Establishment and verification of a real-time quantitative PCR method for determination of exogenous antibody gene copy number in CHO cells / 中国生物制品学杂志

@#Objective To establish a real-time quantitative PCR method using SYBR GreenⅠto detect the copy numbers of light chain(LC)and heavy chain(HC)of exogenous antibody gene in CHO cells,and verify and preliminarily apply this method.Methods With the B2m(β2-microglobulin)expressed stably in CHO cells as the internal reference gene,suitable primers of LC,HC genes and internal reference gene were designed respectively,and the reaction system and program of the real-time quantitative PCR method were determined. The established method was verified for the specificity,linearity,precision and durability,and used to detect the copy numbers of LC and HC genes in the recombinant cell lines of working cell bank(WCB)and cells of different passages.Results The primers of exogenous genes and internal reference gene showed specific binding to the target fragments;The efficiency of primer amplification for the B2m gene,LC gene,and HC gene was 106. 7%,106. 3% and 99. 1%,respectively,and the correlation coefficients of the linear equations were all greater than 0. 99 with a good linear relationship;The relative standard deviations(RSDs)of precision verification were all less than 1%;Few cycles of freeze-thaw in a short period had little effect on the detection results. The copy numbers of LC and HC genes in different generations of recombinant cell lines detected by the established method showed no obvious changes.Conclusion A real-time quantitative PCR method for the determination of the copy number of exogenous genes in CHO cells was successfully established with good specificity,linearity,precision and durability,which provides a reference for detecting the copy number of exogenous genes expressed in other CHO cell lines

Advances in epigenetic regulation of Chinese hamster ovary cells / 生物工程学报

Chinese hamster ovary (CHO) cells play an irreplaceable role in biopharmaceuticals because the cells can be adapted to grow in suspension cultures and are capable of producing high quality biologics exhibiting human-like post-translational modifications. However, gene expression regulation such as transgene silencing and epigenetic modifications may reduce the recombinant protein production due to the decrease of expression stability of CHO cells. This paper summarized the role of epigenetic modifications in CHO cells, including DNA methylation, histone modification and miRNA, as well as their effects on gene expression regulation.

Application of monoclonal inoculation/imaging equipment VIPS in monoclonal screening of CHO engineered cell lines / 中国生物制品学杂志

@#Objective To develop a method for monoclonal screening of CHO engineered cell lines using Verified In-situ Plate Seeding(VIPS). Methods Cell pool 1 stably transfected with target gene was inoculated by using monoclonal inoculation/imaging equipment(VIPS)in 96-well plates containing culture medium of different combinations(18 combinations,numbered 1～18)and volumes(100 and 200 μL/well). Monoclonal origin tracing pictures were taken,according to which,the monoclonal inoculation rate,clone formation rate and monoclonal proliferation rate were calculated and the image effects of monoclonal origin were evaluated. The applicability of this method was verified by cell pool 2,cell pool 3 and cell pool 4 stably transfected with target gene. Results The optimum monoclonal medium was Medium Ⅱ,and the volume of medium was 100 μL/well. Under the optimum process conditions,the monoclonal inoculation rate of Cell pool 1 was 80%,the clone formation rate was 83%,the proliferation rate was fast,and the monoclonal origin image was clear. While for Cell pool2,Cell pool 3 and Cell pool 4,the average rate of monoclonal inoculation was 78%,the average rate of clone formation was67%,the proliferation rate was slightly different and the image of cell division process was clear under the optimum process conditions. Conclusion In this study,the monoclonal screening method of CHO engineered cell lines developed using VIPS can improve the clone formation rate of CHO engineered cell lines and provide sufficient proof of monoclonal origin.

