Liposome-mediated, nonviral gene transfer induces a systemic inflammatory response which can exacerbate pre-existing inflammation

Added to pre-existing inflammation, mRNA-lipid nanoparticles induce inflammation exacerbation (IE)

Current nucleoside-modified RNA lipid nanoparticle (modmRNA-LNP) technology has successfully paved the way for the highest clinical efficacy data from next-generation vaccinations against SARS-CoV-2 during the COVID-19 pandemic. However, such modmRNA-LNP technology has not been characterized in common pre-existing inflammatory or immune-challenged conditions, raising the risk of adverse clinical effects when administering modmRNA-LNPs in such cases. Herein, we induce an acute-inflammation model in mice with lipopolysaccharide (LPS) intratracheally (IT), 1 mg kg-1, or intravenously (IV), 2 mg kg-1, and then IV administer modmRNA-LNP, 0.32 mg kg-1, after 4 h, and screen for inflammatory markers, such as pro-inflammatory cytokines. ModmRNA-LNP at this dose caused no significant elevation of cytokine levels in naive mice. In contrast, shortly after LPS immune stimulation, modmRNA-LNP enhanced inflammatory cytokine responses, Interleukin-6 (IL-6) in serum and Macrophage Inflammatory Protein 2 (MIP-2) in liver significantly. Our report identifies this phenomenon as inflammation exacerbation (IE), which was proven to be specific to the LNP, acting independent of mRNA cargo, and was demonstrated to be time- and dose-dependent. Macrophage depletion as well as TLR3 -/- and TLR4-/- knockout mouse studies revealed macrophages were the immune cells involved or responsible for IE. Finally, we show that pretreatment with anti-inflammatory drugs, such as corticosteroids, can partially alleviate IE response in mice. Our findings characterize the importance of LNP-mediated IE phenomena in gram negative bacterial inflammation, however, the generalizability of modmRNA-LNP in other forms of chronic or acute inflammatory and immune contexts needs to be addressed.

Blood-Brain Barrier and Delivery of Protein and Gene Therapeutics to Brain

Alzheimer’s disease (AD) and treatment of the brain in aging require the development of new biologic drugs, such as recombinant proteins or gene therapies. Biologics are large molecule therapeutics that do not cross the blood-brain barrier (BBB). BBB drug delivery is the limiting factor in the future development of new therapeutics for the brain. The delivery of recombinant protein or gene medicines to the brain is a binary process: either the brain drug developer re-engineers the biologic with BBB drug delivery technology, or goes forward with brain drug development in the absence of a BBB delivery platform. The presence of BBB delivery technology allows for engineering the therapeutic to enable entry into the brain across the BBB from blood. Brain drug development may still take place in the absence of BBB delivery technology, but with a reliance on approaches that have rarely led to FDA approval, e.g., CSF injection, stem cells, small molecules, and others. CSF injection of drug is the most widely practiced approach to brain delivery that bypasses the BBB. However, drug injection into the CSF results in limited drug penetration to the brain parenchyma, owing to the rapid export of CSF from the brain to blood. A CSF injection of a drug is equivalent to a slow intravenous (IV) infusion of the pharmaceutical. Given the profound effect the existence of the BBB has on brain drug development, future drug or gene development for the brain will be accelerated by future advances in BBB delivery technology in parallel with new drug discovery.

Advances and perspectives in nanoprobes for noninvasive lymph node mapping

Sentinel lymph node (SLN) biopsy is now being well accepted as a practical approach to determine axillary lymph node status. For SLN biopsy, the mapping of SLN is an important procedure. However, blue dyes and radioactive colloids used for clinical SLN mapping are associated with a few issues such as adverse side effects and short retention time in SLN. In recent years, nanoscale probes for noninvasive SLN mapping have received attention due to their adaptable synthesis methods, adjustable optical properties and good biocompatibility. This review thoroughly summarizes the design of the nanoprobes and their properties in SLN mapping. The aim is to understand the status of nanomaterials for SLN mapping, challenging work and potential clinical translation in the future.

The role of ex-vivo gene therapy of vein grafts with Egr-1 decoy in the suppression of intimal hyperplasia

OBJECTIVES

To test the hypothesis that vein graft intimal hyperplasia can be significantly suppressed by a single intra-operative transfection of the graft with a decoy oligonucleotide (ODN) binding the transcription factor Egr-1.

DESIGN

Experimental study.

MATERIALS AND METHODS

Jugular vein to carotid artery interposition grafts in rabbits were treated with Egr-1 decoy, mutant decoy ODN, vehicle alone, using a non-distending pressure of 300 mm Hg for 20 min, or were left untreated. All animals were fed a 2% cholesterol diet. The animals were sacrificed after 48h, 6 weeks and 12 weeks. Paraffin-embedded vein sections were subjected to angiometric analysis.

