Kinetic characterization of baculovirus-induced cell death in insect cell cultures

The death process of baculovirus-infected insect cells was divided into two phases: a constant viability (or delay) phase characterized by a delay time (t(d)) and a first-order death phase characterized by a half-life (t(1/2)). These two parameters were used in conjunction with the n-target theory to classify the kinetics of cell death under various conditions, including different multiplicity of infection (MOI), host cell lines, virus types, incubation volumes, cell density and extracellular L(+)-lactate and ammonium concentrations. Two groups of kinetic effects were found: one characterized by a constant number of hypothetical targets and the other by decreased numbers of hypothetical targets. The first group includes effects such as MOI, virus types, and host cell lines. The second includes the effects of environmental perturbations, such as incubation volume, cell density, and extracellular concentrations of L(+)-lactate and ammonium. Although the underlying mechanisms of these effects are as yet unknown, the death kinetics of infected cells significantly affects the recombinant protein production. In general, foreign protein production does not correlate with the cell life after infection (c) 1993 John Wiley & Sons, Inc.     

The silk protein, sericin, protects against cell death caused by acute serum deprivation in insect cell culture

Sericin is the silk protein that covers fibroin fibers and functions as a `glue' in the cocoons of silkworms, and its most abundant component, Ser1, contains repeats of Ser- and Thr-rich 38 amino acid residues. The viability of Sf9 insect cells was 20, 57 and 49% on the fifth day and 41, 91 and 70% on the ninth day after serum deprivation in the presence of no additives, 3000 g sericin hydrolysate and 350 g SerD (the peptide containing the two repetitive units) ml^–1, respectively. Thus, the sericin samples were useful in preventing cell death and promoting cellular growth after acute serum deprivation.     

动物细胞培养过程中的细胞自然凋亡

细胞培养过程中的细胞自然凋亡是细胞受环境压力的影响而发生的现象。随着细胞自然凋亡的分子生物学和生物化学研究的深入,对以动物细胞产品生产为目的的细胞培养产业将产生极有价值的影响。采用DNA重组技术把预防细胞自然凋亡的基因导入细胞和在培基中加入具有抗细胞自然凋亡的化合物等手段已用于预防或减缓细胞培养过程中的细胞自然凋亡。这些技术将大大延长细胞达到饱和密度后的培养时间,从而使细胞培养系统的生产效率得以显著提高。     

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.     

A cytotoxic substance in insect cell culture spent media

Summary Spent media from five different insect cell lines when inoculated intoTrichoplusia ni (TN-368) cultures produced cytotoxicity resulting in rounding and detachment of cells. The substance in spent medium from the established cell lineCarpocapsa pomonella (CP-169) is believed to be a toxin, based on the failure to serially passage the agent, the early appearance of the cytotoxic effect, and the inability to detect microbes by culturing techniques as well as by electron microscopy. The ability to extract the toxic substance from CP-169 cells indicates that it is cell associated. Biophysical and biochemical properties of the CP-169 cytotoxin are presented.     

Intrinsic glycosylation potentials of insect cell cultures and insect larvae

Summary The glycosylation and subsequent processing of native and recombinant glycoproteins expressed in established insect cell lines and insect larvae were compared. TheSpodoptera frugiperda (Sf21) andTrichoplusia ni (TN-368 and BTI-Tn-5B1-4) cell lines possessed several intrinsic glycoproteins that are modified with both N- and O-linked oligosaccharides. The N-linked oligosaccharides were identified as both the simple (high mannose) and complex (containing sialic acid) types. Similarly, theT. ni larvae also possessed intrinsic glycoproteins that were modified with O-linked and simple and complex N-linked oligosaccharides. Additionally, human placental, secreted alkaline phosphatase (SEAP) produced during replication of a recombinant baculovirus inT. ni larvae was modified with complex oligosaccharide having sialic acid linked α(2–6) to galactose.     

Quantification of cell culture factors affecting recombinant protein yields in baculovirus-infected insect cells

An experimental study was undertaken to quantify the effects of infection cell density, medium condition, and surface aeration on recombinant protein yields in insect cells. In the absence of surface aeration and fresh medium, insect cells generated higher product yields (on a per cell basis) when infected with recombinant baculovirus at low cell densities, LCD (3 x 10(5)-4 x 10(5) cells/mL), than at high cell densities, HCD (>0.9 x 10(6) cells/mL), for two distinct baculovirus types. Surface aeration of a HCD culture infected in spent medium improved beta-glactosidase yields 5-fold over the nonaerated case. Surface aeration and medium replenishment improved beta-galactosidase yields of a HCD culture by 20-fold (compared to a 1.6-fold improvement for a LCD culture), resulting in cultures with productivties that were independent of the cell density at infection.     

