The art of CHO cell engineering: A comprehensive retrospect and future perspectives

Overexpression of transcription factor Foxa1 and target genes remediate therapeutic protein production bottlenecks in Chinese hamster ovary cells

Despite extensive research conducted to increase protein production from Chinese hamster ovary (CHO) cells, cellular bottlenecks often remain, hindering high yields. In this study, a transcriptomic analysis led to the identification of 32 genes that are consistently upregulated in high producer clones and thus might mediate high productivity. Candidate genes were associated with functions such as signaling, protein folding, cytoskeleton organization, and cell survival. We focused on two engineering targets, Erp27, which binds unfolded proteins and the Erp57 disulfide isomerase in the endoplasmic reticulum, and Foxa1, a pioneering transcription factor involved in organ development. Erp27 moderate overexpression increased production of an easy-to-express antibody, whereas Erp27 and Erp57 co-overexpression increased cell density, viability, and the yield of difficult-to-express proteins. Foxa1 overexpression increased cell density, cell viability, and easy- and difficult-to-express protein yields, whereas it decreased reactive oxygen species late in fed-batch cultures. Foxa1 overexpression upregulated two other candidate genes that increased the production of difficult- and/or easy-to-express proteins, namely Ca3, involved in protecting cells from oxidative stress, and Tagap, involved in signaling and cytoskeleton remodeling. Overall, several genes allowing to overcome CHO cell bottlenecks were identified, including Foxa1, which mediated multiple favorable metabolic changes that improve therapeutic protein yields.

Validation and identification of reference genes in Chinese hamster ovary cells for Fc-fusion protein production

IMPACT STATEMENT

In order to reveal potential genotype-phenotype relationship, RT-qPCR reactions are frequently applied which require validated and reliable reference genes. With the investigation on long-term passage and fed-batch cultivation of CHO cells producing an Fc-fusion protein, four new reference genes-Akr1a1, Gpx1, Aprt, and Rps16, were identified from 20 candidates with the aid of geNorm, NormFinder, BestKeeper, and ΔCt programs and methods. This article provided more verified options in reference gene selection in related research on CHO cells.

Glycosylated Biotherapeutics: Immunological Effects of N-Glycolylneuraminic Acid

The emerging field of biotherapeutics provides successful treatments for various diseases, yet immunogenicity and limited efficacy remain major concerns for many products. Glycosylation is a key factor determining the pharmacological properties of biotherapeutics, including their stability, solubility, bioavailability, pharmacokinetics, and immunogenicity. Hence, an increased attention is directed at optimizing the glycosylation properties of biotherapeutics. Currently, most biotherapeutics are produced in non-human mammalian cells in light of their ability to produce human-like glycosylation. However, most mammals produce the sialic acid N-glycolylneuraminic acid (Neu5Gc), while humans cannot due to a specific genetic defect. Humans consume Neu5Gc in their diet from mammalian derived foods (red meat and dairy) and produce polyclonal antibodies against diverse Neu5Gc-glycans. Moreover, Neu5Gc can metabolically incorporate into human cells and become presented on surface or secreted glycans, glycoproteins, and glycolipids. Several studies in mice suggested that the combination of Neu5Gc-containing epitopes and anti-Neu5Gc antibodies could contribute to exacerbation of chronic inflammation-mediated diseases (e.g., cancer, cardiovascular diseases, and autoimmunity). This could potentially become complicated with exposure to Neu5Gc-containing biotherapeutics, bio-devices or xenografts. Indeed, Neu5Gc can be found on various approved and marketed biotherapeutics. Here, we provide a perspective review on the possible consequences of Neu5Gc glycosylation of therapeutic protein drugs due to the limited published evidence of Neu5Gc glycosylation on marketed biotherapeutics and studies on their putative effects on immunogenicity, drug efficacy, and safety.

Distance effect characteristic of the matrix attachment region increases recombinant protein expression in Chinese hamster ovary cells

OBJECTIVES

Previously, we have found that the matrix attachment region (MAR) may confer a 'distance effect' on transgene expression. This work aims to systematically explore the increased transgene expression in transfected Chinese hamster ovary (CHO) cells due to the characteristics of MAR and its mechanism.

