High-level secretion of the extracellular domain of the human growth hormone receptor using a baculovirus system

A chemically synthesized gene (hGHR-ED) coding for the extracellular domain (ED) of the human growth hormone (hGH) receptor (hGHR) was inserted into the genome of Autographa californica nuclear polyhedrosis virus adjacent to the polyhedrin promoter. Spodoptera frugiperda cells infected with the recombinant virus secreted a protein with hGH-binding activity into the medium. The secreted 35-kDa protein was purified to near homogeneity. The purified protein exhibited a high binding affinity (Kd = 0.2-0.3 nM) to hGH. The highest cell production capability was estimated at more than 10-20 micrograms hGHR-ED/ml of culture. The inhibition of the hGHR-ED secretion by treatment with tunicamycin suggests that glycosylation is important for secretion.     

Propagation ofSpodoptera frugiperda cells (Sf9) and production of recombinant proteins with the baculovirus expression system using improved spinner flasks with membrane aeration

Summary It has been shown that the growth of Spodoptera frugiperda cells is significantly reduced or ceased under oxygen limiting culture conditions. This paper describes the use of a new membrane-aerated spinner flask which was compared to conventional surface-aerated spinner flasks with regard to growth of the insect cell line Sf9 and recombinant protein production after infection with baculovirus. Using a commercially available serum-free culture medium Sf9 cells reached highest cell densities (3×10⁶ ml^–1) in the membrane-aerated spinner flask. Production of recombinant protein was also influenced by the oxygen supply. In the membrane-aerated spinner flask and in a surface-aerated spinner flask with reduced filling volume more than 20000 U ml^–1 of a recombinant interleukin-2 variant were accumulated whereas only 100 U ml^–1 were produced in a surface-aerated spinner flask with insufficient oxygen supply. Sufficient oxygenation appears to be essential for proliferation of Sf9 cells as well as recombinant protein production after infection with baculovirus. Membrane oxygenation allows sufficient oxygen supply at high cell density and an at least 2.5 fold higher filling volume per spinner unit.     

Replication of Variola Virus in Suspended Cultures of Mammalian Cells

The studies reported here describe the successful propagation of variola virus in spinner cultures of mammalian cells, and the factors which influence its growth. Five established cell lines were used for the propagation of variola virus in a spinner culture system. Low doses of virus did initiate an infection but virus yields did not approach those obtained when an intermediate inoculum was used. Although the nonviable cell population remained low during the course of infection with an intermediate amount of virus, with an inoculum of 10⁵ infectious units per ml or higher, the percentage of nonviable cells increased rapidly and by the sixth day after infection the population was totally nonviable. Intracellular replication of variola virus occurred early and rapidly in a spinner culture of guinea pig lung cells, whereas the liberation of virus into the suspending medium was a more gradual process. Several complete medium changes tend to maintain a suitable environment for the infected cell culture resulting in fairly high and constant viral titers over a period of 7 days.     

Selection of host cell lines for scale-up growth conditions of a recombinant baculovirus vector expressing the measles virus nucleocapsid protein

Summary Various insect cell lines were grown as suspension cultures in spinner vessels and infected with a recombinant baculovirus vector expressing the measles virus nucleoprotein. The highest yields of recombinant protein production were achieved using Trichoplusia ni (BTI-Tn 5B1-4) cells growing as natural aggregates in suspension and cell line Mb as a single cell suspension culture.     

Evaluation of the new serum-free medium (MDSS2) for the production of different biologicals: Use of various cell lines

