Complexation of retrovirus with cationic and anionic polymers increases the efficiency of gene transfer

Concise review on optimized methods in production and transduction of lentiviral vectors in order to facilitate immunotherapy and gene therapy

Lentiviral vectors (LVs) have provided an efficient way to integrate our gene of interest into eukaryote cells. Human immunodeficiency virus (HIV)-derived LVs have been vastly studied to become an invaluable asset in gene delivery. This abled LVs to be used in both research laboratories and gene therapy. Pseudotyping HIV-1 based LVs, abled it to transduce different types of cells, especially hematopoietic stem cells. A wide range of tropism, plus to the ability to integrate genes into target cells, made LVs an armamentarium in gene therapy. The third and fourth generations of self-inactivating LVs are being used to achieve safe gene therapy. Not only advanced methods enabled the clinical-grade LV production on a large scale, but also considerably heightened transduction efficiency. One of which is microfluidic systems that revolutionized gene delivery approaches. Since gene therapy using LVs attracted lots of attention to itself, we provided a brief review of LV structure and life-cycle along with methods for improving both LV production and transduction. Also, we mentioned some of their utilization in immunotherapy and gene therapy.

YPEL4 modulates HAC15 adrenal cell proliferation and is associated with tumor diameter

Yippee-like (YPEL) proteins are thought to be related to cell proliferation because of their structure and location in the cell. The aim of this study was to clarify the effects of YPEL4 on aldosterone production and cell proliferation in the human adrenocortical cell line (HAC15) and aldosterone producing adenoma (APA). Basal aldosterone levels in HAC15 cells over-expressing YPEL4 was higher than those of control HAC15 cells. The positive effects of YPEL4 on cell proliferation were detected by XTT assay and crystal violet staining. YPEL4 levels in 39 human APA were 2.4-fold higher compared to those in 12 non-functional adrenocortical adenomas, and there was a positive relationship between YPEL4 levels and APA diameter (r = 0.316, P < 0.05). In summary, we have demonstrated that YPEL4 stimulates human adrenal cortical cell proliferation, increasing aldosterone production as a consequence. These results in human adrenocortical cells are consistent with the clinical observations with APA in humans.

Combining Protein Cages and Polymers: from Understanding Self-Assembly to Functional Materials

Protein cages, such as viruses, are well-defined biological nanostructures which are highly symmetrical and monodisperse. They are found in various shapes and sizes and can encapsulate or template non-native materials. Furthermore, the proteins can be chemically or genetically modified giving them new properties. For these reasons, these protein structures have received increasing attention in the field of polymer-protein hybrid materials over the past years, however, advances are still to be made. This Viewpoint highlights the different ways polymers and protein cages or their subunits have been combined to understand self-assembly and create functional materials.

Optimization of the transductional efficiency of lentiviral vectors: effect of sera and polycations

Lentiviral vectors are widely used as effective gene-delivery vehicles. Optimization of the conditions for efficient lentiviral transduction is of a high importance for a variety of research applications. Presence of positively charged polycations reduces the electrostatic repulsion forces between a negatively charged cell and an approaching enveloped lentiviral particle resulting in an increase in the transduction efficiency. Although a variety of polycations are commonly used to enhance the transduction with retroviruses, the relative effect of various types of polycations on the efficiency of transduction and on the potential bias in the determination of titer of lentiviral vectors is not fully understood. Here, we present data suggesting that DEAE-dextran provides superior results in enhancing lentiviral transduction of most tested cell lines and primary cell cultures. Specific type and source of serum affects the efficiency of transduction of target cell populations. Non-specific binding of enhanced green fluorescent protein (EGFP)-containing membrane aggregates in the presence of DEAE-dextran does not significantly affect the determination of the titer of EGFP-expressing lentiviral vectors. In conclusion, various polycations and types of sera should be tested when optimizing lentiviral transduction of target cell populations.

Comparison of ectopic gene expression methods in rat neural stem cells

Neural stem cells (NSCs) have the ability to proliferate and differentiate into various types of cells that compose the nervous system. To study functions of genes in stem cell biology, genes or siRNAs need to be transfected. However, it is difficult to transfect ectopic genes into NSCs. Thus to identify the suitable method to achieve high transfection efficiency, we compared lipid transfection, electroporation, nucleofection and retroviral transduction. Among the methods that we tested, we found that nucleofection and retroviral transduction showed significantly increased transfection efficiency. In addition, with retroviral transduction of Ngn2 that is known to induce neurogenesis in various types of cells, we observed facilitated final cell division in rat NSCs. These data suggest that nucleofection and retroviral transduction provide high efficiency of gene delivery system to study functions of genes in rat NSCs.

MicroSCALE screening reveals genetic modifiers of therapeutic response in melanoma

Cell microarrays are a promising tool for performing large-scale functional genomic screening in mammalian cells at reasonable cost, but owing to technical limitations they have been restricted for use with a narrow range of cell lines and short-term assays. Here, we describe MicroSCALE (Microarrays of Spatially Confined Adhesive Lentiviral Features), a cell microarray-based platform that enables application of this technology to a wide range of cell types and longer-term assays. We used MicroSCALE to uncover kinases that when overexpressed partially desensitized B-RAFV600E-mutant melanoma cells to inhibitors of the mitogen-activated protein kinase kinase kinase (MAPKKK) RAF, the MAPKKs MEK1 and 2 (MEK1/2, mitogen-activated protein kinase kinase 1 and 2), mTOR (mammalian target of rapamycin), or PI3K (phosphatidylinositol 3-kinase). These screens indicated that cells treated with inhibitors acting through common mechanisms were affected by a similar profile of overexpressed proteins. In contrast, screens involving inhibitors acting through distinct mechanisms yielded unique profiles, a finding that has potential relevance for small-molecule target identification and combination drugging studies. Further, by integrating large-scale functional screening results with cancer cell line gene expression and pharmacological sensitivity data, we validated the nuclear factor κB pathway as a potential mediator of resistance to MAPK pathway inhibitors. The MicroSCALE platform described here may enable new classes of large-scale, resource-efficient screens that were not previously feasible, including those involving combinations of cell lines, perturbations, and assay outputs or those involving limited numbers of cells and limited or expensive reagents.

Angiopoietin-1 requires IQ domain GTPase-activating protein 1 to activate Rac1 and promote endothelial barrier defense

OBJECTIVE

IQ domain GTPase-activating protein 1 (IQGAP1) contributes to cytoskeletal network regulation in epithelial cells by its scaffolding properties and by binding the Rho GTPase Rac1 to maintain its activity. The functions of IQGAP1 in endothelial cells beyond angiogenesis remain unclear. We hypothesized that IQGAP1 participates in the regulation of endothelial barrier function.

METHODS AND RESULTS

Silencing IQGAP1 in human microvascular endothelial cells resulted in a disruption of adherens junctions, formation of interendothelial gaps, and a reduction in barrier function. Furthermore, silencing of IQGAP1 abrogated the barrier enhancement effect of angiopoietin-1 (Angpt-1) and abolished the barrier-stabilizing effect of Angpt-1 on thrombin-stimulated cells. Coimmunoprecipitation detected binding of endogenous IQGAP1 with Rac1 at baseline that was stronger when Rac1 was activated and weaker when it was deactivated. Measurement of GTP-bound Rac1 revealed that Angpt-1 failed to activate Rac1 not only if IQGAP1 was silenced but also if cells were transfected with a mutant disabled in Rac1 binding (T1050AX2). Furthermore, a dominant-active Rac1 was sufficient to completely reverse the morphological and functional changes induced by reduction in IQGAP1.

CONCLUSION

These experiments are the first demonstration of IQGAP1 regulating barrier function in any cell type. Further, our data show that Angpt-1 requires IQGAP1 as an indispensable activator of Rac1.

