High cloning capacity of in vitro packaged SV40 vectors with no SV40 virus sequences

pH stability and disassembly mechanism of wild-type simian virus 40

Viruses are remarkable self-assembled nanobiomaterial-based machines, exposed to a wide range of pH values. Extreme pH values can induce dramatic structural changes, critical for the function of the virus nanoparticles, including assembly and genome uncoating. Tuning cargo-capsid interactions is essential for designing virus-based delivery systems. Here we show how pH controls the structure and activity of wild-type simian virus 40 (wtSV40) and the interplay between its cargo and capsid. Using cryo-TEM and solution X-ray scattering, we found that wtSV40 was stable between pH 5.5 and 9, and only slightly swelled with increasing pH. At pH 3, the particles aggregated, while capsid protein pentamers continued to coat the virus cargo but lost their positional correlations. Infectivity was only partly lost after the particles were returned to pH 7. At pH 10 or higher, the particles were unstable, lost their infectivity, and disassembled. Using time-resolved experiments we discovered that disassembly began by swelling of the particles, poking a hole in the capsid through which the genetic cargo escaped, followed by a slight shrinking of the capsids and complete disassembly. These findings provide insight into the fundamental intermolecular forces, essential for SV40 function, and for designing virus-based nanobiomaterials, including delivery systems and antiviral drugs.

Engineered Nanodelivery Systems to Improve DNA Vaccine Technologies

DNA vaccines offer a flexible and versatile platform to treat innumerable diseases due to the ease of manipulating vaccine targets simply by altering the gene sequences encoded in the plasmid DNA delivered. The DNA vaccines elicit potent humoral and cell-mediated responses and provide a promising method for treating rapidly mutating and evasive diseases such as cancer and human immunodeficiency viruses. Although this vaccine technology has been available for decades, there is no DNA vaccine that has been used in bed-side application to date. The main challenge that hinders the progress of DNA vaccines and limits their clinical application is the delivery hurdles to targeted immune cells, which obstructs the stimulation of robust antigen-specific immune responses in humans. In this updated review, we discuss various nanodelivery systems that improve DNA vaccine technologies to enhance the immunological response against target diseases. We also provide possible perspectives on how we can bring this exciting vaccine technology to bedside applications.

Virus-Like Particles as an Instrument of Vaccine Production

The paper discusses the techniques which are currently implemented for vaccine production based on virus-like particles (VLPs). The factors which determine the characteristics of VLP monomers assembly are provided in detail. Analysis of the literature demonstrates that the development of the techniques of VLP production and immobilization of target antigens on their surface have led to the development of universal platforms which make it possible for virtually any known antigen to be exposed on the particle surface in a highly concentrated form. As a result, the focus of attention has shifted from the approaches to VLP production to the development of a precise interface between the organism's immune system and the peptides inducing a strong immune response to pathogens or the organism's own pathological cells. Immunome-specified methods for vaccine design and the prospects of immunoprophylaxis are discussed. Certain examples of vaccines against viral diseases and cancers are considered.

Symmetry-Directed Design of Protein Cages and Protein Lattices and Their Applications

The assembly of individual protein subunits into large-scale structures is important in many biological contexts. Proteins may assemble into geometrical cages or extended lattices that are characterized by a high degree of symmetry; examples include viral capsids and bacterial S-layers. The precisely defined higher order structure exhibited by these assemblies has inspired efforts to design such structures de novo by applying the principles of symmetry evident in natural protein assemblies. Here we discuss progress towards this goal and also examples of natural protein cages and lattices that have been engineered to repurpose them towards a diverse range of applications in materials science and nano-medicine.

