A new seed-train expansion method for recombinant mammalian cell lines

Seed Train Intensification Using an Ultra-High Cell Density Cell Banking Process

A current focus of biopharmaceutical research and production is seed train process intensification. This allows for intermediate cultivation steps to be avoided or even for the direct inoculation of a production bioreactor with cells from cryovials or cryobags. Based on preliminary investigations regarding the suitability of high cell densities for cryopreservation and the suitability of cells from perfusion cultivations as inoculum for further cultivations, an ultra-high cell density working cell bank (UHCD-WCB) was established for an immunoglobulin G (IgG)-producing Chinese hamster ovary (CHO) cell line. The cells were previously expanded in a wave-mixed bioreactor with internal filter-based perfusion and a 1 L working volume. This procedure allows for cryovial freezing at 260 × 106 cells mL−1 for the first time. The cryovials are suitable for the direct inoculation of N−1 bioreactors in the perfusion mode. These in turn can be used to inoculate subsequent IgG productions in the fed-batch mode (low-seed fed-batch or high-seed fed-batch) or the continuous mode. A comparison with the standard approach shows that cell growth and antibody production are comparable, but time savings of greater than 35% are possible for inoculum production.

Developments and opportunities in continuous biopharmaceutical manufacturing

Today's biologics manufacturing practices incur high costs to the drug makers, which can contribute to high prices for patients. Timely investment in the development and implementation of continuous biomanufacturing can increase the production of consistent-quality drugs at a lower cost and a faster pace, to meet growing demand. Efficient use of equipment, manufacturing footprint, and labor also offer the potential to improve drug accessibility. Although technological efforts enabling continuous biomanufacturing have commenced, challenges remain in the integration, monitoring, and control of traditionally segmented unit operations. Here, we discuss recent developments supporting the implementation of continuous biomanufacturing, along with their benefits.

Design, Optimization, and Adaptive Control of Cell Culture Seed Trains

For the production of biopharmaceuticals, a procedure called seed train or inoculum train is required to generate an adequate number of cells for the inoculation of the production bioreactor. This seed train is time- and cost-intensive but offers potential for optimization. A method and a protocol are described for seed train mapping, directed modeling, and simulation as well as its optimization regarding selected optimization criteria such as optimal points in time for cell passaging. Furthermore, the method can also be applied for the transfer of a seed train to a different production plant or the design of a new seed train, for example, for a new cell line. Another application is to support the selection of the optimal clone for a new process. Seed train prediction can be performed for different clones, and so it can be analyzed how the seed train protocol would look like and for which clones a suitable seed train protocol could be found.Although the chapter is directed toward suspension cell lines, the method is also generally applicable, e.g., for adherent cell lines.

Innovation in Cell Banking, Expansion, and Production Culture

Cell culture-based production processes enable the development and commercial supply of recombinant protein products. Such processes consist of the following elements: thaw and initiation of culture, seed expansion, and production culture. A robust cell source storage system in the form of a cell bank is developed and cells are thawed to initiate the cell culture process. Seed culture expansion generates sufficient cell mass to initiate the production culture. The production culture provides an environment where the cells can synthesize the product and is optimized to deliver the highest possible product concentration with acceptable product quality. This chapter describes the significant innovations made in these process elements and the resulting improvements in the overall efficiency, robustness, and safety of the processes and products.

Model-based strategy for cell culture seed train layout verified at lab scale

Cell culture seed trains-the generation of a sufficient viable cell number for the inoculation of the production scale bioreactor, starting from incubator scale-are time- and cost-intensive. Accordingly, a seed train offers potential for optimization regarding its layout and the corresponding proceedings. A tool has been developed to determine the optimal points in time for cell passaging from one scale into the next and it has been applied to two different cell lines at lab scale, AGE1.HN AAT and CHO-K1. For evaluation, experimental seed train realization has been evaluated in comparison to its layout. In case of the AGE1.HN AAT cell line, the results have also been compared to the formerly manually designed seed train. The tool provides the same seed train layout based on the data of only two batches.

A scale down process for the development of large volume cryopreservation

The process of ice formation and propagation during cryopreservation impacts on the post-thaw outcome for a sample. Two processes, either network solidification or progressive solidification, can dominate the water–ice phase transition with network solidification typically present in small sample cryo-straws or cryo-vials. Progressive solidification is more often observed in larger volumes or environmental freezing. These different ice phase progressions could have a significant impact on cryopreservation in scale-up and larger volume cryo-banking protocols necessitating their study when considering cell therapy applications.

This study determines the impact of these different processes on alginate encapsulated liver spheroids (ELS) as a model system during cryopreservation, and develops a method to replicate these differences in an economical manner.

