Balancing GFP reporter plasmid quantity in large-scale transient transfections for recombinant anti-human Rhesus-D IgG1 synthesis

Repeated Transient Transfection: An Alternative for the Recombinant Production of Difficult-to-Express Proteins Like BMP2

Human bone morphogenetic protein 2 (hBMP2) is routinely used in medical applications as an inducer of osteoformation. The recombinant production of BMP2 is typically performed using stable Chinese hamster ovary (CHO) cell lines. However, this process is inefficient, resulting in low product titers. In contrast, transient gene expression (TGE), which also enables the production of recombinant proteins, suffers from short production times and hence limited total product amounts. Here, we show that TGE-based BMP2 production is more efficient in HEKsus than in CHOsus cells. Independently of the cell lines, a bicistronic plasmid co-expressing EGFP and BMP2 facilitated the determination of the transfection efficiency but led to inferior BMP2 titers. Finally, we used a high cell density transient transfection (HCD-TGE) protocol to improve and extend the BMP2 expression by performing four rounds of serial transfections on one pool of HEKsus cells. This repeated transient transfection (RTT) process in HEKsus cells was implemented using EGFP as a reporter gene and further adapted for BMP2 production. The proposed method significantly improves BMP2 production (up to 509 ng/106 cells) by extending the production phase (96–360 h). RTT can be integrated into the seed train and is shown to be compatible with scale-up to the liter range.

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

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A brief overview of principles of TGE using mammalian cells.

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Description of TGE processes for HEK293 and CHO cells.

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Description of orbitally shaken bioreactors for suspension cell cultivation.

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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.

Large-scale transfection of mammalian cells

The large-scale transfection of mammalian cells allows moderate (milligram to gram) amounts of recombinant proteins (r-proteins) to be obtained for fundamental or clinical research. In this article, we describe a one-liter transfection using polyethyleneimine (PEI) for DNA delivery into human embryonic kidney (HEK-293) cells cultivated in serum-free suspension to produce a recombinant human monoclonal antibody that yields up to about 1 g/L in a 10-day process. The method is based on a DNA delivery step performed at high cell density (20×10(6) cells/mL) by direct addition of DNA and PEI to the culture. Subsequently, the cells are diluted 20-fold for the 10-day production phase in the presence of valproic acid (VPA), a histone deacetylase inhibitor. The methods for plasmid purification, antibody quantification by enzyme-linked immunosorbent assay (ELISA), and affinity purification with protein A are also described.

Using matrix attachment regions to improve recombinant protein production

Chinese hamster ovary (CHO) cells are the system of choice for the production of complex molecules, such as monoclonal antibodies. Despite significant progress in improving the yield from these cells, the process to the selection, identification, and maintenance of high-producing cell lines remains cumbersome, time consuming, and often of uncertain outcome. Matrix attachment regions (MARs) are DNA sequences that help generate and maintain an open chromatin domain that is favourable to transcription and may also facilitate the integration of several copies of the transgene. By incorporating MARs into expression vectors, an increase in the proportion of high-producer cells as well as an increase in protein production are seen, thereby reducing the number of clones to be screened and time to production by as much as 9 months. In this chapter, we describe how MARs can be used to increase transgene expression and provide protocols for the transfection of CHO cells in suspension and detection of high-producing antibody cell clones.

Transient Gene Expression in Suspension HEK-293 Cells: Application to Large-Scale Protein Production

Recent advances in genomics, proteomics, and structural biology raised the general need for significant amounts of pure recombinant protein (r-protein). Because of the difficulty in obtaining in some cases proper protein folding in bacteria, several methods have been established to obtain large amounts of r-proteins by transgene expression in mammalian cells. We have developed three nonviral DNA transfer protocols for suspension-adapted HEK-293 and CHO cells: (1) a calcium phosphate based method (Ca-Pi), (2) a calcium-mediated method called Calfection, and (3) a polyethylenimine-based method (PEI). The first two methods have already been scaled up to 14 L and 100 L for HEK-293 cells in bioreactors. The third method, entirely serum-free, has been successfully applied to both suspension-adapted CHO and HEK-293 cells. We describe here the application of this technology to the transient expression in suspension cultivated HEK-293 EBNA cells of some out of more than 20 secreted r-proteins, including antibodies, dimeric proteins, and tagged proteins of various complexity. Most of the proteins were expressed from different plasmid vectors within 5-10 days after the availability of the DNA. Transfections were successfully performed from the small scale (1 mL in 12-well microtiter plates) to the 2 L scale. The results reported made it possible to establish an optimized cell culture and transfection protocol that minimizes batch-to-batch variations in protein expression. The work presented here proves the applicability and robustness of transient transfection technology for the expression of a variety of recombinant proteins.

