Differential protein expression following low temperature culture of suspension CHO-K1 cells

Advances in screening, synthesis, modification, and biomedical applications of peptides and peptide aptamers

Peptides and peptide aptamers have emerged as promising molecules for a wide range of biomedical applications due to their unique properties and versatile functionalities. The screening strategies for identifying peptides and peptide aptamers with desired properties are discussed, including high-throughput screening, display screening technology, and in silico design approaches. The synthesis methods for the efficient production of peptides and peptide aptamers, such as solid-phase peptide synthesis and biosynthesis technology, are described, along with their advantages and limitations. Moreover, various modification techniques are explored to enhance the stability, specificity, and pharmacokinetic properties of peptides and peptide aptamers. This includes chemical modifications, enzymatic modifications, biomodifications, genetic engineering modifications, and physical modifications. Furthermore, the review highlights the diverse biomedical applications of peptides and peptide aptamers, including targeted drug delivery, diagnostics, and therapeutic. This review provides valuable insights into the advancements in screening, synthesis, modification, and biomedical applications of peptides and peptide aptamers. A comprehensive understanding of these aspects will aid researchers in the development of novel peptide-based therapeutics and diagnostic tools for various biomedical challenges.

A reflection on the improvement of Chinese Hamster ovary cell-based bioprocesses through advances in proteomic techniques

Chinese hamster ovary (CHO) cells are the preferred mammalian host for the large-scale production of recombinant proteins in the biopharmaceutical industry. Research endeavors have been directed to the optimization of CHO-based bioprocesses to increase protein quantity and quality, often in an empirical manner. To provide a rationale for those achievements, a myriad of CHO proteomic studies has arisen in recent decades. This review gives an overview of significant advances in LC-MS-based proteomics and sheds light on CHO proteomic studies, with a particular focus on CHO cells with superior bioprocessing phenotypes (growth, viability, titer, productivity and cQA), that have exploited novel proteomic or sub-omic techniques. These proteomic findings expand the current knowledge and understanding about the underlying protein clusters, protein regulatory networks and biological pathways governing such phenotypic changes. The proteomic studies, highlighted herein, will help in the targeted modulation of these cell factories to the desired needs.

Two-Dimensional Gel Electrophoresis and 2D-DIGE

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) continues to be one of the most versatile and widely used techniques to study the proteome of a biological system, particularly in the separation of intact proteins. A modified version of 2D-PAGE, two-dimensional difference gel electrophoresis (2D-DIGE), which uses differential labeling of protein samples with up to three fluorescent tags, offers greater sensitivity and reproducibility over conventional 2D-PAGE gels for differential quantitative analysis of protein expression between experimental groups. Both these methods have distinct advantages in the separation and identification of thousands of individual protein species including protein isoforms and post-translational modifications. This chapter discusses the principles of 2D-PAGE and 2D-DIGE including limitations to the methods. 2D-PAGE and 2D-DIGE continue to be popular methods in bioprocessing-related research, particularly on recombinant Chinese hamster ovary cells, which are also discussed in this chapter.

Comparative study of commercial media to improve GMP manufacturing of recombinant human interferon β-1a by CHO cells in perfusion bioreactor

Chinese hamster ovary cells are the main cellular factories for production of a wide range of recombinant proteins in biopharmaceutical industry. Recombinant human Interferon beta-1a (rh-IFN β-1a), as a cytokine is broadly used to treat multiple sclerosis. In this work, the cell line producing rh-IFN β-1a was studied to improve cell density along with the specific expression. For this reason different cell culture experiments were done using different commercial serum-free media to find the appropriate media providing higher cell density. It was shown DMEMF12, DMEM:ProCHO5, and CHO-S-SFM II led to higher cell density and shorter doubling time. Next, using these media, fed-batch, and perfusion culture with temperature shift were implemented to investigate the best condition for industrial-scale manufacturing of rh-IFN β-1a in terms of higher cell density and product expression yield. The results demonstrated that CHO-S-SFM II media and a thermally biphasic condition provide enhanced expression of rh-IFN β-1a in perfusion bioreactor.

