Scalable transient gene expression in Chinese hamster ovary cells in instrumented and non-instrumented cultivation systems

Development of a high cell density transient CHO platform yielding mAb titers greater than 2 g/L in only 7 days

We developed a simple transient Chinese Hamster Ovary expression platform. Titers for a random panel of 20 clinical monoclonal antibodies (mAbs) ranged from 0.6 to 2.7 g/L after 7 days. Two factors were the key in obtaining these high titers. First, we utilized an extremely high starting cell density (20 million cells/ml), and then arrested further cell growth by employing mild hypothermic conditions (32°C). Second, we performed a 6-variable Design of Experiments to find optimal concentrations of plasmid DNA (coding DNA), boost DNA (DNA encoding the XBP1S transcription factor), transfection reagent (polyethylenimine [PEI]), and nutrient feed amounts. High coding DNA concentrations (12.5 mg/L) were found to be optimal. We therefore diluted expensive coding DNA with inexpensive inert filler DNA (herring sperm DNA). Reducing the coding DNA concentration by 70% from 12.5 to 3.75 mg/L did not meaningfully reduce mAb titers. Titers for the same panel of 20 clinical mAbs ranged from 0.7 to 2.2 g/L after reducing the coding DNA concentration to 3.75 mg/L. Finally, we found that titer and product quality attributes were similar for a clinical mAb (rituximab) expressed at very different scales (volumes ranging from 3 ml to 2 L).

The transient expression of CHIKV VLP in large stirred tank bioreactors

Transient gene expression (TGE) bioprocesses have been difficult to scale up in large stirred tank bioreactors with volumes of more than 1.5 L. Low production levels are often observed, but the causes have not been investigated (Gutierrez-Granados et al. in Crit Rev Biotechnol 38:918-940, 2018). Chikungunya Virus-like particle (VLP), expressed by DNA-PEI transient transfection, is a representative case study for these difficulties. Clinical materials were produced in shake flasks, but the process suffered when transferred to large stirred tank bioreactors. The resulting process was not operationally friendly nor cost effective. In this study, a systematic approach was used to investigate the root causes of the poor scale up performance. The transfection conditions were first screened in ambr® 15 high throughput mini bioreactors then examined in 3 L stirred-tank systems. The studies found that production level was negatively correlated with inoculum cell growth status (P < 0.05). The pH range, DNA and PEI levels, order of the reagent addition, and gas-sparging systems were also studied and found to affect process performance. Further hydromechanical characterizations (Re, energy dissipation rates, and P/V, etc.) of shake flasks, ambr® 15, and 3-L stirred tank systems were performed. Overall, the study discovered that the shear stress (caused by a microsparger) and PEI toxicity together were the root causes of scale-up failure. Once the microsparger was replaced by a macrosparger, the scale-up was successful.

Production process reproducibility and product quality consistency of transient gene expression in HEK293 cells with anti-PD1 antibody as the model protein

Demonstration of reproducibility and consistency of process and product quality is one of the most crucial issues in using transient gene expression (TGE) technology for biopharmaceutical development. In this study, we challenged the production consistency of TGE by expressing nine batches of recombinant IgG antibody in human embryonic kidney 293 cells to evaluate reproducibility including viable cell density, viability, apoptotic status, and antibody yield in cell culture supernatant. Product quality including isoelectric point, binding affinity, secondary structure, and thermal stability was assessed as well. In addition, major glycan forms of antibody from different batches of production were compared to demonstrate glycosylation consistency. Glycan compositions of the antibody harvested at different time periods were also measured to illustrate N-glycan distribution over the culture time. From the results, it has been demonstrated that different TGE batches are reproducible from lot to lot in overall cell growth, product yield, and product qualities including isoelectric point, binding affinity, secondary structure, and thermal stability. Furthermore, major N-glycan compositions are consistent among different TGE batches and conserved during cell culture time.