RESULTS

Compared with the control vector, 500 and 1000 bp DNA distances between MAR and the cytomegalovirus promoter can increase transgene expression by 1.77- and 1.56-fold, respectively. Meanwhile, transgene expression was not affected when 2000 and 2500 bp spacer DNAs were inserted, but a declining trend was observed when a 1500 bp spacer DNA was inserted. The vector containing a 500 bp DNA distance significantly increased the expression of the enhanced green fluorescent protein, and this increase was not related to transgene copy numbers.

CONCLUSIONS

A short DNA distance-containing MAR confers high transgene expression level in transfected CHO cells, but a distance threshold does not exist in the vector system.

Enzyme-free release of adhered cells from standard culture dishes using intermittent ultrasonic traveling waves

Cell detachment is essential in culturing adherent cells. Trypsinization is the most popular detachment technique, even though it reduces viability due to the damage to the membrane and extracellular matrix. Avoiding such damage would improve cell culture efficiency. Here we propose an enzyme-free cell detachment method that employs the acoustic pressure, sloshing in serum-free medium from intermittent traveling wave. This method detaches 96.2% of the cells, and increases its transfer yield to 130% of conventional methods for 48 h, compared to the number of cells detached by trypsinization. We show the elimination of trypsinization reduces cell damage, improving the survival of the detached cells. Acoustic pressure applied to the cells and media sloshing from the intermittent traveling wave were identified as the most important factors leading to cell detachment. This proposed method will improve biopharmaceutical production by expediting the amplification of tissue-cultured cells through a more efficient transfer process.

Enhanced transient expression of an anti-CD52 monoclonal antibody in CHO cells through utilization of miRNA sponge technology

Chinese hamster ovary (CHO) cells are the dominant mammalian host system for the production of recombinant therapeutic proteins. Improving the viable cell density during culture of recombinant CHO cells can greatly affect the production yield. MicroRNAs (miRs) -15a and 16-1 are known as negative regulators of multiple genes involved in cell cycle progression and apoptotic inhibition. miR sponges, which act as decoy targets, are transcripts which contain complementary binding sites to the seed region of related miRs. Stably expressed miR sponges are known as efficient tools for miR loss of function studies. In this study, stable CHO cell pools and clones expressing miRs-15a and 16-1 specific decoy transcript downstream of an enhanced green fluorescent protein reporter gene was developed. Analysis of cell growth during 12 days of batch culture indicated improved maximum viable cell density of CHO cells and clones expressing the decoy transcript. In addition, transient expression of a recombinant anti-CD52 monoclonal antibody was significantly improved in a decoy harboring CHO cell clone, representing a 3.37-fold increase in yield after 4 days of culture. Our results indicated that miR sponge technology can be successfully applied for the improvement of cell viability and transient monoclonal antibody expression in CHO host cells.

Nanoscale integration of single cell biologics discovery processes using optofluidic manipulation and monitoring

The new and rapid advancement in the complexity of biologics drug discovery has been driven by a deeper understanding of biological systems combined with innovative new therapeutic modalities, paving the way to breakthrough therapies for previously intractable diseases. These exciting times in biomedical innovation require the development of novel technologies to facilitate the sophisticated, multifaceted, high-paced workflows necessary to support modern large molecule drug discovery. A high-level aspiration is a true integration of "lab-on-a-chip" methods that vastly miniaturize cellulmical experiments could transform the speed, cost, and success of multiple workstreams in biologics development. Several microscale bioprocess technologies have been established that incrementally address these needs, yet each is inflexibly designed for a very specific process thus limiting an integrated holistic application. A more fully integrated nanoscale approach that incorporates manipulation, culture, analytics, and traceable digital record keeping of thousands of single cells in a relevant nanoenvironment would be a transformative technology capable of keeping pace with today's rapid and complex drug discovery demands. The recent advent of optical manipulation of cells using light-induced electrokinetics with micro- and nanoscale cell culture is poised to revolutionize both fundamental and applied biological research. In this review, we summarize the current state of the art for optical manipulation techniques and discuss emerging biological applications of this technology. In particular, we focus on promising prospects for drug discovery workflows, including antibody discovery, bioassay development, antibody engineering, and cell line development, which are enabled by the automation and industrialization of an integrated optoelectronic single-cell manipulation and culture platform. Continued development of such platforms will be well positioned to overcome many of the challenges currently associated with fragmented, low-throughput bioprocess workflows in biopharma and life science research.