The presence of serum in cell culture raises safety problems for the production of biologicals, thus a new serum-free medium (MDSS2) was developed. The evaluation of this medium for the growth of different cell lines (BHK-21 C13, BSR and Vero) has shown that cells grew in this medium similarly to standard serum-containing medium, independently of the culture system used: in static (as monolayer) as well as in agitated systems (in suspension in spinner and perfusion reactors). BHK-21 and BSR cells grew as aggregate cultures and could proliferate in both static and agitated culture systems. Vero cells stayed attached to a substrate and proliferated equally in static and in agitated microcarrier-culture systems. The cell densities obtained with BHK-21 cells depended only on the culture system used. They ranged from 2–3×10⁶ to 6–12×10⁶ cells per ml for static batch and perfusion reactor cultures respectively. The cell concentration was 3 to 6 times higher than in classical cultures performed in serum-containing medium. The cell densities obtained with Vero cells were indistinguishable from those obtained in serum-containing medium, whatever the cell culture system used. These cell lines have been used for the production of rabies virus. With respect to BHK-21 and BSR, similar production rates of rabies glycoprotein have been found as in the standard roller bottle process. The production of rabies virus and of viral glycoprotein by Vero cells cultivated in serum-free medium was augmented 1.5-fold and 2.5-fold, respectively, when compared to serum-containing medium.A recombinant BHK-21 cell line, producing human IL-2, can also proliferate in MDSS2, after addition of insulin. The specific IL-2 production rate was augmented 3–4 fold in comparison to serum-containing medium.For the cells tested, the MDSS2 serum-free medium is a good growth and production medium. Its use for cultivating other cell lines and/or for the production of other biologicals is discussed.     

Cell Culture Derived AgMNPV Bioinsecticide: Biological Constraints and Bioprocess Issues

We have studied parameters for optimizing the Spodoptera frugiperda (Sf9) cell culture and viral infection for the production of Anticarsia gemmatalis multiple nucleopolyhedrosis virus (AgMNPV) polyhedra inclusion bodies (PIBs) in shaker-Schott or spinner bottles and bioreactors. We have assayed the k_La of the systems, initial cell seeding, cell culture volume, dissolved oxygen (DO), multiplicity of infection (MOI), nutrients consumption, and metabolites production. The medium surface oxygen transfer was shown to be higher in shaker bottles than in spinner ones, which was in direct correlation to the higher cell density obtained. Best quantitative performances of PIBs production were obtained with a SF900II medium volume/shaker-bottle volume ratio of 15% and MOI of 0.5 to 1 performed at a cell concentration at infection (CCI) of 1 to 2.5×10⁶ cells/ml in a medium containing enough glucose and glutamine. Upon infection, a decrease in the cell multiplication was observed to be dependent on the MOI used, and the μX at the exponential growth phase in infected and non-infected cultures were, respectively, of 0.2832 and 0.3914 (day⁻¹). The glucose consumption and lactate production were higher in the infected cultures (μGlucose and μLactate of, respectively, 0.0248 and 0.0089×10⁻⁸ g/cell×day in infected cultures and 0.0151 and 0.0046×10⁻⁸ g/cell×day in non infected ones). The glutamine consumption did not differ in both cultures (μGlutamine of 0.0034 and 0.0037×10⁻⁸ g/cell×day in, respectively, infected and non infected cultures). When a virus MOI of 0.1 to 1 was used for infection, a higher concentration of PIBs/ml was obtained. This was in direct correlation to a higher cell concentration present in these cultures, where a decrease in cell multiplication due to virus infection is minimized. When a MOI of 1 was used, a more effective decrease in cell multiplication was observed and a lower concentration of PIBs/ml was obtained, but with the best performance of PIBs/cell. Correlations between MOI and CCI indicate that a MOI 0.1 to 1.4 and a CCI of 10⁶ to 2×10⁶ cells/ml led to the best PIBs production performances. The virulence of PIBs produced in cultures infected at low or high MOI showed comparable DL₅₀. Culture and infection in scaling-up conditions, performed in a bioreactor, were shown to provide the cells with a better environment and be capable of potentially improving the shaker-Schott findings. For an accurate qualitative control of PIB virulence, hemolymph from AgMNPV infected Anticarsia gemmatalis was used as starting material for passages in Sf9 cells. These led to a loss of virulence among the PIBs with an increase in the DL₅₀. The loss of virulence was accompanied by a loss in budded virus titer, a decreased number of PIBs produced and an altered DNA restriction pattern, suggesting the generation of defective interference particles (DIPs). Transmission electron microscopy (TEM) studies revealed that after cell passages, PIBs lacking virions were progressively synthesized. The study described here point out the biological constraints and bioprocess issues for the preparation of AgMNPV PIBs for biological control.     

