Development of a highly-efficient CHO cell line generation system with engineered SV40E promoter

Trends and challenges in bispecific antibody production

Bispecific antibodies (bsAbs) represent a rapidly growing field of therapeutic agents. More bsAbs are being approved worldwide and are in various stages of clinical trials. However, the discovery and production of novel bsAbs presents significant challenges due to their complex structure. Thus, precise control of assembly and stability is required, given the many formats developed. This review examines recent trends in bsAb production, focusing on advancements in engineering platforms, production strategies, and challenges in large-scale manufacturing. Key developments include improvements in modular antibody design, novel expression systems, and optimization of bioprocessing techniques to enhance stability, yield, and efficacy. Additionally, the article explores the future potential of bsAbs as next-generation therapeutics, underscoring the growing impact of these innovations on expanding treatment options for patients with unmet medical needs.

Building blocks needed for mechanistic modeling of bioprocesses: A critical review based on protein production by CHO cells

This paper reviews the key building blocks needed to develop a mechanistic model for use as an operational production tool. The Chinese Hamster Ovary (CHO) cell, one of the most widely used hosts for antibody production in the pharmaceutical industry, is considered as a case study. CHO cell metabolism is characterized by two main phases, exponential growth followed by a stationary phase with strong protein production. This process presents an appropriate degree of complexity to outline the modeling strategy. The paper is organized into four main steps: (1) CHO systems and data collection; (2) metabolic analysis; (3) formulation of the mathematical model; and finally, (4) numerical solution, calibration, and validation. The overall approach can build a predictive model of target variables. According to the literature, one of the main current modeling challenges lies in understanding and predicting the spontaneous metabolic shift. Possible candidates for the trigger of the metabolic shift include the concentration of lactate and carbon dioxide. In our opinion, ammonium, which is also an inhibiting product, should be further investigated. Finally, the expected progress in the emerging field of hybrid modeling, which combines the best of mechanistic modeling and machine learning, is presented as a fascinating breakthrough. Note that the modeling strategy discussed here is a general framework that can be applied to any bioprocess.

Therapeutic proteins: developments, progress, challenges, and future perspectives

Proteins are considered magic molecules due to their enormous applications in the health sector. Over the past few decades, therapeutic proteins have emerged as a promising treatment option for various diseases, particularly cancer, cardiovascular disease, diabetes, and others. The formulation of protein-based therapies is a major area of research, however, a few factors still hinder the large-scale production of these therapeutic products, such as stability, heterogenicity, immunogenicity, high cost of production, etc. This review provides comprehensive information on various sources and production of therapeutic proteins. The review also summarizes the challenges currently faced by scientists while developing protein-based therapeutics, along with possible solutions. It can be concluded that these proteins can be used in combination with small molecular drugs to give synergistic benefits in the future.

Recent advances in the application of genetic and epigenetic modalities in the improvement of antibody-producing cell lines

There are numerous applications for recombinant antibodies (rAbs) in biological and toxicological research. Monoclonal antibodies are synthesized using genetic engineering and other related processes involved in the generation of rAbs. Because they can identify specific antigenic sites on practically any molecule, including medicines, hormones, microbial antigens, and cell receptors, rAbs are particularly useful in scientific research. The key benefits of rAbs are improved repeatability, control, and consistency, shorter manufacturing times than with hybridoma technology, an easier transition from one format of antibody to another, and an animal-free process. The engineering of the host cell has recently been developed method for enhancing the production efficiency and improving the quality of antibodies from mammalian cell lines. In this light, genetic engineering is mostly utilized to manage cellular chaperones, decrease cell death, increase cell viability, change the microRNAs (miRNAs) pattern in mammalian cells, and glycoengineered cell lines. Here, we shed light on how genetic engineering can be used therapeutically to produce antibodies at higher levels with greater potency and effectiveness.