Consequences of trace metal variability and supplementation on Chinese hamster ovary (CHO) cell culture performance: A review of key mechanisms and considerations

Trace metals are supplied to chemically-defined media (CDM) for optimal Chinese hamster ovary (CHO) cell culture performance during the production of monoclonal antibodies and other therapeutic proteins. However, lot-to-lot and vendor-to-vendor variability in raw materials consequently leads to an imbalance of trace metals that are supplied to CDM. This imbalance can yield detrimental effects rooted in several primary mechanisms and pathways including oxidative stress, apoptosis, lactate accumulation, and unfavorable glycan synthesis. Recent research endeavors involve supplying zinc, copper, and manganese to CDM in excess to further maximize culture productivity and product quality. These treatments significantly impact critical quality attributes and furthermore highlight the degree to which trace metal availability can affect CHO cell culture performance. This review highlights the role of trace metal variability, supplementation, and interplay on key cellular mechanisms responsible for overall culture performance and the production and quality of therapeutic proteins.

Real-time quantification and supplementation of bioreactor amino acids to prolong culture time and maintain antibody product quality

Real‐time monitoring of cell cultures in bioreactors can enable expedited responses necessary to correct potential batch failure perturbations which may normally go undiscovered until the completion of the batch and result in failure. Currently, analytical technologies are dedicated to real‐time monitoring of bioreactor parameters such as pH, dissolved oxygen, and temperature, nutrients such as glucose and glutamine, or metabolites such as lactate. Despite the importance of amino acids as the building blocks of therapeutic protein products, other than glutamine their concentrations are not commonly measured. Here, we present a study into amino acid monitoring, supplementation strategies, and how these techniques may impact the cell growth profiles and product quality. We used preliminary bioreactor runs to establish baselines by determining initial amino acid consumption patterns, the results of which were used to select a pool of amino acids which gets depleted in the bioreactor. These amino acids were combined into blends which were supplemented into bioreactors during a subsequent run, the concentrations of which were monitored using a mass spectrometry based at‐line method we developed to quickly assess amino acid concentrations from crude bioreactor media. We found that these blends could prolong culture life, reversing a viable cell density decrease that was leading to batch death. Additionally, we assessed how these strategies might impact protein product quality, such as the glycan profile. The amino acid consumption data were aligned with the final glycan profiles in principal component analysis to identify which amino acids are most closely associated with glycan outcomes.

BiP Inducer X: An ER Stress Inhibitor for Enhancing Recombinant Antibody Production in CHO Cell Culture

Prolonged endoplasmic reticulum (ER) stress reduces protein synthesis and induces apoptosis in mammalian cells. When dimethyl sulfoxide (DMSO), a specific monoclonal antibody productivity (q_mAb )-enhancing reagent, is added to recombinant Chinese hamster ovary (rCHO) cell cultures (GSR cell line), it induces ER stress and apoptosis in a dose-dependent manner. To determine an effective ER stress inhibitor, three ER stress inhibitors (BiP inducer X [BIX], tauroursodeoxycholic acid, and carbazole) are examined and BIX shows the best production performance. Coaddition of BIX (50 μm) with DMSO extends the culture longevity and enhances q_mAb . As a result, the maximum mAb concentration is significantly increased with improved galactosylation. Coaddition of BIX significantly increases the expression level of binding immunoglobulin protein (BiP) followed by increased expression of chaperones (calnexin and GRP94) and galactosyltransferase. Furthermore, the expression levels of CHOP, a well-known ER stress marker, and cleaved caspase-3 are significantly reduced, suggesting that BIX addition reduces ER stress-induced cell death by relieving ER stress. The beneficial effect of BIX on mAb production is also demonstrated with another q_mAb -enhancing reagent (sodium butyrate) and a different rCHO cell line (CS13-1.00). Taken together, BIX is an effective ER stress inhibitor that can be used to increase mAb production in rCHO cells.