Chimeric antigen receptors for T-cell based therapy

The Chimeric Antigen Receptor (CAR) consists of an antibody-derived targeting domain fused with T-cell signaling domains that, when expressed by a T-cell, endows the T-cell with antigen specificity determined by the targeting domain of the CAR. CARs can potentially redirect the effector functions of a T-cell towards any protein and nonprotein target expressed on the cell surface as long as an antibody or similar targeting domain is available. This strategy thereby avoids the requirement of antigen processing and presentation by the target cell and is applicable to nonclassical T-cell targets like carbohydrates. This circumvention of HLA-restriction means that the CAR T-cell approach can be used as a generic tool broadening the potential of applicability of adoptive T-cell therapy. Proof-of-principle studies focusing upon the investigation of the potency of CAR T-cells have primarily focused upon the genetic modification of human and mouse T-cells for therapy. This chapter focuses upon methods to modify T-cells from both species to generate CAR T-cells for functional testing.

Identification of personal lubricants that can cause rectal epithelial cell damage and enhance HIV type 1 replication in vitro

Over-the-counter personal lubricants are used frequently during vaginal and anal intercourse, but they have not been extensively tested for biological effects that might influence HIV transmission. We evaluated the in vitro toxicity anti-HIV-1 activity and osmolality of popular lubricants. A total of 41 lubricants were examined and compared to Gynol II and Carraguard as positive and negative controls for toxicity, respectively. Cytotoxicity was assessed using the XTT assay. The MAGI assay with R5 and X4 HIV-1 laboratory strains was used to evaluate antiviral activity. The effect of the lubricants on differentiated Caco-2 cell monolayers (transepithelial electrical resistance, TEER) was also measured. None of the lubricants tested showed significant activity against HIV-1. Surprisingly, four of them, Astroglide Liquid, Astroglide Warming Liquid, Astroglide Glycerin & Paraben-Free Liquid, and Astroglide Silken Secret, significantly enhanced HIV-1 replication (p<0.0001). A common ingredient in three of these preparations is polyquaternium-15. In vitro testing of a chemically related compound (MADQUAT) confirmed that this similarly augmented HIV-1 replication. Most of the lubricants were found to be hyperosmolar and the TEER value dropped approximately 60% 2 h after exposure to all lubricants tested. Cells treated with Carraguard, saline, and cell controls maintained about 100% initial TEER value after 2-6 h. We have identified four lubricants that significantly increase HIV-1 replication in vitro. In addition, the epithelial damage caused by these and many other lubricants may have implications for enhancing HIV transmission in vivo. These data emphasize the importance of performing more rigorous safety testing on these products.

Transduction of human cells with polymer-complexed ecotropic lentivirus for enhanced biosafety

Stem and tumor cell biology studies often require viral transduction of human cells with known or suspected oncogenes, raising major safety issues for laboratory personnel. Pantropic lentiviruses, such as the commonly used VSV-G pseudotype, are a valuable tool for studying gene function because they can transduce many cell types, including non-dividing cells. However, researchers may wish to avoid production and centrifugation of pantropic viruses encoding oncogenes due to higher biosafety level handling requirements and safety issues. Several potent oncogenes, including c-Myc and SV40 large T antigen, are known to enhance production of induced pluripotent stem cells (iPSC). All other known iPSC-inducing genetic changes (OCT4, SOX2, KLF4, NANOG, LIN28, and p53 loss of function) also have links to cancer, making them of relatively high safety concern as well.

While these cancer-related viruses are useful in studying cellular reprogramming and pluripotency, they must be used safely. To address these biosafety issues, we demonstrate a method for transduction of human cells with ecotropic lentivirus, with additional emphasis on reduced cost and convenient handling. We have produced ecotropic lentivirus with sufficiently high titer to transduce greater than 90% of receptor-expressing human cells exposed to the virus, validating the efficacy of this approach.

Lentivirus is often concentrated by ultracentrifugation; however, this process takes several hours and can produce aerosols infectious to human biomedical researchers. As an alternative, viral particles can be more safely sedimented onto cells by complexation with chondroitin sulfate and polybrene (CS/PB). This technique increases the functional viral titer up to 3-fold in cells stably expressing murine retrovirus receptor, with negligible added time and cost. Transduction of human dermal fibroblasts (HDFs) is maximally enhanced using CS/PB concentrations approximately 4-fold lower than the optimal value previously reported for cancer cell lines, suggesting that polymer concentration should be titrated for the target cell type of interest. We therefore describe the use of methylthiazolyldiphenyl-tetrazolium bromide (MTT) to assay for polymer toxicity in a new cell type. We observe equivalent viability of HDFs after viral transduction using either polymer complexation or the standard dose of polybrene (PB, 6 μg/ml), indicating minimal acute toxicity.

In this protocol, we describe the use of ecotropic lentivirus for overexpression of oncogenes in human cells, reducing biosafety risks and increasing the transduction rate. We also demonstrate the use of polymer complexation to enhance transduction while avoiding aerosol-forming centrifugation of viral particles.

Entry kinetics and cell-cell transmission of surface-bound retroviral vector particles

BACKGROUND

Transduction with recombinant HIV-1 derived lentivirus vectors is a multi-step process initiated by surface attachment and subsequent receptor-directed uptake into the target cell. We previously reported the retention of vesicular stomatitis virus G protein pseudotyped particles on murine progenitor cells and their delayed cell-cell transfer.

METHODS

To examine the underlying mechanism in more detail, we used a combination of approaches focused on investigating the role of receptor-independent factors in modulating attachment.

RESULTS

The investigation of synchronized transduction reveals cell-type specific rates of vector particle clearance with substantial delays during particle entry into murine hematopoietic progenitor cells. The observed uptake kinetics from the surface of the 1 degrees cell correlate inversely with the magnitude of transfer to 2 degrees targets, corresponding with our initial observation of preferential cell-cell transfer in the context of brief vector exposures. We further demonstrate that vector particle entry into cells is associated with the cell-type specific abundance of extracellular matrix fibronectin. Residual particle-extracellular fibronectin matrix binding and 2 degrees transfer can be competitively disrupted by heparin exposure without affecting murine progenitor homing and repopulation.

CONCLUSIONS

Although cellular attachment factors, including fibronectin, aid gene transfer by colocalizing particles to cells and disfavoring early dissociation from targets, they also appear to stabilize particles on the cell surface. The present study highlights the inadvertent consequences for cell entry and cell-cell transfer.

Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1

Architecturally defective, leaky blood vessels typify pathologic angiogenesis induced by vascular endothelial growth factor-A (VEGF-A). Such neovascular defects aggravate disease pathology and seriously compromise the therapeutic utility of VEGF. Endothelial cell (EC) transduction with active L61Rac1 strongly improved VEGF-driven angiogenesis in vivo as measured by increased neovascular density, enhanced lumen formation, and reduced vessel leakiness. Conversely, transduction with dominant-negative N17Rac1 strongly inhibited neovascularization. In vitro, active L61Rac1 promoted organization of cortical actin filaments and vascular cords and improved EC-EC junctions, indicating that improved cytoskeletal dynamics are important to the mechanism by which active L61Rac1 rectifies VEGF-driven angiogenesis. SEW2871, a sphingosine 1-phosphate receptor-1 agonist that activates Rac1 in ECs, improved cord formation and EC-EC junctions in vitro similarly to active L61Rac. Moreover, SEW2871 administration in vivo markedly improved VEGF neovessel architecture and reduced neovascular leak. Angiopoietin-1, a cytokine that "normalizes" VEGF neovessels in vivo, activated Rac1 and improved cord formation and EC-EC junctions in vitro comparably to active L61Rac1, and a specific Rac1 inhibitor blocked these effects. These studies distinguish augmentation of Rac1 activity as a means to rectify the pathologic angioarchitecture and dysfunctionality of VEGF neovessels, and they identify a rational pharmacologic strategy for improving VEGF angiogenesis.

