Reducing the immunostimulatory activity of CpG-containing plasmid DNA vectors for non-viral gene therapy

Codon-optimization in gene therapy: promises, prospects and challenges

Codon optimization has evolved to enhance protein expression efficiency by exploiting the genetic code's redundancy, allowing for multiple codon options for a single amino acid. Initially observed in E. coli, optimal codon usage correlates with high gene expression, which has propelled applications expanding from basic research to biopharmaceuticals and vaccine development. The method is especially valuable for adjusting immune responses in gene therapies and has the potenial to create tissue-specific therapies. However, challenges persist, such as the risk of unintended effects on protein function and the complexity of evaluating optimization effectiveness. Despite these issues, codon optimization is crucial in advancing gene therapeutics. This study provides a comprehensive review of the current metrics for codon-optimization, and its practical usage in research and clinical applications, in the context of gene therapy.

Acute Effects of Intratumor DNA Electrotransfer

Intratumor therapeutic DNA electroporation or electrotransfer is in clinical trials in the United States and is under development in many other countries. Acute changes in endogenous gene expression in response to DNA or to pulse application may significantly modulate the therapeutic efficacy of the expressed proteins. Oligonucleotide arrays were used in this study to quantify changes in mRNA expression in B16-F10 mouse melanoma tumors four hours after DNA electrotransfer. The data were subjected to the DAVID v6.8 web server for functional annotation to reveal regulated genes and genetic pathways. Gene ontology analysis revealed several molecular functions related to cytoskeletal remodeling and inflammatory signaling. In B16-F10 cells, F-actin remodeling was confirmed by phalloidin staining in cells that received pulse application alone or in the presence of DNA. Chemokine secretion was confirmed in cells receiving DNA electrotransfer. These results indicate that pulse application alone or in the presence of DNA may modulate the therapeutic efficacy of therapeutic DNA electrotransfer.

Rational engineering of a functional CpG-free ITR for AAV gene therapy

Inverted terminal repeats (ITRs) are the only wild-type components retained in the genome of adeno-associated virus (AAV) vectors. To determine whether ITR modification is a viable approach for AAV vector engineering, we rationally deleted all CpG motifs in the ITR and examined whether CpG elimination compromises AAV-vector production and transduction. Modified ITRs were stable in the plasmid and maintained the CpG-free nature in purified vectors. Replacing the wild-type ITR with the CpG-free ITR did not affect vector genome encapsidation. However, the vector yield was decreased by approximately 3-fold due to reduced vector genome replication. To study the biological potency, we made micro-dystrophin (μDys) AAV vectors carrying either the wild-type ITR or the CpG-free ITR. We delivered the CpG-free μDys vector to one side of the tibialis anterior muscle of dystrophin-null mdx mice and the wild-type μDys vector to the contralateral side. Evaluation at four months after injection showed no difference in the vector genome copy number, microdystrophin expression, and muscle histology and force. Our results suggest that the complete elimination of the CpG motif in the ITR does not affect the biological activity of the AAV vector. CpG-free ITRs could be useful in engineering therapeutic AAV vectors.

Molecular characterization of SARS-CoV-2 from Bangladesh: implications in genetic diversity, possible origin of the virus, and functional significance of the mutations

