Hyperosmotic pressure on HEK 293 cells during the growth phase, but not the production phase, improves adenovirus production

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.

Recent advances in upstream process development for production of recombinant adeno-associated virus

Recombinant adeno-associated virus (rAAV) is rapidly emerging as the preferred delivery vehicle for gene therapies, with promising advantages in safety and efficacy. Key challenges in systemic in-vivo rAAV gene therapy applications are the gap in production capabilities versus potential market demand and complex production process. This review summarizes current available information on rAAV upstream manufacturing processes and proposed optimizations for production. The advancements in rAAV production media were reviewed with proposals to speed up the cell culture process development. Furthermore, major methods for genetic element delivery to host cells were summarized with their advantages, limitations, and future directions for optimization. In addition, culture vessel selection criteria were listed based on production cell system, scale, and development stage. Process control at the production step was also outlined with an in-depth understanding of production kinetics and quality control.

Culture media selection and feeding strategy for high titer production of a lentiviral vector by stable producer clones cultivated at high cell density

The growing interest in the use of lentiviral vectors (LVs) for various applications has created a strong demand for large quantities of vectors. To meet the increased demand, we developed a high cell density culture process for production of LV using stable producer clones generated from HEK293 cells, and improved volumetric LV productivity by up to fivefold, reaching a high titer of 8.2 × 10⁷ TU/mL. However, culture media selection and feeding strategy development were not straightforward. The stable producer clone either did not grow or grow to lower cell density in majority of six commercial HEK293 media selected from four manufacturers, although its parental cell line, HEK293 cell, grows robustly in these media. In addition, the LV productivity was only improved up to 53% by increasing cell density from 1 × 10⁶ and 3.8 × 10⁶ cells/mL at induction in batch cultures using two identified top performance media, even these two media supported the clone growth to 5.7 × 10⁶ and 8.1 × 10⁶ cells/mL, respectively. A combination of media and feed from different companies was required to provide diverse nutrients and generate synergetic effect, which supported the clone growing to a higher cell density of 11 × 10⁶ cells/mL and also increasing LV productivity by up to fivefold. This study illustrates that culture media selection and feeding strategy development for a new clone or cell line can be a complex process, due to variable nutritional requirements of a new clone. A combination of diversified culture media and feed provides a broader nutrients and could be used as one fast approach to dramatically improve process performance.

Development of an efficient veterinary rabies vaccine production process in the avian suspension cell line AGE1.CR.pIX

Background

Mass vaccination of dogs as important rabies reservoir is proposed to most effectively reduce and eliminate rabies also in humans. However, a minimum coverage of 70% needs to be achieved for control of the disease in zoonotic regions. In numerous developing countries, dog vaccination rate is still dangerously low because of economic constraints and due to a high turnover in dog populations. Improved vaccine production processes may help to alleviate cost and supply limitations. In this work, we studied and optimized the replication and vaccine potency of PV rabies virus strain in the muscovy-duck derived AGE1.CR and AGE1.CR.pIX suspension cell lines.

Results

The BHK-21-adapted PV rabies virus strain replicated efficiently in the avian cell lines without requirement for prior passaging. CR.pIX was previously shown to augment heat shock responses and supported slightly higher infectious titers compared to the parental CR cell line. Both cell lines allowed replication of rabies virus also in absence of recombinant IGF, the only complex component of the chemically defined medium that was developed for the two cell lines. After scale-up from optimization experiments in shake flask to production in 7-l bioreactors peak virus titers of 2.4 × 10⁸ FFU/ml were obtained. The potency of inactivated rabies virus harvest according to the NIH test was 3.5 IU/ml. Perfusion with the chemically defined medium during the virus replication phase improved the potency of the vaccine twofold, and increased the number of doses 9.6 fold.

Conclusion

This study demonstrates that a rabies vaccine for animal vaccination can be produced efficiently in the AGE1.CR.pIX suspension cell line in a scalable process in chemically defined medium.

