Monitoring recombinant human interferon-gamma N-glycosylation during perfused fluidized-bed and stirred-tank batch culture of CHO cells

Unveiling cytokine charge disparity as a potential mechanism for immune regulation

Cytokines are small signaling proteins that regulate the immune responses to infection and tissue damage. Surface charges of cytokines determine their in vivo fate in immune regulation, e.g., half-life and distribution. The overall negative charges in the extracellular microenvironment and the acidosis during inflammation and infection may differentially impact cytokines with different surface charges for fine-tuned immune regulation via controlling tissue residential properties. However, the trend and role of cytokine surface charges has yet to be elucidated in the literature. Interestingly, we have observed that most pro-inflammatory cytokines have a negative charge, while most anti-inflammatory cytokines and chemokines have a positive charge. In this review, we extensively examined the surface charges of all cytokines and chemokines, summarized the pharmacokinetics and tissue adhesion of major cytokines, and analyzed the link of surface charge with cytokine biodistribution, activation, and function in immune regulation. Additionally, we identified that the general trend of charge disparity between pro- and anti-inflammatory cytokines represents a unique opportunity to develop precise immune modulation approaches, which can be applied to many inflammation-associated diseases including solid tumors, chronic wounds, infection, and sepsis.

Insights into the quality of recombinant proteins produced by two different Bombyx mori expression systems

The silkworm, Bombyx mori, is an attractive host for recombinant protein production due to its high expression efficiency, quality, and quantity. Two expression systems have been widely used for recombinant protein production in B. mori: baculovirus/silkworm expression system and transgenic silkworm expression system. Both expression systems enable high protein production, but the qualities of the resulting recombinant proteins have not been well evaluated. In this study, we expressed bovine interferon γ (IFN-γ) using the two systems and examined the quality of the resulting proteins in terms of N-glycosylation and protein cleavage. Both expression systems successfully produced IFN-γ as an N-glycoprotein. Although the production in the baculovirus/silkworm expression system was much more efficient than that in the transgenic silkworm expression system, unexpected variants of IFN-γ were also produced in the former system due to the different N-glycosylation and C-terminal truncations. These results indicate that while high protein production could be achieved in the baculovirus/silkworm expression system, unintentional protein modification might occur, and therefore protein expression in the transgenic silkworm expression system is preferable from the point-of-view of N-glycosylation of the recombinant protein and evasion of unexpected attack by a protease in B. mori.

Scale-Up Technologies for the Manufacture of Adherent Cells

Great importance is being given to the impact our food supply chain and consumers' food habits are having on the environment, human health, and animal welfare. One of the latest developments aiming at positively changing the food ecosystem is represented by cultured meat. This form of cellular agriculture has the objective to generate slaughter-free meat products starting from the cultivation of few cells harvested from the animal tissue of interest. As a consequence, a large number of cells has to be generated at a reasonable cost. Just to give an idea of the scale, there were billions of cells just in a bite of the first cultured-meat burger. Thus, one of the major challenges faced by the scientists involved in this new ambitious and fascinating field, is how to efficiently scale-up cell manufacture. Considering the great potential presented by cultured meat, audiences from different backgrounds are very interested in this topic and eager to be informed of the challenges and possible solutions in this area. In light of this, we will provide an overview of the main existing bioprocessing technologies used to scale-up adherent cells at a small and large scale. Thus, giving a brief technical description of these bioprocesses, with the main associated advantages and disadvantages. Moreover, we will introduce an alternative solution we believe has the potential to revolutionize the way adherent cells are grown, helping cultured meat become a reality.

Osmolality as a lever to modulate the N-glycolylneuraminicacid (Neu5Gc) level of a recombinant glycoprotein produced in Chinese hamster ovary cells

Glycoproteins could be highly sialylated, and controlling the sialic acid levels for some therapeutic proteins is critical to ensure product consistency and efficacy. N-acetylneuraminic acid (Neu5Ac, or NANA) and N-glycolylneuraminic acid (Neu5Gc, or NGNA) are the two most common forms of sialic acids produced in mammalian cells. As Neu5Gc is not produced in humans and can elicit immune responses, minimizing Neu5Gc formation is important in controlling this quality attribute for complex glycoproteins. In this study, a sialylated glycoprotein was used as the model molecule to study the effect of culture osmolality on Neu5Gc. A 14-day fed-batch process with osmolality maintained at physiological levels produced high levels of Neu5Gc. Increase of culture osmolality reduced the Neu5Gc level up to 70-80%, and the effect was proportional to the osmolality level. Through evaluating different osmolality conditions (300-450 mOsm/kg) under low or high pCO₂ , we demonstrated that osmolality could be an effective process lever to modulate the Neu5Gc level. Potential mechanism of osmolality impact on Neu5Gc is discussed and is hypothesized to be cytosol NADH availability related. Compared with cell line engineering efforts, this simple process lever provides the opportunity to readily modulate the Neu5Gc level in a cell culture environment.

N-Glycosylation of IgG and IgG-Like Recombinant Therapeutic Proteins: Why Is It Important and How Can We Control It?

Regulatory bodies worldwide consider N-glycosylation to be a critical quality attribute for immunoglobulin G (IgG) and IgG-like therapeutics. This consideration is due to the importance of posttranslational modifications in determining the efficacy, safety, and pharmacokinetic properties of biologics. Given its critical role in protein therapeutic production, we review N-glycosylation beginning with an overview of the myriad interactions of N-glycans with other biological factors. We examine the mechanism and drivers for N-glycosylation during biotherapeutic production and the several competing factors that impact glycan formation, including the abundance of precursor nucleotide sugars, transporters, glycosidases, glycosyltransferases, and process conditions. We explore the role of these factors with a focus on the analytical approaches used to characterize glycosylation and associated processes, followed by the current state of advanced glycosylation modeling techniques. This combination of disciplines allows for a deeper understanding of N-glycosylation and will lead to more rational glycan control.