Features, modulation and analysis of glycosylation patterns of therapeutic recombinant immunoglobulin A

Increasing the production of recombinant antibodies while ensuring high and stable protein quality remains a challenge in mammalian cell culture. This review is devoted to advances in the field of obtaining stable and optimal glycosylation of therapeutic antibodies based on IgA, as well as the subsequent issues of glycosylation control of glycoproteins during their production. Current studies also demonstrate a general need for a more fundamental understanding of the use of CHO cell-based producer cell lines, through which the glycoprofile of therapeutic IgA antibodies is produced and the dependence of glycosylation on culture conditions could be controlled. Optimization of glycosylation improves the therapeutic efficacy and can expand the possibilities for the creation of highly effective glycoprotein therapeutic drugs. Current status and trends in glycan analysis of therapeutic IgA, dominantly based on mass spectrometry and lectin microarrays are herein summarised as well.

Optimization of a GDNF production method based on Semliki Forest virus vector

Human glial cell line-derived neurotrophic factor (hGDNF) is the most potent dopaminergic factor described so far, and it is therefore considered a promising drug for Parkinson's disease (PD) treatment. However, the production of therapeutic proteins with a high degree of purity and a specific glycosylation pattern is a major challenge that hinders its commercialization. Although a variety of systems can be used for protein production, only a small number of them are suitable to produce clinical-grade proteins. Specifically, the baby hamster kidney cell line (BHK-21) has shown to be an effective system for the expression of high levels of hGDNF, with appropriate post-translational modifications and protein folding. This system, which is based on the electroporation of BHK-21 cells using a Semliki Forest virus (SFV) as expression vector, induces a strong shut-off of host cell protein synthesis that simplify the purification process. However, SFV vector exhibits a temperature-dependent cytopathic effect on host cells, which could limit hGDNF expression. The aim of this study was to improve the expression and purification of hGDNF using a biphasic temperature cultivation protocol that would decrease the cytopathic effect induced by SFV. Here we show that an increase in the temperature from 33°C to 37°C during the "shut-off period", produced a significant improvement in cell survival and hGDNF expression. In consonance, this protocol led to the production of almost 3-fold more hGDNF when compared to the previously described methods. Therefore, a "recovery period" at 37°C before cells are exposed at 33°C is crucial to maintain cell viability and increase hGDNF expression. The protocol described constitutes an efficient and highly scalable method to produce highly pure hGDNF.

Thermal conditioning improves quality and speed of keratinocyte sheet production for burn wound treatment

BACKGROUND AIMS

Cultured patient-specific keratinocyte sheets have been used clinically since the 1970s for the treatment of large severe burns. However, despite significant developments in recent years, successful and sustainable treatment is still a challenge. Reliable, high-quality grafts with faster availability and a flexible time window for transplantation are required to improve clinical outcomes.

METHODS

Keratinocytes are usually grown in vitro at 37°C. Given the large temperature differences in native skin tissue, the aim of the authors' study was to investigate thermal conditioning of keratinocyte sheet production. Therefore, the influence of 31°C, 33°C and 37°C on cell expansion and differentiation in terms of proliferation and sheet formation efficacy was investigated. In addition, the thermal effect on the biological status and thus the quality of the graft was assessed on the basis of the release of wound healing-related biofactors in various stages of graft development.

RESULTS

The authors demonstrated that temperature is a decisive factor in the production of human keratinocyte sheets. By using specific temperature ranges, the authors have succeeded in optimizing the individual manufacturing steps. During the cell expansion phase, cultivation at 37°C was most effective. After 6 days of culture at 37°C, three times and six times higher numbers of viable cells were obtained compared with 33°C and 31°C. During the cell differentiation and sheet formation phase, however, the cells benefited from a mildly hypothermic temperature of 33°C. Keratinocytes showed increased differentiation potential and formed better epidermal structures, which led to faster biomechanical sheet stability at day 18. In addition, a cultivation temperature of 33°C resulted in a longer lasting and higher secretion of the investigated immunomodulatory, anti-inflammatory, angiogenic and pro-inflammatory biofactors.

