Anti-c-met nanobody and use thereof

Abstract

A nanobody specifically binding to c-MET or an antigen-binding fragment thereof, a composition containing the nanobody or the antigen-binding fragment thereof, and a nucleic acid molecule encoding the nanobody or the antigen-binding fragment thereof. Also provided is a use of the nanobody or the antigen-binding fragment thereof in the treatment and diagnosis of diseases.

Description

Anti-c-MET nanoantibodies and uses thereof CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Chinese patent application 202311018785.0 filed on August 14, 2023, the entire contents of which are incorporated herein by reference in their entirety. Technical Field The present invention relates to a nanobody or an antigen-binding fragment thereof that specifically binds to c-MET, a composition containing the nanobody or an antigen-binding fragment thereof, and a nucleic acid molecule encoding the antibody or an antigen-binding fragment thereof. In addition, the present invention also relates to the use of the nanobody or an antigen-binding fragment thereof in the treatment and diagnosis of diseases. Technical Background Cellular-mesenchymal epithelial transition factor (c-MET), also known as hepatocyte growth factor receptor (HGFR), is a transmembrane receptor with autonomous phosphorylation activity encoded by the MET gene and belongs to the tyrosine kinase receptor superfamily. [1, 2] The structure of c-MET is composed of α chain and β chain connected by disulfide bonds, which are divided into extracellular domain, transmembrane helical domain and intracellular domain. The extracellular domain of c-MET contains 3 different functional regions: the SEMA domain covering the entire α chain and part of the N-terminus of the β chain is the key region for ligand binding [3] ; Cystine-rich domain with 4 disulfide bonds; 4 immunoglobulin domains [4] The intracellular domain of c-MET is also composed of three regulatory regions, namely the membrane-proximal domain containing Tyr1003 and Ser985 phosphorylation sites, which mainly negatively regulates c-Met signal transduction; the catalytic domain containing Tyr1234 and Tyr1235 phosphorylation sites, which mainly activates downstream signals by self-phosphorylation and plays a role in positively regulating the catalytic activity of tyrosine kinase; and the C-terminal multifunctional binding region containing Tyr1349 and Tyr1356, which mainly recruits various protein factors and adaptor molecules in the cytoplasm to transmit signals. [5,6] . Hepatocyte growth factor (HGF) is the only known high-affinity ligand for c-MET [7] Under normal physiological conditions, when it binds to c-MET, c-Met is activated by forming dimers and phosphorylating several sites in the proximal membrane region, activating a series of downstream signaling pathways, such as PI3K-Akt, Ras-MAPK, STAT-INK, etc., thereby promoting a series of biological effects such as cell proliferation, cell growth, and angiogenesis.[8] Studies have found that abnormal activation of the c-Met pathway can promote the proliferation, invasion and migration of tumor cells, ultimately driving the occurrence and development of malignant tumors. It is reported that the c-Met signaling pathway is abnormally regulated in many types of solid tumors, such as lung cancer, gastric cancer, liver cancer, breast cancer, skin cancer, colorectal cancer, etc., and is also involved in the formation, growth, and metastasis of colorectal cancer and oral squamous cell carcinoma. It plays an important role in the invasion and metastasis of breast cancer, ovarian cancer and gastric cancer, as well as the occurrence and development of liver cancer, lung cancer and pancreatic cancer. Abnormal activation of c-MET pathway mainly includes three types: MET14 exon skipping mutation, MET amplification and MET protein overexpression. [9] MET14 exon skipping mutation is considered to be an independent oncogenic driver gene in lung cancer, with an incidence of 2-3% in NSCLC patients and as high as 31.8% in patients with pulmonary sarcomatoid carcinoma. [9-11] The incidence of MET high amplification in lung adenocarcinoma is 1.0%. Although the incidence of MET amplification is not high, it is often accompanied by strong MET protein expression and is also one of the factors for poor prognosis.

[0012] The incidence of MET protein overexpression in lung adenocarcinoma can be as high as 65%, but it is not a primary carcinogenic driver. More often, it is a secondary event caused by the activation of other driver genes, thereby promoting tumor growth.

