IRES-dependent second gene expression is significantly lower than cap-dependent first gene expression in a bicistronic vector

Viral vector-based reversible neuronal inactivation and behavioral manipulation in the macaque monkey

Viral vectors are promising tools for the dissection of neural circuits. In principle, they can manipulate neurons at a level of specificity not otherwise achievable. While many studies have used viral vector-based approaches in the rodent brain, only a few have employed this technique in the non-human primate, despite the importance of this animal model for neuroscience research. Here, we report evidence that a viral vector-based approach can be used to manipulate a monkey's behavior in a task. For this purpose, we used the allatostatin receptor/allatostatin (AlstR/AL) system, which has previously been shown to allow inactivation of neurons in vivo. The AlstR was expressed in neurons in monkey V1 by injection of an adeno-associated virus 1 (AAV1) vector. Two monkeys were trained in a detection task, in which they had to make a saccade to a faint peripheral target. Injection of AL caused a retinotopic deficit in the detection task in one monkey. Specifically, the monkey showed marked impairment for detection targets placed at the visual field location represented at the virus injection site, but not for targets shown elsewhere. We confirmed that these deficits indeed were due to the interaction of AlstR and AL by injecting saline, or AL at a V1 location without AlstR expression. Post-mortem histology confirmed AlstR expression in this monkey. We failed to replicate the behavioral results in a second monkey, as AL injection did not impair the second monkey's performance in the detection task. However, post-mortem histology revealed a very low level of AlstR expression in this monkey. Our results demonstrate that viral vector-based approaches can produce effects strong enough to influence a monkey's performance in a behavioral task, supporting the further development of this approach for studying how neuronal circuits control complex behaviors in non-human primates.

General principles of retrovirus vector design

An understanding in the life cycle of γ-retroviruses has led to significant progress in the development of murine leukemia virus (MLV)-based vectors for gene delivery and human gene therapy. An MLV-based vector consists of the cis-acting sequences important for viral replication and gene expression. The sequence that encodes viral proteins is replaced with the gene of interest. To generate infectious retroviral vectors, viral-encoded proteins are supplied in trans for virion assembly. Here, we describe a method to rapidly generate MLV vectors from transiently transfected human 293T cells. The strategies to purify and titer the vector and to detect the presence of replication competent retrovirus (RCR) in the vector harvest are also described.

FACS-purified myoblasts producing controlled VEGF levels induce safe and stable angiogenesis in chronic hind limb ischemia

We recently developed a method to control the in vivo distribution of vascular endothelial growth factor (VEGF) by high throughput Fluorescence-Activated Cell Sorting (FACS) purification of transduced progenitors such that they homogeneously express specific VEGF levels. Here we investigated the long-term safety of this method in chronic hind limb ischemia in nude rats. Primary myoblasts were transduced to co-express rat VEGF-A₁₆₄ (rVEGF) and truncated ratCD8a, the latter serving as a FACS-quantifiable surface marker. Based on the CD8 fluorescence of a reference clonal population, which expressed the desired VEGF level, cells producing similar VEGF levels were sorted from the primary population, which contained cells with very heterogeneous VEGF levels. One week after ischemia induction, 12 × 10⁶ cells were implanted in the thigh muscles. Unsorted myoblasts caused angioma-like structures, whereas purified cells only induced normal capillaries that were stable after 3 months. Vessel density was doubled in engrafted areas, but only approximately 0.1% of muscle volume showed cell engraftment, explaining why no increase in total blood flow was observed. In conclusion, the use of FACS-purified myoblasts granted the cell-by-cell control of VEGF expression levels, which ensured long-term safety in a model of chronic ischemia. Based on these results, the total number of implanted cells required to achieve efficacy will need to be determined before a clinical application.

Quantitative evaluation of MRI-based tracking of ferritin-labeled endogenous neural stem cell progeny in rodent brain

Endogenous neural stem cells have the potential to facilitate therapy for various neurodegenerative brain disorders. To increase our understanding of neural stem and progenitor cell biology in healthy and diseased brain, methods to label and visualize stem cells and their progeny in vivo are indispensable. Iron oxide particle based cell-labeling approaches enable cell tracking by MRI with high resolution and good soft tissue contrast in the brain. However, in addition to important concerns about unspecific labeling and low labeling efficiency, the dilution effect upon cell division is a major drawback for longitudinal follow-up of highly proliferating neural progenitor cells with MRI. Stable viral vector-mediated marking of endogenous stem cells and their progeny with a reporter gene for MRI could overcome these limitations. We stably and efficiently labeled endogenous neural stem/progenitor cells in the subventricular zone in situ by injecting a lentiviral vector expressing ferritin, a reporter for MRI. We developed an image analysis pipeline to quantify MRI signal changes at the level of the olfactory bulb as a result of migration of ferritin-labeled neuroblasts along the rostral migratory stream. We were able to detect ferritin-labeled endogenous neural stem cell progeny into the olfactory bulb of individual animals with ex vivo MRI at 30 weeks post injection, but could not demonstrate reliable in vivo detection and longitudinal tracking of neuroblast migration to the OB in individual animals. Therefore, although LV-mediated labeling of endogenous neural stem and progenitor cells resulted in efficient and stable ferritin-labeling of stem cell progeny in the OB, even with quantitative image analysis, sensitivity remains a limitation for in vivo applications.

In vivo imaging of colorectal cancer growth and metastasis by targeting MACC1 with shRNA in xenografted mice

We previously identified the gene metastasis-associated in colon cancer-1 (MACC1) and demonstrated its important role for metastasis prediction in colorectal cancer. MACC1 induces cell motility and proliferation in vitro as well as metastasis in several mouse models. Here we report non-invasive real time imaging of inhibition of colorectal tumor progression and metastasis in xenografted mice by MACC1 shRNA. First, we demonstrated reduction of tumors and liver metastases by endpoint imaging of mice transplanted with MACC1 endogenously high expressing colorectal cancer cells and treated with shRNAs acting on MACC1 or Met. Next, we generated a novel bicistronic IRES vector simultaneously expressing the reporter gene firefly luciferase and MACC1 to ensure a direct correlation of bioluminescence signal with MACC1 expression. We transfected MACC1 endogenously low expressing colorectal cancer cells with this luciferase-IRES-MACC1 construct, transplanted them intrasplenically, and monitored MACC1 induced tumor growth and metastasis by in vivo imaging over time. Transfection of an IRES construct harboring the firefly luciferase reporter gene together with MACC1 lacking the SH3-domain reduced tumor growth and metastasis. Finally, we counteracted the luciferase-IRES-MACC1 induced effects by shRNA targeting MACC1 and monitored reduced tumor growth and metastasis by in vivo imaging over weeks. In summary, the new bicistronic luciferase-IRES-MACC1 construct is suitable for in vivo imaging of tumor progression and metastasis, and moreover, for imaging of therapy response such as treatment with MACC1 shRNA. Thereby, we provide proof-of-concept for employment of this MACC1-based in vivo model for evaluating therapeutic intervention strategies aiming at inhibition of tumor growth and metastasis.

Lentivector transduction improves outcomes over transplantation of human HSCs alone in NOD/SCID/Fabry mice

Fabry disease is a lysosomal storage disorder caused by a deficiency of α-galactosidase A (α-gal A) activity that results in progressive globotriaosylceramide (Gb(3)) deposition. We created a fully congenic nonobese diabetic (NOD)/severe combined immunodeficiency (SCID)/Fabry murine line to facilitate the in vivo assessment of human cell-directed therapies for Fabry disease. This pure line was generated after 11 generations of backcrosses and was found, as expected, to have a reduced immune compartment and background α-gal A activity. Next, we transplanted normal human CD34(+) cells transduced with a control (lentiviral vector-enhanced green fluorescent protein (LV-eGFP)) or a therapeutic bicistronic LV (LV-α-gal A/internal ribosome entry site (IRES)/hCD25). While both experimental groups showed similar engraftment levels, only the therapeutic group displayed a significant increase in plasma α-gal A activity. Gb(3) quantification at 12 weeks revealed metabolic correction in the spleen, lung, and liver for both groups. Importantly, only in the therapeutically-transduced cohort was a significant Gb(3) reduction found in the heart and kidney, key target organs for the amelioration of Fabry disease in humans.

