Modeling and optimization of the baculovirus expression vector system in batch suspension culture

A mathematical model has been developed that predicts the cell population dynamics and production of recombinant protein and infective extracellular virus progeny by insect cells after infection with baculovirus in batch suspension culture. Infection in the model is based on the rate of virus attachment to suspended insect cells under culture conditions. The model links the events following infection with the sequence of gene expression in the baculovirus replicative cycle. Substrate depletion is used to account for the decrease in product yield observed when infecting at high cell densities. Model parameters were determined in shaker flasks for two media: serum-supplemented IPL-41 medium and serum free Sf900II medium. There was good agreement between model predictions and the results from an independent series of experiments performed to validate the mode. The model predicted: (1) the optimal time of infection at high multiplicity of infection: (2) the timing and magnitude of recombinant protein production in a 2-L bioreactor; and (3) the timing and magnitude of recombinant protein production at multiplicities of infection from 0.01 to 100 plaque-forming units per cell. Through its ability to predict optimal infection strategies in batch suspension culture, the model has use in the design and optimization of large-scale systems for the production of recombinant products using the baculovirus expression vector system. (c) 1994 John Wiley & Sons, Inc.     

Purification and characterization of recombinant human soluble guanylate cyclase produced from baculovirus-infected insect cells

Soluble guanylate cyclase (sGC) has been purified from 100 L cell culture infected by baculovirus using the newer and highly effective titerless infected-cells preservation and scale-up (TIPS) method. Successive passage of the enzyme through DEAE, Ni²⁺-NTA, and POROS Q columns obtained approximately 100 mg of protein. The sGC obtained by this procedure was already about 90% pure and suitable for various studies which include high throughput screening (HTS) and hit follow-up. However, in order to obtain enzyme of greater homogeneity and purity for crystallographic and high precision spectroscopic and kinetic studies of sGC with select stimulators, the sGC solution after the POROS Q step was further purified by GTP-agarose affinity chromatography. This additional step led to the generation of 26 mg of enzyme that was about 99% pure. This highly pure and active enzyme exhibited a M_r = 144,933 by static light scattering supportive of a dimeric structure. It migrated as a two-band protein, each of equal intensity, on SDS–PAGE corresponding to the α (M_r 77,000) and β (M_r 70,000) sGC subunits. It showed an A₄₃₀/A₂₈₀ = 1.01, indicating one heme per heterodimer, and a maximum of the Soret band at 430 nm indicative of a penta-coordinated ferrous heme with a histidine as the axial ligand. The Soret band shifted to 398 nm in the presence of an NO donor as expected for the formation of a penta-coordinated nitrosyl-heme complex. Non-stimulated sGC had k_cat/K_m = 1.7 × 10⁻³ s⁻¹ μM⁻¹ that increased to 5.8 × 10⁻¹ s⁻¹ μM⁻¹ upon stimulation with an NO donor which represents a 340-fold increase due to stimulation. The novel combination of using the TIPS method for co-expression of a heterodimeric heme-containing enzyme, along with the application of a reproducible ligand affinity purification method, has enabled us to obtain recombinant human sGC of both the quality and quantity needed to study structure–function relationships.     

Development of an antibody-based assay for determination of baculovirus titers in 10 hours

The baculovirus expression system has been used to produce large amounts of biologically active proteins by infecting insect cells with a recombinant baculovirus expressing the target protein. For an efficient expression of the target protein, it is necessary to infect insect cells with an adequate amount of virus. However, current methods are time-consuming and either have technical difficulties or are limited as a result of virus expression mechanism using a reporter gene. A novel method is developed to yield virus titers in 10 h that is easy to perform using 96-well plates and applicable to both any Autographa californica nucleopolyhyderovirus (AcNPV) and Bombyx mori nucleopolyhedrovirus (BmNPV)-based recombinant baculovirus. This assay uses an antibody to a DNA-binding protein to detect the infected cells via immunostaining. The titer is determined by counting foci produced as a result of infection of the virus under a fluorescent microscope. The required incubation period was shortened considerably because infected cells expressed viral antigens at the post-infection time of 4 h. Therefore, 10 h was enough to estimate the virus titer including virus infection time, insect cell culture, and estimation of virus titer. Titers determined using this immunological assay are comparable, both in value and validity, to those obtained using a traditional method, provided that the stocks have titers above 10(3) pfu/mL.     

