Alpha1-antitrypsin improves survival in murine abdominal sepsis model by decreasing inflammation and sequestration of free heme

Background

Excessive inflammation, hemolysis, and accumulation of labile heme play an essential role in the pathophysiology of multi-organ dysfunction syndrome (MODS) in sepsis. Alpha1-antitrypsin (AAT), an acute phase protein with heme binding capacity, is one of the essential modulators of host responses to inflammation. In this study, we evaluate the putative protective effect of AAT against MODS and mortality in a mouse model of polymicrobial abdominal sepsis.

Methods

Polymicrobial abdominal sepsis was induced in C57BL/6N mice by cecal ligation and puncture (CLP). Immediately after CLP surgery, mice were treated intraperitoneally with three different forms of human AAT-plasma-derived native (nAAT), oxidized nAAT (oxAAT), or recombinant AAT (recAAT)-or were injected with vehicle. Sham-operated mice served as controls. Mouse survival, bacterial load, kidney and liver function, immune cell profiles, cytokines/chemokines, and free (labile) heme levels were assessed. In parallel, in vitro experiments were carried out with resident peritoneal macrophages (MPMΦ) and mouse peritoneal mesothelial cells (MPMC).

Results

All AAT preparations used reduced mortality in septic mice. Treatment with AAT significantly reduced plasma lactate dehydrogenase and s-creatinine levels, vascular leakage, and systemic inflammation. Specifically, AAT reduced intraperitoneal accumulation of free heme, production of cytokines/chemokines, and neutrophil infiltration into the peritoneal cavity compared to septic mice not treated with AAT. In vitro experiments performed using MPMC and primary MPMΦ confirmed that AAT not only significantly decreases lipopolysaccharide (LPS)-induced pro-inflammatory cell activation but also prevents the enhancement of cellular responses to LPS by free heme. In addition, AAT inhibits cell death caused by free heme in vitro.

Conclusion

Data from the septic CLP mouse model suggest that intraperitoneal AAT treatment alone is sufficient to improve sepsis-associated organ dysfunctions, preserve endothelial barrier function, and reduce mortality, likely by preventing hyper-inflammatory responses and by neutralizing free heme.

Human PBMCs Form Lipid Droplets in Response to Spike Proteins

Intracellular lipid droplets (LDs) can accumulate in response to inflammation, metabolic stresses, and other physiological/pathological processes. Herein, we investigated whether spike proteins of SARS-CoV-2 induce LDs in human peripheral blood mononuclear cells (PBMCs) and in pulmonary microvascular endothelial cells (HPMECs). PBMCs or HPMECs were incubated alone or with endotoxin-free recombinant variants of trimeric spike glycoproteins (Alpha, Beta, Delta, and Omicron, 12 µg/mL). Afterward, cells were stained with Oil Red O for LDs, cytokine release was determined through ELISA, and the gene expression was analyzed through real-time PCR using TaqMan assays. Our data show that spikes induce LDs in PBMCs but not in HPMECs. In line with this, in PBMCs, spike proteins lower the expression of genes involving lipid metabolism and LD formation, such as SREBF1, HMGCS1, LDLR, and CD36. On the other hand, PBMCs exposed to spikes for 6 or 18 h did not increase in IL-1β, IL-6, IL-8, MCP-1, and TNFα release or expression as compared to non-treated controls. Thus, spike-induced LD formation in PBMCs seems to not be related to cell inflammatory activation. Further detailed studies are warranted to investigate in which specific immune cells spikes induce LDs, and what are the pathophysiological mechanisms and consequences of this induction in vivo.

A new T-antigen negative HEK293 cell line with improved AAV productivity

Viral vectors for gene therapy, such as recombinant adeno-associated viruses, are produced in human embryonic kidney (HEK) 293 cells. However, the presence of the SV40 T-antigen-encoding CDS SV40GP6 and SV40GP7 in the HEK293T genome raises safety issues when these cells are used in manufacturing for clinical purposes. We developed a new T-antigen-negative HEK cell line from ExcellGene's proprietary HEKExpress,® using the CRISPR-Cas9 strategy. We obtained a high number of clonally-derived cell populations and all of them were demonstrated T-antigen negative. Stability study and AAV production evaluation showed that the deletion of the T-antigen-encoding locus did not impact neither cell growth nor viability nor productivity. The resulting CMC-compliant cell line, named HEKzeroT,® is able to produce high AAV titers, from small to large scale.