Antibody-Based Targeted Delivery of Interleukin-22 Promotes Rapid Clinical Recovery in Mice With DSS-Induced Colitis

BACKGROUND

We have recently described the potential of the alternatively spliced extradomain A of fibronectin as a target for antibody-based pharmacodelivery applications in ulcerative colitis. Here, we report on the cloning and therapeutic properties of novel antibody-based fusion proteins, comprising the F8 antibody specific to extradomain A and murine interleukin (IL)-22, a globular cytokine belonging to the IL10 family. A protective function for IL22 in colitis has previously been described, as this cytokine induces antimicrobial, proliferative, and antiapoptotic pathways, preventing tissue damage and promoting epithelial repair.

METHODS

Two fusion proteins comprising IL22, fused at the N- or at the C-terminus of the F8 antibody in diabody format, were expressed in mammalian cells. The ability of radiolabeled preparations of the 2 fusion proteins to localize at sites of disease was assessed by autoradiography in a murine model of dextran sodium sulfate-induced colitis and by quantitative biodistribution analysis in a syngeneic mouse teratocarcinoma model. Therapeutic activity was assessed in mice with dextran sodium sulfate-induced colitis, which received intravenous injections of antibody-cytokine fusion proteins.

RESULTS

Both fusion proteins were able to selectively accumulate at the site of disease. The fusion protein with the cytokine moiety at the N-terminal extremity (IL22-F8) exhibited better results than the C-terminal fusion, both in terms of targeting selectivity and therapeutic efficacy. Mice treated with IL22-F8 showed a more rapid recovery from clinical symptoms compared with controls and improved macroscopic and microscopic morphology of the colon.

CONCLUSIONS

IL22-F8 is a promising biopharmaceutical drug candidate for the treatment of ulcerative colitis.

Different tissue distribution properties for glycosylation variants of fusion proteins containing the p40 subunit of murine interleukin-12

Antibody-based fusion proteins are gaining increasing importance for therapeutic applications, but the impact of glycosylation on in vivo biopharmaceutical performance is not always completely understood. In this article, we have analyzed biochemical and pharmaceutical properties of fusion proteins, consisting of the F8 antibody (specific to the EDA domain of fibronectin, a marker of tissue remodeling and of angiogenesis) and of the p40 subunit of interleukin-12, an inhibitor of inflammation. The corresponding fusion protein (F8-IL12p40), which inhibits colitis development in mice, is a glycosylated protein with suboptimal disease targeting properties in vivo Since the protein was extensively glycosylated, as evidenced by PNGase F treatment and mass spectrometric analysis, we mutated four asparagine residues in various combinations. The corresponding proteins exhibited similar biochemical and antigen-binding properties, but differences in thermal stability and bioactivity. Asparagine mutations did not lead to recovery of disease targeting performance in vivo, as evidenced by quantitative biodistribution studies with radioiodinated protein preparations in tumor-bearing mice. By contrast, an almost complete recovery of targeting was achieved with an enzymatically deglycosylated protein preparation. These findings reinforce the concept that different glycostructures can have an impact on tissue distribution properties.

Alternatively Spliced EDA Domain of Fibronectin Is a Target for Pharmacodelivery Applications in Inflammatory Bowel Disease

The antibody-based pharmacodelivery of cytokines to sites of disease has been extensively studied for various indications but not for the treatment of inflammatory bowel diseases. Here, we report that the alternatively spliced EDA domain of fibronectin, a marker of angiogenesis and of tissue remodeling, is expressed in the dextran sodium sulfate mouse model of colitis and in patients with inflammatory bowel conditions, while being virtually undetectable in most normal adult tissues. Radiolabeled preparations of the F8 antibody, specific to the EDA domain of fibronectin, were shown to selectively localize to sites of inflammation in mice with colitis, as revealed by autoradiographic analysis. Fusion proteins of the F8 antibody with various murine payloads (interleukin-4, the p40 subunit of interleukin-12, interleukin-13) were administered to mice with colitis. IL12p40-F8 mediated an anti-inflammatory activity, which was comparable with the one of cyclosporine, whereas F8-IL4 did not inhibit colitis and F8-IL13 worsened the inflammatory conditions.