Scaffold properties are a key determinant of the size and shape of self-assembled virus-derived particles

Controlling the geometry of self-assembly will enable a greater diversity of nanoparticles than now available. Viral capsid proteins, one starting point for investigating self-assembly, have evolved to form regular particles. The polyomavirus SV40 assembles from pentameric subunits and can encapsidate anionic cargos. On short ssRNA (≤814 nt), SV40 pentamers form 22 nm diameter capsids. On RNA too long to fit a T = 1 particle, pentamers forms strings of 22 nm particles and heterogeneous particles of 29-40 nm diameter. However, on dsDNA SV40 forms 50 nm particles composed of 72 pentamers. A 7.2-Å resolution cryo-EM image reconstruction of 22 nm particles shows that they are built of 12 pentamers arranged with T = 1 icosahedral symmetry. At 3-fold vertices, pentamers each contribute to a three-helix triangle. This geometry of interaction is not seen in crystal structures of T = 7 viruses and provides a structural basis for the smaller capsids. We propose that the heterogeneous particles are actually mosaics formed by combining different geometries of interaction from T = 1 capsids and virions. Assembly can be trapped in novel conformations because SV40 interpentamer contacts are relatively strong. The implication is that by virtue of their large catalog of interactions, SV40 pentamers have the ability to self-assemble on and conform to a broad range of shapes.

To build a virus on a nucleic acid substrate

Many viruses package their genomes concomitant with assembly. Here, we show that this reaction can be described by three coefficients: association of capsid protein (CP) to nucleic acid (NA), KNA; CP-CP interaction, ω; and α, proportional to the work required to package NA. The value of α can vary as NA is packaged. A phase diagram of average lnα versus lnω identifies conditions where assembly is likely to fail or succeed. NA morphology can favor (lnα > 0) or impede (lnα < 0) assembly. As lnω becomes larger, capsids become more stable and assembly becomes more cooperative. Where (lnα + lnω) < 0, the CP is unable to contain the NA, so that assembly results in aberrant particles. This phase diagram is consistent with quantitative studies of cowpea chlorotic mottle virus, hepatitis B virus, and simian virus 40 assembling on ssRNA and dsDNA substrates. Thus, the formalism we develop is suitable for describing and predicting behavior of experimental studies of CP assembly on NA.

Production and biomedical applications of virus-like particles derived from polyomaviruses

Virus-like particles (VLPs), aggregates of capsid proteins devoid of viral genetic material, show great promise in the fields of vaccine development and gene therapy. These particles spontaneously self-assemble after heterologous expression of viral structural proteins. This review will focus on the use of virus-like particles derived from polyomavirus capsid proteins. Since their first recombinant production 27 years ago these particles have been investigated for a myriad of biomedical applications. These virus-like particles are safe, easy to produce, can be loaded with a broad range of diverse cargoes and can be tailored for specific delivery or epitope presentation. We will highlight the structural characteristics of polyomavirus-derived VLPs and give an overview of their applications in diagnostics, vaccine development and gene delivery.

Transcriptional activity of an ovarian-specific promoter from rat in dairy goat granulosa cells

Ovarian-specific promoter 1 (OSP-1) is a retrovirus-like element isolated from the complementary DNA library of rat that has been thought to be specifically expressed in ovary. To exploit this promoter in dairy goat ovary granulosa cells (GCs), OSP-1 from rat was used to construct the reporter vector pOSP-1-EGFP, in which egfp coding for enhanced green fluorescent protein (EGFP) was used as a reporter to examine the activity of OSP-1 in GCs. EGFP was successfully expressed in dairy goat GCs transfected with pOSP-1-EGFP. Reverse transcriptase-polymerase chain reaction analysis confirmed the tissue-specific transcription of EGFP messenger RNA in dairy goat GCs transfected with pOSP-1-EGFP. We concluded that OSP-1 promoter from rat can specifically drive foreign gene expression in dairy goat GCs. Thus, we obtained a tissue-specific regulation element and provided a potential tool for the research of regulation and development of the ovary in dairy goats.