In a try to understand the pathogenesis, evolution and epidemiology of the SARS-CoV-2 virus, scientists from all over the world are tracking its genomic changes in real-time. Genomic studies can be helpful in understanding the disease dynamics. We have downloaded 324 complete and near complete SARS-CoV-2 genomes submitted in GISAID database from Bangladesh which were isolated between 30 March to 7 September, 2020. We then compared these genomes with Wuhan reference sequence and found 4160 mutation events including 2253 missense single nucleotide variations, 38 deletions and 10 insertions. The C>T nucleotide change was most prevalent (41% of all mutations) possibly due to selective mutation pressure to reduce CpG sites to evade CpG targeted host immune response. The most frequent mutation that occurred in 98% isolates was 3037C>T which is a synonymous change that usually accompanied 3 other mutations that include 241C>T, 14408C>T (P323L in RdRp) and 23403A>G (D614G in spike protein). The P323L was reported to increase mutation rate and D614G is associated with increased viral replication and currently most prevalent variant circulating all over the world. We identified multiple missense mutations in B-cell and T-cell predicted epitope regions and/or PCR target regions (including R203K and G204R that occurred in 86% of the isolates) that may impact immunogenicity and/or RT-PCR based diagnosis. Our analysis revealed 5 large deletion events in ORF7a and ORF8 gene products that may be associated with less severity of the disease and increased viral clearance. Our phylogeny analysis identified most of the isolates belonged to the Nextstrain clade 20B (86%) and GISAID clade GR (88%). Most of our isolates shared common ancestors either directly with European countries or jointly with middle eastern countries as well as Australia and India. Interestingly, the 19B clade (GISAID S clade) was unique to Chittagong, which was originally prevalent in China. This reveals possible multiple introductions of the virus in Bangladesh via different routes. Hence, more genome sequencing and analysis with related clinical data is needed to interpret functional significance and better predict the disease dynamics that may be helpful for policy makers to control the COVID-19 pandemic.

Growth environment influences B16.F10 mouse melanoma cell response to gene electrotransfer

We developed and characterized a 3D collagen hydrogel model for B16.F10 melanoma tumors. Cells in this 3D environment exhibited lower proliferation than cells in the conventional 2D culture environment. Interestingly, the basal expression levels of several genes varied when compared to conventionally grown cells. In each growth environment, a significant number of melanoma cells were transfected by plasmid electroporation (electrotransfer), although expression could only be ascertained on the surface of the 3D constructs. Cellular responses to plasmid entry as demonstrated by pro-inflammatory cytokine and chemokine upregulation varied based on the growth environment, as did the mRNA levels of several putative DNA-specific pattern recognition receptors (DNA sensors). Unexpectedly, when plasmid DNA was delivered while cells where attached in the 2D or 3D environments, the mRNAs of the DNA sensor p204 and the inflammatory mediator TNFα were regulated in cells receiving pulses only. However, we were unable to confirm coordinate upregulation of TNFα and p204 proteins. This study confirms that cell responses differ significantly based on their environment, and demonstrates the difficulty of extending experimental observations between cell environments.

Electrotransfer of CpG free plasmids enhances gene expression in skin

Skin is a very suitable target for gene therapy and DNA vaccination due to its accessibility, its surface and its ability to produce transgenes. Gene electrotransfer (GET) to the skin is under development for clinical applications for DNA vaccine or local treatment such as wound healing. Local treatments are effective if the expression of the plasmid affects only the local environment (skin) by inducing an efficient concentration over a prolonged period. In this study, we evaluate the control of expression in the skin of a plasmid coding a fluorescent protein by its CpG (cytosine-phosphate-guanine motif) content. Two fluorescent reporter genes are evaluated: tdTomato and GFP. The expression is followed on the long term by in vivo fluorescence imaging. Our results show that GET mediated expression in the skin can be controlled by the CpG content of the plasmid. Long term expression (>120 days) can be obtained at high level with CpG-free constructs associated with a proper design of the electrodes where the field distribution mediating the gene electrotransfer is present deep in the skin.

Development of a Recombinant Multifunctional Biomacromolecule for Targeted Gene Transfer to Prostate Cancer Cells

The objective of this study was to genetically engineer a fully functional single chain fusion peptide composed of motifs from diverse biological and synthetic origins that can perform multiple tasks including DNA condensation, cell targeting, cell transfection, particle shielding from immune system and effective gene transfer to prostate tumors. To achieve the objective, a single chain biomacromolecule (vector) consisted of four repeatative units of histone H2A peptide, fusogenic peptide GALA, short elastin-like peptide, and PC-3 cell targeting peptide was designed. To examine the functionality of each motif in the vector sequence, it was characterized in terms of size and zeta potential by Zetasizer, PC-3 cell targeting and transfection by flowcytometry, IgG induction by immunogenicity assay, and PC-3 tumor transfection by quantitative live animal imaging. Overall, the results of this study showed the possibility of using genetic engineering techniques to program various functionalities into one single chain vector and create a multifunctional nonimmunogenic biomacromolecule for targeted gene transfer to prostate cancer cells. This proof-of-concept study is a significant step forward toward creating a library of vectors for targeted gene transfer to any cancer cell type at both in vitro and in vivo levels.