High-Titer Neutralizing Antibodies against the SARS-CoV-2 Delta Variant Induced by Alhydroxyquim-II-Adjuvanted Trimeric Spike Antigens

Global control of COVID-19 will require the deployment of vaccines capable of inducing long-term protective immunity against SARS-CoV-2 variants. In this report, we describe an adjuvanted subunit candidate vaccine that affords elevated, sustained, and cross-variant SARS-CoV-2 neutralizing antibodies (NAbs) in multiple animal models. Alhydroxiquim-II is a Toll-Like Receptor (TLR) 7/8 small-molecule agonist chemisorbed on aluminum hydroxide (Alhydrogel). Vaccination with Alhydroxiquim-II combined with a stabilized, trimeric form of the SARS-CoV-2 spike protein (termed CoVac-II) resulted in high-titer NAbs in mice, with no decay in responses over an 8-month period. NAbs from sera of CoVac-II-immunized mice, horses and rabbits were broadly neutralizing against SARS-CoV-2 variants. Boosting long-term CoVac-II-immunized mice with adjuvanted spike protein from the Beta variant markedly increased levels of NAb titers against multiple SARS-CoV-2 variants; notably, high titers against the Delta variant were observed. These data strongly support the clinical assessment of Alhydroxiquim-II-adjuvanted spike proteins to protect against SARS-CoV-2 variants of concern. IMPORTANCE There is an urgent need for next-generation COVID-19 vaccines that are safe, demonstrate high protective efficacy against SARS-CoV-2 variants and can be manufactured at scale. We describe a vaccine candidate (CoVac-II) that is based on stabilized, trimeric spike antigen produced in an optimized, scalable and chemically defined production process. CoVac-II demonstrates strong and persistent immunity after vaccination of mice, and is highly immunogenic in multiple animal models, including rabbits and horses. We further show that prior immunity can be boosted using a recombinant spike antigen from the Beta variant; importantly, plasma from boosted mice effectively neutralize multiple SARS-CoV-2 variants in vitro, including Delta. The strong humoral and Th1-biased immunogenicity of CoVac-II is driven by use of Alhydroxiquim-II (AHQ-II), the first adjuvant in an authorized vaccine that acts through the dual Toll-like receptor (TLR)7 and TLR8 pathways, as part of the Covaxin vaccine. Our data suggest AHQ-II/spike protein combinations could constitute safe, affordable, and mass-manufacturable COVID-19 vaccines for global distribution.

Naming CHO cells for bio-manufacturing: Genome plasticity and variant phenotypes of cell populations in bioreactors question the relevance of old names

Chinese Hamster Ovary [CHO] cells are the workhorse for production of modern biopharmaceuticals. They are however immortalized cells with a high propensity for genetic change. Judging from published culture records, CHO cell populations have undergone hundreds of population doublings since their origin in the late 1950s. Different cell populations were established and named from 1 to 3 decades after their generation, such as CHO-Pro-, CHO-K1, CHO-DG44, CHO-S, CHO-DUK, CHO-DXB-11 to indicate origin and certain phenotypic features. These names are commonly used in scientific publications still today. This article discusses the relevance of such names. We argue that they provide a false sense of identity. To substantiate this, we provide the long (and poorly recorded) history of CHO cells as well as their highly complex genetics. Finally, we suggest an alternative naming system for CHO cells which provides more relevant information. While the implementation of a new naming convention will require substantial discussions among members of the relevant community, it should improve interpretation and comparability between laboratories. This, in turn will help scientific communities and industrial users to attain and further the full potential of CHO cells.