Moderation of calpain activity promotes neovascular integration and lumen formation during VEGF-induced pathological angiogenesis

Background

Successful neovascularization requires that sprouting endothelial cells (ECs) integrate to form new vascular networks. However, architecturally defective, poorly integrated vessels with blind ends are typical of pathological angiogenesis induced by vascular endothelial growth factor-A (VEGF), thereby limiting the utility of VEGF for therapeutic angiogenesis and aggravating ischemia-related pathologies. Here we investigated the possibility that over-exuberant calpain activity is responsible for aberrant VEGF neovessel architecture and integration. Calpains are a family of intracellular calcium-dependent, non-lysosomal cysteine proteases that regulate cellular functions through proteolysis of numerous substrates.

Methodology/Principal Findings

In a mouse skin model of VEGF-driven angiogenesis, retroviral transduction with dominant-negative (DN) calpain-I promoted neovessel integration and lumen formation, reduced blind ends, and improved vascular perfusion. Moderate doses of calpain inhibitor-I improved VEGF-driven angiogenesis similarly to DN calpain-I. Conversely, retroviral transduction with wild-type (WT) calpain-I abolished neovessel integration and lumen formation. In vitro, moderate suppression of calpain activity with DN calpain-I or calpain inhibitor-I increased the microtubule-stabilizing protein tau in endothelial cells (ECs), increased the average length of microtubules, increased actin cable length, and increased the interconnectivity of vascular cords. Conversely, WT calpain-I diminished tau, collapsed microtubules, disrupted actin cables, and inhibited integration of cord networks. Consistent with the critical importance of microtubules for vascular network integration, the microtubule-stabilizing agent taxol supported vascular cord integration whereas microtubule dissolution with nocodazole collapsed cord networks.

Conclusions/Significance

These findings implicate VEGF-induction of calpain activity and impairment of cytoskeletal dynamics in the failure of VEGF-induced neovessels to form and integrate properly. Accordingly, calpain represents an important target for rectifying key vascular defects associated with pathological angiogenesis and for improving therapeutic angiogenesis with VEGF.

Cdc42-mediated inhibition of GSK-3β improves angio-architecture and lumen formation during VEGF-driven pathological angiogenesis

Vascular endothelial growth factor-A (VEGF) typically induces abnormal angiogenesis in the adult, thereby aggravating disease pathology and limiting utility of VEGF for therapeutic angiogenesis. To identify strategies for rectifying defects in pathological VEGF neovessels, we investigated consequences of modulating the Rho GTPase Cdc42. In a mouse skin model of VEGF-driven pathological angiogenesis, transduction with active Cdc42 (L28Cdc42) markedly improved VEGF neovessels, as measured by increased lumen formation, enlarged vessel diameter, and enhanced perfusion of macromolecular tracers. Conversely, transduction with dominant negative Cdc42 (N17Cdc42) impaired endothelial cell (EC) assembly into lumenized blood vessels and reduced neovessel diameter and tracer perfusion. In vitro, active Cdc42 improved coordination between actin filaments and microtubules and enhanced formation of vascular cords, suggesting that active Cdc42 rectifies defects in angiogenesis by improving cytoskeletal dynamics and capillary morphogenesis. Analyses of Cdc42 signaling in microvascular ECs indicated that active Cdc42 also inhibits glycogen synthase kinase-3β (GSK-3β), a multi-functional serine/threonine protein kinase. Pharmacological inhibition of GSK-3β improved vascular cord formation in vitro and promoted proper neovessel formation in vivo comparably to active Cdc42, thus linking GSK-3β inhibition to the mechanism by which active Cdc42 rectifies pathological neovascularization. These studies identify activation of Cdc42 and inhibition of GSK-3β as novel strategies for correcting abnormalities associated with VEGF-driven angiogenesis, and they suggest new approaches for achieving improved therapeutic neovascularization with VEGF.

Effect of cell lysates on retroviral transduction efficiency of cells in suspension culture

Recombinant retroviruses are effective vectors able to integrate transgenes into the target cell's genome to achieve longer-term expression. This study investigates the effect of cell lysis products, a common cell culture by-product, on the transduction of suspension cells by gammaretroviral vectors. Cell lysates derived from human and murine suspension cell lines significantly increased the transduction of human TF-1 and K-562 cell lines by gibbon ape leukemia virus-pseudotyped retroviral vectors without altering tropism. The transduction efficiency of TF-1 cells increased as a function of lysate concentration and decreased with increasing target cell concentrations. This was adequately predicted using a saturation equation based on the lysed-to-target cell concentration ratio, R, where: Fold increase = 1+Fold_(Max) (R/(K_(L)+R)). Lysate completely masked the effects of fibronectin when the two were added in combination. With protamine sulfate, the transduction efficiency was increased by lysate to 58% from 20% for protamine sulfate alone. Overall, the presence of cell lysate significantly influenced the outcome of the transduction process, either alone or in the presence of protamine sulfate or fibronectin.

Helical conformation of the SEVI precursor peptide PAP248-286, a dramatic enhancer of HIV infectivity, promotes lipid aggregation and fusion

In previous in vivo studies, amyloid fibers formed from a peptide ubiquitous in human seminal fluid (semen-derived enhancer of viral infection (SEVI)) were found to dramatically enhance the infectivity of the HIV virus (3-5 orders of magnitude by some measures). To complement those studies, we performed in vitro assays of PAP(248-286), the most active precursor to SEVI, and other polycationic polymers to investigate the physical mechanisms by which the PAP(248-286) promotes the interaction with lipid bilayers. At acidic (but not at neutral) pH, freshly dissolved PAP(248-286) catalyzes the formation of large lipid flocculates in a variety of membrane compositions, which may be linked to the promotion of convective transport in the vaginal environment rather than transport by a random Brownian motion. Furthermore, PAP(248-286) is itself fusiogenic and weakens the integrity of the membrane in such a way that may promote fusion by the HIV gp41 protein. An alpha-helical conformation of PAP(248-286), lying parallel to the membrane surface, is implicated in promoting bridging interactions between membranes by the screening of the electrostatic repulsion that occurs when two membranes are brought into close contact. This suggests that nonspecific binding of monomeric or small oligomeric forms of SEVI in a helical conformation to lipid membranes may be an additional mechanism by which SEVI enhances the infectivity of the HIV virus.

Rapid dissociation of HIV-1 from cultured cells severely limits infectivity assays, causes the inactivation ascribed to entry inhibitors, and masks the inherently high level of infectivity of virions

By using immunofluorescence microscopy to observe and analyze freshly made HIV-1 virions adsorbed onto cells, we found that they are inherently highly infectious, rather than predominantly defective as previously suggested. Surprisingly, polycations enhance titers 20- to 30-fold by stabilizing adsorption and preventing a previously undescribed process of rapid dissociation, strongly implying that infectivity assays for many viruses are limited not only by inefficient virus diffusion onto cells but also by a postattachment race between entry and dissociation. This kinetic competition underlies inhibitory effects of CCR5 antagonists and explains why adaptive HIV-1 mutations overcome many cell entry limitations by accelerating entry.

