Recent advances in technology supporting biopharmaceutical production from mammalian cells

Enhanced Biosynthesis Performance of Heterologous Proteins in CHO-K1 Cells Using CRISPR-Cas9

Chinese hamster ovary (CHO) cells are the famous expression system for industrial production of recombinant proteins, such as therapeutic antibodies. However, there still remain bottlenecks in protein quality and weakness in expression efficiency because of the intrinsic genetic properties of the cell. Here we have enhanced biosynthesis performance of heterologous proteins in CHO-K1 cells using CRISPR-Cas9 by editing the genome precisely with two genes for improving ER microenvironment and reinforcing antiapoptotic ability. A linear donor plasmid harboring eGFP-HsQSOX1b and Survivin genes was knocked in specific locus in CHO-K1 genome by the CRISPR-Cas9 RNA guided nucleases via NHEJ with efficiencies of up to 3.85% in the CHO-K1 cell pools following FACS, and the hQSOX1 and hSurvivin genes were integrated into expected genome locus successfully. Compared with control, the antiapoptotic viability of edited CHO-K1 cells was increased by 6.40 times, and the yield has been raised by 5.55 times with GLuc as model protein. The possible molecular mechanisms and pathways of remarkable antiapoptotic ability and protein biosynthesis in modified CHO-K1 cells have been elucidated reasonably. In conclusion, the novel ideas and reliable techniques for obtaining foreign proteins more efficiently in engineered animal cells were very valuable to meet large clinical needs.

Extracellular matrix-coated polyethersulfone-TPGS hollow fiber membranes showing improved biocompatibility and uremic toxins removal for bioartificial kidney application

In this study, L-3, 4-dihydroxyphenylalanine and human collagen type IV were coated over the outer surface of the custom-made hollow fiber membranes (HFMs) with the objective of simultaneously improving biocompatibility leading to proliferation of human embryonic kidney cells-293 (HEK-293) and improving separation of uremic toxins, thereby making them suitable for bioartificial kidney application. Physicochemical characterization showed the development of coated HFMs, resulting in low hemolysis (0.25 ± 0.10%), low SC5b-9 marker level (7.95 ± 1.50 ng/mL), prolonged blood coagulation time, and minimal platelet adhesion, which indicated their improved human blood compatibility. Scanning electron microscopy and confocal laser scanning microscopy showed significantly improved attachment and proliferation of HEK-293 cells on the outer surface of the coated HFMs, which was supported by the results of glucose consumption and MTT cell proliferation assay. The solute rejection profile of these coated HFMs was compared favorably with that of the commercial dialyzer membranes. These coated HFMs showed a remarkable 1.6-3.2 fold improvement in reduction ratio of uremic toxins as compared to standard dialyzer membranes. These results clearly demonstrated that these extracellular matrix-coated HFMs can be a potential biocompatible substrate for the attachment and proliferation of HEK-293 cells and removal of uremic toxins from the simulated blood, which may find future application for bioartificial renal assist device.

Glycoengineering in CHO Cells: Advances in Systems Biology

For several decades, glycoprotein biologics have been successfully produced from Chinese hamster ovary (CHO) cells. The therapeutic efficacy and potency of glycoprotein biologics are often dictated by their post-translational modifications, particularly glycosylation, which unlike protein synthesis, is a non-templated process. Consequently, both native and recombinant glycoprotein production generate heterogeneous mixtures containing variable amounts of different glycoforms. Stability, potency, plasma half-life, and immunogenicity of the glycoprotein biologic are directly influenced by the glycoforms. Recently, CHO cells have also been explored for production of therapeutic glycosaminoglycans (e.g., heparin), which presents similar challenges as producing glycoproteins biologics. Approaches to controlling heterogeneity in CHO cells and directing the biosynthetic process toward desired glycoforms are not well understood. A systems biology approach combining different technologies is needed for complete understanding of the molecular processes accounting for this variability and to open up new venues in cell line development. In this review, we describe several advances in genetic manipulation, modeling, and glycan and glycoprotein analysis that together will provide new strategies for glycoengineering of CHO cells with desired or enhanced glycosylation capabilities.

