Increasing Vero viable cell densities for yellow fever virus production in stirred-tank bioreactors using serum-free medium

Sabin inactivated polio vaccine upstream process development using fixed-bed bioreactor technology

Eradication of polio disease remains a challenge for countries with limited health-care infrastructure. Regional vaccine production is expected to secure a sustainable and equitable availability of vaccines supporting the polio eradication end-game. Regional manufacturing of Inactivated Polio Vaccines based on the attenuated Sabin strains and using an isolator-based contained micro-facility is expected to avoid any potential risk of shortage of polio vaccines in the future, ensure equitable access to sufficient doses of IPV while securing a safe manufacturing environment. However, polio vaccine production requires biosafety level 3 containment and is complicated by the restrictions imposed from the adherent nature of the virus-producing Vero cell line. To overcome these issues that have hampered regional polio vaccine production so far, at Batavia Biosciences we developed an inactivated polio vaccine production process based on the polio Sabin strains in a contained microfacility. By incorporating a tangential flow filter coupled to a fixed-bed bioreactor with a large attachment surface area (150 m2), we could increase process efficiency and reduce the production footprint allowing for regional demand-driven production. The reduced square meters of the manufacturing site that handles the live virus were achieved by integrating the fixed-bed bioreactor with the concentration step (TFF). The increased efficiency was realized by using less resources, fully disposable virus production, and a down- and up-scalable process depending on vaccine demand. The here-developed scalable production process with reduced production footprint is considered a useful and cost-effective method for regional vaccine production, for example in pandemic preparedness efforts to efficiently contain virus outbreaks.

Safety and immunogenicity of different 17DD yellow fever vaccines in golden-headed tamarins (Leontopithecus chrysomelas): Inhibition of viremia and RNAemia after homologous live-attenuated vaccination

Yellow fever (YF) is a viral disease that affects both humans and non-human primates (NHPs). Neotropical monkeys are more severely stricken by YF and the impact of the disease can be devastating to the endangered golden-headed lion tamarins (GHLTs, Leontopithecus chrysomelas). Susceptible GHLTs were immunized with the commercial Brazilian YF 17DD live attenuated vaccine or two other experimental non-replicating YF vaccines: a purified whole-virus, b-propiolactone-inactivated vaccine and a plant-derived recombinant subunit vaccine. Safety, immunogenicity and viremia and RNAemia blockade were characterized. No YF clinical manifestations were observed in any of the GHLTs that received the attenuated virus, either as a vaccine or as the homologous vaccination with the live attenuated vaccine used as the challenge virus. All three concentrations of the attenuated vaccine induced neutralizing antibodies and only one in 16 animals had detectable viremia and RNAemia after challenge. The inactivated vaccine elicited neutralizing antibodies preventing post-challenge viremia and RNAemia in five out of six animals. The plant-based vaccine induced neutralizing antibodies in five out of six animals and prevented viremia and RNAemia in three out of six against challenge. The safety profile and the immunogenicity of the YF attenuated vaccine were demonstrated in GHLTs with a blocking effectiveness over 90 %, where blockade can be defined as the capacity to prevent viremia and RNAemia after homologous vaccination with the live attenuated vaccine. The use of the inactivated vaccine in this species served as a preliminary pre-clinical study for this approach and after administration in three-dose regimen demonstrated a blocking profile of 83 %. Using a two-dose regimen, the plant-based vaccine was able to block viremia and RNAemia in 50 % of the animals. The present study can endorse the use of attenuated or non-replicating yellow fever vaccines in New World primates threatened by the recent disease outbreaks in Brazil.

Thawing, Growth, and Maintenance of Vero Cell Lines

Vero cell line is derived from the kidney of an African green monkey and is one of the most common mammalian continuous cell lines used in research. Its deficiency in the production of type 1 interferons allows this cell line to be susceptible and permissible to replication of several viruses, including the yellow fever virus. Continuous cell culture in the laboratory can increase the risk of contamination, as well as loss of characteristics of interest in the strain. To minimize these risks a cultivation standard should be established. This chapter presents useful protocols for the maintenance of Vero cells for laboratorial routine, such as thawing vials from a cell bank stock, maintenance by subcultivation procedures, adaptation of the cells to grow in serum-free media, and production of cell culture plates for laboratory routine assays.