Sequence-Modified Antibiotic Resistance Genes Provide Sustained Plasmid-Mediated Transgene Expression in Mammals

Conventional plasmid vectors are incapable of achieving sustained levels of transgene expression in vivo even in quiescent mammalian tissues because the transgene expression cassette is silenced. Transcriptional silencing results from the presence of the bacterial plasmid backbone or virtually any DNA sequence of >1 kb in length placed outside of the expression cassette. Here, we show that transcriptional silencing can be substantially forestalled by increasing the An/Tn sequence composition in the plasmid bacterial backbone. Increasing numbers of An/Tn sequences increased sustained transcription of both backbone sequences and adjacent expression cassettes. In order to recapitulate these expression profiles in compact and portable plasmid DNA backbones, we engineered the standard kanamycin or ampicillin antibiotic resistance genes, optimizing the number of An/Tn sequence without altering the encoded amino acids. The resulting vector backbones yield sustained transgene expression from mouse liver, providing generic DNA vectors capable of sustained transgene expression without additional genes or mammalian regulatory elements.

Improvement of spinal non-viral IL-10 gene delivery by D-mannose as a transgene adjuvant to control chronic neuropathic pain

BACKGROUND

Peri-spinal subarachnoid (intrathecal; i.t.) injection of non-viral naked plasmid DNA encoding the anti-inflammatory cytokine, IL-10 (pDNA-IL-10) suppresses chronic neuropathic pain in animal models. However, two sequential i.t. pDNA injections are required within a discrete 5 to 72-hour period for prolonged efficacy. Previous reports identified phagocytic immune cells present in the peri-spinal milieu surrounding the i.t injection site that may play a role in transgene uptake resulting in subsequent IL-10 transgene expression.

METHODS

In the present study, we aimed to examine whether factors known to induce pro-phagocytic anti-inflammatory properties of immune cells improve i.t. IL-10 transgene uptake using reduced naked pDNA-IL-10 doses previously determined ineffective. Both the synthetic glucocorticoid, dexamethasone, and the hexose sugar, D-mannose, were factors examined that could optimize i.t. pDNA-IL-10 uptake leading to enduring suppression of neuropathic pain as assessed by light touch sensitivity of the rat hindpaw (allodynia).

RESULTS

Compared to dexamethasone, i.t. mannose pretreatment significantly and dose-dependently prolonged pDNA-IL-10 pain suppressive effects, reduced spinal IL-1β and enhanced spinal and dorsal root ganglia IL-10 immunoreactivity. Macrophages exposed to D-mannose revealed reduced proinflammatory TNF-α, IL-1β, and nitric oxide, and increased IL-10 protein release, while IL-4 revealed no improvement in transgene uptake. Separately, D-mannose dramatically increased pDNA-derived IL-10 protein release in culture supernatants. Lastly, a single i.t. co-injection of mannose with a 25-fold lower pDNA-IL-10 dose produced prolonged pain suppression in neuropathic rats.

CONCLUSIONS

Peri-spinal treatment with D-mannose may optimize naked pDNA-IL-10 transgene uptake for suppression of allodynia, and is a novel approach to tune spinal immune cells toward pro-phagocytic phenotype for improved non-viral gene therapy.