A cross-species whole genome siRNA screen in suspension-cultured Chinese hamster ovary cells identifies novel engineering targets

High-throughput siRNA screens were only recently applied to cell factories to identify novel engineering targets which are able to boost cells towards desired phenotypes. While siRNA libraries exist for model organisms such as mice, no CHO-specific library is publicly available, hindering the application of this technique to CHO cells. The optimization of these cells is of special interest, as they are the main host for the production of therapeutic proteins. Here, we performed a cross-species approach by applying a mouse whole-genome siRNA library to CHO cells, optimized the protocol for suspension cultured cells, as this is the industrial practice for CHO cells, and developed an in silico method to identify functioning siRNAs, which also revealed the limitations of using cross-species libraries. With this method, we were able to identify several genes that, upon knockdown, enhanced the total productivity in the primary screen. A second screen validated two of these genes, Rad21 and Chd4, whose knockdown was tested in additional CHO cell lines, confirming the induced high productivity phenotype, but also demonstrating the cell line/clone specificity of engineering effects.

Novel short synthetic matrix attachment region for enhancing transgenic expression in recombinant Chinese hamster ovary cells

Matrix attachment regions (MARs) are DNA fragments with specific motifs that enhance transgenic expression; however, the characteristics and functions of these elements remain unclear. In this study, we designed and synthesized three short chimeric MARs, namely, SM4, SM5, and SM6, with different numbers and orders of motifs on the basis of the features and motifs of previously reported MARs, namely, SM1, SM2, and SM3, respectively. Expression vectors with six synthetic MARs flanking the down or upstream of the expression cassette for enhanced green fluorescence protein (EGFP) were constructed and introduced into Chinese hamster ovary (CHO) cells. Results indicated that the EGFP expression of the CHO cells with transfection bySM4, SM5, or SM6-containing vectors was higher than that of those containing SM1, SM2, or SM3 regardless of the MAR insertion position. The improving effect of SM5 was particularly pronounced. Transgenic expression was further enhanced with the increasing SM5 copy number. Bioinformatics analysis indicated that several arrangements of the DNA-binding motifs for CEBP, FAST, Hox, glutathione, and NMP4 may help increase transgenic expression levels and the average population of highly expressed cells. Our findings on novel synthetic MARs will help establish stable expression systems in mammalian cells.

Development of an improved lentiviral based vector system for the stable expression of monoclonal antibody in CHO cells

Therapeutic monoclonal antibodies (mAbs) have become the dominant products in biopharmaceutical industry. Mammalian cell expression systems including Chinese hamster ovary (CHO) cells are the most commonly used hosts for the production of complex recombinant proteins. However, development of stable, high producing CHO cell lines suffers from the low expression level and instability of the transgene. The increasing efforts in the development of novel therapeutic antibodies and the advent of biosimilars have revealed the necessity for the development of improved platforms for rapid production of products for initial characterization and testing. In line with this premise, vector design and engineering has been applied to improve the expression level and stability of the transgene. This study reports the application of an improved lentiviral vector system containing the human interferon-β scaffold attachment region (IFN-SAR) for the development of antibody producing stable CHO cells. mAb expressing clones producing 1100 µg/L of IgG1 monoclonal antibody were isolated without extensive screening of a large number of clones. Our results here indicate the positive effects of IFN-SAR on stable mAb expression using lentiviral based expression vectors. We also observed that although IFN-SAR can improve light chain (LC) and heavy chain (HC) gene copy numbers in stable cell pools, mAb expression in single cell clones was not affected by the transgene copy number.