Overexpression of fibulin-5 in retinal pigment epithelial cells inhibits cell proliferation and migration and downregulates VEGF, CXCR4, and TGFB1 expression in cocultured choroidal endothelial cells

PURPOSE OF THE STUDY

Age-related macular degeneration (AMD) is the most common cause of irreversible vision loss. Fibulin-5 (FBLN5) plays a pleiotropic role in the pathogenesis of AMD. We examined whether the in vitro overexpression of FBLN5 in retinal pigment epithelial (RPE) cells alters the proliferation and migration of cocultured choroidal endothelial cells (CECs) and explored the possible mechanisms involved.

MATERIALS AND METHODS

A recombinant lentiviral vector carrying the Fbln5 gene was generated to transduce rat RPE cells. The expression of FBLN5 in transduced RPE cells was detected by quantitative real-time PCR and Western blot. The transduced RPE cells were then cocultured with rhesus macaque CECs in a Transwell coculture system. The impact of overexpression of FBLN5 in RPE cells on CEC proliferation and migration was assessed, as well as the impact on the mRNA expressions of vascular endothelial growth factor (VEGF), C-X-C chemokine receptor type 4 (CXCR4), and transforming growth factor β1 (TGFB1).

RESULTS

Our results showed that a recombinant lentivirus carrying the Fbln5 gene, which could induce overexpression of FBLN5 in RPE cells, was successfully generated. Overexpression of FBLN5 in RPE cells inhibited cell proliferation and migration and downregulated the mRNA expressions of VEGF, CXCR4, and TGFB1 in cocultured CECs.

CONCLUSIONS

These findings suggest that FBLN5 may interfere with choroidal neovascularization by downregulating VEGF, CXCR4, and TGFB1 expression and inhibiting CEC proliferation and invasion, intensifying interest in FBLN5 as a target for therapeutic intervention in neovascular AMD.

ER-alpha-cDNA as part of a bicistronic transcript gives rise to high frequency, long term, receptor expressing cell clones

Within the large group of Estrogen Receptor alpha (ERα)-negative breast cancer patients, there is a subgroup carrying the phenotype ERα(-), PR(-), and Her2(-), named accordingly "Triple-Negative" (TN). Using cell lines derived from this TN group, we wished to establish cell clones, in which ERα is ectopically expressed, forming part of a synthetic lethality screening system. Initially, we generated cell transfectants expressing a mono-cistronic ERα transcription unit, adjacent to a separate dominant selectable marker transcription unit. However, the yield of ERα expressing colonies was rather low (5-12.5%), and only about half of these displayed stable ectopic ERα expression over time. Generation and maintenance of such cell clones under minimal exposure to the ERα ligand, did not improve yield or expression stability. Indeed, other groups have also reported grave difficulties in obtaining ectopic expression of ERα in ERα-deficient breast carcinoma cells. We therefore switched to transfecting these cell lines with pERα-IRES, a plasmid vector encoding a bicistronic translation mRNA template: ERα Open Reading Frame (ORF) being upstream followed by a dominant-positive selectable marker (hygro(R)) ORF, directed for translation from an Internal Ribosome Entry Site (IRES). Through usage of this bicistronic vector linkage system, it was possible to generate a very high yield of ERα expressing cell clones (50-100%). The stability over time of these clones was also somewhat improved, though variations between individual cell clones were evident. Our successful experience with ERα in this system may serve as a paradigm for other genes where ectopic expression meets similar hardships.

Long-term gene therapy causes transgene-specific changes in the morphology of regenerating retinal ganglion cells

Recombinant adeno-associated viral (rAAV) vectors can be used to introduce neurotrophic genes into injured CNS neurons, promoting survival and axonal regeneration. Gene therapy holds much promise for the treatment of neurotrauma and neurodegenerative diseases; however, neurotrophic factors are known to alter dendritic architecture, and thus we set out to determine whether such transgenes also change the morphology of transduced neurons. We compared changes in dendritic morphology of regenerating adult rat retinal ganglion cells (RGCs) after long-term transduction with rAAV2 encoding: (i) green fluorescent protein (GFP), or (ii) bi-cistronic vectors encoding GFP and ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF) or growth-associated protein-43 (GAP43). To enhance regeneration, rats received an autologous peripheral nerve graft onto the cut optic nerve of each rAAV2 injected eye. After 5–8 months, RGCs with regenerated axons were retrogradely labeled with fluorogold (FG). Live retinal wholemounts were prepared and GFP positive (transduced) or GFP negative (non-transduced) RGCs injected iontophoretically with 2% lucifer yellow. Dendritic morphology was analyzed using Neurolucida software. Significant changes in dendritic architecture were found, in both transduced and non-transduced populations. Multivariate analysis revealed that transgenic BDNF increased dendritic field area whereas GAP43 increased dendritic complexity. CNTF decreased complexity but only in a subset of RGCs. Sholl analysis showed changes in dendritic branching in rAAV2-BDNF-GFP and rAAV2-CNTF-GFP groups and the proportion of FG positive RGCs with aberrant morphology tripled in these groups compared to controls. RGCs in all transgene groups displayed abnormal stratification. Thus in addition to promoting cell survival and axonal regeneration, vector-mediated expression of neurotrophic factors has measurable, gene-specific effects on the morphology of injured adult neurons. Such changes will likely alter the functional properties of neurons and may need to be considered when designing vector-based protocols for the treatment of neurotrauma and neurodegeneration.

Improving TCR Gene Therapy for Treatment of Haematological Malignancies

Adoptive immunotherapy using TCR gene modified T cells may allow separation of beneficial Graft versus tumour responses from harmful GvHD. Improvements to this include methods to generate high avidity or high affinity TCR, improvements in vector design and reduction in mispairing. Following adoptive transfer, TCR transduced T cells must be able to survive and persist in vivo to give most effective antitumour responses. Central memory or naive T cells have both been shown to be more effective than effector cells at expanding and persisting in vivo. Lymphodepletion may enhance persistence of transferred T cell populations. TCR gene transfer can be used to redirect CD4 helper T cells, and these could be used in combination with CD8+ tumour specific T cells to provide help for the antitumour response. Antigen specific T regulatory T cells can also be generated by TCR gene transfer and could be used to suppress unwanted alloresponses.

Immunogenic comparison of chimeric adenovirus 5/35 vector carrying optimized human immunodeficiency virus clade C genes and various promoters

Adenovirus vector-based vaccine is a promising approach to protect HIV infection. However, a recent phase IIb clinical trial using the vector did not show its protective efficacy against HIV infection. To improve the vaccine, we explored the transgene protein expression and its immunogenicity using optimized codon usage, promoters and adaptors. We compared protein expression and immunogenicity of adenovirus vector vaccines carrying native or codon usage-optimized HIV-1 clade C gag and env genes expression cassettes driven by different promoters (CMV, CMVi, and CA promoters) and adapters (IRES and F2A). The adenovirus vector vaccine containing optimized gag gene produced higher Gag protein expression and induced higher immune responses than the vector containing native gag gene in mice. Furthermore, CA promoter generated higher transgene expression and elicited higher immune responses than other two popularly used promoters (CMV and CMVi). The second gene expression using F2A adaptor resulted in higher protein expression and immunity than that of using IRES and direct fusion protein. Taken together, the adenovirus vector containing the expression cassette with CA promoter, optimized HIV-1 clade C gene and an F2A adaptor produced the best protein expression and elicited the highest transgene-specific immune responses. This finding would be promising for vaccine design and gene therapy.

