Suspension culture process for H9N2 avian influenza virus (strain Re-2)

Metabolic reprogramming and alteration of the redox state in hyper-productive MDCK cells for influenza a virus production

Influenza is a global public health issue leading to widespread morbidity and mortality with devastating economic loss annually. Madin-Darby Canine Kidney (MDCK) cell line has been a major cell line for influenza vaccine applications. Though many details of the host metabolic responses upon influenza A virus (IAV) infection have been documented, little is known about the metabolic reprogramming features of a hyper-productive host for IAV vaccine production. In this study, a MDCK cell clone H1 was shown to have a particular high productivity of 30 × 10³ virions/cell. The glucose and amino acid metabolism of H1 were evaluated, indicating that the high producer had a particular metabolic reprogramming phenotype compared to its parental cell line (P): elevated glucose uptake, superior tricarboxylic acid cycle flux, moderate amino acid consumption, and better regulation of reactive oxygen species. Combined with the stronger mitochondrial function and mild antiviral and inflammatory responses characterized previously, our results indicated that the high producer had a sufficient intracellular energy supply, and balanced substrate distribution for IAV and host protein synthesis as well as the intracellular redox status. Understanding of these metabolic alterations paves the way for the rational cell line development and reasonable process optimization for high-yield influenza vaccine production.

Towards integrated production of an influenza A vaccine candidate with MDCK suspension cells

Seasonal influenza epidemics occur both in northern and southern hemispheres every year. Despite the differences in influenza virus surface antigens and virulence of seasonal subtypes, manufacturers are well-adapted to respond to this periodical vaccine demand. Due to decades of influenza virus research, the development of new influenza vaccines is relatively straight forward. In similarity with the ongoing coronavirus disease 2019 pandemic, vaccine manufacturing is a major bottleneck for a rapid supply of the billions of doses required worldwide. In particular, egg-based vaccine production would be difficult to schedule and shortages of other egg-based vaccines with high demands also have to be anticipated. Cell culture-based production systems enable the manufacturing of large amounts of vaccines within a short time frame and expand significantly our options to respond to pandemics and emerging viral diseases. In this study, we present an integrated process for the production of inactivated influenza A virus vaccines based on a Madin-Darby Canine Kidney (MDCK) suspension cell line cultivated in a chemically defined medium. Very high titers of 3.6 log₁₀ (HAU/100 µl) were achieved using fast-growing MDCK cells at concentrations up to 9.5 × 10⁶ cells/ml infected with influenza A/PR/8/34 H1N1 virus in 1 L stirred tank bioreactors. A combination of membrane-based steric-exclusion chromatography followed by pseudo-affinity chromatography with a sulfated cellulose membrane adsorber enabled full recovery for the virus capture step and up to 80% recovery for the virus polishing step. Purified virus particles showed a homogenous size distribution with a mean diameter of 80 nm. Based on a monovalent dose of 15 µg hemagglutinin (single-radial immunodiffusion assay), the level of total protein and host cell DNA was 58 µg and 10 ng, respectively. Furthermore, all process steps can be fully scaled up to industrial quantities for commercial manufacturing of either seasonal or pandemic influenza virus vaccines. Fast production of up to 300 vaccine doses per liter within 4-5 days makes this process competitive not only to other cell-based processes but to egg-based processes as well.

High cell density perfusion process for high yield of influenza A virus production using MDCK suspension cells

Similar to the recent COVID-19 pandemic, influenza A virus poses a constant threat to the global community. For the treatment of flu disease, both antivirals and vaccines are available with vaccines the most effective and safest approach. In order to overcome limitations in egg-based vaccine manufacturing, cell culture-based processes have been established. While this production method avoids egg-associated risks in face of pandemics, process intensification using animal suspension cells in high cell density perfusion cultures should allow to further increase manufacturing capacities worldwide. In this work, we demonstrate the development of a perfusion process using Madin-Darby canine kidney (MDCK) suspension cells for influenza A (H1N1) virus production from scale-down shake flask cultivations to laboratory scale stirred tank bioreactors. Shake flask cultivations using semi-perfusion mode enabled high-yield virus harvests (4.25 log₁₀(HAU/100 μL)) from MDCK cells grown up to 41 × 10⁶ cells/mL. Scale-up to bioreactors with an alternating tangential flow (ATF) perfusion system required optimization of pH control and implementation of a temperature shift during the infection phase. Use of a capacitance probe for on-line perfusion control allowed to minimize medium consumption. This contributed to a better process control and a more economical performance while maintaining a maximum virus titer of 4.37 log₁₀(HAU/100 μL) and an infectious virus titer of 1.83 × 10¹⁰ virions/mL. Overall, this study clearly demonstrates recent advances in cell culture-based perfusion processes for next-generation high-yield influenza vaccine manufacturing for pandemic preparedness. KEY POINTS: • First MDCK suspension cell-based perfusion process for IAV produciton was established. • "Cell density effect" was overcome and process was intensified by reduction of medium use and automated process control. • The process achieved cell density over 40 × 10⁶ cells/mL and virus yield over 4.37 log₁₀(HAU/100 μL).

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.