A novel animal-component-free medium for rabies virus production in Vero cells grown on Cytodex 1 microcarriers in a stirred bioreactor

Vero cells growth and rabies production in IPT-AF medium, a property animal-component-free medium are described in this work. Kinetics of cell growth and rabies virus (strain LP 2061) production were first conducted in spinner flasks. Over eight independent experiments, Vero cell growth in IPT-AF medium, on 2 g/l Cytodex 1 was consistent. An average Cd (cell division number) of 3.3 ± 0.4 and a specific growth rate μ of 0.017 ± 0.006 h⁻¹ were achieved. Such performances were comparable to those obtained in serum-containing medium (MEM + 10% FCS). Rabies virus production on Vero cells in IPT-AF medium was also optimised in spinner flasks. The effects of multiplicity of infection (MOI), regulation of glucose level at 1 g/l and cell washing step, were investigated. The highest virus titer was achieved when the cells were infected at an MOI of 0.1; this level was equal to 10⁷ FFU/ml. The step of medium exchange before cell infection can be omitted; nevertheless in this case glucose level should be maintained at 1 g/l to avoid a decrease of specific virus productivity. Process optimisation in a 2-l stirred bioreactor pointed out that the aeration mode was the prominent parameter that affected cell growth in IPT-AF medium and on Cytodex 1 microcarriers. An acceptable level of cell density (cell density level of 1.5 × 10⁶ cells/ml) was achieved when cells were grown in batch mode and using headspace aeration. Nevertheless, this aeration mode is not optimal for large-scale culture. The addition of Pluronic F68 at 0.1% at 24 h post inoculation as well as the switch from surface aeration mode to the sparged mode, 2 days after the start of the culture, had markedly improved cell growth performance. A cell density level of 5.5 × 10⁶ cells/ml was reached when cells were grown in a 2-l bioreactor, on 3 g/l Cytodex 1 in IPT-AF medium and using the recirculation culture mode. Cell infection at an MOI of 0.1 and using perfused culture, resulted in a maximal virus titer of 3.5 × 10⁷ FFU/ml. The activity of the pooled inactivated rabies virus harvests showed a protective activity that meets WHO requirements.     

Japanese encephalitis virus production in Vero cells with serum-free medium using a novel oscillating bioreactor.

A novel oscillating bioreactor, BelloCell, was successfully applied for the cultivation of Vero cells using serum-free medium, and the production of Japanese encephalitis virus. The BelloCell requires no air sparging, pumping, or agitation, and thus provides a low shear environment. Owing to its simple design, BelloCell is extremely easy to handle and operate. Using this BelloCell (500 ml culture), Vero cells reached a maximum number of 2.8 x 10(9) cells and the Japanese encephalitis virus yield reached 6.91 x 10(11) PFU, versus 9.0 x 10(8) cells and 2.98 x 10(11) PFU using a spinner flask (500 ml) with microcarriers. The cell yield and virus production using BelloCell were markedly higher than with microcarrier culture. The neutralizing capacity of the Japanese encephalitis virus produced using BelloCell was equal to that using a microcarrier system. Therefore, these benefits should enable BelloCell to be adopted as a simple system for high population density cell culture and virus production.     

A serum-free Vero production platform for a chimeric virus vaccine candidate

MedImmune Vaccines has engineered a live, attenuated chimeric virus that could prevent infections caused by parainfluenza virus type 3 (PIV3) and respiratory syncytial virus (RSV), causative agents of acute respiratory diseases in infants and young children. The work here details the development of a serum-free Vero cell culture production platform for this virus vaccine candidate. Efforts to identify critical process parameters and optimize culture conditions increased infectious virus titers by approximately 2 log₁₀ TCID₅₀/ml over the original serum-free process. In particular, the addition of a chemically defined lipid concentrate to the pre-infection medium along with the shift to a lower post-infection cultivation temperature increased virus titers by almost 100-fold. This improved serum-free process achieved comparable virus titers to the serum-supplemented process, and demonstrated consistent results upon scale-up: Vero cultures in roller bottles, spinner flasks and bioreactors reproducibly generated maximum infectious virus titers of 8 log₁₀ TCID₅₀/ml.     