Comparison of red-shifted firefly luciferase Ppy RE9 and conventional Luc2 as bioluminescence imaging reporter genes for in vivo imaging of stem cells

One critical issue for noninvasive imaging of transplanted bioluminescent cells is the large amount of light absorption in tissue when emission wavelengths below 600 nm are used. Luciferase with a red-shifted spectrum can potentially bypass this limitation. We assessed and compared a mutant of firefly luciferase (Ppy RE9, PRE9) against the yellow luciferase luc2 gene for use in cell transplantation studies. C17.2 neural stem cells expressing PRE9-Venus and luc2-Venus were sorted by flow cytometry and assessed for bioluminescence in vitro in culture and in vivo after transplantation into the brain of immunodeficient Rag2-/- mice. We found that the luminescence from PRE9 was stable, with a peak emission at 620 nm, shifted to the red compared to that of luc2. The emission peak for PRE9 was pH-independent, in contrast to luc2, and much less affected by tissue absorbance compared to that of luc2. However, the total emitted light radiance from PRE9 was substantially lower than that of luc2, both in vitro and in vivo. We conclude that PRE9 has favorable properties as compared to luc2 in terms of pH independence, red-shifted spectrum, tissue light penetration, and signal quantification, justifying further optimization of protein expression and enzymatic activity.

Retrovirus and lentivirus vector design and methods of cell conditioning

Retroviruses are useful tools for the efficient delivery of genes to mammalian cells, owing to their ability to stably integrate into the host cell genome. Over the past few decades, retroviral vectors have been used in gene therapy clinical trials for the treatment of a number of inherited diseases and cancers. The earliest retrovirus vectors were based on simple oncogenic gammaretroviruses such as Moloney murine leukemia virus (MMLV) which, when pseudotyped with envelope proteins from other viruses such as the gibbon ape leukemia virus envelope protein (GALV) or vesicular stomatitis virus G protein (VSV-G), can efficiently introduce genes to a wide range of host cells. However, gammaretroviral vectors have the disadvantage that they are unable to efficiently transduce nondividing or slowly dividing cells. As a result, specific protocols have been developed to activate cells through the use of growth factors and cytokines. In the case of hematopoietic stem cells, activation has to be carefully controlled so that pluripotency is maintained. For many applications, gammaretroviral vectors are being superseded by lentiviral vectors based on human immunodeficiency virus type-1 (HIV-1) which has additional accessory proteins that enable integration in the absence of cell division. In addition, retroviral and lentiviral vector design has evolved to address a number of safety concerns. These include separate expression of the viral genes in trans to prevent recombination events leading to the generation of replication-competent viruses. Further, the development of self-inactivating (SIN) vectors reduces the potential for transactivation of neighboring genes and allows the incorporation of regulatory elements that may target gene expression more physiologically to particular cell types.

Genetically modulating T-cell function to target cancer

The adoptive transfer of tumor-specific T-lymphocytes holds promise for the treatment of metastatic cancer. Genetic modulation of T-lymphocytes using TCR transfer with tumor-specific TCR genes is an attractive strategy to generate anti-tumor response, especially against large solid tumors. Recently, several clinical trials have demonstrated the therapeutic potential of this approach which lead to impressive tumor regression in cancer patients. Still, several factors may hinder the clinical benefit of this approach, such as the type of cells to modulate, the vector configuration or the safety of the procedure. In the present review we will aim at giving an overview of the recent developments related to the immune modulation of the anti-tumor adaptive response using genetically engineered lymphocytes and will also elaborate the development of other genetic modifications to enhance their anti-tumor immune response.

Generation of human adult mesenchymal stromal/stem cells expressing defined xenogenic vascular endothelial growth factor levels by optimized transduction and flow cytometry purification

Adult mesenchymal stromal/stem cells (MSCs) are a valuable source of multipotent progenitors for tissue engineering and regenerative medicine, but may require to be genetically modified to widen their efficacy in therapeutic applications. For example, overexpression of the angiogenic factor vascular endothelial growth factor (VEGF) at controlled levels is an attractive strategy to overcome the crucial bottleneck of graft vascularization and to avoid aberrant vascular growth. Since the regenerative potential of MSCs is rapidly lost during in vitro expansion, we sought to develop an optimized technique to achieve high-efficiency retroviral vector transduction of MSCs derived from both adipose tissue (adipose stromal cells, ASCs) or bone marrow (BMSCs) and rapidly select cells expressing desired levels of VEGF with minimal in vitro expansion. The proliferative peak of freshly isolated human ASCs and BMSCs was reached 4 and 6 days after plating, respectively. By performing retroviral vector transduction at this time point, >90% efficiency was routinely achieved before the first passage. MSCs were transduced with vectors expressing rat VEGF(164) quantitatively linked to a syngenic cell surface marker (truncated rat CD8). Retroviral transduction and VEGF expression did not affect MSC phenotype nor impair their in vitro proliferation and differentiation potential. Transgene expression was also maintained during in vitro differentiation. Furthermore, three subpopulations of transduced BMSCs homogeneously producing specific low, medium, and high VEGF doses could be prospectively isolated by flow cytometry based on the intensity of their CD8 expression already at the first passage. In conclusion, this optimized platform allowed the generation of populations of genetically modified MSCs, expressing specific levels of a therapeutic transgene, already at the first passage, thereby minimizing in vitro expansion and loss of regenerative potential.

NF-κB activity in perinatal brain during infectious and hypoxic-ischemic insults revealed by a reporter mouse

Infants suffering from infection or hypoxia-ischemia around the time of birth can develop brain damage resulting in life-long impairment such as cerebral palsy, epilepsy and cognitive disability. Inflammation appears to be an important contributor irrespective of whether the primary event is infection or hypoxia-ischemia. Activation of the transcription factor NF-κB is a hallmark of inflammation. To study perinatal brain inflammation, we developed a transgenic reporter mouse for imaging NF-κB activity in live animals and tissue samples. The reporter genes firefly luciferase and a destabilized version of enhanced GFP (dEGFP) were regulated by common NF-κB sites using a bidirectional promoter. Luciferase activity was imaged in vivo, while dEGFP was detected at cellular level in tissue sections. In newborn mice subjected to experimental models of infections or hypoxia-ischemia; luciferase signal increased in brains of live animals. In brain sections dEGFP expression, revealing NF-κB activation was observed in the endothelial cells of the blood-brain barrier in all disease models. In meningitis and hypoxia-ischemia expression of dEGFP was also induced in perivascular astrocytes. In conclusion, by using this transgenic reporter mouse in experimental models of perinatal complications, we could assess NF-κB activity in vivo and subsequently determine the cellular origin in the tissues.

Selection of high expressing mammalian cells by surface display of reporters

A flow cytometry method using a nonfluorescent reporter protein was developed for rapid, early-stage identification of cells producing high levels of a recombinant protein of interest. A cell surface reporter protein is coexpressed with the protein of interest, and the reporter protein is detected using a fluorescently labeled antibody. The genes encoding the reporter protein and the protein of interest are linked by an IRES so that they are transcribed in the same mRNA but are translated independently. Since they each arise from a common mRNA, the reporter protein's expression level accurately predicts, on a per cell basis, the relative expression level of the protein of interest. This method provides an effective process for selecting cells that express high levels of recombinant proteins, with the benefits of rapid and accurate 96-well plate clone screening (that is both quantitative and qualitative) and elimination of unstable clones during subsequent scale up and culture. Furthermore, because this method does not rely on the availability of a detection reagent specific for the protein of interest that is expressed, it can be easily implemented into any cell line development process.

Decrease in the expression of N-methyl-D-aspartate receptors in the nucleus tractus solitarii induces antinociception and increases blood pressure

N-methyl-D-aspartate receptors (NMDAR) have a role in cardiovascular control at the nucleus tractus solitarii (NTS), eliciting increases or decreases in blood pressure (BP), depending on the area injected with the agonists. In spite of the association between cardiovascular control and pain modulation, the effects of manipulating NMDAR in pain responses have never been evaluated. In this study, we decreased the expression of NMDAR in the NTS using gene transfer to target receptor subunits and evaluate long-term effects. Seven days after the injection of lentiviral vectors containing the NR1a subunit cDNA of NMDAR, in antisense orientation, into the intermediate NTS of Wistar rats, BP was measured, and the formalin test of nociception was performed. The antisense vector induced a decrease of NR1 expression in the NTS and elicited BP rises and hypoalgesia. Antisense vectors inhibited formalin-evoked c-Fos expression in the spinal cord, indicating decreased nociceptive activity of spinal neurons. Using a time-course approach, we verified that the onset of both the increases in BP and the hypoalgesia was at 4 days after vector injection into the NTS. The injection of NMDA into the NTS reversed the effects of antisense vectors in pain behavioral responses and spinal neuronal activation and decreased BP and heart rate. The present study shows that the NR1 subunit of the NMDAR at the NTS is critical in the regulation of tonic cardiovascular and nociceptive control and shows an involvement of the nucleus in the modulation of sustained pain.