Glutamine synthetase (GS) knockout (KO) using CRISPR/Cpf1 diversely enhances selection efficiency of CHO cells expressing therapeutic antibodies

The glutamine synthetase (GS)-based Chinese hamster ovary (CHO) selection system is an attractive approach to efficiently identify suitable clones in the cell line generation process for biologics manufacture, for which GS-knockout (GS-KO) CHO cell lines are commonly used. Since genome analysis indicated that there are two GS genes in CHO cells, deleting only 1 GS gene could potentially result in the activation of other GS genes, consequently reducing the selection efficiency. Therefore, in this study, both GS genes identified on chromosome 5 (GS5) and 1 (GS1) of CHO-S and CHO-K1, were deleted using CRISPR/Cpf1. Both single and double GS-KO CHO-S and K1 showed robust glutamine-dependent growth. Next, the engineered CHO cells were tested for their efficiency of selection of stable producers of two therapeutic antibodies. Analysis of pool cultures and subclones after a single round of 25 µM methionine sulfoxinime (MSX) selection indicated that for CHO-K1 the double GS5,1-KO was more efficient as in the case of a single GS5-KO the GS1 gene was upregulated. In CHO-S, on the other hand, with an autologously lower level of expression of both variants of GS, a single GS5-KO was more robust and already enabled selection of high producers. In conclusion, CRISPR/Cpf1 can be efficiently used to knock out GS genes from CHO cells. The study also indicates that for the generation of host cell lines for efficient selection, the initial characterisation of expression levels of the target gene as well as the identification of potential escape mechanisms is important.

Weak promoters to drive selection marker expression: improvement of cell line development process for therapeutic protein production in CHO-K1 cells

Chinese Hamster Ovary cells have been widely used as host cells for production of recombinant therapeutic molecules. Cell line development is a decisive step, which must be carried out with an efficient process. In particular, degree of selection stringency is an important parameter for identification of rare, high-producing cell lines. In the CHOZN® CHO K1 platform, selection of top-producing clones is based on puromycin resistance, whose expression is driven by Simian Virus 40 Early (SV40E) promoter. In this study, novel promoters have been identified to drive expression of selection marker. Decrease of transcriptional activity compared to SV40E promoter was confirmed by RT-qPCR. Selection stringency was increased, as seen by decreased surviving rate of transfected mini-pools and longer recovery duration of transfected bulk pools. Several promoters led to a 1.5-fold increase of maximum titer and a 1.3-fold increase of mean specific productivity of the monoclonal antibody over the clone generation. Expression level was maintained stable over long term cultivation. Finally, productivity increase was confirmed on several monoclonal antibodies and fusion proteins. Lowering the strength of promoter for expression of selective pressure resistance is an efficient strategy to increase selection stringency, which can be applied on industrial CHO-based cell line development platforms.

Attenuation of glutamine synthetase selection marker improves product titer and reduces glutamine overflow in Chinese hamster ovary cells

The glutamine synthetase (GS) expression system is commonly used to ensure stable transgene integration and amplification in CHO host lines. Transfected cell populations are typically grown in the presence of the GS inhibitor, methionine sulfoximine (MSX), to further select for increased transgene copy number. However, high levels of GS activity produce excess glutamine. We hypothesized that attenuating the GS promoter while keeping the strong IgG promoter on the GS-IgG expression vector would result in a more efficient cellular metabolic phenotype. Herein, we characterized CHO cell lines expressing GS from either an attenuated promoter or an SV40 promoter and selected with/without MSX. CHO cells with the attenuated GS promoter had higher IgG specific productivity and lower glutamine production compared to cells with SV40-driven GS expression. Selection with MSX increased both specific productivity and glutamine production, regardless of GS promoter strength. ¹³ C metabolic flux analysis (MFA) was performed to further assess metabolic differences between these cell lines. Interestingly, central carbon metabolism was unaltered by the attenuated GS promoter while the fate of glutamate and glutamine varied depending on promoter strength and selection conditions. This study highlights the ability to optimize the GS expression system to improve IgG production and reduce wasteful glutamine overflow, without significantly altering central metabolism. Additionally, a detailed supplementary analysis of two "lactate runaway" reactors provides insight into the poorly understood phenomenon of excess lactate production by some CHO cell cultures. This article is protected by copyright. All rights reserved.