CONCLUSIONS

These results show that by using specific temperature ranges, it is possible to accelerate the large-scale production of cultivated keratinocyte sheets while at the same time improving quality. Cultivated keratinocyte sheets are available as early as 18 days post-biopsy and at any time for 7 days thereafter, which increases the flexibility of the process for surgeons and patients alike. These findings will help to provide better clinical outcomes, with an increased take rate in severe burn patients.

Tracking changes in adaptation to suspension growth for MDCK cells: cell growth correlates with levels of metabolites, enzymes and proteins

Abstract

Adaptations of animal cells to growth in suspension culture concern in particular viral vaccine production, where very specific aspects of virus-host cell interaction need to be taken into account to achieve high cell specific yields and overall process productivity. So far, the complexity of alterations on the metabolism, enzyme, and proteome level required for adaptation is only poorly understood. In this study, for the first time, we combined several complex analytical approaches with the aim to track cellular changes on different levels and to unravel interconnections and correlations. Therefore, a Madin-Darby canine kidney (MDCK) suspension cell line, adapted earlier to growth in suspension, was cultivated in a 1-L bioreactor. Cell concentrations and cell volumes, extracellular metabolite concentrations, and intracellular enzyme activities were determined. The experimental data set was used as the input for a segregated growth model that was already applied to describe the growth dynamics of the parental adherent cell line. In addition, the cellular proteome was analyzed by liquid chromatography coupled to tandem mass spectrometry using a label-free protein quantification method to unravel altered cellular processes for the suspension and the adherent cell line. Four regulatory mechanisms were identified as a response of the adaptation of adherent MDCK cells to growth in suspension. These regulatory mechanisms were linked to the proteins caveolin, cadherin-1, and pirin. Combining cell, metabolite, enzyme, and protein measurements with mathematical modeling generated a more holistic view on cellular processes involved in the adaptation of an adherent cell line to suspension growth.

Key points

• Less and more efficient glucose utilization for suspension cell growth

• Concerted alteration of metabolic enzyme activity and protein expression

• Protein candidates to interfere glycolytic activity in MDCK cells

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11150-z.

A Review on the Current Methods of Chinese Hamster Ovary (CHO) Cells Cultivation for the Production of Therapeutic Protein

Most of the clinical approved protein-based drugs or under clinical trials have a profound impact on the treatment of critical diseases. The mammalian eukaryotic cells culture approaches, particularly the CHO (Chinese Hamster Ovary) cells are mainly used in the biopharmaceutical industry for the mass-production of the therapeutic protein. Recent advances in CHO cell bioprocessing to yield recombinant proteins and monoclonal antibodies have enabled the expression of quality protein. The developments of cell lines are possible to enhance specific productivity. As a result, it holds an interesting area for academic as well as industrial researchers around the world. This review will focus on the recent progress of the mammalian CHO cells culture technology and the future scope of further development for the mass-production of protein therapeutics.

'Omics driven discoveries of gene targets for apoptosis attenuation in CHO cells

Chinese hamster ovary (CHO) cells are widely used in biopharmaceutical production. Improvements to cell lines and bioprocesses are constantly being explored. One of the major limitations of CHO cell culture is that the cells undergo apoptosis, leading to rapid cell death, which impedes reaching high recombinant protein titres. While several genetic engineering strategies have been successfully employed to reduce apoptosis, there is still room to further enhance CHO cell lines performance. 'Omics analysis is a powerful tool to better understand different phenotypes and for the identification of gene targets for engineering. Here, we present a comprehensive review of previous CHO 'omics studies that revealed changes in the expression of apoptosis-related genes. We highlight targets for genetic engineering that have reduced, or have the potential to reduce, apoptosis or to increase cell proliferation in CHO cells, with the final aim of increasing productivity.