2A peptide-based, lentivirus-mediated anti-death receptor 5 chimeric antibody expression prevents tumor growth in nude mice

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, induces tumor cell death via death receptors on target cells, without adverse effects on most normal cells. Its receptors are therefore an attractive target for antibody-mediated tumor therapy. Here, we report the creation of a lentivirus vector constructed by linking the heavy chain and the light chain of the antibody with a 2A/furin self-processing peptide in a single open reading frame that expresses a novel chimeric antibody (named as zaptuximab) with tumoricidal activity, which is consisted of the variable region of a mouse anti-human DR5 monoclonal antibody, AD5-10, and the constant region of human immunoglobulin G1. Lentivirus-expressed zaptuximab bound specifically to its antigen, DR5, and exhibited significant apoptosis-inducing activity in various tumor cell lines. The packaged recombinant virus lenti-HF2AL showed strong apoptosis-inducing activity in vitro. Meanwhile, inoculated subcutaneous human colon HCT116 tumor formation in nude mice were inhibited significantly. Moreover, there was a synergistic effect of mitomycin C (MMC) on the observed tumoricidal efficacy, prolonging the life span of nude mice with orthotopic human lung tumor cancers. These data suggest that lentivirus-mediated, 2A peptide-based anti-DR5 chimeric antibody expression may have clinical utility as an anticancer treatment and may represent a rational adjuvant therapy in combination with chemotherapy.

Suicidal gene therapy in the effective control of primary human hepatocellular carcinoma as monitored by noninvasive bioimaging

Hepatocellular carcinoma (HCC) is usually refractory to the available treatments. For cancer gene therapy purposes, real-time imaging of therapeutic gene expression is of great importance because there are multiple factors that modulate the therapeutic gene expression in a complex tumor microenvironment. As a consequence, multiple doses of therapeutic viral vectors may be required for improved efficacy. In the present study, the luciferase reporter gene and the yeast cytosine deaminase (yCD) genes were bicistronically expressed using the foot-and-mouth disease virus 2A peptide under the regulation of the cytomegalovirus (CMV) promoter. The effectiveness of the yCD/5-FC (5-fluorocytosine) killing efficacy mediated by the herpes simplex virus type 1 (HSV-1) amplicon viral vector was shown using HCC and non-HCC cell lines in vitro. In addition, in vivo experiment also showed tumor regression of a primary HCC 26-1004 tumor xenograft in tumor expressing high levels of the yCD gene (as determined by noninvasive imaging) after intratumoral injection of 1.5 × 10(6) TU HGCX-L2C HSV-1 amplicon viral vector and 5-FC administration. The HSV-1 amplicon viral vector coupled with the yCD/5-FC prodrug activated suicide gene could potentially be of use in clinical gene therapy for HCC.

Generation of stable Drosophila cell lines using multicistronic vectors

Insect cell culture is becoming increasingly important for applications including recombinant protein production and cell-based screening with chemical or RNAi libraries. While stable mammalian cell lines expressing a protein of interest can be efficiently prepared using IRES-based vectors or viral-based approaches, options for stable insect cell lines are more limited. Here, we describe pAc5-STABLEs, new vectors for use in Drosophila cell culture to facilitate stable transformation. We show that viral-derived 2A-like (or "CHYSEL") peptides function in Drosophila cells and can mediate the multicistronic expression of two or three proteins of interest under control of the Actin5C constitutive promoter. The current vectors allow mCherry and/or GFP fusions to be generated for positive selection by G418 resistance in cells and should serve as a flexible platform for future applications.

Novel highly sensitive IL-10-beta-lactamase reporter mouse reveals cells of the innate immune system as a substantial source of IL-10 in vivo

In this study, we report on a novel, highly sensitive IL-10 reporter mouse based on the reporter enzyme β-lactamase and the fluorescence resonance energy transfer substrate coumarin-cephalosporin-fluorescein (4). In contrast to an IL-10 reporter mouse model that we generated by using enhanced GFP as reporter and allowed tracking IL-10 expression only in T cells, the IL-10-β-lactamase reporter (ITIB) mouse enables us to easily analyze and quantify IL-10 production at the single-cell level in all myeloid and lymphoid cell types. Furthermore, the ITIB mouse allows studying of the kinetics of IL-10 expression on a single-cell basis and provides a valuable tool for in vivo screening of cell type-specific IL-10-modulating drugs. Remarkably, the ITIB mouse revealed that, although a significant portion of each myeloid and lymphoid cell type produces IL-10, macrophages represent the major IL-10 producer population in several organs of naive mice. Moreover, using the examples of bacterial infection and transplantable skin melanoma models, we demonstrate the exceptional applicability of the ITIB mouse for the identification of IL-10-producing cells during immune responses in vivo. In this study, we identified tumor-infiltrating F4/80(+) macrophages as the major source for IL-10 in B16-F10 melanoma in vivo. During systemic infection with Yersinia enterocolitica, although the proportion of IL-10(+) cells increased in each myeloid and lymphoid cell type population, infiltrating CD11b(+)Ly6G(+) neutrophils represent a majority among IL-10-producing cells at the site of infection. We conclude that cells of the innate immune system that are involved in immune homeostasis or immune responses are substantial sources of IL-10.

Bicistronic lentiviruses containing a viral 2A cleavage sequence reliably co-express two proteins and restore vision to an animal model of LCA1

The disease processes underlying inherited retinal disease are complex and are not completely understood. Many of the corrective gene therapies designed to treat diseases linked to mutations in genes specifically expressed in photoreceptor cells restore function to these cells but fail to stop progression of the disease. There is growing consensus that effective treatments for these diseases will require delivery of multiple therapeutic proteins that will be selected to treat specific aspects of the disease process. The purpose of this study was to design a lentiviral transgene that reliably expresses all of the proteins it encodes and does so in a consistent manner among infected cells. We show, using both in vitro and in vivo analyses, that bicistronic lentiviral transgenes encoding two fluorescent proteins fused to a viral 2A-like cleavage peptide meet these expression criteria. To determine if this transgene design is suitable for therapeutic applications, we replaced one of the fluorescent protein genes with the gene encoding guanylate cyclase-1 (GC1) and delivered lentivirus carrying this transgene to the retinas of the GUCY1*B avian model of Leber congenital amaurosis-1 (LCA1). GUCY1*B chickens carry a null mutation in the GC1 gene that disrupts photoreceptor function and causes blindness at hatching, a phenotype that closely matches that observed in humans with LCA1. We found that treatment of these animals with the 2A lentivector encoding GC1 restored vision to these animals as evidenced by the presence of optokinetic reflexes. We conclude that 2A-like peptides, with proper optimization, can be successfully incorporated into therapeutic vectors designed to deliver multiple proteins to neural retinal. These results highlight the potential of this vector design to serve as a platform for the development of combination therapies designed to enhance or prolong the benefits of corrective gene therapies.