Designs and Characterization of Subunit Ebola GP Vaccine Candidates: Implications for Immunogenicity

The humoral responses of Ebola virus (EBOV) survivors mainly target the surface glycoprotein GP, and anti-GP neutralizing antibodies have been associated with protection against EBOV infection. In order to elicit protective neutralizing antibodies through vaccination a native-like conformation of the antigen is required. We therefore engineered and expressed in CHO cells several GP variants from EBOV (species Zaire ebolavirus, Mayinga variant), including a soluble GP ΔTM, a mucin-like domain-deleted GP ΔTM-ΔMUC, as well as two GP ΔTM-ΔMUC variants with C-terminal trimerization motifs in order to favor their native trimeric conformation. Inclusion of the trimerization motifs resulted in proteins mimicking GP metastable trimer and showing increased stability. The mucin-like domain appeared not to be critical for the retention of the native conformation of the GP protein, and its removal unmasked several neutralizing epitopes, especially in the trimers. The soluble GP variants inhibited mAbs neutralizing activity in a pseudotype transduction assay, further confirming the proteins' structural integrity. Interestingly, the trimeric GPs, a native-like GP complex, showed stronger affinity for antibodies raised by natural infection in EBOV disease survivors rather than for antibodies raised in volunteers that received the ChAd3-EBOZ vaccine. These results support our hypothesis that neutralizing antibodies are preferentially induced when using a native-like conformation of the GP antigen. The soluble trimeric recombinant GP proteins we developed represent a novel and promising strategy to develop prophylactic vaccines against EBOV and other filoviruses.

The Delivery of α1-Antitrypsin Therapy Through Transepidermal Route: Worthwhile to Explore

Human α1-antitrypsin (AAT) is an abundant acute phase glycoprotein expressing anti-protease and immunomodulatory activities, and is used as a biopharmaceutical to treat patients with inherited AAT deficiency. The pleiotropic properties of AAT provide a rationale for using this therapy outside of inherited AAT deficiency. Therapy with AAT is administrated intravenously, yet the alternative routes are being considered. To examine the putative transepidermal application of AAT we used epiCS®, the 3D human epidermis equivalents reconstructed from human primary epidermal keratinocytes. We topically applied various concentrations of AAT protein with a constant volume of 50 µl, prepared in Hank's balance solution, HBSS, to epiCS cultured under bas\al condition or when culture medium supplemented with 100 µg/ml of a combined bacterial lipopolysaccharide (LPS) and peptidoglycan (PGN) mixture. AAT freely diffused across epidermis layers in a concentration and time-dependent manner. Within 18 h topically provided 0.2 mg AAT penetrated well the stratum corneum and localizes within the keratinocytes. The treatments with AAT did not induce obvious morphological changes and damages in keratinocyte layers. As expected, LPS/PGN triggered a strong pro-inflammatory activation of epiCS. AAT exhibited a limited capacity to neutralize the effect of LPS/PGN, but more importantly, it lowered expression of IL-18 and IL-8, and preserved levels of filaggrin, a key protein for maintaining the epidermal barrier integrity. Our findings suggest that the transepidermal route for delivering AAT is worthwhile to explore further. If successful, this approach may offer an easy-to-use therapy with AAT for skin inflammatory diseases.

Scalable Production of AAV Vectors in Orbitally Shaken HEK293 Cells

Adeno-associated virus (AAV) vectors are currently among the most commonly applied for in vivo gene therapy approaches. The evaluation of vectors during clinical development requires the production of considerable amounts of highly pure and potent vectors. Here, we set up a scalable process for AAV production, using orbitally shaken bioreactors and a fully characterized suspension-adapted cell line, HEKExpress. We conducted a proof-of-concept production of AAV2/8 and AAV2/9 vectors using HEKExpress cells. Furthermore, we compared the production of AAV2/9 vectors using this suspension cell line to classical protocols based on adherent HEK293 cells to demonstrate bioequivalence in vitro and in vivo. Following upstream processing, we purified vectors via gradient centrifugation and immunoaffinity chromatography. The in vitro characterization revealed differences due to the purification method, as well as the transfection protocol and the corresponding HEK293 cell line. The purification method and cell line used also affected in vivo transduction efficiency after bilateral injection of AAV2/9 vectors expressing a GFP reporter fused with a nuclear localization signal (AAV2/9-CBA-nlsGFP) into the striatum of adult mice. These results show that AAV vectors deriving from suspension HEKExpress cells are bioequivalent and may exhibit higher potency than vectors produced with adherent HEK293 cells.

