WO2020088301A1 - Application of nw_006884764-1 in cho cell genome to stable expression of protein - Google Patents

Abstract

Provided is application of a site in a CHO cell genome to stable expression of a protein. The site in the CHO cell genome for stably expressing the protein is positioned at the 66645th basic group of CHO cell gene NW_006884764.1, and 5'NNNNNNNNNNNNNNNNNNNNNGG3' that can be identified by a CRISPR/Cas9 technology within a range of 66571 to 66691 near the site is a target sequence. Different protein genes can be introduced at a fixed position in the CHO cell genome and then stably expressed.

Description

Application of NW_006884764-1 stable protein expression in CHO cell genome Technical field

The present invention relates to the field of gene technology, and in particular to a recombinant gene of CHO cells for stable protein expression.

Background technique

Chinese hamster ovary cells (Chinese Hamster Ovary cells, CHO) as the main cell line in the field of biopharmaceuticals, has developed many different types of CHO cell lines, including cell lines that can be used to expand gene copy number. However, the increase in the number of transgenic copies and the increase in the yield of the target protein is not a clear positive correlation. And even if the protein expression increases, the expression level of most CHO cells is unstable. The currently widely used methods for constructing stable transfected cells are time-consuming and labor-intensive, mainly because of the need to repeat a large number of monoclonal screening processes, so the current field of cell line construction is generally expected to develop a method that can achieve high The method of expressing and stably expressing cells, and can ensure that the constructed recombinant cell line has the same quality level as the traditional method to ensure the approval of the regulatory agency.

The traditional method for constructing exogenous protein-expressing cell lines is to randomly integrate exogenous genes into the cell genome, and then screen through a series of high-expression monoclonal cells to obtain exogenous protein high-expression cell lines. Due to the diversity of site effect differences, the expression levels of recombinant cells produced by random integration are different, so it takes a long time and many steps in the later stage to select high-expression monoclonal cells. Monoclonal cells obtained through random integration cannot guarantee the stable expression of peptides / proteins during cell passage, and each recombination cell construction requires repeated monoclonal screening, increasing the research and development costs of biopharmaceuticals.

Site effect hinders the efficiency of traditional random integration to construct recombinant cell lines, and repeated high-expression monoclonal screening is time-consuming, laborious, and expensive. How to overcome the site effect, and use the fixed-point integration technology to quickly and efficiently obtain stable expression of monoclonal cells has been discussed in the academic community for many years, and there has been no breakthrough progress.

Summary of the invention

In response to the above problems in the prior art, the applicant of the present invention provides an application of NW_006884764-1 stably expressing proteins in the CHO cell genome. The application of the present invention introduces different protein genes at a fixed position in the CHO cell genome and performs stable expression; in addition, in the process of realizing this fixed-point integration, there is no need to select monoclonals multiple times to obtain higher expression cell lines, saving a lot time.

The technical solution of the present invention is as follows:

An application for stably expressing a protein in a site of a CHO cell genome, where the site for stably expressing a protein in the CHO cell genome is located at base 66645 of the CHO cell gene NW_006884764.1;

5'NNNNNNNNNNNNNNNNNNNNNGG3 'which can be recognized by CRISPR / Cas9 technology in the range of 66571-66691 near the site is the target sequence.

The protein is a protein with a molecular weight of less than 160 KDa.

The protein is one of a polypeptide, a functional protein, an antibody, and a fusion protein.

The target sequence is 66619-66641 bases near the 66645th base of the CHO cell gene NW_006884764.1.

Further, the target sequence is

A targeting vector containing the 5'NNNNNNNNNNNNNNNNNNNNNGNG3 'target sequence that can be used for site editing and can be recognized by CRISPR / Cas9 technology.

The manufacturing method of the targeting vector is as follows: the PSK-u6-gRNA plasmid is digested with BbsI, and the target sequence DNA fragment containing the sticky end of BbsI is connected to obtain the targeting vector.

A recombinant donor vector for expressing foreign genes in CHO cells. The recombinant donor vector contains a homologous arm of 500 bp to 800 bp upstream and downstream at base 66645 of the site NW_006884764.1.

The preparation method of the recombinant donor vector is as follows: the protein gene is inserted into the region between the 5'arm and the 3'arm of the plasmid, so that the nucleotide sequence is located downstream of the promoter and regulated by it, and is expressed by recombinant CHO cells Plasmid.