[0013] . Currently, monoclonal antibodies targeting human c-MET, such as Telisotuzumab, have been reported, and antibody-drug conjugates based on these monoclonal antibodies have shown good potential in the treatment of patients with non-small cell lung cancer. However, the demand for anti-tumor methods targeting c-MET with better characteristics has not been met in this field. Summary of the invention After extensive research, the inventors of the present application screened and obtained humanized nanobodies and their antigen-binding fragments that can specifically recognize the extracellular region of c-MET. The present invention uses nanobodies derived from alpacas, which have a molecular weight of only half that of conventional antibodies (150 kDa). They can penetrate into the core parts of the tumor, maximize the chances of antibody drugs binding to tumor cells, and produce better tumor treatment effects. Nanobodies and their antigen-binding fragments In one aspect, the present invention provides a nanobody or an antigen-binding fragment thereof that specifically binds to c-MET. The nanobodies described herein are generally composed of 4 framework regions (FRs) and 3 complementary determining regions (CDRs), referred to as FR1, CDR1, FR2, CDR2, FR3, CDR3 and FR4, and the antigen-binding fragment comprises at least a portion of the nanobody, which is sufficient to confer the ability of the fragment to specifically bind to c-MET. In some embodiments, the nanobodies described in the present invention may be truncated at the N-terminus or C-terminus so that it contains only part of FR1 and / or FR4, or lacks one or two of those framework regions, as long as it substantially maintains antigen binding and specificity. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises: CDR1, CDR2 and CDR3 contained in the VHH shown in any one of SEQ ID NOs: 1, 14, and 15. In certain embodiments, the CDRs are defined according to the Kabat, Chothia, or IMGT numbering systems. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises: a CDR1 as shown in SEQ ID NO: 2, a CDR2 as shown in SEQ ID NO: 3, and a CDR3 as shown in SEQ ID NO: 4, wherein: The CDRs are defined according to the Kabat numbering system. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises: a CDR1 as shown in SEQ ID NO: 5, a CDR2 as shown in SEQ ID NO: 6, and a CDR3 as shown in SEQ ID NO: 7, wherein the CDRs are defined according to the Chothia numbering system. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises: a CDR1 as shown in SEQ ID NO: 8, a CDR2 as shown in SEQ ID NO: 9, and a CDR3 as shown in SEQ ID NO: 10, wherein the CDRs are defined according to the IMGT numbering system. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the framework region sequence of a camelid antibody. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 1, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or several amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 1. In certain embodiments, the Nanobodies or antigen-binding fragments thereof are humanized, ie, wherein one or more framework regions have been replaced by essentially human framework regions. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises a heavy chain framework region of a human immunoglobulin (e.g., a heavy chain framework region contained in the amino acid sequence encoded by a human heavy chain germline antibody gene), which optionally comprises one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10) back mutations from human residues to camel residues. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 14, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or several amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 14. In certain embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 15, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or having one or more amino acid substitutions, deletions or additions (e.g. In some embodiments, the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 15. In certain embodiments, the Nanobody or antigen-binding fragment thereof specifically binds human and / or monkey c-MET. Peptide constructs In another aspect, the present invention also provides a polypeptide construct that specifically binds to c-MET, which comprises the Nanobody or antigen-binding fragment thereof of the present invention, and an immunoglobulin Fc domain. In this article, the Fc domain is also referred to as the Fc region, which refers to a portion of the heavy chain constant region that includes CH2 and CH3. In some embodiments, the Fc domain includes a hinge, CH2, and CH3. When the Fc domain includes a hinge, the hinge regulates the dimerization between two Fc-containing polypeptides. The Fc domain can be any antibody heavy chain constant region isotype. In some embodiments, the Fc domain is IgG1, IgG2, IgG3, or IgG4. In certain embodiments, the Fc domain included in the polypeptide construct of the present invention is a native Fc region, which includes an amino acid sequence consistent with the amino acid sequence of the Fc region found in nature. For example, the Fc domain can be a native sequence human IgG1 Fc region, a native sequence human IgG2 Fc region, a native sequence human IgG3 Fc region, or a native sequence human IgG4 Fc region. The native Fc region may have effector functions. Exemplary "effector functions" include binding to Fc receptors; Clq binding and complement dependent cytotoxicity (CDC); antibody-dependent cell-mediated cytotoxicity (ADCC); phagocytosis; downregulation of cell surface receptors (e.g., B cell receptors); and B cell activation, etc. Functional changes can be produced by replacing at least one amino acid residue in the native Fc region with a different residue or chemical modification, for example, changing the affinity of the antibody for effector ligands (such as FcR or complement Clq), thereby changing the effector function (e.g., reducing or enhancing). Therefore, in certain embodiments, the Fc domain contained in the polypeptide construct of the present invention may also be a variant Fc region, which may contain one or more (e.g., 1-10, e.g., 1-5) amino acid mutations or chemical modifications compared to the native Fc region to change one or more of the following properties of the antibody of the present invention: Fc receptor binding, antibody glycosylation, the number of cysteine ​​residues, effector cell function or complement function, etc. In certain embodiments, the Fc domain contained in the polypeptide construct of the present invention has reduced or removed effector function, such as an Fc domain containing a LALA mutation. In certain embodiments, the immunoglobulin Fc domain is linked to the N-terminus and / or C-terminus (eg, C-terminus) of the Nanobody or antigen-binding fragment thereof, optionally via a peptide linker. In certain embodiments, the immunoglobulin Fc domain is an Fc domain of IgG (eg, an Fc domain of IgG1, IgG2, IgG3, or IgG4). In certain embodiments, the immunoglobulin Fc domain is a human immunoglobulin Fc domain, such as an Fc domain of human IgG (eg, an Fc domain of human IgG1, IgG2, IgG3, or IgG4). In certain embodiments, the immunoglobulin Fc domain comprises the sequence shown in SEQ ID NO: 16, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or more amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto. In certain embodiments, the immunoglobulin Fc domain comprises the sequence shown in SEQ ID NO: 16. In certain embodiments, the polypeptide construct comprises a sequence as shown in any one of SEQ ID NOs: 11-13, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or several amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto. Preparation of Nanobodies and Peptide Constructs The nano antibodies or polypeptide constructs of the present invention can be prepared by various methods known in the art, for example, by genetic engineering recombinant technology. For example, a DNA molecule encoding a nano antibody or polypeptide construct of the present invention is obtained by chemical synthesis or PCR amplification. The resulting DNA molecule is inserted into an expression vector and then transfected into a host cell. Then, the transfected host cell is cultured under specific conditions and the antibody or polypeptide construct of the present invention is expressed. In another aspect, the invention also provides an isolated nucleic acid molecule encoding a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention. In another aspect, the present invention also provides a vector comprising the nucleic acid molecule of the present invention. In certain embodiments, the vector is a cloning vector or an expression vector. In another aspect, the present invention also provides a host cell comprising a nucleic acid molecule or a vector of the present invention. Such host cells include, but are not limited to, prokaryotic cells such as bacterial cells (such as Escherichia coli cells), and eukaryotic cells such as fungal cells (such as yeast cells), insect cells, plant cells and animal cells (such as mammalian cells, such as mouse cells, human cells, etc.). In another aspect, the invention also provides a method for preparing a Nanobody or an antigen-binding fragment thereof of the invention or a polypeptide construct of the invention, which comprises culturing a host cell of the invention under conditions that allow protein expression, and recovering the Nanobody or its antigen-binding fragment or the polypeptide construct from the cultured host cell culture. Bispecific or multispecific antibodies In another aspect, the present invention also provides a bispecific or multispecific antibody comprising a nanobody or antigen-binding fragment thereof of the present invention or a polypeptide construct of the present invention. The present invention also provides the use of a nanobody or antigen-binding fragment thereof or a polypeptide construct of the present invention, or a nucleic acid molecule, vector or host cell encoding them for the preparation of a bispecific or multispecific antibody. In certain embodiments, the bispecific or multispecific antibody specifically binds c-MET, and additionally specifically binds one or more other targets. In certain embodiments, the bispecific or multispecific antibody further comprises at least one second antibody having a second binding specificity for a second target. Conjugate In another aspect, the invention also provides a conjugate comprising a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention or a bispecific or multispecific antibody of the invention and a coupling portion linked thereto. In certain embodiments, the conjugated moiety is selected from a therapeutic agent (eg, a cytotoxic agent, a cytokine, a toxin, or a radionuclide). Pharmaceutical composition In another aspect, the invention also provides a pharmaceutical composition comprising a Nanobody or antigen-binding fragment thereof, a polypeptide construct, an isolated nucleic acid molecule, a vector, a host cell, a bispecific or multispecific antibody or a conjugate of the invention, and a pharmaceutically acceptable carrier and / or excipient. In certain embodiments, the pharmaceutical composition further comprises an additional pharmaceutically active agent, such as an anti-tumor agent. In certain embodiments, in the pharmaceutical composition, the Nanobodies or antigen-binding fragments thereof, polypeptide constructs, isolated nucleic acid molecules, vectors, host cells, bispecific or multispecific antibodies or conjugates of the invention and the additional pharmaceutically active agent can be provided as separate components or as mixed components. The nanobodies or antigen-binding fragments thereof, polypeptide constructs, isolated nucleic acid molecules, vectors, host cells, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the invention can be formulated into any dosage form known in the medical field, for example, tablets, pills, suspensions, emulsions, solutions, gels, capsules, powders, granules, elixirs, lozenges, suppositories, injections (including injection solutions, sterile powders for injection and concentrated solutions for injection), inhalants, sprays, Aerosol, etc. Preferred dosage forms depend on the intended mode of administration and therapeutic use. A preferred dosage form is an injection. Such injections can be sterile injection solutions. For example, sterile injection solutions can be prepared by the following method: in an appropriate solvent, the antibody of the present invention or its antigen-binding fragment is mixed with the necessary dose, and optionally, other desired ingredients (including but not limited to, pH regulator, surfactant, adjuvant, ionic strength enhancer, isotonic agent, preservative, diluent, or any combination thereof) are mixed at the same time, followed by filtration sterilization. In addition, sterile injection solutions can be prepared as sterile lyophilized powders (e.g., by vacuum drying or freeze drying) for storage and use. Such sterile lyophilized powders can be dispersed in a suitable carrier before use. In certain exemplary embodiments, the pharmaceutically acceptable carrier and / or excipient comprises a sterile injectable liquid (e.g., an aqueous or non-aqueous suspension or solution). In certain exemplary embodiments, such sterile injectable liquid is selected from water for injection (WFI), bacteriostatic water for injection (BWFI), sodium chloride solution (e.g., 0.9% (w / v) NaCl), glucose solution (e.g., 5% glucose), a solution containing a surfactant (e.g., 0.01% polysorbate 20), a pH buffer solution (e.g., phosphate buffer solution), Ringer's solution, and any combination thereof. The pharmaceutical compositions of the invention may include a "therapeutically effective amount" or a "prophylactically effective amount" of the Nanobodies or antigen-binding fragments thereof, isolated nucleic acid molecules, vectors, host cells, bispecific or multispecific antibodies, or conjugates described herein. A "prophylactically effective amount" refers to an amount sufficient to prevent, prevent, or delay the onset of a disease. A "therapeutically effective amount" refers to an amount sufficient to cure or at least partially prevent the disease and its complications in a patient already suffering from the