RESULTS

Successful delivery of the ODN was confirmed by DAPI staining. Quantitative real-time PCR revealed a 60% decrease of the Egr-1 gene expression in the animals in which the Egr-1 decoy ODN was delivered. Cellular proliferation was also significantly decreased as indicated by the Ki-67 labelling index. An increase in intimal and medial thickness was found in all vein grafts. However, intimal thickness was significantly reduced in the grafts treated with Egr-1 decoy ODN, whereas luminal area was significantly increased.

CONCLUSION

A single intra-operative pressure-mediated transfection of vein grafts with Egr-1 decoy ODN significantly suppresses intimal hyperplasia in a rabbit hypercholesterolaemic model.

Preparation of Trojan horse liposomes (THLs) for gene transfer across the blood-brain barrier

Nonviral plasmid DNA is delivered to the brain via a transvascular route across the blood-brain barrier (BBB) following intravenous administration of DNA encapsulated within Trojan horse liposomes (THLs), also called PEGylated immunoliposomes (PILs). The liposome surface is covered with several thousand strands of polymer (e.g., polyethylene glycol [PEG]), and the tips of 1%-2% of the polymer strands are conjugated with a targeting monoclonal antibody that acts as a molecular Trojan horse (MTH). The MTH binds to a receptor (e.g., for transferrin or insulin) on the BBB and brain cell membrane, triggering receptor-mediated transcytosis of the THL across the BBB in vivo, and receptor-mediated endocytosis into brain cells beyond the BBB. The persistence of transgene expression in the brain is inversely related to the rate of degradation of the episomal plasmid DNA. THL technology enables an exogenous gene to be widely expressed in the majority of cells in adult brain (or other organs) within 1 d of a single intravenous administration. Applications of the THLs include tissue-specific gene expression with tissue-specific promoters, complete normalization of striatal tyrosine hydroxylase in experimental Parkinson's disease following intravenous tyrosine hydroxylase gene therapy, a 100% increase in survival time of mice with brain tumors following weekly intravenous antisense gene therapy using THLs, and a 90% increase in survival time with weekly intravenous RNA interference (RNAi) gene therapy in mice with intracranial brain tumors. This protocol describes the preparation of THLs for use in gene transfer in vitro or in vivo.

TLR9 and IRF3 cooperate to induce a systemic inflammatory response in mice injected with liposome:DNA

Liposome:DNA is a promising gene therapy vector. However, this vector can elicit a systemic inflammatory response syndrome (SIRS). Prior reports indicate that liposome:DNA vectors activate Toll-like receptor (TLR)9. We hypothesized that liposome:DNA vectors also activate the cytosolic DNA-sensing pathway, which signals via interferon (IFN) regulatory factor (IRF)3. To test this, we treated dendritic cells (DCs) with liposome:DNA in vitro and found that IRF3 was phosphorylated independent of TLR9. To test the contribution of this pathway in vivo, we injected a liposome:DNA vector into wild-type (WT), TLR9-knockout (KO), IRF3-KO, and TLR9-IRF3-double-KO (DKO) mice. WT mice exhibited a systemic inflammatory response, evidenced by elevations in serum cytokines, serum enzyme changes indicating organ damage, hypothermia, and mortality. The cytokine response was reduced in TLR9-KO, IRF3-KO, and TLR9-IRF3-DKO mice and all three groups survived. We found that IFN-gamma-KO mice that receive liposome:DNA had a reduced cytokine response and 100% survival. CD11c(+) and NK1.1(+) cells produced IFN-gamma and depleting CD11c(+) cells reduced the cytokine response in mice injected with liposome:DNA. These findings may facilitate the development of immunologically inert gene therapy vectors and may provide general insight into the mechanisms of SIRS.

Safety and in vivo expression of a GNE-transgene: a novel treatment approach for hereditary inclusion body myopathy-2

Hereditary inclusion body myopathy-2 (HIBM2) is an adult-onset, muscular disease caused by mutations in the GNE gene. HIBM2-associated GNE mutations causing hyposialyation have been proposed to contribute to reduced muscle function in patients with HIBM2, though the exact cause of this disease is unknown. In the current studies we examined pre-clinical in vivo toxicity, and expression of the plasmid-based, CMV driven wild-type GNE plasmid vector. The plasmid vector was injected intramuscularly (IM) or systemically (IV) into BALB/c mice, following encapsulation in a cationic liposome (DOTAP:Cholesterol). Single IM injections of the GNE-lipoplex at 40 μg did not produce overt toxicity or deaths, indicating that the no observable adverse effect level (NOAEL) dose for IM injection was ≥40 μg. Single intravenous (IV) infusion of GNE-lipoplex was lethal in 33% of animals at 100 μg dose, with a small proportion of animals in the 40 μg cohort demonstrating transient toxicity. Thus the NOAEL dose by the IV route was greater than 10 μg and less than or equal to 40 μg. Real-time RT-qPCR analysis demonstrated recombinant human GNE mRNA expression in 100% of muscle tissues that received IM injection of 40 μg GNE-lipoplex, at 2 weeks. These results indicate that GNE-lipoplex gene transfer is safe and can produce durable transgene expression in treated muscles. Our findings support future exploration of the clinical efficacy of GNE-lipoplex for experimental gene therapy of HIBM2.

