Sustaining an efficient and effective CHO cell line development platform by incorporation of 24-deep well plate screening and multivariate analysis

Novel and effective screening system for recombinant protein production in CHO cells

At present, biopharmaceuticals have received extensive attention from the society, among which recombinant proteins have a good growth trend and a large market share. Chinese hamster ovary (CHO) cells are the preferred mammalian system to produce glycosylated recombinant protein drugs. A highly efficient and stable cell screening method needs to be developed to obtain more and useful recombinant proteins. Limited dilution method, cell sorting, and semi-solid medium screening are currently the commonly used cell cloning methods. These methods are time-consuming and labor-intensive, and they have the disadvantage of low clone survival rate. Here, a method based on semi-solid medium was developed to screen out high-yielding and stable cell line within 3 weeks to improve the screening efficiency. The semi-solid medium was combined with an expression vector containing red fluorescent protein (RFP) for early cell line development. In accordance with the fluorescence intensity of RFP, the expression of upstream target gene could be indicated, and the fluorescence intensity was in direct proportion to the expression of upstream target gene. In conclusion, semi-solid medium combined with bicistronic expression vector provides an efficient method for screening stable and highly expressed cell lines.

Establishment of a semi-continuous scale-down clone screening model for intensified perfusion culture

PURPOSE

Perfusion cultures have been extensively used in the biotechnology industry to achieve high yields of recombinant products, especially those with stability issue. The WuXiUP™ platform represents a novel intensified perfusion that can achieve ultra-high productivity. This study describes a representative scale-down 24-deep well plate (24-DWP) cell culture model for intensified perfusion clone screening.

METHODS

Clonal cell lines were expanded and evaluated in 24-DWP semi-continuous culture. Cell were sampled and counted daily with the aid of an automated liquid handler and high-throughput cell counter. To mimic perfusion culture, 24-DWP plates were spun down and resuspended with fresh medium daily. Top clones were ranked based on growth profiles and productivities. The best performing clones were evaluated on bioreactors.

RESULTS

The selected clones achieved volumetric productivity (Pv) up to 5 g/L/day when expressing a monoclonal antibody, with the accumulative harvest Pv exceeding 60 g/L in a 21-day cell culture. Product quality attributes of clones cultured in 24-DWP were comparable with those from bioreactors. A high seeding strategy further shortened the clone screening timeline.

CONCLUSION

In this study, a 24-DWP semi-continuous scale-down model was successfully developed to screen for cell lines suitable for intensified perfusion culture.

A deep-well plate enabled automated high-throughput cell line development platform

Cell line development (CLD) plays a crucial role in the manufacturing process development of therapeutic biologics. Most biologics are produced in Chinese hamster ovary (CHO) cell. Because of the nature of random transgene integration in CHO genome and CHO's inherent plasticity, stable CHO transfectants usually have a vast diversity in productivity, growth, and product quality. Thus, we often must resort to screening a large number of cell pools and clones to increase the probability of identifying the ideal production cell line, which is a very laborious and resource-demanding process. Here we have developed a deep-well plate (DWP) enabled high throughput (DEHT) CLD platform using 24-well DWP (24DWP), liquid handler, and other automation components. This platform has capabilities covering the key steps of CLD including cell passaging, clone imaging and expansion, and fed-batch production. We are the first to demonstrate the suitability of 24DWP for CLD by confirming minimal well-to-well and plate-to-plate variability and the absence of well-to-well cross contamination. We also demonstrated that growth, production, and product quality of 24DWP cultures were comparable to those of conventional shake flask cultures. The DEHT platform enables scientists to screen five times more cultures than the conventional CLD platform, thus significantly decreases the resources needed to identify an ideal production cell line for biologics manufacturing.

Online monitoring of the respiration activity in 96-deep-well microtiter plate Chinese hamster ovary cultures streamlines kill curve experiments

