Hyperosmotic stress and elevated pCO2 alter monoclonal antibody charge distribution and monosaccharide content

Development of bioreactor scale-down model using orthogonal projections to latent structures method and CO2 supplementation

Scale-down model qualification is an important step for developing a large-scale cell culture process to enhance process understanding and support process characterization studies. Traditionally, only harvest data are used to show consistency between small-scale and large-scale bioreactor performance, allowing attributes that are dynamic over the cell culture period to be overlooked. A novel statistical method, orthogonal projections to latent structures (OPLS) analysis, can be utilized to compare time-course cell culture data across scales. Here we describe an example where OPLS is used to identify gaps between small-scale and large-scale bioreactor performances. In this case, differences in the partial pressure of carbon dioxide (pCO2) and lactate profiles were observed between small- and large-scale bioreactors, which were linked to differences in the product-quality attributes fragments and galactosylation. An improved small-scale model was developed, leading to improved consistency in the process performance and product qualities across scales and qualification of the scale-down model for regulatory submissions. This new statistical approach can provide valuable insights into process understanding and process scale-up.

Accelerating the speed of innovative anti-tumor drugs to first-in-human trials incorporating key de-risk strategies

Pharmaceutical companies have recently focused on accelerating the timeline for initiating first-in-human (FIH) trials to allow quick assessment of biologic drugs. For example, a stable cell pool can be used to produce materials for the toxicology (Tox) study, reducing time to the clinic by 4-5 months. During the coronavirus disease 2019 (COVID-19) pandemic, the anti-COVID drugs timeline from DNA transfection to the clinical stage was decreased to 6 months using a stable pool to generate a clinical drug substrate (DS) with limited stability, virus clearance, and Tox study package. However, a lean chemistry, manufacturing, and controls (CMC) package raises safety and comparability risks and may leave extra work in the late-stage development and commercialization phase. In addition, whether these accelerated COVID-19 drug development strategies can be applied to non-COVID projects and established as a standard practice in biologics development is uncertain. Here, we present a case study of a novel anti-tumor drug in which application of "fast-to-FIH" approaches in combination with BeiGene's de-risk strategy achieved successful delivery of a complete CMC package within 10 months. A comprehensive comparability study demonstrated that the DS generated from a stable pool and a single-cell-derived master cell bank were highly comparable with regards to process performance, product quality, and potency. This accomplishment can be a blueprint for non-COVID drug programs that approach the pace of drug development during the pandemic, with no adverse impact on the safety, quality, and late-stage development of biologics.

A novel approach to noninvasive monitoring of dissolved carbon dioxide in small-scale cell culture processes

Disposable small-scale vessels are commonly used in cell culture studies in academia as well as early stages of bioprocess development. These types of research are crucial for our understanding about cells and bioprocesses as they provide important information regarding different parameters affecting cells. Dissolved carbon dioxide (DCO2) is one main parameter affecting cell metabolism. It is also an indicator of cell culture well-being. Despite CO2 being a critical process parameter, there is a lack of appropriate monitoring system for CO2 in small-scale vessels. Here, we present a membrane-based noninvasive method for measuring DCO2 in cell culture medium. The idea was achieved by modifying a T-flask and replacing a small area of it with CO2 permeable silicone membrane. In the proposed method, the concentration of CO2 dissolved in the cell culture medium is determined by measuring the initial diffusion rate of CO2 through a silicone membrane attached to the bottom wall of the T-flask. The measurement method was validated previously, and the efficacy of the noninvasive method was evaluated by growing E.coli, Pichia pastoris, and CHO cells in the proposed prototype. The results obtained from this method were verified with other quantitative data obtained from the process such as optical density (OD), cell density, dissolved oxygen (DO) and pH. The results show that the proposed membrane-based method is an effective way for completely noninvasive monitoring of DCO2 in small-scale cell culture processes. Additional diffusing species such as oxygen could also be measured using the same approach.