A Variant of t-PA (T103N, KHRR 296-299 AAAA) that, by Bolus, Has Increased Potency and Decreased Systemic Activation of Plasminogen

In the accompanying paper, we reported that the properties of decreased plasma clearance rate, increased fibrin specificity, and resistance to inactivation by PAI-1 could be effectively combined in the t-PA variant T103N, KHRR 296-299 AAAA. In the current study we evaluated the in vivo efficacy of this variant as well as variants containing the individual mutations T103N and KHRR 296-299 AAAA. Plasma clearance and in vivo lysis of whole blood and platelet-rich clots were determined in a rabbit arterio-venous shunt model. The T103N containing variants were administered as an intravenous (i.v.) bolus. KHRR 296-299 AAAA and t-PA were infused i.v. over 90 min. The clearance rate of the KHRR 296-299 AAAA variant was similar to t-PA. However, the clearance of the T103N and T103N, KHRR 296-299 AAAA variants were 8 and 6-fold reduced, respectively. Potency of the variants relative to t-PA on whole blood clots ranged from 0.9 (T103N, KHRR 296-299 AAAA) to 1.7 (T103N). Relative potency on platelet-rich clots ranged from 2.4 (T103N) to 4.2 (T103N, KHRR 296-299 AAAA). Fibrinogen concentrations in rabbits 120 min after dosing with a 2.5 mg/kg bolus were: 24, 16, 82, and 77% of initial for t-PA; T103N; KHRR 296-299 AAAA; and T103N, KHRR 296-299 AAAA treatment groups, respectively. These results suggest that the T103N, KHRR 296-299 AAAA variant of t-PA, given as a bolus, could result in greater efficacy, particularly on refractory platelet-rich clots, without inducing the severe systemic lytic state produced by a bolus of a less fibrin specific variant.

A Slow Clearing, Fibrin-Specific, PAI-1 Resistant Variant of t-PA (T103N, KHRR 296-299 AAAA)

Site directed mutagenesis was used to construct a t-PA variant that contains an additional glycosylation site in the first kringle domain (T103N) combined with a tetra-alanine substitution in the protease domain (KHRR 296-299 AAAA). This combination variant has a plasma clearance rate that is 4.5-fold slower in rats and 5.4-fold slower in rabbits than t-PA. It is also less than one tenth as active as t-PA towards plasminogen in the presence of fibrinogen, and has approximately twice the normal activity in the presence of fibrin. It shows substantial resistance to the fast acting inhibitor, plasminogen activator inhibitor-1 (PAI-1), requiring a 10-fold greater molar excess of PAI-1 to reduce its activity by 50%, compared to t-PA. This is the result of a reduction of nearly 100-fold in the second order rate constant for PAI-1 inactivation. These results show that it is possible to combine mutations in different domains of t-PA to construct a variant which is simultaneously slower clearing, less reactive towards plasminogen in the absence of a fibrin clot, and resistant to inactivation by PAI-1.

Improved process conditions for increasing expression of MHC class II protein from a stable Drosophila S2 cell line

OBJECTIVES

To investigate the effects of operational process conditions on expression of MHC class II protein from a stable Drosophila S2 cell line.

RESULTS

When the Drosophila S2 cells were grown in vented orbitally shaken TubeSpin bioreactor 600 containers, cell growth was improved three-fold and the yield of recombinant major histocompatibility (MHC) class II protein (HLA-DR1_2xHis) increased four-fold over the levels observed for the same cells cultivated in roller bottles (RB) without vented caps. Culturing in RB with vented caps while increasing the rotation speed from 6 rpm to 18 rpm also improved cell growth five-fold and protein productivity three-fold which is comparable to the levels observed in the orbitally shaken containers. Protein activity was found to be almost identical between the two vessel systems tested.