Structure-guided selection of puromycin N-acetyltransferase mutants with enhanced selection stringency for deriving mammalian cell lines expressing recombinant proteins

Puromycin and the Streptomyces alboniger-derived puromycin N-acetyltransferase (PAC) enzyme form a commonly used system for selecting stably transfected cultured cells. The crystal structure of PAC has been solved using X-ray crystallography, revealing it to be a member of the GCN5-related N-acetyltransferase (GNAT) family of acetyltransferases. Based on structures in complex with acetyl-CoA or the reaction products CoA and acetylated puromycin, four classes of mutations in and around the catalytic site were designed and tested for activity. Single-residue mutations were identified that displayed a range of enzymatic activities, from complete ablation to enhanced activity relative to wild-type (WT) PAC. Cell pools of stably transfected HEK293 cells derived using two PAC mutants with attenuated activity, Y30F and A142D, were found to secrete up to three-fold higher levels of a soluble, recombinant target protein than corresponding pools derived with the WT enzyme. A third mutant, Y171F, appeared to stabilise the intracellular turnover of PAC, resulting in an apparent loss of selection stringency. Our results indicate that the structure-guided manipulation of PAC function can be utilised to enhance selection stringency for the derivation of mammalian cell lines secreting elevated levels of recombinant proteins.

Expression vector cassette engineering for recombinant therapeutic production in mammalian cell systems

Human tissue plasminogen activator was the first recombinant therapy protein that successfully produced in Chinese hamster ovary cells in 1986 and approved for clinical use. Since then, more and more therapeutic proteins are being manufactured in mammalian cells, and the technologies for recombinant protein production in this expression system have developed rapidly, with the optimization of both upstream and downstream processes. One of the most promising strategies is expression vector cassette optimization based on the expression vector cassette. In this review paper, these approaches and developments are summarized, and the future strategy on the utilizing of expression cassettes for the production of recombinant therapeutic proteins in mammalian cells is discussed.

Attenuated glutamine synthetase as a selection marker in CHO cells to efficiently isolate highly productive stable cells for the production of antibodies and other biologics

Chinese hamster ovary (CHO) cells are the biopharmaceutical industry’s primary means of manufacturing therapeutic proteins, including monoclonal antibodies. The major challenge in cell line development for the production of recombinant biopharmaceuticals lies in generating and isolating rare high-producing stable clones, amongst thousands of low-producing or unstable clones, in a short period of time. One approach to accomplish this is to use the glutamine synthetase (GS) selection system, together with the GS inhibitor, methionine sulfoximine (MSX). However, MSX can only increase protein productivity to a limited extent. Often productivity will drop when MSX is removed from the system. We evaluated a congenital GS mutation, R324C, which causes glutamine deficiency in human as an attenuated selection marker for CHO cell line generation. We also created a panel of GS mutants with diminished GS activity. Our results demonstrated that using attenuated GS mutants as selection markers significantly increased antibody production of stably transfected pools. Furthermore, these stably transfected pools sustained high productivity levels for an extended period of time, whereas cells transfected with wild-type GS lost considerable protein productivity over time, particularly after MSX was removed. In summary, the use of attenuated GS as a selection marker in CHO cell line development bypasses the need for MSX, and generates stable clones with significantly higher antibody productivity.Abbreviations: CHO: Chinese hamster ovary; CMV: Cytomegalovirus; DHFR: Dihydrofolate reductase; GFP: Green fluorescent protein; GOI: gene-of-interest; GS: Glutamine synthetase; IRES: internal ribosomal entry site; MSX: Methionine sulfoximine; MTX: Methotrexate; psGS: pseudoGS; RVDs: Repeated variable di-residues; TALENs: transcription activator-like effector nucleases; VCD: Viable cell density; ZFNs: zinc finger nucleases.

Study of the mechanism for increased protein expression via transcription potency reduction of the selection marker

Stable transfection of mammalian cells using various expression cassettes for exogenous gene expression has been well established. The impact of critical factors in these cassettes, such as promoter and enhancer elements, on recombinant protein production in mammalian cells has been studied extensively to optimize the expression efficiency. However, few studies on the correlation between the strength of selection marker and the expression of gene of interest (GOI) have been reported. Here we investigated the correlation between the strength of a widely used selection marker, glutamine synthetase (GS) gene, and gene of interest in which the expression of GOI is driven by mouse cytomegalovirus (mCMV) major immediate early (MIE) promoter whereas the expression of GS is controlled by SV40E (Simian vacuolating virus 40E) promoter. We used a green fluorescent protein and the adalimumab antibody (heavy and light chain) as two distinct examples for the gene of interest. We then decreased the expression of GS gene by engineering a specific region of its SV40E promoter in these expression cassettes. By comparing the expression of GS and GOI at transcription and translation level before and after the SV40E promoter was weakened, we found that lower GS expression due to weaker SV40E transcription correlated well with the higher expression of recombinant proteins, mainly by increasing the copy number of GS and GOI integration into host cell genome.