Efficient sleeping beauty DNA transposition from DNA minicircles

DNA transposon-based vectors have emerged as new potential delivery tools in therapeutic gene transfer. Such vectors are now showing promise in hematopoietic stem cells and primary human T cells, and clinical trials with transposon-engineered cells are on the way. However, the use of plasmid DNA as a carrier of the vector raises safety concerns due to the undesirable administration of bacterial sequences. To optimize vectors based on the Sleeping Beauty (SB) DNA transposon for clinical use, we examine here SB transposition from DNA minicircles (MCs) devoid of the bacterial plasmid backbone. Potent DNA transposition, directed by the hyperactive SB100X transposase, is demonstrated from MC donors, and the stable transfection rate is significantly enhanced by expressing the SB100X transposase from MCs. The stable transfection rate is inversely related to the size of circular donor, suggesting that a MC-based SB transposition system benefits primarily from an increased cellular uptake and/or enhanced expression which can be observed with DNA MCs. DNA transposon and transposase MCs are easily produced, are favorable in size, do not carry irrelevant DNA, and are robust substrates for DNA transposition. In accordance, DNA MCs should become a standard source of DNA transposons not only in therapeutic settings but also in the daily use of the SB system.

Spinal interleukin-10 therapy to treat peripheral neuropathic pain

INTRODUCTION

  Current research indicates that chronic peripheral neuropathic pain includes a role for glia and the actions of proinflammatory factors. This review briefly discusses the glial and cytokine responses that occur following peripheral nerve damage in support of utilizing anti-inflammatory cytokine interleukin-10 (IL-10) therapy to suppress chronic peripheral neuropathic pain. SPINAL NONVIRAL INTERLEUKIN-10 GENE THERAPY:  IL-10 is one of the most powerful endogenous counter-regulators of proinflammatory cytokine function that acts in the nervous system. Subarachnoid (intrathecal) spinal injection of the gene encoding IL-10 delivered by nonviral vectors has several advantages over virally mediated gene transfer methods and leads to profound pain relief in several animal models. NONVIRAL GENE DELIVERY:  Lastly, data are reviewed that nonviral deoxyribonucleic acid (DNA) encapsulated by a biologically safe copolymer, poly(lactic-co-glycolic) acid (PLGA), thought to protect DNA, leads to significantly improved therapeutic gene transfer in animal models, which additionally and significantly extends pain relief.

CONCLUSIONS

  The impact of these early studies exploring anti-inflammatory genes emphasizes the exceptional therapeutic potential of new biocompatible intrathecal nonviral gene delivery approaches such as PLGA microparticles. Ultimately, ongoing expression of therapeutic genes is a viable option to treat chronic neuropathic pain in the clinic.

Sustained, high transgene expression in liver with plasmid vectors using optimized promoter-enhancer combinations

BACKGROUND

Plasmid-based gene therapy approaches often lack long-term transgene expression in vivo as a result of silencing or loss of the vector. One way to overcome these limitations is to combine nonsilenced promoters with strong enhancers.

METHODS

In the present study, we combine murine or human cytomegalovirus (CMV)-derived enhancer elements with the human elongation factor 1α (EF1α) promoter in a plasmid backbone devoid of potentially immunostimulating cytosine-guanine repeat sequences. Luciferase transgene activity was monitored in mouse liver after hydrodynamic plasmid delivery.

RESULTS

Luciferase activity of a CMV-promoter driven plasmid rapidly declined within days, whereas the activity of the EF1α driven plasmid remained high for 2 weeks (murine enhancer) and detectable for > 80 days (human enhancer). Expression levels clearly correlated with higher plasmid copy number found in the liver at 2 months after gene delivery. Furthermore, we developed a novel synthetic CMV-EF1α hybrid promoter (SCEP) combining the high activity of CMV and sustained activity of EF1α promoter. The SCEP led to a constitutive three-fold increase in expression levels compared to the EF1α promoter in vivo.

CONCLUSIONS

This novel combination of enhancer and promoter element with optimized plasmid backbones will pave the way for more efficient nonviral approaches in gene therapy.