The effect of surface modification of adenovirus with an arginine-grafted bioreducible polymer on transduction efficiency and immunogenicity in cancer gene therapy

Adenoviral vectors offer many advantages for cancer gene therapy, including high transduction efficiency, but safety concerns related to severe immunogenicity and other side effects have led to careful reconsideration of their use in human clinical trials. To overcome these issues, a strategy of generating hybrid vectors that combine viral and non-viral elements as more intelligent gene carriers has been employed. Here, we coated adenovirus (Ad) with an arginine-grafted bioreducible polymer (ABP) via electrostatic interaction. We examined the effect of ABP-coated Ad complex at various ABP molecules/Ad particle ratios. Enhanced transduction efficiency was observed in cells treated with cationic ABP polymer-coated Ad complex compared to naked Ad. We also examined the coating of Ad with ABP polymers at the optimal polymer ratio using dynamic light scattering and transmission electron microscopy. In both high and low coxsackie virus and adenovirus receptor (CAR)-expressing cells, ABP-coated Ad complex produced higher levels of transgene expression than cationic polymer 25K PEI. Notably, high cytotoxicity was observed with 25K PEI-coated Ad complex treatment, but not with ABP-coated Ad complex treatment. In addition, ABP-coated Ad complex was not significantly inhibited by serum, in contrast to naked Ad. Moreover, ABP-coated Ad complex significantly reduced the innate immune response relative to naked Ad, as assessed by interleukin-6 (IL-6) cytokine release from macrophage cells. Overall, our studies demonstrate that Ad complex formed with ABP cationic polymer may improve the efficiency of Ad and be a promising tool for cancer gene therapy.

Hydroxyethyl starch-based preservation solutions enhance gene therapy vector delivery under hypothermic conditions

Isolated liver perfusion offers a unique prospect for safe, effective targeting of gene therapies that can be directed against allograft rejection or recurrent diseases such as reinfection by hepatitis C virus (HCV). We aimed to examine the effect of organ preservation solutions on vector-based gene therapy delivery under hypothermic conditions. University of Wisconsin (UW) solution, histidine tryptophan ketoglutarate (HTK), EloHaes, sodium-poly(ethylene glycol)-UW solution [Institut Georges Lopez 1 solution (IGL-1)], and Dulbecco's modified Eagle's medium (DMEM) culture medium (control) were tested at 2 degrees C or 37 degrees C for lentiviral vector transduction efficiencies to the hepatoma cell line Huh-7 and primary human or mouse hepatocytes. Lentiviral vectors expressing short hairpin RNA were used to target HCV replication. With a potent short hairpin RNA vector, transductions were directly correlated to the therapeutic effect, with low transduction yielding low knockdown and vice versa. Green fluorescent protein (GFP) reporter gene expression was observed with vector incubation times as short as 10 minutes. The highest transductions were seen, after 2-hour 37 degrees C incubation, in UW (62% +/- 6 SEM); they were significantly higher than those in HTK (21% +/- 7 SEM). Neither adenosine nor glutathione, present in UW, provided any increase in transduction when supplemented to HTK, although the addition of hydroxyethyl starch (HES) significantly improved transductions. To rule out size exclusion as a mechanism of HES, IGL-1 was tested but did not result in better transductions than HTK or DMEM. When supplemented to UW, anionic compounds reduced transduction, and this indicated a charge interaction mechanism of HES. In conclusion, this study demonstrates that effective vector delivery can be achieved under conditions of hypothermic liver perfusion. UW provides superior transduction to hepatocytes over nonstarch solutions.

Targeted Receptor Trafficking Affects the Efficiency of Retrovirus Transduction

We describe the development of an experimental system to test the hypothesis that the efficiency of retrovirus transduction is dependent on the pathway of virus entry into the host cell and the intracellular trafficking itinerary of the cellular receptor with which it interacts. The experimental system consists of three model target cell lines, derived from HeLa cells, that stably express one of three interleukin-2 receptor alpha chain (CD25) chimeras, TAC, TAC-CD16, and TAC-DKQTLL, which have identical extracellular domains but different intracellular trafficking itineraries, and a targeted amphotropic murine leukemia retrovirus whose envelope proteins were modified to include a binding site for TAC at their N-termini. We found that the efficiency of retrovirus transduction was affected by the distribution and trafficking itinerary of the TAC receptors. Transduction of cells that expressed TAC-DKQTLL was nearly 4-fold lower than transduction of control cells that did not express any of the TAC receptors. In contrast, transduction of cells that expressed TAC was 1.6-fold higher than transduction of control cells, whereas transduction was not significantly affected by the expression of TAC-CD16. Our results suggest that in the course of designing a targeted retrovirus it may be prudent to target only those receptors that internalize retroviruses via pathways that most efficiently support post-binding steps of infection.

Polymers for viral gene delivery

BACKGROUND

The development of viral vectors capable of providing efficient gene transfer in diseased tissues without causing any pathogenic effects is pivotal for overcoming the many challenges facing gene therapy.

OBJECTIVE

Immune responses against viral vectors, inadequate gene expression and inefficient targeting to specific cells in vivo are some of the major problems limiting the clinical utility of viral gene therapy.

METHODS

This review will focus on recent progress in strategic polymer-based modifications to improve the performance and biocompatibility of a variety of viral vectors. We will discuss the preclinical development of four approaches involving injectable polymers, polyelectrolytes, polymer microspheres and polymer-virus conjugates.

RESULTS/CONCLUSION

Much progress has been made in creating 'hybrid' gene delivery vectors that combine the strengths of polymers and viruses. With further optimization, these hybrid vectors, which may be safer and more effective, are likely to succeed in clinical applications.

Engineering graded tissue interfaces

Interfacial zones between tissues provide specialized, transitional junctions central to normal tissue function. Regenerative medicine strategies focused on multiple cell types and/or bi/tri-layered scaffolds do not provide continuously graded interfaces, severely limiting the integration and biological performance of engineered tissue substitutes. Inspired by the bone-soft tissue interface, we describe a biomaterial-mediated gene transfer strategy for spatially regulated genetic modification and differentiation of primary dermal fibroblasts within tissue-engineered constructs. We demonstrate that zonal organization of osteoblastic and fibroblastic cellular phenotypes can be engineered by a simple, one-step seeding of fibroblasts onto scaffolds containing a spatial distribution of retrovirus encoding the osteogenic transcription factor Runx2/Cbfa1. Gradients of immobilized retrovirus, achieved via deposition of controlled poly(L-lysine) densities, resulted in spatial patterns of transcription factor expression, osteoblastic differentiation, and mineralized matrix deposition. Notably, this graded distribution of mineral deposition and mechanical properties was maintained when implanted in vivo in an ectopic site. Development of this facile and robust strategy is significant toward the regeneration of continuous interfacial zones that mimic the cellular and microstructural characteristics of native tissue.

Differential interaction of retroviral vector with target cell: quantitative effect of cellular receptor, soluble proteoglycan, and cell type on gene delivery efficiency

Retroviral vectors are powerful tools for gene therapy and stem cell engineering. To improve efficiency of retroviral gene delivery, quantitative understanding of interactions of a retroviral vector and a cell is crucial. Effects of nonspecific adsorption of retrovirus on a cell via proteoglycans and receptor-mediated binding of retrovirus to a cell on overall transduction efficiency were quantified by combining a mathematical model and experimental data. Results represented by transduction rate constant, a lumped parameter of overall transduction efficiency, delineated that chondroitin sulfate C (CSC) plays dual roles as either enhancer or inhibitor of retroviral transduction, depending on its concentrations in the retroviral supernatant. At the concentration of 20 microg/mL, CSC enhanced the transduction efficiency up to threefold but inhibited more than sevenfold at the concentration of 100 microg/mL. Transduction rate constants for amphotropic retroviral infection of NIH 3T3 cells under phosphate-depleted culture condition showed a proportional relationship between cellular receptor density on a cell and transduction efficiency. It was finally shown that amphotropic retrovirus transduced human fibroblast HT1080 cells more efficiently than NIH 3T3 cells. On the contrary, the transduction efficiency of NIH 3T3 cells by vesicular stomatitis virus G protein pseudotyped retroviruses was eightfold higher than that of HT1080 cells. This study implies usefulness of using quantitative analysis of retroviral transduction in understanding and optimizing retroviral gene delivery systems for therapeutic approaches to tissue engineering.