Human Cell Line-Derived Monoclonal IgA Antibodies for Cancer Immunotherapy

IgA antibodies have great potential to improve the functional diversity of current IgG antibody-based cancer immunotherapy options. However, IgA production and purification is not well established, which can at least in part be attributed to the more complex glycosylation as compared to IgG antibodies. IgA antibodies possess up to five N-glycosylation sites within their constant region of the heavy chain as compared to one site for IgG antibodies. The human GlycoExpress expression system was developed to produce biotherapeutics with optimized glycosylation and used here to generate a panel of IgA isotype antibodies directed against targets for solid (TA-mucin 1, Her2, EGFR, Thomsen–Friedenreich) and hematological (CD20) cancer indications. The feasibility of good manufacturing practice was shown by the production of 11 g IgA within 35 days in a one liter perfusion bioreactor, and IgA antibodies in high purity were obtained after purification. The monoclonal IgA antibodies possessed a high sialylation degree, and no non-human glycan structures were detected. Kinetic analysis revealed increased avidity antigen binding for IgA dimers as compared to monomeric antibodies. The IgA antibodies exhibited potent Fab- and Fc-mediated functionalities against cancer cell lines, whereby especially granulocytes are recruited. Therefore, for patients who do not sufficiently benefit from therapeutic IgG antibodies, IgA antibodies may complement current regiment options and represent a promising strategy for cancer immunotherapy. In conclusion, a panel of novel biofunctional IgA antibodies with human glycosylation was successfully generated.

A framework for real-time glycosylation monitoring (RT-GM) in mammalian cell culture

Glycosylation is a critical characteristic of biotherapeutics because of its central role in in vivo efficacy. Multiple factors including medium composition and process conditions impact protein glycosylation and characterizing cellular response to these changes is essential to understand the underlying relationships. Current practice typically involves glycosylation characterization at the end of a fed-batch culture, which in addition to being an aggregate of the process, reflects a bias towards the end of the culture where a majority of the product is made. In an attempt to rigorously characterize the entire time-course of a fed-batch culture, a real-time glycosylation monitoring (RT-GM) framework was developed. It involves using the micro sequential injection (μSI) system as a sample preparation platform coupled with an ultra-performance liquid chromatography (UPLC) system for real-time monitoring of the antibody glycan profile. Automated sampling and sample preparations were performed using the μSI system and this framework was used to study manganese (Mn)-induced glycosylation changes over the course of a fed-batch culture. As expected, Mn-supplemented cultures exhibited higher galactosylation levels compared to control while the fucosylation and mannosylation were consistent for both supplemented and control cultures. Overall, the approach presented in the study allows real time monitoring of glycosylation changes and this information can be rapidly translated into process control and/or process optimization decisions to accelerate process development.

Comparative investigation of the use of various commercial microcarriers as a substrate for culturing mammalian cells

Microcarriers provide large adhesion area allowing high cell densities in bioreactor systems. This study focused on the investigation of cell adhesion and cell growth characteristics of both anchorage-dependent CHO-K1 and anchorage-independent Ag8 myeloma cell lines cultivated on four different microcarriers (Biosilon®, Microhex®, Cytodex 3®, Cytoline 2®) by considering the cell kinetics and physiological data. Experiments were performed in both static and agitated cell culture systems by using 24-well tissue culture plates and then 50-ml spinner flasks. In agitated cultures, the highest specific growth rates (0.026 h for CHO-K1 and 0.061 h for Ag8 cell line) were obtained with Cytodex 3® and Cytoline 2® microcarriers for CHO-K1 and Ag8 cell line, respectively. Metabolic characteristics showed some variation among the cultures with the four microcarriers. The most significant being the higher production of lactate with microcarriers with CHO-K1 cells relative to the Ag8 cells. SEM analyses revealed the differences in the morphology of the cells along with microcarriers. On Cytodex 3® and Cytoline 2®, CHO-K1 cells attached to the substratum through long, slender filopodia, whereas the cells showed a flat morphology by covering the substratum on the Biosilon® and Microhex®. Ag8 cells maintained their spherical shapes throughout the culture for all types of microcarriers. In an attempt to scale-up, productions were carried out in 50-ml spinner flasks. Cytodex 3® (for CHO-K1 cells) and Cytoline 2® (for Ag8 cells) were evaluated. The results demonstrate that high yield of biomass could be achieved through the immobilization of the cells in each culture system. And cell cultures on microcarriers, especially on Cytodex 3® and Cytoline 2®, represented a good potential as microcarriers for larger scale cultures of CHO-K1 and Ag8, respectively. Moreover, owing to the fact that the cell lines and culture media are specific, outcomes will be applicable for other clones derived from the same host cell lines.