Isolation and characterization of charge variants of infliximab biosimilar HS626

Charge variants are the most commonly observed sources of heterogeneity in the routine manufacturing of monoclonal antibodies. To gain further insight into the structural foundation of charge heterogeneity and its influence on biological functions, an infliximab biosimilar HS626 from a biopharmaceutical facility was isolated by semipreparative cation exchange chromatography (CEX) to obtain fractions of acidic and basic charge variants and determine the main species. It was assessed again by CEX to ensure purities. Through a series of structural and physicochemical characterizations, we concluded that the acidic variants were caused by fragments, Met oxidation, Asn deamidation, higher levels of sialylation and galactosylation of N-linked glycans, and less high mannose. The basic variants resulted mainly from aggregates, fragments, and Met oxidation. Through further analysis of antigen binding affinity, cell death inhibitory activity, ADCC, and CDC, as well as FcRn, FcγRIIIa, and C1q affinity, we demonstrated that the charge heterogeneity did not affect biological functions. This research enhances the understanding of charge variants, which are usually effective components that should not be intentionally reduced unless biological functions are affected.

Development, characterization, and application of a 2-Compartment system to investigate the impact of pH inhomogeneities in large-scale CHO-based processes

Large-scale bioreactors for the production of monoclonal antibodies reach volumes of up to 25 000 L. With increasing bioreactor size, mixing is however affected negatively, resulting in the formation of gradients throughout the reactor. These gradients can adversely affect process performance at large scale. Since mammalian cells are sensitive to changes in pH, this study investigated the effects of pH gradients on process performance. A 2-Compartment System was established for this purpose to expose only a fraction of the cell population to pH excursions and thereby mimicking a large-scale bioreactor. Cells were exposed to repeated pH amplitudes of 0.4 units (pH 7.3), which resulted in decreased viable cell counts, as well as the inhibition of the lactate metabolic shift. These effects were furthermore accompanied by increased absolute lactate levels. Continuous assessment of molecular attributes of the expressed target protein revealed that subunit assembly or N-glycosylation patterns were only slightly influenced by the pH excursions. The exposure of more cells to the same pH amplitudes further impaired process performance, indicating this is an important factor, which influences the impact of pH inhomogeneity. This knowledge can aid in the design of pH control strategies to minimize the effects of pH inhomogeneity in large-scale bioreactors.

Scale-down simulators for mammalian cell culture as tools to access the impact of inhomogeneities occurring in large-scale bioreactors

During the scale-up of a bioprocess, not all characteristics of the process can be kept constant throughout the different scales. This typically results in increased mixing times with increasing reactor volumes. The poor mixing leads in turn to the formation of concentration gradients throughout the reactor and exposes cells to varying external conditions based on their location in the bioreactor. This can affect process performance and complicate process scale-up. Scale-down simulators, which aim at replicating the large-scale environment, expose the cells to changing environmental conditions. This has the potential to reveal adaptation mechanisms, which cells are using to adjust to rapidly fluctuating environmental conditions and can identify possible root causes for difficulties maintaining similar process performance at different scales. This understanding is of utmost importance in process validation. Additionally, these simulators also have the potential to be used for selecting cells, which are most robust when encountering changing extracellular conditions. The aim of this review is to summarize recent work in this interesting and promising area with the focus on mammalian bioprocesses, since microbial processes have been extensively reviewed.

Lectin bio-layer interferometry for assessing product quality of Fc- glycosylated immunoglobulin G

Glycosylation, as the most prominent posttranslational modification, is recognized as an important quality attribute of monoclonal antibodies affected by various bioprocess parameters and cellular physiology. A method of lectin‐based bio‐layer interferometry (LBLI) to relatively rank galactosylation and fucosylation levels was developed. For this purpose, Fc‐glycosylated immunoglobulin G (IgG) was recombinantly produced with varying bioprocess conditions in 15 L bioreactor and accumulated IgG was harvested. The reliability, the robustness and the applicability of LBLI to different samples has been proven. Data obtained from LC–MS analysis served as reference and were compared to the LBLI results. The introduced method is based on non‐fluidic bio‐layer interferometry (BLI), which becomes recently a standard tool for determining biomolecular interactions in a label‐free, real‐time and high‐throughput manner. For the intended purpose, biotinylated lectins were immobilized on disposable optical fiber streptavidin (SA) biosensor tips. Aleuria aurantia lectin (AAL) was used to detect the core fucose and Ricinus communis agglutinin 120 (RCA120) to determine galactosylation levels. In our case study it could be shown that fucosylation was not affected by variations in glucose feed concentration and cultivation temperature. However, the galactosylation could be correlated with the ratio of mean specific productivity (q_P) and ammonium (q_NH4+) but was unrelated to the ratio of mean q_P and the specific glucose consumption (q_gluc). This presented method strengthens the applicability of the BLI platform, which already enables measurement of several product related characteristics, such as product quantity as well as kinetic rates (k_d,k_on) and affinity constants (k_D) analysis.

