Stable High-level Expression Research Articles

Mage transposon: a novel gene delivery system for mammalian cells.

Transposons, as non-viral integration vectors, provide a secure and efficient method for stable gene delivery. In this study, we have discovered Mage (MG), a novel member of the piggyBac(PB) family, which exhibits strong transposability in a variety of mammalian cells and primary T cells. The wild-type MG showed a weaker insertion preference for near genes, transcription start sites (TSS), CpG islands, and DNaseI hypersensitive sites in comparison to PB, approaching the random insertion pattern. Utilizing in silico virtual screening and feasible combinatorial mutagenesis in vitro, we effectively produced the hyperactive MG transposase (hyMagease). This variant boasts a transposition rate 60% greater than its native counterpart without significantly altering its insertion pattern. Furthermore, we applied the hyMagease to efficiently deliver chimeric antigen receptor (CAR) into T cells, leading to stable high-level expression and inducing significant anti-tumor effects both in vitro and in xenograft mice models. These findings provide a compelling tool for gene transfer research, emphasizing its potential and prospects in the domains of genetic engineering and gene therapy.

The effect of 5′ and 3′ non-translated regions on the expression of a transgene from a Newcastle disease virus vector

Newcastle disease virus (NDV) is an avian virus and a promising vector for the development of vaccines for veterinary and human use. The optimal vaccine vector performance requires a stable high-level expression of a transgene. The foreign genes are usually incorporated in the genome of NDV as individual transcription units, whose transcription and subsequent translation of the mRNA are regulated by the 5′ and 3′ untranslated regions (UTRs) flanking the open reading frame of the transgene. Here, we investigated if the UTRs derived from the cognate NDV genes would increase the expression of a model protective antigene from an NDV vector. Our results show that in chicken DF1 cells, none of the UTRs tested significantly outperformed generic short sequences flanking the transgene, while in human HeLa cells, UTRs derived from the M gene of NDV statistically significantly increased the expression of the transgene. The UTRs derived from the HN gene significantly downregulated the transgene expression in both cell cultures. Further experiments demonstrated that NDV UTRs differently affect the mRNA abundance and translation efficacy. While both M and HN UTRs decreased the level of the transgene mRNA in infected cells compared to the mRNA flanked by generic UTRs, M, and particularly, HN UTRs strongly increased the mRNA translation efficacy. The major determinants of translation enhancement are localized in the 5′UTR of HN. Thus, our data reveal a direct role of NDV UTRs in translational regulation, and inform future optimization of NDV vectors for vaccine and therapeutic use.

Promoter from Chinese hamster elongation factor-1a gene and Epstein-Barr virus terminal repeats concatemer fragment maintain stable high-level expression of recombinant proteins.

The Chinese hamster ovary (CHO) cell line is the main host for the high-titer production of therapeutic and diagnostic proteins in the biopharmaceutical industry. In most cases, plasmids for efficient protein expression in CHO cells are based on the cytomegalovirus (CMV) promoter. The autologous Chinese hamster eukaryotic translation elongation factor 1α (EEF1A1) promoter is a viable alternative to the CMV promoter in industrial applications. The EEF1A1 promoter and its surrounding DNA regions proved to be effective at maintaining high-level and stable expression of recombinant proteins in CHO cells. EEF1A1-based plasmids' large size can lead to low transfection efficiency and hamper target gene amplification. We hypothesized that an efficient EEF1A1-based expression vector with a long terminal repeat fragment from the Epstein-Barr virus (EBVTR) could be truncated without affecting promoter strength or the long-term stability of target gene expression. We made a series of deletions in the downstream flanking region of the EEF1A1 gene, and then in its upstream flanking region. The resulting plasmids, which coded for the enhanced green fluorescent protein (eGFP), were tested for the level of eGFP expression in the populations of stably transfected CHO DG44 cells and the stability of eGFP expression in the long-term culture in the absence of selection agents. It was shown that in the presence of the EBVTR fragment, the entire downstream flanking region of the EEF1A1 gene could be excluded from the plasmid vector. Shortening of the upstream flanking region of the EEF1A1 gene to a length of 2.5 kbp also had no significant effect on the level of eGFP expression or long-term stability. The EBVTR fragment significantly increased expression stability for both the CMV and EEF1A1 promoter-based plasmids, and the expression level drop during the two-month culture was more significant for both CMV promoter-based plasmids. Target protein expression stability for the truncated plasmid, based on the EEF1A1 gene and EBVTR fragment, is sufficient for common biopharmaceutical applications, making these plasmid vectors a viable alternative to conventional CMV promoter-based vectors.