The impact of microcarrier culture optimization on the glycosylation profile of a monoclonal antibody

Microcarriers are widely used for the large-scale culture of attachment-dependent cells with increased cell densities and, ultimately, higher product yield. In these processes, the specific culture conditions can affect the quality of the product, which is closely related to its glycosylation pattern. Furthermore, the lack of studies in the area reinforces the need to better understand the effects of microcarrier culture in product glycosylation. Consequently, in this work, the glycosylation profile of a monoclonal antibody (mAb) produced by adherent CHO-K1 cells grown in Cytodex 3 was evaluated under different conditions, and compared to that obtained of typical adherent cultures. It was found that microcarrier cultures result in a glycosylation profile with different characteristics from T-flask cultures, with a general increase in galactosylation and decrease in fucosylation levels, both with a potentially positive impact on mAb activity. Sialylation also varied but without a general tendency. This study then showed that the specific culture conditions used in microcarrier culture influence the mAb glycan profile, and each functional element (galactose, core fucose, sialic acid) is independently affected by these conditions. In particular, great reductions of fucosylation (from 79 to 55%) were obtained when using half volume at inoculation, and notable decreases in sialylation (from 23 to 2%) and glycoform heterogeneity (from 20 to 11 glycoforms) were observed for shake flask culture, potentially associated with the improved cell densities achieved in these culture vessels.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

A new generation of carbohydrate-based therapeutics: recombinant mucin-type fusion proteins as versatile inhibitors of protein-carbohydrate interactions

Cell surface carbohydrates are essential for a multitude of biomedically important interactions that take place at the cell surface. Carbohydrate-binding proteins are, therefore, significant targets for the development of carbohydrate-based inhibitors. Due to their multivalent character, monovalent low-molecular-weight sugar homologues or analogues are usually poor inhibitors of these interactions. Recent advances in organic and chemoenzymatic synthesis of carbohydrates will undoubtedly increase the pace by which new multivalent carbohydrate-based drugs are developed. Knowledge gained on the glycosyltransferases that are involved in glycan biosynthesis can be used to engineer host cells for recombinant production of proteins with tailored glycan substitution. In particular, recombinant mucin-type proteins can serve as natural scaffolds for multivalent presentation of therapeutic carbohydrate determinants.

Plant protein hydrolysates support CHO-320 cells proliferation and recombinant IFN-gamma production in suspension and inside microcarriers in protein-free media

We have recently developed a protein-free medium (PFS) able to support the growth of Chinese hamster ovary (CHO) cells in suspension. Upon further supplementation with some plant protein hydrolysates, medium performances reached what could be observed in serum-containing media [Burteau et al. In Vitro Cell. Dev. Biol.-Anim. 39 (2003) 291]. Now, we describe the use of rice and wheat protein hydrolysates, as non-nutritional additives to the culture medium to support productivity and cell growth in suspension or in microcarriers. When CHO-320 cells secreting recombinant interferon-gamma (IFN-gamma) were cultivated in suspension in a bioreactor with our PFS supplemented with wheat hydrolysates, the maximum cell density increased by 25% and the IFN-gamma secretion by 60% compared to the control PFS. A small-scale perfusion system consisting of CHO-320 cells growing on and inside fibrous microcarriers under discontinuous operation was first developed. Under these conditions, rice protein hydrolysates stimulated recombinant IFN-gamma secretion by 30% compared to the control PFS. At the bioreactorscale, similar results were obtained but when compared to shake-flasks studies, nutrients, oxygen or toxic by-products gradients inside the microcarriers seemed to be the main limitation of the system. An increase of the perfusion rate to maintain glucose concentration over 5.5 mM and dissolved oxygen (DO) at 60% was able to stimulate the production of IFN-gamma to a level of 6.6 mug h(-1) g(-1) of microcarriers after 160 h when a cellular density of about 4 x 10(8) cell g(-1) of carriers was reached.

Detachment factors for enhanced carrier to carrier transfer of CHO cell lines on macroporous microcarriers

In this publication different detachment factors were tested for enhancing carrier to carrier transfer for scale-up of macroporous microcarrier based bioprocesses. Two Chinese hamster ovary cell lines, CHO-K1 and a genetically engineered CHO-K1 derived cell line (CHO-MPS), producing recombinant human Arylsulfatase B, were examined. The cells were grown on Cytoline 1microcarriers (Amersham Biosciences, Uppsala, Sweden) in protein-free and chemically defined medium respectively. Fully colonised microcarriers were used at passage ratios of approximately 1:10 for carrier to carrier transfer experiments. To accelerate the colonisation of the non-colonised, freshly added microcarriers the detachment reagents trypsin, papain, Accutasetrade mark (PAA, Linz, Austria), heparin and dextransulphate were used. Both cell lines showed good results with trypsin, Accutase and dextransulphate (Amersham Biosciences, Uppsala, Sweden), while papain failed to enhance carrier to carrier transfer in comparison to the non-treated reference. The maximum growth rate of cells on microcarriers with 2% dextransulphate in the medium was 0.25 +/- 0.02d(-1) and 0.27 +/- 0.03d(-1) for the CHO-MPS and CHO-K1, respectively. TheCHO-K1 grew best after detachment with trypsin (mu = 0.36 +/- 0.03d(-1)). This indicates, that one of the key parameters for carrier to carrier transfer is the uniform distribution of cells on the individual carriers during the initial phase. When this distribution can be improved, growth rate increases, resulting in a faster and more stable process.

Protein glycosylation control in mammalian cell culture: past precedents and contemporary prospects

Protein glycosylation is a post-translational modification of paramount importance for the function, immunogenicity, and efficacy of recombinant glycoprotein therapeutics. Within the repertoire of post-translational modifications, glycosylation stands out as having the most significant proven role towards affecting pharmacokinetics and protein physiochemical characteristics. In mammalian cell culture, the understanding and controllability of the glycosylation metabolic pathway has achieved numerous successes. However, there is still much that we do not know about the regulation of the pathway. One of the frequent conclusions regarding protein glycosylation control is that it needs to be studied on a case-by-case basis since there are often conflicting results with respect to a control variable and the resulting glycosylation. In attempts to obtain a more multivariate interpretation of these potentially controlling variables, gene expression analysis and systems biology have been used to study protein glycosylation in mammalian cell culture. Gene expression analysis has provided information on how glycosylation pathway genes both respond to culture environmental cues, and potentially facilitate changes in the final glycoform profile. Systems biology has allowed researchers to model the pathway as well-defined, inter-connected systems, allowing for the in silico testing of pathway parameters that would be difficult to test experimentally. Both approaches have facilitated a macroscopic and microscopic perspective on protein glycosylation control. These tools have and will continue to enhance our understanding and capability of producing optimal glycoform profiles on a consistent basis.