The promoters are: CMV (human cytomegalovirus-derived strong mammalian expression promoter), EF-1a (human elongation factor 1α-derived strong mammalian expression promoter), SV40 (simian vesicular virus 40-derived lactation) Animal expression promoter), PGK1 (a mammalian promoter derived from the phosphoglycerate kinase gene), UBC (a mammalian promoter derived from the human ubiquitin C gene), human beta-actin (a mammal derived from the β-actin gene) Animal promoter), CAG (strong hybrid mammalian promoter).

A CHO recombinant cell line for stably expressing foreign proteins. The recombinant cell line uses the vector or plasmid during the construction process.

A method for CHO cell gene expression protein, characterized in that it includes the following steps:

(1) Transform CHO cells with Cas9, the targeting vector and the recombinant donor vector, and the three vectors together to obtain recombinant CHO cells; (2) Recombinant CHO cells are cultured on a plate, collect the supernatant to detect the expression level Adhering to adherent recombinant CHO cells for suspension and domestication;

(3) Suspension-acclimated recombinant CHO cells were cultured in small shake flasks, and the protein expression level was detected.

The present application also provides a selection of stable expression sites in the CHO cell genome:

1) Construct a lentivirus with a fluorescent label and calculate its titer. After integrating the igk-luc gene into the multiple cloning site of the pLVX-CMV-MCS-T2A-Zsgreen vector, the three plasmids were simultaneously transfected into HEK-293T cells using pSPAX2 and pMD2G plasmids at 48 hours and 72 hours The cell supernatant was taken twice, and after collection, the supernatant was ultracentrifuged to obtain lentivirus.

2) Spread the CHO cells on a 6-well plate and culture overnight. The next day, the lentivirus was diluted and the CHO cells were infected with a lower MOI (MOI <1) (each cell corresponds to a virus particle). 96 hours after infection, the cells were sorted by flow cytometry, and the brightest fluorescent cells were directly seeded into 96-well plates. One week later, when the cells grow into monoclonal colonies, observe the cells under a fluorescent microscope, select the morphological and growth colonies with the brightest colonies, and transfer them to a 24-well plate to expand the culture. When the cultured cells reach a confluence of nearly 90%, they are transferred to a 6-well plate for cultivation, and finally expanded to a culture dish of 10 cm, a part of the cells are frozen, and the remaining cells continue to be expanded.

3) Using chromosome walking technology Lenti-X Integration Site Analysis Kit (Clontech: 631263) to find all lentivirus CHO cell gene integration sites.

Using several cell lines with the brightest fluorescence intensity and normal cell morphology and growth rate as materials, genomic DNA was digested with three restriction enzymes ADraI, SspI and HpaI overnight. The genomic DNA is 2.5μg, the restriction enzyme is 80U, and the reaction system is 100μL. Place at 37 ° C overnight for digestion (16-18 hours).

Use the DNA recovery kit to purify and recover the digested product. The digested genomic DNA was 4.8μL, plus 1.9μL chromosome walking joint GenomeWalkerAdaptor (25μM) and 0.5μL T4 ligase, to make 8μL system for ligation experiment. Place at 16 ° C for overnight connection. The ligation enzyme was inactivated by heating the ligation system at 70 ° C for 5 minutes. 32μL TE buffer is added to each system to configure the corresponding library.

Two rounds of nested PCR were performed on the library to amplify the LTR region and the adjacent genomic region. Relevant PCR reaction operation steps can be performed by referring to Lenti-X Integration Analysis Kit (Clontech: 631263) kit instructions.

Finally, the PCR products are electrophoresed, and the main band is cut and recovered for sequencing. After obtaining all the lentiviral integration information of each cell line, select the relevant information of the CHO cell line with only a single copy of lentivirus integration, and compare its sequence information with the CHO-K1 genome information on BLAST to find high expression Integration site.

Due to the database update, after sequence alignment, the original site information was changed from the 66645th base of the CHO cell gene NW_006884764.1 to the 1813403th base of the CHO cell gene NW_003613642.1. The range was changed from 66571-66691 to 181329-181449.

The beneficial technical effects of the present invention are:

The invention adopts a fixed-point integration method. By integrating the targeted gene into a stable expression region, it can well overcome the problem of integration site uncertainty caused by random integration, and effectively avoids repeated multiple rounds of high-expression monoclonal screening , Can effectively reduce the research and development time of biopharmaceutical construction of stable expression cell lines, and reduce costs.

