Effect of refeed strategies and non-ammoniagenic medium on adenovirus production at high cell densities

Optimization of Culture Media and Feeding Strategy for High Titer Production of an Adenoviral Vector in HEK 293 Fed-Batch Culture

Adenoviruses are efficient and safe vectors for delivering target antigens and adenovirus-based vaccines have been used against a wide variety of pathogens, including tuberculosis and COVID-19. Cost-effective and scalable biomanufacturing processes are critical for the commercialization of adenovirus-vectored vaccines. Adenoviral vectors are commonly produced through the infection of batch cultures at low cell density cultures, mostly because infections at high cell densities result in reduced cell-specific virus productivity and does not improve volumetric productivity. In this study, we have investigated the feasibility of improving the volumetric productivity by infecting fed-batch cultures at high cell densities. Four commercial and one in-house developed serum-free media were first tested for supporting growth of HEK 293 cells and production of adenovirus type 5 (Ad5) in batch culture. Two best media were then selected for development of fed-batch culture to improve cell growth and virus productivity. A maximum viable cell density up to 16 × 106 cells/mL was achieved in shake flask fed-batch cultures using the selected media and commercial or in-house developed feeds. The volumetric virus productivity was improved by up to six folds, reaching 3.0 × 1010 total viral particles/mL in the fed-batch culture cultivated with the media and feeds developed in house and infected at a cell density of 5 × 106 cells/mL. Additional rounds of optimization of media and feed were required to maintain the improved titer when the fed-batch culture was scaled up in a bench scale (3 L) bioreactor. Overall, the results suggested that fed-batch culture is a simple and feasible process to significantly improve the volumetric productivity of Ad5 through optimization and balance of nutrients in culture media and feeds.

Accelerated and intensified manufacturing of an adenovirus-vectored vaccine to enable rapid outbreak response

The Coalition for Epidemic Preparedness Innovations' "100-day moonshot" aspires to launch a new vaccine within 100 days of pathogen identification, followed by large-scale vaccine availability within the "second hundred days." Here, we describe work to optimize adenoviral vector manufacturing for rapid response, by minimizing time to clinical trial and first large-scale supply, and maximizing output from the available manufacturing footprint. We describe a rapid virus seed expansion workflow that allows vaccine release to clinical trials within 60 days of antigen sequence identification, followed by vaccine release from globally distributed sites within a further 40 days. We also describe a perfusion-based upstream production process, designed to maximize output while retaining simplicity and suitability for existing manufacturing facilities. This improves upstream volumetric productivity of ChAdOx1 nCoV-19 by approximately fourfold and remains compatible with the existing downstream process, yielding drug substance sufficient for 10,000 doses from each liter of bioreactor capacity. This accelerated manufacturing process, along with other advantages such as thermal stability, supports the ongoing value of adenovirus-vectored vaccines as a rapidly adaptable and deployable platform for emergency response.

High-Titer Recombinant Adenovirus 26 Vector GMP Manufacturing in HEK 293 Cells with a Stirred Single-Use Bioreactor for COVID-19 Vaccination Purposes

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 virus) pandemic has shown the importance of pursuing various vaccine manufacturing strategies. In the present study, the HEK 293 cells were infected with recombinant adenovirus serotype 26 (rAd26), and the effects of critical process parameters (CPPs) including viable cell density (VCD) at infection time (0.5 × 106, 0.8 × 106, 1.4 × 106, 1.8 × 106, and 2.5 × 106 cells/mL), the multiplicity of infection (MOI) = 3, 6, 9, 12, and 15, and two aeration strategies (high-speed agitation with a sparging system and low-speed agitation with an overlay system) were investigated experimentally. The results of small-scale experiments in 2 L shake flasks (SF 2L) demonstrated that the initial VCD and MOI could affect the cell proliferation and viability. The results at these experiments showed that VCD = 1.4 × 106 cells/mL and MOI = 9 yielded TCID50 /mL = 108.9, at 72 h post-infection (hpi), while the virus titer at VCD = 0.5 × 106 and 0.8 × 106 cells/mL was lower compared to that of VCD = 1.4 × 106 cells/mL. Moreover, our findings showed that VCDs > 1.8 × 106 cells/m with MOI = 9 did not have a positive effect on TCID50 /mL and MOI = 3 and 6 were less efficient, whereas MOI > 12 decreased the viability drastically. In the next step, the optimized CPPs in a small scale were exploited in a 200 L single-use bioreactor (SUB), with good manufacturing practice (GMP) conditions, at RPM = 25 with an overlay system, yielding high-titer rAd26 manufacturing, i.e., TCID50/mL = 108.9, at 72 hpi.

