., Blood (1993) 81, 2658, Billadedeau, D. et al., J. Exp. Med. (1993) 178, 1023) and the like. Since such detection using antibody required a sample that contained a large amount of myeloma cells, it was particularly unsuitable for early detection in which myeloma cells were not always present.
On the other hand, Goto, T. et al. reported that they immunized mice with human plasma cells and obtained a mouse monoclonal anti-HM1.24 antibody that recognizes an antigen having a molecular weight of 29-33 kDa specifically expressed on B cell lines (Blood (1994) 84, 1922). It was further reported that the antigen (HM1.24) recognized by monoclonal anti-HM1.24 antibody is considered to be an antigen associated with the terminal differentiation of B cells (Goto, T. et al., Jpn. J. Clin. Immun. (1992) 16, 688), and that monoclonal anti-HM1.24 antibody reacts to plasmacytoma in a specific manner (Shuji Ozaki et al., the program of The 19th General Meeting of Japan Myeloma Study Group, General presentation 3). It was not known, however, that the diagnosis of plasmacytoma could be effected using the gene of HM1.24.
It is an object of the present invention to provide a method that permits a simple and sensitive detection or measurement even with a small amount of tumor cells, and that permits the diagnosis of plasmacytoma.
In order to attain the above object, the present inventors have devised a combination of primers and a probe based on the already-known sequence of the HM1.24 gene (Japanese Patent Application No. 9-271536), attempted to detect and measure the amount expressed of HM1.24 mRNA in a simple and sensitive manner and to quantitate the amount expressed. As a result of intensive research, the present inventors have found that plasmacytoma cells can be specifically detected or measured by PCR-amplifying HM1.24 mRNA from a small amount of tumor cells and using a probe labeled with fluorescence, and that plasmacytoma can be diagnosed by amplifying similarly normal cells or tumor cells other than plasmacytoma cells as a control sample and then comparing the amount of the amplified product, and thereby have completed the present invention.
Thus, the present invention provides a method of detecting or determining plasmacytoma cells in a sample, said method comprising amplifying a polynucleotide that is specifically or strongly expressed in plasmacytoma cells and then detecting or measuring the amplified product.
As said plasmacytoma, there can be mentioned multiple myeloma, plasma cell leukemia, solitary plasmacytoma, extramedullary plasmacytoma, smoldering multiple myeloma, asymptomatic myeloma and the like.
Preferably, said polynucleotide is DNA or mRNA, in particular mRNA, that encodes the HM1.24 antigen.
Preferably, said amplification method is the PCR method.
Preferably, said measurement method is a method that employs a labeled probe.
Preferably, said label is a fluorophore, a radioisotope, an enzyme or a combination thereof.
The present invention also provides a method of diagnosing plasmacytoma by detecting or measuring plasmacytoma cells in a sample, said method comprising amplifying a polynucleotide that is specifically or strongly expressed in said plasmacytoma cells, detecting or measuring the amplified product, and then comparing the amount of the amplified product to that in a control sample.
Plasmacytoma that is the subject of the detection or measurement method of the present invention is a tumor that expresses the HM1.24 antigen having the amino acid sequence as set forth in SEQ ID NO: 1 or the amino acid sequence substantially identical to said amino acid sequence, and includes multiple myeloma, plasma cell leukemia, solitary plasmacytoma, extramedullary plasmacytoma, smoldering multiple myeloma, asymptomatic myeloma and the like.
Samples containing plasmacytoma cells may be prepared by isolating leukocytes from the peripheral blood or the bone marrow of patients with plasmacytoma and collecting RNA therefrom. Since many of the myelomas tend to form a tumor mass in the bone marrow, it is desirable to collect leukocytes containing plasmacytoma cells by the bone marrow puncture to said tumor mass. In cases where there is a marked appearance of tumor cells in the peripheral blood as in plasma cell leukemia etc., the use of peripheral blood is preferred because of simplicity in handling.
In order to isolate leukocytes containing plasmacytoma cells from the peripheral blood or the bone marrow collected from patients with plasmacytoma, a commercially available reagent may be used for separation by gradient centrifugation. As the commercially available reagent, there can be used Ficoll-Paque (manufactured by PHARMACIA BIOTECH), a Mono-Poly Resolving Medium (manufactured by Dainippon Pharmaceuticals), and the like. It is also possible to prepare leukocytes by lysing red blood cells in a hypotonic buffer and then washing by centrifugation. As a solution used in washing, there can be used isotonic solutions such as PBS and MEM.
In order to prepare RNA from the thus obtained leukocytes, a method well known to those skilled in the art may be used (see, for example, Idensi Sousa Jikkenhou (Experiments on Genetic Manipulation), Yasutaka Takagi, Kodansha Scientific, pp. 24-39, 1980). RNA may be total RNA or mRNA. Total RNA or mRNA can be extracted using a commercially available kit, for example TRIZOL (manufactured by GIBCO BRL), ISOGEN (manufactured by Wako Pure Chemicals Industries, Ltd.), and mRNA Purification Kit (manufactured by PHARMACIA BIOTECH).
Any target polynucleotide can be used as long as it is specifically or strongly expressed in plasmacytoma cells. However, due to ease of detection, it is preferably DNA or mRNA, in particular mRNA, encoding the HM1.24 antigen that is specifically expressed in plasmacytoma cells.
