Type I interferons potently suppress gene expression following gene delivery using liposome(-)DNA complexes

Exosomes as an Emerging Plasmid Delivery Vehicle for Gene Therapy

Despite its introduction more than three decades ago, gene therapy has fallen short of its expected potential for the treatment of a broad spectrum of diseases and continues to lack widespread clinical use. The fundamental limitation in clinical translatability of this therapeutic modality has always been an effective delivery system that circumvents degradation of the therapeutic nucleic acids, ensuring they reach the intended disease target. Plasmid DNA (pDNA) for the purpose of introducing exogenous genes presents an additional challenge due to its size and potential immunogenicity. Current pDNA methods include naked pDNA accompanied by electroporation or ultrasound, liposomes, other nanoparticles, and cell-penetrating peptides, to name a few. While the topic of numerous reviews, each of these methods has its own unique set of limitations, side effects, and efficacy concerns. In this review, we highlight emerging uses of exosomes for the delivery of pDNA for gene therapy. We specifically focus on bovine milk and colostrum-derived exosomes as a nano-delivery "platform". Milk/colostrum represents an abundant, scalable, and cost-effective natural source of exosomes that can be loaded with nucleic acids for targeted delivery to a variety of tissue types in the body. These nanoparticles can be functionalized and loaded with pDNA for the exogenous expression of genes to target a wide variety of disease phenotypes, overcoming many of the limitations of current gene therapy delivery techniques.

Mutations in the non-structural protein coding region regulate gene expression from replicon RNAs derived from Venezuelan equine encephalitis virus

Self-replicating RNA (repRNA) derived from Venezuelan equine encephalitis (VEE) virus is a promising platform for gene therapy and confers prolonged gene expression due to its self-replicating capability, but repRNA suffers from a suboptimal transgene expression level due to its induction of intracellular innate response which may result in inhibition of translation. To improve transgene expression of repRNA, we introduced point mutations in the non-structural protein 1-4 (nsP1-4) coding region of VEE replicon vectors. As a proof of concept, inflammatory cytokines served as genes of interest and were cloned in their wild type and several mutant replicon vectors, followed by transfection in mammalian cells. Our data show that VEE replicons bearing nsP1GGAC-nsP2T or nsP1GGAC-nsP2AT mutations in the nsP1-4 coding region could significantly reduce the recognition by innate immunity as evidenced by the decreased production of type I interferon, and enhance transgene expression in host cells. Thus, the newly discovered mutant VEE replicon vectors could serve as promising gene expression platforms to advance VEE-derived repRNA-based gene therapies.

The Regulation of Nucleic Acid Vaccine Responses by the Microbiome

Nucleic acid vaccines, including both RNA and DNA platforms, are key technologies that have considerable promise in combating both infectious disease and cancer. However, little is known about the extrinsic factors that regulate nucleic acid vaccine responses and which may determine their effectiveness. The microbiome is recognized as a significant regulator of immune development and response, whose role in regulating some traditional vaccine platforms has recently been discovered. Using germ-free and specific-pathogen-free mouse models in combination with different protein, DNA, and mRNA vaccine regimens, we demonstrate that the microbiome is a significant regulator of nucleic acid vaccine immunogenicity. While the presence of the microbiome enhances CD8+ T cell responses to mRNA lipid nanoparticle (LNP) immunization, the microbiome suppresses immunoglobulin and CD4+ T cell responses to DNA-prime, DNA-protein-boost immunization, indicating contrasting roles for the microbiome in the regulation of these different nucleic acid vaccine platforms. In the case of mRNA-LNP vaccination, germ-free mice display reduced dendritic cell/macrophage activation that may underlie the deficient vaccine response. Our study identifies the microbiome as a relevant determinant of nucleic acid vaccine response with implications for their continued therapeutic development and deployment.

The Effect of Repeat Administration of Lipoplexes on Gene Delivery, Biodistribution, and Cytokine Response in Immunocompetent Tumor-bearing Mice

It is becoming increasingly clear that the intravenous administration of nanoparticles elicits an immune response that compromises delivery efficiency and can be life threatening. This study investigated both the systemic and tissue-level cytokine response to repeat administration of lipoplexes coated with either lactose or PEG. We report that blood cytokine levels differ significantly from that observed in individual tissues. While we consistently observed a reduced cytokine response to lactosylated particles, this did not result in enhanced delivery or expression as compared to PEGylated formulations. We also document that repeat injection did not increase plasmid levels in the liver, lung, or spleen, but delivery to the tumor was enhanced under these conditions. In addition, we show that changes in neither blood nor tissue cytokines correlated strongly with reporter gene expression, and we observed relatively constant expression efficiencies (RLU/ng plasmid) across all tissues despite a considerably reduced cytokine response in the tumor. Together, these results indicate that both biodistribution and cytokine responses are dramatically altered by a repeat intravenous injection of lipoplexes, and that the mechanisms regulating reporter gene expression are not straightforward.