In the present invention, protein genes are introduced at a fixed position of CHO cell genes and are stably expressed.

BRIEF DESCRIPTION

Figure 1 is a schematic diagram of the present invention;

Figure 2 shows the results of gene identification of CHO cells introduced with NGGH 75KDa gene;

Figure 3 is the sequencing of CHO cell genes introduced with NGGH 75KDa gene by OoPCR_fwd and OoPCR_rev;

Figure 4 shows the expression of HSA by cells in different passages;

Figure 5 shows the expression of NGGH by cells in different passages;

Figure 6 shows the quality of antibody protein secreted by each recombinant CHO cell daily.

detailed description

The present invention will be described in detail below with reference to the drawings and embodiments.

FIG. 1 is a schematic diagram of a donor plasmid for integration into the site and a schematic diagram of how to integrate the site into the site by homologous recombination. Among them, GOI is our target gene. It uses 5'arm and 3'arm homologous recombination arms under the pressure of 4μg / mL puromycin screening, and integrates into the target site in a targeted manner. In addition, the sequence upstream of the 5’arm is a negative selection tag, which can be used to remove randomly integrated monoclonal cells to ensure that the resulting recombinant CHO cell line is site-directed integration.

Example 1

Selection of high expression sites;

NW_006884764.1 (NW_003613642.1) (chromosome 1), 66645 (181403) base is integrated, and the Zsgreen1 gene is integrated there. The fluorescent cells were subcultured for at least 50 generations, and the expression level of fluorescence was detected by flow cytometry. The 50th generation of fluorescent cells still have a good green fluorescent protein expression level, and the fluorescent signal can be stably retained during the passage of cells.

In addition, this fluorescent cell was also subjected to suspension acclimation, and the expression level of the fluorescent protein after suspension acclimation was again detected by flow cytometry. The test results show that more than 95% of the recombinant CHO cells suspended for 50 passages still maintain the expression of green fluorescent protein after suspension. It can be considered that the site is extremely stable and will not lose site integration due to cell passage. Fluorescent protein gene.

Example 2

Selection of specific targets;

According to the principle of proximity, the sequence:

Input into the CRISRPRater system to predict and select target sequences with low off-target efficiency. The parameter settings are as follows: 1) The maximum number of mismatched bases at the beginning 15 bp after NGG is 0; 2) The number of mismatched bases at 21 bp after NGG is 2.

According to the above operation, the following sequence with a score of 0.73 is selected as the target sequence according to its score:

According to the CRISPRater system, LOW efficiency (score <0.56); MEDIUM efficiency (0.56 <= score <= 0.74); HIGH efficiency (score> 0.74).

According to the CRISPRater evaluation system, all target sequences within the range of 66571-66691 (181329-181449) near the site NW_006880285.1 (NW_003613642.1) have obtained a score of more than 0.56, which are in the middle effective or high efficiency range, and can be used as CRISPR / Cas9 5'NNNNNNNNNNNNNNNNNNNNNGNG3 'target sequence identified by technology.

Example 3

Promoter selection

Replacing different promoters with the above CMV (human cytomegalovirus-derived strong mammalian expression promoter) promoter positions, including EF-1a (human elongation factor 1α-derived strong mammalian expression promoter), SV40 (simian monkey Mammalian expression promoter derived from vacuolar virus 40), PGK1 (a mammalian promoter derived from phosphoglycerate kinase gene), UBC (a mammalian promoter derived from human ubiquitin C gene), human beta actin (β- Common promoters such as mammalian promoters derived from actin genes) or CAG (strong hybrid mammalian promoters). After testing, the above promoters can regulate the downstream red fluorescent protein gene sequence and express the corresponding red fluorescent protein.

Example 4

Site-specific integration of human serum albumin gene (HSA, 68KDa) at a specific site: In order to later construct CRISPR / Cas9-mediated homologous recombination, sgRNA and DonorPlasmid need to be constructed as follows:

1. Construction of SgRNA, first synthesize the following sequence

sgRNA-1fwd 5’TTTGCACAGCTAGTGACATTCATGGT 3 ’

sgRNA-1rev 5 ’TAAAACCATGAATGTCACTAGCTGTG 3’

1) PSK-u6-gRNA plasmid is digested with BBsI, and the cut vector is recovered;

2) The synthesized fragments are annealed into double strands with sticky ends

Water bath 95 ℃ 5min, the water bath naturally drops to room temperature;

4) Connect and transform;

5) Picking clones, PCR identification, the identification primers used are:

The M13-synthesized R primer can amplify the band as a positive clone.