Proteogenomic Annotation of Chinese Hamsters Reveals Extensive Novel Translation Events and Endogenous Retroviral Elements

A high-quality genome annotation greatly facilitates successful cell line engineering. Standard draft genome annotation pipelines are based largely on de novo gene prediction, homology, and RNA-Seq data. However, draft annotations can suffer from incorrect predictions of translated sequence, inaccurate splice isoforms, and missing genes. Here, we generated a draft annotation for the newly assembled Chinese hamster genome and used RNA-Seq, proteomics, and Ribo-Seq to experimentally annotate the genome. We identified 3529 new proteins compared to the hamster RefSeq protein annotation and 2256 novel translational events (e.g., alternative splices, mutations, and novel splices). Finally, we used this pipeline to identify the source of translated retroviruses contaminating recombinant products from Chinese hamster ovary (CHO) cell lines, including 119 type-C retroviruses, thus enabling future efforts to eliminate retroviruses to reduce the costs incurred with retroviral particle clearance. In summary, the improved annotation provides a more accurate resource for CHO cell line engineering, by facilitating the interpretation of omics data, defining of cellular pathways, and engineering of complex phenotypes.

New Mammalian Expression Systems

There are an increasing number of recombinant antibodies and proteins in preclinical and clinical development for therapeutic applications. Mammalian expression systems are key to enabling the production of these molecules, and Chinese hamster ovary (CHO) cell platforms continue to be central to delivery of the stable cell lines required for large-scale production. Increasing pressure on timelines and efficiency, further innovation of molecular formats and the shift to new production systems are driving developments of these CHO cell line platforms. The availability of genome and transcriptome data coupled with advancing gene editing tools are increasing the ability to design and engineer CHO cell lines to meet these challenges. This chapter aims to give an overview of the developments in CHO expression systems and some of the associated technologies over the past few years.

Apoptosis: A mammalian cell bioprocessing perspective

Apoptosis is a form of programmed and controlled cell death that accounts for the majority of cellular death in bioprocesses. Cell death affects culture longevity and product quality; it is instigated by several stresses experienced by the cells within a bioreactor. Understanding the factors that cause apoptosis as well as developing strategies that can protect cells is crucial for robust bioprocess development. This review aims to a) address apoptosis from a bioprocess perspective; b) describe the significant apoptotic mechanisms linking them to the most relevant stresses encountered in bioreactors; c) discuss the design of operating conditions in order to avoid cell death; d) focus on industrially relevant cell lines; and e) present anti-apoptosis strategies including cell engineering and model-based optimization of bioprocesses. In addition, the importance of apoptosis in quality-by-design bioprocess development from clone screening to production scale are highlighted.

CRISPR/Cas9-Mediated Knockout of MicroRNA-744 Improves Antibody Titer of CHO Production Cell Lines

MicroRNAs (miRNAs) are noncoding RNAs that serve as versatile molecular engineering tools to improve production cells by overexpression or knockdown of miRNAs showing beneficial or adverse effects on cell-culture performance. The genomic knockout (KO) of noncoding RNAs in Chinese hamster ovary (CHO) production cells has not been reported. However, given the significant number of miRNAs showing negative effects on CHO-bioprocess performance and the development of clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins (CRISPR/Cas9), genome editing tools facilitate precise optimization of CHO cells via modulation of noncoding RNAs. In a previous high-content miRNA screen, miR-744 was identified as a potential target associated with reduced productivity. Hence, the genomic miR-744 precursor sequence is deleted by two single guide RNA (sgRNA)-Cas9-mediated DNA double-strand breaks (DSB) flanking the miR-744 locus. After fluorescence-activated cell sorting (FACS), clonal miR-744 KO cell lines are recovered and three of them are confirmed as miR-744 KOs. Impacts of CRISPR/Cas9 editing are characterized at the genetic, transcript, and phenotypic levels. During batch cultivation, antibody titers of miR-744 KOs are significantly increased to 190-311 mg L-1 compared to a nontargeting (NT) sgRNA transfected clonal control with 156 mg L-1 , pointing towards the potential of miRNA KO for cell line engineering.