BHK 21 C13 cells for Aujeszky’s disease virus production using the multiple harvest process

Production of Aujeszky’s disease virus (ADV) from BHK 21 C13 suspension cells using a simple harvest and multiple harvest process mode was examined. We studied growth kinetics of BHK 21 C31 cells in 750 ml spinner flask containing 500 ml of culture medium. In the simple harvest process of ADV production, 425 ml of virus harvest was obtained with a virus titer of 10^6.4 TCID₅₀ ml⁻¹ which corresponds to 10,676 doses of vaccine. The multiple harvest process resulted in 850 ml of virus harvest with a virus titer of 10^6.5 TCID₅₀ ml⁻¹ corresponding to 26,877 AD vaccine doses. In conclusion, the multiple harvest process mode using BHK 21 C13 can be considered as a favorable process to produce ADV.     

Inactivation of Bacteriophages by Thiol Reducing Agents

Adaptation of the vaccinia virus expression system to HeLa S3 suspension bioreactor culture for the production of recombinant protein was conducted. Evaluation of hollow fiber perfusion of suspension culture demonstrated its potential for increased cell density prior to infection. The hollow fiber was also used for medium manipulations prior to infection. Two process parameters, multiplicity of infection (MOI) and temperature during the protein production phase, were evaluated to determine their effect on expression of the reporter protein, enhanced green fluorescent protein (EGFP). An MOI of 1.0 was sufficient for infection and led to the highest level of intracellular EGFP expression. Reducing the temperature to 34 °C during the protein production phase increased production of the protein two-fold compared to 37 °C in spinner flask culture. Scaling up the process to a 1.5-liter bioreactor with hollow fiber perfusion led to an overall production level of 9.9 μg EGFP/10⁶ infected cells, or 27 mg EGFP per liter.     

High-density perfusion culture of insect cells with a biosep ultrasonic filter

The baculovirus/insect cell expression system has provided a vital tool to produce a high level of active proteins for many applications. We have developed a very high-density insect cell perfusion process with an ultrasonic filter as a cell retention device. The separation efficiency of the filter was studied under various operating conditions. A cell density of over 30 million cells/mL was achieved in a controlled perfusion bioreactor and cell viability remained greater than 90%. Sf9 cells from a high-density culture and a spinner culture were infected with two recombinant baculoviruses expressing genes for the production of human chitinase and monocyte-colony inhibition factor. The protein yield on a cell basis from infecting high-density Sf9 cells was the same as or higher than that from the spinner Sf9 culture. Virus production from the high-density culture was similar to that from the spinner culture. The results show that the ultrasonic filter did not affect insect cells' ability to support protein expression and virus production following infection with baculovirus. The potential applications of the high-density perfusion culture for large-scale protein expression from Sf9 cells are also highlighted.     

Production of Mouse Interferon with High Titers in a Large-Scale Suspension Culture System1

L-MS cells, adapted to grow in suspension, were obtained by selection from a high interferon (IF)-producing line of mouse L cell monolayers. A large volume of L-MS cells (20 liters or more; 1–2 × 10¹⁰ cells) was readily grown in a spinner culture, retaining their ability to produce high yields of IF in serum-free medium following induction with Newcastle disease virus (NDV). The optimal condition for the production of IF in the suspension culture of L-MS cells was established. The system also proved itself to be susceptible to IF induction by polyinosinic-polycytidylic acid (Poly I · Poly C) and by NDV inactivated with ultraviolet light (NDV-UV). By employing the present system, large quantities of mouse IF of a high titer could be routinely prepared.     