CHO genome mining for synthetic promoter design

Synthetic promoters are an attractive alternative for use in mammalian hosts such as CHO cells as they can be designed de novo with user-defined functionalities. In this study, we describe and validate a method for bioprocess-directed design of synthetic promoters utilizing CHO genomic sequence information. We designed promoters with two objective features, (i) constitutive high-level recombinant gene transcription, and (ii) upregulated transcription under mild hypothermia or late-stage culture. CHO genes varying in transcriptional activity were selected based on a comparative analysis of RNA-Seq transcript levels in normal and biphasic cultures in combination with estimates of mRNA half-life from published genome scale datasets. Discrete transcription factor regulatory elements (TFREs) upstream of these genes were informatically identified and functionally screened in vitro to identify a subset of TFREs with the potential to support high activity recombinant gene transcription during biphasic cell culture processes. Two libraries of heterotypic synthetic promoters with varying TFRE combinations were then designed in silico that exhibited a maximal 2.5-fold increase in transcriptional strength over the CMV-IE promoter after transient transfection into host CHO-K1 cells. A subset of synthetic promoters was then used to create stable transfectant pools using CHO-K1 cells under glutamine synthetase selection. Whilst not achieving the maximal 2.5-fold increase in productivity over stable pools harboring the CMV promoter, all stably transfected cells utilizing synthetic promoters exhibited increased reporter production - up to 1.6-fold that of cells employing CMV, both in the presence or absence of intron A immediately downstream of the promoter. The increased productivity of stably transfected cells harboring synthetic promoters was maintained during fed-batch culture, with or without a transition to mild hypothermia at the onset of stationary phase. Our data exemplify that it is important to consider both host cell and intended bioprocess contexts as design criteria in the de novo construction of synthetic genetic parts for mammalian cell engineering.

Efficient development of a stable cell pool for antibody production using a single plasmid

Therapeutic antibodies are the fastest growing group of biopharmaceuticals. Evaluation of drug candidates requires a sufficient amount of antibodies. Production of antibodies with stable cell pools is an efficient strategy to produce grams of proteins for drug candidate selection. Many methods have been described for developing stable cell pools for antibody expression. However, most of the reported methods are laborious due to the low frequency of high producers. In this study, we determined optimal vectors and screening parameters to develop a strategy for efficient construction of stable antibody expressing cell pools. The cell pool constructed using the optimized strategy consistently yielded a higher expression titer, up to 10-fold improvement. Further, this method resulted in a higher ratio of the cell pools with the main product peak above 95% as assessed by size-exclusion chromatography. High producers could be obtained by means of screening five 96-well plates. This strategy will greatly reduce clone-screening size during Clinical Lead Selection. This study provides a platform with efficient design of plasmids and screening strategies for significant cost and labour savings in high expression of two-subunit proteins such as antibodies.

Comprehensive characterization of glutamine synthetase-mediated selection for the establishment of recombinant CHO cells producing monoclonal antibodies

To characterize a glutamine synthetase (GS)-based selection system, monoclonal antibody (mAb) producing recombinant CHO cell clones were generated by a single round of selection at various methionine sulfoximine (MSX) concentrations (0, 25, and 50 μM) using two different host cell lines (CHO-K1 and GS-knockout CHO). Regardless of the host cell lines used, the clones selected at 50 μM MSX had the lowest average specific growth rate and the highest average specific production rates of toxic metabolic wastes, lactate and ammonia. Unlike CHO-K1, high producing clones could be generated in the absence of MSX using GS-knockout CHO with an improved selection stringency. Regardless of the host cell lines used, the clones selected at various MSX concentrations showed no significant difference in the GS, heavy chain, and light chain gene copies (P > 0.05). Furthermore, there was no correlation between the specific mAb productivity and these three gene copies (R² ≤ 0.012). Taken together, GS-mediated gene amplification does not occur in a single round of selection at a MSX concentration up to 50 μM. The use of the GS-knockout CHO host cell line facilitates the rapid generation of high producing clones with reduced production of lactate and ammonia in the absence of MSX.