CONCLUSIONS

Optimized cell culture conditions and a more efficient vessel type can enhance gas transfer and mixing and lead to substantial improvement of recombinant product yields from S2 cells.

A comparison of orbitally-shaken and stirred-tank bioreactors: pH modulation and bioreactor type affect CHO cell growth and protein glycosylation

Orbitally shaken bioreactors (OSRs) support the suspension cultivation of animal cells at volumetric scales up to 200 L and are a potential alternative to stirred-tank bioreactors (STRs) due to their rapid and homogeneous mixing and high oxygen transfer rate. In this study, a Chinese hamster ovary cell line producing a recombinant antibody was cultivated in a 5 L OSR and a 3 L STR, both operated with or without pH control. Effects of bioreactor type and pH control on cell growth and metabolism and on recombinant protein production and glycosylation were determined. In pH-controlled bioreactors, the glucose consumption and lactate production rates were higher relative to cultures grown in bioreactors without pH control. The cell density and viability were higher in the OSRs than in the STRs, either with or without pH control. Volumetric recombinant antibody yields were not affected by the process conditions, and a glycan analysis of the antibody by mass spectrometry did not reveal major process-dependent differences in the galactosylation index. The results demonstrated that OSRs are suitable for recombinant protein production from suspension-adapted animal cells. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1174-1180, 2016.

Disposable orbitally shaken TubeSpin bioreactor 600 for Sf9 cell cultivation in suspension

Disposable orbitally shaken TubeSpin bioreactor 600 tubes (TS600s) were recently developed for the bench-scale cultivation of animal cells in suspension. Here we compared batch cultures of Sf9 insect cells in TS600s, spinner flasks, and shake flasks. Superior cell growth was observed in TS600s and shake flasks as compared with spinner flasks, and more favorable oxygen-enriched cell culture conditions were observed in TS600s as compared with either spinner or shake flasks. The results demonstrated the suitability of TS600s as a disposable vessel for the cultivation of Sf9 cells in suspension.

Production of active glycosylation-deficient γ-secretase complex for crystallization studies

Alzheimer's disease (AD)-associated γ-secretase is a ubiquitously expressed multi-subunit protease complex embedded in the lipid bilayer of cellular compartments including endosomes and the plasma membrane. Although γ-secretase is of crucial interest for AD drug discovery, its atomic structure remains unresolved. γ-Secretase assembly and maturation is a multistep process, which includes extensive glycosylation on nicastrin (NCT), the only γ-secretase subunit having a large extracellular domain. These posttranslational modifications lead to protein heterogeneity that likely prevents the three-dimensional (3D) crystallization of the protease complex. To overcome this issue, we have engineered a Chinese hamster ovary (CHO) cell line deficient in complex sugar modifications (CHO lec1) to overexpress the four subunits of γ-secretase as a functional complex. We purified glycosylation-deficient γ-secretase from this recombinant cell line (CL1-9) and fully glycosylated γ-secretase from a recombinant CHO DG44-derived cell line (SS20). We characterized both complexes biochemically and pharmacologically in vitro. Interestingly, we found that the complex oligosaccharides, which largely decorate the extracellular domain of fully glycosylated NCT, are not involved in the proper assembly and maturation of the complex, and are dispensable for the specific generation, in physiological ratios, of the amyloid precursor protein (APP) cleavage products. In conclusion, we propose a novel bioengineering approach for the production of functional glycosylation-deficient γ-secretase, which may be suitable for crystallization studies. We expect that these findings will contribute both to solving the high-resolution 3D structure of γ-secretase and to structure-based drug discovery for AD.

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.

