Optimization of the physiochemical parameters for the culture of Bombyx mori insect cells used in recombinant protein production

Development of an animal-derived component-free medium for Spodoptera frugiperda (Sf9) cells using response surface methodology

OBJECTIVES

To develop an animal-derived component-free medium for Spodoptera frugiperda (Sf9) growth and green fluorescent protein (GFP) expression.

RESULTS

OSF9-ADCFM contained optimum concentrations of CDLC, YE and ST at 0.5% (v/v), 11.0 g/L, and 3.0 g/L, respectively. A mean viable cell concentration of 1.71 ± 0.14 × 10⁵ cells/mL was obtained from 5 passages (P1-P5). The use of both peptones after 10 kDa ultrafiltration had a significant effect on Sf9 cell growth. Grace's insect medium with 10% FBS gave higher un-infected cell number than SF-900II and OSF9-ADCFM for 4.29 and 5.38 times, respectively. The average cell number of un-infected cells and GFP-fluorescent cells of SF-900II were higher than OSF9-ADCFM 1.25 and 7 times, respectively.

CONCLUSION

In-house OSF9-ADCFM could support growth and GFP expression in Sf9 less than commercial SF-900II. However, it could lower the production cost at least 50% comparing to commercial SF-900II. The development of in- house OSF9-ADCFM would be continued to increase both cell numbers and protein expression in the next step.

Immortalization of shrimp lymphoid cells by hybridizing with the continuous cell line Sf9 leading to the development of 'PmLyO-Sf9 '

Shrimp progressively gets more attention among marine invertebrates from researchers all over the world due to it being a healthy food as well as having economic importance. There were a lot of attempts to develop a continuous cell line from shrimp but none successful. In this context a novel hybrid cell line named 'PmLyO-Sf9' could be developed by fusing shrimp lymphoid organ cells with Sf9 cells after to metabolic blocking of Sf9 cells using puromycin and actinomycin D and effecting the fusion by way of PEG application. The cells are maintained and multiplied in a mixture of SCCM and TNM-FH having osmolality 550 mOsm kg^-1 and pH 6.8. Transmission electron microscopy of the hybrid cells revealed the presence of two nuclei during the initial stages and a single nucleus subsequently. The cell line is with shrimp and Sf9 genomic components and shrimp specific protein and is susceptible to WSSV. Shrimp elongation factor, Sf9 beta-actin, shrimp STAT and peroxinectin could be expresses through RT-PCR in the cell line. This is the first successful report of a hybrid cell line with shrimp genomic components and envisaged to be recognized a model system for multitudes of biomedical research in vitro. The cell line is in the National Cell Line Repository of ICAR - National Bureaue of Fish Genetic Resources, Lucknow, India.

Development of Serum-Free Media for Lepidopteran Insect Cell Lines

Baculovirus-based Insect Cell Technology (ICT) is widely used for the expression of recombinant heterologous proteins and baculovirus bioinsecticides, and has recently gained momentum as a commercial manufacturing platform for human and veterinary vaccines. The three key components of ICT are the Lepidopteran insect cell line, the baculovirus vector, and the growth medium. Insect cell growth media have evolved significantly in the past five decades, from basal media supplemented with hemolymph or animal serum, to highly optimized serum-free media and feeds (SFM and SFF) capable of supporting very high cell densities and recombinant protein yields. The substitution of animal sera with protein hydrolysates in SFM results in greatly reduced medium costs and much improved process scalability. However, both sera and hydrolysates share the disadvantage of lot-to-lot variability, which is detrimental to process reproducibility. Hence, the industrialization of ICT would benefit greatly from chemically defined media (CDM) for insect cells, which are not yet commercially available. On the other hand, applications such as baculovirus bioinsecticides would need truly low cost serum-free media and feeds (LC-SFM and LC-SFF) for economic viability, which require the substitution of a majority of expensive added amino acids with even higher levels of hydrolysates, hence increasing the risk of a variable process. CDM developments are anticipated to benefit both conventional and low cost ICT applications, by identifying key growth factors in hydrolysates for more targeted media and feed design.

Development of quenching and washing protocols for quantitative intracellular metabolite analysis of uninfected and baculovirus-infected insect cells

Metabolomics refer to the global analysis of small molecule metabolites in a biological system, and can be a powerful tool to elucidate and optimize cellular processes, particularly when integrated into a systems biology framework. Determining the endometabolome in cultured animal cells is especially challenging, due to the conflicting demands for rapid quenching of metabolism and retention of membrane integrity, while cells are separated from the complex medium. The challenge is magnified in virus infected cells due to increased membrane fragility. This paper describes an effective methodology for quantitative intracellular metabolite analysis of the baculovirus-insect cell expression system, an important platform for the production of heterologous proteins and baculovirus-based biopesticides. These two applications were represented by Spodoptera frugiperda (Sf9) and Helicoverpa zea (HzAM1) cells infected with recombinant Autographa californica and wild-type Helicoverpa armigera nucleopolyhedroviruses (AcMNPV and HaSNPV), respectively. Specifically, an ice-cold quenching solution comprising 1.1% w/v NaCl and 0.2% w/v Pluronic® F-68 (NaCl+P) was found to be efficacious in preserving cell viability and minimizing cell leakage during quenching and centrifugation-based washing procedures (prior to extraction using cold 50% v/v acetonitrile). Good recoveries of intracellular adenosine triphosphate, total adenosine phosphates and amino acids were obtained after just one wash step, for both uninfected and infected insect cells. The ability to implement wash steps is critical, as insect cell media are metabolites-rich, while infected insect cells are much more fragile than their uninfected counterparts. Hence, a promising methodology has been developed to facilitate endometabolomic analysis of insect cell-baculovirus systems for bioprocess optimization.