The glycosylation design space for recombinant lysosomal replacement enzymes produced in CHO cells

Lysosomal replacement enzymes are essential therapeutic options for rare congenital lysosomal enzyme deficiencies, but enzymes in clinical use are only partially effective due to short circulatory half-life and inefficient biodistribution. Replacement enzymes are primarily taken up by cell surface glycan receptors, and glycan structures influence uptake, biodistribution, and circulation time. It has not been possible to design and systematically study effects of different glycan features. Here we present a comprehensive gene engineering screen in Chinese hamster ovary cells that enables production of lysosomal enzymes with N-glycans custom designed to affect key glycan features guiding cellular uptake and circulation. We demonstrate distinct circulation time and organ distribution of selected glycoforms of α-galactosidase A in a Fabry disease mouse model, and find that an α2-3 sialylated glycoform designed to eliminate uptake by the mannose 6-phosphate and mannose receptors exhibits improved circulation time and targeting to hard-to-reach organs such as heart. The developed design matrix and engineered CHO cell lines enables systematic studies towards improving enzyme replacement therapeutics.

Lysosomal replacement enzymes are taken up by cell surface receptors that recognize glycans, the effects of different glycan features are unknown. Here the authors present a gene engineering screen in CHO cells that allows custom N-glycan-decorated enzymes with improved circulation time and organ distribution.

Transcription factor engineering in CHO cells for recombinant protein production

The continuous increase of approved biopharmaceutical products drives the development of more efficient recombinant protein expression systems. Chinese hamster ovary (CHO) cells are the mainstay for this purpose but have some drawbacks, such as low levels of expression. Several strategies have been applied to increase the productivity of CHO cells with different outcomes. Transcription factor (TF) engineering has emerged as an interesting and successful approach, as these proteins can act as master regulators; the expression and function of a TF can be controlled by small molecules, and it is possible to design tailored TFs and promoters with desired features. To date, the majority of studies have focused on the use of TFs with growth, metabolic, cell cycle or endoplasmic reticulum functions, although there is a trend to develop new, synthetic TFs. Moreover, new synthetic biological approaches are showing promising advances for the development of specific TFs, even with tailored ligand sensitivity. In this article, we summarize the strategies to increase recombinant protein expression by modulating and designing TFs and with advancements in synthetic biology. We also illustrate how this class of proteins can be used to develop more robust expression systems.

A toolbox of IgG subclass-switched recombinant monoclonal antibodies for enhanced multiplex immunolabeling of brain

Generating recombinant monoclonal antibodies (R-mAbs) from mAb-producing hybridomas offers numerous advantages that increase the effectiveness, reproducibility, and transparent reporting of research. We report here the generation of a novel resource in the form of a library of recombinant R-mAbs validated for neuroscience research. We cloned immunoglobulin G (IgG) variable domains from cryopreserved hybridoma cells and input them into an integrated pipeline for expression and validation of functional R-mAbs. To improve efficiency over standard protocols, we eliminated aberrant Sp2/0-Ag14 hybridoma-derived variable light transcripts using restriction enzyme treatment. Further, we engineered a plasmid backbone that allows for switching of the IgG subclasses without altering target binding specificity to generate R-mAbs useful in simultaneous multiplex labeling experiments not previously possible. The method was also employed to rescue IgG variable sequences and generate functional R-mAbs from a non-viable cryopreserved hybridoma. All R-mAb sequences and plasmids will be archived and disseminated from open source suppliers.

The immune system fights off disease-causing microbes using antibodies: Y-shaped proteins that each bind to a specific foreign molecule. Indeed, these proteins bind so tightly and so specifically that they can pick out a single target in a complex mixture of different molecules. This property also makes them useful in research. For example, neurobiologists can use antibodies to mark target proteins in thin sections of brain tissue. This reveals their position inside brain cells, helping to link the structure of the brain to the roles the different parts of this structure perform.

To use antibodies in this way, scientists need to be able to produce them in large quantities without losing their target specificity. The most common way to do this is with cells called hybridomas. A hybridoma is a hybrid of an antibody-producing immune cell and a cancer cell, and it has properties of both. From the immune cell, it inherits the genes to make a specific type of antibody. From the cancer cell, it inherits the ability to go on dividing forever. In theory, hybridomas should be immortal antibody factories, but they have some limitations. They are expensive to keep alive, hard to transport between labs, and their genes can be unstable. Problems can creep into their genetic code, halting their growth or changing the targets their antibodies recognize. When this happens, scientists can lose vital research tools.