Monoclonal antibodies expression improvement in CHO cells by PiggyBac transposition regarding vectors ratios and design

Establishing stable Chinese Hamster Ovary (CHO) cells producing monoclonal antibodies (mAbs) usually pass through the random integration of vectors to the cell genome, which is sensitive to gene silencing. One approach to overcome this issue is to target a highly transcribed region in the genome. Transposons are useful devices to target active parts of genomes, and PiggyBac (PB) transposon can be considered as a good option. In the present study, three PB transposon donor vectors containing both heavy and light chains were constructed, one contained independent expression cassettes while the others utilized either an Internal Ribosome Entry Site (IRES) or 2A element to express mAb. Conventional cell pools were created by transferring donor vectors into the CHO cells, whereas transposon-based cells were generated by transfecting the cells with donor vectors with a companion of a transposase-encoding helper vector, with 1:2.5 helper/donor vectors ratio. To evaluate the influence of helper/donor vectors ratio on expression, the second transposon-based cell pools were generated with 1:5 helper/donor ratio. Expression levels in the transposon-based cells were two to five -folds more than those created by conventional method except for the IRES-mediated ones, in which the observed difference increased more than 100-fold. The results were dependent on both donor vector design and vectors ratios.

Rapid protein production from stable CHO cell pools using plasmid vector and the cumate gene-switch

To rapidly produce large amounts of recombinant proteins, the generation of stable Chinese Hamster Ovary (CHO) cell pools represents a useful alternative to large-scale transient gene expression (TGE). We have developed a cell line (CHO^BRI/rcTA) allowing the inducible expression of recombinant proteins, based on the cumate gene switch. After the identification of optimal plasmid DNA topology (supercoiled vs linearized plasmid) for PEIpro™ mediated transfection and of optimal conditions for methionine sulfoximine (MSX) selection, we were able to generate CHO^BRI/rcTA pools producing high levels of recombinant proteins. Volumetric productivities of up to 900mg/L were reproducibly achieved for a Fc fusion protein and up to 350mg/L for an antibody after 14days post-induction in non-optimized fed-batch cultures. In addition, we show that CHO pool volumetric productivities are not affected by a freeze-thaw cycle or following maintenance in culture for over one month in the presence of MSX. Finally, we demonstrate that volumetric protein production with the CR5 cumate-inducible promoter is three- to four-fold higher than with the human CMV or hybrid EF1α-HTLV constitutive promoters. These results suggest that the cumate-inducible CHO^BRI/rcTA stable pool platform is a powerful and robust system for the rapid production of gram amounts of recombinant proteins.

Transient and stable CHO expression, purification and characterization of novel hetero-dimeric bispecific IgG antibodies

IgG bispecific antibodies (BsAbs) represent one of the preferred formats for bispecific antibody therapeutics due to their native-like IgG properties and their monovalent binding to each target. Most reported studies utilized transient expression in HEK293 cells to produce BsAbs. However, the expression of biotherapeutic molecules using stable CHO cell lines is commonly used for biopharmaceutical manufacturing. Unfortunately, limited information is available in the scientific literature on the expression of BsAbs in CHO cell lines. In this study we describe an alternative approach to express the multiple components of IgG BsAbs using a single plasmid vector (quad vector). This single plasmid vector contains both heavy chain genes and both light chain genes required for the expression and assembly of the IgG BsAb, along with a selectable marker. We expressed, purified, and characterized four different IgG BsAbs or "hetero-mAbs" using transient CHO expression and stable CHO minipools. Transient CHO titers ranged from 90 to 160 mg/L. Stable CHO titers ranged from 0.4 to 2.3 g/L. Following a simple Protein A purification step, the percentage of correctly paired BsAbs ranged from 74% to 98% as determined by mass spectrometry. We also found that information generated from transient CHO expression was similar to information generated using stable CHO minipools. In conclusion, the quad vector approach represents a simple, but effective, alternative approach for the generation of IgG BsAbs in both transient CHO and stable CHO expression systems. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:469-477, 2017.