Pseudovirions as vehicles for the delivery of siRNA

Over the last two decades, small interfering RNA (siRNA)-mediated gene silencing has quickly become one of the most powerful techniques used to study gene function in vitro and a promising area for new therapeutics. Delivery remains a significant impediment to realizing the therapeutic potential of siRNA, a problem that is also tied to immunogenicity and toxicity. Numerous delivery vehicles have been developed, including some that can be categorized as pseudovirions: these are vectors that are directly derived from viruses but whose viral coding sequences have been eliminated, preventing their classification as viral vectors. Characteristics of the pseudovirions discussed in this review, namely phagemids, HSV amplicons, SV40 in vitro-packaged vectors, influenza virosomes, and HVJ-Envelope vectors, make them attractive for the delivery of siRNA-based therapeutics. Pseudovirions were shown to deliver siRNA effector molecules and bring about RNA interference (RNAi) in various cell types in vitro, and in vivo using immune-deficient and immune-competent mouse models. Levels of silencing were not always determined directly, but the duration of siRNA-induced knockdown lasted at least 3 days. We present examples of the use of pseudovirions for the delivery of synthetic siRNA as well as the delivery and expression of DNA-directed siRNA.

Uncatalyzed assembly of spherical particles from SV40 VP1 pentamers and linear dsDNA incorporates both low and high cooperativity elements

The capsid of SV40 virion is comprised of 72 pentamers of the major capsid protein, VP1. We examined the synergism between pentamer-pentamer interaction and pentamer-DNA interaction using a minimal system of purified VP1 and a linear dsDNA 600-mer, comparing electrophoresis with electron microscopy and size exclusion chromatography. At low VP1/DNA ratios, large tubes were observed that apparently did not survive native agarose gel electrophoresis. As the VP1 concentration increased, electrophoretic migration was slower and tubes were replaced by 200 A diameter particles and excess free pentamer. At high VP1/DNA ratios, a progressively larger fraction of particles was similar to 450 A diameter virions. VP1 association with DNA is very strong compared to the concentrations in these experiments yet, paradoxically, stable complexes appear only at high ratios of VP1 to DNA. These data suggest a DNA saturation-dependent nucleation event based on non-specific pentamer-DNA interaction that controls assembly and the ultimate capsid geometry.

Imaging viral behavior in Mammalian cells with self-assembled capsid-quantum-dot hybrid particles

Unique spectral properties of quantum dots (QDs) enable ultrasensitive and long-term biolabeling. Aiming to trace the infection, movement, and localization of viruses in living cells, QD-containing virus-like particles (VLPs) of simian virus 40 (SV40), termed SVLP-QDs, are constructed by in vitro self-assembly of the major capsid protein of SV40. SVLP-QDs show homogeneity in size ( approximately 24 nm), similarity in spectral properties to unencapsidated QDs, and considerable stability. When incubated with living cells, SVLP-QDs are shown to enter the cells by caveolar endocytosis, travel along the microtubules, and accumulate in the endoplasmic reticulum. This process mimics the early infection steps of SV40. This is the first paradigm of imaging viral behaviors with encapsidated QDs in living cells. The method may provide a new alternative for various purposes, such as tracing viruses or viral components, targeted nanoparticle delivery, and probing of drug delivery.

Chemoprotection by transfer of resistance genes

Dose-limiting toxicity of chemotherapeutic agents, i.e., myelosuppression, can limit their effectiveness. The transfer and expression of drug-resistance genes might decrease the risks associated with acute hematopoietic toxicity. Protection of hematopoietic stem/progenitor cells by transfer of drug-resistance genes provides the possibility of intensification or escalation of antitumor drug doses and consequently an improved therapeutic index. This chapter reviews drug-resistance gene transfer strategies for either myeloprotection or therapeutic gene selection. Selecting candidate drug-resistance gene(s), gene transfer methodology, evaluating the safety and the efficiency of the treatment strategy, relevant in vivo models, and oncoretroviral transduction of human hematopoietic stem/progenitor cells under clinically applicable conditions are described.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