Highly efficient production of the Alzheimer's γ-secretase integral membrane protease complex by a multi-gene stable integration approach

Inefficient production of membrane-embedded multi-protein complexes by conventional methods has largely prevented the generation of high-resolution structural information and the performance of high-throughput drug discovery screens for this class of proteins. Not exempt from this rule is γ-secretase, an intramembrane-cleaving protease complex regulating a multitude of signaling pathways and biological processes by influencing gene transcription. γ-Secretase is also implicated in the pathogenesis of Alzheimer's disease and several types of cancer. As an additional challenge, the reconstitution of the protease complex in its active form requires an intricate assembly and maturation process, including a highly regulated endoproteolytic processing of its catalytic component. In this article we report the application of a transposon-mediated multigene stable integration technology to produce active γ-secretase in mammalian cells in amounts adequate for crystallization studies and drug screening. Our strategy is expected to help elucidate the molecular mechanisms of intramembrane proteolysis. It is further expected to be widely used for the production of other multi-protein complexes for applications in structural biology and drug development.

A NanoDrop-based method for rapid determination of viability decline in suspension cultures of animal cells

We describe a rapid method for monitoring the cell growth and decline phases in suspension cultures of animal cells. During the cell growth phase, ultraviolet (UV)-absorbing components in the medium are consumed, but at later times as cells begin to die, UV-absorbing molecules such as proteins are released into the medium. Measuring the absorbance at 280nm (A(280)) with a NanoDrop spectrophotometer, an inverse correlation between the onset of the cell decline phase and A(280) was observed. This simple method can be applied to quickly determine the beginning of the decline phase of cultures of mammalian and insect cells in suspension.

Calcium phosphate transfection optimization for serum-free suspension culture

Aim of this study was to identify optimal conditions for suspension transfection in the absence of serum. Transfection parameters for suspension culture can be very different to ones in adherent cells. Most transfection protocols have been developed and optimizedfor adherent culture. Using green fluorescent protein (GFP) as reporter, FCS was eliminated from the transfection process by altering critical parameters and by substituting serum with albumin. Using standard phosphate and calcium concentrations for transfection in the absence of serum resulted in titers of only 1% of those observed in the presence of serum. A reduction of the calcium concentration from 250 mM to 100 mM, yielded a 25-fold increase in the expression of the recombinant protein compared to the serum-free standard conditions. Altering the phosphate concentration, 1.4 mM in the transfection buffer, did not improve the protein expression. Interestingly, reduction of DNA quantity by half to a concentration of 0.5 μg per milliliter of culture volume resulted in a two-fold increase of protein production. Addition of albumin to serum-free medium protected the cells against the toxicity of the calcium phosphate transfection particles (CaPi) yielding higher protein expression. All the experiments were executed in a shaken multi-well system, allowing high multiplicity parameter screening to speed up optimizations. The culture system is inexpensive, simple and efficient, minimizing costs for labor and consumables.

Extraction of plasmid DNA using reactor scale alkaline lysis and selective precipitation for scalable transient transfection

DNA extracted and purified for vaccination, gene therapy or transfection of cultured cells has to meet different criteria. We describe herein, a scalable process for the primary extraction of plasmid DNA suitable for transient expression of recombinant protein. We focus on the scale up of alkaline lysis for the extraction of plasmid DNA from Escherichia coli, and use a simple stirred tank reactor system to achieve this. By adding a series of three precipitations (including a selective precipitation step with ammonium acetate) we enrich very quickly the plasmid DNA content in the extract. The process has been thus far used to extract up to 100 mg of plasmid from 1.5 l of clarified lysate, corresponding to an E.coli bioreactor fermentation of 3 l.