Exploring the Potential Application of Short Non-Coding RNA-Based Genetic Circuits in Chinese Hamster Ovary Cells

The majority of cell engineering for recombinant protein production to date has relied on traditional genetic engineering strategies, such as gene overexpression and gene knock-outs, to substantially improve the production capabilities of Chinese Hamster Ovary (CHO) cells. However, further improvements in cellular productivity or control over product quality is likely to require more sophisticated rational approaches to coordinate and balance cellular pathways. For these strategies to be implemented, novel molecular tools need to be developed to facilitate more refined control of gene expression. Multiple gene control strategies are developed over the last decades in the field of synthetic biology, including DNA and RNA-based systems, which allows tight and timely control over gene expression. microRNAs has received a lot of attention over the last decade in the CHO field and are used to engineer and improve CHO cells. In this review we focus on microRNA-based gene control systems and discuss their potential use as tools rather than targets in order to gain better control over gene expression.

Identifying HIPK1 as Target of miR-22-3p Enhancing Recombinant Protein Production From HEK 293 Cell by Using Microarray and HTP siRNA Screen

Protein expression from human embryonic kidney cells (HEK 293) is an important tool for structural and clinical studies. It is previously shown that microRNAs (small, noncoding RNAs) are effective means for improved protein expression from these cells, and by conducting a high-throughput screening of the human microRNA library, several microRNAs are identified as potential candidates for improving expression. From these, miR-22-3p is chosen for further study since it increased the expression of luciferase, two membrane proteins and a secreted fusion protein with minimal effect on the cells' growth and viability. Since each microRNA can interact with several gene targets, it is of interest to identify the repressed genes for understanding and exploring the improved expression mechanism for further implementation. Here, the authors describe a novel approach for identification of the target genes by integrating the differential gene expression analysis with information obtained from our previously conducted high-throughput siRNA screening. The identified genes were validated as being involved in improving luciferase expression by using siRNA and qRT-PCR. Repressing the target gene, HIPK1, is found to increase luciferase and GPC3 expression 3.3- and 2.2-fold, respectively.

miR-CATCH Identifies Biologically Active miRNA Regulators of the Pro-Survival Gene XIAP, in Chinese Hamster Ovary Cells

Genetic engineering of mammalian cells is of interest as a means to boost bio-therapeutic protein yield. X-linked inhibitor of apoptosis (XIAP) overexpression has previously been shown to enhance CHO cell growth and prolong culture longevity while additionally boosting productivity. The authors confirmed this across a range of recombinant products (SEAP, EPO, and IgG). However, stable overexpression of an engineering transgene competes for the cells translational machinery potentially compromising product titre. MicroRNAs are attractive genetic engineering candidates given their non-coding nature and ability to regulate multiple genes simultaneously, thereby relieving the translational burden associated with stable overexpression of a protein-encoding gene. The large number of potential targets of a single miRNA, falsely predicted in silico, presents difficulties in identifying those that could be useful engineering tools. The authors explored the identification of direct miRNA regulators of the pro-survival endogenous XIAP gene in CHO-K1 cells by using a miR-CATCH protocol. A biotin-tagged antisense DNA oligonucleotide for XIAP mRNA is designed and used to pull down and capture bound miRNAs. Two miRNAs are chosen out of the 14 miRNAs identified for further validation, miR-124-3p and miR-19b-3p. Transient transfection of mimics for both results in the diminished translation of endogenous CHO XIAP protein whereas their inhibition increases XIAP protein levels. A 3'UTR reporter assay confirms miR-124-3p to be a bona fide regulator of XIAP in CHO-K1 cells. This method demonstrates a useful approach to finding miRNA candidates for CHO cell engineering without competing for the cellular translational machinery.

Amino acid misincorporation in recombinant proteins

Proteins provide the molecular basis for cellular structure, catalytic activity, signal transduction, and molecular transport in biological systems. Recombinant protein expression is widely used to prepare and manufacture novel proteins that serve as the foundation of many biopharmaceutical products. However, protein translation bioprocesses are inherently prone to low-level errors. These sequence variants caused by amino acid misincorporation have been observed in both native and recombinant proteins. Protein sequence variants impact product quality, and their presence can be exacerbated through cellular stress, overexpression, and nutrient starvation. Therefore, the cell line selection process, which is used in the biopharmaceutical industry, is not only directed towards maximizing productivity, but also focuses on selecting clones which yield low sequence variant levels, thereby proactively avoiding potentially inauspicious patient safety and efficacy outcomes. Here, we summarize a number of hallmark studies aimed at understanding the mechanisms of amino acid misincorporation, as well as exacerbating factors, and mitigation strategies. We also describe key advances in analytical technologies in the identification and quantification of sequence variants, and some practical considerations when using LC-MS/MS for detecting sequence variants.