Drug targeting to the brain

The goal of brain drug targeting technology is the delivery of therapeutics across the blood-brain barrier (BBB), including the human BBB. This is accomplished by re-engineering pharmaceuticals to cross the BBB via specific endogenous transporters localized within the brain capillary endothelium. Certain endogenous peptides, such as insulin or transferrin, undergo receptor-mediated transport (RMT) across the BBB in vivo. In addition, peptidomimetic monoclonal antibodies (MAb) may also cross the BBB via RMT on the endogenous transporters. The MAb may be used as a molecular Trojan horse to ferry across the BBB large molecule pharmaceuticals, including recombinant proteins, antibodies, RNA interference drugs, or non-viral gene medicines. Fusion proteins of the molecular Trojan horse and either neurotrophins or single chain Fv antibodies have been genetically engineered. The fusion proteins retain bi-functional properties, and both bind the BBB receptor, to trigger transport into brain, and bind the cognate receptor inside brain to induce the pharmacologic effect. Trojan horse liposome technology enables the brain targeting of non-viral plasmid DNA. Molecular Trojan horses may be formulated with fusion protein technology, avidin-biotin technology, or Trojan horse liposomes to target to brain virtually any large molecule pharmaceutical.

shRNA and siRNA delivery to the brain

The limiting factor in in vivo RNA interference (RNAi) is delivery. Drug delivery methods that are effective in cell culture may not be practical in vivo for intravenous RNAi applications. Nucleic acid drugs are highly charged and do not cross cell membranes by free diffusion. Therefore, the in vivo delivery of RNAi therapeutics must use targeting technology that enables the RNAi therapeutic to traverse biological membrane barriers in vivo. For RNAi of the brain, the nucleic acid-based drug must first cross the brain capillary endothelial wall, which forms the blood-brain barrier (BBB) in vivo, and then traverses the brain cell plasma membrane. Similar to the delivery of non-viral gene therapies, plasmid DNA encoding for short hairpin RNA (shRNA) may be delivered to the brain following intravenous administration with pegylated immunoliposomes (PILs). The plasmid DNA is encapsulated in a 100 nm liposome, which is pegylated, and conjugated with receptor specific targeting monoclonal antibodies (MAb). Weekly, intravenous RNAi with PILs enables a 90% knockdown of the human epidermal growth factor receptor, which results in a 90% increase in survival time in mice with intra-cranial brain cancer. Similar to the delivery of antisense agents, short interfering RNAi (siRNA) duplexes can be delivered with the combined use of targeting MAb's and avidin-biotin technology. The siRNA is mono-biotinylated in parallel with the production of a conjugate of the targeting MAb and streptavidin. Intravenous RNAi requires the combined use of RNAi technology and a drug targeting technology that is effective in vivo.

Rationale for the Selection of an Aerosol Delivery System for Gene Delivery

Genetic therapeutics show great promise toward the treatment of illnesses associated with the lungs; however, current methods of delivery such as jet and ultrasonic nebulization decrease the activity and effectiveness of these treatments. Extremely low transfection rates exhibited by non-complexed plasmid DNA in these nebulizers have been primarily attributed to poor translocation and loss of molecular integrity as a consequence of shear-induced degradation. Current research focusing on methods to increase transfection rates via the pulmonary delivery route has largely concentrated on the incorporation of carbon dioxide in the air stream to increase breath depth as well as the addition of cationic agents that condense DNA into compact, ordered complexes. The purpose of this study was to examine the impact of several classic as well as the latest atomization devices on the structure of non-complexed DNA. Various sizes of plasmid and cosmid DNA were processed through an electrostatic spray, ultrasonic nebulizer, vibrating mesh nebulizer, and jet nebulizer. Results varied dramatically based upon atomization device as well as DNA size. This may explain the inefficiency experienced by genetic therapeutics during pulmonary delivery. More importantly, this suggests that the selection of an atomization device should consider DNA size in order to achieve optimal gene delivery to the lungs.