Perfusion Control for High Cell Density Cultivation and Viral Vaccine Production

The global demand for complex biopharmaceuticals like recombinant proteins, vaccines, or viral vectors is steadily rising. To further improve process productivity and to reduce production costs, process intensification can contribute significantly. The design and optimization of perfusion processes toward very high cell densities require careful selection of strategies for optimal perfusion rate control. In this chapter, various options are discussed to guarantee high cell-specific virus yields and to achieve virus concentrations up to 10¹⁰ virions/mL. This includes reactor volume exchange regimes and perfusion rate control based on process variables such as cell concentration and metabolite or by-product concentration. Strategies to achieve high cell densities by perfusion rate control and their experimental implementation are described in detail for pseudo-perfusion or small-scale perfusion bioreactor systems. Suspension cell lines such as MDCK, BHK-21, EB66^®, and AGE1.CR.pIX^® are used to exemplify production of influenza, yellow fever, Zika, and modified vaccinia Ankara virus.

Efficient influenza A virus production in high cell density using the novel porcine suspension cell line PBG.PK2.1

Seasonal and pandemic influenza respiratory infections are still a major public health issue. Vaccination is the most efficient way to prevent influenza infection. One option to produce influenza vaccines is cell-culture based virus propagation. Different host cell lines, such as MDCK, Vero, AGE1.CR or PER.C6 cells have been shown to be a good substrate for influenza virus production. With respect to the ease of scale-up, suspension cells should be preferred over adherent cells. Ideally, they should replicate different influenza virus strains with high cell-specific yields. Evaluation of new cell lines and further development of processes is of considerable interest, as this increases the number of options regarding the design of manufacturing processes, flexibility of vaccine production and efficiency. Here, PBG.PK2.1, a new mammalian cell line that was developed by ProBioGen AG (Germany) for virus production is presented. The cells derived from immortal porcine kidney cells were previously adapted to growth in suspension in a chemically-defined medium. Influenza virus production was improved after virus adaptation to PBG.PK2.1 cells and optimization of infection conditions, namely multiplicity of infection and trypsin concentration. Hemagglutinin titers up to 3.24 log₁₀(HA units/100 µL) were obtained in fed-batch mode in bioreactors (700 mL working volume). Evaluation of virus propagation in high cell density culture using a hollow-fiber based system (ATF2) demonstrated promising performance: Cell concentrations of up to 50 × 10⁶ cells/mL with viabilities exceeding 95%, and a maximum HA titer of 3.93 log₁₀(HA units/100 µL). Analysis of glycosylation of the viral HA antigen expressed showed clear differences compared to HA produced in MDCK or Vero cell lines. With an average cell-specific productivity of 5000 virions/cell, we believe that PBG.PK2.1 cells are a very promising candidate to be considered for next-generation influenza virus vaccine production.