Cell line generation of mammalian cells is a time-consuming and labor-intensive process, especially because of challenges in clone selection after transfection. Antibiotics are common selection agents for mammalian cells due to their simplicity of use. However, the optimal antibiotic concentration must be determined with a kill curve experiment before clone selection starts. The traditional kill curve experiments are resource-intensive and time-consuming due to necessary sampling and offline analysis effort. This study, thus, explores the potential of online monitoring the oxygen transfer rate (OTR), as a non-invasive and efficient alternative for kill curve experiments. The OTR is monitored using the Transfer-rate Online Measurement (TOM) system and the micro(μ)-scale Transfer-rate Online Measurement (μTOM) device, which was used for mammalian cells first. It could be shown that the OTR curves for both devices align perfectly, affirming consistent cultivation conditions. The μTOM device proves effective in performing kill curve experiments in 96-deep-well plates without the need for sampling and offline analysis. The streamlined approach reduces medium consumption by 95%, offering a cost-effective and time-efficient solution for kill curve experiments. The study validates the generalizability of the method by applying it to two different CHO cell lines (CHO-K1 and sciCHO) with two antibiotics (puromycin and hygromycin B) each. In conclusion, the broad application of OTR online monitoring for CHO cell cultures in 96-deep-well plates is highlighted. The μTOM device proves as a valuable tool for high-throughput experiments, paving the way for diverse applications, such as media and clone screening, cytotoxicity tests, and scale-up experiments.

Scale-down of CHO cell cultivation from shake flasks based on oxygen mass transfer allows application of parallelized, non-invasive, and time-resolved monitoring of the oxygen transfer rate in 48-well microtiter plates

Cultivating Chinese hamster ovary (CHO) cells in microtiter plates (MTPs) with time-resolved monitoring of the oxygen transfer rate (OTR) is highly desirable to provide process insights at increased throughput. However, monitoring of the OTR in MTPs has not been demonstrated for CHO cells, yet. Hence, a CHO cultivation process was transferred from shake flasks to MTPs to enable monitoring of the OTR in each individual well of a 48-well MTP. For this, the cultivation of an industrially relevant, antibody-producing cell line was transferred from shake flask to MTP based on the volumetric oxygen mass transfer coefficient (kL a). Culture behavior was well comparable (deviation of the final IgG titer less than 10%). Monitoring of the OTR in 48-well MTPs was then used to derive the cytotoxicity of dimethyl sulfoxide (DMSO) based on a dose-response curve in a single experiment using a second CHO cell line. Logistic fitting of the dose-response curve determined after 100 h was used to determine the DMSO concentration that resulted in a cytotoxicity of 50% (IC50). A DMSO concentration of 2.70% ± 0.25% was determined, which agrees with the IC50 previously determined in shake flasks (2.39% ± 0.1%). Non-invasive, parallelized, and time-resolved monitoring of the OTR of CHO cells in MTPs was demonstrated and offers excellent potential to speed up process development and assess cytotoxicity.

Hybrid deep modeling of a CHO-K1 fed-batch process: combining first-principles with deep neural networks

Introduction: Hybrid modeling combining First-Principles with machine learning is becoming a pivotal methodology for Biopharma 4.0 enactment. Chinese Hamster Ovary (CHO) cells, being the workhorse for industrial glycoproteins production, have been the object of several hybrid modeling studies. Most previous studies pursued a shallow hybrid modeling approach based on three-layered Feedforward Neural Networks (FFNNs) combined with macroscopic material balance equations. Only recently, the hybrid modeling field is incorporating deep learning into its framework with significant gains in descriptive and predictive power. Methods: This study compares, for the first time, deep and shallow hybrid modeling in a CHO process development context. Data of 24 fed-batch cultivations of a CHO-K1 cell line expressing a target glycoprotein, comprising 30 measured state variables over time, were used to compare both methodologies. Hybrid models with varying FFNN depths (3-5 layers) were systematically compared using two training methodologies. The classical training is based on the Levenberg-Marquardt algorithm, indirect sensitivity equations and cross-validation. The deep learning is based on the Adaptive Moment Estimation Method (ADAM), stochastic regularization and semidirect sensitivity equations. Results and conclusion: The results point to a systematic generalization improvement of deep hybrid models over shallow hybrid models. Overall, the training and testing errors decreased by 14.0% and 23.6% respectively when applying the deep methodology. The Central Processing Unit (CPU) time for training the deep hybrid model increased by 31.6% mainly due to the higher FFNN complexity. The final deep hybrid model is shown to predict the dynamics of the 30 state variables within the error bounds in every test experiment. Notably, the deep hybrid model could predict the metabolic shifts in key metabolites (e.g., lactate, ammonium, glutamine and glutamate) in the test experiments. We expect deep hybrid modeling to accelerate the deployment of high-fidelity digital twins in the biopharma sector in the near future.

Development of a mammalian cell-based ZZ display system for IgG quantification

BACKGROUND

Biological laboratories and companies involved in antibody development need convenient and versatile methods to detect highly active antibodies.