Overexpression, overproduction, purification, and characterization of rhGH in Escherichia coli

Overexpression of insoluble human growth hormone (hGH) in cytoplasm was achieved by E. coli Rosetta-gami B(DE3) [pET21a (+)-hGH]). For overexpression of hGH, effects of eight factors including temperature, type and concentration of carbon source, IPTG and MgSO₄ , buffering capacity, induction time, yeast extract/peptone ratio on rhGH production were studied by Plackett-Burman screening. Maximum production of rhGH was 0.681 g/L, and results of statistical analysis showed that induction temperature and glucose have the greatest effect and the presence of MgSO₄ increases rhGH expression and reduces biomass concentration. So, the effect of ethanol and MgSO₄ concentrations on the rhGH production was examined according to the central composite experimental design. The ANOVA of the results showed rhGH production increases to 1.128 g/L in 4 g/L MgSO₄ and 1% ethanol. Then, the impact of glucose concentration and induction time on the rhGH production was evaluated in two levels in the fermenter by Taguchi statistical method. Under optimum conditions, OD_600nm 4 and 10 g/L glucose crude rhGH concentration 4.17 g/L was obtained, which is one of the highest value ever reported. Finally, rhGH was purified using the biophysical and biochemical techniques comprising circular dichroism, fluorescent spectroscopy, and dynamic light scattering, and it was confirmed that the produced protein is comparable to the commercial standard sample.

Automated cell segmentation in FIJI® using the DRAQ5 nuclear dye

BACKGROUND

Image segmentation and quantification are essential steps in quantitative cellular analysis. In this work, we present a fast, customizable, and unsupervised cell segmentation method that is based solely on Fiji (is just ImageJ)®, one of the most commonly used open-source software packages for microscopy analysis. In our method, the "leaky" fluorescence from the DNA stain DRAQ5 is used for automated nucleus detection and 2D cell segmentation.

RESULTS

Based on an evaluation with HeLa cells compared to human counting, our algorithm reached accuracy levels above 92% and sensitivity levels of 94%. 86% of the evaluated cells were segmented correctly, and the average intersection over union score of detected segmentation frames to manually segmented cells was above 0.83. Using this approach, we quantified changes in the projected cell area, circularity, and aspect ratio of THP-1 cells differentiating from monocytes to macrophages, observing significant cell growth and a transition from circular to elongated form. In a second application, we quantified changes in the projected cell area of CHO cells upon lowering the incubation temperature, a common stimulus to increase protein production in biotechnology applications, and found a stark decrease in cell area.

CONCLUSIONS

Our method is straightforward and easily applicable using our staining protocol. We believe this method will help other non-image processing specialists use microscopy for quantitative image analysis.

Therapeutic Fc fusion protein misfolding: A three-phasic cultivation experimental design

Cell culture process optimization is a critical solution to most of the challenges faced by the pharmaceutical manufacturing. One of the major problems encountered in large-scale production of therapeutic proteins is misfolded protein production. The accumulation of misfolded therapeutic proteins is an immunogenic signal and a risk factor for immunogenicity of the final product. The aim of this study was the statistical optimization of three-phasic temperature shift and timing for enhanced production of correctly folded Fc-fusion protein. The effect of culture temperatures were investigated using the biphasic culture system. Box-Behnken design was then used to compute temperature and time of shifting optimum. Response surface methodology revealed that maximum production with low level of misfolded protein was achieved at two-step temperature shift from 37°C to 30°C during the late logarithmic phase and 30°C to 28°C in the mid-stationary phase. The optimized condition gave the best results of 1860 mg L-1 protein titer with 24.5% misfolding level. The validation experiments were carried out under optimal conditions with three replicates and the protein misfolding level was decreased by two times while productivity increased by ~ 1.3-fold. Large-scale production in 250 L bioreactor under the optimum conditions was also verified the effectiveness and the accuracy of the model. The results showed that by utilizing two-step temperature shift, productivity and the quality of target protein have been improved simultaneously. This model could be successfully applied to other products.