Effect of surfactant pluronic F-68 on CHO cell growth, metabolism, production, and glycosylation of human recombinant IFN-γ in mild operating conditions

The control of glycosylation to satisfy regulatory requirements and quality consistency of recombinant proteins produced by different processes has become an important issue. With two N-glycosylation sites, γ-interferon (IFN-γ) can be seen as a prototype of a recombinant therapeutic glycoprotein for this purpose. The effect of the nonionic surfactant Pluronic F-68 (PF-68) on cell growth and death was investigated, as well as production and glycosylation of recombinant IFN-γ produced by a CHO cell line that was maintained in a rich protein-free medium in the absence or presence of low agitation. Under these conditions, a dose-dependent effect of PF-68 (0-0.1%) was shown not only to significantly enhance growth but also to reduce cell lysis. Interestingly, supplementing the culture medium with PF-68 led to increased IFN-γ production as a result of both higher cell densities and a higher specific production rate of IFN-γ. If cells were grown with agitation, lack of PF-68 in the culture medium decreased the fraction of the fully glycosylated IFN-γ glycoform (2N) from 80% to 65-70% during the initial period. This effect appeared to be due to a lag phase in cell growth observed during this period. Finally, a global kinetic study of CHO cell metabolism indicated higher efficiency in the utilization of the two major carbon substrates when cultures were supplemented with PF-68. Therefore, these results highlight the importance of understanding how media surfactant can affect cell growth as well as cell death and the product quality of a recombinant glycoprotein expressed in CHO cell cultures.

Glycosylation: An intrinsic sign of "danger"

The "danger" model of immunity posits that the immune system is triggered by endogenous danger signals, rather than exogenous non-self signals per se. It has been proposed that danger signals may consist of both intracellular "pre-packed" molecules released from damaged cells and stress-induced proteins. Here we focus on glycosylation aberrancies as a unifying concept for danger signaling. According to this proposition glycosylation patterns reliably reflect cellular phenotypic state and appearance of altered carbohydrate structures may constitute a pivotal phenotypic alteration that alarms the immune system to danger and initiates immunity. Viewed from this vantage point, healthy cells avert immune recognition by virtue of their normal terminal glycosylation patterns. By contrast, abnormal cells display and release glycoproteins and glycolipids with aberrant terminal glycosylation trees, which in turn immunologically flag these cells. Diverse carbohydrate-binding receptors are expressed on immune cells and are used to detect these phenotypic changes. Thus, in addition to the "pre-packed" and stress-induced signals this glycosylation-based signal represents an endogenous signal reliably reflecting the cell phenotypic status, enabling the immune system to monitor the tissue/cell's physical condition and to respond accordingly.

Mcl-1 overexpression leads to higher viabilities and increased production of humanized monoclonal antibody in Chinese hamster ovary cells

Bioreactor stresses, including nutrient deprivation, shear stress, and byproduct accumulation can cause apoptosis, leading to lower recombinant protein yields and increased costs in downstream processing. Although cell engineering strategies utilizing the overexpression of antiapoptotic Bcl-2 family proteins such as Bcl-2 and Bcl-x(L) potently inhibit apoptosis, no studies have examined the use of the Bcl-2 family protein, Mcl-1, in commercial mammalian cell culture processes. Here, we overexpress both the wild type Mcl-1 protein and a Mcl-1 mutant protein that is not degraded by the proteasome in a serum-free Chinese hamster ovary (CHO) cell line producing a therapeutic antibody. The expression of Mcl-1 led to increased viabilities in fed-batch culture, with cell lines expressing the Mcl-1 mutant maintaining approximately 90% viability after 14 days when compared with 65% for control cells. In addition to enhanced culture viability, Mcl-1-expressing cell lines were isolated that consistently showed increases in antibody production of 20-35% when compared with control cultures. The quality of the antibody product was not affected in the Mcl-1-expressing cell lines, and Mcl-1-expressing cells exhibited 3-fold lower caspase-3 activation when compared with the control cell lines. Altogether, the expression of Mcl-1 represents a promising alternative cell engineering strategy to delay apoptosis and increase recombinant protein production in CHO cells.

Kinetic simulation of a centrifugal bioreactor for high population density hybridoma culture

Demand for increasingly complex post-translationally modified proteins, such as monoclonal antibodies (mAbs), necessitates the use of mammalian hosts for production. The focus of this article is a continuous centrifugal bioreactor (CCBR) capable of increasing volumetric productivity for mAb production through high density hybridoma culture, exceeding 10(8) cells/mL. At these extreme densities, environmental conditions such as substrate and inhibitor concentrations rapidly change dramatically affecting the growth rate. The development of a kinetic model predicting glucose, mAb, lactate, and ammonium concentrations based on dilution rate and cell density is shown in this article. Additionally, it is found that pH affects both growth rate and viability, and a range of 6.9-7.4 is needed to maintain growth rate above 90% of the maximum. Modeling shows that operating an 11.4 mL CCBR inoculated with 2.0 x 10(7) cells/mL at a dilution rate of 1.3 h(-1), results in a predicted growth rate 82% of the maximum value. At the same dilution rate increasing density to 6.0 x 10(7) cells/mL decreases the predicted growth rate to 60% of the maximum; however, by increasing dilution rate to 6.1 h(-1) the growth rate can be increased to 86% of the maximum. Using the kinetic model developed in this research, the concentration of glucose, mAb, lactate, and ammonium are all predicted within 13% of experimental results. This model and an understanding of how RPM impacts cell retention serve as valuable tools for maintaining high density CCBR cultures, ensuring maximum growth associated mAb production rates.