2. Donor plasma construction

The specific information of donor plasmaid is shown in Figure 1: The rest are all synthesized except GOI; the 600bp sequence upstream and downstream of the target is the sequence information of the left and right homology arms of donor plasma, and GOI is the HSA gene that passes the existing Novizan company The C115 kit completes the process of integrating HSA into donor plasma.

3. Co-transfect Cas9 (donated by Dr. Helene F Kildegaard, Danish University of Science and Technology), SgRNA and Donor plasmid to CHO cells cultured at 37 ℃ and 5% CO _{2 at a} molar ratio of 1: 1: 1. The transfection reagent is Lipofectamine 3000 (Thermo Fisher Scientific), the specific transfection method refers to the instruction manual, and then the cells are added with 4μg / mL puromycin for screening, and the process takes 10 days in total; then the MoFloXDP FACS machine (Beckman Coulter) is used for monoclonal cell separation Select, select cells that do not contain any fluorescence, and seed them into 96-well plates.

4. After 2 weeks of cell growth, take a part for identification, do PCR identification, do 5’junction PCR, 3’Junction PCR and out-out PCR for identification. Keep the positive cells.

Example 5

Integrate glucagon-like peptide-1-human serum albumin fusion protein gene (NGGH, 75KDa) at a specific site: in order to perform CRISPR / Cas9-mediated homologous recombination at a later stage, it is necessary to construct sgRNA and DonorPlasmid, Methods as below:

1. Construct sgRNA as in Example 4.

2. Donor plasma construction.

The specific information of the donor plasmaid is shown in Figure 1: Except GOI, the rest are synthetic; the 600bp sequence upstream and downstream of the target is the sequence information of the left and right homology arms of the donor plasma, GOI is the NGGH gene passed the existing Novizan company The C115 kit completes the process of integrating NGGH onto the donor plasmad.

3, the Cas9, SgRNA Donor plasmid 3 and plasmid cotransfected 37 ℃, 5%, cultured under CO ₂ for CHO cells, three plasmids molar ratio of 1: 1: 1, the transfection reagent Lipofectamine 3000 (Thermo Fisher Scientific), refer to the instructions for the specific transfection method. After that, cells were added with 4μg / mL puromycin for screening, and the process totaled 10 days. Then use MoFloXDP FACS machine (Beckman Coulter) for monoclonal cell sorting, select cells that do not contain any fluorescence, and seed them into 96-well plates.

4. After 2 weeks of cell growth, take a portion for identification. Identify by doing PCR identification, doing 5’junction PCR, 3’Junction PCR and out-out PCR. Keep the positive cells.

Figure 2 shows the identification result of the CHO gene introduced with the 75KDa gene of NGGH. Lanes 1-3 are the 5'jucntion PCR results of the three monoclonal cells, and lanes 4-6 are the 3'junction PCR results. All of them have significant bands. Gene knock-in.

Figure 3 uses OoPCR_fwd and OoPCR_rev for sequencing to determine the sequence accuracy at the junction (5'junction and the junction of the 5 'upstream of the 3'junction and the genome). The sequencing results verify that the GOI is accurately inserted into the target location area .

Example 6

Integrate the antibody gene (Avastin, 160KDa) at a specific site: In order to later construct CRISPR / Cas9-mediated homologous recombination, sgRNA and DonorPlasmid need to be constructed as follows:

1. The sgRNA construction is the same as in Example 4.

2. Donor plasma construction.

The specific information of the donor plasmaid is shown in Figure 1: Except for GOI, the rest are synthetic; the 600bp sequence upstream and downstream of the target is the sequence information of the left and right homology arms of the donor plasma, and GOI is the Avastin gene through the existing Novizan company The C115 kit completes the process of antibody gene integration into donor plasma.

3. Cas9 (donated by Dr. Helene F Kildegaard, Danish University of Science and Technology), SgRNA and Donor plasmid were co-transfected into CHO cells cultured at 37 ℃, 5% and CO _{2 with a} molar ratio of three plasmids of 1: 1 : 1, the transfection reagent is Lipofectamine 3000 (Thermo Fisher Scientific), please refer to the instruction manual for the specific transfection method. After that, cells were added with 4μg / mL puromycin for screening, and the process totaled 10 days. Then use MoFloXDP FACS machine (Beckman Coulter) for monoclonal cell sorting, select cells that do not contain any fluorescence, and seed them into 96-well plates.