Neisseria gonorrhoeae-induced human defensins 5 and 6 increase HIV infectivity: role in enhanced transmission

Sexually transmitted infections (STIs) increase the likelihood of HIV transmission. Defensins are part of the innate mucosal immune response to STIs and therefore we investigated their role in HIV infection. We found that human defensins 5 and 6 (HD5 and HD6) promoted HIV infection, and this effect was primarily during viral entry. Enhancement was seen with primary viral isolates in primary CD4(+) T cells and the effect was more pronounced with R5 virus compared with X4 virus. HD5 and HD6 promoted HIV reporter viruses pseudotyped with vesicular stomatitis virus and murine leukemia virus envelopes, indicating that defensin-mediated enhancement was not dependent on CD4 and coreceptors. Enhancement of HIV by HD5 and HD6 was influenced by the structure of the peptides, as loss of the intramolecular cysteine bonds was associated with loss of the HIV-enhancing effect. Pro-HD5, the precursor and intracellular form of HD5, also exhibited HIV-enhancing effect. Using a cervicovaginal tissue culture system, we found that expression of HD5 and HD6 was induced in response to Neisseria gonorrhoeae (GC, for gonococcus) infection and that conditioned medium from GC-exposed cervicovaginal epithelial cells with elevated levels of HD5 also enhanced HIV infection. Introduction of small interfering RNAs for HD5 or HD6 abolished the HIV-enhancing effect mediated by GC. Thus, the induction of these defensins in the mucosa in the setting of GC infection could facilitate HIV infection. Furthermore, this study demonstrates the complexity of defensins as innate immune mediators in HIV transmission and warrants further investigation of the mechanism by which defensins modulate HIV infection.

Amphotropic retrovirus transduction is inhibited by high doses of particle-associated envelope proteins

Using a panel of amphotropic murine leukemia virus packaging cell lines that differed only in their levels of envelope protein (gp70) expression, we examined the relationship between transduction and the number of envelope proteins per virus. We generated virus stocks that contained different levels of virus-associated envelope proteins, purified them from gp70 that was not associated with the viruses, quantified their titers, and measured the efficiency with which they transduced NIH 3T3, TE671, and HeLa cells. As expected, titers increased monotonically with viral envelope protein number. Titers are measured using highly dilute virus, however, and are often not predictive of gene transfer when high doses of virus are used, as is done in gene therapy protocols. Interestingly, when we used high doses of virus, we observed significantly different trends: gene transfer increased, reached a maximum, and then declined sharply as the number of envelope proteins per virus increased. The highest levels of gene transfer occurred when cells were transduced with a moderate dose of virus that contained low levels of envelope protein. Our results indicate that transduction is inhibited when viruses that contain large numbers of envelope proteins are used. This is most likely because each virus, when it binds to a cell, delivers a large payload of envelope proteins that occupy or inactivate multiple virus receptors, reducing or eliminating the susceptibility of the cell to being transduced by additional viruses. The implications of our findings for the design of improved retroviral vectors for human gene therapy are discussed.

Biomaterial-mediated retroviral gene transfer using self-assembled monolayers

Biomaterial-mediated gene delivery has recently emerged as a promising alternative to conventional gene transfer technologies that focus on direct delivery of viral vectors or DNA-polymer/matrix complexes. However, biomaterial-based strategies have primarily targeted transient gene expression vehicles, including plasmid DNA and adenovirus particles. This study expands on this work by characterizing biomaterial properties conducive to the surface immobilization of retroviral particles and subsequent transduction of mammalian cells at the cell-material interface. Self-assembled monolayers (SAMs) of functionally-terminated alkanethiols on gold were used to establish biomaterial surfaces of defined chemical composition. Gene transfer was observed to be greater than 90% on NH(2)-terminated surfaces, approximately 50% on COOH-functionalized surfaces, and undetectable on CH(3)-terminated SAMs, similar to controls of tissue culture-treated polystyrene. Gene delivery via the NH(2)-SAM was further characterized as a function of retrovirus coating time, virus concentration, and cell seeding density. Finally, SAM-mediated gene delivery was comparable to fibronectin- and poly-l-lysine-based methods for gene transfer. This work is significant to establishing safe and effective gene therapy strategies, developing efficient methods for gene delivery, and supporting recent progress in the field of biomaterial-mediated gene transfer.

Exploiting heparin-binding properties of MoMLV-based retroviral vectors for affinity chromatography

Chromatography is deemed the most promising technology for large-scale purification of viral vectors. The authors have previously shown that heparin affinity chromatography could be successfully employed for the purification of VSV-G pseudotyped Moloney murine leukemia virus (MoMLV)-derived vectors giving excellent results in terms of recovery of active particles, reproducibility and selectivity. In this study, the authors examined whether the ability of retrovirus particles to specifically bind to heparin ligands is restricted to VSV-G pseudotypes produced by 293-based packaging cells. It is shown that VSV-G deficient retrovirus particles are captured by a heparin chromatography column as efficiently as VSV-G containing particles. Most strikingly, RD114 pseudotyped retrovirus particles derived from a HT1080-based cell line were found to bind heparin with the same affinity as 293-derived VSV-G pseudotypes. RD114 pseudotyped retrovirus particles were successfully isolated using heparin affinity chromatography obtaining good recoveries of functional particles (43%). These results indicate that heparin affinity chromatography can be extended to the purification of retroviral vectors produced by different packaging cell lines independently of the Env-protein used for pseudotyping.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

A natural structural variant of the mouse TCR beta-chain displays intrinsic receptor function and antigen specificity

The Cbeta0 alternate cassette exon is located between the Jbeta1 and Cbeta1 genes in the mouse TCR beta-locus. In T cells with a VDJbeta1 rearrangement, the Cbeta0 exon may be included in TCRbeta transcripts (herein called TCRbeta-Cbeta0 transcripts), potentially inserting an additional 24 aa between the V and C domains of the TCR beta-chain. These TCRbeta splice isoforms may be differentially regulated after Ag activation, because we detected TCRbeta-Cbeta0 transcripts in a high proportion (>60%) of immature and mature T cells having VDJbeta1 rearrangements but found a substantially reduced frequency (<35%) of TCRbeta-Cbeta0 expression among CD8 T cells selected by Ag in vivo. To study the potential activity of the TCRbeta-Cbeta0 splice variant, we cloned full-length TCR cDNAs by single-cell RT-PCR into retroviral expression vectors. We found that the TCRbeta-Cbeta0 splice isoform can function during an early stage of T cell development normally dependent on TCR beta-chain expression. We also demonstrate that T hybridoma-derived cells expressing a TCRbeta-Cbeta0 isoform together with the clonally associated TCR alpha-chain recognize the same cognate peptide-MHC ligand as the corresponding normal alphabetaTCR. This maintenance of receptor function and specificity upon insertion of the Cbeta0 peptide cassette signifies a remarkable adaptability for the TCR beta-chain, and our findings open the possibility that this splice isoform may function in vivo.