METHODS

To develop a mammalian cell-based ZZ display system for antibody quantification, the eukaryotic ZZ-displayed plasmid was constructed and transfected into CHO cells. After screening by flow cytometric sorting, the stable ZZ display cells were incubated with reference IgG and samples with unknown IgG content for 40 min at 4℃, the relative fluorescence intensity of cells was analyzed and the concentration of IgG was calculated.

RESULTS

By investigating the effects of different display-associated genetic elements, a eukaryotic ZZ-displaying plasmid with the highest display efficiency were constructed. After transfection and screening, almost 100% of the cells were able to display the ZZ peptide (designated CHO-ZZ cells). These stable CHO-ZZ cells were able to capture a variety of IgG, including human, rabbit, donkey and even mouse and goat. CHO-ZZ cells could be used to quantify human IgG in the range of approximately 12.5-1000 ng/mL, and to identify high-yielding engineered monoclonal cell lines.

CONCLUSIONS

We have established a highly efficient CHO-ZZ display system in this study, which enables the quantification of IgG from various species under physiological conditions. This system offers the advantage of eliminating the need for antibody purification and will contribute to antibody development.

Rapidly accelerated development of neutralizing COVID-19 antibodies by reducing cell line and CMC development timelines

Since the Coronavirus Disease 2019 (COVID-19) outbreak, unconventional cell line development (CLD) strategies have been taken to enable development of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-neutralizing antibodies at expedited speed. We previously reported a novel chemistry, manufacturing, and control (CMC) workflow and demonstrated a much-shortened timeline of 3-6 months from DNA to investigational new drug (IND) application. Hereafter, we have incorporated this CMC strategy for many SARS-CoV-2-neutralizing antibody programs at WuXi Biologics. In this paper, we summarize the accelerated development of a total of seven antibody programs, some of which have received emergency use authorization  approval in less than 2 years. Stable pools generated under good manufacturing practice (GMP) conditions consistently exhibited similar productivity and product quality at different scales and batches, enabling rapid initiation of phase I clinical trials. Clones with comparable product quality as parental pools were subsequently screened and selected for late-stage development and manufacturing. Moreover, a preliminary stability study plan was devised to greatly reduce the time required for final clone determination and next-generation sequencing-based viral testing was implemented to support rapid conditional release of the master cell bank for GMP production. The successful execution of these COVID-19 programs relies on our robust, fit for purpose, and continuously improving CLD platform. The speed achieved for pandemic-related biologics development may innovate typical biologics development timelines and become a new standard in the industry.

Online 2D Fluorescence Monitoring in Microtiter Plates Allows Prediction of Cultivation Parameters and Considerable Reduction in Sampling Efforts for Parallel Cultivations of Hansenula polymorpha

Multi-wavelength (2D) fluorescence spectroscopy represents an important step towards exploiting the monitoring potential of microtiter plates (MTPs) during early-stage bioprocess development. In combination with multivariate data analysis (MVDA), important process information can be obtained, while repetitive, cost-intensive sample analytics can be reduced. This study provides a comprehensive experimental dataset of online and offline measurements for batch cultures of Hansenula polymorpha. In the first step, principal component analysis (PCA) was used to assess spectral data quality. Secondly, partial least-squares (PLS) regression models were generated, based on spectral data of two cultivation conditions and offline samples for glycerol, cell dry weight, and pH value. Thereby, the time-wise resolution increased 12-fold compared to the offline sampling interval of 6 h. The PLS models were validated using offline samples of a shorter sampling interval. Very good model transferability was shown during the PLS model application to the spectral data of cultures with six varying initial cultivation conditions. For all the predicted variables, a relative root-mean-square error (RMSE) below 6% was obtained. Based on the findings, the initial experimental strategy was re-evaluated and a more practical approach with minimised sampling effort and elevated experimental throughput was proposed. In conclusion, the study underlines the high potential of multi-wavelength (2D) fluorescence spectroscopy and provides an evaluation workflow for PLS modelling in microtiter plates.

High-throughput and automation advances for accelerating single-cell cloning, monoclonality and early phase clone screening steps in mammalian cell line development for biologics production

Mammalian cell line development is a multistep process wherein timelines for developing clonal cells to be used as manufacturing cell lines for biologics production can commonly extend to 9 months when no automation or modern molecular technologies are involved in the workflow. Steps in the cell line development workflow involving single-cell cloning, monoclonality assurance, productivity and stability screening are labor, time and resource intensive when performed manually. Introduction of automation and miniaturization in these steps has reduced the required manual labor, shortened timelines from months to weeks, and decreased the resources needed to develop manufacturing cell lines. This review summarizes the advances, benefits, comparisons and shortcomings of different automation platforms available in the market for rapid isolation of desired clonal cell lines for biologics production.