Influence of intracellular nucleotide and nucleotide sugar contents on recombinant interferon-gamma glycosylation during batch and fed-batch cultures of CHO cells

Both the macroheterogeneity of recombinant human IFN-gamma produced by CHO cells and intracellular levels of nucleotides and sugar nucleotides, have been characterized during batch and fed-batch cultures carried out in different media. Whereas PF-BDM medium was capable to maintain a high percentage of the doubly- glycosylated glycoforms all over the process, mono-glycosylated and non-glycosylated forms increased during the batch culture using SF-RPMI medium. Intracellular level of UTP was higher in PF-BDM all over the batch culture compared to the SF-RPMI process. UDP-Gal accumulated only during the culture performed in PF-BDM medium, probably as a consequence of the reduced UDP-Glc synthesis flux in SF-RPMI medium. When the recombinant CHO cells were cultivated in fed-batch mode, the UTP level remained at a relatively high value in serum-containing RPMI and its titer increased during the fed-phase indicating an excess of biosynthesis. Besides, an accumulation of UDP-Gal occurred as well. Those results all together indicate that UTP and UDP-Glc syntheses in CHO cells cultivated in SF-RPMI medium in batch process, could be limiting during the glycosylation processes of the recombinant IFN-gamma. At last, the determination of the energetic status of the cells over the three studied processes suggested that a relationship between the adenylate energy charge and the glycosylation macroheterogeneity of the recombinant IFN-gamma may exist.

The effects of culture conditions on the glycosylation of secreted human placental alkaline phosphatase produced in Chinese hamster ovary cells

The effects of different culture conditions, suspension and microcarrier culture and temperature reduction on the structures of N-linked glycans attached to secreted human placental alkaline phosphatase (SEAP) were investigated for CHO cells grown in a controlled bioreactor. Both mass spectrometry and anion-exchange chromatography were used to probe the N-linked glycan structures and distribution. Complex-type glycans were the dominant structures with small amounts of high mannose glycans observed in suspension and reduced temperature cultures. Biantennary glycans were the most common structures detected by mass spectrometry, but triantennary and tetraantennary forms were also detected. The amount of sialic acid present was relatively low, approximately 0.4 mol sialic acid/mol SEAP for suspension cultures. Microcarrier cultures exhibited a decrease in productivity compared with suspension culture due to a decrease in both maximum viable cell density (15-20%) and specific productivity (30-50%). In contrast, a biphasic suspension culture in which the temperature was reduced at the beginning of the stationary phase from 37 to 33 degrees C, showed a 7% increase in maximum viable cell density, a 62% increase in integrated viable cell density, and a 133% increase in specific productivity, leading to greater than threefold increase in total productivity. Both microcarrier and reduced temperature cultures showed increased sialylation and decreased fucosylation when compared to suspension culture. Our results highlight the importance of glycoform analysis after process modification as even subtle changes (e.g., changing from one microcarrier to another) may affect glycan distributions.

Antibody-based enzyme-linked lectin assay (ABELLA) for the sialylated recombinant human erythropoietin present in culture supernatant

The terminal sialic acid of human erythropoietin (hEPO) is essential for in vivo activity. The current resorcinol and HPLC methods for analyzing alpha2,3-linked sialic acid require more than a microgram of purified rhEPO, and purification takes a great deal of time and labor. In this study, we assessed the use of an antibody-based enzyme-linked lectin assay (ABELLA) for analyzing non-purified recombinant hEPO (rhEPO). The major problem of this method was the high background due to terminal sialylation of components of the assay (antibody and bovine serum albumin) other than rhEPO. To solve this problem, we used a monoclonal antibody (Mab 287) to capture the rhEPO, and oxidized the bovine serum albumin used for blocking with meta-periodate. The sialic acid content of non-purified rhEPO measured by ABELLA was similar to that obtained by the resorcinol method on purified rhEPO. ABELLA has advantages such as adaptability and need for minimal amounts of rhEPO (40 ng/ml). Our observations suggest that ABELLA should reduce the time and labor needed to improve culture conditions so as to increase protein sialylation, and also facilitate the study of sialylation mechanisms.

Determination of interferon-gamma in Chinese hamster ovary cell culture supernatant by coupled-column liquid chromatography

A robust tandem HPLC method coupling size-exclusion (Shodex Asahipak GS-320HQ) and reversed phase (Vydac 218TP54) columns with ultraviolet detection was developed for quantitative determination of interferon-gamma (IFN-gamma) in Chinese hamster ovary cell culture supernatant. The 2D-HPLC system was linked up by a 6-port 2-position low hold-up volume switch valve. Compared to a commercial ELISA kit for IFN-gamma, the coupled column LC approach was able to detect and quantify soluble IFN-gamma, regardless of the glycoprotein's molecular/conformational variability and sample background. Each LC-LC analysis took 90 minutes inclusive of column regeneration. The relative standard deviation of measurements (n = 5) was less than 3%. The limit of detection (LOD) was determined to be 0.35 microg IFN-gamma.

Living with heterogeneities in bioreactors: understanding the effects of environmental gradients on cells

The presence of spatial gradients in fundamental culture parameters, such as dissolved gases, pH, concentration of substrates, and shear rate, among others, is an important problem that frequently occurs in large-scale bioreactors. This problem is caused by a deficient mixing that results from limitations inherent to traditional scale-up methods and practical constraints during large-scale bioreactor design and operation. When cultured in a heterogeneous environment, cells are continuously exposed to fluctuating conditions as they travel through the various zones of a bioreactor. Such fluctuations can affect cell metabolism, yields, and quality of the products of interest. In this review, the theoretical analyses that predict the existence of environmental gradients in bioreactors and their experimental confirmation are reviewed. The origins of gradients in common culture parameters and their effects on various organisms of biotechnological importance are discussed. In particular, studies based on the scale-down methodology, a convenient tool for assessing the effect of environmental heterogeneities, are surveyed.