disease. The therapeutically effective amount may vary depending on the severity of the disease to be treated, the overall state of the patient's own immune system, the patient's general condition such as age, weight and sex, the mode of administration of the drug, and other treatments administered simultaneously, etc. Pharmaceutical use In another aspect, the invention also provides the use of the Nanobodies or antigen-binding fragments thereof, polypeptide constructs, isolated nucleic acid molecules, vectors, host cells, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the invention for the preparation of a medicament for preventing and / or treating a tumor in a subject. In certain embodiments, the tumor is a c-MET positive tumor. Herein, c-MET positivity can be obtained by immunohistochemistry and staining intensity evaluation. In certain embodiments, the tumor is a tumor in which the c-MET pathway is abnormally activated. In certain embodiments, the tumor is selected from a solid tumor, such as gastric cancer, lung cancer (such as non-small cell lung cancer), liver cancer, head and neck cancer, skin cancer, colorectal cancer, ovarian cancer, esophageal cancer, pancreatic cancer, cervical cancer, mesothelioma, breast cancer, colorectal cancer or oral squamous cell carcinoma. In certain embodiments, the subject is a mammal, such as a human. In certain embodiments, the Nanobody or antigen-binding fragment thereof, polypeptide construct, isolated nucleic acid molecule, vector, host cell, bispecific or multispecific antibody, conjugate or pharmaceutical composition is used alone or in combination with another pharmaceutically active agent (e.g., an anti-tumor agent). Methods for preventing and / or treating tumors In another aspect, the invention also provides a method for preventing and / or treating a tumor in a subject, comprising: administering to a subject in need thereof an effective amount of a Nanobody or antigen-binding fragment thereof, a polypeptide construct, an isolated nucleic acid molecule, a vector, a host cell, a bispecific or multispecific antibody, a conjugate or a pharmaceutical composition of the invention. In certain embodiments, the tumor is a c-MET positive tumor. In certain embodiments, the tumor is a tumor in which the c-MET pathway is abnormally activated. In certain embodiments, the tumor is selected from a solid tumor, such as gastric cancer, lung cancer (such as non-small cell lung cancer), liver cancer, head and neck cancer, skin cancer, colorectal cancer, ovarian cancer, esophageal cancer, pancreatic cancer, cervical cancer, mesothelioma, breast cancer, colorectal cancer or oral squamous cell carcinoma. In certain embodiments, the subject is a mammal, such as a human. The nanobodies or antigen-binding fragments thereof, polypeptide constructs, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the present invention can be formulated into any dosage form known in the medical field, for example, tablets, pills, suspensions, emulsions, solutions, gels, capsules, powders, granules, elixirs, lozenges, suppositories, injections (including injections, sterile powders for injection and concentrated solutions for injection), inhalants, sprays, etc. The preferred dosage form depends on the intended mode of administration and therapeutic use. The nanobodies or antigen-binding fragments thereof, polypeptide constructs, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the present invention should be sterile and stable under production and storage conditions. A preferred dosage form is an injection. Such injections can be sterile injection solutions. For example, a sterile injectable solution can be prepared by the following method: incorporating the necessary dose of the nanobody or antigen-binding fragment thereof, polypeptide construct, bispecific or multispecific antibody, conjugate or pharmaceutical composition of the invention in an appropriate solvent, and optionally, simultaneously incorporating other desired ingredients (including but not limited to, pH adjusters, surfactants, adjuvants, ionic strength enhancers, isotonic agents, preservatives, diluents, or any combination thereof), followed by filtration sterilization. In addition, a sterile injectable solution can be prepared as a sterile lyophilized powder (e.g., by vacuum drying or freeze drying) for ease of storage and use. Such sterile lyophilized powders can be dispersed in a suitable carrier before use, such as water for injection (WFI), bacteriostatic water for injection (BWFI), sodium chloride solution (e.g., 0.9% (w / v) NaCl), glucose solution (e.g., 5% glucose), a solution containing a surfactant (e.g., 0.01% polysorbate 20), a pH buffer solution (e.g., phosphate buffer solution), Ringer's solution, and any combination thereof. Nanobodies or antigen-binding fragments thereof, polypeptide constructs, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the invention can be administered by any suitable method known in the art, including but not limited to, oral, buccal, sublingual, ocular, topical, parenteral, rectal, intrathecal, intracytoplasmic, inguinal, intravesical, topical (e.g., powders, ointments or drops), or nasal routes. However, for many therapeutic uses, the preferred route / mode of administration is parenteral administration (e.g., intravenous or bolus, subcutaneous, intraperitoneal, intramuscular). The skilled person will appreciate that the route and / or mode of administration will vary depending on the intended purpose. In certain embodiments, Nanobodies or antigen-binding fragments thereof, polypeptide constructs, bispecific or multispecific antibodies, conjugates or pharmaceutical compositions of the invention are administered by intravenous or bolus injection. Detection Application Reagent test kit In another aspect, the invention also provides a kit comprising a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention. In certain embodiments, the kit comprises a conjugate comprising a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention and a detectable label linked to the Nanobody or antigen-binding fragment thereof or polypeptide construct, such as an enzyme (e.g. horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (e.g. acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (e.g. fluorescein or a fluorescent protein), a radionuclide or biotin. In certain embodiments, the kit comprises a Nanobody or an antigen-binding fragment thereof of the invention or a polypeptide construct of the invention, and a second antibody that specifically recognizes the Nanobody or its antigen-binding fragment or polypeptide construct; optionally, the second antibody further comprises a detectable label, such as an enzyme (e.g. horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (e.g. acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (e.g. fluorescein or fluorescent protein), a radionuclide or biotin. Detection Methods In another aspect, the present invention also provides a method for detecting the presence or level of c-MET in a sample, comprising using a nanobody or antigen-binding fragment thereof of the present invention or a polypeptide construct of the present invention. In certain embodiments, the method is used for therapeutic purposes, diagnostic purposes, or non-therapeutic non-diagnostic purposes. In certain embodiments, the method is an immunological assay, such as an immunoblot, an enzyme immunoassay (eg, ELISA), a chemiluminescent immunoassay, a fluorescent immunoassay, or a radioimmunoassay. In certain embodiments, the method comprises the use of a conjugate comprising a Nanobody of the invention Or an antigen-binding fragment thereof or a polypeptide construct of the invention, and a detectable label linked to the Nanobody or its antigen-binding fragment or polypeptide construct, such as an enzyme (such as horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (such as acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (such as fluorescein or a fluorescent protein), a radionuclide or biotin. In certain embodiments, the method comprises the use of a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention, and the method further comprises detecting the Nanobody or antigen-binding fragment thereof or polypeptide construct using a second antibody carrying a detectable label (e.g. an enzyme (e.g. horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (e.g. acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (e.g. fluorescein or fluorescent protein), a radionuclide or biotin). In certain embodiments, the method comprises: (1) contacting the sample with a Nanobody or antigen-binding fragment thereof of the invention, a polypeptide construct of the invention, or a conjugate comprising a Nanobody or antigen-binding fragment thereof of the invention or a polypeptide construct of the invention, and a detectable label linked to the Nanobody or antigen-binding fragment thereof or polypeptide construct, such as an enzyme (e.g., horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (e.g., acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (e.g., fluorescein or fluorescent protein), a radionuclide or biotin; (2) detecting the formation of an antigen-antibody immune complex or detecting the amount of the immune complex. The formation of the immune complex indicates the presence of c-MET or cells expressing c-MET. In certain embodiments, the method is used to detect whether a tumor can be treated by an anti-tumor therapy targeting c-MET. In such embodiments, the sample is from a subject who has a tumor, is suspected of having a tumor, or is at risk of having a tumor. In certain embodiments, the sample is a cell sample (e.g., a sample comprising tumor cells) or a body fluid sample (e.g., blood) from a subject (e.g., a mammal, such as a human). In certain embodiments, when c-MET or cells expressing c-MET are present, and / or compared to a reference level (e.g., compared to a patient without a tumor disease), the amount of c-MET or cells expressing c-MET increases, indicating that the subject is suitable for anti-tumor therapy targeting c-MET. Preparation and use of detection reagents In another aspect, the present invention also provides the use of the Nanobodies or antigen-binding fragments thereof of the present invention or the polypeptide constructs of the present invention in the preparation of a detection reagent for detecting the presence or level of c-MET in a sample or for detecting whether a tumor can be treated by an anti-tumor therapy targeting c-MET. In certain embodiments, the detection agent detects the presence or level of c-MET in a sample by the method of the present invention as described above and optionally detects whether a tumor can be treated by an anti-tumor therapy targeting c-MET. In certain embodiments, the sample is a cell sample (eg, a human) from a subject (eg, a mammal). Such as samples containing tumor cells) or body fluid samples (such as blood). Definition of terms In the present invention, unless otherwise specified, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. In addition, the cell culture, molecular biology, biochemistry, nucleic acid chemistry, immunology and other operating steps used herein are conventional steps widely used in the corresponding fields. At the same time, in order to better understand the present invention, the definitions and explanations of the relevant terms are provided below. As used herein, the term "cellular-mesenchymal epithelial transition factor (c-MET)" refers to a transmembrane receptor with autonomous phosphorylation activity encoded by the MET gene, which belongs to the tyrosine kinase receptor superfamily, and its sequence is well known to those skilled in the art (see, for example, NCBI GENBANK database accession number: AAI30421.1). c-MET can bind to hepatocyte growth factor (HGF) and activate multiple important downstream signaling pathways such as PI3K-Akt, Ras-MAPK, and STAT-INK. When the c-MET pathway is normally expressed, it promotes tissue differentiation and repair, and when it is abnormally regulated, it promotes the proliferation and metastasis of tumor cells. As used herein, the term "abnormal activation of the c-MET pathway" has a meaning known to those skilled in the art, including MET14 exon skipping mutation, MET amplification and / or MET protein overexpression. Abnormal activation of the c-MET pathway occurs in many types of solid tumors, including but not limited to gastric cancer, lung cancer, liver cancer, head and neck cancer, skin cancer, colorectal cancer, ovarian cancer, esophageal cancer, pancreatic cancer, cervical cancer, mesothelioma, breast cancer, colorectal cancer and oral squamous cell carcinoma. As used herein, the term "camel-derived antibody" refers to an antibody against an antigen produced by Camelidae animals (including camels, alpacas and llamas) after immunization or antigen invasion. It is known to those skilled in the art that there are "heavy chain antibodies" (HCAb) lacking light chains in the antibodies produced by Camelidae animals. This antibody contains only one variable domain of heavy chain of HCAb (VHH) and two conventional CH2 and CH3 regions, and the VHH region cloned and expressed separately has good structural stability and antigen binding activity. VHH is the smallest unit known to bind to the target antigen. As used herein, the term "nanobody" has a meaning generally understood by those skilled in the art, and refers to an antibody fragment consisting of a single monomeric variable antibody domain (e.g., a single heavy chain variable region), usually derived from the variable region of a heavy chain antibody (e.g., a camelid antibody or a shark antibody). Typically, a nanobody consists of four framework regions and three complementarity determining regions, with a structure of FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4. A nanobody may be truncated at the N-terminus or C-terminus to It can contain only part of FR1 and / or FR4, or lack one or two of those framework regions, as long as it substantially maintains antigen binding and specificity. Nanobodies are also called single-domain antibodies (sdAb), and the two can be used interchangeably. As used herein, the term "antigen-binding fragment" of a nanobody refers to a polypeptide comprising a fragment of a nanobody that retains the ability to specifically bind to the same antigen to which the nanobody binds, and / or competes with the nanobody for specific binding to the antigen, which is also referred to as an "antigen-binding portion". See generally, Fundamental Immunology, Ch.7 (Paul, W., ed., 2nd edition, Raven Press, NY (1989)), which is incorporated herein by reference in its entirety for all purposes. Antigen-binding fragments of the antibodies of the invention may be produced by recombinant DNA technology or by enzymatic or chemical cleavage of the nanobodies of the invention. In some embodiments, the "antigen-binding fragment" of the nanobody may be truncated at the N-terminus or C-terminus compared to the full-length nanobody so that it contains only part of FR1 and / or FR4, or lacks one or two of those framework regions, as long as it substantially retains antigen binding and specificity. Antigen-binding fragments of Nanobodies can be obtained from a given Nanobody (e.g., the Nanobodies provided herein) using conventional techniques known to those skilled in the art (e.g., recombinant DNA techniques or enzymatic or chemical cleavage methods), and antigen-binding fragments of Nanobodies can be screened for specificity in the same manner as for intact Nanobodies. In this document, unless the context clearly indicates otherwise, when referring to the term "Nanobody", it includes not only complete Nanobodies but also antigen-binding fragments of Nanobodies. As used herein, the term "complementarity determining region" or "CDR" refers to the amino acid residues in the variable region of an antibody that are responsible for antigen binding. In nanobodies, there are three CDRs, named CDR1, CDR2 and CDR3. The precise boundaries of these CDRs can be defined according to various numbering systems known in the art, for example, according to the IMGT numbering system (Lefranc et al., Dev. Comparat. Immunol. 