Microfluidic chip-based single-cell cloning to accelerate biologic production timelines

Cell line development (CLD) represents a critical, yet time‐consuming, step in the biomanufacturing process as significant resources are devoted to the scale‐up and screening of several hundreds to thousands of single‐cell clones. Typically, transfected pools are fully recovered from selection and characterized for growth, productivity, and product quality to identify the best pools suitable for single‐cell cloning (SCC) using limiting dilution or fluorescence‐activated cell sorting (FACS). Here we report the application of the Berkeley Lights Beacon Instrument (BLI) in an early SCC process to accelerate the CLD timeline. Transfected pools were single‐cell cloned when viabilities reached greater than 85% or during selection when viabilities were less than 30%. Clones isolated from these accelerated processes exhibited comparable growth, productivity, and product quality to those derived from a standard CLD process and fit into an existing manufacturing platform. With these approaches, up to a 30% reduction in the overall CLD timeline was achieved. Furthermore, early process‐derived clones demonstrated equivalent long‐term stability compared with standard process‐derived clones over 50 population doubling levels (PDLs). Taken together, the data supported early SCC on the BLI as an attractive approach to reducing the standard CLD timeline while still identifying clones with acceptable manufacturability.

Method to transfer Chinese hamster ovary (CHO) batch shake flask experiments to large-scale, computer-controlled fed-batch bioreactors

Chinese hamster ovary (CHO) cell cultures in industry are most commonly conducted as fed-batch cultures in computer-controlled bioreactors, though most preliminary studies are conducted in fed-batch shake flasks. To improve comparability between bioreactor studies and shake flask studies, shake flask studies should be conducted as fed-batch. However, the smaller volumes and reduced control in shake flasks can impact pH and aeration, which leads to performance differences. Planning and awareness of these vessel and control differences can assist with experimental design as well as troubleshooting. This method will highlight several of the configuration and control issues that should be considered during the transitions from batch to fed-batch and shake flasks to bioreactors, as well as approaches to mitigate the differences. Furthermore, if significant differences occur between bioreactor and shake flask studies, approaches will be presented to isolate the main contributors for these differences.

Model-based workflow for scale-up of process strategies developed in miniaturized bioreactor systems

Miniaturized bioreactor (MBR) systems are routinely used in the development of mammalian cell culture processes. However, scale-up of process strategies obtained in MBR- to larger scale is challenging due to mainly non-holistic scale-up approaches. In this study, a model-based workflow is introduced to quantify differences in the process dynamics between bioreactor scales and thus enable a more knowledge-driven scale-up. The workflow is applied to two case studies with antibody-producing Chinese hamster ovary cell lines. With the workflow, model parameter distributions are estimated first under consideration of experimental variability for different scales. Second, the obtained individual model parameter distributions are tested for statistical differences. In case of significant differences, model parametric distributions are transferred between the scales. In case study I, a fed-batch process in a microtiter plate (4 ml working volume) and lab-scale bioreactor (3750 ml working volume) was mathematically modeled and evaluated. No significant differences were identified for model parameter distributions reflecting process dynamics. Therefore, the microtiter plate can be applied as scale-down tool for the lab-scale bioreactor. In case study II, a fed-batch process in a 24-Deep-Well-Plate (2 ml working volume) and shake flask (40 ml working volume) with two feed media was investigated. Model parameter distributions showed significant differences. Thus, process strategies were mathematically transferred, and model predictions were simulated for a new shake flask culture setup and confirmed in validation experiments. Overall, the workflow enables a knowledge-driven evaluation of scale-up for a more efficient bioprocess design and optimization.

