Enhancing enterovirus A71 vaccine production yield by microcarrier profusion bioreactor culture

The trajectory patterns of single HIV-1 virus-like particle in live CD4 cells: A real time three-dimensional multi-resolution microscopy study using encapsulated nonblinking giant quantum dot

BACKGROUND

The exploration of virology knowledge was limited by the optical technology for the observation of virus. Previously, a three-dimensional multi-resolution real-time microscope system (3D-MRM) was developed to observe the uptake of HIV-1-tat peptide-modified nanoparticles in cell membrane. In this study, we labeled HIV-1 virus-like particles (VLPs) with passivated giant quantum dots (gQDs) and recorded their interactive trajectories with human Jurkat CD4 cells through 3D-MRM.

METHODS

The labeled of gQDs of the HIV-1 VLPs in sucrose-gradient purified viral lysates was first confirmed by Cryo-electronic microscopy and Western blot assay. After the infection with CD4 cells, the gQD-labeled VLPs were visualized and their extracellular and intracellular trajectories were recorded by 3D-MRM.

RESULTS

A total of 208 prime trajectories was identified and classified into three distinct patterns: cell-free random diffusion pattern, directional movement pattern and cell-associated movement pattern, with distributions and mean durations were 72.6%/87.6 s, 9.1%/402.7 s and 18.3%/68.7 s, respectively. Further analysis of the spatial-temporal relationship between VLP trajectories and CD4 cells revealed the three stages of interactions: (1) cell-associated (extracellular) diffusion stage, (2) cell membrane surfing stage and (3) intracellular directional movement stage.

CONCLUSION

A complete trajectory of HIV-1 VLP interacting with CD4 cells was presented in animation. This encapsulating method could increase the accuracy for the observation of HIV-1-CD4 cell interaction in real time and three dimensions.

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.

Vero cell upstream bioprocess development for the production of viral vectors and vaccines

The Vero cell line is considered the most used continuous cell line for the production of viral vectors and vaccines. Historically, it is the first cell line that was approved by the WHO for the production of human vaccines. Comprehensive experimental data on the production of many viruses using the Vero cell line can be found in the literature. However, the vast majority of these processes is relying on the microcarrier technology. While this system is established for the large-scale manufacturing of viral vaccine, it is still quite complex and labor intensive. Moreover, scale-up remains difficult and is limited by the surface area given by the carriers. To overcome these and other drawbacks and to establish more efficient manufacturing processes, it is a priority to further develop the Vero cell platform by applying novel bioprocess technologies. Especially in times like the current COVID-19 pandemic, advanced and scalable platform technologies could provide more efficient and cost-effective solutions to meet the global vaccine demand. Herein, we review the prevailing literature on Vero cell bioprocess development for the production of viral vectors and vaccines with the aim to assess the recent advances in bioprocess development. We critically underline the need for further research activities and describe bottlenecks to improve the Vero cell platform by taking advantage of recent developments in the cell culture engineering field.

Rapid process development of serum-free pseudorabies virus production with the Quality by Design approach

This study described a successful application of the Quality by Design (QbD) approach to pseudorabies virus (PRV) production process development in a fixed-bed bioreactor using the serum-free medium (SFM). The innovated tube-fixed-bed bioreactor was used as a scale-down model of the fixed-bed bioreactor for process development. Risk analysis was performed using Ishikawa diagram combined with failure mode effects analysis (FMEA). The comparative experiment was performed to screen proper medium for adherent African green monkey kidney (Vero) cells from three commercially available SFMs (VP-SFM, ProVERO-1 and Vero-A). The Vero-A medium showed as an outstanding one for further study. The PRV titer in harvest medium was consider as Critical Quality Attribute (CQA) and the Critical Process Parameters (CPPs) [time of infection (TOI), multiplicity of infection (MOI) and initial inoculation cell density] ranked high with risk priority number (RPN) were taken into design of experiment (DoE) methodology. Then prediction model of PRV production process was established and a robust PRV production process was explored. Under the robust setpoint conditions, the Xcell 1 L laboratory-scale fixed-bed bioreactor yielded PRV titer up to 7.87 log₁₀ TCID₅₀/mL at 3 dpi, which was comparable with that in the tube-fixed-bed bioreactor. Combination of the tube-fixed-bed bioreactor and QbD approach could further accelerate the development of a robust virus production process.