Combining metabolic and process engineering strategies to improve recombinant glycoprotein production and quality

Increasing recombinant protein production while ensuring a high and consistent protein quality remains a challenge in mammalian cell culture process development. In this work, we combined a nutrient substitution approach with a metabolic engineering strategy that improves glucose utilization efficiency. This combination allowed us to tackle both lactate and ammonia accumulation and investigate on potential synergistic effects on protein production and quality. To this end, HEK293 cells overexpressing the pyruvate yeast carboxylase (PYC2) and their parental cells, both stably producing the therapeutic glycoprotein interferon α2b (IFNα2b), were cultured in media deprived of glutamine but containing chosen substitutes. Among the tested substitutes, pyruvate led to the best improvement in growth (integral of viable cell density) for both cell lines in batch cultures, whereas the culture of PYC2 cells without neither glutamine nor any substitute displayed surprisingly enhanced IFNα2b production. The drastic reduction in both lactate and ammonia in the cultures translated into extended high viability conditions and an increase in recombinant protein titer by up to 47% for the parental cells and the PYC2 cells. Product characterization performed by surface plasmon resonance biosensing using Sambucus nigra (SNA) lectin revealed that the increase in yield was however accompanied by a reduction in the degree of sialylation of the product. Supplementing cultures with glycosylation precursors and a cofactor were effective at counterbalancing the lack of glutamine and allowed improvement in IFNα2b quality as evaluated by lectin affinity. Our study provides a strategy to reconcile protein productivity and quality and highlights the advantages of PYC2-overexpressing cells in glutamine-free conditions.

Influenza viruses production: Evaluation of a novel avian cell line DuckCelt®-T17

The influenza vaccine manufacturing industry is looking for production cell lines that are easily scalable, highly permissive to multiple viruses, and more effective in term of viral productivity. One critical characteristic of such cell lines is their ability to grow in suspension, in serum free conditions and at high cell densities. Influenza virus causing severe epidemics both in human and animals is an important threat to world healthcare. The repetitive apparition of influenza pandemic outbreaks in the last 20years explains that manufacturing sector is still looking for more effective production processes to replace/supplement embryonated egg-based process. Cell-based production strategy, with a focus on avian cell lines, is one of the promising solutions. Three avian cell lines, namely duck EB66®cells (Valneva), duck AGE.CR® cells (Probiogen) and quail QOR/2E11 cells (Baxter), are now competing with traditional mammalian cell platforms (Vero and MDCK cells) used for influenza vaccine productions and are currently at advance stage of commercial development for the manufacture of influenza vaccines. The DuckCelt®-T17 cell line presented in this work is a novel avian cell line developed by Transgene. This cell line was generated from primary embryo duck cells with the constitutive expression of the duck telomerase reverse transcriptase (dTERT). The DuckCelt®-T17 cells were able to grow in batch suspension cultures and serum-free conditions up to 6.5×10⁶cell/ml and were easily scaled from 10ml up to 3l bioreactor. In the present study, DuckCelt®-T17 cell line was tested for its abilities to produce various human, avian and porcine influenza strains. Most of the viral strains were produced at significant infectious titers (>5.8 log TCID50/ml) with optimization of the infection conditions. Human strains H1N1 and H3N2, as well as all the avian strains tested (H5N2, H7N1, H3N8, H11N9, H12N5) were the most efficiently produced with highest titre reached of 9.05 log TCID50/ml for A/Panama/2007/99 influenza H3N2. Porcine strains were also greatly rescued with titres from 4 to 7 log TCID50/ml depending of the subtypes. Interestingly, viral kinetics showed maximal titers reached at 24h post-infection for most of the strains, allowing early harvest time (Time Of Harvest: TOH). The B strains present specific production kinetics with a delay of 24h before reaching the maximal viral particle release. Process optimization on H1N1 2009 human pandemic strain allowed identifying best operating conditions for production (MOI, trypsin concentration, cell density at infection) allowing improving the production level by 2 log. Our results suggest that the DuckCelt®-T17 cell line is a very promising platform for industrial production of influenza viruses and particularly for avian viral strains.