SV40 vectors carrying minimal sequence of viral origin with exchangeable capsids

Polyomaviral vectors are generated by transfecting 293T cells with three sets of DNAs: DNA for the expression of simian virus 40 (SV40) T antigen; DNA for the expression of SV40 capsid proteins, and vector DNA harboring a reporter gene expression cassette carrying a SV40 origin. The vector DNA harbors a minimal sequence originating from SV40, and thus can carry a longer transgene. Moreover, the viable recombinants are not detectable in the vector preparation, and the vectors can transduce the DNA with efficiency similar to that of virions. Vector particles bearing capsid proteins of BK virus, JC virus, and B-lymphotropic papovavirus instead of SV40 were prepared, and they exhibited differential efficiency of gene transduction to the target cells. This method can be used to develop a surrogate system to study the functions of capsid proteins of polyomaviruses and to generate a set of polyomaviral vectors targeted at specific cell types.

Pancreatic acinar and islet cell infection by low-dose SV40 administration

OBJECTIVES

Viral vector uptake into the pancreas is rare. The few viral vectors reported to transduce in vivo pancreatic islets after systemic injection required additional physical measures, such as direct pancreatic injection or hepatic vessel clamping. Because pancreatic islet uptake of the human polyomavirus family member BK virus was previously reported in hamsters after systemic administration, we hypothesized that SV40, a polyomavirus member remarkably similar to BK virus, may also infect the pancreas.

METHODS

We injected intravenously a low dose of SV40, unaided by any other physical or chemical means, and evaluated viral uptake by pancreatic islets and pancreatic exocrine tissue via polymerase chain reaction, Western blot, electron microscopy, immunofluorescent microscopy, and protein A-gold immunocytochemistry.

RESULTS

Pancreatic uptake of SV40 was comparable to other major organs (ie, liver and spleen). SV40 viral particles were detected in both pancreatic islets and acini. In pancreatic islets, all islet cell types were infected by SV40, albeit the infection rate of glucagon-producing alpha cells surpassed beta- and delta-islet cells. Low-dose SV40 administration was not sufficient to induce heterologous gene expression in the pancreas.

CONCLUSIONS

Our study shows that pancreatic islet and acinar cell uptake of SV40 is feasible with a single, low-dose intravenous injection. However, this dose did not result in gene delivery into the murine pancreas.

SV40 reporter viruses

Three simian virus 40 (SV40) reporter viruses were constructed in this study. One expresses the green fluorescent protein (GFP) as a fusion protein with the first exon of large-T (LT) antigen and is useful for live-cell imaging. A second reporter virus has a FLAG epitope tag at the C-terminus of large-T antigen (vC-LT(FLAG)), and a third has the FLAG tag at the N-terminus of LT (vN-LT(FLAG)). The vC-LT(FLAG) construct grows to titers near those of wild-type (WT) virus and functions well as a reporter virus for SV40 infection. The vN-LT(FLAG) construct, while viable, has a defect in the production and spread of infectious particles. All three viruses are useful in detecting superinfecting virus in cells in which nuclear LT is already present, such as persistently infected human mesothelial cells.

Simian virus 40 vectors for pulmonary gene therapy

Background

Sepsis remains the leading cause of death in critically ill patients. One of the primary organs affected by sepsis is the lung, presenting as the Acute Respiratory Distress Syndrome (ARDS). Organ damage in sepsis involves an alteration in gene expression, making gene transfer a potential therapeutic modality. This work examines the feasibility of applying simian virus 40 (SV40) vectors for pulmonary gene therapy.

Methods

Sepsis-induced ARDS was established by cecal ligation double puncture (2CLP). SV40 vectors carrying the luciferase reporter gene (SV/luc) were administered intratracheally immediately after sepsis induction. Sham operated (SO) as well as 2CLP rats given intratracheal PBS or adenovirus expressing luciferase served as controls. Luc transduction was evaluated by in vivo light detection, immunoassay and luciferase mRNA detection by RT-PCR in tissue harvested from septic rats. Vector abundance and distribution into alveolar cells was evaluated using immunostaining for the SV40 VP1 capsid protein as well as by double staining for VP1 and for the surfactant protein C (proSP-C). Immunostaining for T-lymphocytes was used to evaluate the cellular immune response induced by the vector.