Minicircle DNA-based gene therapy coupled with immune modulation permits long-term expression of α-L-iduronidase in mice with mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease characterized by mutations to the α-L-iduronidase (IDUA) gene resulting in inactivation of the IDUA enzyme. The loss of IDUA protein results in the progressive accumulation of glycosaminoglycans within the lysosomes resulting in severe, multi-organ system pathology. Gene replacement strategies have relied on the use of viral or nonviral gene delivery systems. Drawbacks to these include laborious production procedures, poor efficacy due to plasmid-borne gene silencing, and the risk of insertional mutagenesis. This report demonstrates the efficacy of a nonintegrating, minicircle (MC) DNA vector that is resistant to epigenetic gene silencing in vivo. To achieve sustained expression of the immunogenic IDUA protein we investigated the use of a tissue-specific promoter in conjunction with microRNA target sequences. The inclusion of microRNA target sequences resulted in a slight improvement in long-term expression compared to their absence. However, immune modulation by costimulatory blockade was required and permitted for IDUA expression in MPS I mice that resulted in the biochemical correction of pathology in all of the organs analyzed. MC gene delivery combined with costimulatory pathway blockade maximizes safety, efficacy, and sustained gene expression and is a new approach in the treatment of lysosomal storage disease.

Design of gene therapy trials in CF patients

The report of the first CF patients to receive CFTR gene therapy appeared in 1993; since then, there have been over 20 clinical trials of both viral and non-viral gene transfer agents. These have largely been single dose to either nose or lower airway and have been designed around molecular or bioelectrical outcome measures. Both transgene mRNA and partial correction of chloride secretion have been reported, although sodium hyperabsorption has not been improved. The UK CF Gene Therapy Consortium is focussed on a clinical programme to establish whether these proof-of-principle measures translate into clinical benefit. Here, we discuss the considerations in designing such a programme, focusing in particular on our choice of the optimal, currently available delivery method and established and novel outcome measures. We highlight the logistic and regulatory complexities of such a clinical programme and finally, we look to the future and consider possible alternative strategies.

pEPito: a significantly improved non-viral episomal expression vector for mammalian cells

BACKGROUND

The episomal replication of the prototype vector pEPI-1 depends on a transcription unit starting from the constitutively expressed Cytomegalovirus immediate early promoter (CMV-IEP) and directed into a 2000 bp long matrix attachment region sequence (MARS) derived from the human beta-interferon gene. The original pEPI-1 vector contains two mammalian transcription units and a total of 305 CpG islands, which are located predominantly within the vector elements necessary for bacterial propagation and known to be counterproductive for persistent long-term transgene expression.

RESULTS

Here, we report the development of a novel vector pEPito, which is derived from the pEPI-1 plasmid replicon but has considerably improved efficacy both in vitro and in vivo. The pEPito vector is significantly reduced in size, contains only one transcription unit and 60% less CpG motives in comparison to pEPI-1. It exhibits major advantages compared to the original pEPI-1 plasmid, including higher transgene expression levels and increased colony-forming efficiencies in vitro, as well as more persistent transgene expression profiles in vivo. The performance of pEPito-based vectors was further improved by replacing the CMV-IEP with the human CMV enhancer/human elongation factor 1 alpha promoter (hCMV/EF1P) element that is known to be less affected by epigenetic silencing events.

CONCLUSIONS

The novel vector pEPito can be considered suitable as an improved vector for biotechnological applications in vitro and for non-viral gene delivery in vivo.

Effects of inflammatory response on in vivo transgene expression by plasmid DNA in mice

To examine the effects of inflammatory response to plasmid DNA (pDNA) on transgene expression, serum tumor necrosis factor-alpha (TNF-alpha) was measured after intravenous injection of pDNA or calf thymus DNA (CT DNA) in the naked or complexed form with cationic liposomes (lipoplex). pDNA with many CpG motifs induced TNF-alpha production regardless of the forms. No significant TNF-alpha production was detected when CT DNA or methylated pDNA was injected. Clodronate liposomes and dexamethasone were used to deplete phagocytes or to inhibit inflammatory responses, respectively. Transient depletion of phagocytes, such as liver Kupffer cells and splenic macrophages, by clodronate liposomes slightly altered the tissue distribution of (32)P-pDNA lipoplex, but significantly reduced the TNF-alpha production and transgene expression. Dexamethasone significantly inhibited the initial transgene expression, but increased the duration of the expression slightly. Use of NF-kappaB activity-dependent plasmid vector suggested that the inhibition of NF-kappaB activation is involved in the reduced expression by these treatments. These findings indicate that tissue macrophages are closely involved in the CpG motif-dependent TNF-alpha production. It is also suggested that TNF-alpha activates NF-kappaB and increases transgene expression by pDNA having many NF-kappaB binding sites, but TNF-alpha also reduces transgene expression at later time periods, leading to short-term transgene expression.

