Perfusion Control for High Cell Density Cultivation and Viral Vaccine Production

Innovations in cell culture-based influenza vaccine manufacturing - from static cultures to high cell density cultivations

Influenza remains a serious global health concern, causing significant morbidity and mortality each year. Vaccination is crucial to mitigate its impact, but requires rapid and efficient manufacturing strategies to handle timing and supply. Traditionally relying on egg-based production, the field has witnessed a paradigm shift toward cell culture-based methods offering enhanced flexibility, scalability, and process safety. This review provides a concise overview of available cell substrates and technological advancements. We summarize crucial steps toward process intensification - from roller bottle production to dynamic cultures on carriers and from suspension cultures in batch mode to high cell density perfusion using various cell retention devices. Moreover, we compare single-use and conventional systems and address challenges including defective interfering particles. Taken together, we describe the current state-of-the-art in cell culture-based influenza virus production to sustainably meet vaccine demands, guarantee a timely supply, and keep up with the challenges of seasonal epidemics and global pandemics.

Platform development for high-throughput optimization of perfusion processes-Part II: Variation of perfusion rate strategies in microwell plates

The biopharmaceutical industry is replacing fed-batch with perfusion processes to take advantage of reduced capital and operational costs due to the operation at high cell densities (HCD) and improved productivities. HCDs are achieved by cell retention and continuous medium exchange, which is often based on the cell-specific perfusion rate (CSPR). To obtain a cost-productive process the perfusion rate must be determined for each process individually. However, determining optimal operating conditions remain labor-intensive and time-consuming experiments, as investigations are performed in lab-scale perfusion bioreactors. Small-scale models such as microwell plates (MWPs) provide an option for screening multiple perfusion rates in parallel in a semi-perfusion mimic. This study investigated two perfusion rate strategies applied to the MWP platform operated in semi-perfusion. The CSPR-based perfusion rate strategy aimed to maintain multiple CSPR values throughout the cultivation and was compared to a cultivation with a perfusion rate of 1 RV d-1. The cellular performance was investigated with the dual aim (i) to achieve HCD, when inoculating at conventional and HCDs, and (ii) to maintain HCDs, when applying an additional manual cell bleed. With both perfusion rate strategies viable cell concentrations up to 50 × 106 cells mL-1 were achieved and comparable results for key metabolites and antibody product titers were obtained. Furthermore, the combined application of cell bleed and CSPR-based medium exchange was successfully shown with similar results for growth, metabolites, and productivities, respectively, while reducing the medium consumption by up to 50% for HCD cultivations.

Application of bioreactor technology for cell culture-based viral vaccine production: Present status and future prospects

Bioreactors are widely used in cell culture-based viral vaccine production, especially during the coronavirus disease 2019 (COVID-19) pandemic. In this context, the development and application of bioreactors can provide more efficient and cost-effective vaccine production to meet the global vaccine demand. The production of viral vaccines is inseparable from the development of upstream biological processes. In particular, exploration at the laboratory-scale is urgently required for further development. Therefore, it is necessary to evaluate the existing upstream biological processes, to enable the selection of pilot-scale conditions for academic and industrial scientists to maximize the yield and quality of vaccine development and production. Reviewing methods for optimizing the upstream process of virus vaccine production, this review discusses the bioreactor concepts, significant parameters and operational strategies related to large-scale amplification of virus. On this basis, a comprehensive analysis and evaluation of the various process optimization methods for the production of various viruses (SARS-CoV-2, Influenza virus, Tropical virus, Enterovirus, Rabies virus) in bioreactors is presented. Meanwhile, the types of viral vaccines are briefly introduced, and the established animal cell lines for vaccine production are described. In addition, it is emphasized that the co-development of bioreactor and computational biology is urgently needed to meet the challenges posed by the differences in upstream production scales between the laboratory and industry.