Development of a Moloney murine leukemia virus-based pseudotype anti-HIV assay suitable for accurate and rapid evaluation of HIV entry inhibitors

There has been increasing interest in the identification of novel HIV entry inhibitors. For the discovery of these entry inhibitors, robust surrogate anti-HIV assays are highly desired. The authors report a novel anti-HIV assay system using Moloney murine leukemia viruses (MMLVs) pseudotyped with cytoplasmic tail-truncated HIV envelope protein gp140. These pseudotyped MMLV-HIVgp140 viral particles carry luciferase transcripts; therefore, robust luciferase signal can be detected in cells infected by these pseudotypes. Polycationic agent polybrene and spinoculation markedly enhanced the infection efficiency of these pseudotypes. It was demonstrated that the tropism of these pseudotypes is dependent on the pseudotyped HIV envelope proteins. MMLV viruses pseudotyped with gp140 from an R5 HIV virus specifically infect CCR5-expressing cells, and viruses pseudotyped with gp140 from an X4 HIV virus specifically infect CXCR4-expressing cells. Furthermore, CCR5 antagonists inhibited only MMLV-gp140(R5) infections, and CXCR4 antagonists inhibited only MMLV-gp140(X4) infections. A variety of known HIV entry inhibitors were tested in both R5- and X4-dependent pseudotype antiviral assays, and the IC50 values generated were consistent with published results. The pseudotype antiviral assay was also used in the characterization of hundreds of novel CCR5 antagonists. The IC50 values determined in this assay were compared with those determined in HIV antiviral and cell-cell fusion (CCF) assays, and good correlation was found between pseudotype antiviral assay and HIV antiviral assay (R2 = 0.9) or CCF assay (R2 = 0.8).

Murine leukemia virus particles activate Rac1 in HeLa cells

A number of viruses, when they bind to cells, activate intracellular signals that facilitate post-binding steps of infection. To determine if retroviruses activate intracellular signaling, we transduced HeLa cells with amphotropic retroviruses produced by TelCeB6 cells and examined cell lysates for activated Rac1. We found that retroviruses activate Rac1. Rac1 activation was blocked when cells were depleted of cholesterol, cultured in suspension, or incubated with an anti-beta(1) integrin antibody, and when viruses were treated with heparinase III. Retrovirus activation of Rac1 did not require the amphotropic envelope protein. Gene transfer was reduced 2.4-fold when viruses were treated with heparinase III, but did not change when cells were transduced in the presence of function-blocking anti-beta(1) integrin antibodies. The implications of these findings with respect to retrovirus-cell interactions are discussed.

Rapid concentration and purification of retrovirus by flocculation with Polybrene

We have previously shown that the combined addition of Polybrene (PB) and chondroitin sulfate C (CSC) to retrovirus stocks leads to the formation of retrovirus-polymer complexes (i.e., flocs) that rapidly sediment onto cells, increases the efficiency of gene transfer, and can be used to rapidly concentrate and purify retrovirus stocks. The viruses remain associated with the polyelectrolyte complexes, however, which may complicate their use in downstream applications. In this study we determined if retrovirus could be flocculated using only one polymer (PB). We found that when retrovirus stocks were incubated with 320 microg/ml of PB, more than 70% of the viruses, and fewer than 0.3% of all other proteins, were pelleted by low-speed centrifugation. In contrast to retrovirus complexes formed with two polymers, retrovirus flocculated with PB disaggregated when they were resuspended in fresh medium. We conclude that flocculation of retroviruses with a single cationic polymer (PB) is a useful method for rapidly concentrating and purifying retroviruses, and may prove particularly useful when it is desirable to generate purified virus that is not part of a polymer complex.

Upregulation of TGF-β1 Expression May Be Necessary but Is Not Sufficient for Excessive Scarring

Transforming growth factor beta 1 (TGF-beta1) upregulation has been implicated in hypertrophic scars and keloids, but it is unclear if it is the cause or an effect of excessive scar formation. In this study, we overexpressed TGF-beta1 in fibroblasts and characterized its role. Normal human dermal fibroblasts were genetically modified to overexpress TGF-beta1 as the wild-type latent molecule or as a mutant constitutively active molecule. TGF-beta1 secretion was measured, as were the effects of TGF-beta1 upregulation on cell proliferation, expression of smooth muscle cell alpha actin (SMC alpha-actin) and ability to contract collagen lattices. Fibroblasts were implanted intradermally into athymic mice and tissue formation was analyzed over time by histology and immunostaining. Gene-modified fibroblasts secreted approximately 20 times the TGF-beta1 released by control cells, but only cells expressing mutant TGF-beta1 secreted it in the active form. Fibroblasts expressing the active TGF-beta1 gene had increased levels of SMC alpha-actin and enhanced ability to contract a collagen lattice. After intradermal injection into athymic mice, only fibroblasts expressing active TGF-beta1 formed "keloid-like" nodules containing collagen, which persisted longer than implants of the other cell types. We conclude that upregulation of TGF-beta1 by fibroblasts may be necessary, but is not sufficient for excessive scarring. Needed are other signals to activate TGF-beta1 and prolong cell persistence.

A TGF-β1-Dependent Autocrine Loop Regulates the Structure of Focal Adhesions in Hypertrophic Scar Fibroblasts

Following injury, fibroblasts migrate into wounds and differentiate into alpha smooth muscle cell actin (SMCA)-positive cells, termed myofibroblasts, that assemble and remodel the scar. Cultured myofibroblasts assemble larger focal adhesions than do normal dermal fibroblasts and these focal adhesions attach to alpha SMCA-rich stress fibers. Following severe traumatic or thermal injury to the dermis, hypertrophic scars (HTSs) often develop and these scar fibroblasts (HTSFs) express alpha SMCA persistently. We now report that HTSFs stably display large focal adhesions as a consequence of both the autocrine production and activation of transforming growth factor beta1 (TGF-beta1). We also observe that myofibroblasts elaborating larger focal adhesions adhere more tightly to fibronectin. Conditioned medium from HTSFs induces focal adhesion growth in normal fibroblasts and this is blocked by pre-incubation with a soluble TGF-beta1 receptor mimetic. Human foreskin fibroblasts transduced with a retrovirus encoding active TGF-beta1 elaborate large focal adhesions, whereas fibroblasts overexpressing normal, latent TGF-beta1 do not. We conclude that the large focal adhesions found in pathogenic myofibroblasts arise through an autocrine loop involving the production and activation of TGF-beta1; these adhesions likely mediate both tighter adhesion to wound matrix and the exuberant wound contraction observed in pathogenic scars.

Complexation with chondroitin sulfate C and Polybrene rapidly purifies retrovirus from inhibitors of transduction and substantially enhances gene transfer

Using amphotropic retrovirus stocks produced by TELCeB6-A cells that encode the Escherichia coli lacZ gene, we found that complexation with chondroitin sulfate C (CSC) and Polybrene (PB) is an effective means to purify retrovirus. Virus stocks contained high levels of inhibitory activity that blocked amphotropic, but not ecotropic, retrovirus transduction. When virus stocks were brought to 80 microg/mL each of CSC and PB, complexes of CSC and PB formed. These complexes incorporated more than 70% of the virus particles but less than 0.4% of all other proteins and no detectable inhibitory activity. Purified virus transduced NIH 3T3 murine fibroblasts 21 to 186-fold more efficiently than virus that was not purified. In addition, virus purification significantly altered the dose response of transduction. When virus that had not been purified was used to transduce cells, the relationship between transduction and virus concentration was highly non-linear. In contrast, when purified virus was used, transduction increased monotonically and was linearly proportional to virus concentration, except when high doses of virus were used. Interestingly, when high doses of virus were used gene transfer reached a maximum plateau level, most likely because particle-associated amphotropic envelope proteins had saturated the cellular receptors for the virus. Our findings illustrate that retrovirus purification increases the maximum number of genes that can be transferred, reduces the amount of virus required to achieve a given level of gene transfer, and reduces uncertainties about the relationship between the amount of virus used and the number of genes transferred.