Gene doping: the hype and the reality

Some spectacular results from genetic manipulation of laboratory rodents and increasing developments in human gene therapy raise the spectre of genetic modification or 'gene doping' in sports. Candidate targets include the induction of muscle hypertrophy through overexpression of specific splice variants of insulin-like growth factor-1 or blockade of the action of myostatin, increasing oxygen delivery by raising the hematocrit through the use of erythropoietin, induction of angiogenesis with vascular endothelial growth factors or related molecules and changes in muscle phenotype through expression of peroxisome-proliferator-activated receptor- delta and associated molecules. Some of these potential genetic enhancements, particularly where the genetic modification and its action are confined to the muscles, may be undetectable using current tests. This had lead to exaggerated predictions that gene doping in athletics will be common within the next few years. However, a review of the methods of gene transfer and the current 'state of the art' in development of genetic treatments for human disease show that the prospects for gene doping remain essentially theoretical at present. Despite this conclusion, it will be important to continue to monitor improvements in the technology and to develop methods of detection, particularly those based on identifying patterns of changes in response to doping as opposed to the detection of specific agents.

Silencing of episomal transgene expression in liver by plasmid bacterial backbone DNA is independent of CpG methylation

Minicircle DNA vectors devoid of plasmid bacterial backbone, (BB) DNAs, are transcriptionally persistent, whereas their parent plasmid counterparts are silenced in the liver. In this study we establish that circular plasmid BB provided in trans did not silence a transgene expression cassette in vivo, further confirming our previous conclusions that the covalent attachment of the plasmid BB to the expression cassette is required for DNA silencing. Given the high concentration of CpG dinucleotides in the plasmid BB, we investigated the role of DNA methylation on transgene silencing in vivo. The presence or absence of methylation in CpG motifs in routine plasmid BBs had no significant effect on transcriptional silencing. Furthermore, the removal of the CpG motifs from the BB did not ameliorate transcriptional silencing. Transgene silencing was partially inhibited when two tandem copies of the chicken cHS4 insulator at each end of a routine plasmid vector were used. These results are consistent with the idea that the transcriptional repression observed with plasmid DNA vectors in the liver is caused by formation of repressive heterochromatin on the plasmid DNA backbone, which then spreads and inactivates the transgene in cis, and that CpG content or methylation has little or no influence in the process.

Design of PCR-amplified DNA fragments for in vivo gene delivery: size-dependency on stability and transgene expression

PCR-amplified DNA fragments can be more efficient and safer vectors than conventional plasmid DNA because of their smaller size and fewer numbers of immunostimulatory cytosine-phosphate-guanine (CpG) motifs. In the present study, the expression unit of plasmid DNA encoding farnesylated enhanced green fluorescent protein (EGFPF; pEGFP-F) or firefly luciferase (pLuc) was amplified by polymerase chain reaction (PCR) to obtain DNA fragments (EGFPF-mini, Luc-mini). EGFPF-mini was as effective as pEGFP-F on the basis of the number of EGFPF-expressing cells after intravenous injection into mice by the hydrodynamics-based procedure. Then, the effects of the length of DNA fragments on transgene expression were examined using luciferase-expressing DNA preparations. Luc-mini preparations showed high levels of luciferase activity in cultured cells as well as in mouse liver, even although the levels did not exceed that of pLuc. An elongation of the DNA fragment on either side of the minimal expression unit was effective in increasing the transgene expression and the stability against nucleases. PCR-amplified DNA fragments showed a sustained luciferase activity in mouse liver compared with pLuc, indicating that they are effective in achieving a prolonged expression. Their stabilization against nucleases will further increase the potential of such short, structure-controlled and synthetic DNA fragments for in vivo gene delivery.