Results

Luc expression measured by in vivo light detection correlated with immunoassay from lung tissue harvested from the same rats. Moreover, our results showed vector presence in type II alveolar cells. The vector did not induce significant cellular immune response.

Conclusion

In the present study we have demonstrated efficient uptake and expression of an SV40 vector in the lungs of animals with sepsis-induced ARDS. These vectors appear to be capable of in vivo transduction of alveolar type II cells and may thus become a future therapeutic tool.

Vaccination, immune and gene therapy based on virus-like particles against viral infections and cancer

Virus-like particles (VLPs) are self-assembling, non-replicating particles lacking the viral genome that are formed by one or several viral structural proteins. VLPs can be purified after expression in yeast cells, insect cells using baculoviruses, Escherichia coli or mammalian cells. Recently, vaccines based on VLPs have come into focus with the FDA approval of a VLP-based vaccine against human papilloma viruses. However, this application of VLPs is just one of many developments within the VLP field. Other potential applications under development besides vaccines against viruses or cancers also include gene delivery and treatment of different disorders.

High cooperativity of the SV40 major capsid protein VP1 in virus assembly

SV40 is a small, non enveloped DNA virus with an icosahedral capsid of 45 nm. The outer shell is composed of pentamers of the major capsid protein, VP1, linked via their flexible carboxy-terminal arms. Its morphogenesis occurs by assembly of capsomers around the viral minichromosome. However the steps leading to the formation of mature virus are poorly understood. Intermediates of the assembly reaction could not be isolated from cells infected with wt SV40. Here we have used recombinant VP1 produced in insect cells for in vitro assembly studies around supercoiled heterologous plasmid DNA carrying a reporter gene. This strategy yields infective nanoparticles, affording a simple quantitative transduction assay. We show that VP1 assembles under physiological conditions into uniform nanoparticles of the same shape, size and CsCl density as the wild type virus. The stoichiometry is one DNA molecule per capsid. VP1 deleted in the C-arm, which is unable to assemble but can bind DNA, was inactive indicating genuine assembly rather than non-specific DNA-binding. The reaction requires host enzymatic activities, consistent with the participation of chaperones, as recently shown. Our results demonstrate dramatic cooperativity of VP1, with a Hill coefficient of ∼6. These findings suggest that assembly may be a concerted reaction. We propose that concerted assembly is facilitated by simultaneous binding of multiple capsomers to a single DNA molecule, as we have recently reported, thus increasing their local concentration. Emerging principles of SV40 assembly may help understanding assembly of other complex systems. In addition, the SV40-based nanoparticles described here are potential gene therapy vectors that combine efficient gene delivery with safety and flexibility.

Murine polyomavirus virus-like particles as vectors for gene and immune therapy and as vaccines

Polyomavirus virus-like particles (VLPs) can be produced free from viral genes and used as vectors for gene and immune therapy and as vaccines. For large-scale VLP manufacture, the major viral capsid protein (VP)1, is produced in a baculovirus insect cell system, Escherichia coli or yeast, and will self-assemble into VLPs under appropriate conditions. Murine polyomavirus (MPyV) VLP vaccination prevents primary MPyV infection and outgrowth of some MPyV-tumors in mice. Furthermore, MPyV-VLPs bind and introduce eukaryotic DNA into various cells in vitro and in vivo, while MPyV-VLPs containing fusion proteins between capsid proteins VP1, -2 or -3 and selected antigens can be used as vaccines. Similar findings apply to other polyomavirus VLPs. In summary, polyomavirus VLPs are useful vectors for immune and gene therapy and as vaccines, and different polyomavirus VLPs can be used for prime-boost therapy.