Investigation into the use of gamma irradiated Cytodex-1 microcarriers to produce a human cytomegalovirus (HCMV) vaccine candidate in epithelial cells

V160 is a viral vaccine candidate against human cytomegalovirus (HCMV) that is manufactured using Adult Retinal Pigment Epithelial cells (ARPE-19) grown on Cytodex-1 microcarriers. The microcarriers are generally hydrated, washed, and autoclaved prior to use, which can be limiting at large production scales. To minimize microcarrier preparation and sterilization, the use of gamma irradiated Cytodex-1 was investigated. Similar ARPE-19 cell growth was observed on heat-sterilized and gamma irradiated Cytodex-1; however, significantly reduced virus production was observed in cultures exposed to gamma irradiated Cytodex-1. Additional experiments suggest that infection inhibition is not exclusive to ARPE-19 but is most directly linked to HCMV V160, as evidenced by similar inhibition of V160 with Vero cells and no inhibition of Measles virus with either cell type. These observations suggest a putative impact on HCMV infection from the presence of extractable(s)/leachable(s) in the gamma irradiated microcarriers. Thorough aseptic rinsing of gamma irradiated Cytodex-1 prior to use can mitigate this impact and enable comparable process performance to heat-sterilized Cytodex-1. Though not fully a "ready-to-use" product for the HCMV V160 production process, utilization of Cytodex-1 microcarriers was possible without requiring heat sterilization, suggesting a potential path forward for large scale production of V160.

Development and scale-up of rVSV-SARS-CoV-2 vaccine process using single use bioreactor

The outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the Coronavirus Disease 2019 (COVID-19) has spread through the globe at an alarming speed. The disease has become a global pandemic affecting millions of people and created public health crises worldwide. Among many efforts to urgently develop a vaccine against this disease, we developed an industrial-scale closed, single use manufacturing process for V590, a vaccine candidate for SARS-CoV-2. V590 is a recombinant vesicular stomatitis virus (rVSV) genetically engineered to express SARS-CoV-2 glycoprotein. In this work, we describe the development and optimization of serum-free microcarrier production of V590 in Vero cells in a closed system. To achieve the maximum virus productivity, we optimized pH and temperature during virus production in 3 liters (L) bioreactors. Virus productivity was improved (by ∼1 log) by using pH 7.0 and temperature at 34.0 °C. The optimal production condition was successfully scaled up to a 2000 L Single Use Bioreactor (SUB), producing a maximum virus titer of ∼1.0e+7 plaque forming units (PFU)/mL. Further process intensification and simplification, including growing Vero cells at 2 gs per liter (g/L) of Cytodex-1 Gamma microcarriers and eliminating the media exchange (MX) step prior to infection helped to increase virus productivity by ∼2-fold.

Evaluation of Two Adjuvant Formulations for an Inactivated Yellow Fever 17DD Vaccine Candidate in Mice

The attenuated yellow fever (YF) vaccine is one of the most successful vaccines ever developed. After a single dose administration YF vaccine can induce balanced Th1/Th2 immune responses and long-lasting neutralizing antibodies. These attributes endorsed it as a model of how to properly stimulate the innate response to target protective immune responses. Despite their longstanding success, attenuated YF vaccines can cause rare fatal adverse events and are contraindicated for persons with immunosuppression, egg allergy and age < 6 months and >60 years. These drawbacks have encouraged the development of a non-live vaccine. The aim of the present study is to characterize and compare the immunological profile of two adjuvant formulations of an inactivated YF 17DD vaccine candidate. Inactivated YF vaccine formulations based on alum (Al(OH)3) or squalene (AddaVax®) were investigated by immunization of C57BL/6 mice in 3-dose or 2-dose schedules, respectively, and compared with a single dose of attenuated YF virus 17DD. Sera were analyzed by ELISA and Plaque Reduction Neutralization Test (PRNT) for detection of total IgG and neutralizing antibodies against YF virus. In addition, splenocytes were collected to evaluate cellular responses by ELISpot. Both inactivated formulations were able to induce high titers of IgG against YF, although neutralizing antibodies levels were borderline on pre-challenge samples. Analysis of IgG subtypes revealed a predominance of IgG2a associated with improved neutralizing capacity in animals immunized with the attenuated YF vaccine, and a predominance of IgG1 in groups immunized with experimental non-live formulations (alum and AddaVax®). After intracerebral (IC) challenge, attenuated and inactivated vaccine formulations showed an increase in neutralizing antibodies. The AddaVax®-based inactivated vaccine and the attenuated vaccine achieved 100% protection, and alum-based equivalent formulation achieved 70% protection.