Production of recombinant herpes simplex virus protease in 10-L stirred vessels using a baculovirus–insect cell expression system

A gene expression system using recombinant Autographa californica nuclear polyhedrosis virus (baculovirus) and Sf-9 cells has been scaled up to the 10-L tank level and shown to be capable of producing herpes simplex virus (HSV) protease in serum-free media. High densities of Spodoptera frugiperda (Sf-9) cells were achieved by modifying two 10-L Biolafitte fermenters specifically for insect cell growth. The existing Rushton impellers were replaced by marine impellers to reduce shear and the aeration system was modified to allow external addition of air/O₂ mixtures at low flow rates through either the sparge line or into the head space of the fermenter. To inoculate the tanks, Sf-9 cells were adapted to grow to high cell densities (6–10 × 10⁶ cells ml⁻¹) in shake flasks in serum-free media. With these procedures, cell densities of 5 × 10⁶ cells ml⁻¹ were routinely achieved in the 10-L tanks. These cells were readily infected with recombinant baculovirus expressing the 247-amino acid catalytic domain of the HSV-1 strain 17 protease UL26 gene as a glutathione-S-transferase (GST) fusion protein (GST-247). Three days after infection at a multiplicity of infection (MOI) of 3 pfu cell⁻¹, the GST-247 fusion protein was purified from a cytoplasmic lysate by Glutathione Sepharose 4-B affinity chromatography with reproducible yields of 11–38 mg L⁻¹ of recombinant protein and ≥ 90% purity. Maximum production of this protein was observed at a cell density of 5.0 × 10⁶ cells ml⁻¹. Received 09 December 1996/ Accepted in revised form 13 April 1997     

The kinetics of baculovirus adsorption to insect cells in suspension culture

The influence of various culture parameters on the attachment of a recombinant baculovirus to suspended insect cells was examined under normal culture conditions. These parameters included cell density, multiplicity of infection, and composition of the cell growth medium. It was found that the fractional rate of virus attachment was independent of the multiplicity of infection but dependent on the cell density. A first order mathematical model was used to simulate the adsorption kinetics and predict the efficiency of virus attachment under the various culture conditions. This calculated efficiency of virus attachment was observed to decrease at high cell densities, which was attributed to cell clumping. It was also observed that virus attachment was more efficient in Sf900II serum free medium than it was in IPL-41 serum-supplemented medium. This effect was attributed to the protein in serum which may coat the cells and so inhibit adsorption. A general discussion relating the observations made in-these experiments to the kinetics of recombinant baculovirus adsorption to suspended insect cells is presented.     

High-level expression of orange fluorescent protein in the silkworm larvae by the Bac-to-Bac system

This novel orange fluorescent protein (OFP) emits brilliant orange fluorescent light. OFP has high fluorescence quantum yield, fast maturation rate, and stability, which imply this protein should be the most favorable biotechnological tools used to investigate the function of target gene by visualizing, monitoring, and quantifying in living cells. B. mori, silkworm has been used as an important bioreactor for the production of recombinant proteins through baculovirus expression system (BES). In this paper, we used infection technique which introduced the baculovirus DNA into silkworms using a cationic lipofectin reagent instead of directly injecting the virus, and demonstrated a high-level expression of the orange fluorescent protein (OFP) gene in the Bombyx mori, silkworm larvae. When recombinant rBacmid/BmNPV/OFP DNA ranging from 50–100 ng/larval was injected, a sufficient OFP expression in hemolymph was harvested. The recombinant viruses could be obtained from the hemolymph of infected larvae and stored as seed which could be used for the large-scale expression. This procedure omitted the costly and labor-consumed insect cell culture. Further investigation of OFP should provide us with more insight in unlocking the mystery of the mechanisms of autocatalytic bioluminescence and its utilization in biotechnology.     

Expression of Rice Gall Dwarf Virus Outer Coat Protein Gene (S8) in Insect Cells

To obtain the P8 protein of Rice gall dwarf virus (RGDV) with biological activity,its outer coat protein gene S8 was expressed in Spodoptera frugiperda (Sf9) insect cells using the baculovirus expression system.The S8 gene was subcloned into the pFastBacTM1 vector,to produce the recombinant baculovirus transfer vector pFB-S8.After transformation,pFB-S8 was introduced into the competent cells (E.coli DH10Bac) containing a shuttle vector,Bacmid,generating the recombinant bacmid rbpFB-S8.After being infected b...     