Enhanced transient recombinant protein production in CHO cells through the co-transfection of the product gene with Bcl-xL

Transient gene expression is gaining popularity as a method to rapidly produce recombinant proteins in mammalian cells. Although significant improvements have been made, in terms of expression, more improvements are needed to compete with the yields achievable in stable gene expression. Much progress has come from optimization of transfection media and parameters, as well as altering culturing conditions to enhance productivity. Recent studies have included cell lines engineered for apoptosis resistance through the constitutive expression of an anti-apoptotic protein, Bcl-xL. In this study, we examine an alternative method of using the benefits of anti-apoptotic gene expression to enhance the transient expression of biotherapeutics, namely, through the co-transfection of Bcl-xL and the product-coding gene. CHO-S cells were co-transfected with the product-coding gene and a vector containing Bcl-xL using polyethylenimine. Cells co-transfected with Bcl-xL showed reduced levels of apoptosis, increased specific productivity, and an overall increase in product yield of approximately 100%. Similar results were produced by employing another anti-apoptotic protein, Bcl-2 delta, in CHO cells, or through the co-transfection with Bcl-xL using HEK-293E cells. This work provides an alternative method for increasing yields of therapeutic proteins in TGE applications without generating a stable cell line and subsequent screening, which are both time- and resource-consuming. See accompanying commentary by Matthias Hackl and Nicole Borth DOI: 10.1002/biot.201400104.

Polyethyleneimine-based transient gene expression processes for suspension-adapted HEK-293E and CHO-DG44 cells

•

A brief overview of principles of TGE using mammalian cells.

•

Description of TGE processes for HEK293 and CHO cells.

•

Description of orbitally shaken bioreactors for suspension cell cultivation.

•

Description of polyethylenime-based transfection processes.

Transient gene expression (TGE) from mammalian cells is an increasingly important tool for the rapid production of recombinant proteins for research applications in biochemistry, structural biology, and biomedicine. Here we review methods for the transfection of human embryo kidney (HEK-293) and Chinese hamster ovary (CHO) cells in suspension culture using the cationic polymer polyethylenimine (PEI) for gene delivery.

Optimizing the transient transfection process of HEK-293 suspension cells for protein production by nucleotide ratio monitoring

Large scale, transient gene expression (TGE) is highly dependent of the physiological status of a cell line. Therefore, intracellular nucleotide pools and ratios were used for identifying and monitoring the optimal status of a suspension cell line used for TGE. The transfection efficiency upon polyethyleneimine (PEI)-mediated transient gene delivery into HEK-293 cells cultured in suspension was investigated to understand the effect of different culture and transfection conditions as well as the significance of the culture age and the quality of the cell line used. Based on two different bicistronic model plasmids expressing the human erythropoietin gene (rHuEPO) in the first position and green fluorescent protein as reporter gene in the second position and vice versa, a completely serum-free transient transfection process was established. The process makes use of a 1:1 mixture of a special calcium-free DMEM and the FreeStyle™ 293 Expression Medium. Maximum transfectability was achieved by adjusting the ratio for complex formation to one mass part of DNA and three parts of PEI corresponding to an N/P (nitrogen residues/DNA phosphates) ratio of 23 representing a minimum amount of DNA for the polycation-mediated gene delivery. Applying this method, maximum transfectabilities between 70 and 96 % and a rHuEPO concentration of 1.6 μg mL(-1) 72 h post transfection were reached, when rHuEPO gene was expressed from the first position of the bicistronic mRNA. This corresponded to 10 % of the total protein concentration in the cell-free supernatant of the cultures in protein-free medium. Up to 30 % higher transfectabilities were found for cells of early passages compared to those from late passages under protein-free culture conditions. In contrast, when the same cells were propagated in serum-containing medium, higher transfectabilities were found for late-passage cells, while up to 40 % lower transfectabilities were observed for early-passage cells. Nucleotide pools were measured during all cell cultivations and the nucleoside triphosphate/uridine ratios were calculated. These 'nucleotide ratios' changed in an age-dependent manner and could be used to distinguish early- from late-passage cells. The observed effects were also dependent on the presence of serum in the culture. Nucleotide ratios were shown being applied to investigate the optimal passage number of cultured cell lines for achieving a maximum productivity in cultures used for transient gene expression. Furthermore, these nucleotide ratios proved to be different for transfected and untransfected cells, providing a high potential tool to monitor the status of transfection under various culture conditions.