Virus-like particles production in green plants

Viruses-like particles (VLPs), assembled from capsid structural subunits of several different viruses, have found a number of biomedical applications such as vaccines and novel delivery systems for nucleic acids and small molecules. Production of recombinant proteins in different plant systems has been intensely investigated and improved upon in the last two decades. Plant-derived antibodies, vaccines, and microbicides have received great attention and shown immense promise. In the case of mucosal vaccines, orally delivered plant-produced VLPs require minimal processing of the plant tissue, thus offering an inexpensive and safe alternative to more conventional live attenuated and killed virus vaccines. For other applications which require higher level of purification, recent progress in expression levels using plant viral vectors have shown that plants can compete with traditional fermentation systems. In this review, the different methods used in the production of VLPs in green plants are described. Specific examples of expression, assembly, and immunogenicity of several plant-derived VLPs are presented.

SV40 Pseudovirion gene delivery of a toxin to treat human adenocarcinomas in mice

SV40 vectors packaged in vitro (pseudovirions) are an efficient delivery system for plasmids up to 17.7 kb, with or without SV40 sequences. A truncated Pseudomonas exotoxin gene (PE38) was delivered into various human cells (HeLa, KB-3-1, human lymphoblastoids, and erythroleukemia cells), in vitro using pseudovirions. The number of viable cells was reduced significantly in the PE38-transduced cells. Human KB adenocarcinomas growing in mice were treated with intratumoral injection of PE38 packaged in vitro, and tumor size decreased significantly. Intraperitoneal treatments were as effective in reducing tumor size as intratumoral treatments. To check the viability of mock- or PE38-treated mice, every 4 days they were weighed, their blood was tested, and various tissues were screened for pathology. All parameters showed that the in vitro-packaged vectors, injected into tumors or intraperitoneally, caused no abnormalities in mice. The combined treatment of doxorubicin with in vitro-packaged PE38 reduced tumor size slightly more than each of the treatments separately. However, the combined treatment did not cause the weight loss seen with doxorubicin alone. These results indicate that SV40 in vitro packaging is an effective system for cancer gene delivery using two different routes of injection and in combination with chemotherapy.

The VP2/VP3 Minor Capsid Protein of Simian Virus 40 Promotes the in Vitro Assembly of the Major Capsid Protein VP1 into Particles

The SV40 capsid is composed primarily of 72 pentamers of the VP1 major capsid protein. Although the capsid also contains the minor capsid protein VP2 and its amino-terminally truncated form VP3, their roles in capsid assembly remain unknown. An in vitro assembly system was used to investigate the role of VP2 in the assembly of recombinant VP1 pentamers. Under physiological salt and pH conditions, VP1 alone remained dissociated, and at pH 5.0, it assembled into tubular structures. A stoichiometric amount of VP2 allowed the assembly of VP1 pentamers into spherical particles in a pH range of 7.0 to 4.0. Electron microscopy observation, sucrose gradient sedimentation analysis, and antibody accessibility tests showed that VP2 is incorporated into VP1 particles. The functional domains of VP2 important for VP1 binding and for enhancing VP1 assembly were further explored with a series of VP2 deletion mutants. VP3 also enhanced VP1 assembly, and a region common to VP2 and VP3 (amino acids 119-272) was required to promote VP1 pentamer assembly. These results are relevant for controlling recombinant capsid formation in vitro, which is potentially useful for the in vitro development of SV40 virus vectors.

Hematopoietic stem cell gene therapy with drug resistance genes: an update

Transfer of drug resistance genes into hematopoietic stem cells (HSCs) has promise for the treatment of a variety of inherited, that is, X-linked severe combined immune deficiency, adenosine deaminase deficiency, thalassemia, and acquired disorders, that is, breast cancer, lymphomas, brain tumors, and testicular cancer. Drug resistance genes are transferred into HSCs either for providing myeloprotection against chemotherapy-induced myelosuppression or for selecting HSCs that are concomitantly transduced with another gene for correction of an inherited disorder. In this review, we describe ongoing experimental approaches, observations from clinical trials, and safety concerns related to the drug resistance gene transfer.