Cost-effective engineering of a small-scale bioreactor

Several methods exist for increasing the scale of cell culture in the laboratory. While these methods provide significant increases in biomass, they are often prohibitively expensive for many laboratories. We have engineered a small-scale bioreactor with a novel means of introducing oxygen through the catalytic breakdown of hydrogen peroxide using a manganese oxide catalyst. We have also adapted and modified an existing assay for dissolved oxygen to be compatible with culture conditions. In this system we have been able to culture CHO cells at densities of up to 10(7) cells/mL without the use of automated feedback systems.

Bioprocess monitoring and computer control: key roots of the current PAT initiative

This review article has been written for the journal, Biotechnology and Bioengineering, to commemorate the 70th birthday of Daniel I.C. Wang, who served as doctoral thesis advisor to each of the co-authors, but a decade apart. Key roots of the current PAT initiative in bioprocess monitoring and control are described, focusing on the impact of Danny Wang's research as a professor at MIT. The history of computer control and monitoring in biochemical processing has been used to identify the areas that have already benefited and those that are most likely to benefit in the future from PAT applications. Past applications have included the use of indirect estimation methods for cell density, expansion of on-line/at-line and on-line/in situ measurement techniques, and development of models and expert systems for control and optimization. Future applications are likely to encompass additional novel measurement technologies, measurements for multi-scale and disposable bioreactors, real time batch release, and more efficient data utilization to achieve process validation and continuous improvement goals. Dan Wang's substantial contributions in this arena have been one key factor in steering the PAT initiative towards realistic and attainable industrial applications.

Chromatographic and electrophoretic characterization of protein variants

Almost all proteins are expressed in several variants, also known as isoforms. Individual protein variants differ by modifications of the individual amino acid side chains, or the N- or C-terminus. Typical modifications are glycosylation, phosphorylation, acetylation, methylation, deamidation or oxidation. It is of utmost interest to either get a quantitative picture of the variants of a particular protein or to separate the variants in order to be able to identify their molecular structure. Protein variants are present in native as well as in recombinant proteins. In the case of protein production it is interesting, how variants are generated during fermentation, purification processes, storage, and how present individual variants influence the biological activity. This review provides a comparison of chromatographic and electrophoretic separation methods to analyze and to prepare protein variants.

Conversion of a CHO cell culture process from perfusion to fed-batch technology without altering product quality

During the development of a new drug product, it is a common strategy to develop a first-generation process with the aim to rapidly produce material for pre-clinical and early stage clinical trials. At a later stage of the development, a second-generation process is then introduced with the aim to supply late-stage clinical trials as well as market needs. This work was aimed at comparing the performance of two different CHO cell culture processes (perfusion and fed-batch) used for the production of a therapeutically active recombinant glycoprotein at industrial pilot-scale. The first-generation process was based on the Fibra-Cel packed-bed perfusion technology. It appeared during the development of the candidate drug that high therapeutic doses were required (>100mg per dose), and that future market demand would exceed 100 kg per year. This exceeded by far the production capacity of the first-generation process, and triggered a change of technology from a packed-bed perfusion process with limited scale-up capabilities to a fed-batch process with scale-up potential to typical bioreactor sizes of 15m(3) or more. The productivity per bioreactor unit volume (in product m(-3)year(-1)) of the fed-batch process was about 70% of the level reached with the first-generation perfusion process. However, since the packed-bed perfusion system was limited in scale (0.6m(3) maximum) compared to the volumes reached in suspension cultures (15m(3)), the fed-batch was selected as second-generation process. In fact, the overall process performance (in product year(-1)) was about 18-fold higher for the fed-batch compared to the perfusion mode. Data from perfusion and fed-batch harvests samples indicated that comparable product quality (relative abundance of monomers dimers and aggregates; N-glycan sialylation level; isoforms distribution) was obtained in both processes. To further confirm this observation, purification to homogeneity of the harvest material from both processes, followed by a complementary set of studies (e.g. full physico-chemical characterization, assessment of in vitro and in vivo bioactivity, comparative pharmacokinetics and pharmacodynamics studies in relevant species, etc.) would be required. Finally, this illustrates the need to fix the production process early during the development of a new drug product in order to minimize process conversion efforts and to shorten product development time lines.

Tat8-TK/GCV suicide gene therapy induces pancreatic tumor regression in vivo

Suicide gene therapy using the herpes simplex virus thymidine kinase (TK) gene in combination with ganciclovir (GCV) has been shown to produce therapeutic, but limited, efficacy because of poor gene transfer efficiency and reduced bystander effect. Here we report that fusion of TK to an eight-amino acid peptide from the basic domain of the human immunodeficiency virus (HIV) Tat protein significantly increases the cytotoxic efficacy of the TK/GCV system in pancreatic cancer cells. We demonstrate that Tat8-TK protein is released from the intracellular compartment of Tat8-TK-expressing cells to the extracellular medium after GCV treatment. Interestingly, we show that this conditioned medium is then able to mediate cytotoxicity of wildtype cultures, suggesting the internalization of the Tat8-TK protein. Moreover, a strong antitumoral effect of Tat8-TK/GCV treatment could be achieved by two different in vivo approaches. Tumors injected with NIH 3T3/Tat8-TK cells attached to microcarriers (MC+Tat8-TK) and treated with GCV led to a 35.6% reduction in the initial tumor volume and to 50% tumor eradication. Furthermore, electrogene transfer of TK or Tat8-TK followed by administration of high doses of GCV led to an overall statistically significant reduction in tumor growth. However, the reduction in initial tumor volume was statistically significant only for the Tat8-TK group (59.5% reduction). Moreover, in this group 50% complete tumor eradication was achieved. When moderate doses of GCV were administered, the overall reduction in tumor growth was statistically significant only in the Tat8-TK group. Therefore, our results suggest that fusion of TK to the Tat8 peptide enhances TK/GCV suicide gene therapy.