High level expression of recombinant human serum albumin in CHO cells and optimization of its culture technology / 中国生物制品学杂志

@#ObjectiveTo achieve efficient expression of human serum albumin(HSA)in Chinese hamster ovary(CHO)cells and optimize its culture technology,so as to lay a foundation of the large-scale production of HSA.MethodsThe eukaryotic expression vector of HSA was constructed by gene recombination technology,and then electrotransfected into fully suspended CHO cells. The monoclonal cell lines with stable and high expression of HSA were screened by G418 and limited dilution method. By adding glucose,sodium butyrate and supplementalmedium to the basal medium,the cell culture process was optimized to improve the expression of HSA. Finally,the scale-up culture verification was carried out in a 5 L bioreactor.ResultsThe recombinant expression vector pcDNA3.1-HSA was successfully constructed and expressed in fully suspended CHO cells. After two monoclonal screening,the secondary monoclonal cell lines CHO-rHSA-7H2A9 and CHOrHSA-7H2D12 were obtained with high HSA expression of 29. 37 mg/L and 25. 26 mg/L respectively. The HSA expression level reached about 100. 00 mg/L by optimizing the culture process and wasfinally increased to 166. 16 mg/L in the 5 L bioreactor,which was about 30 times higher than that in the supernatant of the first monoclonal cells.Conclusion The high level expression of HSA in CHO cells was achieved,which laid a foundation of the further large-scale production of HSA in the field of biological products and solving the market supply problems.

Site-specific integration and stable expression of exogenous protein at a novel site on CHO cell chromosome / 中国药科大学学报

@#Finding stable expression sites on the chromosomes of Chinese hamster ovary (CHO) cells is an effective method to solve the problem of unstable expression of CHO cells in long-term culture. Our group used lentiviral transfection to integrate the tracer gene (Zsgreen1) into the chromosome of CHO cells and found multiple potential stable expression sites. This study verified the ability of one of the sites located in the 148052-148157 bp region on chromosome NW_003614241.1 to stably express exogenous proteins.The expression of Zsgreen1 gene was first observed, and CRISPR/Cas9 technology was then used to integrate the enhanced green fluorescent protein (EGFP) gene into this site. Three strains of EGFP gene integrated cells were obtained. After 60 generations of suspension culture, the fluorescence intensity of the cells had no significant changes, which proved that this site can stably express the EGFP gene. The same method was used to construct recombinant CHO cell lines expressing the human serum albumin (HSA) gene, and was verified by Western blot that this site could express and secrete HSA. It shows that the above-mentioned sites can be integrated and can stably express exogenous proteins.

Impact of metabolic enzymes overexpression on transient expression of anti-hLAG3 by CHO cells / 生物工程学报

To enhance recombinant protein production by CHO cells, We compared the impact of overexpression of metabolic enzymes, namely pyruvate carboxylase 2 (PYC2), malate dehydrogenase Ⅱ (MDH2), alanine aminotransferase Ⅰ (ALT1), ornithine transcarbamylase (OTC), carbamoyl phosphate synthetase Ⅰ (CPSⅠ), and metabolism related proteins, namely taurine transporter (TAUT) and Vitreoscilla hemoglobin (VHb), on transient expression of anti-hLAG3 by ExpiCHO-S. Overexpression of these 7 proteins could differentially enhance antibody production. OTC, CPSI, MDH2, and PYC2 overexpression could improve antibody titer by 29.2%, 27.6%, 24.1%, and 20.3%, respectively. Specifically, OTC and MDH2 could obviously improve early-stage antibody production rate and the culture period was shortened by 4 days compared with that of the control. In addition, OTC and MDH2 had little impact on the affinity of anti-hLAG3. In most cases, overexpression of these proteins had little impact on the cell growth of ExpiCHO-S. MDH2 and ALT1 overexpression in H293T cells could also improve antibody production. Overall, overexpression of enzymes involved in cellular metabolism is an effective tool to improve antibody production in transient expression system.

Caspase-7 deficiency in Chinese hamster ovary cells reduces cell proliferation and viability