Efficient delivery of RNA interference effectors via in vitro-packaged SV40 pseudovirions

Previously we have shown that in vitro-packaged simian virus 40 (SV40) pseudovirions (IVPs) are an efficient delivery system for supercoiled DNA plasmids of up to 17.7 kb, with or without SV40 sequences. RNA interference (RNAi) is a naturally occurring gene-silencing mechanism mediated by small double-stranded RNA molecules (small interfering RNAs, siRNAs). This study demonstrates the first use of SV40 pseudovirions to deliver into human cells both principal types of RNAi effector molecules: plasmid-expressed short hairpin RNAs (shRNAs) and synthetic siRNAs. We first established the ability of human lymphoblastoid cells to support RNAi, using sequential transduction of .45 cells with packaged plasmid DNA expressing the green fluorescent protein (IVP-GFP), and an shRNA corresponding to the GFP (IVP-shGFP). SV40 mediates DNA transfer of nucleic acid to the cytoplasm, where RNAi-associated cleavage of mRNA principally occurs. Using SV40 pseudovirions, siRNA-mediated RNAi was observed in both .45 cells, after sequential transduction of IVP-GFP and IVP-packaged siRNAs corresponding to GFP (IVP-siGFP), and in HeLa cells stably expressing a GFP transduced with IVP-siGFP. Our findings indicate that SV40 pseudovirions may be a useful addition to the delivery systems currently being used for the transfer of RNAi effector molecules.

Liver-targeted gene therapy by SV40-based vectors using the hydrodynamic injection method

Efficient reconstitution of defective genes in hepatocytes could be used to treat various liver and systemic diseases through gene therapy. To explore the potential of SV40-based vectors in liver gene therapy, we constructed SV/luc, an SV40 T-antigen replacement transduction vector, that was propagated on COS and COT cells, which supply the SV40 T-antigen in trans. For liver targeting, BALB/C mice were injected via the tail vein with SV/luc stocks containing 3 x 10(6) to 10(8) transducing units in a volume of 1-2 ml. Luciferase activity was monitored with a light-detection cooled charged-coupled device (CCCD) camera, which enables continuous in vivo measurement of luc expression. The SV40 vector proved to be efficient in gene delivery to the liver, leading to long-term (> or =107 days) transgene expression in hepatocytes. Optimal results were obtained with 3 x 10(6) to 3 x 10(7) transducing units. The hydrodynamic vector delivery method caused transient liver inflammatory changes, with full recovery within days. Low levels of SV40-neutralizing antibodies were detected in the sera of treated mice; however, there was no indication of vector or transgene-specific cellular immune responses. Vectors packaged in vitro, using recombinant capsid proteins and plasmid DNA, were also effective in liver transduction. These results suggest that SV40 vectors may be useful for liver gene therapy.

Virus-like particles as vaccines and vessels for the delivery of small molecules

Virus-like particles (VLPs) structurally mimic the viral capsid and have therefore been extensively, and quite successfully, used as vaccine and viral serology reagents. The ability of VLPs to include nucleic acids and small molecules has also made them novel vessels for gene and drug delivery. The regular, repetitive surface of VLPs has been exploited as a template for nanoscale synthesis. Recent progress has been made in the development of several virus models.

Polymorphism in the genome of non-passaged human polyomavirus BK: implications for cell tropism and the pathological role of the virus

Worldwide studies have demonstrated that the human polyomavirus BK resides ubiquitously in the human population. After primary infection, which occurs mainly during childhood, the virus seems to establish a life-long harmless infection in the host. However, impaired immune functions may lead to reactivation of BK virus. The recent findings that associate BK virus with an increasing number of clinical conditions, including renal, pulmonary, ophthalmologic, hepatic, neurological, and autoimmune diseases, has resuscitated the interest in this virus as a pathogenic agent. This review focuses on polymorphisms in the genomes of non-passaged BK virus isolates from nonneoplastic tissues, with special focus on the transcriptional control region, the regulatory proteins large T-antigen and agnoprotein, and the major capsid protein VP1. The possible implications of genome diversity with respect to cell tropism, pathogenicity, and therapeutic strategies are discussed.