OXA-23 β-Lactamase Overexpression in Acinetobacter baumannii Drives Physiological Changes Resulting in New Genetic Vulnerabilities.

ABSTRACTβ-Lactamase expression is the major mechanism of resistance to penicillins, cephalosporins, and carbapenems in the multidrug-resistant (MDR) bacterium Acinetobacter baumannii. In fact, stable high-level expression of at least one β-lactamase has been rapidly increasing and reported to occur in up to 98.5% of modern A. baumannii isolates recovered in the clinic. Moreover, the OXA-51 β-lactamase is universally present in the A. baumannii chromosome, suggesting it may have a cellular function beyond antibiotic resistance. However, the consequences associated with OXA β-lactamase overexpression on A. baumannii physiology are not well understood. Using peptidoglycan composition analysis, we show that overexpressing the OXA-23 β-lactamase in A. baumannii drives significant collateral changes with alterations consistent with increased amidase activity. Consequently, we predicted that these changes create new cellular vulnerabilities. As proof of principle, a small screen of random transposon insertions revealed three genes, where mutations resulted in a greater than 19-fold loss of viability when OXA-23 was overexpressed. The identified genes remained conditionally essential even when a catalytically inactive OXA-23 β-lactamase was overexpressed. In addition, we demonstrated a synergistic lethal relationship between OXA-23 overexpression and a CRISPR interference (CRISPRi) knockdown of the essential peptidoglycan synthesis enzyme MurA. Last, OXA-23 overexpression sensitized cells to two inhibitors of peptidoglycan synthesis, d-cycloserine and fosfomycin. Our results highlight the impact of OXA-23 hyperexpression on peptidoglycan integrity and reveal new genetic vulnerabilities, which may represent novel targets for antimicrobial agents specific to MDR A. baumannii and other OXA β-lactamase-overexpressing Enterobacteriaceae, while having no impact on the normal flora.

Construction of an alkaline protease overproducer strain based on Bacillus licheniformis 2709 using an integrative approach

Bacillus licheniformis 2709 is a potential cell factory for the production of alkaline protease AprE, which has important value in industrial application but still lacks sufficient production capacity. To address this problem, we investigated the effects of the secretory viscous materials on the synthesis of AprE, which might seriously affect the industrial fermentation. Furthermore, an iterative chromosomal integration strategy at various chromosomal loci was implemented to achieve stable high-level expression of AprE in B. licheniformis 2709. The host was genetically modified by disrupting the native pgs cluster controlling the biosynthesis of viscous poly-glutamic acid identified in the study by GC/MS, generating a mutant with significantly higher biomass and better bioreactor performance. We further enhanced the expression of alkaline protease by integrating two additional aprE expression cassettes into the genome, generating the integration mutant BL ∆UEP-3 with three aprE expression cassettes, whose AprE enzyme activity in shake flasks reached 25,736 ± 997 U/mL, which was 136% higher than that of the original strain, while the aprE transcription level increased 4.05 times. Thus, an AprE high-yielding strain with excellent fermentation traits was engineered, which was more suitable for bulk-production. Finally, the AprE titer was further increased in a 5-L fermenter, reaching 57,763 ± 1039 U/mL. In summary, genetic modification is an enabling technology for enhancing enzyme production by eliminating the unfavorable characteristics of the host and optimizing the expression of aprE through iterative chromosomal integration. We believe that the protocol developed in this study provides a valuable reference for chromosomal overexpression of proteins or bioactive molecules in other Bacillus species.

Select Porcine Elongation Factor 1α Sequences Mediate Stable High-Level and Upregulated Expression of Heterologous Genes in Porcine Cells in Response to Primate Serum.

Genetically engineered (GE) pigs with various combinations of genetic profiles have been developed using heterologous promoters. This study aimed to identify autologous promoters for high and ubiquitous expression of xenotransplantation relevant genes in GE pigs. A 1.4 kb upstream regulatory sequence of porcine elongation factor 1α (pEF1α) gene was selected and isolated for use as a promoter. Activity of the pEF1α promoter was subsequently compared with that of the cytomegalovirus (CMV) promoter, CMV enhancer/chicken β-actin (CAG) promoter, and human EF1α (hEF1α) promoter in different types of pig-derived cells. Comparative analysis of luciferase and mutant human leukocyte antigen class E-F2A-β-2 microglobulin (HLA-E) expression driven by pEF1α, CMV, CAG, and hEF1α promoters revealed the pEF1α promoter mediated comparable expression levels with those of the CAG promoter in porcine ear skin fibroblasts (PEFs) and porcine kidney-15 (PK-15) cells, but lower than those of the CAG promoter in porcine aortic endothelial cells (PAECs). The pEF1α promoter provided long-term stable HLA-E expression in PEFs, but the CAG promoter failed to sustain those levels of expression. For xenogeneic serum-induced cytotoxicity assays, the cells were cultured for several hours in growth medium supplemented with primate serum. Notably, the pEF1α promoter induced significant increases in luciferase and HLA-E expression in response to primate serum in PAECs compared with those driven by the CAG promoter, suggesting the pEF1α promoter could regulate temporal expression of heterologous genes under xenogeneic-cytotoxic conditions. These results suggest the pEF1α promoter may be valuable for development of GE pigs spatiotemporally and stably expressing immunomodulatory genes for xenotransplantation.