Calcium-phosphate mediated DNA transfer into HEK-293 cells in suspension: control of physicochemical parameters allows transfection in stirred media. Transfection and protein expression in mammalian cells

This is the first report of transient transfection of suspended cells with purified plasmid DNA in bioreactors or spinner flasks. DNA/calcium phosphate complexes were pumped or injected directly into stirred cultures of the immortalized human embryo kidney cell line 293 (HEK-293) which had been adapted to growth in suspension. We identified culture conditions suitable for this approach and modified the protocol for the generation of precipitate complexes, based on our earlier work. In order to stabilize the 'DNA-vehicle'-complex in the culture medium, we identified pH ranges and ion-concentrations which prevent dissolution or aggregation of the precipitate particles. Such conditions maintained suspended fine particles in spinners or bioreactors for up to 6 hr. During that period, cells and precipitate complexes interacted sufficiently to allow DNA transfer and subsequent expression of recombinant protein. In a simple 5 day batch process, with a starting density of 0.3 × 10(6) cells mL(-1), about 0.5 mg L(-1) of a recombinant tissue plasminogen activator variant was observed.

Poly(ethyleneimine)-mediated large-scale transient gene expression: influence of molecular weight, polydispersity and N-propionyl groups

Three synthesis lots of linear poly(ethyleneimine) (PEI) are compared to a fully hydrolyzed linear PEI (commercially available as PEI "Max") regarding structure, polyplex formation with plasmid DNA, and transfection of suspension-adapted HEK-293E cells. PEI "Max" binds DNA more efficiently than the other PEIs, but it is the least effective in terms of transient recombinant protein yield. One PEI lot is fractionated by means of SEC. The fractions of high-M(n) PEI are the most efficient for complex formation and transfection. Nevertheless, the highest transient recombinant protein yields are achieved with unfractionated PEI. The results demonstrate that the polydispersity and charge density of linear PEI are important parameters for gene delivery to suspension-adapted HEK-293E cells.

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.

Reduced glutamine concentration improves protein production in growth-arrested CHO-DG44 and HEK-293E cells

For most cultivated mammalian cells, glutamine is an essential medium component. However, glutamine consumption results in the production of ammonia, a cytotoxic byproduct. Here we investigated the effect of glutamine reduction on recombinant protein production and ammonia accumulation in transiently transfected CHO and HEK-293E cells maintained under conditions of growth arrest. Maximum transient recombinant protein yields were observed in HEK-293E cultures without glutamine and in CHO cultures with 2 mM glutamine. The initial concentration of glutamine correlated with the level of ammonia accumulation in each culture. For both a stable CHO-derived cell line and a polyclonal population of recombinant CHO cells grown under conditions of mild hypothermia, the highest volumetric protein productivity was observed in cultures without glutamine. Here, the level of ammonia accumulation also corresponded to the initial glutamine concentration. Our data demonstrate that reduction of glutamine in the medium is an effective approach to improve protein production in both transiently and stably transfected mammalian cells when applying conditions that reduce or arrest the growth of these cells.

100-liter transient transfection

This is the first report of two successful 100 l scale transienttransfections in a standard stirred bioreactor. More than half a gram of a monoclonal antibody (IgG) were produced in less than 10 days using a technology called large-scale transient gene expression(LS-TGE). Suspension adapted HEK 293 EBNA SF cells were transfectedwithin a 150 l (nominal) bioreactor by a modified calcium phosphateco-precipitation method with more than 75 mg of plasmid DNA per run.A mixture of three different plasmids, one encoding for the heavychain of a human recombinant immunoglobulin, the other for the corresponding light chain and a third one for the green fluorescent protein (GFP, 2-4% of DNA in transfection cocktail)were co-transfected. The GFP vector was chosen to monitor transfection efficiency. Expression of GFP could be registered asearly as 20 h after DNA addition, using fluorescence microscopy. We demonstrate that transient transfection can be done at the100 l scale, thus providing a new tool to produce hundreds of milligrams or even gram amounts of recombinant protein. Akey advantage of LS-TGE resides in its speed. In the presentedcases, the entire production process for the synthesis of halfa gram of a recombinant antibody, including DNA preparationand necessary expansion of cells prior to transfection, wasexecuted in less than a month. Having an established transfection/expression process allows to run productioncampaigns for any given protein, within one facility, with onesingle host cell line and therefore only one single seed train. Without any need to create and maintain stable cell lines, expression of new r-proteins is not only faster and more economical but also more flexible.