BACKGROUND: Chinese hamster ovary (CHO) cells are the most commonly used mammalian host cell In the commercial-scale production of biopharmaceutical proteins. Modification of genes involved in apoptosis may improve the productivity of CHO cells. Executive caspases, including caspases 3 and 7, play critical roles in apoptosis. The effects of the ablation of the caspase 7 gene on proliferation and viability of CHO cells remains unknown. In this study, we applied clustered regularly interspaced short palindromic repeat (CRISPR/Cas9) to target caspase 7 gene of CHO K1 cell via all in one and homology targeted integration strategies. Consequently, the effect of caspase 7 deficiency on cell proliferation, viability, and apoptosis was studied by MTT assay and flow cytometry. RESULTS: Findings of gel electrophoresis, western blotting, and sequencing confirmed the caspase 7 gene silencing in CHO cells (CHO-KO). Proliferation assay revealed that caspase 7 deficiency in CHO cells resulted in the reduction of proliferation in various CHO-KO clones. Besides, the disruption of caspase 7 had negative effects on cell viability in exposure with NaBu which confirmed by MTT assay. Results of flow cytometry using Anexin V/PI demonstrated that Nabu treatment (11 mM) declined the percentage of live CHO-K1 and CHO-KO cells to 70.3% and 5.79%. These results verified that the CHO-K1 cells were more resistant to apoptosis than CHO-KO, however most of CHO-KO cells undergone early apoptosis (91.9%) which seems to be a fascinating finding. CONCLUSION: These results reveal that caspase 7 may be involved in the cell cycle progression of CHO cells. Furthermore, it seems that targeting caspase 7 is not the ideal route as it had previously been imagined within the prevention of apoptosis but the relation between caspase 7 deficiency, cell cycle arrest, and the occurrence of early apoptosis will require more investigation.

Retrovectors packaged in CHO cells to generate GLP-1-Fc stable expression CHO cell lines

Background: Chinese hamster ovary (CHO) cells are the most dependable mammalian cells for the production of recombinant proteins. Replication-incompetent retroviral vector (retrovector) is an efficient tool to generate stable cell lines. Multiple copies of integrated genes by retrovector transduction results in improved recombinant protein yield. HEK-293 and their genetic derivatives are principal cells for retrovector production. Retrovectors packaged in HEK-293 cells pose a risk of infectious agent transmission, such as viruses and mycoplasmas, from serum and packaging cells. Results: In this report, retrovectors were packaged in CHO cells cultured in chemically defined (CD) media. The retrovectors were then used to transduce CHO cells. This method can block potential transmission of infectious agents from serum and packaging cells. With this method, we generated glucagon-like protein-1 Fc fusion protein (GLP-1-Fc) stable expression CHO cell lines. Productivity of GLP-1-Fc can reach 3.15 g/L. The GLP-1-Fc protein produced by this method has comparable bioactivity to that of dulaglutide (Trulicity). These stable cell lines retain 95­100% of productivity after 40 days of continuous culture (~48­56 generations). Conclusions: Suspension CHO cells are clean, safe, and reliable cells for retrovector packaging. Retrovectors packaged from this system could be used to generate CHO stable cell lines for recombinant protein expression.

Possible radioprotective effect of folic acid supplementation on low dose ionizing radiation-induced genomic instability in vitro.

Ionizing radiation (IR) induces DNA damage through production of single and double-strand breaks and reactive oxygen species (ROS). Folic acid (FA) prevents radiation-induced DNA damage by modification of DNA synthesis and/or repair and as a radical scavenger. We hypothesized that in vitro supplementation with FA will decrease the sensitivity of cells to genetic damage induced by low dose of ionizing radiation. Annexin V, comet and micronucleus assays were performed in cultured CHO cells. After 7 days of pre-treatment with 0, 100, 200 or 300 nM FA, cultures were exposed to radiation (100 mSv). Two un-irradiated controls were executed (0 and 100 nM FA). Data were statistically analyzed with X2-test and linear regression analysis (P 0.05). We observed a significantly decreased frequency of apoptotic cells with the increasing FA concentration (P <0.05). The same trend was observed when analyzing DNA damage and chromosomal instability (P <0.05 for 300 nM). Only micronuclei frequencies showed significant differences for linear regression analysis (R2=94.04; P <0.01). Our results have demonstrated the radioprotective effect of folic acid supplementation on low dose ionizing radiation-induced genomic instability in vitro; folate status should be taken into account when studying the effect of low dose radiation in environmental or occupational exposure.

