Process optimization for the rapid production of adenoviral vectors for clinical trials in a disposable bioreactor system

Development of Adenovirus-Based Covid-19 Vaccine Candidate in Indonesia

Covid-19 pandemic has struck worldwide by end of 2019 and the use of various vaccine platforms was one of the main strategies to end this. To meet the needs for vaccine technology equality among many countries, we developed adenovirus-based Covid-19 vaccine candidate in Indonesia. SARS-CoV-2 Spike gene (S) was constructed into pAdEasy vector. The recombinant serotype 5 Adenovirus (AdV_S) genome was transfected into AD293 cells to produce recombinant adenovirus. Characterization using PCR confirmed the presence of spike gene. Transgene expression analysis showed the expression of S protein in AdV_S infected AD293 and A549 cells. Optimization of viral production showed the highest titer was obtained at MOI of 0.1 and 1 at 4 days. The in vivo study was performed by injecting Balb/c mice with 3.5 × 107 ifu of purified adenovirus. The result showed that S1-specific IgG was increased up to 56 days after single-dose administration of AdV_S. Interestingly, significant increase of S1 glycoprotein-specific IFN-γ ELISpot was observed in AdV_S treated Balb/c mice. In conclusion, the AdV_S vaccine candidate was successfully produced at laboratory scale, immunogenic, and did not cause severe inflammation in Balb/c mice. This study serves as initial step towards manufacturing of adenovirus-based vaccine in Indonesia.

Rapid and inexpensive purification of adenovirus vectors using an optimised aqueous two-phase technology

Adenoviruses (AdVs) are used as gene therapy vectors to treat human diseases and as vaccines against COVID-19. AdVs are produced by transfecting human embryonic kidney 239 (HEK293) or PER.C6 virus producer cells with AdV plasmid vectors or infecting these cells withcell lysates containing replication-defective AdV. Cell lysates can be purified further by caesium chloride or chromatographic protocols to research virus seed stocks (RVSS) for characterisation to high quality master virus seed stocks (MVSS) and working virus seed stocks (WVSS) before downstream production of pure, high titre AdV. Lysates are poorly infectious, block filtration columns and have limited storage capability. Aqueous two-phase systems (ATPS) are an alternative method for AdV purification that rapidly generates cleaner RVSS for characterisation to MVSS. After testing multiple ATPS formulations, an aqueous mixture of 20 % PEG 600 and 20 % (NH₄)₂SO₄ (w/w) was found most effective for AdV partitioning, producing up to 97+3% yield of high-titre virus that was devoid of aggregates both effective in vitro and in vivo with no observable cytotoxicity. Importantly, AdV preparations stored at -20 °C or 4 °C show negligible loss of titre and are suitable for downstream processing to clinical grade to support the need for AdV vaccines.

Optimization of Vero Cells Grown on a Polymer Fiber Carrier in a Disposable Bioreactor for Inactivated Coxsackievirus A16 Vaccine Development

At present, there are no vaccines available for hand, foot, and mouth disease, which is caused by Coxsackie virus A16 (CVA16) infection. In the present study, we isolated epidemic strains of CVA16 and optimized the production of the virus in Vero cells. The system comprised growing the infected cells on polymer fiber paper carriers in a serum-free medium containing 0.5% (w/v) lactalbumin hydrolysate a mini bioreactor. Disposable Bioflo310 and AmProtein Current perfusion bioreactors were used to monitor virus infection and Vero cell culture. The total number of cells increased from 1.5 × 10⁹ to 3.0 × 10¹⁰. In our optimized culture process, the virus titer reached 7.8 × 10⁷ TCID₅₀/mL at three days after infection. The inactivated CVA16 prepared from our optimized culture procedure elicited a slightly higher neutralizing antibody titer compared with that derived from routine culture procedures. These results will promote the large-scale production of inactivated CVA16 vaccines using nonwoven polymer fiber paper cell cultures.

Viral Vectors for COVID-19 Vaccine Development

Vaccine development against SARS-CoV-2 has been fierce due to the devastating COVID-19 pandemic and has included all potential approaches for providing the global community with safe and efficient vaccine candidates in the shortest possible timeframe. Viral vectors have played a central role especially using adenovirus-based vectors. Additionally, other viral vectors based on vaccinia viruses, measles viruses, rhabdoviruses, influenza viruses and lentiviruses have been subjected to vaccine development. Self-amplifying RNA virus vectors have been utilized for lipid nanoparticle-based delivery of RNA as COVID-19 vaccines. Several adenovirus-based vaccine candidates have elicited strong immune responses in immunized animals and protection against challenges in mice and primates has been achieved. Moreover, adenovirus-based vaccine candidates have been subjected to phase I to III clinical trials. Recently, the simian adenovirus-based ChAdOx1 vector expressing the SARS-CoV-2 S spike protein was approved for use in humans in the UK.

Process optimization for the rapid production of Enterovirus 71

Enterovirus 71 (EV71) infection can cause hand-foot-and-mouth disease (HFMD). Inactivated EV71 vaccine was effective to prevent EV71 derived HFMD. A highly efficient and economical process for producing EV71 is needed. In our study, the epidemic strain of EV71 (EV71-2013ZJHFMD) was obtained and purified. The Vero cells were cultured for production of EV71. The mini-bioreactor vessel (Amprotein Inc., China) packed with a 0.6 g polymer fiber carrier was used to determine the best seeding cell density, multiplicity of infection (MOI) and temperature. Then the optimized procedure was further applied in a 10 L disposable perfusion bioreactor ACPB (AmProtein Current Perfusion Bioreactor). The Vero cell culture and viral titer were monitored. The seeding density of 1.5 × 10⁷ cells per 0.6 g disk was considered to be the most appropriate for the culture. The best MOI was 0.1 and the temperature was 32 °C. The total cell number increased from 1.5 × 10⁹ to 3.0 × 10¹⁰. The maximum viral titers reached 1.0 × 10⁸/mL 3 days post-infection in our optimized special culture procedure (serum-free during the harvest period, supplemented with 0.25% Lactalbumin Hydrolysate). The total volume of the harvested supernatant was 25 L and the total virus yield was 1.93 × 10¹². The procedure using Vero cells grown on polymer fiber paper carriers was effective for the large-scale production of EV71.