Impact of mammalian cell culture conditions on monoclonal antibody charge heterogeneity: an accessory monitoring tool for process development

Recombinant monoclonal antibodies are predominantly produced in mammalian cell culture bioprocesses. Post-translational modifications affect the micro-heterogeneity of the product and thereby influence important quality attributes, such as stability, solubility, pharmacodynamics and pharmacokinetics. The analysis of the surface charge distribution of monoclonal antibodies provides aggregated information about these modifications. In this work, we established a direct injection pH gradient cation exchange chromatography method, which determines charge heterogeneity from cell culture supernatant without any purification steps. This tool was further applied to monitor processes that were performed under certain process conditions. Concretely, we were able to provide insights into charge variant formation during a fed-batch process of a Chinese hamster ovary cell culture, in turn producing a monoclonal antibody under varying temperatures and glucose feed strategies. Glucose concentration impacted the total emergence of acidic variants, whereas the variation of basic species was mainly dependent on process temperature. The formation rates of acidic species were described with a second-order reaction, where a temperature increase favored the conversion. This platform method will aid as a sophisticated optimization tool for mammalian cell culture processes. It provides a quality fingerprint for the produced mAb, which can be tested, compared to the desired target and confirmed early in the process chain.

Generation of site-distinct N-glycan variants for in vitro bioactivity testing

Glycosylation, a critical product quality attribute, may affect the efficacy and safety of therapeutic proteins in vivo. Chinese hamster ovary fed-batch cell culture batches yielded consistent glycoprofiles of a Fc-fusion antibody comprizing three different N-glycosylation sites. By adding media supplements at specific concentrations in cell culture and applying enzymatic glycoengineering, a diverse N-glycan variant population was generated, including high mannose, afucosylated, fucosylated, agalactosylated, galactosylated, asialylated, and sialylated forms. Site-specific glycosylation profiles were elucidated by glycopeptide mapping and the effect of the glycosylation variants on the FcγRIIIa receptor binding affinity and the biological activity (cell-based and surface plasmon resonance) was assessed. The two fusion body glycosylation sites were characterized by a high degree of sialic acid, more complex N-glycan structures, a higher degree of antennarity, and a site-specific behavior in the presence of a media supplement. On the other hand, the media supplements affected the Fc-site glycosylation heterogeneity similarly to the various studies described in the literature with classical monoclonal antibodies. Enzymatic glycoengineering solely managed to generate high levels of galactosylation at the fusion body sites. Variants with low core fucosylation, and to a lower extent, high mannose glycans exhibited increased FcγRIIIa receptor binding affinity. All N-glycan variants exhibited weak effects on the biological activity of the fusion body. Both media supplementation and enzymatic glycoengineering are suitable to generate sufficient diversity to assess the effect of glycostructures on the biological activity.

Main Quality Attributes of Monoclonal Antibodies and Effect of Cell Culture Components

The culture media optimization is an inevitable part of upstream process development in therapeutic monoclonal antibodies (mAbs) production. The quality by design (QbD) approach defines the assured quality of the final product through the development stage. An important step in QbD is determination of the main quality attributes. During the media optimization, some of the main quality attributes such as glycosylation pattern, charge variants, aggregates, and low-molecular-weight species, could be significantly altered. Here, we provide an overview of how cell culture medium components affects the main quality attributes of the mAbs. Knowing the relationship between the culture media components and the main quality attributes could be successfully utilized for a rational optimization of mammalian cell culture media for industrial mAbs production.