It was found in the current studies that progressive solidification resulted in fewer, but proportionally more viable cells 24 h post-thaw compared with network solidification. The differences between the groups diminished at later time points post-thaw as cells recovered the ability to undertake cell division, with no statistically significant differences seen by either 48 h or 72 h in recovery cultures.

Thus progressive solidification itself should not prove a significant hurdle in the search for successful cryopreservation in large volumes. However, some small but significant differences were noted in total viable cell recoveries and functional assessments between samples cooled with either progressive or network solidification, and these require further investigation.

GMP cryopreservation of large volumes of cells for regenerative medicine: active control of the freezing process

Cryopreservation protocols are increasingly required in regenerative medicine applications but must deliver functional products at clinical scale and comply with Good Manufacturing Process (GMP). While GMP cryopreservation is achievable on a small scale using a Stirling cryocooler-based controlled rate freezer (CRF) (EF600), successful large-scale GMP cryopreservation is more challenging due to heat transfer issues and control of ice nucleation, both complex events that impact success. We have developed a large-scale cryocooler-based CRF (VIA Freeze) that can process larger volumes and have evaluated it using alginate-encapsulated liver cell (HepG2) spheroids (ELS). It is anticipated that ELS will comprise the cellular component of a bioartificial liver and will be required in volumes of ∼2 L for clinical use. Sample temperatures and Stirling cryocooler power consumption was recorded throughout cooling runs for both small (500 μL) and large (200 mL) volume samples. ELS recoveries were assessed using viability (FDA/PI staining with image analysis), cell number (nuclei count), and function (protein secretion), along with cryoscanning electron microscopy and freeze substitution techniques to identify possible injury mechanisms. Slow cooling profiles were successfully applied to samples in both the EF600 and the VIA Freeze, and a number of cooling and warming profiles were evaluated. An optimized cooling protocol with a nonlinear cooling profile from ice nucleation to -60°C was implemented in both the EF600 and VIA Freeze. In the VIA Freeze the nucleation of ice is detected by the control software, allowing both noninvasive detection of the nucleation event for quality control purposes and the potential to modify the cooling profile following ice nucleation in an active manner. When processing 200 mL of ELS in the VIA Freeze-viabilities at 93.4% ± 7.4%, viable cell numbers at 14.3 ± 1.7 million nuclei/mL alginate, and protein secretion at 10.5 ± 1.7 μg/mL/24 h were obtained which, compared well with control ELS (viability -98.1% ± 0.9%; viable cell numbers -18.3 ± 1.0 million nuclei/mL alginate; and protein secretion -18.7 ± 1.8 μg/mL/24 h). Large volume GMP cryopreservation of ELS is possible with good functional recovery using the VIA Freeze and may also be applied to other regenerative medicine applications.

Seed train optimization for cell culture

For the production of biopharmaceuticals a seed train is required to generate an adequate number of cells for inoculation of the production bioreactor. This seed train is time- and cost-intensive but offers potential for optimization. A method and a protocol are described for the seed train mapping, directed modeling without major effort, and its optimization regarding selected optimization criteria such as optimal points in time for cell passaging. Furthermore, the method can also be applied for the set-up of a new seed train, for example for a new cell line. Although the chapter is directed towards suspension cell lines, the method is also generally applicable, e.g. for adherent cell lines.

Very high density of Chinese hamster ovary cells in perfusion by alternating tangential flow or tangential flow filtration in WAVE Bioreactor™-part II: Applications for antibody production and cryopreservation

A high cell density perfusion process of monoclonal antibody (MAb) producing Chinese hamster ovary (CHO) cells was developed in disposable WAVE Bioreactor™ using external hollow fiber (HF) filter as cell separation device. Tangential flow filtration (TFF) and alternating tangential flow (ATF) systems were compared and process applications of high cell density perfusion were studied here: MAb production and cryopreservation. Operations by perfusion using microfiltration (MF) or ultrafiltration (UF) with ATF or TFF and by fed-batch were compared. Cell densities higher than 10⁸ cells/mL were obtained using UF TFF or UF ATF. The cells produced comparable amounts of MAb in perfusion by ATF or TFF, MF or UF. MAbs were partially retained by the MF using ATF or TFF but more severely using TFF. Consequently, MAbs were lost when cell broth was discarded from the bioreactor in the daily bleeds. The MAb cell-specific productivity was comparable at cell densities up to 1.3 × 10⁸ cells/mL in perfusion and was comparable or lower in fed-batch. After 12 days, six times more MAbs were harvested using perfusion by ATF or TFF with MF or UF, compared to fed-batch and 28× more in a 1-month perfusion at 10⁸ cells/mL density. Pumping at a recirculation rate up to 2.75 L/min did not damage the cells with the present TFF settings with HF short circuited. Cell cryopreservation at 0.5 × 10⁸ and 10⁸ cells/mL was performed using cells from a perfusion run at 10⁸ cells/mL density. Cell resuscitation was very successful, showing that this system was a reliable process for cell bank manufacturing. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:768–777, 2013