Rational vector design and multi-pathway modulation of HEK 293E cells yield recombinant antibody titers exceeding 1 g/l by transient transfection under serum-free conditions

Transient transfection allows for fast production of recombinant proteins. However, the current bottlenecks in transient transfection are low titers and low specific productivity compared to stable cell lines. Here, we report an improved transient transfection protocol that yields titers exceeding 1 g/l in HEK293E cells. This was achieved by combining a new highly efficient polyethyleneimine (PEI)-based transfection protocol, optimized gene expression vectors, use of cell cycle regulators p18 and p21, acidic Fibroblast Growth Factor, exposure of cells to valproic acid and consequently the maintenance of cells at high cell densities (4 million cells/ml). This protocol was reproducibly scaled-up to a working volume of 2 l, thus delivering >1 g of purified protein just 2 weeks after transfection. This is the fastest approach to gram quantities of protein ever reported from cultivated mammalian cells and could initiate, upon further scale-up, a paradigm shift in industrial production of such proteins for any application in biotechnology.

High-density transfection with HEK-293 cells allows doubling of transient titers and removes need for a priori DNA complex formation with PEI

Recombinant proteins are of great commercial and scientific interest. Yet, most production methods in mammalian cells involve the time- and labor-consuming step of creating stable cell lines. Production methods based on transient gene expression are advantageous in terms of speed and versatility; yet, depending on the transfection protocol, transient transfection faces some bottlenecks such as a priori complex formation, limitations in terms of transfection and production media used and the need for medium exchange prior to and/or after transfection. Published protocols for transfection of suspension-adapted HEK-293 cells with polyethyleneimine have shown great promise in overcoming some of these bottlenecks, but still require a priori complex formation for optimal yields and limit the choice of transfection and production media. Here, we report successful in situ transfection of suspension-adapted HEK-293 cells with 25-kDa linear polyethyleneimine at densities up to 20 x 10(6) cells/mL in complex media followed by production at lower cell densities (1 x 10(6) cells/mL). After concentrating cells to such high densities, transfection of HEK-293 cells becomes possible in most commonly used media and is not restricted to a specific medium. Furthermore, there is no need to make transfection complexes a priori, a step that prevents inline sterile filtration of the DNA bulk for transfection, an important consideration when scaling processes up to 100 or 1,000 L. Finally, transfecting HEK-293 cells at high density in complex media is superior to existing transfection protocols and doubles yields of recombinant protein obtainable by transient gene expression.

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

Cell expansion, gene transfer and protein production were all executed with a single serum-free, animal protein-free commercial medium designed for suspension-adapted Chinese hamster ovary cells (CHO DG44). This is a most important process to consider for clinical production of recombinant proteins. The transfection with polyethylenimine (PEI) was shown here to be scalable using both stirred-tank bioreactors of 3- and 150-l and novel agitated cultivation vessels (50 ml ventilated centrifuge tubes and 1-l square-shaped glass bottles) that lack any instrumentation. The transient transfections spanned a range of working volumes from 2 ml to 80 l. The maximum transient recombinant antibody yield was 22 mg/l, the highest ever reported for a multiliter transfection in CHO. The transiently expressed protein had the same extent of glycosylation as the same antibody produced from a stably transfected recombinant CHO cell line.

Engineered Streptomyces quorum-sensing components enable inducible siRNA-mediated translation control in mammalian cells and adjustable transcription control in mice

BACKGROUND

Recent advances in functional genomics, gene therapy, tissue engineering, drug discovery and biopharmaceuticals production have been fostered by precise small-molecule-mediated fine-tuning of desired transgenes.

METHODS

Capitalizing on well-evolved quorum-sensing regulatory networks in Streptomyces coelicolor we have designed a mammalian regulation system inducible by the non-toxic butyrolactone SCB1. Fusion of the S. coelicolor SCB1 quorum-sensing receptor ScbR to the human Kox-1-derived transsilencing domain reconstituted a mammalian transsilencer (SCS) able to repress transcription from SCS-specific operator-containing promoters in a reverse SCB1-adjustable manner.