27: 55-77, 2003), the Kabat numbering system (Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md., 1991), or the Chothia numbering system (Chothia & Lesk (1987) J. Mol. Biol. 196: 901-917; Chothia et al. (1989) Nature 342: 878-883). For a given Nanobody, a person skilled in the art will easily identify the CDRs defined by each numbering system. Moreover, the correspondence between different numbering systems is well known to those skilled in the art (for example, see Lefranc et al., Dev. Comparat. Immunol. 27: 55-77, 2003). In the present invention, the CDRs contained in the Nanobodies or antigen-binding fragments thereof of the invention can be determined according to various numbering systems known in the art. In certain embodiments, the CDRs contained in the Nanobodies or antigen-binding fragments thereof of the invention are preferably determined by the IMGT, Kabat, or Chothia numbering systems. As used herein, the term "framework region" or "FR" residues refers to those amino acid residues in the variable region of an antibody other than the CDR residues as defined above. As used herein, the term "Fc domain" or "Fc region" means a portion of the heavy chain constant region comprising CH2 and CH3. The Fc fragment of an antibody has a variety of different functions, but does not participate in the binding of an antigen. The "effector functions" mediated by the Fc region include Fc receptor binding; Clq binding and complement dependent cytotoxicity (CDC); antibody-dependent cell-mediated cytotoxicity (ADCC); phagocytosis; downregulation of cell surface receptors (e.g., B cell receptors); and B cell activation, etc. In some embodiments, the Fc region comprises a hinge, CH2, and CH3. When the Fc region comprises a hinge, the hinge regulates the dimerization between two Fc-containing polypeptides. The Fc region can be any antibody heavy chain constant region isotype, such as IgG1, IgG2, IgG3, or IgG4. The Fc domain may include both a native Fc region and a variant Fc region. A native Fc region comprises an amino acid sequence that is consistent with the amino acid sequence of an Fc region found in nature, for example, a native sequence human Fc region includes a native sequence human IgG1 Fc region (non-A and A allotypes); a native sequence human IgG2 Fc region; a native sequence human IgG3 Fc region; and a native sequence human IgG4 Fc region, as well as naturally occurring variants thereof. A variant Fc region comprises an amino acid sequence that differs from the amino acid sequence of a native sequence Fc region due to at least one amino acid modification. In some embodiments, a variant Fc region may have an effector function that is altered compared to a native Fc region (e.g., Fc receptor binding, antibody glycosylation, the number of cysteine ​​residues, effector cell function, or complement function). As used herein, the term "humanized antibody" refers to a non-human antibody that has been genetically engineered, and its amino acid sequence has been modified to improve the homology with the sequence of a human antibody. Generally speaking, all or part of the CDR region of a humanized antibody comes from a non-human antibody (donor antibody), and all or part of the non-CDR region (e.g., variable region FR and / or constant region) comes from a human immunoglobulin (receptor antibody). In certain embodiments, the CDR region of a humanized antibody comes from a non-human antibody (donor antibody), and all or part of the non-CDR region (e.g., variable region FR and / or constant region) comes from a human immunoglobulin (receptor antibody). Humanized antibodies generally retain the expected properties of donor antibodies, including but not limited to, antigen specificity, affinity, reactivity, etc. In the present application, the donor antibody can be a camel-derived antibody with expected properties (e.g., antigen specificity, affinity, reactivity, etc.). To prepare a humanized antibody, the CDR region of an immune animal can be inserted into a human framework sequence using methods known in the art. In the context of nanobodies, humanized antibodies may refer to humanized VHHs, i.e., VHHs in which one or more framework regions have been substantially replaced by human framework regions. In some cases, certain framework regions (FRs) of human immunoglobulins are replaced by corresponding non-human residues. In addition, humanized VHHs may include residues that are not found in the original VHH or human framework sequences, but are included to further improve and optimize the performance of VHH or VHH-containing polypeptides. As used herein, the term "specific binding" refers to a non-random binding reaction between two molecules, such as an antibody and its antigen. The strength or affinity of a specific binding interaction can be measured by the equilibrium dissociation constant (K) of the interaction. D In the present invention, the term "K D ” refers to the dissociation equilibrium constant of a specific antibody-antigen interaction, which is used to describe the binding affinity between the antibody and the antigen. The smaller the equilibrium dissociation constant, the tighter the antibody-antigen binding and the higher the affinity between the antibody and the antigen. The specific binding properties between two molecules can be determined using methods known in the art. One method involves measuring the speed of formation and dissociation of the antigen binding site / antigen complex. Both the "association rate constant" (ka or kon) and the "dissociation rate constant" (kdis or koff) can be calculated from the concentration and the actual rate of association and dissociation (see Malmqvist M, Nature, 1993, 361: 186-187). The ratio of kdis / kon is equal to the dissociation constant K D (See Davies et al., Annual Rev Biochem, 1990; 59: 439-473). K can be measured by any effective method. D, kon and kdis values, for example, using surface plasmon resonance (SPR) to measure the dissociation constant in Biacore or using bioluminescence interferometry or Kinexa to measure the dissociation constant. As used herein, the term "vector" refers to a nucleic acid delivery vehicle into which a polynucleotide can be inserted. When a vector can express the protein encoded by the inserted polynucleotide, the vector is called an expression vector. The vector can be introduced into a host cell by transformation, transduction or transfection, so that the genetic material elements it carries are expressed in the host cell. Vectors are well known to those skilled in the art, and include but are not limited to: plasmids; phagemids; cosmids; artificial chromosomes, such as yeast artificial chromosomes (YAC), bacterial artificial chromosomes (BAC) or P1-derived artificial chromosomes (PAC); bacteriophages such as lambda phage or M13 phage and animal viruses, etc. Animal viruses that can be used as vectors include but are not limited to retroviruses (including lentiviruses), adenoviruses, adeno-associated viruses, herpes viruses (such as herpes simplex virus), poxviruses, baculoviruses, papillomaviruses, papillomaviruses (such as SV40). A vector can contain a variety of elements that control expression, including but not limited to promoter sequences, transcription initiation sequences, enhancer sequences, selection elements and reporter genes. In addition, the vector may also contain a replication initiation site. As used herein, the term "host cell" refers to a cell that can be used to introduce a vector, including but not limited to prokaryotic cells such as Escherichia coli or Bacillus subtilis, fungal cells such as yeast cells or Aspergillus, insect cells such as S2 Drosophila cells or Sf9, or animal cells such as fibroblasts, CHO cells, COS cells, NSO cells, HeLa cells, BHK cells, HEK 293 cells or human cells. As used herein, the term "identity" is used to refer to the matching of sequences between two polypeptides or between two nucleic acids. When a position in the two sequences being compared is occupied by the same base or amino acid monomer subunit (e.g., a position in each of the two DNA molecules is occupied by adenine, or a position in each of the two polypeptides is occupied by lysine), then the molecules are identical at that position. The "percent identity" is a function of the number of matching positions shared by the two sequences divided by the number of positions compared x 100. For example, if 6 out of 10 positions of the two sequences match, then the two sequences have 60% identity. For example, the DNA sequences CTGACT and CAGGTT share 50% identity (3 out of a total of 6 positions match). Typically, two sequences are compared when they are aligned to produce maximum identity. Such an alignment can be achieved using, for example, the method of Needleman et al. (1970) J. Mol. Biol. 48: 443-453, which can be conveniently performed by a computer program such as the Align program (DNAstar, Inc.). The percent identity between two amino acid sequences can also be determined using the algorithm of E. Meyers and W. Miller (Comput. Appl Biosci., 4: 11-17 (1988)), which has been incorporated into the ALIGN program (version 2.0), using a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4. In addition, the percent identity between two amino acid sequences can be determined using the Needleman and Wunsch (J MoI Biol. 48: 444-453 (1970)) algorithm, which has been incorporated into the GAP program in the GCG software package (available at www.gcg.com), using a Blossum 62 matrix or a PAM250 matrix and a gap weight of 16, 14, 12, 10, 8, 6, or 4 and a length weight of 1, 2, 3, 4, 5, or 6. As used herein, the term "conservative substitution" means an amino acid substitution that does not adversely affect or change the expected properties of the protein / polypeptide comprising the amino acid sequence. For example, conservative substitutions can be introduced by standard techniques known in the art such as site-directed mutagenesis and PCR-mediated mutagenesis. Conservative amino acid substitutions include substitutions of amino acid residues with amino acid residues having similar side chains, such as substitutions with residues physically or functionally similar to the corresponding amino acid residues (e.g., having similar size, shape, charge, chemical properties, including the ability to form covalent bonds or hydrogen bonds, etc.). Families of amino acid residues with similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine and histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Thus, it is preferred to replace a corresponding amino acid residue with another amino acid residue from the same side chain family. In addition, amino acid residues can also be divided into categories defined by optional physical and functional properties. For example, alcohol-containing residues (S and T), aliphatic residues (I, L, V, and M), cycloalkenyl-related residues (F, H, W, and Y), hydrophobic residues (A, C, F, G, H, I, L, M, R, T, V, W, and Y), negatively charged residues (D and E), polar residues (C, D, E, H, K, N, Q, R, S, and T), positively charged residues (H, K, and R), small residues (A, C, D, G, N, P, S, T, and V), very small residues (A, G, and S), residues involved in turn formation (A, C, D, E, The methods for identifying conservative amino acid substitutions are well known in the art (see, e.g., Brummell et al., Biochem. 