Full-length human CCBE1 production and purification: leveraging bioprocess development for high quality glycosylation attributes and functionality

Collagen and calcium-binding EGF domain-1 (CCBE1) is a secreted protein critical for lymphatic/cardiac vascular development and regeneration. However, the low efficient production of the recombinant full-length CCBE1 (rCCBE1) has been a setback for functional studies and therapeutic applications using this protein. The main goal of this work was to implement a robust bioprocess for efficient production of glycosylated rCCBE1. Different bioprocess strategies were combined with proteomic tools for process/product characterization, evaluating the impact of process parameters on cell performance, rCCBE1 production and quality. We have shown that rCCBE1 volumetric yield was positively correlated with higher cell density at transfection (HDT), and under these conditions the secreted protein presented a mature glycosylated profile (complex N-glycans). Mild hypothermia was also applied to HDT condition that resulted in enhanced cell viability; however an enrichment of immature rCCBE1 variants was detected. Mass spectrometry-based tools allowed the identification of rCCBE1 peptides confirming protein identity in the affinity chromatography enriched product. rCCBE1 biological activity was validated by in vitro angiogenesis assay, where enhanced vessel formation was observed. Herein, we report a step forward in the production and characterization of human glycosylated rCCBE1, amenable for in vitro and in vivo studies to explore its regenerative therapeutic potential.

Two-Dimensional Gel Electrophoresis and 2D-DIGE

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) continues to be one of the most versatile and widely used techniques to study the proteome of a biological system. In particular, a modified version of 2D-PAGE, two-dimensional difference gel electrophoresis (2D-DIGE), which uses differential labeling of protein samples with up to three fluorescent tags, offers greater sensitivity and reproducibility over conventional 2D-PAGE gels for differential quantitative analysis of protein expression between experimental groups. Both these methods have distinct advantages in the separation and identification of thousands of individual proteins species including protein isoforms and post-translational modifications. This review will discuss the principles of 2D-PAGE and 2D-DIGE including limitations to the methods. 2D-PAGE and 2D-DIGE continue to be popular methods in bioprocessing-related research (particularly on recombinant Chinese hamster ovary cells), which will also be discussed in the review chapter.

Cascading effect in bioprocessing-The impact of mild hypothermia on CHO cell behavior and host cell protein composition

A major challenge in downstream purification of monoclonal antibodies (mAb) is the removal of host cell proteins (HCPs). Previous studies have shown that cell culture conditions significantly impact the HCP content at harvest. However, it is currently unclear how process conditions affect physiological changes in the host cell population, and how these changes, in turn, cascade down to change the HCP profile. We examined how temperature downshift (TDS) to mild hypothermia affects key upstream performance indicators, that is antibody titre, HCP concentration and HCP species, across the cell culture decline phase and at harvest through the lens of changes in cellular behavior. Mild hypothermic conditions introduced on day 5 of fed-batch Chinese hamster ovary (CHO) cell bioreactors resulted in a lower cell proliferation rate but larger percentages of healthier cells across the cell culture decline phase compared to bioreactors maintained at standard physiological temperature. Moreover, the onset of apoptosis was less evident in mild hypothermic cultures. Consequently, mild hypothermic cultures took an extra 5 days to reach an integral viable cell concentration (IVCC) and antibody yield similar to that of the control at standard physiological temperature. When cell viability dropped below 80%, mild hypothermic cell cultures had a reduced variety of HCP species by 36%, including approximately 44% and 27% lower proteases and chaperones, respectively, despite having similar HCP concentration. This study suggests that TDS may be a good strategy to provide cleaner downstream feedstocks by reducing the variety of HCPs and to maintain product integrity by reducing the number of proteases and chaperones.

The 'Omics Revolution in CHO Biology: Roadmap to Improved CHO Productivity

Increased understanding of Chinese hamster ovary (CHO) cell physiology has been ushered in upon availability of the parental CHO-K1 cell line genome. Free and openly accessible sequence information has complemented transcriptomic and proteomic studies. The previous decade has also seen an increase in sensitivity and accuracy of proteomic methods due to technology development. In this genomic era, high-throughput screening methods, sophisticated informatic tools, and models continually drive major innovations in cell line development and process engineering. This review describes the various achievements in 'omics techniques and their application to improve recombinant protein expression from CHO cell lines.

pEVL: A Linear Plasmid for Generating mRNA IVT Templates With Extended Encoded Poly(A) Sequences