Insect cell culture for industrial production of recombinant proteins

Insect cells used in conjunction with the baculovirus expression vector system (BEVS) are gaining ground rapidly as a platform for recombinant protein production. Insect cells present several comparative advantages to mammalian cells, such as ease of culture, higher tolerance to osmolality and by-product concentration and higher expression levels when infected with a recombinant baculovirus. Here we review some of the recent developments in protein expression by insect cells and their potential application in large-scale culture. Our current knowledge of insect cell metabolism is summarised and emphasis is placed on elements useful in the rational design of serum-free media. The culture of insect cells in the absence of serum is reaching maturity, and promising serum substitutes (hydrolysates, new growth and production-enhancing factors) are being evaluated. Proteolysis is a problem of the BEVS system due to its lytic nature, and can, therefore, be a critical issue in insect cell bioprocessing. Several cell- or baculovirus proteases are involved in degradation events during protein production by insect cells. Methods for proteolysis control, the optimal inhibitors and culture and storage conditions which affect proteolysis are discussed. Finally, engineering issues related to high-density culture (new bioreactor types, gas exchange, feeding strategies) are addressed in view of their relevance to large-scale culture.     

Reduction of the infectivity of baculovirus stocks frozen at ultra‐low temperature in serum‐free media: The role of lipid emulsions

The infectivity of stocks of baculoviruses produced in serum‐free media is sensitive to freezing at ultra‐low temperatures. The objective of this work was to elucidate the causes of such sensitivity, using as a model the freezing of stocks of Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV), a baculovirus widely employed as biological insecticide. Titers of supernatants of cell cultures infected with AgMNPV in four different serum‐free media supplemented with lipid emulsions were reduced by 50 to 90% after six months freezing. By using a full factorial experiment, freezing and lipid emulsion, as well as the interaction between them, were identified as the main factors reducing the viral titer. The virucidal effect of the lipid emulsion was reproduced by one of their components, the surfactant Polysorbate 80. Damaged viral envelopes were observed by transmission electron microscopy in most particles frozen in a medium supplemented with lipid emulsion or Polysorbate 80. Additionally, Polysorbate 80 also affected the infectivity of AgMNPV stocks that were incubated at 27°C. The identification of the roles played by the lipid emulsion and Polysorbate 80 is not only a contribution to the understanding of the mechanisms underlying the inactivation of baculovirus stocks produced in serum‐free media during storage at ultra‐low temperature, but is also an input for the rational development of new procedures aimed at improving both the preservation of baculovirus stocks and the composition of culture media for the production of baculovirus‐based bioproducts in insect cells. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1559–1569, 2016     

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.     

HCV结构蛋白在昆虫细胞中的表达及病毒样颗粒的组装

本文利用Bac-to-Bac杆状病毒表达系统构建了含有丙型肝炎病毒(Hepatitis C Virus,HCV)结构蛋白编码基因的重组杆状病毒vAcHCVspl,并获得了HCV结构蛋白在昆虫细胞Sf21中的表达。HCV mRNA转录和蛋白质表达时相分析表明,感染后16h HCV结构蛋白编码基因开始转录,72h达最高峰;蛋白质表达则是在感染后48h开始,72h达到高峰。电镜观察表明vAcHCVspl感染的Sf21细胞96h时在细胞质中可见很多空泡,空泡中可见50nm的球形颗粒,为HCV结构蛋白组装的病毒样颗粒。     

Improved baculovirus vectors expressing barnase using promoters from Cotesia plutellae bracovirus

The goal of this study was to create a novel baculovirus expression system that does not require recombinant virus purification steps. Transfection of insect cells with transfer vectors containing barnase under control of the Cotesia plutellae bracovirus (CpBV) promoters ORF3004 or ORF3005 reduced cell growth. Co-transfection with bApGOZA DNA yielded no recombinant viruses and non-recombinant backgrounds. To further investigate the detrimental effects of barnase on insect cells, two recombinant bacmids harboring the barnase gene under control of the CpBV promoters, namely bAcFast-3004ProBarnase and bAcFast-3005ProBarnase, were constructed. While no viral replication was observed when only the recombinant bacmids were transfected, recombinant viruses were generated when the bacmids were co-transfected with the transfer vector, pAcUWPolh, through substitution of the barnase gene with the native polyhedrin gene by homologous recombination. Moreover, no non-recombinant backgrounds were detected from unpurified recombinant stocks using PCR analysis. These results indicate that CpBV promoters can be used to improve baculovirus expression vectors by means of lethal gene expression under the control of these promoters.     