Sophisticated Cloning, Fermentation, and Purification Technologies for an Enhanced Therapeutic Protein Production: A Review

The protein productions strategies are crucial towards the development of application based research and elucidating the novel purification strategies for industrial production. Currently, there are few innovative avenues are studies for cloning, upstream, and purification through efficient bioprocess development. Such strategies are beneficial for industries as well as proven to be vital for effectual therapeutic protein development. Though, these techniques are well documented, but, there is scope of addition to current knowledge with novel and new approaches and it will pave new avenues in production of recombinant microbial and non-microbial proteins including secondary metabolites. In this review, we have focussed on the recent development in clone selection, various modern fermentation and purification technologies and future directions in these emerging areas. Moreover, we have also highlighted notable perspectives and challenges involved in the bioengineering of such proteins, including quality by design, gene editing and pioneering ideas. The biopharmaceutical industries continue to shift towards more flexible, automated platforms and economical product development, which in turn can help in developing the cost effective processes and affordable drug development for a large community.

Industrial Production of Therapeutic Proteins: Cell Lines, Cell Culture, and Purification

A central pillar of the biotechnology and pharmaceutical industries continues to be the development of biological drug products manufactured from engineered mammalian cell lines. Since the hugely successful launch of human tissue plasminogen activator in 1987 and erythropoietin in 1988, the biopharmaceutical market has grown immensely. In 2014, biotherapeutics made up a significant portion of global drug sales as 7 of the top 10 and 21 of top 50 selling pharmaceuticals in the world were biologics with over US$100 billion in global sales (Table 1, [1]).

Main Quality Attributes of Monoclonal Antibodies and Effect of Cell Culture Components

The culture media optimization is an inevitable part of upstream process development in therapeutic monoclonal antibodies (mAbs) production. The quality by design (QbD) approach defines the assured quality of the final product through the development stage. An important step in QbD is determination of the main quality attributes. During the media optimization, some of the main quality attributes such as glycosylation pattern, charge variants, aggregates, and low-molecular-weight species, could be significantly altered. Here, we provide an overview of how cell culture medium components affects the main quality attributes of the mAbs. Knowing the relationship between the culture media components and the main quality attributes could be successfully utilized for a rational optimization of mammalian cell culture media for industrial mAbs production.

Cell culture media supplemented with raffinose reproducibly enhances high mannose glycan formation

Glycosylation plays a pivotal role in pharmacokinetics and protein physiochemical characteristics. In particular, effector functions including antibody-dependent cell-mediated cytotoxicity (ADCC) can be desired, and it has been described that high-mannose species exhibited enhanced ADCC. In this work we present the trisaccharide raffinose as a novel cell culture medium supplement to promote high mannose N-glycans in fed-batch cultures, which is sought after in the development of biosimilars to match the quality profile of the reference medicinal product (RMP) also. Up to six-fold increases of high mannose species were observed with increasing raffinose concentrations in the medium of shaken 96-deepwell plates and shake tubes when culturing two different CHO cell lines in two different media. The findings were confirmed in a pH-, oxygen- and CO₂-controlled environment in lab-scale 3.5-L bioreactors. To circumvent detrimental effects on cell growth and productivity at high raffinose concentrations, the media osmolality was adjusted to reach the same value independently of the supplement concentration. Interestingly, raffinose predominantly enhanced mannose 5 glycans, and to a considerably smaller degree, mannose 6. While the underlying mechanism is still not fully understood, minor effects on the nucleotide sugar levels have been observed and transcriptomics analysis revealed that raffinose supplementation altered the expression levels of a number of glycosylation related genes. Among many genes, galactosyltransferase was downregulated and sialyltransferase upregulated. Our results highlight the potential of cell culture medium supplementation to modulate product quality.