Orbitally shaken single-use bioreactors

: Orbitally shaken single-use reactors are promising reactors for upstream processing, because they fulfill three general requirements for single-use equipment. First, the design of the disposable parts is inherently simple and cost-efficient, because no complex built-in elements such as baffles or rotating stirrers are required. Second, the liquid distribution induced by orbital shaking is well-defined and accurately predictable. Third, the scale-up from small-scale systems, where shaken bioreactors are commonly applied, is simple and has been successfully proven up to the cubic meter scale. However, orbitally shaken single-use reactors are only suitable for certain applications such as cultivating animal or plant cells with low oxygen demand. Thus, detailed knowledge about the performance of such systems on different scales is essential to exploit their full potential. This article presents an overview about opportunities and limitations of shaken single-use reactors.

Single-use disposable technologies for biopharmaceutical manufacturing

The manufacture of protein biopharmaceuticals is conducted under current good manufacturing practice (cGMP) and involves multiple unit operations for upstream production and downstream purification. Until recently, production facilities relied on the use of relatively inflexible, hard-piped equipment including large stainless steel bioreactors and tanks to hold product intermediates and buffers. However, there is an increasing trend towards the adoption of single-use technologies across the manufacturing process. Technical advances have now made an end-to-end single-use manufacturing facility possible, but several aspects of single-use technology require further improvement and are continually evolving. This article provides a perspective on the current state-of-the-art in single-use technologies and highlights trends that will improve performance and increase the market penetration of disposable manufacturing in the future.

The antibody-based delivery of interleukin-12 to the tumor neovasculature eradicates murine models of cancer in combination with paclitaxel

PURPOSE

Interleukin-12 (IL12) is a potent proinflammatory cytokine with antitumor activity. Its heterodimeric nature makes it compatible with a large variety of different immunocytokine formats. Here we report the design, production, and characterization of a novel immunocytokine, based on the fusion of the F8 antibody (specific to the alternatively spliced EDA domain of fibronectin, a marker of tumor neovasculature) with IL12 (termed IL12-F8-F8).

EXPERIMENTAL DESIGN

We developed a novel immunocytokine based on the sequential fusion of interleukin-12 as a single polypeptide with two F8 antibodies in single-chain Fv (scFv) format. The fusion protein was characterized in vitro, and its targeting performance was assessed in vivo. The immunocytokine antitumor activity was studied as monotherapy as well as in combination therapies in three different murine tumor models. Moreover, depletion experiments and tumor analysis revealed a dominant role of natural killer cells for the mechanism of action.

RESULTS

IL12-F8-F8 can be produced in mammalian cells, yielding a product of good pharmaceutical quality, capable of selective localization on the tumor neovasculature in vivo, as judged by quantitative biodistribution analysis with radioiodinated protein preparations. The protein potently inhibited tumor growth in three different immunocompetent syngeneic models of cancer. The treatment was generally well tolerated. Moreover, the IL12-F8-F8 fusion protein could be produced both with murine IL12 (mIL12) and with human IL12 (hIL12).

CONCLUSIONS

The potent antitumor activity of mIL12-F8-F8, studied alone or in combination with paclitaxel in different tumor models, paves the way to the clinical development of the fully human immunocytokine.