Dynamic Control of Oligosaccharide Modification in the Mammary Gland: Linking Recombinant Human Erythropoietin

We analyzed two transgenic mouse lines that secrete rhEPO in their milk to assess the dynamic control of N-linked oligosaccharides. Since pharmaceutically available epoetin alpha and beta are produced in CHO cells, we compared transgenic mammary gland-derived rhEPO to its CHO cell-derived counterpart. The major glycosyltransferases that determine the N-oligosaccharides patterns of rhEPO include N-acetylglycosaminyltransferase (GnT) and alpha1,3/4 fucosyltransferase (Fuc-TIV), GnT-III, -V and Fuc-TIV expression in the mouse mammary gland is significantly higher than that in Chinese hamster ovary (CHO)-derived cells, where the protein is not detectable. The data suggest that N-linked sugar chain patterns of recombinant glycoproteins, produced by the mammary gland differ, since GnT-III alters the sugar pattern extensively. In our experiments, rhEPO produced by the transgenic mice contains more tetra-acidic oligosaccharide structures than epoetin alpha derived from CHO cells, a rhEPO that is widely used therapeutically. Accordingly, we examined milk-derived rhEPO activity, both in vitro and in vivo. The rhEPO protein purified from the milk of mammary glands upregulates the EPO receptor-mediated expression of the STAT5 gene in MCF-7 cells in a dose-dependent manner, similar to the effects of epoetin alpha. Furthermore, direct injection of rhEPO into the mouse tail vein leads to an increase in the levels of blood components, such as red blood cells and platelets. In light of these findings, we suggest that the mammary glands of transgenic animals provide a sufficient environment to generate rhEPO with post-translational modifications for biopharmaceutical use.

Production and glycosylation of recombinant beta-interferon in suspension and cytopore microcarrier cultures of CHO cells

Microcarriers are suitable for high-density cultures of cells requiring surface attachment and also offer the advantage of easy media removal for product recovery. We have used the macroporous microcarriers Cytopore 1 and 2 for the growth of CHO cells producing recombinant human beta-interferon (beta-IFN) in stirred batch cultures. Although these cells may grow in suspension, in the presence of Cytopore microcarriers they become entrapped in the inner bead matrix where they can be maintained at high densities. Cell growth rates were reduced in microcarrier cultures compared to suspension cultures. However, the beta-IFN yield was up to 3-fold greater as a result of an almost 5-fold higher specific productivity. Maximum productivity was found in cultures containing 1.0 mg/mL of Cytopore 1 or 0.5 mg/mL of Cytopore 2 with a cell/bead ratio of 1029 and 822, respectively. Beta-IFN molecules aggregated in the later stages of all cultures, causing a decrease in response by ELISA. However, the degree of aggregation was significantly less in the microcarrier cultures. The N-linked glycans from beta-IFN were isolated and analyzed by normal phase HPLC. There was no apparent difference in the profile of glycans obtained from each of the suspension and Cytopore culture systems. This suggests that Cytopore microcarriers may be useful in bioprocess development for enhanced recombinant glycoprotein production without affecting the glycosylation profile of the protein.

Effect of production method and gene amplification on the glycosylation pattern of a secreted reporter protein in CHO cells

We have investigated the independent effects of selective gene amplification (using the dhfr amplifiable selection marker) and culture operating strategy (batch vs repeated fed-batch vs semicontinuous perfusion) on the glycosylation of a recombinant reporter protein (secreted alkaline phosphatase, SEAP) produced in transfected Chinese hamster ovary (CHO) cells. HPLC analyses coupled with susceptibility to various exoglycosidases were used to determine the N-glycosylation profile of SEAP samples. The dhfr amplified cell line yielded an almost 10-fold increase in specific productivity as compared to that of the unamplified cell line. The glycosylation pattern of the reporter protein produced in batch bioreactor cultures of the amplified cell line showed only slight differences as compared to the glycosylation pattern of the protein from batch bioreactor cultures of the unamplified cell line. In contrast, analysis of SEAP glycosylation structures from the protein isolated from semicontinuous perfusion cultures indicated that both relative glycan content and extent of sialylation were increased as compared to samples isolated from repeated fed-batch cultures. These results suggest that the slow growing perfusion cultures produce more completely glycosylated proteins than the faster growing repeated fed-batch cultures.

Optimization of the medium perfusion rate in a packed-bed bioreactor charged with CHO cells

In the present study, the optimal medium perfusion rate to be used for the continuous culture of a recombinant CHO cell line in a packed-bed bioreactor made of Fibra-Cel((R)) disk carriers was determined. A first-generation process had originally been designed with a high perfusion rate, in order to rapidly produce material for pre-clinical and early clinical trials. It was originally operated with a perfusion of 2.6 vvd during production phase in order to supply the high cell density (2.5x10(7) cell ml(-1) of packed-bed) with sufficient fresh medium. In order to improve the economics of this process, a reduction of the medium perfusion rate by -25% and -50% was investigated at small-scale. The best option was then implemented at pilot scale in order to further produce material for clinical trials with an improved second-generation process. With a -25% reduction of the perfusion rate, the volumetric productivity was maintained compared to the first-generation process, but a -30% loss of productivity was obtained when the medium perfusion rate was further reduced to -50% of its original level. The protein quality under reduced perfusion rate conditions was analyzed for purity, N-glycan sialylation level, abundance of dimers or aggregates, and showed that the quality of the final drug substance was comparable to that obtained in reference conditions. Finally, a reduction of -25% medium perfusion was implemented at pilot scale in the second-generation process, which enabled to maintain the same productivity and the same quality of the molecule, while reducing costs of media, material and manpower of the production process. For industrial applications, it is recommended to test whether and how far the perfusion rate can be decreased during the production phase - provided that the product is not sensitive to residence time - with the benefits of reduced cost of goods and to simplify manufacturing operations.