In accordance with the present invention, a specific example of a strongly expressed polynucleotide includes a polynucleotide that is expressed five-fold or more, preferably 10-fold or more, and most preferably 20-fold or more than normal cells or tumor cells other than plasmauytoma cells.
A relative amount of the polynucleotide expressed in a sample may be determined by subjecting RNA or mRNA extracted from said cells to agarose gel electrophoresis, allowing the product to be adsorbed to a membrane, performing Northern blot hybridization using a radio-labeled probe, and then determining and comparing the radioactivity. Alternatively, the competitive RT-PCR method (Competitive RNA Transcription Kit, Takara) may be used to amplify, at the same time, the RNA competitor and the mRNA of interest in the same reaction mixture with the same primer. Then, based on the ratio of the amplified products, the original amount of mRNA can be estimated. Furthermore, it can be simply determined using ABI PRISM7700 according to the method described in Examples.
As the method of amplification, the PCR method (polymerase chain reaction method) can be used. When the polynucleotide of interest is mRNA, the use of RT-PCR is preferred. For the PCR method or the RT-PCR method, a commercially available reagent may be used including the TaKaRa RNA LA PCR(trademark) Kit (AMV) Ver 1.1 (manufactured by Takara Shuzo), the RT-PCR high-Plus-(manufactured by Toyoboseki), or the TaqMan EZ RT-PCR Kit (manufactured by Perkin-Elmer) and the like.
As a method of amplification, in addition to the PCR method, the TMA method (Transcription Mediated Amplification method: Japanese PCT Publication No. 4-500759) that amplifies RNA may be used.
The primer is a pair of oligonucleotides that can amplify a segment of the nucleotide sequence as set forth in SEQ ID NO: 1, specifically a pair of oligonucleotides that can hybridize, at a certain interval, to a nucleic acid having the nucleotide sequence as set forth in SEQ ID NO: 1 or a nucleic acid complementary thereto. The distance on the sequence of SEQ ID NO: 1 to which the pair of oligonucleotides hybridize is, but is not limited to, a range of 30 to 400 nucleotides, preferably 50 to 200 nucleotides.
The primer is preferably selected from the region in which the amino acid sequence is well conserved among the species and mainly in the extracellular region from positions 48 to 124 in the amino acid sequence of SEQ ID NO: 1.
Based on the above conditions, the primer can be selected using, for example, a commercially available analytic al software such as Primer Express (manufactured by Perkin-Elmer).
The length of the primer to be used for amplification is, but is not limited to, 10 to 100 nucleotides, preferably 10 to 50 nucleotides, more preferably 15 to 30 nucleotides, and more preferably 20 to 25 nucleotides, for example about 20 nucleotides.
Specific examples of such a primer pair include the forward primer (SEQ ID NO: 3) (corresponding to positions 153 to 172 in the nucleotide sequence as set forth in SEQ ID NO: 1) and the reverse primer (SEQ ID NO: 4) (corresponding to positions 304 to 323 in the nucleotide sequence as set forth in SEQ ID NO: 1).
The probe is an oligonucleotide that specifically hybridizes to a nucleotide sequence defined by said one pair of primers. Thus, such a probe is selected from the region between the forward primer and the reverse primer. Though the positions on SEQ ID NO: 1 corresponding to the probe depend on the sites to which the primer pair hybridizes, those that hybridize to the region of nucleotide number 173 to 303 in SEQ ID NO: 1, preferably the region of nucleotide number 224 to 249 are preferred. The length of the probe to be used is, but is not limited to, 10 to 200 nucleotides, preferably 20 to 100 nucleotides, for example 25 to 50 nucleotides, for example about 30 nucleotides.
The amplified polynucleotide can be detected or measured by subjecting the PCR reaction mixture to agarose gel electrophoresis in the presence of a luminescent substance such as ethidium bromide and then measuring the light emitted by said band. When a probe is used, the polynucleotide is detected by allowing it to be adsorbed to a nitrocellulose membrane followed by hybridization to the labeled probe. The sequence or the length of the probe is not limited as long as it can specifically detect the target polynucleotide to be detected.
For labeling, a fluorogenic substance, a radioisotope, an enzyme or a combination thereof may be used. As the fluorogenic substance, FAM (6-carboxyfluorescein), JOE (6-carboxy-4,5-dichloro-2,7-dimethoxyfluorescein), TET (6-carboxy-4,7,2xe2x80x2,7xe2x80x2-tetrachlorofluorescein), and HEX (6-carboxy-4,7,2xe2x80x2,4xe2x80x2,5xe2x80x2,7xe2x80x2-hexachlorofluorescein) may be used. As the radioisotope, 32P may be used.
As the enzyme, alkaline phosphatase may be used, and as the substrate for the enzyme, CDP-Star(trademark) (manufactured by BOEHRINGER MANNHEIM), for example, may be used. By using ABI PRISM7700 developed by Perkin-Elmer that permits the determination of the product with time while performing the PCR reaction, simple determination can be attained. As the reagent for RT-PCR in this case, TaqMan EZ RT-PCR Kit (manufactured by Perkin-Elmer) is preferably used.