Site-specific traceless coupling of potent cytotoxic drugs to recombinant antibodies for pharmacodelivery

Aldehyde drugs are gaining increasing research interest, considering that aldehyde dehydrogenases overexpression is characteristic of cancer stem cells. Here, we describe the traceless site-specific coupling of a novel potent drug, containing an aldehyde moiety, to recombinant antibodies, which were engineered to display a cysteine residue at their N-terminus, or a 1,2-aminothiol at their C-terminus. The resulting chemically defined antibody-drug conjugates represent the first example in which a thiazolidine linkage is used for the targeted delivery and release of cytotoxic agents.

Effect of addition of 'carrier' DNA during transient protein expression in suspension CHO culture

Transient protein expression using polyethyleneimine as a transfection agent is useful for the rapid production of small amounts of recombinant proteins. It is known that an increase in extracellular DNA concentration during transfection can lead to a nonlinear increase in intracellular DNA concentration. We present an approach that hypothesizes that this nonlinearity can be used to decrease the amount of plasmid required for productive transfections. Through addition of non coding 'carrier' DNA to increase total DNA concentration during transfection, we report a statistically significant increase in protein (IgG) expression per unit plasmid used for transfection. This approach could be useful to increase protein yields for large scale transfections under conditions where plasmid availability is limited.

Bridging the gap: facilities and technologies for development of early stage therapeutic mAb candidates

Therapeutic monoclonal antibodies (mAbs) currently dominate the biologics marketplace. Development of a new therapeutic mAb candidate is a complex, multistep process and early stages of development typically begin in an academic research environment. Recently, a number of facilities and initiatives have been launched to aid researchers along this difficult path and facilitate progression of the next mAb blockbuster. Complementing this, there has been a renewed interest from the pharmaceutical industry to reconnect with academia in order to boost dwindling pipelines and encourage innovation. In this review, we examine the steps required to take a therapeutic mAb from discovery through early stage preclinical development and toward becoming a feasible clinical candidate. Discussion of the technologies used for mAb discovery, production in mammalian cells and innovations in single-use bioprocessing is included. We also examine regulatory requirements for product quality and characterization that should be considered at the earliest stages of mAb development. We provide details on the facilities available to help researchers and small-biotech build value into early stage product development, and include examples from within our own facility of how technologies are utilized and an analysis of our client base.

Cloning and characterization of novel tumor-targeting immunocytokines based on murine IL7

We generated and characterized novel antibody-cytokine fusion proteins ("immunocytokines") based on murine interleukin-7 (IL7), an immunomodulatory protein which has previously shown anti-cancer activity in preclinical models and whose human counterpart is currently being investigated in clinical trials. The sequential fusion of the clinical-stage antibody fragment scFv(F8), specific to a tumor-associated splice isoform of fibronectin, yielded an immunocytokine (termed "F8-mIL7") of insufficient pharmaceutical quality and in vivo tumor targeting performance, with a striking dose dependence on tumor targeting selectivity. By contrast, a novel immunocytokine design (termed "F8-mIL7-F8"), in which two scFv moieties were fused at the N- and C-terminus of murine IL7, yielded a protein of excellent pharmaceutical quality and with improved tumor-targeting performance [tumor: blood ratio=16:1, 24h after injection]. Both F8-mIL7 and F8-mIL7-F8 could induce tumor growth retardation in immunocompetent mice, but were not able to eradicate F9 tumors. The combination of F8-mIL7-F8 with paclitaxel led to improved therapeutic results, which were significantly better compared to those obtained with saline treatment. The study indicates how the engineering of novel immunocytokine formats may help generate fusion proteins of acceptable pharmaceutical quality, for those immunomodulatory proteins which do not lend themselves to a direct fusion with antibody fragments.