Strategies to improve drug delivery across the blood-brain barrier

The blood-brain barrier (BBB), together with the blood-cerebrospinal-fluid barrier, protects and regulates the homeostasis of the brain. However, these barriers also limit the transport of small-molecule and, particularly, biopharmaceutical drugs such as proteins, genes and interference RNA to the brain, thereby limiting the treatment of many brain diseases. As a result, various drug delivery and targeting strategies are currently being developed to enhance the transport and distribution of drugs into the brain. In this review, we discuss briefly the biology and physiology of the BBB as the most important barrier for drug transport to the brain and, in more detail, the possibilities for delivering large-molecule drugs, particularly genes, by receptor-mediated nonviral drug delivery to the (human) brain. In addition, the systemic and intracellular pharmacokinetics of nonviral gene delivery, together with targeted brain imaging, are reviewed briefly.

Regulated expression of the interferon-β gene in mice

A single plasmid regulated expression vector based upon a mifepristone-inducible two plasmid system, termed pBRES, has been constructed and tested in mice using murine interferon-b (mIFNb) as the transgene. The expression of mIFNb in the circulation was followed by measuring the systemic induction of IP-10, a validated biomarker for mIFNb in mice. Long-term, inducible expression of mIFNb was demonstrated following a single intramuscular (i.m.) injection of the pBRES mIFNb plasmid vector into the hind limb of mice. Induction of mIFNb expression was achieved by administration of the small molecule inducer, mifepristone (MFP). Plasmid DNA and mIFNb mRNA levels in the injected muscles correlated with mIFNb expression as monitored by IP-10 over a 3-month time period. Renewable transgene expression was achieved following repeat administration of the plasmid at 3 months following the first plasmid injection. A dose-dependent increase in expression was demonstrated by varying the amount of injected plasmid or the amount of the inducer administered to the mice. Finally, the pBRES plasmid expressing mIFNb under control of the inducer, MFP, was shown to be efficacious in a murine model of experimental allergic encephalomyelitis, supporting the feasibility of gene-based therapeutic approaches for treating diseases such as multiple sclerosis.

Electroporation-mediated transfer of plasmids to the lung results in reduced TLR9 signaling and inflammation

Electroporation can deliver DNA efficiently and safely to tissues in live animals, including the lung where it causes little inflammation or lung injury. In contrast, cationic lipid-mediated gene transfer has been shown to induce an inflammatory response caused by unmethylated plasmid CpG residues, which activate the toll-like receptor (TLR9) signaling pathway. As TLR9 is located in the endosomal/lysosomal compartment, we hypothesized that plasmids do not activate TLR9 during electroporation because they enter the cytoplasm directly through transient pores in the plasma membrane. To test this, plasmids were transfected into kidney epithelial cells overexpressing TLR9 (HEK293-TLR9+) and cells lacking TLR9 (HEK293-TLR9-null). Interleukin (IL)-8 expression, an indicator of TLR9 activation, increased more than 10-fold at 24 h post-liposome transfection in HEK293-TLR9+ cells, but showed no significant increase in electroporated cells, compared with untransfected cells. In vivo liposome-mediated gene transfer caused increases in IL-6, IL-12, tumor necrosis factor alpha and interferon gamma in mouse bronchial alveolar lavage fluid, whereas the levels of these cytokines were more than 10-fold lower by comparison following electroporation. Depletion of alveolar macrophages suggested that this inflammatory response is mediated by resident pulmonary epithelial cells. These results suggest that electroporation-mediated gene transfer bypasses the TLR-9 pathway, thus accounting for the low levels of inflammation seen with this approach.