Screening and selection strategy for the establishment of biosimilar to trastuzumab-expressing CHO-K1 cell lines

The high prices of biopharmaceuticals or biologics used in the treatment of many diseases limit the access of patients to these novel therapies. One example is the monoclonal antibody trastuzumab, successfully used for breast cancer treatment. An economic alternative is the generation of biosimilars to these expensive biopharmaceuticals. Since antibody therapies may require large doses over a long period of time, robust platforms and strategies for cell line development are essential for the generation of recombinant cell lines with higher levels of expression. Here, we obtained trastuzumab-expressing CHO-K1 cells through a screening and selection strategy that combined the use of host cells pre-adapted to protein-free media and suspension culture and lentiviral vectors. The results demonstrated that the early screening strategy obtained recombinant CHO-K1 cell populations with higher enrichment of IgG-expressing cells. Moreover, the measurement of intracellular heavy chain polypeptide by flow cytometry was a useful metric to characterize the homogeneity of cell population, and our results suggest this could be used to predict the expression levels of monoclonal antibodies in early stages of cell line development. Additionally, we propose an approach using 25 cm2 T-flasks in suspension and shaking culture conditions as a screening tool to identify high producing cell lines. Finally, trastuzumab-expressing CHO-K1 clones were generated and characterized by batch culture, and preliminary results related to HER2-recognition capacity were successful. Further optimization of elements such as gene optimization, vector selection, type of amplification/selection system, cell culture media composition, in combination with this strategy will allow obtaining high producing clones.

Spectroscopy integration to miniature bioreactors and large scale production bioreactors-Increasing current capabilities and model transfer

Spectroscopy techniques are being implemented within the biopharmaceutical industry due to their non-destructive ability to measure multiple analytes simultaneously, however, minimal work has been applied focussing on their application at small scale. Miniature bioreactor systems are being applied across the industry for cell line development as they offer a high-throughput solution for screening and process optimization. The application of small volume, high-throughput, automated analyses to miniature bioreactors has the potential to significantly augment the type and quality of data from these systems and enhance alignment with large-scale bioreactors. Here, we present an evaluation of 1. a prototype that fully integrates spectroscopy to a miniature bioreactor system (ambr®15, Sartorius Stedim Biotech) enabling automated Raman spectra acquisition, 2. In 50 L single-use bioreactor bag (SUB) prototype with an integrated spectral window. OPLS models were developed demonstrating good accuracy for multiple analytes at both scales. Furthermore, the 50 L SUB prototype enabled on-line monitoring without the need for sterilization of the probe prior to use and minimal light interference was observed. We also demonstrate the ability to build robust models due to induced changes that are hard and costly to perform at large scale and the potential of transferring these models across the scales. The implementation of this technology enables integration of spectroscopy at the small scale for better process understanding and generation of robust models over a large design space while facilitating model transfer throughout the scales enabling continuity throughout process development and utilization and transfer of ever-increasing data generation from development to manufacturing.

High-Throughput Quantification and Glycosylation Analysis of Antibodies Using Bead-Based Assays

A novel version of bead -based assays with fluorescence detection enables the high-throughput analysis of antibodies and proteins. The protocols are carried out in special 384-well plates, require very few manual interventions, and are easy to automate. Here we describe how the technology can be used to determine antibody titers and screen for product glycosylation, a critical quality attribute, early in cell line and bioprocess development.

Early integration of Design of Experiment (DOE) and multivariate statistics identifies feeding regimens suitable for CHO cell line development and screening

In Chinese Hamster Ovary (CHO) cell lines, the establishment of the ideal fed-batch regimen promotes metabolic conditions advantageous for the bioproduction of therapeutic molecules. A tailored, cell line-specific feeding scheme is typically defined during process development (PD) activities, through the incorporation of Design of Experiment (DOE) and late stage cell culture approaches. The feeding during early stage cell line development (CLD) was a simplified "one-fits-all" design, inherited from PD lab, that didn't account for CLD needs of throughput and streamlined workflow. The "one-fits-all" efficiency was not routinely verified when novel technologies were incorporated in CLD and sub-optimal feeding carried the risk of not selecting the most desirable cell lines amenable to late stage PD. In our work we developed the DOE-feed method; a streamlined, three-stages framework for identifying efficient feeding schemes as the CLD technologies evolved. We combined early stage cell culture input data with late-stage techniques, such as statistical modelling, principal component analysis (PCA), DOE and Prediction Profiler. Novel in our DOE-feed work, we deliberately anticipated the application of statistics and approached the method development as an early-stage, continuously updated process, by building iterative datasets and statistically interpreting their responses. We capitalized on the statistical models defined by the DOE-feed methodology to study the influence of feeds on daily productivity and growth and to extrapolate feeding-schemes that improved the cell line screening. The DOE-feed became a methodology suited for CLD needs at AbbVie, and optimized the early stage screening, reduced the operational hands-on time and improved the overall workstream efficiency.