Viruses and Virus-Like Particles in Biotechnology: Fundamentals and Applications

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this chapter, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitoring, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Process Development of Adenoviral Vector Production in Fixed Bed Bioreactor: From Bench to Commercial Scale

Large-scale vector manufacturing for phase III and beyond has proven to be challenging. Upscaling the process with suspension cells is increasingly feasible, but many viral production applications are still applicable only in adherent settings. Scaling up the adherent system has proven to be troublesome. The iCELLis(®) disposable fixed-bed bioreactors offer a possible option for viral vector manufacturing in large quantities in an adherent environment. In this study, we have optimized adenovirus serotype 5 manufacturing using iCELLis Nano with a cultivation area up to 4 m(2). HEK293 cell cultivation, infection, and harvest of the virus (by lysing the cells inside the bioreactor) proved possible, reaching total yield of up to 1.6×10(14) viral particles (vp)/batch. The iCELLis 500 is designed to satisfy demand for large-scale requirements. Inoculating a large quantity of cell mass into the iCELLis 500 was achieved by first expanding the cell mass in suspension. Upscaling the process into an iCELLis 500/100 m(2) cultivation area cassette was practical and produced up to 6.1×10(15) vp. Flask productivity per cm(2) in iCELLis Nano and iCELLis 500 was in the same range. As a conclusion, we showed for the first time that iCELLis 500 equipment has provided an effective way to manufacture large batches of adenoviral vectors.

Impact of Adenovirus infection in host cell metabolism evaluated by (1)H-NMR spectroscopy

Adenovirus-based vectors are powerful vehicles for gene transfer applications in vaccination and gene therapy. Although highly exploited in the clinical setting, key aspects of the adenovirus biology are still not well understood, in particular the subversion of host cell metabolism during viral infection and replication. The aim of this work was to gain insights on the metabolism of two human cell lines (HEK293 and an amniocyte-derived cell line, 1G3) after infection with an adenovirus serotype 5 vector (AdV5). In order to profile metabolic alterations, we used (1)H-NMR spectroscopy, which allowed the quantification of 35 metabolites in cell culture supernatants with low sample preparation and in a relatively short time. Significant differences between both cell lines in non-infected cultures were identified, namely in glutamine and acetate metabolism, as well as by-product secretion. The main response to AdV5 infection was an increase in glucose consumption and lactate production rates. Moreover, cultures performed with or without glutamine supplementation confirmed the exhaustion of this amino acid as one of the main causes of lower AdV5 production at high cell densities (10- and 1.5-fold less specific yields in HEK293 and 1G3 cells, respectively), and highlighted different degrees of glutamine dependency of adenovirus replication in each cell line. The observed metabolic alterations associated with AdV5 infection and specificity of the host cell line can be useful for targeted bioprocess optimization.

Metabolic flux profiling of MDCK cells during growth and canine adenovirus vector production

Canine adenovirus vector type 2 (CAV2) represents an alternative to human adenovirus vectors for certain gene therapy applications, particularly neurodegenerative diseases. However, more efficient production processes, assisted by a greater understanding of the effect of infection on producer cells, are required. Combining [1,2-(13)C]glucose and [U-(13)C]glutamine, we apply for the first time (13)C-Metabolic flux analysis ((13)C-MFA) to study E1-transformed Madin-Darby Canine Kidney (MDCK) cells metabolism during growth and CAV2 production. MDCK cells displayed a marked glycolytic and ammoniagenic metabolism, and (13)C data revealed a large fraction of glutamine-derived labelling in TCA cycle intermediates, emphasizing the role of glutamine anaplerosis. (13)C-MFA demonstrated the importance of pyruvate cycling in balancing glycolytic and TCA cycle activities, as well as occurrence of reductive alphaketoglutarate (AKG) carboxylation. By turn, CAV2 infection significantly upregulated fluxes through most central metabolism, including glycolysis, pentose-phosphate pathway, glutamine anaplerosis and, more prominently, reductive AKG carboxylation and cytosolic acetyl-coenzyme A formation, suggestive of increased lipogenesis. Based on these results, we suggest culture supplementation strategies to stimulate nucleic acid and lipid biosynthesis for improved canine adenoviral vector production.