Activation of antigen-presenting cells by DNA delivery vectors

Gene-based modulation of immune functions is a promising means of eliciting protective immunity and induction of tolerance. Novel viral and non-viral DNA delivery systems are being investigated to achieve efficient gene transfer into mammalian cells. Antigen-presenting cells (APCs), in particular dendritic cells, are crucial targets in this context due to their capacity to initiate and direct effector functions. The increasing relevance of APCs as targets of DNA vectors calls for an assessment of vector-driven activation of these cells. For viral vectors, a putative pathway of APC activation would be Toll-like receptor signalling for certain RNA genome viruses. On the other hand, non-viral vectors appear to mature APCs by interaction of polymeric particulates or bioactive lipids with cellular mechanisms. The rational design of DNA-based therapies is possible only when the intrinsic effects of the vector and immune modulation originating from the DNA are delineated. This paper will summarise recent reports of adjuvant properties of viral and non-viral delivery systems.

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

The mammalian innate immune system has the ability to recognise and direct a response against incoming foreign DNA. The primary signal that triggers this response is unmethylated CpG motifs present in the DNA sequence of various disease-causing pathogens. These motifs are rare in vertebrate DNA, but abundant in bacterial and some viral DNAs. Because gene therapy generally involves the delivery of DNA from either plasmids of bacterial origin or recombinant viruses, an acute inflammatory response of variable severity inevitably results. The response is most serious for non-viral gene delivery vectors composed of cationic lipid-DNA complexes, producing adverse effects at lower doses and lethality at higher doses of complex. This review examines the role of immunostimulatory CpG motifs in the acute inflammatory response to non-viral gene therapy vectors. Strategies to neutralise or eliminate CpG motifs within plasmid DNA vectors, and the existing limitations of CpG reduction on improving the safety profile of non-viral vectors, will be discussed.

RNA interference for alpha-ENaC inhibits rat lung fluid absorption in vivo

We used siRNA against the alpha-ENaC (epithelial Na channel) subunit to investigate ENaC involvement in lung fluid absorption in rats by the impermeable tracer technique during baseline and after beta-adrenoceptor stimulation by terbutaline. Terbutaline stimulation of lung fluid absorption increased fluid absorption by 165% in pSi-0-pretreated rat lungs (irrelevant siRNA-generating plasmid). Terbutaline failed to increase lung fluid absorption in rats given the specific alpha-ENaC siRNA-generating plasmid (pSi-4). pSi-4 pretreatment reduced baseline lung fluid absorption by approximately 30%. alpha-ENaC was undetectable in pSi-4-pretreated lungs, regardless of condition but was normal in pSi-0-pretreated lungs. We carried out a dose-response analysis where rats were given 0-200 microg/kg body wt pSi-4, and alpha-ENaC mRNA and protein expressions were analyzed. To reach IC(50) for alpha-ENaC mRNA expression, 32 microg/kg body wt pSi-4 was needed, and to reach IC(50) for alpha-ENaC protein expression, 59 microg/kg body wt pSi-4 was needed. We tested for lung tissue specificity and found no changes in beta-ENaC expression, at either mRNA or protein level, as well as no changes in alpha(1)-Na-K-ATPase protein expression. We isolated alveolar epithelial type II cells 24 h after in vivo pSi-4 pretreatment. In these cells, alpha-ENaC mRNA was undetectable, demonstrating that alveolar epithelial ENaC expression was attenuated after intratracheal alpha-ENaC siRNA-generating plasmid DNA instillation. We tested for organ specificity and found no changes in kidney alpha- and beta-ENaC mRNA and protein expression. Thus we provide conclusive evidence that beta-adrenoceptor stimulation of lung fluid absorption is critically ENaC dependent, whereas baseline lung fluid absorption seemed less ENaC dependent.

Phase I study of liposome-DNA complexes encoding the interleukin-2 gene in dogs with osteosarcoma lung metastases

Systemic gene delivery using cationic liposome-DNA complexes (LDCs) has been shown to elicit potent antitumor activity in mice with tumor metastases to the lungs. However, intravenous gene delivery for treatment of established cancer has not been evaluated previously in a spontaneous, large animal model. We therefore evaluated the safety, toxicity, and efficacy of intravenous gene delivery, using LDCs in dogs with established tumor metastases. Twenty dogs with chemotherapy-resistant osteosarcoma metastases to the lungs received a series of intravenous infusions of cationic liposomes and plasmid DNA encoding the canine interleukin-2 (IL-2) cDNA. Effects of intravenous gene delivery on immune activation, clinical and hematologic parameters, tumor responses, and survival times were assessed. We found that slow intravenous administration of IL-2 LDCs resulted in detectable IL-2 transgene expression in lung tissues of dogs. Repeated intravenous infusions of LDCs were well tolerated by dogs with lung tumor metastases and elicited systemic immune activation, as reflected by fever, leukogram changes, monocyte activation, and increased natural killer cell activity. Three of 20 dogs experienced partial or complete regression of lung metastases after infusion of IL-2 LDCs. Overall survival times were significantly increased in treated dogs compared with historical control animals with the same stage of disease. We conclude that repeated intravenous infusion of LDCs in cancerbearing dogs is safe and well tolerated at low doses and may be capable of eliciting antitumor activity in some animals with advanced tumor metastases.