Nonviral gene delivery to T cells with Lipofectamine LTX

Retroviral gene delivery is widely used in T cell therapies for hematological cancers. However, viral vectors are expensive to manufacture, integrate genes in semirandom patterns, and their transduction efficiency varies between patients. In this study, several nonviral gene delivery vehicles, promoters, and additional variables were compared to optimize nonviral transgene delivery and expression in both Jurkat and primary T cells. Transfection of Jurkat cells was maximized to a high efficiency (63.0% ± 10.9% EGFP⁺  cells) by transfecting cells with Lipofectamine LTX in X-VIVO 15 media. However, the same method yielded a much lower transfection efficiency in primary T cells (8.1% ± 0.8% EGFP⁺ ). Subsequent confocal microscopy revealed that a majority of the lipoplexes did not enter the primary T cells, which might be due to relatively low expression levels of heparan sulfate proteoglycans detected via messenger RNA-sequencing. Pyrin and HIN (PYHIN) DNA sensors (e.g., AIM2 and IFI16) that can induce apoptosis or repress transcription after binding cytoplasmic DNA were also detected at high levels in primary T cells. Therefore, transfection of primary T cells appears to be limited at the level of cellular uptake or DNA sensing in the cytoplasm. Both of these factors should be considered in the development of future viral and nonviral T cell gene delivery methods.

Inhibition of cGAS-Mediated Interferon Response Facilitates Transgene Expression

DNA transfection is often the bottleneck of research and gene therapy practices. To explore the mechanism regulating transgene expression, we investigated the role of the cGAS-STING signaling pathway, which induces type-I interferons in response to DNA. We confirmed that deletion of cGAS enhances transgene expression at the protein level by ~2- to 3-fold. This enhancement is inversely correlated with the expression of interferons and interferon stimulated genes (ISGs), which suppress expression of transfected genes at the mRNA level. Mechanistically, DNA transfection activates the cGAS-STING pathway and induces the expression of the OAS family proteins, leading to the activation of RNaseL and degradation of mRNA derived from transgenes. Administration of chemical inhibitors that block cGAS-mediated signaling cascades improves the expression of transgenes by ~1.5- to 3-fold in multiple cell lines and primary cells, including T cells. These data suggest that targeting the cGAS-STING pathway can improve transgene expression, and this strategy may be applied to gene therapy.

The Use of Lactose as an Alternative Coating for Nanoparticles

Nanoparticle-mediated drug delivery has long utilized PEGylation as a mechanism for reducing uptake by the reticuloendothelial system and extending circulation lifetimes. However, studies over the past 2 decades have established that immune responses to PEG can promote clearance on repeat injection and elicit life-threatening anaphylactic reactions in some patients. As a potential alternative to PEGylation, we explored the ability of utilizing lactose, a naturally occurring sugar that is common on the surface of blood cells, as a coating for lipoplexes. Our data indicate that lactose imparts similar effects as PEG in terms of reducing leukocyte uptake, extending circulation half-life, and enhancing delivery to the tumor and other organs. In addition, measurements of blood cytokine levels after repeat injection indicate that reduced levels of inflammatory cytokines (IL-6, IFN-γ, TNFα) are elicited in response to lipoplexes coated with lactose as compared to PEG. These data indicate that a lactose coating on lipoplexes results in slightly improved tumor accumulation as compared to PEGylated formulations while eliciting a reduced innate immune response.

Immunological and Toxicological Considerations for the Design of Liposomes

Liposomes hold great potential as gene and drug delivery vehicles due to their biocompatibility and modular properties, coupled with the major advantage of attenuating the risk of systemic toxicity from the encapsulated therapeutic agent. Decades of research have been dedicated to studying and optimizing liposomal formulations for a variety of medical applications, ranging from cancer therapeutics to analgesics. Some effort has also been made to elucidate the toxicities and immune responses that these drug formulations may elicit. Notably, intravenously injected liposomes can interact with plasma proteins, leading to opsonization, thereby altering the healthy cells they come into contact with during circulation and removal. Additionally, due to the pharmacokinetics of liposomes in circulation, drugs can end up sequestered in organs of the mononuclear phagocyte system, affecting liver and spleen function. Importantly, liposomal agents can also stimulate or suppress the immune system depending on their physiochemical properties, such as size, lipid composition, pegylation, and surface charge. Despite the surge in the clinical use of liposomal agents since 1995, there are still several drawbacks that limit their range of applications. This review presents a focused analysis of these limitations, with an emphasis on toxicity to healthy tissues and unfavorable immune responses, to shed light on key considerations that should be factored into the design and clinical use of liposomal formulations.