Vaccination with recombinant adenoviruses expressing the peste des petits ruminants virus F or H proteins overcomes viral immunosuppression and induces protective immunity against PPRV challenge in sheep

Peste des petits ruminants (PPR) is a highly contagious disease of small ruminants caused by the Morbillivirus peste des petits ruminants virus (PPRV). Two recombinant replication-defective human adenoviruses serotype 5 (Ad5) expressing either the highly immunogenic fusion protein (F) or hemagglutinin protein (H) from PPRV were used to vaccinate sheep by intramuscular inoculation. Both recombinant adenovirus vaccines elicited PPRV-specific B- and T-cell responses. Thus, neutralizing antibodies were detected in sera from immunized sheep. In addition, we detected a significant antigen specific T-cell response in vaccinated sheep against two different PPRV strains, indicating that the vaccine induced heterologous T cell responses. Importantly, no clinical signs and undetectable virus shedding were observed after virulent PPRV challenge in vaccinated sheep. These vaccines also overcame the T cell immunosuppression induced by PPRV in control animals. The results indicate that these adenovirus constructs could be a promising alternative to current vaccine strategies for the development of PPRV DIVA vaccines.

Peste des petits ruminants virus infection of small ruminants: a comprehensive review

Peste des petits ruminants (PPR) is caused by a Morbillivirus that belongs to the family Paramyxoviridae. PPR is an acute, highly contagious and fatal disease primarily affecting goats and sheep, whereas cattle undergo sub-clinical infection. With morbidity and mortality rates that can be as high as 90%, PPR is classified as an OIE (Office International des Epizooties)-listed disease. Considering the importance of sheep and goats in the livelihood of the poor and marginal farmers in Africa and South Asia, PPR is an important concern for food security and poverty alleviation. PPR virus (PPRV) and rinderpest virus (RPV) are closely related Morbilliviruses. Rinderpest has been globally eradicated by mass vaccination. Though a live attenuated vaccine is available against PPR for immunoprophylaxis, due to its instability in subtropical climate (thermo-sensitivity), unavailability of required doses and insufficient coverage (herd immunity), the disease control program has not been a great success. Further, emerging evidence of poor cross neutralization between vaccine strain and PPRV strains currently circulating in the field has raised concerns about the protective efficacy of the existing PPR vaccines. This review summarizes the recent advancement in PPRV replication, its pathogenesis, immune response to vaccine and disease control. Attempts have also been made to highlight the current trends in understanding the host susceptibility and resistance to PPR.

Recombinant adenovirus expressing the haemagglutinin of Peste des petits ruminants virus (PPRV) protects goats against challenge with pathogenic virus; a DIVA vaccine for PPR

Peste des petits ruminants virus (PPRV) is a morbillivirus that can cause severe disease in sheep and goats, characterised by pyrexia, pneumo-enteritis, and gastritis. The socio-economic burden of the disease is increasing in underdeveloped countries, with poor livestock keepers being affected the most. Current vaccines consist of cell-culture attenuated strains of PPRV, which induce a similar antibody profile to that induced by natural infection. Generation of a vaccine that enables differentiation of infected from vaccinated animals (DIVA) would benefit PPR control and eradication programmes, particularly in the later stages of an eradication campaign and for countries where the disease is not endemic. In order to create a vaccine that would enable infected animals to be distinguished from vaccinated ones (DIVA vaccine), we have evaluated the immunogenicity of recombinant fowlpox (FP) and replication-defective recombinant human adenovirus 5 (Ad), expressing PPRV F and H proteins, in goats. The Ad constructs induced higher levels of virus-specific and neutralising antibodies, and primed greater numbers of CD8⁺ T cells than the FP-vectored vaccines. Importantly, a single dose of Ad-H, with or without the addition of Ad expressing ovine granulocyte macrophage colony-stimulating factor and/or ovine interleukin-2, not only induced strong antibody and cell-mediated immunity but also completely protected goats against challenge with virulent PPRV, 4 months after vaccination. Replication-defective Ad-H therefore offers the possibility of an effective DIVA vaccine.