NaCl and KCl mediate log increase in AAV vector particles and infectious titers in a specific/timely manner with the HSV platform

The increasing demand for adeno-associated virus (AAV) vectors, a result from the surging interest for their potential to cure human genetic diseases by gene transfer, tumbled on low-performing production systems. Innovative improvements to increase both yield and quality of the vector produced have become a priority undertaking in the field. In a previous study, we showed that adding a specific concentration of sodium chloride (NaCl) to the production medium resulted in a dramatic increase of AAV vector particle and infectious titers when using the herpes simplex virus (HSV) production system, both in adherent or suspension platforms. In this work, we studied additional salts and their impact on AAV vector production. We found that potassium chloride (KCl), or a combination of KCl and NaCl, resulted in the highest increase in AAV vector production. We determined that the salt-mediated effect was the most impactful when the salt was present between 8 and approximately 16 h post-infection, with the highest rate increase occurring within the first 24 h of the production cycle. We showed that the AAV vector yield increase did not result from an increase in cell growth, size, or viability. Furthermore, we demonstrated that the impact on AAV vector production was specifically mediated by NaCl and KCl independently of their impact on the osmolality of the production media. Our findings convincingly showed that NaCl and KCl were uniquely efficacious to promote up to a 10-fold increase in the production of highly infectious AAV vectors when produced in the presence of HSV. We think that this study will provide unique and important new insights in AAV biology toward the establishment of more successful production protocols.

Protective effect of adenovirus-mediated erythropoietin expression on the spiral ganglion neurons in the rat inner ear

The aim of the present study was to evaluate the expression of erythropoietin (Epo) and the Epo receptor (Epo-R) in the spiral ganglion neurons (SGNs) of the rat inner ear, and to assess the effect of Epo adenovirus vector (Ad-Epo) on the spontaneous apoptosis of SGNs. A total of 60 ears from 30 healthy neonatal (2-3 days postnatal) Sprague-Dawley rats were used to examine the expression of Epo in the SGNs. The rats were divided into three groups: The negative control group, the vector control group [infected with a green fluorescent protein expression vector (Ad-GFP)] and the Ad-Epo group (infected with Ad-Epo). The expression of Epo and Epo-R was detected by immunohistochemistry and dual immunofluorescence staining using polyclonal antibodies directed against Epo and Epo-R, followed by confocal laser-scanning microscopy. An adenovirus vector was constructed and used to transfect the cultured SGNs. Following adenovirus infection, apoptosis of the SGNs was evaluated and Epo protein expression was assessed. Epo and Epo-R were widely expressed in the plasma membrane and the cytoplasm of the SGNs, as well as in the organ of Corti and the stria vascularis within the inner ear. Epo protein expression was upregulated in the Ad-Epo group compared with that in the other two groups (P<0.05). Apoptotic cells were seldom observed at day 4 of SGN culture in the negative control group. At day 7, marked apoptotic cells were detected in the negative control group and the vector control group. The apoptosis level in the Ad-Epo group was significantly decreased compared with that in the negative control group or the vector control group at day 7 (P<0.05). In conclusion, Epo and Epo-R are expressed in the SGNs of the inner ear of the rat, and Ad-Epo can decrease the spontaneous apoptosis of SGNs, which may provide a basis for the prevention or alleviation of sensorineural hearing loss.

3D printing of HEK 293FT cell-laden hydrogel into macroporous constructs with high cell viability and normal biological functions

3D printing has evolved into a versatile technology for fabricating tissue-engineered constructs with spatially controlled cells and biomaterial distribution to allow biomimicking of in vivo tissues. In this paper, we reported a novel study of 3D printing of cell lines derived from human embryonic kidney tissue into a macroporous tissue-like construct. Nozzle temperature, chamber temperature and the composition of the matrix material were studied to achieve high cell viability (>90%) after 3D printing and construct formation. Long-term construct stability with a clear grid structure up to 30 days was observed. Cells continued to grow as cellular spheroids with strong cell-cell interactions. Two transfected cell lines of HEK 293FT were also 3D printed and showed normal biological functions, i.e. protein synthesis and gene activation in responding to small molecule stimulus. With further refinement, this 3D cell printing technology may lead to a practical fabrication of functional embryonic tissues in vitro.