4. After 2 weeks of cell growth, take a portion for identification. Identify by doing PCR identification, doing 5’junction PCR, 3’Junction PCR and out-out PCR. Keep the positive cells.

Test case:

The three cell lines prepared in Examples 4-6 were subjected to ELISA test to observe whether the target protein was expressed and whether it was stable long-term expression.

Detection method: The detection of the three is carried out by ELISA method. All the positive cells selected in the 6-well plate are cultured to check whether they have long-term stable expression of the target protein. The kit used is the Abclonal Human Albumin ELISA Kit ( RK00157) and Human IgG (Total) ELISA Kit (RK00393).

Figures 4 and 5 show the cell expression of HSA and NGGH under different passages, and the ordinate is the amount of secreted protein per cell per day.

It can be seen that the NGGH and HSA can stably express the corresponding genes within 50 generations in the plate, and the target protein expression levels of the three selected NGGH site-integrated cell lines and two HSA site-integrated cell lines tend to be close.

Figure 6 shows the mass of antibody protein secreted by each recombinant CHO cell daily. Obviously, the cells can stably express and secrete the corresponding protein under different passage conditions, which shows good stability, which is consistent with the previous results of fluorescent cells. The results show that the site can perform CRISPR / Cas9-mediated site-directed integration, and can stably express the corresponding protein.

After selecting the 5'-CACAGCTAGTGACATTCATGTGG-3 'sequence for the above test, good results were obtained. Therefore, the target sequences described in claims 5-11 can successfully construct a fixed-point integration and stable expression cell line, and all can be stably expressed. Target protein.

Claims (15)

1. An application for stably expressing a protein in a CHO cell genome, characterized in that the site for stable protein expression in the CHO cell genome is located at base 66645 of the CHO cell gene NW_006884764.1;

   5'NNNNNNNNNNNNNNNNNNNNNGG3 'which can be recognized by CRISPR / Cas9 technology in the range of 66571-66691 near the site is the target sequence.
2. The use according to claim 1, characterized in that the protein is a protein with a molecular weight of less than 160 KDa.
3. The use according to claim 1, characterized in that the protein is a polypeptide, functional
4. The use according to claim 1, wherein the target sequence is 66619-66641 bases near the 66645th base of the CHO cell gene NW_006884764.1; the target sequence is 5'-AGCAGTGATCATTTATGCTGAGG-3 '.
5. The use according to claim 1, wherein the target sequence is 5'-ATTAAGTTGGCACAGAGGGCTGG-3 '.
6. The use according to claim 1, characterized in that the target sequence is 5'-ATCTGAAAAACAAATCCATATGG-3 '.
7. The use according to claim 1, characterized in that the target sequence is 5'-CAGTAGCTATTGTTTCCATATGG-3 '.
8. The use according to claim 1, characterized in that the target sequence is 5'-GGACTATTAAGTTGGCACAGAGG-3 '.
9. The use according to claim 1, characterized in that the target sequence is 5'-TTTCTTGAGGACTATTAAGTTGG-3 '.
10. The use according to claim 1, wherein the target sequence is 5'-CTAAGTATTTTACTTTCTTGAGG-3 '.
11. The use according to claim 1, characterized in that the target sequence is 5'-ACAATAGCTACTGTATTTTAAGG A-3 '.
12. A targeting vector, characterized in that the targeting vector contains the target sequence of 5′NNNNNNNNNNNNNNNNNNNNNGG3 ′ which can be used for site editing as described in claim 1 and can be recognized by CRISPR / Cas9 technology.
13. A recombinant donor vector for expressing foreign genes in CHO cells, characterized in that the recombinant donor vector contains homology 500bp-800bp upstream and downstream at the 66645th base of the site NW_006884764.1 of claim 1 arm.
14. The recombinant donor vector according to claim 13, characterized in that the method for producing the vector is: inserting the protein gene into the region between the 5'arm and 3'arm of the plasmid, so that the nucleotide sequence is located in the promoter Downstream of and controlled by it, recombinant CHO cell expression plasmids are obtained.
15. A CHO recombinant cell line for stably expressing foreign proteins, characterized in that the vector or plasmid according to claim 12, 13 or 14 is used in the construction of the recombinant cell line.

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