Increasing demand for large-scale synthesis of in vitro transcribed (IVT) mRNA is being driven by the increasing use of mRNA for transient gene expression in cell engineering and therapeutic applications. An important determinant of IVT mRNA potency is the 3′ polyadenosine (poly(A)) tail, the length of which correlates with translational efficiency. However, present methods for generation of IVT mRNA rely on templates derived from circular plasmids or PCR products, in which homopolymeric tracts are unstable, thus limiting encoded poly(A) tail lengths to ~120 base pairs (bp). Here, we have developed a novel method for generation of extended poly(A) tracts using a previously described linear plasmid system, pJazz. We find that linear plasmids can successfully propagate poly(A) tracts up to ~500 bp in length for IVT mRNA production. We then modified pJazz by removing extraneous restriction sites, adding a T7 promoter sequence upstream from an extended multiple cloning site, and adding a unique type-IIS restriction site downstream from the encoded poly(A) tract to facilitate generation of IVT mRNA with precisely defined encoded poly(A) tracts and 3′ termini. The resulting plasmid, designated pEVL, can be used to generate IVT mRNA with consistent defined lengths and terminal residue(s).

Effect of Temperature Downshift on the Transcriptomic Responses of Chinese Hamster Ovary Cells Using Recombinant Human Tissue Plasminogen Activator Production Culture

Recombinant proteins are widely used as biopharmaceuticals, but their production by mammalian cell culture is expensive. Hence, improvement of bioprocess productivity is greatly needed. A temperature downshift (TDS) from 37°C to 28–34°C is an effective strategy to expand the productive life period of cells and increase their productivity (q_p). Here, TDS in Chinese hamster ovary (CHO) cell cultures, initially grown at 37°C and switched to 30°C during the exponential growth phase, resulted in a 1.6-fold increase in the q_p of recombinant human tissue plasminogen activator (rh-tPA). The transcriptomic response using next-generation sequencing (NGS) was assessed to characterize the cellular behavior associated with TDS. A total of 416 (q > 0.8) and 3,472 (q > 0.9) differentially expressed transcripts, with more than a 1.6-fold change at 24 and 48 h post TDS, respectively, were observed in cultures with TDS compared to those at constant 37°C. In agreement with the extended cell survival resulting from TDS, transcripts related to cell growth arrest that controlled cell proliferation without the activation of the DNA damage response, were differentially expressed. Most upregulated genes were related to energy metabolism in mitochondria, mitochondrial biogenesis, central metabolism, and avoidance of apoptotic cell death. The gene coding for rh-tPA was not differentially expressed, but fluctuations were detected in the transcripts encoding proteins involved in the secretory machinery, particularly in glycosylation. Through NGS the dynamic processes caused by TDS were assessed in this biological system.

Responses of CHO cell lines to increased pCO2 at normal (37 °C) and reduced (33 °C) culture temperatures

The correlation between dissolved carbon dioxide (pCO2) and cell growth, cell metabolism, productivity and product quality has often been reported. However, since pCO2 values in bioprocesses always vary concurrently with other bioprocess variables, it is very difficult to distinguish only the effect of pCO2. The aim of our work was to investigate further the specific effect of pCO2 and cell response on a proteome level. Proteome responses of three different CHO-Der3 cell lines in the exponential growth phase at normal (37 °C) and reduced (33 °C) culture temperatures, with normal (10%) and increased (20%) pCO2, were studied by comparative proteomic analysis (2D-DIGE). Cell viability and cell density, and the concentration of glucose, glutamine and lactate monitored over 72-h cultures showed that elevated pCO2 did not affect cell viability or productivity at either culture temperature, while metabolic activity was reduced. The specific metabolic profile also indicated altered glucose metabolism toward a less efficient anaerobic metabolism. Two-way ANOVA of proteomic data discriminated many more pCO2-specific changes in protein abundance (p<0.01) at 33 °C than at 37 °C and PCA analysis was able to distinguish clusters distinguishing cell lines and culture conditions at low temperature and elevated pCO2, indicating substantial proteome changes under these culture conditions. Cell sensitivity to increased pCO2 at the lower temperature was further confirmed by a significantly increased abundance of twelve proteins involved in anti- oxidative mechanisms and increased abundance of six proteins involved in glycolysis, including L-lactate dehydrogenase. Proteomic results support the metabolic data and the proposed pCO2 invoked metabolic switch toward anaerobic pathways. Anti- oxidative mechanisms, together with the anaerobic metabolism, allow the cells to detoxify while maintaining sufficient energy levels to preserve their vitality and functionality. This study provides further insight into the proteome responses of CHO cell lines to increased pCO2 at the two culture temperatures.