32: 1180-1187 (1993); Kobayashi et al., Protein Eng. 12(10): 879-884 (1999); and Burks et al., Proc. Natl Acad. Set USA 94: 412-417 (1997), which are incorporated herein by reference). The compilation of the twenty conventional amino acids involved in this article follows conventional usage. See, for example, Immunology-A Synthesis (2nd Edition, ES Golub and DR Gren, Eds., Sinauer Associates, Sunderland, Mass. (1991)), which is incorporated herein by reference. In the present invention, the terms "polypeptide" and "protein" have the same meaning and are used interchangeably. And in the present invention, amino acids are generally represented by single-letter and three-letter abbreviations known in the art. For example, alanine can be represented by A or Ala. As used herein, the term "pharmaceutically acceptable carrier and / or excipient" refers to a carrier and / or excipient that is pharmacologically and / or physiologically compatible with the subject and the active ingredient, which is well known in the art (see, e.g., Remington's Pharmaceutical Sciences. Edited by Gennaro AR, 19th ed. Pennsylvania: Mack Publishing Company, 1995), and includes, but is not limited to, pH regulators, surfactants, adjuvants, ionic strength enhancers, diluents, agents that maintain osmotic pressure, agents that delay absorption, preservatives. For example, pH regulators include, but are not limited to, phosphate buffers. Surfactants include, but are not limited to, cationic, anionic or nonionic surfactants, such as Tween-80. Ionic strength enhancers include, but are not limited to, sodium chloride. Preservatives include, but are not limited to, various antibacterial and antifungal agents, such as parabens, chlorobutanol, phenol, sorbic acid, and the like. Agents that maintain osmotic pressure include, but are not limited to, sugars, NaCl, and the like. Agents that delay absorption include, but are not limited to, monostearate and gelatin. Diluents include, but are not limited to, water, aqueous buffers (such as buffered saline), alcohols and polyols (such as glycerol), etc. Stabilizers have the meanings commonly understood by those skilled in the art, which can stabilize the desired activity of the active ingredient in the drug, including but not limited to sodium glutamate, gelatin, SPGA, sugars (such as sorbitol, mannitol, starch, sucrose, lactose, dextran, or glucose), amino acids (such as glutamic acid, glycine), proteins (such as dry whey, albumin or casein) or their degradation products (such as lactalbumin hydrolysate), etc. In certain exemplary embodiments, the pharmaceutically acceptable carrier or excipient includes a sterile injectable liquid (such as an aqueous or non-aqueous suspension or solution). In certain exemplary embodiments, such sterile injectable liquids are selected from water for injection (WFI), bacteriostatic water for injection (BWFI), sodium chloride solution (such as 0.9% (w / v) NaCl), glucose solution (such as 5% glucose), a solution containing a surfactant (such as 0.01% polysorbate 20), a pH buffer solution (such as a phosphate buffer solution), Ringer's solution, and any combination thereof. As used herein, the term "prevention" refers to a method performed to prevent or delay the occurrence of a disease or condition or symptom (e.g., a tumor) in a subject. As used herein, the term "treatment" refers to a method performed to obtain A method for achieving a beneficial or desired clinical outcome. For purposes of the present invention, a beneficial or desired clinical outcome includes, but is not limited to, alleviating symptoms, reducing the extent of the disease, stabilizing (i.e., not worsening) the state of the disease, delaying or slowing the progression of the disease, improving or alleviating the state of the disease, and relieving symptoms (whether partial or complete), whether detectable or undetectable. In addition, "treating" may also refer to prolonging survival compared to the expected survival if not receiving treatment. As used herein, the term "subject" refers to a mammal, such as a human, monkey, or mouse. In certain embodiments, the subject (e.g., a human, monkey, or mouse) suffers from a disease associated with c-MET (e.g., involving a c-MET-positive tumor), or has a risk of suffering from the above-mentioned disease. As used herein, the term "effective amount" refers to an amount sufficient to obtain or at least partially obtain the desired effect. For example, an effective amount for preventing a disease (e.g., involving a c-MET-positive tumor) refers to an amount sufficient to prevent, stop, or delay the occurrence of the disease; an effective amount for treating a disease refers to an amount sufficient to cure or at least partially stop the disease and its complications in a patient already suffering from the disease. Determining such an effective amount is well within the capabilities of those skilled in the art. For example, an effective amount for therapeutic use will depend on the severity of the disease to be treated, the overall state of the patient's own immune system, the patient's general condition such as age, weight and sex, the mode of administration of the drug, and other treatments administered simultaneously, etc. As used herein, the term "antibody-mediated endocytosis" refers to a phenomenon in which an antibody passes through a cell membrane after binding to a cell surface antigen. As used herein, the terms "cancer" and "tumor" are used interchangeably and refer to a broad class of diseases characterized by the uncontrolled growth of abnormal cells in the body. Unregulated cell division may lead to the formation of malignant tumors or cells that invade adjacent tissues and may metastasize to distant parts of the body via the lymphatic system or bloodstream. Cancer includes benign and malignant cancers as well as dormant tumors or micrometastases. Cancer also includes hematological malignancies. Advantageous Effects of the Invention The nano antibodies of the present invention can specifically recognize c-MET, and have good endocytic activity and endocytic-mediated cell killing activity, and have good potential for the treatment of tumors (especially tumors expressing c-MET). In addition, the humanized nano antibodies of the present invention not only retain the functions and properties of the parent antibody, but also have a high degree of humanization, so that they can be safely administered to human subjects without inducing immunogenic reactions. In addition, the molecular weight of the nano antibodies of the present invention is only half of that of conventional antibodies, and can penetrate into the core part of the tumor, maximizing the chance of antibody drugs binding to tumor cells, and producing better tumor treatment effects. In summary, the nano antibodies of the present invention have important clinical value. Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings and examples, but it will be appreciated by those skilled in the art that the following drawings and examples are only used to illustrate the present invention, rather than to limit the scope of the present invention. According to the following detailed description of the accompanying drawings and preferred embodiments, various objects and advantages of the present invention will become practicable to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: ELISA results of the binding of candidate antibodies to human c-MET antigen. FIG. 2 : FACS assay results of the binding of candidate antibodies to human c-MET antigen. Figures 3A-3B: Results of endocytic activity detection of candidate antibodies using human gastric cancer cell Hs746T endogenously expressing human c-MET. Figure 3A is the curve of endocytic percentage at different time periods; Figure 3B is the result of endocytic activity at 37°C for 4 hours. FIG. 4 : Antibody internalization-mediated cell killing assay based on the Fab-ZAP method for candidate antibodies. FIG. 5 : FACS assay results of the binding of MHAB07-3 and its humanized antibodies to human c-MET antigen. FIG6 : FACS assay results of the binding of MHAB07-3, its humanized antibody and positive control antibody to human c-MET antigen. Figures 7A-7B: MHAB07-3 and its humanized antibodies were used to detect the endocytic activity of human gastric cancer cells Hs746T endogenously expressing human c-MET. Figure 7A is the endocytic percentage curve at each time period; Figure 7B is the endocytic result at 37°C for 4 hours. FIG8 : Antibody internalization-mediated cell killing experiment of MHAB07-3 and its humanized antibody based on Fab-ZAP method. FIG. 9 : Detection results of the binding ability of MHAB07-3-2 to c-MET antigens of different species (human, monkey, mouse and rat). Sequence information Table 1: The information of the sequences involved in the present invention is described in the table below: DETAILED DESCRIPTION The invention is now described in the following non-limiting examples. Those skilled in the art will appreciate that the embodiments describe the present invention by way of example and are not intended to limit the scope of protection claimed in the present application. The experimental methods in the embodiments are conventional methods unless otherwise specified. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially. Example 1: Acquisition of anti-human c-MET nanobody sequences 1-1. Screening and identification of specific nanoantibodies Peripheral blood was collected from the immune alpacas, RNA was extracted, and cDNA samples were prepared. VHH antibody encoding genes were cloned by PCR to construct a single-domain antibody phage display library. Clones were randomly selected to identify the library capacity and diversity. After panning and enrichment experiments were performed on the single-domain antibody phage display library using c-MET antigen (ACRO, Cat. MET-H5227), single clones were selected for Phage-ELISA testing after screening, and candidate clones with different amino acid sequences in the CDR region were selected, and finally 43 unique sequences were selected. 1-2. Unique sequence solubility verification and antibody expression The plasmids of the above 43 positive clones were extracted and transferred into E.coli Rosetta, 0.4mM IPTG, 20℃200rpm to induce expression overnight. The next day, centrifugation was performed, the precipitate was resuspended in PBS, ultrasonically broken, and centrifuged to obtain the supernatant of the 43 clones. ELISA was used to detect the binding activity of the supernatant of the 43 clones with human c-MET antigen (OD450 is shown in Table 2 below). Some clones showed negative results (it may be a false negative caused by the inability of the VHH secondary antibody to recognize, which needs to be verified, so these unique sequences are not directly eliminated in this screening step). Table 2: Binding activity of 43 clones to human c-MET antigen A unique sequence with strong binding activity to human c-MET, no cysteine ​​residues (C) in the CDR3 region, and a theoretical PI value of >7 was selected, and the VHH sequence was integrated into the Fc (LALA) sequence of human IgG1 (SEQ ID NO: 16). Shanghai Baiying Biotechnology Co., Ltd. was commissioned to perform CHO transient expression services to produce 18 MHB07 candidate antibodies (as shown in Table 3). After expression, the antibodies were purified by Protein A and dissolved in PBS. The purity of the antibody solution (SEC, 280nm) was >95%, and the endotoxin (EU / mg) was <1. After aliquoting, it was stored at -80°C. Table 3: MHB07 candidate antibodies Example 2: Antibody purification and activity detection 2-1.ELISA binding assay The binding ability of the MHB07 candidate antibody (anti-human c-MET nanobody) to the human c-MET antigen was detected by ELISA. Human c-MET, His Tag (Sino Biological, Cat. No. 10692-H08H) was diluted to 0.5 μg / mL with PBS, added to an ELISA plate (Corning, Cat. No. 9018) at 100 μL / well, and coated overnight at 4°C. Rinse 3 times with PBST, add 200μL 3% BSA / PBST to each well, block at room temperature for 1 hour, then rinse 5 times with PBST, add the antibody to be tested (the antibody number to be tested is MHAB07-01~14 / 16 / 17, the positive control antibody is MHB07-PC (Telisotuzumab), the initial concentration is 10μg / mL, and a 4-fold gradient dilution is performed), incubate at room temperature for 1 hour, rinse 7 times with PBST, wash away the unbound antibody, add 100μL 1:50,000 dilution of goat anti-human IgG Fc (HRP) (Abcam, Cat. No. ab97225) to each well, and incubate at room temperature for 30 minutes. Rinse 7 times with PBST to wash away the excess secondary antibody, and add 100μL 1-Step TM Ultra TMB-ELISA Substrate Solution (Absin, Cat. No. 9178) was used for color development at room temperature in the dark for 15 min, and then 100 μL of TMB stop solution (Absin, Cat. No. abs9472) was added to each well to terminate the reaction. The absorbance at a wavelength of 450 nm was read using an ELISA reader, and a four-parameter curve was drawn using Graphpad. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The results are shown in FIG. 1 and Table 4. The 10 antibodies with the strongest binding activity to human c-MET antigen among the MHB07 candidate antibodies are: MHAB07-01 to 11. These 11 sequences will be subsequently tested for binding activity by FACS. Table 4: ELISA binding assay of MHB07 candidate antibodies 2-2. FACS binding experiment In the FACS experiment, human gastric cancer cells Hs746T cells endogenously expressing human c-MET (cultured in Hs746T complete cell culture medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)) were used to detect the binding of the candidate antibodies. The starting concentration of the candidate antibodies was 30 μg / mL, and a 3-fold gradient dilution (30000 ng / mL, 10000 ng / mL, 3333.33ng / mL, 1111.11ng / mL, 370.37ng / mL, 123.46ng / mL, 41.15ng / mL and 13.72ng / mL), 100μL / well FITC anti-human IgG Fc antibody secondary antibody (1:200Biolegend, Cat.No.410720) was added to detect the binding of the test antibody, and the FITC fluorescence intensity (Mean Fluorescence Intensity, MFI) was detected by flow cytometry. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The FACS binding results are shown in Figure 2 and Table 5. The binding activity of MHAB07-01 / 02 / 03 / 04 / 05 to Hs746T is stronger than that of MHB07-PC. These five antibodies will be subsequently tested for endocytosis and endocytosis-mediated cell killing activity. Table 5: FACS binding experiment of MHB07 candidate antibodies 2-3. Endocytosis Experiment The endocytic activity of the selected antibodies was detected using human gastric cancer cells Hs746T cells endogenously expressing human c-MET (cultured in Hs746T complete cell culture medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)). 