Freezing mammalian cells for production of biopharmaceuticals

Cryopreservation techniques utilize very low temperatures to preserve the structure and function of living cells. Various strategies have been developed for freezing mammalian cells of biological and medical significance. This paper highlights the importance and application of cryopreservation for recombinant mammalian cells used in the biopharmaceutical industry to produce high-value protein therapeutics. It is a primer that aims to give insight into the basic principles of cell freezing for the benefit of biopharmaceutical researchers with limited or no prior experience in cryobiology. For the more familiar researchers, key cell banking parameters such as the cell density and hold conditions have been reviewed to possibly help optimize their specific cell freezing protocols. It is important to understand the mechanisms underlying the freezing of complex and sensitive cellular entities as we implement best practices around the techniques and strategies used for cryopreservation.

Development and implementation of a perfusion-based high cell density cell banking process

A perfusion-based high cell density (HD) cell banking process has been developed that offers substantial advantages in time savings and simplification of upstream unit operations. HD cell banking provides the means to reduce the time required for culture inoculum expansion and scale-up by eliminating the need for multiple small to intermediate scale shake flask-based operations saving up to 9 days of operation during large-scale inoculum expansion. HD perfusion cultures were developed and optimized in a disposable Wave bioreactor system. Through optimization of perfusion rate, rocking speed and aeration rate, the perfusion system supported peak cell densities of >20 × 10(6) cells/mL while maintaining high cell viability (≥ 90%). The cells were frozen at HD (90-100 × 10(6) viable cells/mL) in 5-mL CryoTube vials. HD cell banks were demonstrated to enable direct inoculation of culture into a Wave bioreactor in the inoculum expansion train thus eliminating the need for intermediate shake flask expansion unit operations. The simplicity of the disposable perfusion system and high quality of the cell banks resulted in the successful implementation in a 2000 L scale manufacturing facility.

Characterization of cell-banking parameters for the cryopreservation of mammalian cell lines in 100-mL cryobags

This article describes a cell banking process for rBHK cell lines in 100-mL cryobags. As the use of larger volume cell banks requires greater cell numbers and longer preparation time, extensive characterization of key process parameters beyond the conventional ranges was performed to support a cGMP banking process. All experiments were conducted using two recombinant BHK21 cell lines, one of them cotransfected with Hsp70. The results show that the entire cell banking process for these BHK cell lines can be performed at room temperature. A DMSO exposure time up to 5 h either directly in a bioreactor or in shaker flasks did not result in any significant negative effect after cell thaw, when the cryocontainers were frozen immediately after filling. Extensive characterization did not indicate any significant apoptotic effects after thaw. However, the Hsp70 cotransfected cell line did show a slightly better protection from potential cryopreservation-induced apoptosis. Surprisingly, it was found that cells transferred into cryobags showed a low recovery rate after thaw if the incubation time exceeded 1.5 h before freezing. Additional experiments confirmed that the DMSO exposure time inside the cryocontainer in contrast to the DMSO exposure in a reactor or shaker flasks is much more critical. The cryobag cell banking process should therefore be performed within a 1(1/2)-2 h window; a banking process for vials should not exceed 2(1/2) h.

Optimal conditions for freezing CHO-S and HEK293-EBNA cell lines: influence of Me2SO, freeze density, and PEI-mediated transfection on revitalization and growth of cells, and expression of recombinant protein

To avoid the time consuming, labor intensive seed-train expansion and to improve production reliability and consistency, portions of bulk cryopreserved cells from the same cultivation can be utilized as inocula or alternatively may be used to undertake transient transfections for large-scale bioreactor production. In this study, the conditions for large-scale freezing in cryobags were optimized utilizing a design of experiment approach. We showed that relatively high density of 30-40 x 10(6) cells/mL and relatively low Me(2)SO concentrations of 5-6% in the freezing media are optimal to freeze HEK293-EBNA and CHO-S cells in a controlled manner in order to achieve high viable cell recovery and growth post-thawing. The immediate transfer of freshly thawed cells into culture medium resulted in better cell growth compared to cells that were centrifuged in order to remove Me(2)SO. This was the case as long as the residual Me(2)SO did not exceed 0.2-0.3%. The best time to perform transient 25 kDa polyethylenimine-mediated transfection of pCEP4-EGFP plasmid into freshly thawed, one-step inoculated cells is after 72-96 h in culture. At this time point, the numbers of EGFP-positive cells in the freshly thawed culture mimic perfectly that of cells grown continuously. Finally, our data showed that it is possible to freeze transiently polyethyleneimine-transfected HEK293-EBNA cells and maintain growth rate and expression of recombinant protein following thawing. The optimal time point for freezing cells was 4 h after transfection.