Downstream processing of oncoretroviral and lentiviral gene therapy vectors

Retroviral vectors from both oncoretroviral and lentiviral origins have a great potential as gene delivery vehicles. A number of research groups have devoted considerable effort to the development of large-scale production strategies for retroviral vectors. However, the manufacturing of clinical-grade vectors for gene therapy, especially for in vivo applications, additionally requires scaleable purification strategies to remove the contaminants present in the harvested supernatants while preserving the functionality of the vectors. In this article, we review recent advances made in the field of downstream processing of retroviral vectors. The methods currently described in the literature for clarification, concentration and purification of retroviral vectors will be presented, with special emphasis on novel chromatography methods that open up the possibility to selectively and efficiently purify retroviruses on a large-scale. Problems associated with stability and quantification of retroviral particles will be outlined and future challenges will be discussed.

Enhancement of enveloped virus entry by phosphatidylserine

Enveloped virus vectors are used in a wide variety of applications. We have discovered that treatment of cultured cells with phosphatidylserine (PS) liposomes can increase virus vector infection by up to 20-fold. This effect does not abrogate virus receptor requirements, is specific to PS compared to other phospholipids, and is limited to enveloped viruses. Furthermore, the enhancement of infection does not occur through increases in virus receptor levels or virus binding, indicating that virus fusion is enhanced. The liposomes are easily generated, store well, and allow enhanced infection with a variety of virus vectors and cell types.

Envelope glycoprotein gB of Kaposi's sarcoma-associated herpesvirus is essential for egress from infected cells

Kaposi's sarcoma-associated herpesvirus (KSHV) envelope glycoprotein gB interacts with cell surface heparan sulfate (HS) and alpha3beta1 integrin and plays roles in the initial binding and entry into the target cells and in the induction of preexisting host cell signal pathways. To define gB function further, using a bacterial artificial chromosome (BAC) system carrying the KSHV genome (BAC36wt-KSHV), we constructed a recombinant virus genome with the gB open reading frame (ORF) deleted by replacing a 2-kb gB ORF with a 1.3-kb Kan(r) gene. Stable 293T cells carrying BAC36wt-KSHV and DeltagBBAC36-KSHV genomes were generated. Transcript analyses and immunoprecipitation reactions confirmed the absence of gB in the 293T-DeltagBBAC36 cells. When monolayers of 293T-BAC36wt and 293T-DeltagBBAC36 cells were induced with tetradecanoylphorbol-13-acetate, infectious virus was detected only from the 293T-BAC36wt cell supernatants. No significant amount of DNase I-resistant viral DNA was detected in the supernatants of 293T-DeltagBBAC36 cells. BAC36wt-KSHV infected the target cells, and in contrast, no viral DNA and transcripts could be detected in cells infected with DeltagBBAC36-KSHV. Electron microscopy of 293T-DeltagBBAC36 cells revealed capsids in the nuclei, cytoplasmic vesicles with core-containing capsids, and occasional enveloped virions in the cytoplasm. However, enveloped virus particles were observed in the extracellular compartments of 293T-BAC36wt cells only and not in 293T-DeltagBBAC36 cells. Transfection of 293T-DeltagBBAC36 cells with plasmid expressing full-length gB restored the recovery of infectious KSHV in the supernatant. These results suggest that, besides its role in virus binding and entry into the target cells, KSHV gB also plays a role in the maturation and egress of virus from the infected cells.

ERK1/2 and MEK1/2 induced by Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) early during infection of target cells are essential for expression of viral genes and for establishment of infection

Kaposi's sarcoma-associated herpesvirus (KSHV) in vitro target cell infection is characterized by the expression of the latency-associated genes ORF 73 (LANA-1), ORF 72, and K13 and by the transient expression of a very limited number of lytic genes such as lytic cycle switch gene ORF 50 (RTA) and the immediate early (IE) lytic K5, K8, and v-IRF2 genes. During the early stages of infection, several overlapping multistep complex events precede the initiation of viral gene expression. KSHV envelope glycoprotein gB induces the FAK-Src-PI3K-RhoGTPase (where FAK is focal adhesion kinase) signaling pathway. As early as 5 min postinfection (p.i.), KSHV induced the extracellular signal-regulated kinase 1 and 2 (ERK1/2) via the PI3K-PKCzeta-MEK pathway. In addition, KSHV modulated the transcription of several host genes of primary human dermal microvascular endothelial cells (HMVEC-d) and fibroblast (HFF) cells by 2 h and 4 h p.i. Neutralization of virus entry and infection by PI-3K and other cellular tyrosine kinase inhibitors suggested a critical role for signaling molecules in KSHV infection of target cells. Here we investigated the induction of ERK1/2 by KSHV and KSHV envelope glycoproteins gB and gpK8.1A and the role of induced ERK in viral and host gene expression. Early during infection, significant ERK1/2 induction was observed even with low multiplicity of infection of live and UV-inactivated KSHV in serum-starved cells as well as in the presence of serum. Entry of UV-inactivated virus and the absence of viral gene expression suggested that ERK1/2 induction is mediated by the initial signal cascade induced by KSHV binding and entry. Purified soluble gpK8.1A induced the MEK1/2 dependent ERK1/2 but not ERK5 and p38 mitogen-activated protein kinase (MAPK) in HMVEC-d and HFF. Moderate ERK induction with soluble gB was seen only in HMVEC-d. Preincubation of gpK8.1A with heparin or anti-gpK8.1A antibodies inhibited the ERK induction. U0126, a selective inhibitor for MEK/ERK blocked the gpK8.1A- and KSHV-induced ERK activation. ERK1/2 inhibition did not block viral DNA internalization and had no significant effect on nuclear delivery of KSHV DNA during de novo infection. Analyses of viral gene expression by quantitative real-time reverse transcriptase PCR revealed that pretreatment of cells with U0126 for 1 h and during the 2-h infection with KSHV significantly inhibited the expression of ORF 73, ORF 50 (RTA), and the IE-K8 and v-IRF2 genes. However, the expression of lytic IE-K5 gene was not affected significantly. Expression of ORF 73 in BCBL-1 cells was also significantly inhibited by preincubation with U0126. Inhibition of ERK1/2 also inhibited the transcription of some of the vital host genes such as DUSP5 (dual specificity phosphatase 5), ICAM-1 (intercellular adhesion molecule 1), heparin binding epidermal growth factor, and vascular endothelial growth factor that were up-regulated early during KSHV infection. Several MAPK-regulated host transcription factors such as c-Jun, STAT1alpha, MEF2, c-Myc, ATF-2 and c-Fos were induced early during infection, and ERK inhibition significantly blocked the c-Fos, c-Jun, c-Myc, and STAT1alpha activation in the infected cells. AP1 transcription factors binding to the RTA promoter in electrophoretic mobility shift assays were readily detected in the infected cell nuclear extracts which were significantly reduced by ERK inhibition. Together, these results suggest that very early during de novo infection, KSHV induces the ERK1/2 to modulate the initiation of viral gene expression and host cell genes, which further supports our hypothesis that beside the conduit for viral DNA delivery into the cytoplasm, KSHV interactions with host cell receptor(s) create an appropriate intracellular environment facilitating infection.

In vitro Characterization of TGF-??1 Release from Genetically Modified Fibroblasts in Ca2+-Alginate Microcapsules

This study was undertaken to develop an in situ source of transforming growth factor-beta1 (TGF-beta1), one of several molecules potentially useful for a tissue-engineered bioartificial cartilage. Primary human fibroblasts and murine NIH 3T3 cells were genetically modified via viral transfection to express human TGF-beta1. Two viral constructs were used, one expressing a gene encoding for the latent and the other for the constitutively active form of the growth factor. Unmodified cells served as controls. Four genetically modified cohorts and two controls were separately encapsulated in a 1.8% alginate solution using a vibrating nozzle and 0.15M calcium chloride crosslinking bath. Diameter of the spherical capsules was 410 +/- 87 microm. In vitro release rate measured over 168 hours varied with cell types and ranged from 2-17 pg/(milligram of capsules x 24 h) or 2-17 ng/(10(6) cells x 24 h). None of the formulations exhibited a large initial bolus release. Even when serum-supplemented medium was not replenished, cell viabilities remained over 55% after 1 week for all cell types. Microencapsulated genetically modified cells were capable of a constitutive synthesis and delivery of biologically significant quantity of TGF-beta1 for at least 168 hours and thus are of potential utility for artificial cartilage and other orthopedic tissue engineering applications.