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.     

Highly passage of <Emphasis Type="Italic">Spodoptera litura</Emphasis> cell line causes its permissiveness to baculovirus infection

It is well known that the characteristics of cell lines possibly alter when cell lines are at high-passage number because of the environmental selection. We do not know whether non-permissive or low-permissive cell lines could become permissive or more permissive to virus infection after over-high passage. In the present studies, the alteration of the permissiveness of Spodoptera litura cell line Sl-zsu-1 to three baculovirus infection was investigated after over-high passage, and the possible mechanisms are also investigated. Vigorous apoptosis in Sl-zsu-1 cells was induced by both the recombinant Autographa californica multiple nucleopolyhedrovirus AcMNPV-GFP-actin and the celery looper Anagrapha falcifera multiple nucleopolyhedrovirus AfMNPV, suggesting the replication of the two viruses was blocked by apoptosis. However, the cells infected by S. litura multicapsid nucleopolyhedrovirus SpltMNPV did not undergo apoptosis, but the SpltMNPV titre of the supernatant was not detectable, suggesting this cell line was low-permissive for this virus infection and other factor(s) involved in blockage of the virus replication except apoptosis. However, when Sl-zsu-1 cells had been subcultured continuously for more than 4 years (high-passage cell), which was named as Sl-HP cell line afterwards, no significant apoptosis was induced by the three baculovirus in Sl-HP cells, and many replicated virions or nucleocapsids were observed in the cells. But the permissiveness of Sl-HP cells to the three viruses was very different according to the titre of viruses in the cell cultures. Interestingly, the DNA extracted from SpltMNPV could induce vigorous apoptosis of Sl-HP cells. Altogether, Sl-zsu-1 cell line becomes more permissive to baculovirus infection after over-high passage and multiple paths can block the baculovirus infectivity.     

Identification of Epstein-Barr virus terminal protein 1 (TP1) in extracts of four lymphoid cell lines, expression in insect cells, and detection of antibodies in human sera.

The terminal proteins TP1 and TP2 are putative products of Epstein-Barr virus (EBV) genes expressed during the latent cycle of the virus. They are predicted to code for 53- and 40-kilodalton integral membrane proteins. We used the baculovirus Autographa californica nuclear polyhedrosis virus as an expression vector to produce TP1 in large amounts in insect cells. The DNA sequences used to express TP1 originated from a TP1 cDNA derived from an M-ABA/CBL1 cDNA library. Rabbit antisera raised against procaryotic TP1 fusion proteins recognized a monomer and a dimer of the recombinant TP1 protein in the infected insect cells. Immunofluorescence studies of living insect cells showed that the recombinant protein is located in the plasma membrane. The insect cells infected with the recombinant baculovirus producing TP1 provided a test system to screen human antisera for TP1 antibodies. A total of 168 human EBV-positive and EBV-negative antisera were studied. TP1 antibodies were detected only in sera from nasopharyngeal carcinoma patients (16 out of 42). Rabbit antiserum raised against the recombinant TP1 protein expressed in the baculovirus system specifically recognized a protein of about 54 kilodaltons in the lymphoblastoid cell lines M-ABA and M-ABA/CBL1 and in the Burkitt's lymphoma cell lines BL18 and BL72. This protein could be located in the total membrane fraction of M-ABA cells and is upregulated by treating the cells with 12-O-tetradecanoylphorbol-13-acetate.     