Large-scale plasmid preparation for transient gene expression

Large-scale transient gene expression of recombinant protein in mammalian cells requires a great amount of plasmid. An economical method for large-scale plasmid preparation, based on fed-batch fermentation and an improved plasmid extraction process, has been established. Fed-batch growth of E. coli was carried out in 5 l bioreactor by controlling the glucose concentration below 1 g l(-1) after the feeding was started. Plasmid yields of 490 and 580 mg l(-1) were achieved with two strains of E. coli cells bearing pCEP4-EGFP and pID-EG respectively, representing 24.5- and 26-fold increases over those of the batch culture in shake-flask. To improve the procedure for large-scale preparation of plasmid DNA, addition of RNase to resuspension buffer and ultrafiltration of clarified lysate were adopted, and the quality of the resultant plasmid was comparable to that of commercial kit as disclosed in the small-scale transient transfection. This plasmid production process has great potential in the large scale transient gene expression which needs a large quantity of plasmid DNA.

Generation of stable, high-producing CHO cell lines by lentiviral vector-mediated gene transfer in serum-free suspension culture

Lentivirus-derived vectors (LVs) were studied for the generation of stable recombinant Chinese hamster ovary (CHO) cell lines. Stable pools and clones expressing the enhanced green fluorescent protein (eGFP) were selected via fluorescence-activated cell sorting (FACS). For comparison, cell pools and cell lines were also generated by transfection, using the LV transfer plasmid alone. The level and stability of eGFP expression was greater in LV-transduced cell lines and pools than in those established by transfection. CHO cells were also infected at two different multiplicities of infection with an LV co-expressing eGFP and a tumor necrosis factor receptor:Fc fusion protein (TNFR:Fc). At 2-day post-infection, clonal cell lines with high eGFP-specific fluorescence were recovered by FACS. These clones co-expressed TNFR:Fc with yields of 50-250 mg/L in 4-day cultures. The recovered cell lines maintained stable expression over 3 months in serum-free suspension culture without selection. In conclusion, LV-mediated gene transfer provided an efficient alternative to plasmid transfection for the generation of stable and high-producing recombinant cell lines.

Hyperosmolarity enhances transient recombinant protein yield in Chinese hamster ovary cells

The effect of hyperosmolarity on transient recombinant protein production in Chinese hamster ovary (CHO) cells was investigated. Addition of 90 mM NaCl to the production medium ProCHO5 increased the volumetric yield of recombinant antibody up to 4-fold relative to transfection in ProCHO5 alone. Volumetric yields up to 50 mg l(-1) were achieved in a 6 day batch culture of 3 l. In addition, hyperosmolarity reduced cell growth and increased cell size. The addition of salt to cultures of transiently transfected CHO cells is a simple and cost-effective method to increase TGE yields in this host.

Serum-free transfection of CHO cells with chemically defined transfection systems and investigation of their potential for transient and stable transfection

The generation of transgenic cell lines is acquired by facilitating the uptake and integration of DNA. Unfortunately, most of the systems generating stable expression systems are cost and time-consuming and transient expression is optimized to generate milligram amounts of the recombinant protein. Therefore we improved and compared two transfection systems, one based on cationic liposomes consisting of DOTAP/DOPE and the second one on polyethylenimine (PEI). Both systems have been used as chemically defined transfection systems in combination with serum-free cultivated host cell line. At first we had determined the toxicity and ideal ratio of DNA to PEI followed by determination of the optimal transfection conditions in order to achieve maximum transfection efficiency. We then directly compared DOTAP/DOPE and PEI in transient transfection experiments using enhanced green fluorescence protein (EGFP) and a human monoclonal antibody, mAb 2F5, as a model protein. The results which were achieved in case of EGFP were more than 15% transfectants at a viability of 85%. Despite the fact that expression of the mAb was found negligible we used both techniques to generate stable mAb 2F5 expressing cell lines that underwent several cycles of screening and amplification with methotrexate, and resulted in cell lines with similar volumetric production titers. These experiments serve to demonstrate the potential of stable cell lines even in case where the transient systems did not show satisfying results.