Bioluminescence Imaging of Transplanted Mesenchymal Stem Cells by Overexpression of Hepatocyte Nuclear Factor4α: Tracking Biodistribution and Survival.

The purposes of this study were to construct immortalized human bone marrow mesenchymal stem cells (UE7T-13) with overexpression of the hepatocyte nuclear factor4α (hHNF4α) and luciferase2-mKate2 dual-fusion reporter gene, further investigate their impact on treating acute liver injury (ALI) in rats, and track their biodistribution and survival by bioluminescence imaging (BLI). The hHNF4α and luciferase2-mKate2 genes were transduced by a lentiviral vector into UE7T-13 cells (named E7-hHNF4α-R cells), and expression was verified by immunofluorescence, RT-PCR, and flow cytometry. E7-hGFP-R cells expressing the luciferase2-mKate2/hGFP gene served as a negative group. A correlation between the bioluminescence signal and cell number was detected by BLI. The ALI rats were established and divided into three groups: PBS, E7-hGFP-R, and E7-hHNF4α-R. After transplantation of 2.0 × 106 cells, BLI was used to dynamically track their biodistribution and survival. The restoration of biological functions was assessed by serum biochemical and histological analyses. Stable high-level expression of hHNF4α and mKate2 protein was established in the E7-hHNF4α-R cells in vitro. The E7-hHNF4α-R cells strongly expressed hGFP, hHNF4α, and mKate2 proteins, and the hHNF4α gene. hGFP-mKate2 dual-positive cell expression reached approximately 93%. BLI verified that a linear relationship existed between the cell number and bioluminescence signal (R2 = 0.9991). The cells improved liver function in vivo after transplantation into the ALI rat liver, as evidenced by the fact that AST and ALT temporarily returned to normal levels in the recipient ALI rats. The presence of the transplanted E7-hGFP-R and E7-hHNF4α-R cells in recipient rat livers was confirmed by BLI and immunohistochemistry. However, the cells were cleared by the immune system a short time after transplantation into ALI rats with a normal immune system. Our data revealed that the E7-hHNF4α-R cells can transiently improve damaged liver function and were rapidly cleared by the immune system. In addition, BLI is a useful tool to track transplanted cell biodistribution and survival.

Arabidopsis thaliana cold-regulated 47 gene 5′-untranslated region enables stable high-level expression of transgenes

Transgene expression is regulated through several steps, this study focuses on the mRNA translation step. The expression level of transgenes can be increased by 5'-untranslated region (5'UTR) sequences in certain genes which act as translational enhancers. On the other hand, translation in most mRNA species is repressed by growth, development, and stress events. There is a possibility that transgene mRNA is also repressed in these conditions, despite the use of a translational enhancer. Therefore, a consistently efficient translational enhancer is needed to develop a reliable transgene expression system. Herein we searched for mRNAs translated stably under different growth, development and environmental conditions using data sets of polysome fraction assays and microarray analysis. Correct 5'UTR sequences of candidate genes were determined by cap analysis of gene expression and we tested translational ability of the candidate 5'UTRs by reporter assays. We found the 5'UTR of cold-regulated 47 gene to be an effective translational enhancer, contributing to stable high-level expression under various conditions.

Stable high-level expression of factor VIII in Chinese hamster ovary cells in improved elongation factor-1 alpha-based system

BackgroundRecombinant factor VIII (FVIII), used for haemophilia A therapy, is one of the most challenging among the therapeutic proteins produced in heterologous expression systems. Deletion variant of FVIII, in which the entire domain B is replaced by a short linker peptide, was approved for medical use. Efficacy and safety of this FVIII deletion variant are similar to full-length FVIII preparations while the level of production in CHO cells is substantially higher.Typical levels of productivity for CHO cell lines producing deletion variant FVIII-BDD SQ, described elsewhere, are 0.5–2 IU/ml, corresponding to the concentration of FVIII of about 0.2 μg/ml. Using standard vectors based on the cytomegalovirus promoter (CMV) and the dihydrofolate reductase cDNA we have previously obtained the cell line secreting 0.5 IU/ml of FVIII-BDD, which roughly corresponds to the previously published data.ResultsAn expression system based on CHO genomic sequences including CHO-EEF1A promoter and Epstein-Barr virus terminal repeat fragment allowed us to achieve 80-fold increase in the production level as compared with the conventional expression system based on the CMV promoter.Immediately after the primary selection FVIII -producing cells secreted 5–10 IU/ml of FVIII-BDD, and after multi-stage methotrexate-driven amplification a stable clonal line 11A4H was selected, secreting 39 IU/ml of FVIII-BDD in the simple batch culturing conditions, which considerably exceeds known indicators for industrial producers of this protein. In contrast to other FVIII-BDD producing lines 11A4H accumulates low proportion of the secreted FVIII on the membrane. Its productivity may be further increased approximately two-fold by adding sodium butyrate and butylated hydroxyanisol to the culture medium.A five-stage purification process for the factor VIII was employed. It allowed isolation of the intact FVIII-BDD as was confirmed by mass spectrometry. Purified FVIII-BDD has a specific activity of 11,000 IU/mg, similar to known recombinant FVIII drugs.ConclusionsThe recombinant FVIII-BDD was produced in CHO cells without addition of any animal-derived materials, purified and characterized. Novel genetic constructions for the expression of heterologous proteins combined with optimized cultivation method allowed to obtain the secretion level of biologically active recombinant FVIII increased by almost ten times as compared with the previously published analogues.

Early transduction produces highly functional chimeric antigen receptor-modified virus-specific T-cells with central memory markers: a Production Assistant for Cell Therapy (PACT) translational application.

BackgroundVirus-specific T-cells (VSTs) proliferate exponentially after adoptive transfer into hematopoietic stem cell transplant (HSCT) recipients, eliminate virus infections, then persist and provide long-term protection from viral disease. If VSTs behaved similarly when modified with tumor-specific chimeric antigen receptors (CARs), they should have potent anti-tumor activity. This theory was evaluated by Cruz et al. in a previous clinical trial with CD19.CAR-modified VSTs, but there was little apparent expansion of these cells in patients. In that study, VSTs were gene-modified on day 19 of culture and we hypothesized that by this time, sufficient T-cell differentiation may have occurred to limit the subsequent proliferative capacity of the transduced T-cells. To facilitate the clinical testing of this hypothesis in a project supported by the NHLBI-PACT mechanism, we developed and optimized a good manufacturing practices (GMP) compliant method for the early transduction of VSTs directed to Epstein-Barr virus (EBV), Adenovirus (AdV) and cytomegalovirus (CMV) using a CAR directed to the tumor-associated antigen disialoganglioside (GD2).ResultsAd-CMVpp65-transduced EBV-LCLs effectively stimulated VSTs directed to all three viruses (triVSTs). Transduction efficiency on day three was increased in the presence of cytokines and high-speed centrifugation of retroviral supernatant onto retronectin-coated plates, so that under optimal conditions up to 88% of tetramer-positive VSTs expressed the GD2.CAR. The average transduction efficiency of early-and late transduced VSTs was 55 ± 4% and 22 ± 5% respectively, and early-transduced VSTs maintained higher frequencies of T cells with central memory or intermediate memory phenotypes. Early-transduced VSTs also had higher proliferative capacity and produced higher levels of TH1 cytokines IL-2, TNF-α, IFN-γ, MIP-1α, MIP-1β and other cytokines in vitro.ConclusionsWe developed a rapid and GMP compliant method for the early transduction of multivirus-specific T-cells that allowed stable expression of high levels of a tumor directed CAR. Since a proportion of early-transduced CAR-VSTs had a central memory phenotype, they should expand and persist in vivo, simultaneously protecting against infection and targeting residual malignancy. This manufacturing strategy is currently under clinical investigation in patients receiving allogeneic HSCT for relapsed neuroblastoma and B-cell malignancies (NCT01460901 using a GD2.CAR and NCT00840853 using a CD19.CAR).Electronic supplementary materialThe online version of this article (doi:10.1186/s40425-015-0049-1) contains supplementary material, which is available to authorized users.

Improved elongation factor-1 alpha-based vectors for stable high-level expression of heterologous proteins in Chinese hamster ovary cells.

BackgroundEstablishing highly productive clonal cell lines with constant productivity over 2–3 months of continuous culture remains a tedious task requiring the screening of tens of thousands of clonal colonies. In addition, long-term cultivation of many candidate lines derived in the absence of drug selection pressure is necessary. Expression vectors based on the elongation factor-1 alpha (EEF1A) gene and the dihydrofolate reductase (DHFR) selection marker (with separate promoters) can be used to obtain highly productive populations of stably transfected cells in the selection medium, but they have not been tested for their ability to support target gene amplification under gradually increasing methotrexate pressure.ResultsWe have modified EEF1A-based vectors by linking the DHFR selection marker to the target gene in the bicistronic RNA, shortening the overall plasmid size, and adding an Epstein-Barr virus terminal repeat fragment (EBVTR) element. Presence of the EBVTR element increased the rate of stable transfection by the plasmid by 24 times that of the EBVTR-minus control and improved the rate of methotrexate-driven gene amplification. The mean expression level of the enhanced green fluorescent protein (eGFP) used herein as a model protein, increased up to eight-fold using a single round of amplification in the case of adherent colonies formation and up to 4.5-fold in the case of suspension polyclonal cultures. Several eGFP-expressing cell populations produced using vectors with antibiotic resistance markers instead of the DHFR marker were compared with each other. Stable transfection of Chinese hamster ovary (CHO) DG44 cells by the p1.2-Hygro-eGFP plasmid (containing a hygromycin resistance marker) generated highest eGFP expression levels of up to 8.9% of the total cytoplasmic protein, with less than 5% of the cell population being eGFP-negative.ConclusionsThe p1.1 vector was very effective for stable transfection of CHO cells and capable of rapid MTX-driven target gene amplification, while p1.2-Hygro achieved similar eGFP expression levels as p1.1. The set of vectors we have developed should speed-up the process of generating highly productive clonal cell lines while substantially decreasing the associated experimental effort.

Hollow-Fiber Pharmacodynamic Studies and Mathematical Modeling To Predict the Efficacy of Amoxicillin for Anthrax Postexposure Prophylaxis in Pregnant Women and Children

Amoxicillin is considered an option for postexposure prophylaxis of Bacillus anthracis in pregnant and postpartum women who are breastfeeding and in children because of the potential toxicities of ciprofloxacin and doxycycline to the fetus and child. The amoxicillin regimen that effectively kills B. anthracis and prevents resistance is unknown. Fourteen-day dose range and dose fractionation studies were conducted in in vitro pharmacodynamic models to identify the exposure intensity and pharmacodynamic index of amoxicillin that are linked with optimized killing of B. anthracis and resistance prevention. Studies with dicloxacillin, a drug resistant to B. anthracis beta-lactamase, evaluated the role of beta-lactamase production in the pharmacodynamic indices for B. anthracis killing and resistance prevention. Dose fractionation studies showed that trough/MIC and not time above MIC was the index for amoxicillin that was linked to successful outcome through resistance prevention. Failure of amoxicillin regimens was due to inducible or stable high level expression of beta-lactamases. Studies with dicloxacillin demonstrated that a time above MIC of ≥94% was linked with treatment success when B. anthracis beta-lactamase activity was negated. Recursive partitioning analysis showed that amoxicillin regimens that produced peak concentrations of <10.99 μg/ml and troughs of >1.75 μg/ml provided a 100% success rate. Other amoxicillin peak and trough values produced success rates of 28 to 67%. For postpartum and pregnant women and children, Monte Carlo simulations predicted success rates for amoxicillin at 1 g every 8 h (q8h) of 53, 33, and 44% (30 mg/kg q8h), respectively. We conclude that amoxicillin is suboptimal for postexposure prophylaxis of B. anthracis in pregnant and postpartum women and in children.

Establishment of orthotopic lung cancer model expressing enhanced green fluorescent protein

背景与目的小鼠活体分子成像模型可以连续实时监测活体肿瘤的变化。本研究拟通过外科原位移植法建立表达绿色荧光蛋白的肺癌裸鼠原位移植模型并探讨其肿瘤生物学特性，从而建立一个良好的肺癌动物实验研究平台。方法利用逆转录病毒转染法将增强型绿色荧光蛋白基因导入人肺癌大细胞系NCI-H460，采用外科原位移植法建立肺癌原位移植模型。定期通过小动物活体荧光成像系统观察肿瘤生长，利用相关性检验分析荧光面积和肿瘤体积之间的相关关系，并观察原位移植术后裸鼠的生存期和肿瘤转移情况。结果模型建立后1周通过皮瓣在荧光体视镜下可观察到肺部肿瘤的绿色荧光，成瘤率为100%。荷瘤裸小鼠平均生存期为34.2天。解剖裸鼠观察到肿瘤侵及对侧肺、纵隔及肺门淋巴结、胸膜和膈肌，转移率分别为87.5%、75%、25%和12.5%。肿瘤体积和荧光面积具有相关性（r=0.873, P=0.001）。结论外科原位移植法建立的表达EGFP的裸鼠肺癌原位模型是肺癌临床前研究的理想的实验工具。应用小动物活体荧光成像系统能够定量客观评价肿瘤在动物体内的生长、侵袭和转移，该模型可应用于肺癌的基础研究和新药开发。

Stable high level expression of the violacein indolocarbazole anti-tumour gene cluster and the Streptomyces lividans amyA gene in E. coli K12

Previous studies showed that when pPSX- vioABCDE was used to transform E. coli K12 DH5α the strain retained the plasmid even after 100 generations of unselected growth but produced a low level of the anti-tumour antibiotic violacein. Markedly higher levels of violacein synthesis were obtained from E. coli K12 DH5α pUC18- vioABCDE and Sphingomonas sp. JMP4092 pPSX- vioABCDE. Unfortunately, both strains were extremely unstable regardless of presence or absence of antibiotic selection to retain the plasmid. The current study was undertaken to determine if strains of E. coli K12 could be isolated which stably over produce violacein. When a range of E. coli K12 strains were transformed with pPSX -vioABCDE, most produced small amounts of violacein. However, a small number of related strains of E. coli K12 JM101, JM105 and JM109 not only over-produced violacein, but also maintained the high stability. In addition, E. coli K12 JM109 strongly expressed an alpha amylase gene ( amyA) from Streptomyces lividans indicating that the S. lividans amyA promoter is highly active in E. coli K12 JM109. In another set of experiments, a violacein overproduction mutation ( opv-1) of the plasmid pPSX-v ioABCDE was isolated which enabled E. coli K12 DH5α to overproduce violacein while retaining high stability. The plasmid pPSX- vioABCDE opv-1 possesses a single base pair deletion in the promoter region of the violacein operon. By combining the over producing strain E. coli K12 JM109 and the over producing plasmid pPSX- vioABCDE opv-1, a stable hyper producing strain ( E. coli K12 JM109 pPSX- vioABCDE opv-1) was constructed. Finally, two additional stable vectors, pPSX10 and pPSX20, were constructed to facilitate subcloning and functional analysis studies.

Preparation of Anti-hTM Monoclonal Antibody by Using hTM Expression Cell Line

To produce monoclonal antibody (mAb) specifically against human thrombomodulin (hTM), an immune-tolerizing procedure was employed to generate monoclonal antibodies specific to hTM. Female BALB/c mice were first immunized with CHO cells following at 10 min, 24 h, 48 h by intraperitoneal injection of different doses of cyclophosphamide (CP) 2 times at an interval of 2 weeks, thereby tolerizing the mice to common epitopes shared between CHO and CHO-TM5 cells. Subsequently the selected mice with the lowest titer of serum polyclonal antibody by cellular enzyme-linked immunoabsorbent assay (CELISA) were immunized with CHO-TM5 cells, which have stable high level expression of hTM, to produce antibodies specific to hTM 3 times at an interval of 2 weeks. On the third day after the third immunization, mouse with the highest titer of serum polyclonal antibody was sacrificed and spleen cells were harvested to prepare hybridoma cells with SP2/0 cells at the ratio of 10 to 1. Hybridoma cells were then cultured at 96 well plates for screening with CELISA. To improve probability to obtain specific mAb, CELISA was applied twice. The first CELISA was done with polyethylene ELISA plate with a mono layer of CHO-TM5 cells. The positive clones from the first screen were then selected by reacting with similar screening ELISA plate but having CHO cells monolayer instead. Only clones that were positive for the first screening and negative for the second screening were kept, and called as CHO-TM5(+)CHO-hybridoma cells. BALB/c mice were intraperitoneally injected with the selected hybridoma cells. Ascites were collected and monoclonal antibodies were purified using FPLC, and its Ig class, subclass, and titer were then determined respectively. The specificity of the yielded mAb was identified with CELISA, flow cytometry, ABC immunohistochemistry and immunoblotting. Detection of CELISA showed that 100 mg/kg dose of CP could tolerize the mouse to common epitopes shared between CHO and CHO-TM5 cells. And CELISA also discovered that all hybridomas positive for CHO-TM5 cells were negative for CHO cells. Five lines of positive hybridoma cells had been obtained altogether and 2177 was selected randomly for next investigation. The Ig subclass of the mAb 2F7 was IgG1 and the titer of ascitic mAb was 1 x 10(-6). Furthermore, the content of ascitic mAb was 19.56 g/L and chromosome numbers is 98. Flow cytometry, CELISA and Western blotting assays demonstrated that mAb 2F7 could specifically recognize hTM expressed on CHO-TM5 and human umbilical vascular endothelial cells (HUVEC). Meanwhile, the tissue specificity of mAb 2F7 was also identified by immunohistochemical ABC staining. On the other hand, Western blotting assays indicated that mAb 2F7 could recognize the antigen protein with 105 ku molecular mass under reduction condition. Moreover, the dissociation constant of mAb 2177, 1.22 x 10(-9) mol/L, indicated the affinity higher than some others. The results suggest that the immunotolerizing protocol provides a convenient general method for producing antibodies specific to desired protein isoforms. mAb 2F7 can specifically recognize the natural hTM expressed mainly on vascular endothelial cells, which will potentially useful for investigating the functions and clinic values of hTM.

Lentivirus-Based DsRed-2-Transfected Pancreatic Cancer Cells for Deep In Vivo Imaging of Metastatic Disease

Pancreatic cancer is one of the most aggressive human malignancies. One of the leading causes of pancreatic cancer death is metastasis. In this report, we developed in vitro, a stable high-expression red fluorescent protein (RFP) transductant of the pancreatic cancer cells with a lentiviral expression vector containing the DsRed-2 RFP gene. These fluorescent pancreatic cancer cells were used to establish an orthotopic metastatic model and an experimental angiogenesis metastatic model of pancreatic cancer in nude mice. The high-level expression of RFP enables the imaging of distant micrometastases in their target organs. RFP expression did not interfere with the biological properties of the transformed cells compared to the parental cell line. We also demonstrated that lentiviral-transduced pancreatic cancer cells maintained stable high-level RFP expression during their growth in vitro and in vivo. The fluorescence was sufficient to noninvasively image tumor growth and metastasis, even in deep tissue such as the lung. The results indicate the benefit of lentivirus transfection of cancer cells for high expression of RFP and for sensitive in vivo imaging of metastatic pancreatic cancer.

Agrobacterium-mediated genetic transformation of embryogenic cell suspension cultures of Santalum album L.

An efficient method for Agrobacterium-mediated genetic transformation of embryogenic cell suspension cultures of Santalum album L. is described. Embryogenic cell suspension cultures derived from stem internode callus were transformed with Agrobacterium tumefaciens harbouring pCAMBIA 1301 plant expression vector. Transformed colonies were selected on medium supplemented with hygromycin (5 mg/l). Continuously growing transformed cell suspension cultures were initiated from these colonies. Expression of β-glucuronidase in the suspension cultures was analysed by RT-PCR and GUS histochemical staining. GUS specific activity in the transformed suspension cultures was quantified using a MUG-based fluorometric assay. Expression levels of up to 105,870 pmol 4-MU/min/mg of total protein were noted in the transformed suspension cultures and 67,248 pmol 4-MU/min/mg of total protein in the spent media. Stability of GUS expression over a period of 7 months was studied. Plantlets were regenerated from the transformed embryogenic cells. Stable insertion of T-DNA into the host genome was confirmed by Southern blot analysis. This is the first report showing stable high-level expression of a foreign protein using embryogenic cell suspension cultures in S. album.

Construction and co-expression of grass carp reovirus VP6 protein and enhanced green fluorescence protein in the insect cells

Grass carp reovirus (GCRV), a disaster agent to aquatic animals, belongs to Genus Aquareovirus of family Reoviridea. Sequence analysis revealed GCRV genome segment 8 (s8) was 1 296 bp nucleotides in length encoding an inner capsid protein VP6 of about 43kDa. To obtain in vitro non-fusion expression of a GCRV VP6 protein containing a molecular of fluorescence reporter, the recombinant baculovirus, which contained the GCRVs8 and eGFP (enhanced green fluorescence protein) genes, was constructed by using the Bac-to-Bac insect expression system. In this study, the whole GCRVs8 and eGFP genes, amplified by PCR, were constructed into a pFastBacDual vector under polyhedron (PH) and p10 promoters, respectively. The constructed dual recombinant plasmid (pFbDGCRVs8/eGFP) was transformed into DH10Bac cells to obtain recombinant Bacmid (AcGCRVs8/eGFP) by transposition. Finally, the recombinant bacluovirus (vAcGCRVs8/eGFP) was obtained from transfected Sf9 insect cells. The green fluorescence that was expressed by transfected Sf9 cells was initially observed 3 days post transfection, and gradually enhanced and extended around 5 days culture in P1(Passage1) stock. The stable high level expression of recombinant protein was observed in P2 and subsequent passage budding virus (BV) stock. Additionally, PCR amplification from P1 and amplified P2 BV stock further confirmed the validity of the dual-recombinant baculovirus. Our results provide a foundation for expression and assembly of the GCRV structural protein in vitro.