虎源流感病毒HA 基因的系统发生分析及其在杆状病毒系统中的表达

通过对虎源流感病毒A/ Tiger/ Harbin/01/ 2003 (H5N1)的HA 基因进行克隆与序列测定,证明该基因全长为1 731 bp,读码框由1 707个碱基组成,编码568 个氨基酸。对HA 基因的进化分析表明,该基因与H5 亚型流感病毒的HA 基因同源性最高,其HA 裂解位点由6 个碱性氨基酸插入序列(RRRKKR)组成,符合高致病性禽流感病毒的分子特征。将HA 基因克隆入杆状病毒转座载体质粒pFastBacⅠ,构建重组质粒pFastBac-HA;再将该重组质粒转化DH10 Bac 感受态细菌,在体内进行重组,并经三重抗性与蓝白斑筛选,得到杆状病毒重组质粒Bacmid-HA;将Bacmid-HA 转染sf9 细胞,获得重组杆状病毒。经Western-blotting 检测,HA 蛋白在重组杆状病毒中获得表达。用感染重组病毒的sf9 细胞免疫小鼠,2 次免疫后2 周可诱导小鼠产生1∶ 8 ～1∶ 16 的血凝抑制抗体,表明虎源流感病毒的HA 基因在重组杆状病毒系统中得到了正确表达。     

人视黄醇结合蛋白4在杆状病毒系统中的表达及其多克隆抗体制备

旨在利用杆状病毒系统表达、制备人视黄醇结合蛋白(RBP4)并检测其免疫原性。将人RBP4基因片段及信号肽SS64片段亚克隆到杆状病毒转移载体pFastBac-dual(pFBd)中,获得相应的重组转移质粒;转化大肠杆菌菌株DH10bac,转座后经筛选获得重组穿梭质粒rbacmid,将重组穿梭质粒转染孔板培养的Sf9细胞,获得含人RBP4表达框的重组杆状病毒,经过扩增获得毒种。毒种感染对数生长期的Sf9细胞并表达人RBP4蛋白(I-RBP4),通过SDS-PAGE和Western blotting对表达蛋白进行检测和鉴定。用毒种感染悬浮培养的Sf9细胞制备一批RBP4蛋白,完成SDS、Western blotting的检测及少量的多抗制备。纯化重组蛋白并与E.coli重组人RBP4(E-RBP4)分别免疫家兔。实验结果,酶切鉴定及测序证实重组转移质粒构建正确;成功构建重组RBP4-bacmid;人RBP4蛋白在昆虫细胞获得高效表达。表达的RBP4蛋白可以分泌到培养基中,分子量约为23 kDa,经过计算表达量为100 mg/L;纯化蛋白免疫兔子制备了多抗血清,血清滴度为1∶100 000,高于原核表达的抗体滴度(1∶10 000),与人体提纯蛋白制备的抗体滴度相近。杆状病毒系统高效表达了人的RBP4蛋白,具有较好的抗原性,并获得高亲和力的抗血清,为下一步的人血RBP4检测试剂盒的制备打下了坚实的基础。     

Baculovirus expression systems for recombinant protein production in insect and mammalian cells

The baculovirus vector systems has been extensively used for the expression of foreign gene products in insect and mammalian cells. New advances increase the possibilities and applications of the baculovirus expression system, which has the capability to express multiple genes simultaneously within a single infected insect cells and to use recombinant virus with mammalian cell-active expression cassettes to permit expression of recombinant proteins in mammalian cells in vitro and in vivo. Future investigations of the baculovirus expression system designed for specific target cells, can open wide variety of applications. This review summarizes the recent achievements in applications the baculovirus vector systems and optimization recombinant protein expression in both insect and mammalian cell lines.     

Comparative study of variola virus and monkeypox virus interferon-gamma-binding

DNA fragments containing genes for coding IFN-gamma-binding proteins (IFNgammaBPs) of variola virus (VARV) and monkeypox virus (MPXV) were obtained from viral genomes using PCR. Isolated genes coding desired proteins were expressed in the insect Sf21 cells using baculovirus expression system. Secreted recombinant IFNgammaBPs were isolated from culture medium of infected Sf21 cells through affinity chromatography procedure. SDS-PAAG and Western blot analysis of culture medium of infected insect cells and preparations of purified recombinant IFNgammaBPs indicated that recombinant viral proteins were dimerized even in the absence of ligand (hIFNgamma) unlike their cell (eucaryotic) analogs. Biological activity of the recombinant IFNgammaBPs were studied in the test of protective effect inhibition of hIFNgamma on L68 cells infected with murine encephalomyocarditis virus. It was shown that recombinant IFNgammaBPs had dose-dependent IFNgamma-inhibiting activity. A possibility of the elaboration of new therapeutics for anti-hIFNgamma therapy on the base of IFNgammaBPs is discussed.