A cellular response linking eIF4AI activity to eIF4AII transcription

The recruitment of ribosomes to eukaryotic cellular mRNAs requires the activity of two prototypic RNA helicases, eukaryotic initiation factor (eIF) 4AI and eIF4AII. The eIF4A isoforms are highly conserved, are thought to be functionally interchangeable, and are directed to the 5' m(7)GpppN cap structure of mRNAs during translation initiation by virtue of their assembly into eIF4F, a heterotrimeric complex that also harbors the eIF4E cap binding protein and eIF4G scaffolding unit. During the course of RNA interference experiments aimed at investigating the respective roles of eIF4AI and eIF4AII in translation, we uncovered a cellular response pathway whereby suppression of eIF4AI increases transcription of the eIF4AII gene, leading to elevated eIF4AII mRNA and protein levels. Inhibition of eIF4AI suppresses protein synthesis, and although eIF4AII protein levels increase above and beyond what should be sufficient to compensate for the decrease in eIF4AI levels, there is no corresponding rescue of translation or of the block on cellular proliferation that occurs upon eIF4AI suppression. These results were phenocopied using the small molecule eIF4A inhibitor hippuristanol. Taken together, our results indicate that eIF4AI and eIF4AII expression appear linked and that the two protein isoforms exhibit functional differences.

Large-scale expansion and exploitation of pluripotent stem cells for regenerative medicine purposes: beyond the T flask

Human pluripotent stem cells will likely be a significant part of the regenerative medicine-driven healthcare revolution. In order to realize this potential, culture processes must be standardized, scalable and able to produce clinically relevant cell numbers, whilst maintaining critical biological functionality. This review comprises a broad overview of important bioprocess considerations, referencing the development of biopharmaceutical processes in an effort to learn from current best practice in the field. Particular focus is given to the recent efforts to grow human pluripotent stem cells in microcarrier or aggregate suspension culture, which would allow geometric expansion of productive capacity were it to be fully realized. The potential of these approaches is compared with automation of traditional T-flask culture, which may provide a cost-effective platform for low-dose, low-incidence conditions or autologous therapies. This represents the first step in defining the full extent of the challenges facing bioprocess engineers in the exploitation of large-scale human pluripotent stem cell manufacture.

Proteomic analysis of endothelial cold-adaptation

BACKGROUND

Understanding how human cells in tissue culture adapt to hypothermia may aid in developing new clinical procedures for improved ischemic and hypothermic protection. Human coronary artery endothelial cells grown to confluence at 37°C and then transferred to 25°C become resistant over time to oxidative stress and injury induced by 0°C storage and rewarming. This protection correlates with an increase in intracellular glutathione at 25°C. To help understand the molecular basis of endothelial cold-adaptation, isolated proteins from cold-adapted (25°C/72 h) and pre-adapted cells were analyzed by quantitative proteomic methods and differentially expressed proteins were categorized using the DAVID Bioinformatics Resource.

RESULTS

Cells adapted to 25°C expressed changes in the abundance of 219 unique proteins representing a broad range of categories such as translation, glycolysis, biosynthetic (anabolic) processes, NAD, cytoskeletal organization, RNA processing, oxidoreductase activity, response-to-stress and cell redox homeostasis. The number of proteins that decreased significantly with cold-adaptation exceeded the number that increased by 2:1. Almost half of the decreases were associated with protein metabolic processes and a third were related to anabolic processes including protein, DNA and fatty acid synthesis. Changes consistent with the suppression of cytoskeletal dynamics provided further evidence that cold-adapted cells are in an energy conserving state. Among the specific changes were increases in the abundance and activity of redox proteins glutathione S-transferase, thioredoxin and thioredoxin reductase, which correlated with a decrease in oxidative stress, an increase in protein glutathionylation, and a recovery of reduced protein thiols during rewarming from 0°C. Increases in S-adenosylhomocysteine hydrolase and nicotinamide phosphoribosyltransferase implicate a central role for the methionine-cysteine transulfuration pathway in increasing glutathione levels and the NAD salvage pathway in increasing the reducing capacity of cold-adapted cells.