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.

Concentrated fed-batch cell culture increases manufacturing capacity without additional volumetric capacity

Biomanufacturing factories of the future are transitioning from large, single-product facilities toward smaller, multi-product, flexible facilities. Flexible capacity allows companies to adapt to ever-changing pipeline and market demands. Concentrated fed-batch (CFB) cell culture enables flexible manufacturing capacity with limited volumetric capacity; it intensifies cell culture titers such that the output of a smaller facility can rival that of a larger facility. We tested this hypothesis at bench scale by developing a feeding strategy for CFB and applying it to two cell lines. CFB improved cell line A output by 105% and cell line B output by 70% compared to traditional fed-batch (TFB) processes. CFB did not greatly change cell line A product quality, but it improved cell line B charge heterogeneity, suggesting that CFB has both process and product quality benefits. We projected CFB output gains in the context of a 2000-L small-scale facility, but the output was lower than that of a 15,000-L large-scale TFB facility. CFB's high cell mass also complicated operations, eroded volumetric productivity, and showed our current processes require significant improvements in specific productivity in order to realize their full potential and savings in manufacturing. Thus, improving specific productivity can resolve CFB's cost, scale-up, and operability challenges.

Clinical considerations for biosimilar antibodies

Biosimilar agents are approximate copies of branded biologic therapies. Since the first biosimilar was authorized in the European Union in 2006, fifteen additional agents have been approved by the European Medicines Agency, including two biosimilar monoclonal antibodies (mAbs). Biosimilar mAbs represent a distinct class given their large molecular size, complex protein structure, and post-translational modifications. While guidelines have been established for the development, approval, and use of biosimilars, further scrutiny and discussion is necessary to fully understand their potential impact on clinical outcomes. This review takes a critical look at the structural complexity of biosimilar mABs, the feasibility of indication extrapolation, the impact of product variability on immunogenicity, the importance of comprehensive pharmacovigilance, and the potential for ongoing pharmacoeconomic impact.

Emergent properties of nanosensor arrays: applications for monitoring IgG affinity distributions, weakly affined hypermannosylation, and colony selection for biomanufacturing

It is widely recognized that an array of addressable sensors can be multiplexed for the label-free detection of a library of analytes. However, such arrays have useful properties that emerge from the ensemble, even when monofunctionalized. As examples, we show that an array of nanosensors can estimate the mean and variance of the observed dissociation constant (KD), using three different examples of binding IgG with Protein A as the recognition site, including polyclonal human IgG (KD μ = 19 μM, σ(2) = 1000 mM(2)), murine IgG (KD μ = 4.3 nM, σ(2) = 3 μM(2)), and human IgG from CHO cells (KD μ = 2.5 nM, σ(2) = 0.01 μM(2)). Second, we show that an array of nanosensors can uniquely monitor weakly affined analyte interactions via the increased number of observed interactions. One application involves monitoring the metabolically induced hypermannosylation of human IgG from CHO using PSA-lectin conjugated sensor arrays where temporal glycosylation patterns are measured and compared. Finally, the array of sensors can also spatially map the local production of an analyte from cellular biosynthesis. As an example, we rank productivity of IgG-producing HEK colonies cultured directly on the array of nanosensors itself.

Fucose content of monoclonal antibodies can be controlled by culture medium osmolality for high antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is dependent on the fucose content of oligosaccharides bound to monoclonal antibodies (MAbs). As MAbs with a low fucose content exhibit high ADCC activity, it is important to control the defucosylation levels (deFuc%) of MAbs and to analyze the factors that affect deFuc%. In this study, we observed that the deFuc% was inversely related to culture medium osmolality for MAbs produced in the rat hybridoma cell line YB2/0, with r (2) values as high as 0.92. Moreover, deFuc% exhibited the same correlation irrespective of the type of compound used for regulating osmolality (NaCl, KCl, fucose, fructose, creatine, or mannitol) at a culture scale ranging from 1 to 400 L. We succeeded in controlling MAb deFuc% by maintaining a constant medium osmolality in both perfusion and fed-batch cultures. In agreement with these observations, reverse transcription PCR analyses revealed decreased transcription of genes involved in glycolysis, GDP-fucose supply, and fucose transfer under hypoosmotic conditions.

Modulation of antibody galactosylation through feeding of uridine, manganese chloride, and galactose

Through process transfer and optimization for increased antibody production to 3 g/L for a GS-CHO cell line, an undesirable drop in antibody Fc galactosylation was observed. Uridine (U), manganese chloride (M), and galactose (G), constituents involved in the intracellular galactosylation process, were evaluated in 2-L bioreactors for their potential to specifically increase antibody galactosylation. These components were placed in the feed medium at proportionally increasing concentrations from 0 to 20 × UMG, where a 1× concentration of U was 1 mM, a 1× concentration of M was 0.002 mM, and a 1× concentration of G was 5 mM. Antibody galactosylation increased rapidly from 3% at 0× UMG up to 21% at 8× UMG and then more slowly to 23% at 20× UMG. The increase was primarily due to a shift from G0F to G1F, with minimal impact on other glycoforms or product quality attributes. Cell culture performance was largely not impacted by addition of up to 20× UMG except for suppression of glucose consumption and lactate production at 16 and 20× UMG and a slight drop in antibody concentration at 20× UMG. Higher accumulation of free galactose in the medium was observed at 8× UMG and above, coincident with achieving the plateau of maximal galactosylation. A concentration of 4× UMG resulted in achieving the target of 18% galactosylation at 2-L scale, a result that was reproduced in a 1,000-L run. Follow-up studies to evaluate the addition of each component individually up to 12× concentration revealed that the effect was synergistic; the combination of all three components gave a higher level of galactosylation than addition of the each effect independently. The approach was found generally useful since a second cell line responded similarly, with an increase in galactosylation from 5% to 29% from 0 to 8× UMG and no further increase or impact on culture performance up to 12× UMG. These results demonstrate a useful approach to provide exact and specific control of antibody galactosylation through manipulation of the concentrations of uridine, manganese chloride, and galactose in the cell culture medium.

[Permissive and non-permissive hypercapnia: mechanisms of action and consequences of high carbon dioxide levels]

Acute lung injury is a disease with high incidence of mortality and its treatment is still controversial. Increasing the levels of CO2 beyond the physiological range has been proposed as a potential protective strategy for patients on mechanical ventilation, as it could moderate the inflammatory response. In this article we review the published evidence on the role of CO2 during acute lung injury. We conclude that although there are reports suggesting benefits from hypercapnia, more recent evidence suggests that hypercapnia could be deleterious, contributing to worsening of the lung injury.

Scale-up analysis for a CHO cell culture process in large-scale bioreactors

Bioprocess scale-up is a fundamental component of process development in the biotechnology industry. When scaling up a mammalian cell culture process, it is important to consider factors such as mixing time, oxygen transfer, and carbon dioxide removal. In this study, cell-free mixing studies were performed in production scale 5,000-L bioreactors to evaluate scale-up issues. Using the current bioreactor configuration, the 5,000-L bioreactor had a lower oxygen transfer coefficient, longer mixing time, and lower carbon dioxide removal rate than that was observed in bench scale 5- and 20-L bioreactors. The oxygen transfer threshold analysis indicates that the current 5,000-L configuration can only support a maximum viable cell density of 7 x 10(6) cells mL(-1). Moreover, experiments using a dual probe technique demonstrated that pH and dissolved oxygen gradients may exist in 5,000-L bioreactors using the current configuration. Empirical equations were developed to predict mixing time, oxygen transfer coefficient, and carbon dioxide removal rate under different mixing-related engineering parameters in the 5,000-L bioreactors. These equations indicate that increasing bottom air sparging rate is more efficient than increasing power input in improving oxygen transfer and carbon dioxide removal. Furthermore, as the liquid volume increases in a production bioreactor operated in fed-batch mode, bulk mixing becomes a challenge. The mixing studies suggest that the engineering parameters related to bulk mixing and carbon dioxide removal in the 5,000-L bioreactors may need optimizing to mitigate the risk of different performance upon process scale-up.