1×10 6 / mL cell suspension and 10μg / mL anti-c-MET test antibody solution, add the cell suspension to a 15mL EP tube, centrifuge at 1200rpm, 4℃ for 3min, and discard the supernatant. Pipette 2mL of the test antibody solution and add it to the cells, incubate on ice for 30min after resuspending, and then wash 3 times with pre-cooled FACS buffer. Resuspend the cells with 2mL DMEM complete medium, mix well and add the cells to a 96-well plate, 100μL / well. Incubate at 4℃ and 37℃ for 0h, 1h, 2h and 4h (double wells). After each time period of incubation, centrifuge at 1200 rpm and 4°C for 3 min, add 100 μL of FITC anti-human IgG Fc antibody dilution (1:200, Biolegend, Cat. no. 410720) to each well, incubate at 4°C in the dark for 30 min, wash off the unbound secondary antibody, and use flow cytometry to detect FITC fluorescence intensity (Mean Fluorescence Intensity, MFI) to calculate the endocytosis ratio. The calculation formula is as follows: Internalization(%)=100%-MFI T / MFI T0 *100% All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The endocytosis percentage curves at each time period are shown in Figure 3A , and the endocytosis results at 37°C for 4 h in Figure 3B show that MHAB07-01 / 02 / 03 / 04 / 05 has good endocytic activity in Hs746T cells. 2-4. Fab-ZAP assay to detect antibody endocytosis-mediated cell killing Human gastric cancer cell Hs746T cells (cultured in Hs746T cell complete medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)) were digested and resuspended in complete medium for counting. The cell density was adjusted to 4E4 cell / mL, and 50 μL (about 1500 cells) was added to each well of a 96-well cell plate and cultured in a 37°C, 5% CO2 cell culture incubator for 16 hours. Prepare ZAP diluent containing 9nM ZAP-Fab with DMEM complete medium, then dilute the antibody gradient to 10nM to 128fM (8 concentration gradients, 1:5 dilution) with ZAP diluent, incubate at 37℃ for 15min, add the working solution to the cell culture plate, add 50μL to each well, mix well and place the cell culture plate in a 37℃ cell culture incubator for 120hr. Add 7.5μL Triton-X100 to the cell wells not treated with antibody-Fab-ZAP in advance, incubate for 30min, and this well is used as a positive control. The cell wells (NT) not treated with antibody-Fab-ZAP or Triton-X100 are negative controls. Then add 20μL MTS (Promega, Cat: G3598B) to each well of the cell culture plate, incubate in a 37℃ cell culture incubator for 2 hours, shake for 10s in an ELISA reader and read the data, and the detection wavelength is A490. Use the formula killing rate%=100%-(OD sample -OD Triton-X100 ) / (OD NT -OD Triton-X100 )*100% to calculate the cell killing efficiency. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The endocytosis-mediated cell killing curve is shown in Figure 4. The results in Figure 4 and Table 6 show that the killing activity of the candidate antibodies of MHB07 against Hs746T is similar. Based on the FACS binding, endocytosis results and sequence humanization degree, the preferred antibody MHAB07-03 was obtained, whose VHH sequence is shown in SEQ ID NO: 1, the CDR1-CDR3 sequences defined by Kabat are shown in SEQ ID NO: 2-4, the CDR1-CDR3 sequences defined by Chothia are shown in SEQ ID NO: 5-7, and the CDR1-CDR3 sequences defined by IMGT are shown in SEQ ID NO: 8-10. MHAB07-03 will be humanized and screened in the future. Table 6: Fab-ZAP assay for detecting antibody endocytosis-mediated cell killing Example 3: Humanization and activity detection of anti-human c-MET nanobody The VHH of MHAB07-03 was humanized to obtain two humanized nanobodies MHAB07-3-1 (VHH as shown in SEQ ID NO: 14) and MHAB07-3-2 (VHH as shown in SEQ ID NO: 15). According to the method in Example 1, the above VHH sequence was integrated into the Fc (LALA) sequence of human IgG1 (SEQ ID NO: 16), and purified and expressed for subsequent activity experiments. 3-1. FACS binding experiment 3-1-1. FACS binding experiment of anti-human c-MET nanobody and its humanized antibody In the FACS experiment, human gastric cancer cells Hs746T cells endogenously expressing human c-MET (cultured in Hs746T cell complete culture medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)) was used to detect the binding activity of MHAB07-3 and its humanized antibodies. The initial concentration of the antibody to be tested was 30 μg / mL. A 2-fold gradient dilution was performed first, followed by a 5-fold gradient dilution (30000 ng / mL, 15000 ng / mL, 7500 ng / mL, 1500 ng / mL, 300 ng / mL, 60 ng / mL, 12 ng / mL, 2.4 ng / mL, 0.48 ng / mL, 0.096 ng / mL and 0.0192 ng / mL). 100 μL / well of Alexa Fluor The binding of the test antibody was detected by 488AffiniPure goat anti-human IgG (H+L) secondary antibody (1:300 Yeasen, Cat:33126ES60), and the FITC fluorescence intensity (Mean Fluorescence Intensity, MFI) was detected by flow cytometry. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The binding curve is shown in Figure 5. From the results in Figure 5 and Table 7, it can be seen that the binding activity of MHAB07-3-1 and MHAB07-3-2 with human c-MET antigen was not significantly weakened compared with parental MHAB07-3. Therefore, MHAB07-3-1 and MHAB07-3-2 were selected for subsequent endocytosis and endocytosis-mediated cell killing activity detection. Table 7: FACS binding experiment of anti-human c-MET nanobody and its humanized antibody 3-1-2. FACS binding experiment of anti-human c-MET nanobody and its humanized antibody and positive control antibody In the FACS experiment, human gastric cancer cells Hs746T cells endogenously expressing human c-MET (cultured in Hs746T cell complete culture medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)) was used to detect the binding activity of MHAB07-3 and its humanized antibody MHAB07-3-2 compared with the positive control antibody MHB07-PC (Telisotuzumab). The starting concentration of the test antibody was 30 μg / mL, and a 4-fold gradient dilution was performed (30000 ng / mL, 7500 ng / mL, 1875 ng / mL, 468.75 ng / mL, 117.19 ng / mL, 29.30 ng / mL, 7.32 ng / mL, 1.83 ng / mL, 0.46 ng / mL, 0.11 ng / mL, 0.03 ng / mL and 0.007 ng / mL), with a total of 12 dilution points, and 100 μL / well of fluorescent secondary antibody staining (PE Goat anti-Human IgG Fc Secondary The binding of the test antibody was detected by PCR, and the mean fluorescence intensity (MFI) of PE was detected by flow cytometry. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The binding curve is shown in FIG6 . It can be seen from the results in FIG6 and Table 8 that the binding activity of MHAB07-3 and MHAB07-3-2 to the human c-MET antigen on the surface of tumor cells is stronger than that of the positive control antibody MHB07-PC (Telisotuzumab). Table 8: FACS binding experiment of anti-human c-MET nanobody and its humanized antibody and positive control antibody 3-2. Endocytosis experiment Human gastric cancer cells Hs746T endogenously expressing human c-MET were used to detect the endocytic activity of the candidate antibodies. 1×10 6 / mL cell suspension and 10μg / mL anti-c-MET test antibody solution, add the cell suspension to a 15mL EP tube, centrifuge at 1200rpm, 4℃ for 3min, and discard the supernatant. Pipette 2mL of the test antibody solution and add it to the cells. After resuspending, incubate on ice for 30min, and then wash 3 times with pre-cooled FACS buffer. Resuspend the cells with 2mL DMEM complete medium, mix well and add the cells to a 96-well plate, 100μL / well. Incubate at 4℃ and 37℃ for 0h, 1h, 2h and 4h (double wells). After each time period of incubation, centrifuge at 1200rpm, 4℃ for 3min, add 100μL Alexa 488AffiniPure goat anti-human IgG (H+L) secondary antibody (YEASEN, Cat. no. 33126ES60) dilution, incubate at 4°C for 30 min, wash off the unbound secondary antibody, and use flow cytometry to detect FITC fluorescence intensity (Mean Fluorescence Intensity, MFI), calculate the internalization ratio, the calculation formula is as follows: Internalization(%)=100%-MFI T / MFI T0 *100% All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The endocytosis percentage curve is shown in Figure 7A. From the endocytosis results in Figure 7B, it can be seen that after 4 hours of endocytosis at 37°C, MHAB07-3, MHAB07-3-1 and MHAB07-3-2 have good endocytosis activity in Hs746T cells. The endocytosis activity of MHAB07-3-1 and MHAB07-3-2 is not significantly weakened compared with parental MHAB07-3, and is stronger than MHB07-PC. 3-3. Fab-ZAP assay to detect antibody endocytosis-mediated cell killing Human gastric cancer cell Hs746T cells (cultured in Hs746T cell complete medium: Dulbecco's Modified Eagle's Medium (ATCC, Cat. No. 30-2002) + 10% FBS (Sigma-Aldrich, Cat. No. F8687) + 1% P / S (Gibco, Cat. No. 15140-122)) were digested and resuspended in complete medium for counting. The cell density was adjusted to 4E4 cell / mL, and 50 μL (about 1500 cells) was added to each well of a 96-well cell plate and cultured in a 37°C, 5% CO2 cell culture incubator for 16 hours. Prepare ZAP diluent containing 9nM ZAP-Fab with DMEM complete medium, then use ZAP diluent to dilute the antibody gradient to 4nM to 32fM (10 concentration gradients, 1:5 dilution (first 5 points) and 1:2 dilution (last 5 points)). After incubation at 37℃ for 15min, add the working solution to the cell culture plate, add 50μL to each well, mix well, and place the cell culture plate in a 37℃ cell culture incubator for another 120hr. Add 7.5μL Triton-X 100 to the cell wells not treated with antibody-Fab-ZAP in advance and incubate for 30min. This well serves as a positive control. The cell wells (NT) not treated with antibody-Fab-ZAP or Triton-X100 serve as negative controls. Then, 20 μL of MTS (Promega, Cat: G3598B) was added to each well of the cell culture plate, incubated in a 37°C cell culture incubator for 2 hours, and read the data after shaking for 10 seconds in an ELISA reader. The detection wavelength was A490. The killing rate% was calculated using the formula: 100%-(OD sample -OD Triton-X100 ) / (OD NT -OD Triton-X100 )*100% to calculate the cell killing efficiency. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The endocytosis-mediated cell killing curve is shown in Figure 8, and the results are summarized in Table 9. The results showed that the Fab-ZAP killing of Hs746T cells by MHAB07-3-1 and MHAB07-3-2 was similar to that of MHAB07-3. Based on the screening of FACS binding, endocytosis results and sequence humanization degree, MHAB07-3-1 showed the highest humanization level and had good binding activity, endocytosis activity and endocytosis-mediated cell killing. Table 9: Fab-ZAP assay for detecting antibody endocytosis-mediated cell killing 3-4. Cross-species activity The ELISA method was used to detect the binding ability of MHAB07-3-2 (anti-human c-MET nanobody) to c-MET antigens of different species (human, monkey, mouse and rat). Human c-MET (Human c-MET, His Tag (Sino Biological, Cat. No. 10692-H08H)); monkey c-MET (Cynomolgus, Rhesus c-MET Protein, His Tag (Sino Biological, Cat. No. 90304-C08H)); mouse c-MET (Mouse c-MET Protein, His Tag (Sino Biological, Cat. No. 50622-M08H)) and rat c-MET (Rat c-MET Protein, hFc Tag (Sino Biological, Cat. No. 80004-R02H)) were diluted to 0.5 μg / mL with PBS, added to an ELISA plate (Corning, Cat. No. 9018) at 100 μL / well, and coated overnight at 4°C. Rinse 3 times with PBST, add 200μL 3% BSA / PBST to each well, block at room temperature for 1 hour, then rinse 5 times with PBST, add the antibody to be tested, the initial concentration is 10μg / mL, and dilute 10 times), incubate at room temperature for 1 hour, rinse 7 times with PBST, wash away the unbound antibody, add 100μL 1:50,000 dilution of goat anti-human IgG Fc (HRP) (Abcam, Cat. No. ab97225) to each well, add 100μL 1:10,000 dilution of Rabbit Anti-Camelid VHH Cocktail [HRP] (GenScript, A02016) to the wells coated with Rat c-MET Protein, and incubate at room temperature for 30 minutes. Rinse 7 times with PBST, wash away the excess secondary antibody, and add 100μL 1-Step TM Ultra TMB-ELISA Substrate Solution (Absin, Cat. No. 9178) was used for color development at room temperature in the dark for 15 min, and then 100 μL of TMB stop solution (Absin, Cat. No. abs9472) was added to each well to terminate the reaction. The absorbance at a wavelength of 450 nm was read using an ELISA reader, and a four-parameter curve was drawn using Graphpad. All experimental results are expressed as mean ± SEM (standard error of the mean), and Prism 6 (GraphPad) software was used for plotting and data analysis. The results are shown in FIG9 and Table 10 . MHAB07-3-2 only binds to human c-MET and monkey c-MET, and has comparable binding activity to human c-MET and monkey c-MET. It does not bind to mouse c-MET and rat c-MET. Table 10: Species cross-reactivity detection of human, monkey, mouse and rat c-MET antigen Although the specific embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications and changes may be made to the details according to all the teachings that have been published, and these changes are within the scope of protection of the present invention. The full scope of the present invention is given by the attached claims and any equivalents thereof. References [1] Gherardi E, Birchmeier W, Birchmeier C, Vande Woude G. Targeting MET in cancer: rationale and progress. Nat Rev Cancer. 2012; 12(2): 89-103. [2] Stoker M, Gherardi E, Perryman M, Gray J. Scatter factor is a fibroblast-derived modulator of epithelial cell mobility. Nature. 1987; 327(6119): 239-42. [3]Kong-Beltran M, Stamos J, Wickramasinghe D. The Sema domain of Met is necessary for receptor dimerization and activation. Cancer Cell. 2004; 6(1):75-84. [4]Gherardi E, Sandin S, Petoukhov MV, Finch J, Youles ME, Ofverstedt LG, et al. Structural basis of hepatocyte growth factor / scatter factor and MET signaling. Proc Natl Acad Sci US A. 2006; 103(11): 4046-51. [5]Uchikawa E,Chen Z,Xiao GY,Zhang X,Bai XC.Structural basis of the activation of c-MET receptor.Nat Commun.2021;12(1):4074. [6]Ponzetto C,Bardelli A,Zhen Z,Maina F,dalla Zonca P,Giordano S,et al.A multifunctional docking site mediates signaling and transformation by the hepatocyte growth factor / scatter factor receptor family.Cell.1994;77(2):261-71. [7]Fasolo A,Sessa C,Gianni L,Broggini M.Seminars in clinical pharmacology:an introduction to MET inhibitors for the medical oncologist.Ann Oncol.2013;24(1):14-20. [8]Trusolino L,Bertotti A,Comoglio PM.MET signalling:principles and functions in development,organ regeneration and cancer.Nat Rev Mol Cell Biol.2010;11(12):834-48. [9]Drilon A,Clark JW,Weiss J,Ou SI,Camidge DR,Solomon BJ,et al.Antitumor activity of crizotinib in lung cancers harboring a MET exon 14alteration.Nat Med.2020;26(1):47-51.