Metabolic engineering with multi-objective optimization of kinetic models

Kinetic models have a great potential for metabolic engineering applications. They can be used for testing which genetic and regulatory modifications can increase the production of metabolites of interest, while simultaneously monitoring other key functions of the host organism. This work presents a methodology for increasing productivity in biotechnological processes exploiting dynamic models. It uses multi-objective dynamic optimization to identify the combination of targets (enzymatic modifications) and the degree of up- or down-regulation that must be performed in order to optimize a set of pre-defined performance metrics subject to process constraints. The capabilities of the approach are demonstrated on a realistic and computationally challenging application: a large-scale metabolic model of Chinese Hamster Ovary cells (CHO), which are used for antibody production in a fed-batch process. The proposed methodology manages to provide a sustained and robust growth in CHO cells, increasing productivity while simultaneously increasing biomass production, product titer, and keeping the concentrations of lactate and ammonia at low values. The approach presented here can be used for optimizing metabolic models by finding the best combination of targets and their optimal level of up/down-regulation. Furthermore, it can accommodate additional trade-offs and constraints with great flexibility.

Promoter and Terminator Discovery and Engineering

Control of gene expression is crucial to optimize metabolic pathways and synthetic gene networks. Promoters and terminators are stretches of DNA upstream and downstream (respectively) of genes that control both the rate at which the gene is transcribed and the rate at which mRNA is degraded. As a result, both of these elements control net protein expression from a synthetic construct. Thus, it is highly important to discover and engineer promoters and terminators with desired characteristics. This chapter highlights various approaches taken to catalogue these important synthetic elements. Specifically, early strategies have focused largely on semi-rational techniques such as saturation mutagenesis to diversify native promoters and terminators. Next, in an effort to reduce the length of the synthetic biology design cycle, efforts in the field have turned towards the rational design of synthetic promoters and terminators. In this vein, we cover recently developed methods such as hybrid engineering, high throughput characterization, and thermodynamic modeling which allow finer control in the rational design of novel promoters and terminators. Emphasis is placed on the methodologies used and this chapter showcases the utility of these methods across multiple host organisms.

Precision control of recombinant gene transcription for CHO cell synthetic biology

The next generation of mammalian cell factories for biopharmaceutical production will be genetically engineered to possess both generic and product-specific manufacturing capabilities that may not exist naturally. Introduction of entirely new combinations of synthetic functions (e.g. novel metabolic or stress-response pathways), and retro-engineering of existing functional cell modules will drive disruptive change in cellular manufacturing performance. However, before we can apply the core concepts underpinning synthetic biology (design, build, test) to CHO cell engineering we must first develop practical and robust enabling technologies. Fundamentally, we will require the ability to precisely control the relative stoichiometry of numerous functional components we simultaneously introduce into the host cell factory. In this review we discuss how this can be achieved by design of engineered promoters that enable concerted control of recombinant gene transcription. We describe the specific mechanisms of transcriptional regulation that affect promoter function during bioproduction processes, and detail the highly-specific promoter design criteria that are required in the context of CHO cell engineering. The relative applicability of diverse promoter development strategies are discussed, including re-engineering of natural sequences, design of synthetic transcription factor-based systems, and construction of synthetic promoters. This review highlights the potential of promoter engineering to achieve precision transcriptional control for CHO cell synthetic biology.

Optimization of the Expression Conditions of CGA-N46 in Bacillus subtilis DB1342(p-3N46) by Response Surface Methodology

CGA-N46 is a small antifungal-derived peptide and consists of the 31st–76th amino acids of the N-terminus of human chromogranin A. Polycistronic expression of recombinant CGA-N46 in Bacillus subtilis DB1342 was used to improve its production, but the yield of CGA-N46 was still low. In the present study, response surface methodology (RSM) was used to optimize culture medium composition and growth conditions of the engineered strain B. subtilis DB1342(p-3N46) for the further increase in CGA-N46 yield. The results of two-level factorial experiments indicated that dextrin and tryptone were significant factors affecting CGA-N46 expression. Central composite design (CCD) was used to determine the ideal conditions of each significant factors. From the results of CCD, the optimal medium composition was predicted to be dextrin 16.6 g/L, tryptone 19.2 g/L, KH₂PO₄·H₂O 6 g/L, pH 6.5. And the optimal culture process indicated inoculation of B. subtilis DB1342(p-3N46) seed culture into fresh culture medium at 5 % (v/v), followed by expression of CGA-N46 for 56 hours at 30 °C induced by 2 % (v/v) sucrose after one hour of shaking culture. To test optimal CGA-N46 peptide expression, the yeast growth inhibition assay was employed and it was found that under optimal culture conditions, CGA-N46 inhibited the growth of Candida albican by 42.17, 30.86 % more than that in the pre-optimization conditions. In summary, RSM can be used to optimize expression conditions of CGA-N46 in engineered strains B. subtilis DB1342(p-3N46).