Development of Genetically Modified Chinese Hamster Ovary Host Cells for the Enhancement of Recombinant Tissue Plasminogen Activator Expression

Background: Chinese hamster ovary (CHO) cells are the most commonly used host system for the expression of high quality recombinant proteins. However, the development of stable, high-yielding CHO cell lines is a major bottleneck in the industrial manufacturing of therapeutic proteins. Therefore, different strategies such as the generation of more efficient expression vectors and establishment of genetically engineered host cells have been employed to increase the efficiency of cell line development. In order to examine the possibility of generating improved CHO host cells, cell line engineering approaches were developed based on ceramide transfer protein (CERT), and X-box binding protein 1s (XBP1s). Methods: CHO cells were transfected with CERT S132A, a mutant variant of CERT which is resistant to phosphorylation, or XBP1s expression plasmids, and then stable cell pools were generated. Transient expression of t-PA was examined in engineered cell pools in comparison to un-modified CHO host cells. Results: Overexpression of CERT S132A led to the enhancement of recombinant tissue plasminogen activator (t-PA) expression in transient expression by 50%. On the other hand, it was observed that the ectopic expression of the XBP1s, did not improve the t-PA expression level. Conclusion: The results obtained in this study indicate successful development of the improved CHO host cells through CERT S132A overexpression.

Advances in improving mammalian cells metabolism for recombinant protein production

Background: The production of recombinant proteins for therapeutic use represents a great impact on the biotechnology industry. In this context, established mammalian cell lines, especially CHO cells, have become a standard system for the production of such proteins. Their ability to properly configure and excrete proteins in functional form is an enormous advantage which should be contrasted with their inherent technological limitations. These cell systems exhibit a metabolic behaviour associated with elevated cell proliferation which involves a high consumption of glucose and glutamine, resulting in the rapid depletion of these nutrients in the medium and the accumulation of ammonium and lactate. Both phenomena contribute to the limitation of cell growth, the triggering of apoptotic processes and the loss of quality of the recombinant protein. Results: In this review, the use of alternative substrates and genetic modifications (host cell engineering) are analyzed as tools to overcome those limitations. In general, the results obtained are promising. However, metabolic and physiological phenomena involved in CHO cells are still barely understood. Thus, most of publications are focused on specific modifications rather than giving a systemic perspective. Conclusions: A deeper insight in the integrated understanding of metabolism and cell mechanisms is required in order to define complementary strategies at these two levels, so providing effective means to control nutrients consumption, reduce by-products and increase process productivity.

Simultaneous environmental manipulations in semi-perfusion cultures of CHO cells producing rh-tPA

We evaluated the combined effect of decreasing the temperature to a mild hypothermia range (34 and 31ºC) and switching to a slowly metabolizable carbon source (glucose substituted by galactose) on the growth and production of a recombinant human tissue plasminogen activator (rh-tPA) by Chinese hamster ovary cells in batch and semi-perfusion cultures. In batch cultures using glucose as a carbon source, decreasing the temperature caused a reduction in cell growth and an increase in specific productivity of rh-tPA of 32 percent at 34ºC and 55 percent at 31ºC, compared to cultures at 37ºC. Similar behaviour was observed in cultures at 34ºC using galactose as a carbon source. Nonetheless, at 31ºC, the specific productivity of rh-tPA strongly decreased (about 58 percent) compared to the culture at 37ºC. In semi-perfusion culture, the highest rh-tPA specific productivity was obtained at 34ºC. Similarly, whether a decrease in the temperature is accompanied of the replacement of glucose by galactose, the rh-tPA specific productivity improved about 112 percent over that obtained in semi-perfusion culture carried out at 37ºC with glucose as the carbon source. A semi-perfusion culture strategy was implemented based on the combined effect of the chosen carbon source and low temperatures, which was a useful approach for enhance the specific productivity of the recombinant protein.

Cloning of a Recombinant Plasmid Encoding Thiol-Specific Antioxidant Antigen (TSA) Gene of Leishmania major and Expression in the Chinese Hamster Ovary Cell Line

Background: TSA (thiol-specific antioxidant antigen) is the immune-dominant antigen of Leishmania major and is considered to be the most promising candidate molecule for a recombinant or DNA vaccine against leishmaniasis. The aim of the present work was to express a plasmid containing the TSA gene in eukaryotic cells. Methods: Genomic DNA was extracted, and the TSA gene was amplified by polymerase chain reaction (PCR). The PCR product was cloned into the pTZ57R/T vector, followed by subcloning into the eukaryotic expression vector pcDNA3 (EcoRI and HindIII sites). The recombinant plasmid was characterised by restriction digest and PCR. Eukaryotic Chinese hamster ovary cells were transfected with the plasmid containing the TSA gene. Expression of the L. major TSA gene was confirmed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and Western blotting. Results: The plasmid containing the TSA gene was successfully expressed, as demonstrated by a band of 22.1 kDa on Western blots. Conclusion: The plasmid containing the TSA gene can be expressed in a eukaryotic cell line. Thus, the recombinant plasmid may potentially be used as a DNA vaccine in animal models.