Long-Term Polyclonal and Stable Gene Transfer into Rhesus Repopulating Hematopoietic Stem Cells Using a Simian Immunodeficiency Virus-Based Lentiviral Vector System.

Murine leukemia virus (MLV) vectors have been studied extensively in animal models and utilized for over a decade in clinical trials of gene therapy directed at hematopoietic stem and progenitor cells MLV have a number of limitations, including inefficient transduction of quiescent cells and difficulty in maintaining stable high-level expression. More recently concerns have arisen regarding their safety regarding activation of adjacent proto-oncogenes and resultant leukemogenesis. We have previously reported that lentiviral vectors derived from the simian immunodeficiency virus (SIV) were efficient at transducing rhesus CD34+ cells, resulting in high-level in vivo marking with transduced progeny cells up to one year post-transplantation.(Hanawa et al, 2004) A comparison of vector integration sites in these animals compared to animals receiving MLV-transduced cells revealed different patterns, showing that SIV integrants strongly favored entire transcription units and gene-dense regions of the genome, compared to MLV that favored regions surrounding transcription start sites.(Hematti et al, 2004). Animals receiving MLV-transduced cells had highly non-random engraftment with integrants in or near the the MDS1/EVI1 gene complex. To evaluate long-term safety implications of the SIV vector-mediated CD34+ cell gene transfer, we analyzed the insertional sites in granulocytes, T cell, and B cells from 3 rhesus macaques which were transplanted three years ago with transduced, autologous cytokine-mobilized peripheral blood CD34+ cells. All three animals continued to show significant marking and expression levels in T cells, B cells and granulocytes, with mean GFP + levels of 6.7% (range, 3.3–13.0%), 7.4% (4.2–13.4%) and 5.6% (3.1–10.5%), respectively. Vector insertion site analysis by linear amplification-mediated PCR method at three years continued to show highly polyclonal reconstitution. Subsequent cloning and sequencing data confirmed long-term polyclonality with vector-containing cells and there was no evidence for any worrisome common integration sites, with no integrants detected in the MDS1/EVI1 region, in contrast to results with the MLV vector. These results indicate that the SIV vector system can result in stable and efficient long-term expression in progeny of transduced CD34+ cells, without the worrisome integration profile previously reported in our model with MLV vectors.

DRB4-Dependent TAS3 trans-Acting siRNAs Control Leaf Morphology through AGO7

trans-acting siRNAs (ta-siRNAs) are endogenous RNAs that direct the cleavage of complementary mRNA targets . TAS gene transcripts are cleaved by miRNAs; the cleavage products are protected against degradation by SGS3, copied into dsRNA by RDR6, and diced into ta-siRNAs by DCL4 . We describe hypomorphic rdr6 and sgs3 Arabidopsis mutants, which do not exhibit the leaf developmental defects observed in null mutants and which, like null alleles, are impaired in sense-transgene-induced posttranscriptional gene silencing and virus resistance. Null rdr6 and sgs3 mutants lack TAS1, TAS2, and TAS3 ta-siRNAs and overaccumulate ARF3/ETTIN and ARF4 mRNAs, which are TAS3 ta-siRNA targets. A hypomorphic rdr6 mutant accumulates wild-type TAS3 ta-siRNA levels but not TAS1 and TAS2 ta-siRNAs, suggesting that TAS3 is required for proper leaf development. Consistently, tas3 but not tas1 or tas2 mutants exhibits leaf morphology defects, and ago7/zip and drb4 mutants, which exhibit leaf morphology defects, lack TAS3 but not TAS1 and TAS2 ta-siRNAs in leaves. These results indicate that the dsRNA binding protein DRB4 is required for proper ta-siRNA production, presumably by interacting with DCL4, an interaction analogous to that of HYL1 with DCL1 during miRNA production , and that TAS3 ta-siRNAs are required for proper leaf development through the action of AGO7/ZIPPY.