Decline in baculovirus-expressed recombinant protein production with increasing cell density is strongly correlated to impairment of virus replication and mRNA expression

The cell density effect is a well-established constraint in the baculovirus-insect cell expression platform, in which cell-specific productivity declines with increasing cell density, hence limiting the maximum achievable volumetric yield of protein product. A deeper elucidation of this phenomenon is sought in this study, by tracking the peak production of viral DNA (vDNA), recombinant LacZ mRNA, and β-galactosidase (β-gal) protein, over a wide range of cell densities. Sf9 suspension cell cultures were propagated in Sf-900 III serum-free medium and synchronously infected with rAcMNPV at multiple infection cell densities (ICDs) of between 0.5 and 8 × 10(6) cells/mL. There was a strong negative linear correlation between the specific β-gal yield and the peak cell density (PCD) post-infection, but contrary to previous reports, the yield decline started at a lower PCD of around 1 × 10(6) cells/mL. Most interestingly, there also was a corresponding strong negative linear correlation between the specific vDNA or LacZ mRNA yield, and the PCD. Comparing the infections at the highest and lowest PCDs tested, the yield decline was most dramatic for β-gal protein (95 %) and LacZ mRNA (90 %), while it was more moderate for vDNA (50 %). These declines were significantly reduced but not completely arrested, when spent medium was replaced with fresh at the ICD. These findings suggest that protein yield deterioration with increasing cell density originated from limitations during upstream events such as virus gene replication or transcription, rather than during the translational phase. Such limitations may be largely nutritional, but a more complex mechanism may be implicated.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

Viruses and Virus-Like Particles in Biotechnology

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this article, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitorization, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Reassessing culture media and critical metabolites that affect adenovirus production

Adenovirus production is currently operated at low cell density because infection at high cell densities still results in reduced cell-specific productivity. To better understand nutrient limitation and inhibitory metabolites causing the reduction of specific yields at high cell densities, adenovirus production in HEK 293 cultures using NSFM 13 and CD 293 media were evaluated. For cultures using NSFM 13 medium, the cell-specific productivity decreased from 3,400 to 150 vp/cell (or 96% reduction) when the cell density at infection was increased from 1 to 3 x 10(6) cells/mL. In comparison, only 50% of reduction in the cell-specific productivity was observed under the same conditions for cultures using CD 293 medium. The effect of medium osmolality was found critical on viral production. Media were adjusted to an optimal osmolality of 290 mOsm/kg to facilitate comparison. Amino acids were not critical limiting factors. Potential limiting nutrients including vitamins, energy metabolites, bases and nucleotides, or inhibitory metabolites (lactate and ammonia) were supplemented to infected cultures to further investigate their effect on the adenovirus production. Accumulation of lactate and ammonia in a culture infected at 3 x 10(6) cells/mL contributed to about 20% reduction of the adenovirus production yield, whereas nutrient limitation appeared primarily responsible for the decline in the viral production when NSFM 13 medium was used. Overall, the results indicate that multiple factors contribute to limiting the specific production yield at cell densities beyond 1 x 10(6) cells/mL and underline the need to further investigate and develop media for better adenoviral vector productions.

Immobilization of 293 cells using porous support particles for adenovirus vector production

Adenovirus vector production by anchorage-independent 293 cells immobilized using porous biomass support particles (BSPs) was investigated in static and shake-flask cultures for efficient large-scale production of adenovirus vectors for gene therapy applications. The density of cells immobilized within BSPs was evaluated by measuring their WST-8 (2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt) reduction activity. In shake-flask culture, 293-F cells, which were adapted to serum-free suspension culture, were not successfully retained within reticulated polyvinyl formal (PVF) resin BSPs (2 × 2 × 2 mm cubes) with matrices of relatively small pores (pore diameter 60 μm). When the BSPs were coated with a cationic polymer polyethyleneimine, a high cell density of more than 10(7) cells cm(-3)-BSP was achieved in both static and shake-flask cultures with regular replacement of the culture medium. After infection with an adenovirus vector carrying the enhanced green fluorescent protein gene (Ad EGFP), the specific Ad EGFP productivity of the immobilized cells was comparable to the maximal productivity of non-immobilized 293-F cells by maintaining favorable conditions in the culture environment.