Expression, purification and activity determination of humanized anti-HER2 monoelonal antibody in CHO / 中国药学杂志

OBJECTIVE: To screen for the optimal CHO cell clone which stably expresses recombinant humanized anti-HER2 monoclonal antibody(rhHER2-mAb) and to measure its bioactivity. METHODS: Disposable orbital shaking bioreactor, Tubespin, was utilized for high-throughput screening, and then orbital shaking flask was used for scale-up. Protein A affinity chromatography was utilized to purify the fusion protein. SDS-PAGE and HPLC were utilized to detect its purity, ELISA was utilized to detect its production amount, and MTT was utilized to detect its bioactivity. RESULTS: Through the cell clone selection, it was found that #38 cell clone had the best expression performance, with the productivity in shaking flask of(152±20) mg · L-1. After scale up, enough supernatant was got for the purification. The molecular weight of the purified protein was about 150 × 103, and its purity was higher than 96%. Analysis of bioactivity and binding affinity showed that its activity and bind affinity were close to the commercialized product, Herceptin. CONCLUSION: A cell clone with high productivity was obtained by cell clone screening. The antibody protein was successfully obtained by orbital shaking scale-up cultivation and purification. Its bioactivity and binding affinity were consistent with the commercialized drug. This method has laid a foundation for large-scale fermentation of this recombinant protein.

Construction of bicistronic green fluorescent protein labeled pSELECT GFPzeo human bone morphogenetic protein 2 eukaryotic expression vector / 中华骨科杂志

Objective To construct green fluorescent protein (GFP)-labeled pSELECT-GFP zeohBMP2 eukaryotic expression vector. Methods The encoding fragment of hBMP2 gene was obtained from a recombinant plasmid pcDNA3.1/CT-hBMP2 by using polymerase chain reaction (PCR). hBMP2 gene was inserted into pTA2-T-easy and pSELECT-GFPzeo-MCS eukaryotic expression vector, and then transferred into competence DHSα cells. After screening, pSELEC-GFPzeo-hBMP2 was obtained and identified by sequence analysis. The recombinant vector pSELECT-GFP zeo-rhBMP2 was transfected into CHO cells. The successful trasfection was verified by fluorescence microscope in 48-72 hours. The RT-PCR and immunofluorescence was used to confirm the hBMP2 expression. Western Blotting was used to detect the secretion of hBMP2.Results A 1216 bp fragment was obtained by PCR, the same as expectant fragment. The recombined pSE-LECT-GFPzeo-hBMP2 eukaryotic expression vector was identified by restriction mapping and sequence analysis. The results were identical with that of reported hBMP2 sequence (Genebank NM-001200). The successful transfection was verified by fluorescence microscope in 48-72 hours. The stable expression in eukaryotic cells was confirmed by immunofluorescence and RT-PCR which showed an obvious band between 1000-2000 bp. Western Blotting identified the immunogenicity of recombinant human BMP2 with the molecular weight of about 17×103. Conclusion The pSELECT-GFPzeo-hBMP2 eukaryotic expression vector was constructed successfully.

Expression and biological activity analysis of human-mouse chimeric antibody against anthrax protective antigen / 中华微生物学和免疫学杂志