Transduction of multiple cell types using improved conditions for gene delivery and expression of SV40 pseudovirions packaged in vitro

This comprehensive study demonstrates highly efficient transduction of a wide variety of human, murine, and monkey cell lines, using a procedure for in vitro packaging of plasmid DNA in recombinant simian virus 40 (SV40) capsid proteins to form pseudovirions. The pseudovirions are encapsidated by the VP1 major capsid protein, with no SV40 sequence requirement, and are able to carry up to 17.7 kb of supercoiled plasmid DNA. We developed a procedure to scale-up production of SV40 pseudovirions, as well as an efficient protocol to concentrate the virions with no loss of activity. We also developed a method that allows transduction of 10 times more cells than the original protocol. This protocol was tested using supercoiled in vitro-packaged plasmid carrying the human multidrug-resistance gene (MDR1 encoding P-glycoprotein; P-gp), or the enhanced green fluorescent protein reporter gene (EGFP) in .45 human lymphoblastoid cells and in K562 human erythroleukemia cells. Multiple transductions at 24-h intervals were shown to increase expression using the EGFP reporter gene. The protocols developed in this study establish in vitro-packaged SV40 pseudovirions as one of the most efficient gene delivery systems.

Simian Virus-40 as a Gene Therapy Vector

Simian virus-40 (SV40), an icosahedral papovavirus, has recently been modified to serve as a gene delivery vector. Recombinant SV40 vectors (rSV40) are good candidates for gene transfer, as they display some unique features: SV40 is a well-known virus, nonreplicative vectors are easy-to-make, and can be produced in titers of 10(12) IU/ml. They also efficiently transduce both resting and dividing cells, deliver persistent transgene expression to a wide range of cell types, and are nonimmunogenic. Present disadvantages of rSV40 vectors for gene therapy are a small cloning capacity and the possible risks related to random integration of the viral genome into the host genome. Considerable efforts have been devoted to modifing this virus and setting up protocols for viral production. Preliminary therapeutic results obtained both in tissue culture cells and in animal models for heritable and acquired diseases indicate that rSV40 vectors are promising gene transfer vehicles. This article reviews the work performed with SV40 viruses as recombinant vectors for gene transfer. A summary of the structure, genomic organization, and life cycle of wild-type SV40 viruses is presented. Furthermore, the strategies utilized for the development, production, and titering of rSV40 vectors are discussed. Last, the therapeutic applications developed to date are highlighted.

Targeting of therapeutic gene expression to the liver by using liver-type pyruvate kinase proximal promoter and the SV40 viral enhancer active in multiple cell types

To achieve the liver-directed expression in sufficient amounts of therapeutic genes for successful and safe gene therapy, natural liver-specific promoters can be used to direct the expression of therapeutic genes in the liver, whereas strong viral enhancers were used to obtain sufficient amounts of expressed therapeutic gene products. However, very often use of either the former or the latter does not guarantee both potent and liver-specific therapeutic gene expression. Here we conglomerate them and thus create a potent tissue-specific promoter by characterizing and using the liver-type pyruvate kinase proximal promoter (LPKPP) harboring its TATA box and a HNF-1alpha binding site. Alone it hardly activated its reporter gene expression in non-hepatocytes or hepatocytes. However, in the presence of the SV40 viral enhancer (SV40VE), which is active in multiple cell types, it was able to potently activate its reporter gene expression specifically in hepatocytes. The tissue-specific activation of the LPKPP by the viral enhancer was attributed to HNF-1alpha binding to the LPKPP. Taken together, these results support the idea that the constitutively active SV40VE could be used to activate the LPKPP in a tissue-specific manner in the presence of HNF-1alpha. To our knowledge, this is the first study to utilize HNF-1alpha and its binding site, in the context of the LPKPP, to generate a basal promoter that is transcriptionally activated potently in a tissue-specific manner by a viral enhancer that is active in multiple cell types.