Cell-line screening and process development for a fusogenic oncolytic virus in small-scale suspension cultures

Abstract

Oncolytic viruses (OVs) represent a novel class of immunotherapeutics under development for the treatment of cancers. OVs that express a cognate or transgenic fusion protein is particularly promising as their enhanced intratumoral spread via syncytia formation can be a potent mechanism for tumor lysis and induction of antitumor immune responses. Rapid and efficient fusion of infected cells results in cell death before high titers are reached. Although this is an attractive safety feature, it also presents unique challenges for large-scale clinical-grade manufacture of OVs. Here we evaluate the use of four different suspension cell lines for the production of a novel fusogenic hybrid of vesicular stomatitis virus and Newcastle disease virus (rVSV-NDV). The candidate cell lines were screened for growth, metabolism, and virus productivity. Permissivity was evaluated based on extracellular infectious virus titers and cell-specific virus yields (CSVYs). For additional process optimizations, virus adaptation and multiplicity of infection (MOI) screenings were performed and confirmed in a 1 L bioreactor. BHK-21 and HEK293SF cells infected at concentrations of 2 × 10⁶ cells/mL were identified as promising candidates for rVSV-NDV production, leading to infectious titers of 3.0 × 10⁸ TCID₅₀/mL and 7.5 × 10⁷ TCID₅₀/mL, and CSVYs of 153 and 9, respectively. Compared to the AGE1.CR.pIX reference produced in adherent cultures, oncolytic potency was not affected by production in suspension cultures and possibly even increased in cultures of HEK293SF and AGE1.CR.pIX. Our study describes promising suspension cell-based processes for efficient large-scale manufacturing of rVSV-NDV.

Key points

• Cell contact-dependent oncolytic virus (OV) replicates in suspension cells.

• Oncolytic potency is not encompassed during suspension cultivation.

• Media composition, cell line, and MOI are critical process parameters for OV production.

• The designed process is scalable and shows great promise for manufacturing clinical-grade material.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12027-5.

A high cell density perfusion process for Modified Vaccinia virus Ankara production: Process integration with inline DNA digestion and cost analysis

By integrating continuous cell cultures with continuous purification methods, process yields and product quality attributes have been improved over the last 10 years for recombinant protein production. However, for the production of viral vectors such as Modified Vaccinia virus Ankara (MVA), no such studies have been reported although there is an increasing need to meet the requirements for a rising number of clinical trials against infectious or neoplastic diseases. Here, we present for the first time a scalable suspension cell (AGE1.CR.pIX cells) culture-based perfusion process in bioreactors integrating continuous virus harvesting through an acoustic settler with semi-continuous chromatographic purification. This allowed obtaining purified MVA particles with a space-time yield more than 600% higher for the integrated perfusion process (1.05 × 10¹¹ TCID₅₀ /L_bioreactor /day) compared to the integrated batch process. Without further optimization, purification by membrane-based steric exclusion chromatography resulted in an overall product recovery of 50.5%. To decrease the level of host cell DNA before chromatography, a novel inline continuous DNA digestion step was integrated into the process train. A detailed cost analysis comparing integrated production in batch versus production in perfusion mode showed that the cost per dose for MVA was reduced by nearly one-third using this intensified small-scale process.

Process intensification for the production of yellow fever virus-like particles as potential recombinant vaccine antigen

Yellow fever (YF) is a life-threatening viral disease endemic in parts of Africa and Latin America. Although there is a very efficacious vaccine since the 1930s, YF still causes 29,000-60,000 annual deaths. During recent YF outbreaks there were issues of vaccine shortage of the current egg-derived vaccine; rare but fatal vaccine adverse effects occurred; and cases were imported to Asia, where the circulating mosquito vector could potentially start local transmission. Here we investigated the production of YF virus-like particles (VLPs) using stably transfected HEK293 cells. Process intensification was achieved by combining sequential FACS (fluorescence-activated cell sorting) rounds to enrich the stable cell pool in terms of high producers and the use of perfusion processes. At shaken-tube scale, FACS enrichment of cells allowed doubling VLP production, and pseudoperfusion cultivation (with daily medium exchange) further increased VLP production by 9.3-fold as compared to batch operation mode. At perfusion bioreactor scale, the use of an inclined settler as cell retention device showed operational advantages over an ATF system. A one-step steric exclusion chromatography purification allowed significant removal of impurities and is a promising technique for future integration of upstream and downstream operations. Characterization by different techniques confirmed the identity and 3D-structure of the purified VLPs.