Instead of keeping the immune cells alive, an alternative approach is to make recombinant antibodies. Rather than store the whole cell, this approach just stores the parts of the genes that encode antibody target-specificity. Andrews et al. set out to convert a valuable toolbox of neuroscience antibodies into recombinant form. This involved copying the antibody genes from a large library of preserved hybridoma cells. However, many hybridomas also carry genes that produce non-functional antibodies. A step in the process removed these DNA sequences, ensuring that only working antibodies made it into the final library. Using frozen cells made it possible to recover antibody genes from hybridoma cells that could no longer grow.

The recombinant DNA sequences provide a permanent record of useful antibodies. Not only does this prevent the loss of research tools, it is also much more shareable than living cells. Modifications to the DNA sequences in the library allow for the use of many antibodies at once. This could help when studying the interactions between different molecules in the brain. Toolkits like these could also make it easier to collaborate, and to reproduce data gathered by different researchers around the world.

Poxvirus-based vector systems and the potential for multi-valent and multi-pathogen vaccines

INTRODUCTION

With the increasing number of vaccines and vaccine-preventable diseases, the pressure to generate multi-valent and multi-pathogen vaccines grows. Combining individual established vaccines to generate single-shot formulations represents an established path, with significant ensuing public health and cost benefits. Poxvirus-based vector systems have the capacity for large recombinant payloads and have been widely used as platforms for the development of recombinant vaccines encoding multiple antigens, with considerable clinical trials activity and a number of registered and licensed products.

AREAS COVERED

Herein we discuss design strategies, production processes, safety issues, regulatory hurdles and clinical trial activities, as well as pertinent new technologies such as systems vaccinology and needle-free delivery. Literature searches used PubMed, Google Scholar and clinical trials registries, with a focus on the recombinant vaccinia-based systems, Modified Vaccinia Ankara and the recently developed Sementis Copenhagen Vector.

EXPERT COMMENTARY

Vaccinia-based platforms show considerable promise for the development of multi-valent and multi-pathogen vaccines, especially with recent developments in vector technologies and manufacturing processes. New methodologies for defining immune correlates and human challenge models may also facilitate bringing such vaccines to market.

Differential expression of microRNAs in recombinant Chinese hamster ovary cells treated with sodium butyrate using digital RNA counting

Sodium butyrate (NaBu) is an efficient supplement for increasing recombinant protein production in Chinese hamster ovary (CHO) cell culture. To elucidate the effects of NaBu on miRNA expression profile in recombinant CHO (rCHO) cells, differentially expressed miRNAs in NaBu-treated rCHO cells were assessed by NanoString nCounter analysis. This result showed that eight mature mouse miRNAs (let-7b, let-7d, miR-15b, miR-25, miR-27a, miR-99a, miR-125a-5p, and miR-125b-5p) were differentially expressed. Furthermore, quantitative real-time RT-PCR analysis of eight mature CHO miRNAs, annotated using a miRBase database, confirmed the transcriptomic findings. Among the potential corresponding target mRNAs for the selected mature miRNAs, seven cell growth-related target genes (e2f2, akt2, mtor, bcl-2, bim, p38α, and bmf) and five N-glycosylation-related target genes (neu1, b4galt3, gale, man1b1 and mgat4a) were selected by considering the effectiveness of NaBu on rCHO cell culture. The altered expression patterns of the 12 target mRNAs were inversely correlated with those of the selected mature miRNAs. Altogether, NanoString nCounter analysis may be useful for identifying differentially expressed miRNAs in rCHO cells.