A high-throughput platform for lentiviral overexpression screening of the human ORFeome

In response to the growing need for functional analysis of the human genome, we have developed a platform for high-throughput functional screening of genes overexpressed from lentiviral vectors. Protein-coding human open reading frames (ORFs) from the Mammalian Gene Collection were transferred into lentiviral expression vector using the highly efficient Gateway recombination cloning. Target ORFs were inserted into the vector downstream of a constitutive promoter and upstream of an IRES controlled GFP reporter, so that their transfection, transduction and expression could be monitored by fluorescence. The expression plasmids and viral packaging plasmids were combined and transfected into 293T cells to produce virus, which was then used to transduce the screening cell line. We have optimised the transfection and transduction procedures so that they can be performed using robotic liquid handling systems in arrayed 96-well microplate, one-gene-per-well format, without the need to concentrate the viral supernatant. Since lentiviruses can infect both dividing and non-dividing cells, this system can be used to overexpress human ORFs in a broad spectrum of experimental contexts. We tested the platform in a 1990 gene pilot screen for genes that can increase proliferation of the non-tumorigenic mammary epithelial cell line MCF-10A after removal of growth factors. Transduced cells were labelled with the nucleoside analogue 5-ethynyl-2′-deoxyuridine (EdU) to detect cells progressing through S phase. Hits were identified using high-content imaging and statistical analysis and confirmed with vectors using two different promoters (CMV and EF1α). The screen demonstrates the reliability, versatility and utility of our screening platform, and identifies novel cell cycle/proliferative activities for a number of genes.

Lentiviral vector-mediated stable expression of sTNFR-Fc in human macrophage and neuronal cells as a potential therapy for neuroAIDS

Background

Human immunodeficiency virus type 1 (HIV-1) infection frequently causes neurologic disease, which is the result of viral replication and activation of macrophages and microglia in the CNS, and subsequent secretion of high levels of neurotoxic products, including tumor necrosis factor-α (TNF-α). We therefore hypothesized that a soluble TNF-α antagonist might have potential utility as a neuroprotective effecter molecule, and conducted proof-of-concept studies to test this hypothesis.

Methods

To develop novel therapeutics for the treatment of neuroAIDS, we constructed and characterized a soluble TNF receptor (sTNFR)-Fc fusion protein with the goal of neutralizing TNF-α, and tested the stability of expression of this gene following delivery by a lentiviral vector.

Results

High-titer lentiviral vectors were prepared, allowing efficient transduction of macrophage/glial and neuronal cell lines, as well as primary rat cerebellar neurons. Efficient, stable secretion of sTNFR-Fc was demonstrated in supernatants from transduced cell lines over 20 passages, using both western blot and ELISA. Biological activity of the secreted sTNFR-Fc was confirmed by TNF-specific in vitro protein binding and functional blocking assays. Finally, the secreted protein was shown to protect neuronal cells from TNF-α, HIV-1 Tat-, and gp120-mediated neurotoxicity.

Conclusions

These results demonstrate that lentiviral vector mediated expression of sTNFR-Fc may have potential as a novel therapy for neuroAIDS.

Use of the 2A peptide for generation of multi-transgenic pigs through a single round of nuclear transfer

Multiple genetic modifications in pigs can essentially benefit research on agriculture, human disease and xenotransplantation. Most multi-transgenic pigs have been produced by complex and time-consuming breeding programs using multiple single-transgenic pigs. This study explored the feasibility of producing multi-transgenic pigs using the viral 2A peptide in the light of previous research indicating that it can be utilized for multi-gene transfer in gene therapy and somatic cell reprogramming. A 2A peptide-based double-promoter expression vector that mediated the expression of four fluorescent proteins was constructed and transfected into primary porcine fetal fibroblasts. Cell colonies (54.3%) formed under G418 selection co-expressed the four fluorescent proteins at uniformly high levels. The reconstructed embryos, which were obtained by somatic cell nuclear transfer and confirmed to express the four fluorescent proteins evenly, were transplanted into seven recipient gilts. Eleven piglets were delivered by two gilts, and seven of them co-expressed the four fluorescent proteins at equivalently high levels in various tissues. The fluorescence intensities were directly observed at the nose, hoof and tongue using goggles. The results suggest that the strategy of combining the 2A peptide and double promoters efficiently mediates the co-expression of the four fluorescent proteins in pigs and is hence a promising methodology to generate multi-transgenic pigs by a single nuclear transfer.

Whirlin replacement restores the formation of the USH2 protein complex in whirlin knockout photoreceptors

PURPOSE

Whirlin is the causative gene for Usher syndrome type IID (USH2D), a condition manifested as both retinitis pigmentosa and congenital deafness. Mutations in this gene cause disruption of the USH2 protein complex composed of USH2A and VLGR1 at the periciliary membrane complex (PMC) in photoreceptors. In this study, the adeno-associated virus (AAV)-mediated whirlin replacement was evaluated as a treatment option.

METHODS

Murine whirlin cDNA driven by the human rhodopsin kinase promoter (hRK) was packaged as an AAV2/5 vector and delivered into the whirlin knockout retina through subretinal injection. The efficiency, efficacy, and safety of this treatment were examined using immunofluorescent staining, confocal imaging, immunoelectron microscopy, Western blot analysis, histologic analysis, and electroretinogram.

RESULTS

The AAV-mediated whirlin expression started at two weeks, reached its maximum level at 10 weeks, and lasted up to six months post injection. The transgenic whirlin product had a molecular size and an expression level comparable to the wild-type. It was distributed at the PMC in both rod and cone photoreceptors from the central to peripheral retina. Importantly, the transgenic whirlin restored the cellular localization and expression level of both USH2A and VLGR1 and did not cause defects in the retinal histology and function in the whirlin knockout mouse.

CONCLUSIONS

Whirlin transgene recruits USH2A and VLGR1 to the PMC and is sufficient for the formation of the USH2 protein complex in photoreceptors. The combined hRK and AAV gene delivery system could be an effective gene therapy approach to treat retinal degeneration in USH2D patients.

Functional expression of secreted proteins from a bicistronic retroviral cassette based on foot-and-mouth disease virus 2A can be position dependent

The expression of two or more genes from a single viral vector has been widely used to label or select for cells containing the transgenic element. Identification of the foot-and-mouth disease virus (FMDV) 2A cleavage peptide as a polycistronic linker capable of producing equivalent levels of transgene expression has greatly improved this approach in the field of gene therapy. However, as a consequence of 2A posttranslational cleavage the upstream protein is left with a residual 19 amino acids from the 2A sequence on its carboxy terminus, and the downstream protein is left with an additional 2 to 5 amino acids on its amino terminus. Here we have assessed the functional consequences of the FMDV 2A cleavage motif on two secreted proteins (interleukin [IL]-2 and transforming growth factor [TGF]-β) when expressed from a retroviral bicistronic vector. Whereas IL-2 expression and function were found to be unaffected by the 2A motif in either orientation, functional expression of secreted TGF-β was significantly abrogated when the transgene was expressed upstream of the 2A sequence. We believe this is a consequence of aberrant cleavage and intracellular trafficking of the TGF-β polyprotein. These results highlight that to achieve functional expression of secreted proteins consideration must be taken of the transgenic protein's posttranslational modification and trafficking when using 2A-based bicistronic cassettes.

TEV protease-facilitated stoichiometric delivery of multiple genes using a single expression vector

Delivery and expression of multiple genes is an important requirement in a range of applications such as the engineering of synthetic signaling pathways and the induction of pluripotent stem cells. However, conventional approaches are often inefficient, nonstoichiometric and may limit the maximum number of genes that can be simultaneously expressed. We here describe a versatile approach for multiple gene delivery using a single expression vector by mimicking the protein expression strategy of RNA viruses. This was accomplished by first expressing the genes together with TEV protease as a single fusion protein, then proteolytically self-cleaving the fusion protein into functional components. To demonstrate this method in E. coli cells, we analyzed the translation products using SDS-PAGE and showed that the fusion protein was efficiently cleaved into its components, which can then be purified individually or as a binding complex. To demonstrate this method in mammalian cells, we designed a differential localization scheme and used live cell imaging to observe the distinctive subcellular targeting of the processed products. We also showed that the stoichiometry of the processed products was consistent and corresponded with the frequency of appearance of their genes on the expression vector. In summary, the efficient expression and separation of up to three genes was achieved in both E. coli and mammalian cells using a single TEV protease self-processing vector.