25 years of recombinant proteins from reactor-grown cells - where do we go from here?

The purpose of this review is to describe the current status and to highlight several emerging trends in the manufacture of recombinant therapeutic proteins in cultivated mammalian cells, focusing on Chinese hamster ovary cells as the major production host. Over the past 25 years, specific and volumetric productivities for recombinant cell lines have increased about 20-fold as the result of improvements in media and bioprocess design. Future yield increases are expected to come from further developments in gene delivery and genetic selection for more efficient recovery of high-producing cell lines and in high-throughput cultivation systems to simplify medium design and bioprocess development. Other emerging trends in protein manufacturing that are discussed include the use of disposal bioreactors and transient gene expression. We specifically highlight current research in our own laboratories.

Use of orbital shaken disposable bioreactors for mammalian cell cultures from the milliliter-scale to the 1,000-liter scale

Driven by the commercial success of recombinant biopharmaceuticals, there is an increasing demand for novel mammalian cell culture bioreactor systems for the rapid production of biologicals that require mammalian protein processing. Recently, orbitally shaken bioreactors at scales from 50 mL to 1,000 L have been explored for the cultivation of mammalian cells and are considered to be attractive alternatives to conventional stirred-tank bioreactors because of increased flexibility and reduced costs. Adequate oxygen transfer capacity was maintained during the scale-up, and strategies to increase further oxygen transfer rates (OTR) were explored, while maintaining favorable mixing parameters and low-stress conditions for sensitive lipid membrane-enclosed cells. Investigations from process development to the engineering properties of shaken bioreactors are underway, but the feasibility of establishing a robust, standardized, and transferable technical platform for mammalian cell culture based on orbital shaking and disposable materials has been established with further optimizations and studies ongoing.

Enhancement of transient gene expression and culture viability using Chinese hamster ovary cells overexpressing Bcl-x(L)

Transient gene expression (TGE) provides a method for quickly delivering protein for research using mammalian cells. While high levels of recombinant proteins have been produced in TGE experiments in HEK 293 cells, TGE efforts in the commercially prominent CHO cell line still suffer from inadequate protein yields. Here, we describe a cell-engineering strategy to improve transient production of proteins using CHO cells. CHO-DG44 cells were engineered to overexpress the anti-apoptotic protein Bcl-x(L) and transiently transfected using polyethylenimine (PEI) in serum-free media. Pools and cell lines stably expressing Bcl-x(L) showed enhanced viable cell density and increased production of a glycosylated, therapeutic fusion protein in shake flask TGE studies. The improved cell lines showed fusion protein production levels ranging from 12.6 to 27.0 mg/L in the supernatant compared to the control cultures which produced 6.3-7.3 mg/L, representing a 70-270% increase in yield after 14 days of fed-batch culture. All Bcl-xL-expressing cell lines also exhibited an increase in specific productivity during the first 8 days of culture. In addition to increased production, Bcl-x(L) cell lines maintained viabilities above 90% and less apoptosis compared to the DG44 host which had viabilities below 60% after 14 days. Product quality was comparable between a Bcl-xL-engineered cell line and the CHO host. The work presented here provides the foundation for using anti-apoptosis engineered CHO cell lines for increased production of therapeutic proteins in TGE applications.

Recombinant therapeutic protein production in cultivated mammalian cells: current status and future prospects

Recombinant therapeutic proteins produced in mammalian cells represent a major class of biopharmaceuticals. In recent years, their demand has increased dramatically and is now driving the development of a variety of improvements to maximize their expression in mammalian cells. Advances in media- and process optimization have already resulted in more than 100-fold improvement in yield, but further insights and subsequent targeted modifications with respect to the general biology of cells (genomics, physiology, selection and adaptation) in bioreactors are hoped to further improve protein yields and quality in the near future.: