Industrial production of monoclonal antibodies and therapeutic proteins by dialysis fermentation

High-density adherent culture of CHO cells using rolled scaffold bioreactor

Rapid expansion of biopharmaceutical market calls for more efficient and reliable platforms to culture mammalian cells on a large scale. Stirred-tank bioreactors have been widely used for large-scale cell culture. However, it requires months of trials and errors to optimize culture conditions for each cell line. In this article, we extend our earlier studies on rolled scaffold (RS) bioreactors for high-density adherent cell culture and report two new implementations of RSs with greatly enhanced mass-manufacturability, termed as Mesh-RS and Fiber-RS. CHO-K1 cells were successfully expanded in Mesh-RS and Fiber-RS bioreactors with an average growth rate of 1.09 ± 0.04 1/day and 0.95 ± 0.07 1/day, which were higher than those reported in similar studies. Fiber-RS bioreactor exhibited a very high cell density of 72.8 × 10⁶  cells/ml. Besides, a dialyzer was integrated into the RS bioreactor to remove cellular waste and to replenish nutrients without disturbing the cells. By collecting the dialyzed media separately, the dialysis efficiency was significantly improved. In conclusion, the developed RS bioreactor has a strong potential to provide a highly reliable and easily scalable platform for large-scale cell culture in the biopharmaceutical industry.

High viable cell concentration fed-batch cultures of hybridoma cells through on-line nutrient feeding

A hybridoma cell line was cultivated in fed-batch cultures using a low-protein, serum-free medium. On-line oxygen uptake rate (OUR) measurement was used to adjust the nutrient feeding rate based on glucose consumption, which was estimated on-line using the stoichiometric relations between glucose and oxygen consumption. Through on-line control of the nutrient feeding rate, not only sufficient were supplied for cell growth and antibody production, but also the concentrations of glucose and other important nutrients such as amino acids were maintained at low levels during the cell growth phase. During the cultivation, cell metabolism changed from high lactate production and low oxygen consumption to low lactate production and high oxygen consumption. As a result the accumulation of lactate was reduced and the growth phase was extended. In comparison with the batch cultures, in which cells reached a concentration of approximately 2 x 10(6) cells/mL, a very high concentration of 1.36 x 10(7) cells/mL with a high cell viability (>90%) was achieved in the fed-batch culture. By considering the consumption of glucose and amino acids, as well as the production of cell mass, metabolites, and antibodies, a well-closed material balance was established. Our results demonstrate the value of coupling on-line OUR measurement and the stoichiometric relations for dynamic nutrient feeding in high cell concentration fed batch cultures.

On-line characterization of a hybridoma cell culture process

The on-line determination of the physiological state of a cell culture process requires reliable on-line measurements of various parameters and calculations of specific rates from these measurements. The cell concentration of a hybridoma culture was estimated on-line by measuring optical density (OD) with a laser turbidity probe. The oxygen uptake rate (OUR) was determined by monitoring dynamically dissolved oxygen concentration profiles and closing oxygen balances in the culture. The base addition for neutralizing lactate produced by cells was also monitored on-line via a balance. Using OD and OUR measurements, the specific growth and specific oxygen consumption rates were determined on-line. By combining predetermined stoichiometric relationships among oxygen and glucose consumption and lactate production, the specific glucose consumption and lactate production rates were also calculated on-line. Using these on-line measurements and calculations, the hybridoma culture process was characterized on-line by identifying the physiological states. They will also facilitate the implementation of nutrient feeding strategies for fed-batch and perfusion cultures. (c) 1994 John Wiley & Sons, Inc.

Analysis of the use of fortified medium in continuous culture of mammalian cells

Continuous culture is frequently used in the cultivation of mammalian cells for the manufacturing of recombinant protein pharmaceuticals. In such operations a large volume of medium is turned over each day, especially in the case where cell recycle, or perfusion cultivation, is practiced. In principle, the volumetric throughput of medium can be reduced by using a more concentrated feed while maintaining the same nutrient provision rate. Overall, the medium components are divided into two categories: 'consumable nutrients' and 'unconsumable inorganic bulk salts'. In such fortified medium, the concentrations of consumable nutrients, but not bulk salts, are increased. With a stoichiometrically-balanced medium, the large amount of nutrients fed into the culture is largely consumed by cells to give rise to residual concentrations of these nutrients in their optimal range. However, unless care is taken to initiate the continuous culture, overshoot of nutrients may occur during the transient period. The high nutrient concentration during overshoot may be inhibitory by itself, or the resulting high osmolality may retard the growth. Using a mathematical model that incorporates the growth inhibitory effect of high osmolality we demonstrate such a potentially catastrophic effect of nutrient and osmolality overshoot by simulation. To avoid overshoot a controlled nutrient feeding scheme should be devised at the initiation of continuous culture.

Influence of bcl-2 on antibody productivity in high cell density perfusion cultures of hybridoma

Apoptosis is an active, genetically determined death mechanism which can be induced by a wide range of physiological factors and by mild stress. It is the predominant form of cell death during the production of antibodies from murine hybridoma cell lines. A number of studies have now demonstrated that the suppression of this death pathway, by means of over-expression of survival genes such as bcl-2, results in improved cellular robustness and antibody productivity during batch culture. In the present study, the influence of bcl-2 expression on hybridoma productivity in two high density perfusion bioreactor systems was investigated. In the first system, a fixed-bed reactor, the DNA content in the spent medium was 25% higher in the control (TB/C3-pEF) culture than that found in the bcl-2 transfected (TB/C3-bcl2) cultures at all perfusion rates. This is indicative of a higher level of cell death in the control cell line. The average antibody concentration for the TB/C3-pEF cell line was 14.9 mg L-1 at perfusion rates of 2.6 and 5.2 d-1. However, for the TB/C3-bcl2 cell line it was 33 mg L-1 at dilution rates of 2 and 4 d-1. A substantial increase in antibody concentration was also found in the Integra Tecnomouse hollow fibre reactor. The antibody titre in the TB/C3-bcl2 cassette was nearly 100% higher than that in the TB/C3-pEF cassette during the cultivation period which lasted 6 weeks. Clearly, these results demonstrate the positive impact of bcl-2 over-expression on production of antibody in hybridoma perfusion cultures.

Development and optimisation of a procedure for the production of Parapoxvirus ovis by large-scale microcarrier cell culture in a non-animal, non-human and non-plant-derived medium

For the production of a chemically inactivated Parapoxvirus ovis (PPVO), an adherent bovine kidney cell line was cultivated on Cytodex-3 microcarriers in suspension culture. The inactivated and purified virus particles have shown immune modulatory activity in several animal models. PPVO was produced by a biphasic batch process at the 3.5 and 10 L scale. Aeration was realised by bubble-free membrane oxygenation via a tube stator with a central two-blade anchor impeller. In order to increase efficiency, process robustness and safety, the established process was optimised. The cell line was adapted to a protein-free medium (except recombinant insulin) in order to increase biosafety. A scale up to a 50 L pilot plant with direct cell expansion was performed successfully. In parallel, the biphasic batch process was optimised with special emphasis on different operating conditions (cell number, Multiplicity of Infection (MOI), etc.) and process management (fed-batch, dialysis, etc.). The quality and concentration of the purified virus particles was assessed by quantitative electron microscopy, residual host cell protein and DNA-content and, finally, biologic activity in a transgenic mouse model. This integrated approach led to a new, safe, robust and highly productive large-scale production process, called "Volume-Expanded-Fed" Batch with cell densities up to 6-7e06 cells/mL. By subsequent dilution of infected cells into the next process scale, an increase in total productivity by a factor of 40 (related to an established biphasic batch process) was achieved.

Hybridoma growth and monoclonal antibody production in a dialysis perfusion system

Hybridoma cells were grown in perfusion culture using a stirred reactor within which a tubular membrane was suspended. Nutrient and product flows through the membrane to and from the culture environment occurred by diffusion processes alone. A mathematical model of the transfer and reaction process enabled both the characterization of a membrane mass transfer coefficient and the prediction of the maximum cell number achievable under set conditions. Steady states in cell concentration were observed for a range of perfusion rates and membrane areas. Steady states could be maintained for over 180 h without further addition of serum. Antibody was accumulated within the reactor to high concentrations, and at yields on both basal medium and serum that were many times those achieved in other forms of batch culture.

Mass spectrometry: a tool for on-line monitoring of animal cell cultures

The magnetic sector mass spectrometer is able to detect oxygen uptake and carbon dioxide production rates from animal cell cultivations performed in 101 bioreactors. Such data have not been available with the use of classic exhaust gas analysis applying paramagnetic analyzers and infra-red sensors due to the insensitivity of the apparatus available. In the course of the present work we were able to demonstrate, that the oxygen uptake rate correlates to the number of viable cells. Additionally oxygen uptake rates supplied on-line information about the actual physiology of the cells: When the rates changed during the cultivation process, this immediately indicated the occurrence of limitations of components in the medium. The information could be useful in timing key events, such as performing splits or harvesting the bioreactor.

Increase of hybridoma productivity using an original dialysis culture system

Hybridoma cell growth and monoclonal antibody production were investigated with a laboratory-made system in which cells were grown in dialysis tubing (MW cut-off 25 kD). The dialysis system contained 10 ml of cell suspension and was immersed in 200 ml of culture medium which when replaced or was at 4-day intervals. With this system, monoclonal antibody concentrations similar to those observed in ascites (concentrations in the order of one gram per liter) were obtained. With no medium replacement, the antibody production was 3.3 g/l and the cell productivity 3.2 x 10(-8) micrograms of IgM produced per cell in one minute. With medium replacement the antibody production was higher, 4.4 g/l but the cell productivity was lower, 1.49 x 10(-8) micrograms per cell in one minute. Cells cultivated in non-optimized conditions were better producers than cells growing in a good environment.

Determination of division rates of rCHO cells in high density and immobilized fermentation systems by flow cytometry

As most high density and immobilized fermentation systems do not allow the direct quantitative determination of cell density, two flow cytometric methods (the determination of incorporation of bromodeoxyuridine into newly synthesized DNA and the increase in mitotic cells by colchicine blockage) were evaluated as to their suitability to measure true division rates of cells in bioreactors. The BrdU method gave division rates identical to the growth rates measured by cell count, while the colchicine block method gave values that were lower and varied with the cell line. This is due to the cytotoxicity of colchicine and makes a calibration of the method for each cell line necessary. Both methods have been successfully used to measure division rates of rCHO cells immobilized in an alginate matrix as well as in macroporous carriers in a fluidised bed system and in dialysis culture.

Growth and production kinetics of human x mouse and mouse hybridoma cells at reduced temperature and serum content

The growth and production kinetics of a mouse hybridoma cell line and a human-mouse heterohybridoma were analyzed under conditions of reduced temperature and serum content. The mouse hybridoma P24 had a constant cell specific production rate and RNA content, while the heterohybridoma 3D6-LC4 showed growth associated production kinetics and an increased RNA content at higher growth rates. This behaviour of 3D6-LC4 cells can be explained by the unusual cell cycle kinetics of this line, which can be arrested in any phase under growth limiting conditions, so that a low growth rate does not result in a greater portion of high producing G1-phase cells. Substrate limitation changes the cell cycle distribution of this cell line to a greater extent than low temperature or serum content, which indicates that this stress factor exerts a greater physiological control than assumed.

Growth limitation in hybridoma cell cultures: the role of inhibitory or toxic metabolites

Hybridoma cells usually grow to fairly low cell densities in batch cultures (1-3 x 10(6) cells/ml). The reason for this is either that essential nutritional components of the medium are consumed, or that the cells produce some kind of inhibitory or toxic metabolite. This investigation presents evidence for the latter. Spent medium from cultures of hybridoma cells did not support growth of cells at lower cell densities (1-3 x 10(5) cells/ml). The ability to support cell growth could not be restored by adding additional serum, energy sources (glucose, pyruvate) or L-glutamine. Furthermore, the consumption of amino acids could not account for this growth inhibition. On the contrary, the spent medium contained a substance that inhibited cell growth. This substance or metabolite was found in a fraction eluted from a gel filtration column when spent medium was applied to the column. This substance was found in the spent medium from all hybridoma and myeloma cell lines that were tested. The molecular weight of the substance was about 5 kD. Spent medium from two hybridoma cell lines also contained a substance that was eluted in the same fraction as albumin (67 kD). It is likely that this (or these) substance(s) is responsible for the growth limitation in hybridoma cell cultures.

Modular integrated fluidized bed bioreactor technology

We describe the design and demonstrate the application of a modular integrated fluidized bed bioreactor system. Basically the system is a reactor vessel equipped with an extending cylinder and a liquid distributor plate. Instead of an external recirculation loop, as used in existing fluidized bed systems, a low shear stress impeller is used as the recirculation pump. The system has several unique features, such as modular exchangeable elements, efficient oxygenation and the option of operating as a stirred tank-, a packed bed- or a fluidized bed reactor. An example of a fluidized bed run using CHO-K1 cells is shown. Under standard culture conditions a 100-fold increase in cell density (up to 1.2 x 10(8) cells/ml) was achieved.

Large-scale mammalian cell culture: methods, applications and products

Animal cell cultures are used to generate products of enormous biotechnological value. These systems rely on conventional manufacturing techniques using organisms that are the result of either cell fusions or genetic engineering. A wealth of new techniques has allowed improvements and developments to be made in culture medium composition, cell modification, and bioreactor design and operation. This progress is expected to be commercially exploited as new products reach the market place.