A bidirectional promoter architecture enhances lentiviral transgenesis in embryonic and extraembryonic stem cells

The two main challenges facing retroviral transgenesis are variable expression and epigenetic silencing. Although modern lentiviral vectors incorporate several elements to increase transgene expression and reduce position effect variegation and silencing, therapeutic research in stem cells, as well as production of transgenic animals, is still hampered by these two key problems. On the basis of recent studies demonstrating the chromatin insulating properties of divergent promoters, we sought to develop a bidirectional lentiviral vector with which to conduct RNA interference (RNAi)-based genetic screens in embryonic and extraembryonic stem cells. To this end, we designed and tested a series of synthetic bidirectional promoters, combining the mouse phosphoglycerate kinase 1 (Pgk1) promoter with other strong mammalian and viral promoters. Here, we demonstrate that a back-to-back configuration of the mouse Pgk1 and human eukaryotic translation elongation factor 1 alpha 1 promoters provided a substantive increase in both transgene expression and RNAi-based transcript depletion as compared with previous designs and other promoter combinations. Using this vector, we were able to achieve stable and robust depletion of a transfected luciferase reporter, as well as an endogenous non-coding RNA. The described constructs are an improved transgene delivery system capable of conducting RNAi screens in stem cells at single copy.

In vitro and in vivo comparison of viral and cellular internal ribosome entry sites for bicistronic vector expression

Bicistronic vectors are essential to achieve efficient expression of multiple genes in gene therapy protocols and biomedical applications. Internal ribosome entry site (IRES) elements have been utilized to initiate expression of an additional protein from a bicistronic vector. The IRES element commonly used in current bicistronic vectors originates from the encephalomyocarditis virus (EMCV). As IRES-mediated translation is dependent on availability of IRES trans-acting factors, which vary between cell types and species, adequate gene expression from the EMCV IRES element is not always achieved. To identify a novel IRES element that mediates gene expression consistently with a higher efficiency than the EMCV IRES, we tested 13 bicistronic reporter constructs containing different viral and cellular IRES elements. The in vitro screening in human and mouse fibroblast and hepatocarcinoma cells revealed that the vascular endothelial growth factor and type 1 collagen-inducible protein (VCIP) IRES was the only IRES element that directed translation more efficiently than the EMCV IRES in all cell lines. Furthermore, the VCIP IRES initiated greater reporter expression levels than the EMCV IRES in transfected mouse livers. These results suggest that VCIP-IRES containing vectors improve gene expression compared with those harboring an EMCV-IRES. This could increase the potential benefits of bicistronic vectors for experimental and therapeutic purposes.

Retroviral vectors for gene therapy

Since their first clinical trial 20 years ago, retroviral (gretroviral and lentiviral) vectors have now been used in more than 350 gene-therapy studies. Retroviral vectors are particularly suited for gene-correction of cells due to long-term and stable expression of the transferred transgene(s), and also because little effort is required for their cloning and production. Several monogenic inherited diseases, mostly immunodeficiencies, can now be successfully treated. The occurrence of insertional mutagenesis in some studies allowed extensive analysis of integration profiles of retroviral vectors, as well as the design of lentiviral vectors with increased safety properties. These new-generation vectors will enable us to continue the successful story of gene therapy, and treat more patients and even more complex diseases.

Inducible gene and shRNA expression in resident hematopoietic stem cells in vivo

Hematopoietic stem cells (HSC) are probably the best understood somatic stem cells and often serve as a paradigm for other stem cells. Nevertheless, most current techniques to genetically manipulate them in vivo are either constitutive and/or induced in settings of hematopoietic stress such as after irradiation. Here, we present a conditional expression system that allows for externally controllable transgenesis and knockdown in resident HSCs, based on a lentiviral vector containing a tet-O sequence and a transgenic mouse line expressing a doxycyclin-regulated tTR-KRAB repressor protein. HSCs harvested from tTR-KRAB mice are transduced with the lentiviral vector containing a cDNA (i.e., Green Fluorescent Protein (GFP)) and/or shRNA (i.e., p53) of interest and then transplanted into lethally irradiated recipients. While the vector is effectively repressed by tTR-KRAB during homing and engraftment, robust GFP/shp53 expression is induced on doxycyclin treatment in HSCs and their progeny. Doxycylin-controllable transcription is maintained on serial transplantation, indicating that repopulating HSCs are stably modified by this approach. In summary, this easy to implement conditional system provides inducible and reversible overexpression or knock down of genes in resident HSCs in vivo using a drug devoid of toxic or activating effects.

Generation of diffuse large B cell lymphoma-associated antigen-specific Vα6/Vβ13+T cells by TCR gene transfer

Background

Our previous study had amplified antigen-specific full-length TCR α and β genes of clonally expanded T cells in the peripheral blood (PB) of patients with diffuse large B-cell lymphoma (DLBCL). The transfer of T cell receptor (TCR) genes endows T cells with new antigen specificity. Therefore, the aim of this study is to generate diffuse large B cell lymphoma (DLBCL)-specific T cells by T cell receptor (TCR) gene transfer.

Materials and methods

Two different eukaryotic expression plasmids harboring TCR Vα6 and TCR Vβ13 genes specific for DLBCL-associated antigens were constructed and subsequently transferred into human T cells using Nucleofector™ technique. The expression of targeted genes in TCR gene-modified cells was detected by real-time PCR, and western blot using TCR Vβ antibody. The specific cytotoxicity of TCR gene-transferred T cells in vitro was estimated using a lactate dehydrogenase (LDH) release assay.

Results

Two different eukaryotic expression plasmids harboring TCR Vα6 and TCR Vβ13 genes specific for DLBCL-associated antigens were constructed and subsequently transferred into T cells from healthy donors. Specific anti-DLBCL cytotoxic T lymphocytes (CTL) could be induced by transduction of specific TCR gene to modify healthy T cells. The transgene cassette of TCR Vβ13-IRES-TCR Vα6 was superior to the other in the function of TCR-redirected T cells.

Conclusions

Specific anti-DLBCL cytotoxic T lymphocyte (CTL) could be inducted by transduction of specific TCR gene to modify healthy T cells.

Synthetic physiology strategies for adapting tools from nature for genetically targeted control of fast biological processes

The life and operation of cells involve many physiological processes that take place over fast timescales of milliseconds to minutes. Genetically encoded technologies for driving or suppressing specific fast physiological processes in intact cells, perhaps embedded within intact tissues in living organisms, are critical for the ability to understand how these physiological processes contribute to emergent cellular and organismal functions and behaviors. Such "synthetic physiology" tools are often incredibly complex molecular machines, in part because they must operate at high speeds, without causing side effects. We here explore how synthetic physiology molecules can be identified and deployed in cells, and how the physiology of these molecules in cellular contexts can be assessed and optimized. For concreteness, we discuss these methods in the context of the "optogenetic" light-gated ion channels and pumps that we have developed over the past few years as synthetic physiology tools and widely disseminated for use in neuroscience for probing the role of specific brain cell types in neural computations, behaviors, and pathologies. We anticipate that some of the insights revealed here may be of general value for the field of synthetic physiology, as they raise issues that will be of importance for the development and use of high-performance, high-speed, side-effect free physiological control tools in heterologous expression systems.

Mapping the architecture of the HIV-1 Tat circuit: A decision-making circuit that lacks bistability and exploits stochastic noise

Upon infection of a CD4(+) T cell, HIV-1 appears to 'choose' between two alternate fates: active replication or a long-lived dormant state termed proviral latency. A transcriptional positive-feedback loop generated by the HIV-1 Tat protein appears sufficient to mediate this decision. Here, we describe a coupled wet-lab and computational approach that uses mathematical modeling and live-cell time-lapse microscopy to map the architecture of the HIV-1 Tat transcriptional regulatory circuit and generate predictive models of HIV-1 latency. This approach provided the first characterization of a 'decision-making' circuit that lacks bistability and instead exploits stochastic fluctuations in cellular molecules (i.e. noise) to generate a decision between an on or off transcriptional state.