TubeSpin bioreactor 50 for the high-density cultivation of Sf-9 insect cells in suspension

Here we present the TubeSpin bioreactor 50 (TubeSpins) as a simple and disposable culture system for Sf-9 insect cells in suspension. Sf-9 cells had substantially better growth in TubeSpins than in spinner flasks. After inoculation with 10⁶ cells/ml, maximal cell densities of 16 × 10⁶ and 6 × 10⁶ cells/ml were reached in TubeSpins and spinner flasks, respectively. In addition the cell viability in these batch cultures remained above 90% for 10 days in TubeSpins but only for 4 days in spinner flasks. Inoculation at even higher cell densities reduced the duration of the lag phase. After inoculation at 2.5 × 10⁶ cells/ml, the culture reached the maximum cell density within 3 days instead of 7 days as observed for inoculation with 10⁶ cells/ml. Infection of Sf-9 cells in TubeSpins or spinner flasks with a recombinant baculovirus coding for green fluorescent protein (GFP) resulted in similar GFP-specific fluorescence levels. TubeSpins are thus an attractive option for the small-scale cultivation of Sf-9 cells in suspension and for baculovirus-mediated recombinant protein production.     

Continuous insect cell (Sf-9) culture with aeration through sparging

The continuous growth of Spodoptera frugiperda Sf-9 cells in a 250-ml blown-glass jacketed spinner flask under a direct air sparging environment was investigated. Even at 220 ml working volume (about 90% of total volume), this spinner flask provided good mixing and oxygenation as demonstrated by a higher cell density compared with fermentor cultures. This eliminates a common limitation of the traditional spinner flask, namely much lower cell density at high working volume. Furthermore, this spinner flask has been run with Sf-9 cell culture at five different dilution rates and two different air sparging rates at steady state, demonstrating its utility in research applications where cell size, metabolic activity and environmental conditions can be constantly maintained. In addition to demonstrating the utility of the reactor, three novel points are made in this report. First, cell density in continuous cultures is increased significantly due to a high agitation rate and, especially, air sparging rate, which is seldom used in animal cell or insect cell culture. Second, there is no apparent difference in the specific death rate at two different sparging rates (0.0093 vvm and 0.0125 vvm). Finally, we have maintained Sf-9 cells for more than 4 months in a continuous culture using a serum-free medium without loss of recombinant protein expression in infected cells.     

Stirred tank bioreactor culture combined with serum‐/xenogeneic‐free culture medium enables an efficient expansion of umbilical cord‐derived mesenchymal stem/stromal cells

Mesenchymal stem/stromal cells (MSC) are being widely explored as promising candidates for cell‐based therapies. Among the different human MSC origins exploited, umbilical cord represents an attractive and readily available source of MSC that involves a non‐invasive collection procedure. In order to achieve relevant cell numbers of human MSC for clinical applications, it is crucial to develop scalable culture systems that allow bioprocess control and monitoring, combined with the use of serum/xenogeneic (xeno)‐free culture media. In the present study, we firstly established a spinner flask culture system combining gelatin‐based Cultispher^®S microcarriers and xeno‐free culture medium for the expansion of umbilical cord matrix (UCM)‐derived MSC. This system enabled the production of 2.4 (±1.1) x10⁵ cells/mL (n = 4) after 5 days of culture, corresponding to a 5.3 (±1.6)‐fold increase in cell number. The established protocol was then implemented in a stirred‐tank bioreactor (800 mL working volume) (n = 3) yielding 115 million cells after 4 days. Upon expansion under stirred conditions, cells retained their differentiation ability and immunomodulatory potential. The development of a scalable microcarrier‐based stirred culture system, using xeno‐free culture medium that suits the intrinsic features of UCM‐derived MSC represents an important step towards a GMP compliant large‐scale production platform for these promising cell therapy candidates.     

Properties of two insect cell lines useful for the baculovirus expression system in serum-free culture

The properties of Sf9 and Tn5 insect cells were analyzed comparatively under serum-free culture conditions. Sf9 cells in SF900II medium apparently utilized sucrose as a primary nutrient both before and after virus infection, yielding small amounts of lactate and ammonia. Tn5 cells in Excell 401 medium consumed all the nutrients examined, including sucrose. The productivity of a recombinant glycoprotein, OSF-2, by Tn5 cells, was moderate in both monolayer and spinner cultures, but the ability to secrete it was compromised in the former case. Relative to the Tn5 cultures, Sf9 produced 30-fold more OSF-2 in either culture mode. (c) 1996 John Wiley & Sons, Inc.     