Intravenous Delivery of Liposome-mediated Nonviral DNA Is Less Toxic than Intraperitoneal Delivery in Mice

Suicide gene therapy has been shown to be an effective means of destroying pancreatic cancer cells. Liposomes have been described as having better efficacy in gene delivery, and an advantage of using liposomes as gene carriers is that they can be used repeatedly in vivo. The objective of this study is to compare the effect of gene delivery routes and to determine whether systemic delivery of the rat insulin promoter (RIP)-directed suicide gene construct would permit cell-specific gene delivery in vivo. Severe combined immunodeficient (SCID) mice were injected with liposome-RIP-TK (thymidine kinase) complex by either the intraperitoneal or the intravenous route. Twenty-four hours post gene delivery, mice received ganciclovir (GCV) treatment twice daily for 14 days. Mice were sacrificed at various time points. Complete necropsy and serum chemistry analysis were performed. Islet morphology was determined using hematoxylin and eosin (H&E) staining. Serum glucose and insulin levels were also determined. To determine the toxic effect on pancreatic islet cells, immunostaining of insulin-producing and glucagon-producing cells was carried out at each time point. H&E staining indicated that both intravenous and intraperitoneal liposome-RIP-TK gene expression had no effect in normal endocrine islet cells. Both gene-delivery routes in mice resulted in normal glycemia and serum insulin levels. The endocrine islets were intact, with a normal distribution pattern of insulin-producing beta cells and glucagon-secreting alpha cells. However, serum chemistry analysis revealed significantly elevated levels of liver enzymes; suggesting that possible liver damage had occurred with the intraperitoneal gene delivery of liposome-pRIP-TK. Intravenous liposome-mediated gene delivery had no effect on liver enzyme levels. Liposome-mediated gene delivery via intravenous injection was less toxic than intraperitoneal delivery. This gene-delivery route requires fewer liposome-DNA complexes and maintains normal liver function. Thus, intravenous delivery of gene therapy would be superior to intraperitoneal administration of gene therapy in mice.

Contribution of Toll-like receptor 9 signaling to the acute inflammatory response to nonviral vectors

Immunostimulatory CpG motifs have been implicated as a major contributor to the acute inflammatory response associated with nonviral vectors, most prominently seen after systemic delivery of cationic lipid-plasmid DNA (pDNA) complexes. We have shown previously that complexes containing pDNA vectors that have been largely depleted of CpG motifs have significantly reduced acute toxicity when delivered systemically. However, several CpGs remain in these vectors and the toxicity is not negligible, especially at higher doses of complex. To determine the maximal reduction in the acute toxic response that could be achieved by eliminating CpG signaling, we injected cationic lipid-pDNA complexes into transgenic mice that are deficient in Toll-like receptor 9 (TLR9), which is the receptor that recognizes immunostimulatory CpG motifs. We observed significantly decreased adverse hematological changes and liver damage in TLR9(-/-) mice compared to normal mice and increased survival at higher doses of complex. However, a pronounced loss of lymphocytes and platelets was still observed in the TLR9(-/-) mice at higher doses. We also measured the toxicity in normal mice of systemically delivered complexes containing non-CpG oligonucleotides. Although serum transaminase levels were reduced, a loss of lymphocytes and platelets akin to that seen in the TLR9(-/-) mice was observed. Taken together, these findings suggest that signaling through TLR9 contributes to the majority but not all of the toxic responses associated with systemic delivery of cationic lipid-pDNA complexes.

Gene therapy in orthopaedic surgery: the current status

The first successful gene therapy trial was reported in 1991. Since then, successful gene transfer in cultured cells and small animals has been reported by many studies, with achievement of at least transitory high levels of exogenous gene expression. Over 400 clinical protocols for gene therapy have been approved, involving over 4000 patients. However, publication of the results of these gene therapy trials has been limited, with only 80 published reports as of 2002. The majority of clinical gene therapy trials reported so far have been phase I or phase II trials, which are concerned mainly with safety issues and have focused on the treatment of malignancies and other potentially fatal conditions. The death of a patient in 1999 from systemic administration of an adenoviral vector and recent reports of leukaemia in two patients in a clinical gene therapy trial have led to a further re-evaluation of the safety of gene therapy and the role for gene therapy in clinical practice. This review outlines the current status of gene therapy as it relates to orthopaedic diseases and highlights the areas where progress is still to be made.