Production Process Development of Pseudorabies Virus Vaccine by Using a Novel Scale-Down Model of a Fixed-Bed Bioreactor

In this study, a novel tube-fixed-bed bioreactor which consists of a TubeSpin bioreactor 50 tube and 0.44 g macrocarriers was developed as the scale-down model of a fixed-bed bioreactor. The adherent Vero cell-based pseudorabies virus (PRV) production process was tested in this novel model. The Vero cells grew well in the tube-fixed-bed bioreactor, and the cell density reached 5.8 × 10⁶ cells/mL after 7 days of culture. The PRV production parameters (time of infection, multiplicity of infection, and harvest process) were optimized in the tube-fixed-bed bioreactor. Then the optimized process (time of infection = 3 days, multiplicity of infection = 0.001 and multiple harvest process) was scaled up 25-fold to an Xcell 1-L laboratory-scale fixed-bed bioreactor and 125-fold to an Xcell 5-L fixed-bed bioreactor successfully. The total PRV harvest in the Xcell 1-L bioreactor at 5 days after infection (dpi) was 10.25 log₁₀ TCID₅₀ which corresponds to 177,827 doses of vaccine. The total PRV harvest in the Xcell 5-L bioreactor at 5 dpi was 11.13 log₁₀ TCID₅₀ which corresponded to 1,348,962 doses of vaccine. The comparable growth curve, metabolism, and PRV production profile of the scaled-up bioreactors confirmed the feasibility and scalability of the tube-fixed-bed bioreactor as a scale-down model of the fixed-bed bioreactor for virus production process development.

Immunogenicity and safety of an inactivated enterovirus A71 vaccine in children 3-6 years and 2-35 months of age- an open-label, randomized phase IIb clinical trial

BACKGROUND

Enterovirus A71 (EV-A71) infection can cause severe debilitating complications and even death in young children. The immunogenicity and safety of an inactivated whole EV-A71 virus vaccine were assessed in children 2 months to 6 years of age.

METHODS

This was an open-label, multi-center and randomized phase IIb study, which divided into part A and B. In part A, children 36 months to 6 years of age were enrolled and randomized into 3 groups, receiving 0.5 μg total viral protein (TP) with adjuvant Al(OH)3, 1.0 μg TP with Al(OH)3 or 1.0 μg TP only. Two doses of vaccines were administered at a 28-day interval and blood was taken before immunization, at week 4, 8, 28 and 52 (optional) for virus neutralization assay. Safety profiles were also monitored. After safety profiles had shown no concerns, children 2 months to 35 months of age (part B) were subsequently enrolled following the same protocol.

RESULTS

A total of 135 children completed two doses of immunization, including 58 in part A and 77 in part B. Both adjuvanted 0.5 μg and 1.0 μg TP elicited significant raise of neutralizing antibody titers and seroconversion rate was up to 93.75-100.0% after 2 doses of immunization. Adjuvanted 1.0 μg TP induced higher titers of neutralizing antibodies than adjuvanted 0.5 μg TP. By contrast, non-adjuvanted 1.0 μg TP was not immunogenic. No major adverse events were reported.

CONCLUSIONS

This EV-A71 vaccine containing adjuvant is immunogenic and safe in children 2 months to 6 years of age.

CLINICAL TRIALS REGISTRATION

NCT03268083.

Adaptation of Vero cells to suspension growth for rabies virus production in different serum free media

Vero cells are nowadays widely used in the production of human vaccines. They are considered as one of the most productive and flexible continuous cell lines available for vaccine manufacturing. However, these cells are anchorage dependent, which greatly complicates upstream processing and process scale-up. Moreover, there is a recognized need to reduce the costs of vaccine manufacturing to develop vaccines that are affordable worldwide. The use of cell lines adapted to suspension growth contributes to reach this objective. The current work describes the adaptation of Vero cells to suspension culture in different serum free media according to multiple protocols based on subsequent passages. The best one that relies on cell adaption to IPT-AFM an in-house developed animal component free medium was then chosen for further studies. Besides, as aggregates have been observed, the improvement of IPT-AFM composition and mechanical dissociation were also investigated. In addition to IPT-AFM, three chemically defined media (CD293, Hycell CHO and CD-U5) and two serum free media (293SFMII and SFM4CHO) were tested to set up a serum free culture of the suspension-adapted Vero cells (VeroS) in shake flasks. Cell density levels higher than 2 × 10⁶ cells/mL were obtained in the assessed conditions. The results were comparable to those obtained in spinner culture of adherent Vero cells grown on Cytodex 1 microcarriers. Cell infection with LP-2061 rabies virus strain at an MOI (Multiplicity of Infection) of 0.1 and a cell density of 8 ± 0.5 × 10⁵ cells/mL resulted in a virus titer higher than 10⁷ FFU/mL in all media tested. Nevertheless, the highest titer equal to 5.2 ± 0.5 × 10⁷ FFU/mL, was achieved in IPT-AFM containing a reduced amount of Ca⁺⁺ and Mg⁺⁺. Our results demonstrate the suitability of the obtained VeroS cells to produce rabies virus at a high titer, and pave the way to develop VeroS cells bioreactor process for rabies vaccine production.