A high cell density transient transfection system for therapeutic protein expression based on a CHO GS-knockout cell line: process development and product quality assessment

Transient gene expression (TGE) is a rapid method for the production of recombinant proteins in mammalian cells. While the volumetric productivity of TGE has improved significantly over the past decade, most methods involve extensive cell line engineering and plasmid vector optimization in addition to long fed batch cultures lasting up to 21 days. Our colleagues have recently reported the development of a CHO K1SV GS-KO host cell line. By creating a bi-allelic glutamine synthetase knock out of the original CHOK1SV host cell line, they were able to improve the efficiency of generating high producing stable CHO lines for drug product manufacturing. We developed a TGE method using the same CHO K1SV GS-KO host cell line without any further cell line engineering. We also refrained from performing plasmid vector engineering. Our objective was to setup a TGE process to mimic protein quality attributes obtained from stable CHO cell line. Polyethyleneimine (PEI)-mediated transfections were performed at high cell density (4 × 10(6) cells/mL) followed by immediate growth arrest at 32 °C for 7 days. Optimizing DNA and PEI concentrations proved to be important. Interestingly, found the direct transfection method (where DNA and PEI were added sequentially) to be superior to the more common indirect method (where DNA and PEI are first pre-complexed). Moreover, the addition of a single feed solution and a polar solvent (N,N dimethylacetamide) significantly increased product titers. The scalability of process from 2 mL to 2 L was demonstrated using multiple proteins and multiple expression volumes. Using this simple, short, 7-day TGE process, we were able to successfully produce 54 unique proteins in a fraction of the time that would have been required to produce the respective stable CHO cell lines. The list of 54 unique proteins includes mAbs, bispecific antibodies, and Fc-fusion proteins. Antibody titers of up to 350 mg/L were achieved with the simple 7-day process. Titers were increased to 1 g/L by extending the culture to 16 days. We also present two case studies comparing product quality of material generated by transient HEK293, transient CHO K1SV GS-KO, and stable CHO K1SV KO pool. Protein from transient CHO was more representative of stable CHO protein compared to protein produced from HEK293.

Optimization of the expression conditions of CGA-N46 in Bacillus subtilis DB1342(p-3N46) by response surface methodology

CGA-N46 is a small antifungal derived peptide and consists of the 31st to 76th amino acids of the N-terminus of human chromogranin A. Polycistronic expression of recombinant CGA-N46 in Bacillus subtilis DB1342 was used to improve its production, but the yield of CGA-N46 was still low. In the present study, response surface methodology (RSM) was used to optimize culture medium composition and growth conditions of the engineered strain B. subtilis DB1342(p-3N46) for the further increase of CGA-N46 yield. The results of two-level factorial experiments indicated that dextrin and tryptone were significant factors affecting CGA-N46 expression. Central composite design (CCD) was used to determine the ideal conditions of each significant factors. From the results of CCD, the optimal medium composition was predicted to be dextrin 16.6 g/L, tryptone 19.2 g/L, KH2PO4·3H2O 6 g/L, pH 6.5. And the optimal culture process was indicated that B. subtilis DB1342(p-3N46) seed culture was inoculated into fresh culture medium at 5% (v/v), followed by expression of CGA-N46 for 56 hours at 30°C induced by 2% (v/v) sucrose after one hour of shaking culture. To test optimal CGA-N46 peptide expression, the yeast growth inhibition assay was employed and it was found that under optimal culture conditions, CGA-N46 inhibited the growth of C. albican by 42.17%, 30.86% more than that in the pre-optimization conditions. In summary, RSM can be used to optimize expression conditions of CGA-N46 in engineered strains B. subtilis DB1342(p-3N46).