Gene therapy progress and prospects: therapeutic angiogenesis for limb and myocardial ischemia

After extensive investigation in preclinical studies and recent clinical trials, gene therapy has been established as a potential method to induce therapeutic angiogenesis in ischemic myocardial and limb disease. Advancements in viral and nonviral vector technology including cell-based gene transfer will continue to improve transgene transmission and expression efficiency. An alternative strategy to the use of transgenes encoding angiogenic growth factors is therapy based on transcription factors such as hypoxia-inducible factor-1alpha (HIF-1alpha) that regulate the expression of multiple angiogenic genes. Further understanding of the underlying biology of neovascularization is needed to determine the ability of growth factors to induce functionally significant angiogenesis in patients with atherosclerotic disease and associated comorbid conditions including endothelial dysfunction, which may inhibit blood vessel growth. The safety and tolerability of therapeutic angiogenesis by gene transfer has been demonstrated in phase I clinical trials. However, limited evidence of efficacy resulted from early phase II studies of angiogenic gene therapy for ischemic myocardial and limb disease. The utility of therapeutic angiogenesis by gene transfer as a treatment option for ischemic cardiovascular disease will be determined by adequately powered, randomized, placebo-controlled phase II and III clinical trials.

In vivo characteristics of cationic liposomes as delivery vectors for gene therapy

After a decade of clinical trials, gene therapy seems to have found its place between excessive ambitions and feasible aims, with encouraging results obtained in recent years. Intracellular delivery of genetic material is the key step in gene therapy. Optimization of delivery vectors is of major importance for turning gene therapy into a successful therapeutic method. Nonviral gene delivery relies mainly on the complexes formed from cationic liposomes (or cationic polymers) and DNA, i.e., lipoplexes (or polyplexes). Many lipoplex formulations have been studied, but in vivo activity is generally low compared to that of viral systems. This review gives a concise overview of studies on the application of cationic liposomes in vivo in animal models of diseases and in clinical studies. The transfection efficiency, the pharmacokinetic and pharmacodynamic properties of the lipid-DNA complexes, and potentially relevant applications for cationic liposomes are discussed. Furthermore, the toxicity of, and the induction of an inflammatory response in association with the administration of lipoplexes are described. Increasing understanding of lipoplex behavior and gene transfer capacities in vivo offers new possibilities to enhance their efficiency and paves the path to more extensive clinical applications in the future.

Tumor treatment with complexes of cationic lipid and noncoding plasmid DNA results in the induction of cytotoxic T cells and systemic tumor elimination

We have demonstrated recently that treatment of established peritoneal mesothelial tumors with complexes composed of cationic lipid and noncoding plasmid DNA (pNull) results in the inhibition of tumor growth accompanied by the induction of a tumor-specific cellular immune response. In this study, treatment of mice bearing intraperitoneal (i.p.) M3 melanoma tumors with i.p. injections of lipid/pNull complex was found to inhibit tumor growth and induce the development of a cytolytic response against several M3 melanoma-associated antigens. Depletion of CD8(+) T cells, as opposed to natural killer (NK) or CD4(+) T cells, essentially abrogated the therapeutic effect of lipid+pNull complex, thus supporting the involvement of cytotoxic CD8(+) T cells in the antitumor response. The antitumor effect of lipid/pNull complex was maximal following delivery into a tumor-bearing compartment. For example, i.p. delivery of complex was more effective than intravenous (i.v.) or subcutaneous (s.c.) treatment of i.p. M3 tumors. In addition, i.v. injection of complex displayed therapeutic activity against lung metastases caused by i.v. injection of tumor cells, and intratumoral injection of complex into solid s.c. tumors caused regression in most animals. Importantly, the immune response induced by local treatment of tumors with complex also offered systemic protection against tumor cells at distal sites, as illustrated by the eradication of both peritoneal tumors and lung metastases in mice treated with complex delivered i.p. Treatment with lipid/pNull complex, therefore, represents an attractive immune-based treatment modality that could potentially be applied to many tumor types.

CpG-depleted plasmid DNA vectors with enhanced safety and long-term gene expression in vivo

Systemic delivery of cationic lipid-plasmid DNA (pDNA) complexes induces an acute inflammatory response with adverse hematologic changes and liver damage. Immunostimulatory CpG motifs in the pDNA are known to contribute substantially to this response. Here we constructed a pDNA vector (pGZB) that has been depleted of 80% of the CpG motifs present in the original vector. Compared with the unmodified vector, systemic administration of pGZB induced considerably fewer changes in blood parameters, reduced levels of inflammatory cytokines, and decreased liver damage. Despite the extensive sequence modifications within pGZB, there were still robust levels of transgene expression. Furthermore, in contrast to the transient expression observed from the unmodified vector, we observed sustained or increasing expression for up to 49 days from pGZB in the lung and liver of immunocompetent BALB/c mice. Studies adding CpG motifs in trans or in cis indicate that the reduced CpG content of pGZB was the major determinant for its persistent expression. This combination of decreased toxicity and sustained expression suggests that CpG-depleted pDNA vectors can greatly improve the safety and efficacy of synthetic gene delivery systems.