Low glucose concentrations within typical industrial operating conditions have minimal effect on the transcriptome of recombinant CHO cells

Typically, mammalian cell culture medium contains high glucose concentrations that are analogous to diabetic levels in humans, suggesting that mammalian cells are cultivated in excessive glucose. Using RNA-Seq, this study characterized the Chinese hamster ovary (CHO) cell transcriptome under two glucose concentrations to assess the genetic effects associated with metabolic pathways, in addition to other global responses. The initial extracellular glucose concentrations used represented high (30 mM) and low (10 mM) glucose conditions, where at the time the transcriptomes were compared, the glucose concentrations were approximately 24 and 4.4 mM for the mid-exponential cultures, where 4.4 mM represents a common target concentration in the biopharmaceutical industry for controlled fed-batch cultures. A recombinant CHO cell line producing a monoclonal antibody was used, such that the impact on glycosylation genes could be evaluated. Relatively few genes were identified as being significantly different (FDR ≤ 0.01) between the high and low glucose conditions, for example, only 575 genes, and only 40 of these genes had 2-fold or greater differences. Gene expression differences for glycolysis, TCA cycle, and glycosylation-related reactions were minimal and unlikely to have biological significance. This transcriptome study indicates that low glucose concentrations in the culture medium are unlikely to cause any biologically significant or detrimental changes to CHO cells at the transcriptome level. Furthermore, it is well-known that maintaining low glucose concentrations in fed-batch cultures can reduce lactate production, which in turn improves process outcomes. Taken together, the transcriptome data supports the continued development of low glucose-based processes to control lactate. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:771-785, 2017.

Glycoengineering of pertuzumab and its impact on the pharmacokinetic/pharmacodynamic properties

Pertuzumab is an antihuman HER2 antibody developed for HER2 positive breast cancer. Glycosylation profiles are always the important issue for antibody based therapy. Previous findings have suggested the impact of glycosylation profiles on the function of antibodies, like pharmacodynamics, antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). However, the roles of fucose and sialic acid in the function of therapeutic antibodies still need further investigation, especially the role of sialic acid in nonfucosylated antibodies. This study focused on the pharmacokinetic and pharmacodynamic properties of pertuzumab after glycoengineering. Herein, nonfucosylated pertuzumab was produced in CHO^FUT8−/− cells, and desialylated pertuzumab was generated by enzymatic hydrolysis. Present data indicated that fucose was critical for ADCC activity by influencing the interaction between pertuzumab and FcγRIIIa, nevertheless removal of sialic acid increased the ADCC and CDC activity of pertuzumab. Meanwhile, regarding to sialic acid, sialidase hydrolysis directly resulted in asialoglycoprotein receptors (ASGPRs) dependent clearance in hepatic cells in vitro. The pharmacokinetic assay revealed that co-injection of asialofetuin can protect desialylated pertuzumab against ASGPRs-mediated clearance. Taken together, the present study elucidated the importance of fucose and sialic acid for pertuzumab, and also provided further understanding of the relationship of glycosylation/pharmacokinetics/pharmacodynamics of therapeutic antibody.

Magnetic sorting of membrane associated IgG for phenotype-based selection of stable antibody producing cells

To establish a simple and widely accessible technique for rapidly selecting high producing Chinese hamster ovary (CHO) cells engineered to express a monoclonal antibody (mAb), we have exploited the transient display of recombinant protein on their cell surface. In combination with magnetic bead-based methods, we demonstrate the ability to select for cells of high productivity in the absence of any metabolic-based selection method. This technique is sufficient to obtain genetically stable engineered CHO cells via a single step of cell subcloning and yields sought-after stable, high IgG producing clonal cell lines. This technique may also be applied to other types of cells as well as polyclonal Ab cell pools.

Recent advances in (therapeutic protein) drug development

Therapeutic protein drugs are an important class of medicines serving patients most in need of novel therapies. Recently approved recombinant protein therapeutics have been developed to treat a wide variety of clinical indications, including cancers, autoimmunity/inflammation, exposure to infectious agents, and genetic disorders. The latest advances in protein-engineering technologies have allowed drug developers and manufacturers to fine-tune and exploit desirable functional characteristics of proteins of interest while maintaining (and in some cases enhancing) product safety or efficacy or both. In this review, we highlight the emerging trends and approaches in protein drug development by using examples of therapeutic proteins approved by the U.S. Food and Drug Administration over the previous five years (2011–2016, namely January 1, 2011, through August 31, 2016).