N-linked glycosylation is an important parameter for optimal selection of cell lines producing biopharmaceutical human IgG

We studied the variations in N-linked glycosylation of human IgG molecules derived from 105 different stable cell lines each expressing one of the six different antibodies. Antibody expression was based on glutamine synthetase selection technology in suspension growing CHO-K1SV cells. The glycans detected on the Fc fragment were mainly of the core-fucosylated complex type containing zero or one galactose and little to no sialic acid. The glycosylation was highly consistent for the same cell line when grown multiple times, indicating the robustness of the production and glycan analysis procedure. However, a twofold to threefold difference was observed in the level of galactosylation and/or non-core-fucosylation between the 105 different cell lines, suggesting clone-to-clone variation. These differences may change the Fc-mediated effector functions by such antibodies. Large variation was also observed in the oligomannose-5 glycan content, which, when present, may lead to undesired rapid clearance of the antibody in vivo. Statistically significant differences were noticed between the various glycan parameters for the six different antibodies, indicating that the variable domains and/or light chain isotype influence Fc glycosylation. The glycosylation altered when batch production in shaker was changed to fed-batch production in bioreactor, but was consistent again when the process was scaled from 400 to 5,000 L. Taken together, the observed clone-to-clone glycosylation variation but batch-to-batch consistency provides a rationale for selection of optimal production cell lines for large-scale manufacturing of biopharmaceutical human IgG.

Heterogeneity of Monoclonal Antibodies

Heterogeneity of monoclonal antibodies is common due to the various modifications introduced over the lifespan of the molecules from the point of synthesis to the point of complete clearance from the subjects. The vast number of modifications presents great challenge to the thorough characterization of the molecules. This article reviews the current knowledge of enzymatic and nonenzymatic modifications of monoclonal antibodies including the common ones such as incomplete disulfide bond formation, glycosylation, N-terminal pyroglutamine cyclization, C-terminal lysine processing, deamidation, isomerization, and oxidation, and less common ones such as modification of the N-terminal amino acids by maleuric acid and amidation of the C-terminal amino acid. In addition, noncovalent associations with other molecules, conformational diversity and aggregation of monoclonal antibodies are also discussed. Through a complete understanding of the heterogeneity of monoclonal antibodies, strategies can be employed to better identify the potential modifications and thoroughly characterize the molecules.

Charge differences between in vivo deposits in immunoglobulin light chain amyloidosis and non-amyloid light chain deposition disease

Immunoglobulin light chain amyloidosis (AL) and non-amyloid light chain deposition disease (NALCDD) are different forms of protein aggregation disorders that may occur in plasma cell dyscrasias with dysproteinemia. In systemic AL, the deposits are fibrillar and patchy in distribution, within and amongst different organs, whereas in NALCDD, the deposits are granular and diffusely distributed in systemic basement membranes, suggesting different mechanisms of aggregation and deposition. Previous evidence, that charge differences between the light chains in AL and NALCDD might account for their different phenotypes, prompted the present study, which compared the isoelectric points (pIs) of AL and NALCDD protein deposits extracted from human tissues. The pI profiles (5.2-8.8) of polypeptides in AL deposits were heterogenous in four cases, with a spread of both anionic and cationic isoforms; in contrast, in three of NALCDD the pI profiles (8.2-8.8) were homogeneous and restricted in the cationic range. These in vivo findings in human disease, together with other reported in vitro and in vivo experimental data, suggest that the fibrillar deposits in AL may form by electrostatic interaction between oppositely charged polypeptides, whereas the granular deposits in NALCDD form by the binding of cationic polypeptides to anionic proteoglycans sites in basement membranes.