Pseudorabies virus production using a serum-free medium in fixed-bed bioreactors with low cell inoculum density

Fixed-bed bioreactors packed with macrocarriers show great potential to be used for vaccine process development and large-scale production due to distinguishing features of low shear force, high cell adhering surface area, and easy replacement of culture media in situ. As an initial step of utilizing this type of bioreactors for Pseudorabies virus production (PRV) by African green monkey kidney (Vero) cells, we developed a tube-fixed-bed bioreactor in the previous study, which represents a scale-down model for further process optimization. By using this scale-down model, here we evaluated impacts of two strategies (use of serum-free medium and low cell inoculum density) on PRV production, which have benefits of simplifying downstream process and reducing risk of contamination. We first compared Vero cell cultures with different media, bioreactors and inoculum densities, and conclude that cell growth with serum-free medium is comparable to that with serum-containing medium in tube-fixed-bed bioreactor, and low inoculum density supports cell growth only in this bioreactor. Next, we applied serum-free medium and low inoculum cell density for PRV production. By optimization of time of infection (TOI), multiplicity of infection (MOI) and the harvesting strategy, we obtained total amount of virus particles ~ 9 log₁₀ TCID₅₀ at 5 days post-infection (dpi) in the tube-fixed-bed bioreactor. This process was then scaled up by 25-fold to a Xcell 1-L fixed-bed bioreactor, which yields totally virus particles of 10.5 log₁₀ TCID_50, corresponding to ~ 3 × 10⁵ doses of vaccine. The process studied in this work holds promise to be developed as a generic platform for the production of vaccines for animal and human health.

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.

Cell culture-based viral vaccines: current status and future prospects

Cell culture-based viral vaccines are used globally to immunize humans against infections. The cell culture is continuous process of developing substrates for the safe production of viral vaccines. However, increased global demand and strict safety rules for novel vaccines to control and eradicate viral diseases have forced researchers and manufacturers toward cell culture-based vaccines. The choice of cell substrate is a critical step that cannot be generalized for every vaccine formulation, therefore, manufacturers intend to optimize the required processes for particular applications. The recently established cell lines, innovative bioreactor concepts and cultivation schemes are necessary to increase the potential of vaccine production. In this review, we have focused on current cell culture-based viral vaccines and their future prospects.

Cell substrates for the production of viral vaccines

Vaccines have been used for centuries to protect people and animals against infectious diseases. For vaccine production, it has become evident that cell culture technology can be considered as a key milestone and has been the result of decades of progress. The development and implementation of cell substrates have permitted massive and safe production of viral vaccines. The demand in new vaccines against emerging viral diseases, the increasing vaccine production volumes, and the stringent safety rules for manufacturing have made cell substrates mandatory viral vaccine producer factories. In this review, we focus on cell substrates for the production of vaccines against human viral diseases. Depending on the nature of the vaccine, choice of the cell substrate is critical. Each manufacturer intending to develop a new vaccine candidate should assess several cell substrates during the early development phase in order to select the most convenient for the application. First, as vaccine safety is quite naturally a central concern of Regulatory Agencies, the cell substrate has to answer the regulatory rules stringency. In addition, the cell substrate has to be competitive in terms of viral-specific production yields and manufacturing costs. No cell substrate, even the so-called "designer" cell lines, is able to fulfil all the requested criteria for all viral vaccines. Therefore, the availability of a variety of cell substrates for vaccine production is essential because it improves the chance to successfully respond to the current and future needs of vaccines linked to new emerging or re-emerging infectious diseases (e.g. pandemic flu, Ebola, and Chikungunya outbreaks).