Impact of dynamic online fed-batch strategies on metabolism, productivity and N-glycosylation quality in CHO cell cultures

As we pursue the means to improve yields to meet growing therapy demands, it is important to examine the impact of process control on glycosylation patterns to ensure product efficacy and consistency. In this study, we describe a dynamic on-line fed-batch strategy based on low glutamine/glucose concentrations and its impact on cellular metabolism and, more importantly, the productivity and N-glycosylation quality of a model recombinant glycoprotein, interferon gamma (IFN-gamma). We found that low glutamine fed-batch strategy enabled up to 10-fold improvement in IFN-gamma yields, which can be attributed to reduced specific productivity of ammonia and lactate. Furthermore, the low glutamine concentration (0.3 mM) used in this fed-batch strategy could maintain both the N-glycosylation macro- and microheterogeneity of IFN-gamma. However, very low glutamine (<0.1 mM) or glucose (<0.70 mM) concentrations can lead to decreased sialylation and increased presence of minor glycan species consisting of hybrid and high-mannose types. This shows that glycan chain extension and sialylation can be affected by nutrient limitation. In addition to nutrient limitation, we also found that N-glycosylation quality can be detrimentally affected by low culture viability. IFN-gamma purified at low culture viability had both lower sialylation as well as glycans of lower molecular masses, which can be attributed to extensive degradation by intracellular glycosidases released by cytolysis. Therefore, in order to maintain good N-glycosylation quality, there is a need to consider both culture viability and nutrient control setpoint in a nutrient-limiting fed-batch culture strategy. A greater understanding of these major factors that affect N-glycosylation quality would surely facilitate future development of effective process controls.

Scalable inoculation strategies for microcarrier-based animal cell bioprocesses

Scalability is a major demand for high-yield, stable bioprocess systems in animal cell culture-based biopharmaceutical production. Increased yields can be achieved through high-density cell culture, such as in the combination of microcarrier and fluidized bed bioreactor technology. To minimize inocula volume in industrial applications of fluidized bed fermentation systems, it is crucial to increase the bed volume in the reactor during the fermentation process. We tested scale-up strategy for the production of recombinant human arylsulfatase B (ASB) enzyme used in enzyme replacement therapy in patients afflicted with mucopolysaccharidosis type VI (MPS VI). This enzyme was derived from Chinese hamster ovary (CHO) cells cultivated as adherent cell culture on Cytoline macroporous microcarriers (Amersham Biosciences, Uppsala, Sweden) using a Cytopilot Mini fluidized bed bioreactor (FBR; Amersham Biosciences, Vogelbusch, Austria). Both 1:2 expansion (herein referred to as the addition of fresh, not-yet-colonized microcarriers) and 1:6 expansion of the carrier bed were performed successfully; the cells restarted to proliferate for colonizing these newly added carriers; and the stability of the culture was not negatively affected.

Erythropoietin production from CHO cells grown by continuous culture in a fluidized-bed bioreactor

A Chinese hamster ovary (CHO) cell line that expresses human erythropoietin (huEPO) was in a 2-L Cytopilot fluidized-bed bioreactor with 400 mL macroporous Cytoline-1 microcarriers and a variable perfusion rate of serum-free and protein-free medium for 48 days. The cell density increased to a maximum of 23 x 10(6) cells/mL, beads on day 27. The EPO concentration increased to 600 U/mL during the early part of the culture period (on day 24) and increased further to 980 U/mL following the addition of a higher concentration of glucose and the addition of sodium butyrate. The EPO concentration was significantly higher (at least 2x than that in a controlled stirred-tank bioreactor, in a spinner flask, or in a stationary T-flask culture. The EPO accumulated to a total production of 28,000 kUnits over the whole culture period. The molecular characteristics of EPO with respect to size and pattern of glycosylation did not change with scale up. The pattern of utilization and production of 18 amino acids was similar in the Cytopilot culture to that in a stationary batch culture in a T-flask. The concentration of ammonia was maintained at a low level (< 2 mM) over the entire culture period. The specific rate of consumption of glucose, as well as the specific rates of production of lactate and ammonia, were constant throughout the culture period indicating a consistent metabolic behavior of the cells in the bioreactor. These results indicate the potential of the Cytopilot bioreactor culture system for the continuous production of a recombinant protein over several weeks.

Capillary electrophoretic analysis of proteins and peptides of biomedical and pharmacological interest

Capillary electrophoresis (CE) is an automated approach to electrokinetic separations that has had a deep impact in all fields of life sciences, including biomedical and biotechnological research and clinical and forensic practice. The present review highlights aspects of peptides and proteins separations, with particular emphasis on macromolecular analytes of biomedical interest. Among the various CE techniques available, a novel methodology is here illustrated consisting in separations in acidic, isoelectric buffers, which have the advantage of protonating the silica wall, thus minimizing interactions of proteinaceous material with the siliceous surface, while allowing delivery of high voltage gradients, due to their low conductivities. The review ends with applications of CE to the analysis of folding/unfolding/refolding/misfolding of proteins, a field which has deep implications in the biomedical arena, since it is connected to a host of disorders, such as prion protein diseases.