Objective To express human-mouse chimeric antibody against anthrax protective anti-gen and to analyze its biological activities. Methods A new mammalian bipromoter expression vector was constructed with dihydrofolate reduetase(DHFR) gene as the selection and complication marker. First, the light and heavy chain variable region gene of the monoclonal antibody 5E1 were cloned by RT-PCR, at the same time the human IgG1 heavy chain constant region gene and kappa type constant region gene were cloned. Next, the human-mouse chimeric antibody genes were synthesized by fusion PCR. Then, the hu-man-mouse chimeric antibody gene were inserted into MCS of pSecTag and B1 to construct pSecTag-5E1L and B1-5E1H, respectively. Finally, heavy chain expression cassette excised from the B1-5E1H with Bgl Ⅱ/BamH Ⅰ was further cloned into the Bgl Ⅱ site of the pSecTag-5E1L to construct pSecTag-5E1. Plasmid pSecTag-5E1 was transfected into CHO(dhfr) engineering cells and high production cell clones that were screened by enhancing MTX concentration. After collecting medium and purifying chimeric antibody with af-finity chromatogram, purified chimeric antibody was analyzed by SDS-PAGE, Western blot. Results A sta-ble and high production cell line was acquired at MTX concentration 5×10~(-8) mol/L. Conclusion The hu-man-mouse chimeric antibodies were successfully expressed in CHO cells.

MAR increased transgene expression in stable transfected CHO cells / 基础医学与临床

Objective To study the effect of human ?-globin matrix attachment region(MAR) on transgene expression in stably transfected CHO cells.Methods Expression vector was constructed,which contained the ?-globin MAR in both sides of Chloramphenicol acetyltransferase(CAT) reporter gene expression cassette in cis,then transfected into CHO cells.The CAT reporter gene expression was analyzed by ELISA method.Results The ?-globin MAR enhanced the CAT gene expression 5.5-fold in stably transformed CHO cells,while the transgene expression variation among individuals of transformants was decreased.Conclusion MAR increase transgene expression in stably transfected CHO cells.

Construction of decorin expression vector and its expression in CHO cells / 吉林大学学报(医学版)

Objective To construct a eukaryotic expression vector of decorin(DCN),and observe its expression in CHO cells,in order to provide a basis for further study on the anti-tumor effect of DCN. Methods DCN cDNA was amplified by PCR.The human full-length DCN cDNA ligated into pBluescript was used as template.The fragment was ligated to the expression vector pCDNA3 previously digested with XbaⅠ and EcoR Ⅰ.The ligation mixture was transformed into competent E.coli JM109 cells.Transformants containing inserts were confirmed by restrictive digestion and DNA sequencing.The expression vector was transfected into CHO cells using lipofectamine,and transfected cells were cultivated in DMEM containing G418 (800 mg?L-1) for about 2 months.Immunohistochemistry method was used to detect the expression of DCN protein in stably transfected cells.Results The PCR product was about 1 000 bp.The recombinant expression vector was identified by restrictive digestion and DNA sequencing. DCN protein was detectable in stablely transfected cells.Conclusion The recombinant eukaryotic expression vector pCDNA-DEC is constructed successfully and stablely transfected CHO cells are established.

Serum-free Aggregate Perfusion Culture of CHO Cells:an Ultrasonic and Sedimentation Column Combined Perfusion System / 中国生物工程杂志

Using the character of natural aggregation of CHO cells, and an ultrasonic and sedimentation column combined perfusion system to promote cells aggregation and retention into bioreactor,recombinant CHO cell strain MK3-A2 was cultured,which could secrete rhTNK-tPA, by a serum-free perfusion culture system. The culture periods in this two experiments were as long as 77 and 110 days respectively. The cells density reached 2?107 cells /ml. The average volumetric productivity of rhTNK-tPA was 89 mg/L?d, and the highest one was 216mg/L?d.The cells aggregation rate was approximately 90%, and the diameters of most of them were 285～570?m. During the perfusion culture the cells retention rate almost kept in 95% and the viability of cells was more than 85%.Thus, it means that aggregation culture with such perfusion system could be used to scale up produce biopharmaceuticals instead of microcarrier culture system.

Effect of propofol on dopamine uptake by dopamine transporter in Chinese hamster ovary cells / 中华麻醉学杂志

Objective To determine if propofol can affect uptake of dopamine ( DA) by dopamine transporter (DAT) . Methods Chinese hamster ovary (CHO) cells in which DAT was highly expressed were incubated with H-dopamine in the presence or absence of propofol. Uptake of H-DA was measured. The kinetic parameters Vmax and Km were calculated. Results Propofol significantly inhibited uptake of DA by DAT in CHO cells as compared with the control ( P