A high-yield and scaleable adenovirus vector production process based on high density perfusion culture of HEK 293 cells as suspended aggregates

Cells of the human embryonic kidney cell line (HEK 293) were grown as suspended aggregates in stirred vessels and infected with a recombinant adenovirus vector (Ad-TH-GFP). Regular spherical aggregates with the mean diameter less than 300 microm and a viable cell density greater than 5 x 10(6) cells x ml(-1) were readily achieved after 9 day culture in spinner flasks. The HEK 293 cells growing as suspended aggregates could be efficiently infected by Ad-TH-GFP at an MOI of 10 with a prolonging infection time up to 144 hour post-infection (hpi). The time profile of Ad-TH-GFP production was strongly corresponding to the infection process with a virus concentration peak occurred consistently at 144 h after infection. And the infected aggregates essentially maintained spherical in shape, the portion of dissociated cells from the infected aggregates was less than 5% at 144 hpi. Perfusion culture of HEK 293 cells grown as suspended aggregates in a 7.5 L stirred tank bioreactor and infected with Ad-TH-GFP at a density higher than 1 x 10(7) cells x ml(-1) resulted in a similar Ad-TH-GFP production kinetics, but a much higher virus yield approximately at 5.7 x 10(11) GTU ml(-1) at 144 hpi to that of the infected spinner flask cultures. These results demonstrate the feasibility for using suspended cell aggregates as an immobilization system to facilitate perfusion in stirred tank bioreactors, and improve volumetric productivities by eliminating the cell density effect.

From the first to the third generation adenoviral vector: what parameters are governing the production yield?

Human adenoviral viral vector serotype 5 (AdV) is presently the primary viral vector used in gene therapy trials. Advancements in AdV process development directly contribute to the clinical application and commercialization of the AdV gene delivery technology. Notably, the development of AdV production in suspension culture has driven the increase in AdV volumetric and specific productivity, therefore providing large quantities of AdV required for clinical studies. This review focuses on detailing the viral, cell and cell culture parameters governing the productivity of the three generations of AdV vectors.

Scalable culture systems using different cell lines for the production of Peste des Petits ruminants vaccine

Peste des Petits ruminants (PPR) is considered as one of the major constraints to the productivity of small ruminants in Africa and Asian countries. Currently PPR control is done by vaccination with an attenuated PPR strain (Nigeria 75/1) produced in monolayers of Vero cells grown in roller bottles or static flasks. This work focuses on the production of a PPR vaccine strain using stirred conditions as an advanced option for process scale-up. Non-porous microcarriers (Cytodex-1) were used to support Vero cell growth in suspension cultures. The use of Ex-Cell medium could improve cell specific productivities obtained with standard serum containing medium, independently of the type of system used, i.e. static as well as suspension stirred cultures. As an alternative, several cell lines adapted to grow as single cells in suspension (CHO-K1, BHK-21A and 293) and another anchorage-dependent (MRC-5) were evaluated in their capacity to produce a PPR vaccine. BHK-21A and 293 cells grown as single-cell suspension in serum free medium were both suited to produce PPR vaccine with productivities similar to Vero cells, namely 10(6)TCID(50)/mL. However, for the 293 cells, these results were only obtained 2-3 days later. CHO-K1 and MRC-5 cells have shown not to be suitable to adequately produce this virus. These results provide further insights into the feasibility of applying microcarrier cell culture technology to produce PPR vaccine in Vero cells as well as in the alternative use of single-cell suspension cultures of BHK-21A, significantly simplifying the existing production process.