Transplantation of mouse HSCs genetically modified to express a CD4-restricted TCR results in long-term immunity that destroys tumors and initiates spontaneous autoimmunity

The development of effective cancer immunotherapies has been consistently hampered by several factors, including an inability to instigate long-term effective functional antitumor immunity. This is particularly true for immunotherapies that focus on the adoptive transfer of activated or genetically modified mature CD8+ T cells. In this study, we sought to alter and enhance long-term host immunity by genetically modifying, then transplanting, mouse HSCs. We first cloned a previously identified tumor-reactive HLA-DR4-restricted CD4+ TCR specific for the melanocyte differentiation antigen tyrosinase-related protein 1 (Tyrp1), then constructed both a high-expression lentivirus vector and a TCR-transgenic mouse expressing the genes encoding this TCR. Using these tools, we demonstrated that both mouse and human HSCs established durable, high-efficiency TCR gene transfer following long-term transplantation into lethally irradiated mice transgenic for HLA-DR4. Recipients of genetically modified mouse HSCs developed spontaneous autoimmune vitiligo that was associated with the presence of a Th1-polarized memory effector CD4+ T cell population that expressed the Tyrp1-specific TCR. Most importantly, large numbers of CD4+ T cells expressing the Tyrp1-specific TCR were detected in secondary HLA-DR4-transgenic transplant recipients, and these mice were able to destroy subcutaneously administered melanoma cells without the aid of vaccination, immune modulation, or cytokine administration. These results demonstrate the creation of what we believe to be a novel translational model of durable lentiviral gene transfer that results in long-term effective immunity.

T cell receptor gene therapy for cancer

T cell-based adoptive immunotherapy has been shown to be a promising treatment for various types of cancer. However, adoptive T cell therapy currently requires the custom isolation and characterization of tumor-specific T cells from each patient-a process that can be not only difficult and time-consuming but also often fails to yield high-avidity T cells, which together have limited the broad application of this approach as a clinical treatment. Employing T cell receptor (TCR) gene therapy as a component of adoptive T cell therapy strategies can overcome many of these obstacles, allowing autologous T cells with a defined specificity to be generated in a much shorter time period. Initial studies using this approach have been hampered by a number of technical difficulties resulting in low TCR expression and acquisition of potentially problematic specificities due to mispairing of introduced TCR chains with endogenous TCR chains. The last several years have seen substantial progress in our understanding of the multiple facets of TCR gene therapy that will have to be properly orchestrated for this strategy to succeed. Here we outline the challenges of TCR gene therapy and the advances that have been made toward realizing the promise of this approach.

Production of protein complexes via co-expression

Multi-protein complexes are involved in essentially all cellular processes. A protein's function is defined by a combination of its own properties, its interacting partners, and the stoichiometry of each. Depending on binding partners, a transcription factor can function as an activator in one instance and a repressor in another. The study of protein function or malfunction is best performed in the relevant context. While many protein complexes can be reconstituted from individual component proteins after being produced individually, many others require co-expression of their native partners in the host cells for proper folding, stability, and activity. Protein co-expression has led to the production of a variety of biological active complexes in sufficient quantities for biochemical, biophysical, structural studies, and high throughput screens. This article summarizes examples of such cases and discusses critical considerations in selecting co-expression partners, and strategies to achieve successful production of protein complexes.

Persistent expression of biologically active anti-HER2 antibody by AAVrh.10-mediated gene transfer

Trastuzumab (Herceptin) is a recombinant humanized monoclonal antibody (mAb) directed against an extracellular region of the human epidermal growth-factor receptor type 2 (HER2) protein. We hypothesized that a single adeno-associated virus (AAV)-mediated genetic delivery of an anti-HER2 antibody should be effective in mediating long-term production of anti-HER2 and in suppressing the growth of human tumors in a xenograft model in nude mice. The adeno-associated virus gene transfer vector AAVrh.10alphaHER2 was constructed based on a non-human primate AAV serotype rh.10 to express the complementary DNAs for the heavy and light chains of mAb 4D5, the murine precursor to trastuzumab. The data show that genetically transferred anti-HER2 selectively bound human HER2 protein and suppressed the proliferation of HER2(+) tumor cell lines. A single administration of AAVrh.10alphaHER2 provided long-term therapeutic levels of anti-HER2 antibody expression without inducing an anti-idiotype response, suppressed the growth of HER2(+) tumors and increased the survival of tumor bearing mice. In the context that trastuzumab therapy requires frequent and repeated administration, this strategy might be developed as an alternate platform for delivery of anti-HER2 therapy.

Analysis of adenovirus trans-complementation-mediated gene expression controlled by melanoma-specific TETP promoter in vitro

BACKGROUND

Human adenoviruses (Ads) have substantial potential for clinical applications in cancer patients. Conditionally replicating adenoviruses (CRAds) include oncolytic adenoviruses in which expression of the immediate early viral transactivator protein E1A is controlled by a cancer cell-selective promoter. To enhance efficacy, CRAds are further armed to contain therapeutic genes. Due to size constraints of the capsid geometry, the capacity for packaging transgenes into Ads is, however, limited. To overcome this limitation, the employment of E1A-deleted replication-deficient viruses carrying therapeutic genes in combination with replication-competent CRAd vectors expressing E1A in trans has been proposed. Most trans-complementing studies involved transgene expressions from strong ubiquitous promoters, and thereby relied entirely on the cancer cell specificity of the CRAd vector.

RESULTS

Here we tested the trans-complementation of a CRAd and a replication-deficient transgene vector containing the same cancer cell-selective promoter. Hereto, we generated two new vectors expressing IL-2 and CD40L from a bicistronic expression cassette under the control of the melanoma/melanocyte-specific tyrosinase enhancer tyrosinase promoter (TETP), which we previously described for the melanoma-specific CRAd vector AdDeltaEP-TETP. These vectors gave rise to tightly controlled melanoma-specific transgene expression levels, which were only 5 to 40-fold lower than those from vectors controlled by the nonselective CMV promoter. Reporter analyses using Ad-CMV-eGFP in combination with AdDeltaEP-TETP revealed a high level of trans-complementation in melanoma cells (up to about 30-fold), but not in non-melanoma cells, unlike the AdCMV-eGFP/wtAd5 binary vector system, which was equally efficient in melanoma and non-melanoma cells. Similar findings were obtained when replacing the transgene vector AdCMV-eGFP with AdCMV-IL-2 or AdCMV-CD40L. However, the combination of the novel AdTETP-CD40L/IL-2 vector with AdDeltaEP-TETP or wtAd5 gave reproducible moderate 3-fold enhancements of IL-2 by trans-complementation only.

CONCLUSIONS

The cancer cell-selective TETP tested here did not give the expected enforceable transgene expression typically achieved in the Ad trans-complementing system. Reasons for this could include virus-mediated down regulation of limiting transcription factors, and/or competition for such factors by different promoters. Whether this finding is unique to the particular promoter system tested here, or also occurs with other promoters warrants further investigations.

T cell receptor (TCR) gene therapy to treat melanoma: lessons from clinical and preclinical studies

IMPORTANCE OF THE FIELD

Adoptive T cell therapy (ACT) with tumour infiltrating lymphocytes is currently the best treatment option for metastatic melanoma. Despite its clinical successes, ACT has limitations in availability and generation of therapeutic T cells for a larger group of patients. Introduction of tumour-specific T cell receptors into T cells, termed TCR gene therapy, can provide an alternative for ACT that is more widely applicable and might be extended to other types of cancer.

AREAS COVERED IN THIS REVIEW

The current status of TCR gene therapy studies including clinical challenges, such as on-target toxicity, compromised anti-tumour T cell responses, compromised T cell persistence and potential immunogenicity of receptor transgenes. Strategies to address these challenges are covered.

WHAT THE READER WILL GAIN

A listing and discussion of strategies that aim at improving the efficacy and safety of TCR gene therapy. Such strategies address antigen choice, TCR mis-pairing, functional avidity and persistence of T cells, immune responses towards receptor transgenes, and combination of ACT with other therapies.

TAKE HOME MESSAGE

To ensure further clinical development of TCR gene therapy, it is necessary to choose safe T cell target antigens, and implement (combinations of) strategies that enhance the correct pairing of TCR transgenes and the functional avidity and persistence of T cells.