Fabrication of viable and functional pre‐vascularized modular bone tissues by coculturing MSCs and HUVECs on microcarriers in spinner flasks

Slow vascularization often impedes the viability and function of engineered bone replacements. Prevascularization is a promising way to solve this problem. In this study, a new process was developed by integrating microcarrier culture and coculture to fabricate pre‐vascularized bone microtissues with mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs). Initially, coculture medium and cell ratio between MSCs and HUVECs were optimized in tissue culture plates concerning cell proliferation, osteogenesis and angiogenesis. Subsequently, cells were seeded onto CultiSpher S microcarriers in spinner flasks and subjected to a two‐stage (proliferative‐osteogenic) culture process for four weeks. Both cells proliferated and functioned well in chosen medium and a 1 : 1 ratio between MSCs and HUVECs was chosen for better angiogenesis. After four weeks of culture in spinner flasks, the microtissues were formed with high cellularity, evenly distributed cells and tube formation ability. While coculture with HUVECs exerted an inhibitory effect on osteogenic differentiation of MSCs, with downregulated alkaline phosphatase activity, mineralization and gene expression of COLI, RUNX2 and OCN, this could be attenuated by employing a delayed seeding strategy of HUVECs against MSCs during the microtissue fabrication process. Conclusion: Collectively, this work established an effective method to fabricate pre‐vascularized bone microtissues, which would lay a solid foundation for subsequent development of vascularized tissue grafts for bone regeneration.     

Production of seedlings from ovules excised at the zygote stage in Lilium spp.

The present study was undertaken to establish a culture system for ovules excised at the zygote stage in Lilium spp. Ovules of Lilium × `Connecticut King' and L. × `Enchantment' were excised together with placental tissue 3, 5, and 10 days after pollination (DAP) and cultured on B5 medium and half-strength B5 medium containing sucrose at different concentrations. In vitro embryo development in ovules cultured at 3 DAP was influenced by the basal media and the sucrose concentration. The half-strength B5 medium with 9% sucrose was the best condition, but only a few ovules isolated from placental tissue developed into seedlings. Application of embryo culture, in which embryos were excised from ovules after 14 weeks of ovule-with-plancetal-tissue culture, greatly improved the production of seedlings. The present study indicates that a two-step culture procedure, ovule-with-placental-tissue culture and embryo culture, make it possible to produce seedlings from ovules just after fertilization.     

Growth characterizations of a human monocytic leukemia cell line in a serum-free medium

A clone, AH-01S, derived from a human monocytic leukemia cell line, THP-1, grew rapidly in a serum-free medium containing insulin, transferrin, ethanolamine, and sodium selenite. In batch culture using the serum-free medium, the AH-01S cells proliferated at a specific growth rate (μ) of 0.30 to 0.50 (1/day) from a cell concentration of 1 × 10⁴ cells/ml to 1.6 × 10⁶ cells/ml, an increase of 160 times. A higher cell concentration of 0.45 × 10⁷ cells/ml (cell volume ratio was 0.5%) was obtained in spinner flask culture using the serum-free medium. A mean specific growth rate 0.50 (1/day) was also observed in a culture in a fully instrumented cell culture fermentor. However, μ decreased drastically after the cell concentration reached 1.5 × 10⁶ cells/ml. Analyses of medium composition during cultivation revealed that under lower cell concentration, l-glutamine was the main carbon source while glucose was converted to lactate almost stoichiometrically, and that the production of lactate from glucose decreased at higher cell concentrations. To obtain cultures of 1 × 10⁹ cells, 1,200 to 1,300 mg of a carbon source (glucose) and 400 to 500 of amino acids were consumed during high cell concentration cultivation of the AH-01S cells in the serum-free medium.