Optimization of adenoviral production in human embryonic kidney cells using response surface methodology

Adenoviruses are the most commonly used vectors in clinical trials for gene therapy. How to efficiently produce abundant and high-quality adenoviral vectors for therapeutic research is a challenge for biochemical engineers. A recombinant adenovirus carrying a green fluorescent protein (GFP) gene together with an anchorage-dependent 293 cell line is used as a model system for evaluating the effects of chemicals on adenoviral production in this study. Our aim is to develop a formulation to be added to an infection medium that could enhance the in vitro production of adenoviral vectors. Eleven ingredients obtained from a literature survey were screened for their stimulatory effects on adenoviral production using the 50% tissue culture infectious dose (TCID(50)) method. Among these ingredients, sucrose and mannitol when supplemented to the infection medium significantly increased adenovirus titer. Central composite design and response surface methodology were also adopted to determine the optimal concentrations of sucrose and mannitol. The formulation developed, which is composed of DMEM/F12 medium plus 0.54 M sucrose and 0.37 M mannitol, can significantly increase adenoviral production by 13-fold that of the control (DMEM/F12 medium).

Effect of ammonia production on intracellular pH: Consequent effect on adenovirus vector production

Recombinant adenoviral vectors (AdV) have proven to be highly efficient for the delivery and expression of foreign genes in a broad spectrum of cell types and species both for vaccination and gene therapy in a number of specific applications. In this study, the effect of ammonia production on intracellular pH (pH(i)) and consequently inhibition of AdV production at high cell densities is assessed. Different specific ammonia production rates were obtained for 293 cells adapted to grow in glutamate supplemented medium (non-ammoniagenic medium) as compared with 293 cells growing in glutamine supplemented medium (ammoniagenic medium); pH(i) was observed to be lower during cell growth and AdV production at both high and low CCI in the ammoniagenic medium, where the specific ammonia production rate is higher. In addition, after infection at CCI of 3x10(6)cell/ml, the cell viability decreased significantly in the ammoniagenic medium, attributed to the activation of an acidic pathway of apoptosis. Furthermore, AdV DNA was observed to be degraded at the observed pH(i) in the ammoniagenic medium, decreasing significantly the amount of AdV DNA available for encapsulation. To elucidate the pH(i) effect upon AdV production, 293 cells were infected at a CCI of 1 x 10(6)cell/ml in the non-ammoniagenic medium with a manipulated pH(i) as observed at the time of infection at CCI of 3 x 10(6)cell/ml in the ammoniagenic (pH(i) 7.0) and non-ammoniagenic (pH(i) 7.3) media; AdV volumetric productivities were observed to be lower when the cells were exposed to the lower pH(i). Thus, the importance of controlling all the factors contributing to pH(i) on AdV production, such as ammonia production, has been established.

Two different serum-free media and osmolality effect upon human 293 cell growth and adenovirus production

Adenoviruses are promising vectors for gene therapy and vaccination protocols. Consequently, the market demands for adenovirus are increasing, driving the search for new methodologies for large-scale production of concentrated vectors with warranted purity and efficacy, in a cost-effective way. Nevertheless, the production of adenovirus is currently limited by the so-called 'cell density effect', i.e. a drop in cell specific productivity concomitant with increased cell concentration at infection. Of two different serum-free culture media (CD293 and EX-Cell), evaluated for their effect on human 293 cells growth and adenovirus production at cell densities higher than 1x10(6) cells/ml, EX-Cell proved the better medium for cell growth. Although adenovirus production was equivalent in both media when the infection was performed at 1x10(6) cells/ml, at 3x10(6) cells/ml CD293 was the better. This result related to the high ammonia content in EX-Cell medium at the highest cell concentration at infection. Besides this, the large-scale production of these vectors at high cell densities often requires re-feed strategies, which increase medium osmolality. While a negative effect on cell growth was observed with increasing osmolalities, adenovirus productivity was only affected for osmolalities higher than 430 mOsm.