Functional characterization of two human olfactory receptors expressed in the baculovirus Sf9 insect cell system

Olfactory receptors (ORs) are the largest member of the G-protein-coupled receptors which mediate early olfactory perception in discriminating among thousands of odorant molecules. Assigning odorous ligands to ORs is a prerequisite to gaining an understanding of the mechanisms of odorant recognition. The functional expression of ORs represents a critical step in addressing this issue. Due to limitations in heterologous expression, very few mammal ORs have been characterized, and so far only one is from human origin. Consequently, OR function still remains poorly understood, especially in humans, whose genome encodes a restricted chemosensory repertoire compared with most mammal species. In this study, we have designed cassette baculovirus vectors to coexpress human OR 17-209 or OR 17-210 with either G(alpha olf) or G(alpha16) proteins in Sf9 cells. Each OR was found to be expressed at the cell surface and colocalized with both G(alpha) proteins. Using Ca2+ imaging, we showed that OR 17-209 and OR 17-210 proteins are activated by esters and ketones respectively. Odorant-induced calcium response was increased when ORs were coexpressed with G(alpha16) protein, whereas coexpression with G(alpha olf) abolished calcium signaling. This strategy has been found to overcome most of the limitations encountered when expressing an OR protein and has permitted odorant screening of functional ORs. Our approach could thus be of interest for further expression and ligand assignment of other orphan receptor proteins.     

Baculovirus expression system scaleup by perfusion of high-density Sf-9 cell cultures

A perfusion system based on a 4-L stirred tank bioreactor and a custom-designed tangential (cross-flow) filter was assembled to realize a scaleup of the Baculovirus Expression Vector System (BEVS). When perfused with 1 to 1.5 vol/day, Spodoptera frugiperda (Sf-9) insect cell cultures grew from 4 x 10(6) to 15 x 10(6) cells/mL over 3 to 4 days. The possibility of maintaining high specific production of recombinant VP6 protein (from bovine rotavirus) after baculovirus infection of the high-density cultures was then assessed. The process consisted of a growth phase in TNMFH + 10% FBS, followed by infection with Bac-BRV6L recombinant baculovirus and a shift to a low-serum (0 to 1%) medium for perfusion during the production phase. Multiple runs were executed, each including a battery of shaker flask controls at various cell densities and serum concentrations. On average, specific rVP6 production in the bioreactor amounted to 76% of that found in 20-mL shaker cultures simulatingthe bioreactor's high cell density, low serum concentration, and medium renewal rate. Mechanical stress generated by cell/medium separation in theperfusion process reduced cell growth rate but had minimal effect on rVP6production. Our results also indicated that serum concentration during the infection phase affected the rVP6 specific production in a cell density-dependent fashion. Although the feasibility of the cell density scale up was demonstrated, optimization is still needed to achieve a truly cost-effective process.     

The dissociation of insect embryos for cell culture

Summary Procedures and solutions were developed for dissociating embryos ofBlattella germanica in preparation for primary cell culture. Trypsin solutions were maximally effective at 0.01% for germ bands but higher concentrations, 0.05 to 0.1% were needed for embryos in later stages. This investigation was supported by U.S. Public Health Service Research Grant No. AI 09914 from the National Institute of Allergy and Infectious Diseases. This is paper No. 8855, Scientific Journal Series, Minnesota Agricultural Experiment Station. The work was selected from the dissertation of T. J. K. presented for the Ph. D. degree at the University of Minnesota.     

Protein production using the baculovirus‐insect cell expression system

The baculovirus‐insect cell expression system is widely used in producing recombinant proteins. This review is focused on the use of this expression system in developing bioprocesses for producing proteins of interest. The issues addressed include: the baculovirus biology and genetic manipulation to improve protein expression and quality; the suppression of proteolysis associated with the viral enzymes; the engineering of the insect cell lines for improved capability in glycosylation and folding of the expressed proteins; the impact of baculovirus on the host cell and its implications for protein production; the effects of the growth medium on metabolism of the host cell; the bioreactors and the associated operational aspects; and downstream processing of the product. All these factors strongly affect the production of recombinant proteins. The current state of knowledge is reviewed. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:1–18, 2014     

Rapid assessment of Autographa californica nuclear polyhedrosis virus infection of Sf-9 insect cells by analyzing suppression of reagent-induced apoptosis

Spodoptera frugiperda Sf-9 insect cells that undergo apoptosis by the treatment of apoptosis-inducing reagents were individually determined as `comet cells' having a tail of fragmented DNA during single cell gel electrophoresis, the fragmented DNA being migrated from the cells under an electric field of the electrophoresis. However, the apoptosis induction of the cells infected with a recombinant strain of Autographa californica nuclear polyhedrosis virus (AcMNPV) was blocked, probably by an intrinsic anti-apoptotic p35 gene of the virus, because the virus-infected cells did not have a tail of fragmented DNA on a single cell gel electrophoresis. The virus-infected cells were individually discriminated from non-infected cells by determining the anti-apoptotic nature of the cells. At higher multiplicity of infection and under better aeration conditions of virus-infected cultures, the apoptosis-suppressive ratio, which represented a ratio of non-comet cells, was increased more rapidly. This apoptosis-suppressive behavior was a good benchmark for assessing successful infection of insect cells with AcMNPV during very early infectious period and forecasting the subsequent production of recombinant proteins.     