A recombinant humanized monoclonal antibody completely protects mice against lethal challenge with Venezuelan equine encephalitis virus

A recombinant humanized antibody to Venezuelan equine encephalitis virus (VEEV) was constructed in a monocistronic adenoviral expression vector with a foot-and-mouth-disease virus-derived 2A self-cleavage oligopeptide inserted between the antibody heavy and light chains. After expression in mammalian cells, the heavy and light chains of the humanized antibody (hu1A4A1IgG1-2A) were completely cleaved and properly dimerized. The purified hu1A4A1IgG1-2A retained VEEV binding affinity and neutralizing activity similar to its parental murine antibody. The half-life of hu1A4A1IgG1-2A in mice was approximately 2 days. Passive immunization of hu1A4A1IgG1-2A in mice (50 microg/mouse) 24 h before or after virulent VEEV challenge provided complete protection, indicating that hu1A4A1IgG1-2A has potent prophylactic and therapeutic effects against VEEV infection.

High-throughput flow cytometry purification of transduced progenitors expressing defined levels of vascular endothelial growth factor induces controlled angiogenesis in vivo

Delivery of therapeutic genes by genetically modified progenitors is a powerful tool for regenerative medicine. However, many proteins remain localized within or around the expressing cell, and heterogeneous expression levels can lead to reduced efficacy or increased toxicity. For example, the matrix-binding vascular endothelial growth factor (VEGF) can induce normal, stable, and functional angiogenesis or aberrant angioma growth depending on its level of expression in the microenvironment around each producing cell, and not on its total dose. To overcome this limitation, we developed a flow cytometry-based method to rapidly purify transduced cells expressing desired levels of a therapeutic transgene. Primary mouse myoblasts were transduced with a bicistronic retrovirus expressing VEGF linked to a nonfunctional, truncated form of the syngenic molecule CD8a. By using a clonal population uniformly expressing a known VEGF level as a reference, cells producing similar VEGF amounts were rapidly sorted from the primary population on the basis of their CD8a fluorescence intensity. A single round of sorting with a suitably designed gate yielded a purified population that induced robust, normal, and stable angiogenesis, and completely avoided angioma growth, which was instead always caused by the heterogeneous parent population. This clinically applicable high-throughput technique allowed the delivery of highly controlled VEGF levels in vivo, leading to significantly improved safety without compromising efficacy. Furthermore, when applied to other suitable progenitor populations, this technique could help overcome a significant obstacle in the development of safe and efficacious vascularization strategies in the fields of regenerative medicine and tissue engineering.

Dengue virus replicons: production of an interserotypic chimera and cell lines from different species, and establishment of a cell-based fluorescent assay to screen inhibitors, validated by the evaluation of ribavirin's activity

The prevention and treatment of flavivirus infections are public health priorities. Dengue fever is the most prevalent mosquito-borne viral disease of humans, affecting more than 50 million people annually. Despite the urgent need to control dengue infections, neither specific antiviral therapies nor licensed vaccines exist and the molecular basis of dengue pathogenesis is not well understood. In this study we produced a novel dengue virus type 2 (DV2) subgenomic replicon that expresses a fusion protein comprised of Enhanced Green Fluorescent Protein (EGFP) and Puromycin N-Acetyltransferase (PAC). We successfully established BHK, COS and Huh7 cell lines that stably expressed the DV2 replicon. Using EGFP as a reporter of DV replication complex activity, we set up a new HTS assay. The assay was validated using the inhibitor ribavirin, confirmed by flow cytometry analysis and the analysis of NS5 expression by Western-blot analysis. In order to develop a system to test antivirals against the NS5 proteins of all four DV serotypes in a similar cellular environment, the replicon was further modified, to allow easy exchange of the NS5 gene between DV serotypes. As proof of principle, a chimeric replicon in which the DV2 NS5 gene was substituted with that of DV type 3 was stably expressed in BHK cells and used in ribavirin inhibition studies. The assays described in this study will greatly facilitate DV drug discovery by serving as primary or complementary screening. The approach should be applicable to the development of fluorescent cell-based HTS assays for other flaviviruses, and useful for the study of many aspects of DV, including viral replication and pathogenesis.

Optimal promoter usage for lentiviral vector-mediated transduction of cultured central nervous system cells

Lentiviral vectors transduce both dividing and non-dividing cells and can support sustained expression of transgenes. These properties make them attractive for the transduction of neurons and other neural cell types in vitro and in vivo. Lentiviral vectors can be targeted to specific cell types by using different promoters in the lentiviral shuttle vector. Even with identical constructs, however, levels of expression can vary significantly in different types of neurons and different culture preparations; expression levels in the same neuronal subtypes can be very different in primary cell culture and in vivo. We systematically assessed the ability of different promoters to direct expression of foreign transgenes in primary murine neocortical neurons, cerebellar granule cells and in undifferentiated and differentiated neuroblastoma cells. In primary cortical neurons, constructs using the ubiquitin C promoter directed the highest level of transgene expression; the phosphoglycerate kinase (PGK) promoter also directed robust transgene expression, while the cytomegalovirus (CMV) and MND (a synthetic promoter that contains the U3 region of a modified MoMuLV LTR with myeloproliferative sarcoma virus enhancer) promoters resulted in the expression of the transgenes in only limited number of neurons. In contrast, in cerebellar granule cells and in differentiated SH-SY5Y neuroblastoma cultures, the CMV promoter directed the most robust transgene expression. There was similar variability in transgene expression directed by these promoters in primary cultures of oligodendrocytes and astrocytes. These findings may prove useful in the design of lentiviral vectors for use in cell culture models of the nervous system.

A dual promoter lentiviral vector for the in vivo evaluation of gene therapeutic approaches to axon regeneration after spinal cord injury

The identification of axon growth-promoting genes, and overexpression of these genes in central nervous system (CNS) neurons projecting to the spinal cord, has emerged as one potential approach to enhancing CNS regeneration. Assessment of the regenerative potential of candidate genes usually requires axonal tracing of spinal projections, ideally limited to neurons that express the candidate gene. Alternatively, coexpression of a reporter gene such as enhanced green fluorescent protein (GFP) from an internal ribosomal entry site can be used to identify neurons expressing the candidate gene, but this strategy does not label corticospinal axons in the spinal cord. We therefore developed a dual promoter lentiviral vector in which a potentially therapeutic transgene is expressed from the cytomegalovirus-enhanced chicken beta-actin promoter and the fluorescent protein copGFP is expressed from the elongation factor-1alpha promoter. The vector was constructed to be compatible with the Gateway recombination system for efficient introduction of transgenes through entry shuttle vectors. We show both simultaneous expression of a candidate and reporter gene in corticospinal and red nucleus neurons, and efficient labeling of their axons after lesions in the cervical spinal cord. This expression system is therefore an accurate and efficient means of screening candidate genes in vivo for enhancement of axonal growth.

Effects of adenoviral-mediated coexpression of bone morphogenetic protein-7 and insulin-like growth factor-1 on human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Bone morphogenetic protein-7 (BMP-7) and insulin-like growth factor-1 (IGF-1) are important in periodontal reconstruction. However, their synergistic effect in periodontal regeneration by gene delivery has not been reported. In this study, gene delivery of these two growth factors to human periodontal ligament cells (hPDLCs) was examined for its effects on cell proliferation and differentiation.

MATERIAL AND METHODS

Recombinant adenoviruses containing both human BMP-7 and IGF-1 cDNA created by introducing the internal ribosome entry site (IRES) sequence were used to transfer the genes into hPDLCs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell cycle analysis were used to observe their effects on cell proliferation, while alkaline phosphatase activity measurement, RT-PCR and in vivo tests were conducted to investigate their effects on cell differentiation.

RESULTS

The proliferation of hPDLCs transduced by adenoviruses coexpressing BMP-7 and IGF-1 was suppressed while their differentiation ability was enhanced. There was a synergism of BMP-7 and IGF-1 in up-regulating alkaline phosphatase activity and mRNA levels of collagen type I and Runx2. Implantation in vivo with scaffolds illustrated that the transduced cells exhibited osteogenic differentiation and formed bone-like structures.

CONCLUSION

The combined delivery of BMP-7 and IGF-1 genes using an IRES-based strategy synergistically enhanced differentiation of hPDLCs. It is suggested that this could be a new potential method in gene therapy for periodontal reconstruction.