Complexation of retroviruses with charged polymers enhances gene transfer by increasing the rate that viruses are delivered to cells

BACKGROUND

We have previously found that retrovirus transduction is enhanced when an anionic polymer (chondroitin sulfate C) is added to virus stocks that contain an equal weight concentration of a cationic polymer (Polybrene). This observation was unexpected given that previous work has shown that cationic polymers enhance transduction while anionic polymers have the opposite effect.

METHODS

Using model recombinant retroviruses and lentiviruses that encode for the Escherichia coli lacZ gene and quantitative assays of virus adsorption and transduction, we examined the mechanism of enhancement.

RESULTS

We found that addition of oppositely charged polymers (Polybrene and chondroitin sulfate C) to virus stocks enhanced gene transfer by increasing the flux of active viruses to the cells. Virus-polymer complexes formed that did not reduce the stability of the viruses, yet were large enough to sediment, delivering the viruses to the cells more rapidly than by simple diffusion. The size of the complexes, the rate of sedimentation, and the levels of gene transfer increased with increasing concentrations of polymers. The degree to which transduction was enhanced ranged from 2- to nearly 40-fold, and varied depending on the type of cells and viruses used. Interestingly, we found that association of the viruses with the polymer complexes did not significantly hinder their ability to complete post-binding steps of transduction.

CONCLUSIONS

Complexation of retroviruses with charged polymers significantly improves the efficiency of ex vivo gene transfer by increasing the number of active viruses that reach the cells.

Highly efficient transduction of repopulating bone marrow cells using rapidly concentrated polymer-complexed retrovirus

Using the cationic polymer, Polybrene, and the anionic polymer, chondroitin sulfate C, we concentrated recombinant retrovirus pseudotyped with an ecotropic envelope, which is susceptible to inactivation by high-speed concentration methods. To evaluate gene marking, murine bone marrow was harvested from C3H mice, transduced with polymer-concentrated GFP virus, and transplanted into lethally irradiated recipients. Total gene marking in mice averaged 30-35% at 8 weeks post-transplant and transgene expression remained stable for over 16 weeks. Using the polymer concentration method, a second retroviral vector encoding the drug resistant variant of dihydrofolate reductase (L22Y-DHFR) was concentrated and tested. Approximately 40% of transduced murine bone marrow progenitor cells were protected against trimetrexate concentrations that completely eliminated the growth of non-modified cells. These results show that anionic and cationic polymers can be combined to rapidly concentrate viruses that are normally difficult to concentrate, and the concentrated virus efficiently transduces hematopoietic stem cells.

Nanoparticulate System for Efficient Gene Transfer into Refractory Cell Targets

A biocompatible, nanoparticulate formulation has been designed to retain, protect, and deliver adenoviral gene constructs over an extended time course. Such devices can be administered locally or systemically with low toxicity. A multipolymeric nanoparticulate system, featuring very high stability in physiologic media, was designed to allow efficient in vitro gene transfer. The efficacy of nanoparticulate delivery is effective in cell systems that are normally refractory to gene transfer, such as pancreatic islets and antigen-presenting cells. The findings suggest a nonspecific uptake system that permits adenoviral particle release within the transfected cells. A comparison with literature data revealed that our system is efficient at much lower levels (at least three orders of magnitude) of infectious viral particles.

Biocompatible polymer enhances thein vitro andin vivo transfection efficiency of HVJ envelope vector

BACKGROUND

Vector development is critical for the advancement of human gene therapy. However, the use of viral vectors raises many safety concerns and most non-viral methods are less efficient for gene transfer. One of the breakthroughs in vector technology is the combination of the vector with various polymers.

METHODS

HVJ (hemagglutinating virus of Japan) envelope vector (HVJ-E) has been developed as a versatile gene transfer vector. In this study, we combined HVJ-E with cationized gelatin to make it a more powerful tool and assessed its transfection efficiency in vitro and in vivo. In addition, we investigated the mechanism of the gene transfer by means of the inhibition of fusion or endocytosis.

RESULTS

The combination of both protamine sulfate and cationized gelatin with HVJ-E, referred to as PS-CG-HVJ-E, further enhanced the in vitro transfection efficiency. In CT26 cells, the luciferase gene expression of PS-CG-HVJ-E was approximately 10 times higher than that of the combination of protamine sulfate with HVJ-E or the combination of cationized gelatin with HVJ-E, referred to as PS-HVJ-E or CG-HVJ-E, respectively. Furthermore, the luciferase gene expression in liver mediated by intravenous administration of CG-HVJ-E was much higher than the luciferase gene expression mediated by PS-HVJ-E or PS-CG-HVJ-E and approximately 100 times higher than that mediated by HVJ-E alone.

CONCLUSIONS

Cationized gelatin-conjugated HVJ-E enhanced gene transfection efficiency both in vitro and in vivo. These results suggest that low molecular weight cationized gelatin may be appropriate for complex formation with various envelope viruses, such as retrovirus, herpes virus and HIV.

Quantification of infectious HIV-1 plasma viral load using a boosted in vitro infection protocol

Methods currently used for HIV-1 viral load measurements are very sensitive, but cannot distinguish between infectious and noninfectious particles. Here we describe the development of a novel, sensitive, and highly reproducible method that allows rapid isolation and quantification of infectious particles from patient plasma. By immobilizing HIV-1 particles in human plasma to platelets using polybrene, we observed a 10- to 1000-fold increase in infectivity over infection protocols using free virus particles. Using this method, we evaluated infectivity in plasma from 52 patients at various disease stages. At plasma viral loads of 1000-10000 HIV-1 RNA copies/ml 18%, at 10,000-50,000 copies/ml 73%, at 50,000-100,000 copies/ml 90%, and above 100,000 copies 96% of cultures were positive. We found that infectious titers among patients vary distinctively but are characteristic for a patient over extended time periods. Furthermore, we demonstrate that by evaluating infectious titers in conjunction with total HIV RNA loads, subtle effects of treatment intervention on viremia levels can be detected. The immobilization procedure does not interfere with viral entry and does not restore the infectivity of neutralized virus. Therefore, this assay system can be utilized to investigate the influence of substances that specifically affect virion infectivity such as neutralizing antibodies, soluble CD4, or protease inhibitors. Measuring viral infectivity may thereby function as an additional, useful marker in monitoring disease progression and evaluating efficacy of antivirals in vivo.

An improved method for detection of replication-competent retrovirus in retrovirus vector products

Contamination by replication-competent retrovirus (RCR) is one of the most important safety issues of retrovirus vector products for gene therapy clinical research. To improve the sensitivity of RCR detection and to shorten the assay period, we have developed a novel RCR detection method (infectivity RT-PCR method) based on real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) in combination with virus infection and a novel virus concentration method using polyethyleneimine (PEI)-conjugated magnetic beads. In this method, permissive cells were infected with RCR samples, and amplified RCR in the culture supernatants was adsorbed by PEI-beads. Then RCR RNA extracted from PEI-beads was quantified by real-time RT-PCR. We demonstrated that 1 infectious unit (iu) of RCR spiked in 10(6) cfu/ml of vector products could be detected within 3 days, and the sensitivity for viral detection was increased 3- to 10-fold compared with the direct S+L- assay. By this method, the presence of retroviral vector interfered with RCR detection only slightly. In conclusion, infectivity RT-PCR conducted in conjunction with virus concentration using PEI-beads can detect RCR more sensitively and rapidly than the conventional infectivity assay.