Gene therapy in transplantation

Gene transfer and gene therapy represent a relatively new field that has grown and expanded enormously in the last 5-10 years. The application of gene transfer and gene medicines to transplantation is currently in its infancy. Consideration for gene medicines in transplantation requires delivery of vectors, either to the graft or to the immune system. Delivery of vectors to the graft provides a choice of potential immunologic targets including: costimulatory signals; inhibitory cytokines; adhesion molecules; and molecules relating to apoptosis. In addition, non-immunologic targets, that increase graft protective mechanisms by reducing ischemic and immunologic damage, represent significant targets for gene transfer. Delivery of vectors to the immune system includes potential targets to modify the immune system, and results in tolerance. Other considerations for gene therapy include the development of additional technologies, such as gene conversion or transgenesis coupled with xenotransplantation, which may provide genetically modified organs. Another important aspect of gene transfer relates to regulation of the transgene expression. A variety of issues concerning innate immunity, adaptive immunity, response to vector components, response to transgene products, and entry of vectors into the antigen presentation and processing pathway require further investigation and refinement of approaches. Lastly, regulatable promoters and the understanding of their interaction with individual cells, tissues and organs, and their interaction with innate and adaptive immunity, are of paramount importance to improving the efficacy and utility of gene transfer. There is no doubt that there is much exciting basic and translational science to be accomplished in the next decade in order to solve these potential barriers and advance gene medicines into the clinical realm in transplantation.

Perspectives on gene therapy for cystic fibrosis airway disease

Since the discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene nearly 12 years ago, cystic fibrosis (CF) has become one of the most intensively investigated monogenetic disorders considered approachable by gene therapy. This has resulted in over 20 clinical trials currently under way, concluded or awaiting approval. Despite the initial promise of gene therapy for CF, and the demonstration of successful gene transfer to the nose and airways of individuals, it has not so far been as effective as initially projected. Here we discuss the rationale behind CF gene therapy and dissect the vast array of literature representing the work that ultimately brought about the current phase I/II clinical trials. In the context of human trials, we review the limitations of current vector systems for CF gene therapy. We come to the conclusion that at present none of the application methods and vector systems are able to achieve the level and persistence of CFTR gene expression in the affected epithelia of CF patients that is required for therapeutic success. We also outline the challenges that must be overcome and describe some of the novel approaches to be taken in order to attain the curative therapy that was originally envisaged for this disease.

High-efficiency gene transfer into nontransformed cells: utility for studying gene regulation and analysis of potential therapeutic targets

The elucidation of the signalling pathways involved in inflammatory diseases, such as rheumatoid arthritis, could provide long sought after targets for therapeutic intervention. Gene regulation is complex and varies depending on the cell type, as well as the signal eliciting gene activation. However, cells from certain lineages, such as macrophages, are specialised to degrade exogenous material and consequently do not easily transfect. Methods for high-efficiency gene transfer into primary cells of various lineages and disease states are desirable, as they remove the uncertainties associated with using transformed cell lines. Significant research has been undertaken into the development of nonviral and viral vectors for basic research, and as vehicles for gene therapy. We briefly review the current methods of gene delivery and the difficulties associated with each system. Adenoviruses have been used extensively to examine the role of various cytokines and signal transduction molecules in the pathogenesis of rheumatoid arthritis. This review will focus on the involvement of different signalling molecules in the production of tumour necrosis factor alpha by macrophages and in rheumatoid synovium. While the NF-kappaB pathway has proven to be a major mediator of tumour necrosis factor alpha production, it is not exclusive and work evaluating the involvement of other pathways is ongoing.