A protein chimera strategy supports production of a model "difficult-to-express" recombinant target

Due in part to the needs of the biopharmaceutical industry, there has been an increased drive to generate high quality recombinant proteins in large amounts. However, achieving high yields can be a challenge as the novelty and increased complexity of new targets often makes them 'difficult-to-express'. This study aimed to define the molecular features that restrict the production of a model 'difficult-to-express' recombinant protein, Tissue Inhibitor Metalloproteinase-3 (TIMP-3). Building from experimental data, computational approaches were used to rationalize the redesign of this recombinant target to generate a chimera with enhanced secretion. The results highlight the importance of early identification of unfavourable sequence attributes, enabling the generation of engineered protein forms that bypass 'secretory' bottlenecks and result in efficient recombinant protein production.

Cell Line Techniques and Gene Editing Tools for Antibody Production: A Review

The present day modern formulation practices for drugs are based on newer tools and techniques toward effective utilization. The methods of antibody formulations are to be revolutionized based on techniques of cell engineering and gene editing. In the present review, we have discussed innovations in cell engineering toward production of novel antibodies for therapeutic applications. Moreover, this review deciphers the use of RNAi, ribozyme engineering, CRISPR-Cas-based techniques for better strategies for antibody production. Overall, this review describes the multidisciplinary aspects of the production of therapeutic proteins that has gained more attention due to its increasing demand.

A CRISPR/Cas9 based engineering strategy for overexpression of multiple genes in Chinese hamster ovary cells

Manipulation of multiple genes to engineer Chinese Hamster Ovary (CHO) cells for better performance in production processes of biopharmaceuticals has recently become more and more popular. Yet, identification of useful genes and the unequivocally assessment of their effect alone and in combination(s) on the cellular phenotype is difficult due to high variation between subclones. Here, we present development and proof-of-concept of a novel engineering strategy using multiplexable activation of artificially repressed genes (MAARGE). This strategy will allow faster screening of overexpression of multiple genes in all possible combinations. MAARGE, in its here presented installment, comprises four different genes of interest that can all be stably integrated into the genome from one plasmid in a single transfection. Three of the genes are initially repressed by a repressor element (RE) that is integrated between promoter and translation start site. We show that an elongated 5'-UTR with an additional transcription termination (poly(A)) signal most efficiently represses protein expression. Distinct guide RNA (gRNA) targets flanking the REs for each gene then allow to specifically delete the RE by CRISPR/Cas9 and thus to activate the expression of the corresponding gene(s). We show that both individual and multiplexed activation of the genes of interest in a stably transfected CHO cell line is possible. Also, upon transfection of this stable cell line with all three gRNAs together, it was possible to isolate cells that express all potential gene combinations in a single experiment.

Rapid development of stable transgene CHO cell lines by CRISPR/Cas9-mediated site-specific integration into C12orf35

Chinese hamster ovary (CHO) cells are the most widely used mammalian hosts for recombinant protein production. However, by conventional random integration strategy, development of a high-expressing and stable recombinant CHO cell line has always been a difficult task due to the heterogenic insertion and its caused requirement of multiple rounds of selection. Site-specific integration of transgenes into CHO hot spots is an ideal strategy to overcome these challenges since it can generate isogenic cell lines with consistent productivity and stability. In this study, we investigated three sites with potential high transcriptional activities: C12orf35, HPRT, and GRIK1, to determine the possible transcriptional hot spots in CHO cells, and further construct a reliable site-specific integration strategy to develop recombinant cell lines efficiently. Genes encoding representative proteins mCherry and anti-PD1 monoclonal antibody were targeted into these three loci respectively through CRISPR/Cas9 technology. Stable cell lines were generated successfully after a single round of selection. In comparison with a random integration control, all the targeted integration cell lines showed higher productivity, among which C12orf35 locus was the most advantageous in both productivity and cell line stability. Binding affinity and N-glycan analysis of the antibody revealed that all batches of product were of similar quality independent on integrated sites. Deep sequencing demonstrated that there was low level of off-target mutations caused by CRISPR/Cas9, but none of them contributed to the development process of transgene cell lines. Our results demonstrated the feasibility of C12orf35 as the target site for exogenous gene integration, and strongly suggested that C12orf35 targeted integration mediated by CRISPR/Cas9 is a reliable strategy for the rapid development of recombinant CHO cell lines.

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.