Glycoengineering of CHO Cells to Improve Product Quality

Chinese hamster ovary (CHO) cells represent the predominant platform in biopharmaceutical industry for the production of recombinant biotherapeutic proteins, especially glycoproteins. These glycoproteins include oligosaccharide or glycan attachments that represent one of the principal components dictating product quality. Especially important are the N-glycan attachments present on many recombinant glycoproteins of commercial interest. Furthermore, altering the glycan composition can be used to modulate the production quality of a recombinant biotherapeutic from CHO and other mammalian hosts. This review first describes the glycosylation network in mammalian cells and compares the glycosylation patterns between CHO and human cells. Next genetic strategies used in CHO cells to modulate the sialylation patterns through overexpression of sialyltransfereases and other glycosyltransferases are summarized. In addition, other approaches to alter sialylation including manipulation of sialic acid biosynthetic pathways and inhibition of sialidases are described. Finally, this review also covers other strategies such as the glycosylation site insertion and manipulation of glycan heterogeneity to produce desired glycoforms for diverse biotechnology applications.

The 'Omics Revolution in CHO Biology: Roadmap to Improved CHO Productivity

Increased understanding of Chinese hamster ovary (CHO) cell physiology has been ushered in upon availability of the parental CHO-K1 cell line genome. Free and openly accessible sequence information has complemented transcriptomic and proteomic studies. The previous decade has also seen an increase in sensitivity and accuracy of proteomic methods due to technology development. In this genomic era, high-throughput screening methods, sophisticated informatic tools, and models continually drive major innovations in cell line development and process engineering. This review describes the various achievements in 'omics techniques and their application to improve recombinant protein expression from CHO cell lines.

Development of adsorptive hybrid filters to enable two-step purification of biologics

Recent progress in mammalian cell culture process has resulted in significantly increased product titers, but also a substantial increase in process- and product-related impurities. Due to the diverse physicochemical properties of these impurities, there is constant need for new technologies that offer higher productivity and improved economics without sacrificing the process robustness required to meet final drug substance specifications. Here, we examined the use of new synthetic adsorptive hybrid filters (AHF) modified with the high binding capacity of quaternary amine (Emphaze™ AEX) and salt-tolerant biomimetic (Emphaze™ ST-AEX) ligands for clearance of process-related impurities like host cell protein (HCP), residual DNA, and virus. The potential to remove soluble aggregates was also examined. Our aim was to develop a mechanistic understanding of the interactions governing adsorptive removal of impurities during filtration by evaluating the effect of various filter types, feed streams, and process conditions on impurity removal. The ionic capacity of these filters was measured and correlated with their ability to remove impurities for multiple molecules. The ionic capacity of AHF significantly exceeded that of traditional adsorptive depth filters (ADF) by 40% for the Emphaze™ AEX and by 700% for the Emphaze™ ST-AEX, providing substantially higher reduction of soluble anionic impurities, including DNA, HCPs and model virus. Nevertheless, we determined that ADF with filter aid provided additional hydrophobic functionality that resulted in removal of higher molecular weight species than AHF. Implementing AHF demonstrated improved process-related impurity removal and viral clearance after Protein A chromatography and enabled a two-step purification process. The consequences of enhanced process performance are far reaching because it allows the downstream polishing train to be restructured and simplified, and chromatographic purity standards to be met with a reduced number of chromatographic steps.

Rapid high-throughput cloning and stable expression of antibodies in HEK293 cells

Single-cell based amplification of immunoglobulin variable regions is a rapid and powerful technique for cloning antigen-specific monoclonal antibodies (mAbs) for purposes ranging from general laboratory reagents to therapeutic drugs. From the initial screening process involving small quantities of hundreds or thousands of mAbs through in vitro characterization and subsequent in vivo experiments requiring large quantities of only a few, having a robust system for generating mAbs from cloning through stable cell line generation is essential. A protocol was developed to decrease the time, cost, and effort required by traditional cloning and expression methods by eliminating bottlenecks in these processes. Removing the clonal selection steps from the cloning process using a highly efficient ligation-independent protocol and from the stable cell line process by utilizing bicistronic plasmids to generate stable semi-clonal cell pools facilitated an increased throughput of the entire process from plasmid assembly through transient transfections and selection of stable semi-clonal cell pools. Furthermore, the time required by a single individual to clone, express, and select stable cell pools in a high-throughput format was reduced from 4 to 6months to only 4 to 6weeks.