[0010] Baldacci S,Kherrouche Z,Descarpentries C,Wislez M,Dansin E,Furlan A,et al.[MET exon 14 splicing sites mutations:A new therapeutic opportunity in lung cancer].Rev Mal Respir.2018;35(8):796-812.

[0011] Tong JH,Yeung SF,Chan AW,Chung LY,Chau SL,Lung RW,et al.MET Amplification and Exon 14 Splice Site Mutation Define Unique Molecular Subgroups of Non-Small Cell Lung Carcinoma with Poor Prognosis.Clin Cancer Res.2016;22(12):3048-56.

[0012] Cappuzzo F,Marchetti A,Skokan M,Rossi E,Gajapathy S,Felicioni L,et al.Increased MET gene copy number negatively affects survival of surgically resected non-small-cell lung cancer patients.J Clin Oncol.2009;27(10):1667-74.

[0013] Comoglio PM,Trusolino L,Boccaccio C.Known and novel roles of the MET oncogene in cancer:a coherent approach to targeted therapy.Nat Rev Ca ncer.2018;18(6):341-58.

Claims

1. A nanobody or antigen-binding fragment thereof that specifically binds to c-MET, wherein: The nanobody or antigen-binding fragment thereof comprises: CDR1, CDR2 and CDR3 contained in the VHH shown in any one of SEQ ID NOs: 1, 14 and 15; Preferably, the CDRs are defined according to the Kabat, Chothia or IMGT numbering systems.