CONCLUSIONS

Endothelial adaptation to mild-moderate hypothermia down-regulates anabolic processes and increases the reducing capacity of cells to enhance their resistance to oxidation and injury associated with 0°C storage and rewarming. Inducing these characteristics in a clinical setting could potentially limit the damaging effects of energy insufficiency due to ischemia and prevent the disruption of integrated metabolism at low temperatures.

RNA interference of cofilin in Chinese hamster ovary cells improves recombinant protein productivity

RNA interference (RNAi) has been recently applied to improve the yield and quality of recombinant proteins produced in Chinese hamster ovary (CHO) cells, the most commonly used mammalian cell line for production of complex biopharmaceuticals. Proteomic profiling of CHO cells undergoing gene amplification identified cofilin, a key regulatory protein of actin cytoskeletal dynamics, as a cellular target for genetic engineering studies. Transient reduction of cofilin by small interfering RNA (siRNA) enhanced specific productivity in recombinant CHO cells by up to 80%. CHO cell lines expressing cofilin-specific short hairpin RNA (shRNA) vectors showed up to a 65% increase in specific productivity. These results suggest that modulation of cofilin, and its regulatory pathways, may be a new approach to enhance recombinant protein productivity in CHO cells.

Expansion of human mesenchymal stem cells on microcarriers

The effects on human mesenchymal stem cell growth of choosing either of two spinner flask impeller geometries, two microcarrier concentrations and two cell concentrations (seeding densities) were investigated. Cytodex 3 microcarriers were not damaged when held at the minimum speed, N(JS), for their suspension, using either impeller, nor was there any observable damage to the cells. The maximum cell density was achieved after 8-10 days of culture with up to a 20-fold expansion in terms of cells per microcarrier. An increase in microcarrier concentration or seeding density generally had a deleterious or neutral effect, as previously observed for human fibroblast cultures. The choice of impeller was significant, as was incorporation of a 1 day delay before agitation to allow initial attachment of cells. The best conditions for cell expansion on the microcarriers in the flasks were 3,000 microcarriers ml(-1) (ca. 1 g dry weight l(-1)), a seeding density of 5 cells per microcarrier with a 1 day delay before agitation began at N(JS) (30 rpm), using a horizontally suspended flea impeller with an added vertical paddle. These findings were interpreted using Kolmogorov's theory of isotropic turbulence.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

Advancing biopharmaceutical process development by system-level data analysis and integration of omics data

Development of efficient bioprocesses is essential for cost-effective manufacturing of recombinant therapeutic proteins. To achieve further process improvement and process rationalization comprehensive data analysis of both process data and phenotypic cell-level data is essential. Here, we present a framework for advanced bioprocess data analysis consisting of multivariate data analysis (MVDA), metabolic flux analysis (MFA), and pathway analysis for mapping of large-scale gene expression data sets. This data analysis platform was applied in a process development project with an IgG-producing Chinese hamster ovary (CHO) cell line in which the maximal product titer could be increased from about 5 to 8 g/L.Principal component analysis (PCA), k-means clustering, and partial least-squares (PLS) models were applied to analyze the macroscopic bioprocess data. MFA and gene expression analysis revealed intracellular information on the characteristics of high-performance cell cultivations. By MVDA, for example, correlations between several essential amino acids and the product concentration were observed. Also, a grouping into rather cell specific productivity-driven and process control-driven processes could be unraveled. By MFA, phenotypic characteristics in glycolysis, glutaminolysis, pentose phosphate pathway, citrate cycle, coupling of amino acid metabolism to citrate cycle, and in the energy yield could be identified. By gene expression analysis 247 deregulated metabolic genes were identified which are involved, inter alia, in amino acid metabolism, transport, and protein synthesis.