RESULTS

This quorum-sensing-derived mammalian transgene control system (Q-ON) enabled precise SCB1-specific fine-tuning of (i) desired transgene transcription in a variety of mammalian/human cell lines and human primary cells, (ii) small interfering RNA-mediated posttranscriptional knockdown (siRNA) in mammalian cells, and (iii) dosing of a human glycoprotein in mice.

CONCLUSIONS

As exemplified by Q-ON technology, bacterial quorum-sensing regulons may represent a near-infinite source for the design of mammalian gene control systems compatible with molecular interventions relevant to future gene therapy and tissue engineering scenarios.

Transient transfection of CHO-K1-S using serum-free medium in suspension: a rapid mammalian protein expression system

With the recent completion of the human genome sequencing project, scientists now face the daunting challenge of deciphering the function of these newly found genes quickly and efficiently. For biotechnology, it is equally important to identify the therapeutically relevant genes as quickly as possible. Mammalian expression systems provide many advantages to aid in this task. Mammalian cell lines have the capacity for proper post-translational modifications, including proper protein folding and glycosylation. In response to these needs, a CHO-K1 cell line that grows in suspension and in serum-free media was initially established and designated CHO-K1-S. An antibody gene of interest was chosen as the target for optimization rather than a reporter gene system. A comparison of various lipid transfection reagents was made using recombinant protein expression as the endpoint readout. Various other parameters including lipid:DNA ratios, cell density, and transfections in shaker versus spinner flasks were tested using the CHO-K1-S cell line. As a result, a rapid and reliable transient transfection protocol was developed. Using this procedure, we have produced milligram/per liter quantities of bioactive recombinant proteins from several genes of interest.

Orbital shaker technology for the cultivation of mammalian cells in suspension

For large-scale applications in biotechnology, cultivation of mammalian cells in suspension is an essential prerequisite. Typically, suspension cultures are grown in glass spinner flasks filled to less than 50% of the nominal volume. We propose a superior system for suspension cultures of mammalian cells based on orbital shaker technology. We found that "square-shaped" bottles (square bottles) provide an inexpensive but efficient means to grow HEK-293 EBNA and CHO-DG44 cells to high density. Cultures in agitated 1-L square bottles exceeded the performance of cultures in spinner flasks, reaching densities up to 7 x 10(6) cells/mL for HEK-293 EBNA cells and 5 x 10(6) cells/mL for CHO-DG44 cells in comparison to (2.5-4) x 10(6) cells/mL for cultures of the same cells grown in spinner flasks. For 1-L square bottles, optimal cell growth and viability were observed with a filling volume of 30-40% of the nominal volume and an agitation speed of 130 rpm at a rotational diameter of 2.5 cm. Transient reporter gene expression following gene delivery by calcium phosphate-DNA co-precipitation was the same or slightly better for HEK-293 EBNA cells grown in square bottles as compared to spinner flasks. Reductions in cost, simplified handling, and better performance in cell growth and viability make the agitated square bottle a new and very promising tool for the cultivation of mammalian cells in suspension.

Reduction of adenovirus E1A mRNA by RNAi results in enhanced recombinant protein expression in transiently transfected HEK293 cells

Human embryonic kidney 293 (HEK293) cells, a widely used host for large-scale transient expression of recombinant proteins, are transformed with the adenovirus E1A and E1B genes. Because the E1A proteins function as transcriptional activators or repressors, they may have a positive or negative effect on transient transgene expression in this cell line. Suspension cultures of HEK293 EBNA (HEK293E) cells were co-transfected with a reporter plasmid expressing the GFP gene and a plasmid expressing a short hairpin RNA (shRNA) targeting the E1A mRNAs for degradation by RNA interference (RNAi). The presence of the shRNA in HEK293E cells reduced the steady state level of E1A mRNA up to 75% and increased transient GFP expression from either the elongation factor-1alpha (EF-1alpha) promoter or the human cytomegalovirus (HCMV) immediate early promoter up to twofold. E1A mRNA depletion also resulted in a twofold increase in transient expression of a recombinant IgG in both small- and large-scale suspension cultures when the IgG light and heavy chain genes were controlled by the EF-1alpha promoter. Finally, transient IgG expression was enhanced 2.5-fold when the anti-E1A shRNA was expressed from the same vector as the IgG light chain gene. These results demonstrated that E1A has a negative effect on transient gene expression in HEK293E cells, and they established that RNAi can be used to enhance recombinant protein expression in mammalian cells.