A Single-use Strategy to Enable Manufacturing of Affordable Biologics

The current processing paradigm of large manufacturing facilities dedicated to single product production is no longer an effective approach for best manufacturing practices. Increasing competition for new indications and the launch of biosimilars for the monoclonal antibody market have put pressure on manufacturers to produce at lower cost. Single-use technologies and continuous upstream processes have proven to be cost-efficient options to increase biomass production but as of today the adoption has been only minimal for the purification operations, partly due to concerns related to cost and scale-up. This review summarizes how a single-use holistic process and facility strategy can overcome scale limitations and enable cost-efficient manufacturing to support the growing demand for affordable biologics. Technologies enabling high productivity, right-sized, small footprint, continuous, and automated upstream and downstream operations are evaluated in order to propose a concept for the flexible facility of the future.

5' and 3' Untranslated Regions Strongly Enhance Performance of Geminiviral Replicons in Nicotiana benthamiana Leaves

We previously reported a recombinant protein production system based on a geminivirus replicon that yields high levels of vaccine antigens and monoclonal antibodies in plants. The bean yellow dwarf virus (BeYDV) replicon generates massive amounts of DNA copies, which engage the plant transcription machinery. However, we noticed a disparity between transcript level and protein production, suggesting that mRNAs could be more efficiently utilized. In this study, we systematically evaluated genetic elements from human, viral, and plant sources for their potential to improve the BeYDV system. The tobacco extensin terminator enhanced transcript accumulation and protein production compared to other commonly used terminators, indicating that efficient transcript processing plays an important role in recombinant protein production. Evaluation of human-derived 5' untranslated regions (UTRs) indicated that many provided high levels of protein production, supporting their cross-kingdom function. Among the viral 5' UTRs tested, we found the greatest enhancement with the tobacco mosaic virus omega leader. An analysis of the 5' UTRs from the Arabidopsis thaliana and Nicotinana benthamiana photosystem I K genes found that they were highly active when truncated to include only the near upstream region, providing a dramatic enhancement of transgene production that exceeded that of the tobacco mosaic virus omega leader. The tobacco Rb7 matrix attachment region inserted downstream from the gene of interest provided significant enhancement, which was correlated with a reduction in plant cell death. Evaluation of Agrobacterium strains found that EHA105 enhanced protein production and reduced cell death compared to LBA4301 and GV3101. We used these improvements to produce Norwalk virus capsid protein at >20% total soluble protein, corresponding to 1.8 mg/g leaf fresh weight, more than twice the highest level ever reported in a plant system. We also produced the monoclonal antibody rituximab at 1 mg/g leaf fresh weight.

Transcriptome analysis of a CHO cell line expressing a recombinant therapeutic protein treated with inducers of protein expression

The search for specific productivity (qP) determinants in Chinese hamster ovary (CHO) cells has been the focus of the biopharmaceutical cell line engineering efforts aimed at creating "super-producer" cell lines. In this study, we evaluated the impact of small-molecule inducers and temperature shift on recombinant protein production, and used transcriptomic analysis to define gene-phenotype correlations for qP in our biological system. Next-generation RNA Sequencing (RNA-Seq) analysis revealed that each individual inducer (caffeine, hexamethylene bisacetamide (HMBA) and sodium butyrate (NaBu)) or a combination treatment had a distinct impact on the gene expression program of the RANK-Fc cell line. Temperature shift to 31 °C impacted inducer action with respect to transcriptional changes and phenotypic cell line parameters. We showed that inducer treatment was able to increase expression level of the Fc- fusion mRNA and the selectable marker mRNA from 16% up to 45% of total mRNA in the cell. We further demonstrated that qP exhibited a strong positive linear correlation to transcript levels of both the RANK-Fc fusion protein and the dihydrofolate reductase (DHFR) selectable marker. In fact, these were 2 out of 7 transcripts with significant positive correlation to qP at both temperatures. Many more transcripts were anti- correlated to qP, and gene set enrichment analysis (GSEA) revealed that those were involved in cell cycle progression, transcription, mRNA processing, translation and protein folding. Therefore, we postulate that the transcript level of the recombinant protein is a major qP determinant in our biological system, while downregulation of routine activity within the cell is necessary to divert cellular resources towards recombinant protein production.