Dependence on glucose limitation of thepCO2 influences on CHO cell growth, metabolism and IgG production

The culture levels of glucose and CO(2) have been reported to independently have important influences on mammalian cell processes. In this work the combined effects of glucose limitation and CO(2) partial pressure (pCO(2)) on monoclonal antibody (IgG) producing Chinese Hamster Ovary cells were investigated in a perfusion reactor operated with controlled cell specific medium feed rate, pH and osmolality. Under high glucose conditions (14.3 +/- 0.8 mM), the apparent growth rate decreased (from 0.021 to 0.009 h(-1)) as the pCO(2) increased to approximately 220 mmHg, while the cell specific IgG productivity was almost unchanged. The lactate yield from glucose was not affected by pCO(2) up to approximately 220 mmHg and glucose was mainly converted to lactate. A feed medium modification from high (33 mM) to low (6 mM) glucose resulted in <0.1 mM glucose in the culture. As a result of apparently shifting metabolism towards the conversion of pyruvate to CO(2), both the ratio of lactate to glucose and the alanine production rate were lowered (1.51-1.14 and 17.7-0.56 nmol/10(6) cells h, respectively). Interestingly, when the pCO(2) was increased to approximately 140 mmHg, limiting glucose resulted in 1.7-fold higher growth rates, compared to high glucose conditions. However, at approximately 220 mmHg pCO(2) this beneficial effect of glucose limitation on these CHO cells was lost as the growth rate dropped dramatically to 0.008 h(-1) and the IgG productivity was lowered by 15% (P < 0.01) relative to the high glucose condition. The IgG galactosylation increased under glucose- limited compared to high-glucose conditions.

Production technologies for monoclonal antibodies and their fragments

In recent years, monoclonal antibodies have emerged as an increasingly important class of human therapeutics. A variety of forms of antibodies, including fragments such as Fabs, Fab'2s and single-chain Fvs, are also being evaluated for a range of different purposes. A variety of expression systems and improvements within these systems have been developed to address these growing and diverse needs.

Heterogeneous conditions in dissolved oxygen affect N-glycosylation but not productivity of a monoclonal antibody in hybridoma cultures

It is known that heterogeneous conditions exist in large-scale animal cell cultures. However, little is known about how heterogeneities affect cells, productivities, and product quality. To study the effect of non-constant dissolved oxygen tension (DOT), hybridomas were subjected to sinusoidal DOT oscillations in a one-compartment scale-down simulator. Oscillations were forced by manipulating the inlet oxygen partial pressure through a feedback control algorithm in a 220-mL bioreactor maintained at a constant agitation. Such temporal DOT oscillations simulate spatial DOT gradients that can occur in large scales. Different oscillation periods, in the range of 800 to 12,800 s (axis of 7% (air saturation) and amplitude of 7%), were tested and compared to constant DOT (10%) control cultures. Oscillating DOT decreased maximum cell concentrations, cell growth rates, and viability indexes. Cultures at oscillating DOT had an increased glycolytic metabolism that was evidenced by a decrease in yield of cells on glucose and an increase in lactate yield. DOT gradients, even several orders of magnitude higher than those expected under practical large-scale conditions, did not significantly affect the maximum concentration of an IgG(1) monoclonal antibody (MAb). The glycosylation profile of the MAb produced at a constant DOT of 10% was similar to that reported in the literature. However, MAb produced under oscillating culture conditions had a higher amount of triantennary and sialylated glycans, which can interfere with effector functions of the antibody. It was shown that transient excursions of hybridomas to limiting DOT, as occurs in deficiently mixed large-scale bioreactors, is important to culture performance as the oscillation period, and thus the time cells spent at low DOT, affected cell growth, metabolism, and the glycosylation pattern of MAb. Such results underline the importance of monitoring protein characteristics for the development of large-scale processes.

Characterizing biological products and assessing comparability following manufacturing changes

Changes in production methods of a biological product may necessitate an assessment of comparability to ensure that these manufacturing changes have not affected the safety, identity, purity, or efficacy of the product. Depending on the nature of the protein or the change, this assessment consists of a hierarchy of sequential tests in analytical testing, preclinical animal studies and clinical studies. Differences in analytical test results between pre- and post-change products may require functional testing to establish the biological or clinical significance of the observed difference. An underlying principle of comparability is that under certain conditions, protein products may be considered comparable on the basis of analytical testing results alone. However, the ability to compare biological materials is solely dependent on the tests used, since no single analytical method is able to compare every aspect of protein structure or function. The advantages and disadvantages of any given method depends on the protein property being characterized.