Adaptation of an insect cell line (Agallia constricta) in a mammalian cell culture medium

Summary An established insect cell line (AC20) from the leafhopperAgallia constricta has been adapted to a mammalian cell culture medium based on the formulation of two commercially available media. The cell population doubling time of the adapted line in this medium is approximately 45 hr at 30°C. This research was supported in part by National Science Foundation Grant GB29277X.     

A physiological product-release model for baculovirus infected insect cells

Existing models describe the product release from baculovirus infected insect cells as an unspecific protein leakage occurring in parallel with protein production. The model presented here shows that the observed product release of normally non-secreted proteins can be described through cell death alone. This model avoids the implicit non-physiological assumption of previous models that cells permeable to recombinant protein as well as trypan blue continue to produce protein.     

人白血病抑制因子在昆虫细胞Sf9中的表达

人白血病抑制因子(hLIF)cDNA装入p2bac,受其多角蛋白启动子控制,并与野生型线性杆状病毒DNA共转染昆虫细胞Sf9。经ELISA和免疫印迹证实,该重组病毒感染Sf9 24h后(胞解液)和48h后(培养液),均可测得表达的hLIF,在72h时蛋白浓度可达每毫升(1×10~7细胞)4～10μg;经细胞活性观察表明,该蛋白可促进人白血病细胞U937分化,并使U937内信号分子STAT_3合成增加。结果表明,昆虫细胞表达的hLIF可分泌于培养液中且含量高。它的高表达、易纯化、强活性,有实用价值。     

A two-stage bioreactor system for the production of recombinant proteins using a genetically engineered baculovirus/insect cell system

A two-stage bioreactor scheme was developed for the large-scale production of recombinant proteins using a genetically engineered baculovirus/insect cell system. The first bioreactor was employed for cell growth and the second for cell infection. Silkworm Bm5 cells were infected with a recombinant baculovirus, BmNPV/P5.cat, containing a bacterial chloramphenicol acetyltransferase (CAT) gene under the control of the polyhedrin gene promoter of Bombyx mori nuclear polyhedrosis virus (BmNPV). This recombinant baculovirus has been used as an expression vector for the production of recombinant CAT enzyme. A specific productivity of 82 to 90 mug CAT/(10(6) cells) was obtained using the BmNPV/Bm5 expression system, a yield similar to that achieved using the AcNPV/Sf expression system. Repeated infection of high-density cell cultures did not reduce the specific productivity of the CAT enzyme. Most importantly, the problems associated with the infection of high-density cell cultures were resolved by means of controlled infection conditions and appropriate replenishment of spent culture medium following infection. The glucose uptake rate by the cells following infection was 50% higher than that by the cells before infection. Not only did the infection of high-density cell cultures result in consistent yields of 250 mg/L of CAT enzyme, but also the two-stage bioreactor system was proven to be reliable for a long-term operation beyond 600 h. (c) 1993 John Wiley & Sons, Inc.     

Expression of epoxide hydrolase in insect cells: a focus on the infected cell

Insect cell culture and the baculovirus vector expression system have emerged to be a promising production technique for heterologous proteins. In this article, expression characteristics for membrane-bound epoxide hydrolase are examined. A generic process is presented whereby cells are grown in serum-free media supplemented with serum and then resuspended in serum-free media to simplify purification after infection. The infected cells retain significant metabolic activity during the postinfection stage. Thus, maintaining nutrient supply during the postinfection period is critical, and a low stirring rate will result in oxygen depletion and shift the metabolism of the infected cells toward lactate production which then lowers product yield. This is the first report indicating that glucose is supplied from sucrose decomposition and then metabolized for viral DNA and recombinant protein production in recombinant baculovirus insect expression system. (c) 1993 John Wiley & Sons, Inc.     

A tubular segmented-flow bioreactor for the infection of insect cells with recombinant baculovirus

A continuous process of insect cell (S f9) growth and baculovirus infection is tested with the sequential combination of a CSTR and a tubular reactor. A tubular infection reactor enables continuous introduction of baculovirus and therefore avoids the ‘passage effect’ observed in two-stage CSTR systems. Moreover, a tubular reactor can be used to test cell infection kinetics and the subsequent metabolism of infected insect cells. Unlike batch and CSTR culture, cells in a horizontally positioned tubular reactor settle due to poor mixing. We have overcome this problem by alternately introducing air bubbles and media and by maintaining a linear velocity sufficient to keep cells suspended. This article addresses the development of the tubular reactor and demonstrates its use as an infection system that complements the two-stage CSTR. This revised version was published online in July 2006 with corrections to the Cover Date.