Enhanced protein production by microRNA-30 family in CHO cells is mediated by the modulation of the ubiquitin pathway

Functional genomics represent a valuable approach to improve culture performance of Chinese hamster ovary (CHO) cell lines for biopharmaceutical manufacturing. Recent advances in applied microRNA (miRNAs) research suggest that these small non-coding RNAs are critical for the regulation of cell phenotypes in CHO cells. However, the notion that individual miRNAs usually control the expression of hundreds of different genes makes miRNA target identification highly complex. We have recently reported that the entire miR-30 family enhances recombinant protein production in CHO cells. To better understand the pro-productive effects of this miRNA family, we set out to identify their downstream target genes in CHO cells. Computational target prediction combined with a comprehensive functional validation enabled the discovery of a set of twenty putative target genes for all productivity enhancing miR-30 family members. We demonstrate that all miR-30 isoforms contribute to the regulation of the ubiquitin pathway in CHO cells by directly targeting the ubiquitin E3 ligase S-phase kinase-associated protein 2 (Skp2). Finally, we provide several lines of evidence that miR-30-mediated modulation of the ubiquitin pathway may enhance recombinant protein expression in CHO cells. In summary, this study supports the importance of non-coding RNAs, especially of miRNAs, in the context of cell line engineering.

Improving recombinant protein production in the Chlamydomonas reinhardtii chloroplast using vivid Verde Fluorescent Protein as a reporter

Microalgae have potential as platforms for the synthesis of high-value recombinant proteins due to their many beneficial attributes including ease of cultivation, lack of pathogenic agents, and low-cost downstream processing. However, current recombinant protein levels are low compared to other microbial platforms and stable insertion of transgenes is available in only a few microalgal species. We have explored different strategies aimed at increasing growth rate and recombinant protein production in the Chlamydomonas reinhardtii chloroplast. A novel fluorescent protein (vivid Verde Fluorescent Protein, VFP) was expressed under the control of the native atpA promoter/5'UTR element. VFP levels were detected by western blotting, with increased protein levels observed when co-expressed with a gene encoding the Escherichia coli Spy chaperone. We used these transformant lines to study the effect of temperature, light and media on recombinant protein production and cell growth. VFP levels and fluorescence, assessed by flow cytometry, allowed a determination of improved cultivation conditions as 30°C under mixotrophic mode. These conditions were tested for the accumulation of an antimicrobial endolysin (Cpl-1) of potential commercial interest, observing that the outcome obtained for VFP could not be easily replicated for Cpl-1. This study suggests that recombinant protein expression is product-specific and needs to be optimized individually.

Glycosylation-related genes in NS0 cells are insensitive to moderately elevated ammonium concentrations

NS0 and Chinese hamster ovary (CHO) cell lines are used to produce recombinant proteins for human therapeutics; however, ammonium accumulation can negatively impact cell growth, recombinant protein production, and protein glycosylation. To improve product quality and decrease costs, the relationship between ammonium and protein glycosylation needs to be elucidated. While ammonium has been shown to adversely affect glycosylation-related gene expression in CHO cells, NS0 studies have not been performed. Therefore, this study sought to determine if glycosylation in NS0 cells were ammonium-sensitive at the gene expression level. Using a DNA microarray that contained mouse glycosylation-related and housekeeping genes, these genes were analyzed in response to various culture conditions - elevated ammonium, elevated salt, and elevated ammonium with proline. Surprisingly, no significant differences in gene expression levels were observed between the control and these conditions. Further, the elevated ammonium cultures were analyzed using real-time quantitative reverse transcriptase PCR (qRT-PCR) for key glycosylation genes, and the qRT-PCR results corroborated the DNA microarray results, demonstrating that NS0 cells are ammonium-insensitive at the gene expression level. Since NS0 are known to have elevated nucleotide sugar pools under ammonium stress, and none of the genes directly responsible for these metabolic pools were changed, consequently cellular control at the translational or substrate-level must be responsible for the universally observed decreased glycosylation quality under elevated ammonium.

Trends in Upstream and Downstream Process Development for Antibody Manufacturing

A steady increase of product titers and the corresponding change in impurity composition represent a challenge for development and optimization of antibody production processes. Additionally, increasing demands on product quality result in higher complexity of processes and analytics, thereby increasing the costs for product work-up. Concentration and composition of impurities are critical for efficient process development. These impurities can show significant variations, which primarily depend on culture conditions. They have a major impact on the work-up strategy and costs. The resulting "bottleneck" in downstream processing requires new optimization, technology and development approaches. These include the optimization and adaptation of existing unit operations respective to the new separation task, the assessment of alternative separation technologies and the search for new methods in process development. This review presents an overview of existing methods for process optimization and integration and indicates new approaches for future developments.