Antitumor activity of cationic lipid complexed with immunostimulatory DNA

We previously reported that treatment of intraperitoneal tumors with complexes of cationic lipid and noncoding plasmid DNA leads to the development of a specific, cytotoxic T-cell response correlating with the rejection of established tumor cells as well as subsequent tumor re-challenge. Here, focusing on an intraperitoneal AB12 mesothelioma model, we show that the anticancer effects of the lipid:DNA complex are associated with DNA containing immunostimulatory CpG motifs. Complexes prepared with cationic lipid and bacterial plasmid DNA, Escherichia coli genomic DNA fragments, or synthetic immunostimulatory CpG oligodeoxynucleotides provided a substantial survival benefit, whereas eukaryotic DNA and methylated bacterial DNA had little or no therapeutic activity. Alternative inflammatory stimuli such as thioglycolate, poly(I:C), and incomplete or complete Freund's adjuvant failed to reproduce the antitumor activity obtained with the lipid:DNA complex. The innate immune response triggered by lipid:DNA complexes led to the development of a systemic immune response against tumor cells that allowed animals to reject tumors not only at the intraperitoneal treatment site, but also at a distal subcutaneous site. These data demonstrate that immunostimulatory DNA complexed with cationic lipid is a potent inducer of innate and adaptive immune responses against tumor cells and represents a potentially useful tool in the immunotherapy of cancers for which tumor-associated antigens have not been identified.

Adenoviral delivery of human and viral IL-10 in murine sepsis

Adenovirus (Ad) gene therapy has been proposed as a drug-delivery system for the targeted administration of protein-based therapies, including growth factors and biological response modifiers. However, inflammation associated with Ad transduction has raised concern about its safety and efficacy in acute inflammatory diseases. In the present report, intratracheal and i.v. administration of a first-generation adenoviral recombinant (E1,E3 deleted) either containing an empty cassette or expressing the anti-inflammatory cytokines viral or human IL-10 (IL-10) was administered to mice subjected to zymosan-induced multisystem organ failure or to acute necrotizing pancreatitis. Pretreatment of mice with the intratracheal instillation of Ad expressing human IL-10 or viral IL-10 reduced weight loss, attenuated the proinflammatory cytokine response, and reduced mortality in the zymosan-induced model, whereas pretreatment with a control adenoviral recombinant did not significantly exacerbate the response. Pretreatment of mice with pancreatitis using adenoviral vectors expressing IL-10 significantly reduced the degree of pancreatic and liver injury and liver inflammation when administered systemically, but not intratracheally. We conclude that adenoviral vectors can be administered prophylactically in acute inflammatory syndromes, and expression of the anti-inflammatory protein IL-10 can be used to suppress the underlying inflammatory process.

An araC-controlled bacterial cre expression system to produce DNA minicircle vectors for nuclear and mitochondrial gene therapy

The presence of CpG motifs and their associated sequences in bacterial DNA causes an immunotoxic response following the delivery of these plasmid vectors into mammalian hosts. We describe a biotechnological approach to the elimination of this problem by the creation of a bacterial cre recombinase expression system, tightly controlled by the arabinose regulon. This permits the Cre-mediated and -directed excision of the entire bacterial vector sequences from plasmid constructs to create supercoiled gene expression minicircles for gene therapy. Minicircle yields using standard culture volumes are sufficient for most in vitro and in vivo applications whereas minicircle expression in vitro is significantly increased over standard plasmid transfection. By the simple expedient of removing the bacterial DNA complement, we significantly reduce the size and CpG content of these expression vectors, which should also reduce DNA-induced inflammatory responses in a dose-dependent manner. We further describe the generation of minicircle expression vectors for mammalian mitochondrial gene therapy, for which no other vector systems currently exist. The removal of bacterial vector sequences should permit appropriate transcription and correct transcriptional cleavage from the mitochondrial minicircle constructs in a mitochondrial environment and brings the realization of mitochondrial gene therapy a step closer.

Direct gene delivery strategies for the treatment of rheumatoid arthritis

Gene therapy offers a novel and innovative approach to the delivery of therapeutic proteins to the joints of patients with arthritis. Several viral vectors, including adenovirus, adeno-associated virus, retrovirus and herpes simplex virus, are capable of delivering exogenous cDNAs to the synovial lining, enabling effective levels of intra-articular transgene expression following direct injection to the joint. The expression of certain gene products has proven to be sufficient to inhibit the progression of disease in animals with experimental arthritis. Non-viral methods of gene transfer, however, are less satisfactory, and are limited by toxicity and transience of expression. Although the principle of direct gene delivery to the joint has been demonstrated, maintaining persistent intra-articular transgene expression remains a challenge.

Developing non-viral DNA delivery systems for cancer and infectious disease

Efforts to deliver therapeutic genes are frequently rebuffed by the body's adaptive immune response against viral delivery vectors. Attempts to circumvent this problem using non-viral delivery systems have encountered problems with transient expression and inflammatory responses induced by reaction of the innate immune system reacting against bacterial DNA. However, within the past decade, these barriers to non-viral DNA delivery have been recognized as potential allies in the development of novel vaccines for cancer and infectious disease. This review summarizes preclinical and current clinical studies testing the formulation, delivery route and adjuvant options in the development of novel DNA-based vaccines.