[Optimization of in-vivo gene transfer through regulating biological response to vectors]

The spatiotemporal distribution of transgenes determines the therapeutic efficacy of in vivo gene transfer. The important parameters of gene transfer are the level, duration, and cell specificity of expression, and the number of transfected cells. Interaction of vectors with blood cells, antigen-presenting cells, serum proteins, and other biological components affects the tissue distribution of vectors and the profile of transgene expression. Although plasmid DNA is less immunogenic than viral vectors, it can induce inflammatory cytokine release, due mainly to the presence of unmethylated CpG dinucleotides (CpG motifs). It was clearly demonstrated that intravenous injection of a plasmid DNA/cationic liposome complex resulted not only in the induction of inflammatory cytokines, but also in the activation of nuclear factor kappaB (NF-kappaB) in the lung. Insertion of additional NF-kappaB-binding sequences into conventional plasmid DNA resulted in a high transgene expression in the lung, suggesting that the biological response to vectors can be used to increase transgene expression. In a marked contrast to this strategy, long-term transgene expression was achieved by reducing the number of the CpG motifs in plasmid DNA. A plasmid encoding murine interferon (IFN)-beta or IFN-gamma with reduced numbers of CpG motifs was highly effective in inhibiting metastatic tumor growth in mice. These results clearly demonstrate the importance of the regulation of biological responses to plasmid vectors to optimize plasmid-based in vivo gene transfer.

Sleeping beauty transposon-mediated nonviral gene therapy

Safe and effective delivery of genetic material to mammalian tissues would significantly expand the therapeutic possibilities for a large number of medical conditions. Unfortunately, the promise of gene therapy has been hampered by technical challenges, the induction of immune responses, and inadequate expression over time. Despite these setbacks, progress continues to be made and the anticipated benefits may come to fruition for certain disorders. In terms of delivery, nonviral vector systems are particularly attractive as they are simple to produce, can be stored for long periods of time, and induce no specific immune responses. A significant drawback to nonviral systems has been the lack of persistent expression, as plasmids are lost or degraded when delivered to living tissues. The recent application of integrating transposons to nonviral gene delivery has significantly helped to overcome this obstacle, because it allows for genomic integration and long-term expression. Recent advances in transposon-based vector systems hold promise as new technologies that may unlock the potential of gene therapy; however, technical and safety issues still need refinement.

Improved anti-cancer effect of interferon gene transfer by sustained expression using CpG-reduced plasmid DNA

Plasmid DNA (pDNA) expressing mouse interferon (IFN)-beta or IFN-gamma (pCMV-Mu beta and pCMV-Mu gamma, respectively) has been shown to be effective in inhibiting the growth of colon carcinoma CT-26 cells in the liver (Kobayashi et al., Molecular Therapy 2002;6:737-44). The therapeutic effect of such IFN gene transfer could be significantly increased by the sustained expression of IFNs. In the present study, CpG-reduced pDNA encoding IFN-beta or IFN-gamma (pGZB-Mu beta and pGZB-Mu gamma, respectively) was constructed. pCMV-Mu beta and pCMV-Mu gamma were used as conventional CpG-replete pDNAs. Each pDNA was injected into the tail vein of mice by the hydrodynamics-based procedure. An injection of pGZB-Mu beta resulted in very high IFN-beta activities in the serum for at least 24 hr after injection, whereas the IFN-beta activity after pCMV-Mu beta injection declined quickly. About a 14-fold greater amount of IFN-beta was produced from pGZB-Mu beta than from pCMV-Mu beta. pGZB-Mu beta markedly inhibited the pulmonary metastasis of CT-26 cells. Similar, but more marked results were obtained with pGZB-Mu gamma: it increased the area under the concentration-time curve by more than a 60-fold and the mean residence time of IFN-gamma 4-fold compared with pCMV-Mu gamma. The survival time of the pGZB-Mu gamma-treated mice was significantly (p<0.05) longer than that of the saline- or pCMV-Mu gamma-treated mice. These results indicate that long-term expression of IFN can be achieved by CpG-reduced pDNA and sustained IFN gene expression results in enhanced therapeutic effects of IFN gene transfer against tumor metastasis.