Stably Transformed Insect Cell Lines: Tools for Expression of Secreted and Membrane‐anchored Proteins and High‐throughput Screening Platforms for Drug and Insecticide Discovery

Insect cell-based expression systems are prominent amongst current expression platforms for their ability to express virtually all types of heterologous recombinant proteins. Stably transformed insect cell lines represent an attractive alternative to the baculovirus expression system, particularly for the production of secreted and membrane-anchored proteins. For this reason, transformed insect cell systems are receiving increased attention from the research community and the biotechnology industry. In this article, we review recent developments in the field of insect cell-based expression from two main perspectives, the production of secreted and membrane-anchored proteins and the establishment of novel methodological tools for the identification of bioactive compounds that can be used as research reagents and leads for new pharmaceuticals and insecticides.

Optimization of a feed medium for fed-batch culture of insect cells using a genetic algorithm

Insect cells have been cultured for over 30 years, but their application is still hampered by low cell densities in batch fermentations and expensive culture media. With respect to the culture method, the fed-batch culture mode is often found to give the best yields. However, optimization of the feed composition is usually a laborious task. In this report, the successful use of genetic algorithms (GAs) to optimize the growth of insect cells is described. A feed was developed from 11 different medium components, each used at a wide range of concentrations. The feed was optimized within four sets of 20 experiments. The optimized feed was tested in bioreactors and the addition scheme was further improved. The viable-cell density of HzAm1 (Helicoverpa zea) insect cells improved 550% to 19.5 x 10(6) cells/mL compared to a control fermentation in an optimized commercial medium. No accumulation of waste products was found, and none of the amino acids was depleted. Glucose was depleted, which suggests that even further improvement is possible. We show that GAs are a successful method to optimize a complex fermentation in a relatively short time frame and without the need of detailed information concerning the cellular physiology or metabolism.

Production of the baculovirus-expressed dengue virus glycoprotein NS1 can be improved dramatically with optimised regimes for fed-batch cultures and the addition of the insect moulting hormone, 20-Hydroxyecdysone

A perennial problem in recombinant protein expression is low yield of the product of interest. A strategy which has been shown to increase the production of baculovirus-expressed proteins is to utilise fed-batch cultures. One disadvantage of this approach is the time-consuming task of optimising the feeding strategy. Previously, a statistical optimisation routine was applied to develop a feeding strategy that increased the yield of beta-Galactosidase (beta-Gal) by 2.4-fold (Biotechnol. Bioeng. 59 (1998) 178). This involves the single addition of nutrient concentrates (amino acids, lipids, glucose and yeastolate ultrafiltrate) into Sf 9 cell cultures grown in SF 900II medium. In this study, it is demonstrated that this optimised fed-batch strategy developed for a high-yielding intracellular product beta-Gal could be applied successfully to a relatively low-yielding glycosylated and secreted product such as the dengue virus glycoprotein NS1. Optimised batch infections yielded 4 microg/ml of NS1 at a peak cell density of 4.2 x 10 (6) cells/ml. In contrast, optimised fed-batch infections exhibited a 3-fold improvement in yield, with 12 microg/ml of NS1 produced at a peak cell density of 11.3 x 10 (6) cells/ml. No further improvements in yield were recorded when the feed volumes were doubled and the peak cell density was increased to 23 x 10 (6) cells/ml, unless the cultures were stimulated by the addition of 4 microg/ml of 20-Hydroxyecdysone (an insect moulting hormone). In this case, the NS1 yield was increased to 20 microg/ml, which was nearly 5-fold higher than optimised batch cultures.

Optimising fed-batch production of recombinant proteins using the baculovirus expression vector system

Fed-batch culture can offer significant improvement in recombinant protein production compared to batch culture in the baculovirus expression vector system (BEVS), as shown by Nguyen et al. (1993) and Bedard et al. (1994) among others. However, a thorough analysis of fed-batch culture to determine its limits in improving recombinant protein production over batch culture has yet to be performed. In this work, this issue is addressed by the optimisation of single-addition fed-batch culture. This type of fed-batch culture involves the manual addition of a multi-component nutrient feed to batch culture before infection with the baculovirus. The nutrient feed consists of yeastolate ultrafiltrate, lipids, amino acids, vitamins, trace elements, and glucose, which were added to batch cultures of Spodoptera frugiperda (Sf9) cells before infection with a recombinant Autographa californica nuclear polyhedrosis virus (AcNPV) expressing beta-galactosidase (beta-Gal). The fed-batch production of beta-Gal was optimised using response surface methods (RSM). The optimisation was performed in two stages, starting with a screening procedure to determine the most important variables and ending with a central-composite experiment to obtain a response surface model of volumetric beta-Gal production. The predicted optimum volumetric yield of beta-Gal in fed-batch culture was 2.4-fold that of the best yields in batch culture. This result was confirmed by a statistical analysis of the best fed-batch and batch data (with average beta-Gal yields of 1.2 and 0.5 g/L, respectively) obtained from this laboratory. The response surface model generated can be used to design a more economical fed-batch operation, in which nutrient feed volumes are minimised while maintaining acceptable improvements in beta-Gal yield.