Production of Modified Vaccinia Ankara Virus by Intensified Cell Cultures: A Comparison of Platform Technologies for Viral Vector Production

Modified Vaccinia Ankara (MVA) virus is a promising vector for vaccination against various challenging pathogens or the treatment of some types of cancers, requiring a high amount of virions per dose for vaccination and gene therapy. Upstream process intensification combining perfusion technologies, the avian suspension cell line AGE1.CR.pIX and the virus strain MVA-CR19 is an option to obtain very high MVA yields. Here the authors compare different options for cell retention in perfusion mode using conventional stirred-tank bioreactors. Furthermore, the authors study hollow-fiber bioreactors and an orbital-shaken bioreactor in perfusion mode, both available for single-use. Productivity for the virus strain MVA-CR19 is compared to results from batch and continuous production reported in literature. The results demonstrate that cell retention devices are only required to maximize cell concentration but not for continuous harvesting. Using a stirred-tank bioreactor, a perfusion strategy with working volume expansion after virus infection results in the highest yields. Overall, infectious MVA virus titers of 2.1-16.5 × 109  virions/mL are achieved in these intensified processes. Taken together, the study shows a novel perspective on high-yield MVA virus production in conventional bioreactor systems linked to various cell retention devices and addresses options for process intensification including fully single-use perfusion platforms.

Highly efficient production of an influenza H9N2 vaccine using MDCK suspension cells

The use of H9N2 subtype avian influenza vaccines is an effective approach for the control of the virus spread among the poultry, and for the upgrading of vaccine manufacturing, cell culture-based production platform could overcome the limitations of conventional egg-based platform and alternate it. The development of serum-free suspension cell culture could allow even higher virus productivity, where a suspension cell line with good performance and proper culture strategies are required. In this work, an adherent Mardin–Darby canine kidney (MDCK) cell line was adapted to suspension growth to cell concentration up to 12 × 106 cells/mL in a serum-free medium in batch cultures. Subsequently, the H9N2 influenza virus propagation in this MDCK cell line was evaluated with the optimization of infection conditions in terms of MOI and cell concentration for infection. Furthermore, various feed strategies were tested in the infection phase for improved virus titer and a maximum hemagglutinin titer of 13 log2 (HAU/50 μL) was obtained using the 1:2 medium dilution strategy. The evaluation of MDCK cell growth and H9N2 virus production in bioreactors with optimized operating conditions showed comparable cell performance and virus yield compared to shake flasks, with a high cell-specific virus yield above 13,000 virions/cell. With the purified H9N2 virus harvested from the bioreactors, the MDCK cell-derived vaccine was able to induce high titers of neutralizing antibodies in chickens. Overall, the results demonstrate the promising application of the highly efficient MDCK cell-based production platform for the avian influenza vaccine manufacturing.

Performance of an acoustic settler versus a hollow fiber-based ATF technology for influenza virus production in perfusion

Process intensification and integration is crucial regarding an ever increasing pressure on manufacturing costs and capacities in biologics manufacturing. For virus production in perfusion mode, membrane-based alternating tangential flow filtration (ATF) and acoustic settler are the commonly described cell retention technologies. While acoustic settlers allow for continuous influenza virus harvesting, the use of commercially available membranes for ATF systems typically results in the accumulation of virus particles in the bioreactor vessel. Accordingly, with one single harvest at the end of a cultivation, this increases the risk of lowering the product quality. To assess which cell retention device would be most suitable for influenza A virus production, we compared various key performance figures using AGE1.CR.pIX cells at concentrations between 25 and 50 × 106 cells/mL at similar infection conditions using either an ATF system or an acoustic settler. Production yields, process-related impurities, and aggregation of viruses and other large molecules were evaluated. Taking into account the total number of virions from both the bioreactor and the harvest vessel, a 1.5-3.0-fold higher volumetric virus yield was obtained for the acoustic settler. In addition, fewer large-sized aggregates (virus particles and other molecules) were observed in the harvest taken directly from the bioreactor. In contrast, similar levels of process-related impurities (host cell dsDNA, total protein) were obtained in the harvest for both retention systems. Overall, a clear advantage was observed for continuous virus harvesting after the acoustic settler operation mode was optimized. This development may also allow direct integration of subsequent downstream processing steps. KEY POINTS: • High suspension cell density, immortalized avian cell line, influenza vaccine.