2. The Nanobody or antigen-binding fragment thereof according to claim 1, comprising: (a) CDR1 as shown in SEQ ID NO:2, CDR2 as shown in SEQ ID NO:3, and CDR3 as shown in SEQ ID NO:4, wherein: The CDRs are defined according to the Kabat numbering system; or, (b) CDR1 as shown in SEQ ID NO:5, CDR2 as shown in SEQ ID NO:6, and CDR3 as shown in SEQ ID NO:7, wherein the CDRs are defined according to the Chothia numbering system; or, (c) CDR1 as shown in SEQ ID NO:8, CDR2 as shown in SEQ ID NO:9, and CDR3 as shown in SEQ ID NO:10, wherein the CDRs are defined according to the IMGT numbering system.

3. The Nanobody or antigen-binding fragment thereof of claim 1 or 2, wherein the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 1, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or several amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto.

4. The Nanobody or antigen-binding fragment thereof of claim 1 or 2, which is humanized; Preferably, the Nanobody or antigen-binding fragment thereof further comprises a heavy chain framework region of a human immunoglobulin (for example, a heavy chain framework region contained in the amino acid sequence encoded by a human heavy chain germline antibody gene), which heavy chain framework region optionally comprises one or more (for example, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10) back mutations from human residues to camel residues.

5. The Nanobody or antigen-binding fragment thereof of claim 4, wherein the Nanobody or antigen-binding fragment thereof comprises the sequence shown in SEQ ID NO: 14 or 15, or a sequence having at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity thereto, or a sequence having one or several amino acid substitutions, deletions or additions (e.g., 1, 2, 3, 4 or 5 amino acid substitutions, deletions or additions) thereto.

6. A polypeptide construct that specifically binds to c-MET, comprising the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5, and an immunoglobulin Fc domain; Preferably, the immunoglobulin Fc domain is optionally connected to the N-terminus and / or C-terminus (e.g., C-terminus) of the Nanobody or antigen-binding fragment thereof via a peptide linker; Preferably, the immunoglobulin Fc domain is an IgG Fc domain (eg, an IgG1, IgG2, IgG3 or IgG4 Fc domain); Preferably, the immunoglobulin Fc domain comprises the sequence shown in SEQ ID NO: 16; Preferably, the polypeptide construct comprises a sequence shown in any one of SEQ ID NOs: 11-13.

7. An isolated nucleic acid molecule encoding a Nanobody or antigen-binding fragment thereof as claimed in any one of claims 1 to 5 or a polypeptide construct as claimed in claim 6.

8. A vector comprising the nucleic acid molecule according to claim 7; preferably, the vector is a cloning vector or an expression vector.

9. A host cell comprising the isolated nucleic acid molecule of claim 7 or the vector of claim 8.

10. A method for preparing a Nanobody or an antigen-binding fragment thereof according to any one of claims 1 to 5 or a polypeptide construct according to claim 6, comprising culturing a host cell according to claim 9 under conditions that allow protein expression, and recovering the Nanobody or its antigen-binding fragment or the polypeptide construct from the cultured host cell culture.

11. A bispecific or multispecific antibody comprising a Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5 or a polypeptide construct according to claim 6; Preferably, the bispecific or multispecific antibody specifically binds to c-MET and additionally specifically binds to one or more other targets; Preferably, the bispecific or multispecific antibody further comprises at least one second antibody having a second binding specificity for a second target.

12. A conjugate comprising a Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5, a polypeptide construct according to claim 6, or a bispecific or multispecific antibody according to claim 11, and a coupling portion connected thereto; Preferably, the conjugated moiety is selected from a therapeutic agent (such as a cytotoxic agent, cytokine, toxin or radionuclide).

13. A pharmaceutical composition comprising a Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5, a polypeptide construct according to claim 6, an isolated nucleic acid molecule according to claim 7, a vector according to claim 8, a host cell according to claim 9, a bispecific or multispecific antibody according to claim 11, or a conjugate according to claim 12, and a pharmaceutically acceptable carrier and / or excipient; Preferably, the pharmaceutical composition further comprises another pharmaceutically active agent, such as an anti-tumor agent.

14. Use of the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5, the polypeptide construct according to claim 6, the isolated nucleic acid molecule according to claim 7, the vector according to claim 8, the host cell according to claim 9, the bispecific or multispecific antibody according to claim 11, the conjugate according to claim 12 or the pharmaceutical composition according to claim 13 for the preparation of a drug for preventing and / or treating a tumor in a subject; Preferably, the tumor is a c-MET positive tumor; Preferably, the tumor is a tumor with abnormally activated c-MET pathway; Preferably, the tumor is selected from solid tumors, such as gastric cancer, lung cancer, liver cancer, head and neck cancer, skin cancer, colorectal cancer, ovarian cancer, esophageal cancer, pancreatic cancer, cervical cancer, mesothelioma, breast cancer, colorectal cancer or oral squamous cell carcinoma; Preferably, the subject is a mammal, such as a human; Preferably, the Nanobody or its antigen-binding fragment, polypeptide construct, isolated nucleic acid molecule, vector, host cell, bispecific or multispecific antibody, conjugate or pharmaceutical composition is used alone or in combination with another drug. The invention is used in combination with a chemically active agent (e.g., an anti-tumor agent).

15. A method for preventing and / or treating a tumor in a subject, comprising: Administering to a subject in need thereof an effective amount of the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5, the polypeptide construct according to claim 6, the isolated nucleic acid molecule according to claim 7, the vector according to claim 8, the host cell according to claim 9, the bispecific or multispecific antibody according to claim 11, the conjugate according to claim 12, or the pharmaceutical composition according to claim 13; Preferably, the tumor is a c-MET positive tumor; Preferably, the tumor is a tumor with abnormally activated c-MET pathway; Preferably, the tumor is selected from solid tumors, such as gastric cancer, lung cancer, liver cancer, head and neck cancer, skin cancer, colorectal cancer, ovarian cancer, esophageal cancer, pancreatic cancer, cervical cancer, mesothelioma, breast cancer, colorectal cancer or oral squamous cell carcinoma; Preferably, the subject is a mammal, such as a human.

16. A kit comprising a Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5 or a polypeptide construct according to claim 6; Preferably, the kit comprises a conjugate comprising the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5 or the polypeptide construct according to claim 6, and a detectable label linked to the Nanobody or antigen-binding fragment thereof or polypeptide construct, such as an enzyme (such as horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (such as acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (such as fluorescein or fluorescent protein), a radionuclide or biotin; Preferably, the kit comprises a Nanobody or an antigen-binding fragment thereof as described in any one of claims 1 to 5 or a polypeptide construct as described in claim 6, and a second antibody that specifically recognizes the Nanobody or its antigen-binding fragment or polypeptide construct; optionally, the second antibody further comprises a detectable label, such as an enzyme (such as horseradish peroxidase or alkaline phosphatase), a chemiluminescent agent (such as acridinium ester compounds, luminol and its derivatives, or ruthenium derivatives), a fluorescent dye (such as fluorescein or fluorescent protein), a radionuclide or biotin.

17. A method for detecting the presence or level of c-MET in a sample, comprising using a Nanobody or antigen-binding fragment thereof as claimed in any one of claims 1 to 5 or a polypeptide construct as claimed in claim 6; Preferably, the method is an immunological assay, such as immunoblotting, enzyme immunoassay (eg ELISA), chemiluminescent immunoassay, fluorescent immunoassay or radioimmunoassay.

18. A method for detecting whether a tumor can be treated by an anti-tumor therapy targeting c-MET, comprising using the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5 or the polypeptide construct according to claim 6 to detect the presence or level of c-MET in a sample from a subject; Preferably, the method is an immunological assay, such as immunoblotting, enzyme immunoassay (eg ELISA), chemiluminescent immunoassay, fluorescent immunoassay or radioimmunoassay; Preferably, the sample is a cell sample (eg, a sample comprising tumor cells) or a body fluid sample (eg, blood) from a subject (eg, a mammal, such as a human).

19. Use of the Nanobody or antigen-binding fragment thereof according to any one of claims 1 to 5 or the polypeptide construct according to claim 6 in the preparation of a detection agent for detecting the presence or level of c-MET in a sample or for detecting whether a tumor can be treated by an anti-tumor therapy targeting c-MET; Preferably, the sample is a cell sample (eg, a sample comprising tumor cells) or a body fluid sample (eg, blood) from a subject (eg, a mammal, such as a human).

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