Durable multitransgene expression in vivo using systemic, nonviral DNA delivery

Recombinant adeno-associated virus (AAV) vectors are transforming therapies for rare human monogenic deficiency diseases. However, adaptive immune responses to AAV and its limited DNA insert capacity, restrict their therapeutic potential. HEDGES (high-level extended duration gene expression system), a nonviral DNA- and liposome-based gene delivery platform, overcomes these limitations in immunocompetent mice. Specifically, one systemic HEDGES injection durably produces therapeutic levels of transgene-encoded human proteins, including FDA-approved cytokines and monoclonal antibodies, without detectable integration into genomic DNA. HEDGES also controls protein production duration from <3 weeks to >1.5 years, does not induce anti-vector immune responses, is reexpressed for prolonged periods following reinjection, and produces only transient minimal toxicity. HEDGES can produce extended therapeutic levels of multiple transgene-encoded therapeutic human proteins from DNA inserts >1.5-fold larger than AAV-based therapeutics, thus creating combinatorial interventions to effectively treat common polygenic diseases driven by multigenic abnormalities.

Analysis of the effect of promoter type and skin pretreatment on antigen expression and antibody response after gene gun-based immunization

Monoclonal antibodies (mAbs) have enabled numerous basic research discoveries and therapeutic approaches for many protein classes. However, there still exist a number of target classes, such as multi-pass membrane proteins, for which antibody discovery is difficult, due in part to lack of high quality, recombinant protein. Here we describe the impact of several parameters on antigen expression and the development of mAbs against human claudin 4 (CLDN4), a potential multi-indication cancer target. Using gene gun-based DNA delivery and bioluminescence imaging, we optimize promoter type by comparing expression profiles of four robust in vivo promoters. In addition, we observe that most vectors rapidly lose expression, ultimately reaching almost background levels by three days post-delivery. Recognizing this limitation, we next explored skin pretreatment strategies as an orthogonal method to further boost the efficiency of mAb generation. We show that SDS pretreatment can boost antigen expression, but fails to significantly increase mAb discovery efficiency. In contrast, we find that sandpaper pretreatment yields 5-fold more FACS⁺ anti-CLDN4 hybridomas, without impacting antigen expression. Our findings coupled with other strategies to improve DNA immunizations should improve the success of mAb discovery against other challenging targets and enable the generation of critical research tools and therapeutic candidates.

Safe and effective interferon-beta gene therapy for the treatment of multiple sclerosis by regulating biological activity through the design of interferon-beta-galectin-9 fusion proteins

Multiple sclerosis (MS) is the most common demyelinating disease. Despite the historical use of interferon-beta (IFN-β) for the treatment of patients with MS, concerns exist regarding the side effects of IFN-β. In this study, we designed a series of novel IFN-β fusion proteins containing galectin-9 (gal-9), which exerts immunosuppressive effects through the binding to its receptor on activated T_h1 cells. We hypothesized that these fusion proteins would improve the therapeutic effects and reduce the side effects of IFN-β. The IFN-β-gal-9 fusion proteins showed less IFN-β biological activity on non-T cells than IFN-β alone. In vitro experiments using re-stimulated T cells isolated from mice with experimental autoimmune encephalomyelitis (EAE) showed that the IFN-β-gal-9 fusion proteins suppressed activated T cells more effectively than IFN-β. Moreover, in our in vivo experiments, the gene transfer of IFN-β-gal-9 fusion protein-expressing plasmid DNA into EAE mice showed beneficial therapeutic effects without cytopenia, a known side effect of IFN-β. In contrast, the gene transfer of IFN-β-expressing plasmid DNA induced a rapid decrease in the white blood cell count, despite its therapeutic effect. These results indicate that gene therapy using IFN-β-gal-9 fusion proteins is expected to be safe and effective for the treatment of MS.

Amelioration of Experimental Autoimmune Encephalomyelitis in Mice by Interferon-Beta Gene Therapy, Using a Long-Term Expression Plasmid Vector

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Repeated injections of the interferon-β (IFN-β) protein are required for relapse prevention therapy in patients with MS. IFN-β gene transfer can be an alternative treatment that continuously supplies IFN-β protein to the patient without requiring repeated injections. In a previous study, we constructed a novel long-term IFN-β-expressing plasmid vector (pMx-IFN-β). In the present study, we examined whether gene transfer of pMx-IFN-β could be effective for the treatment of MS in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. Seven days after injection of the EAE-inducing peptide, the EAE mice received hydrodynamic injections pMx-IFN-β. The severity of EAE symptoms in the pMx-IFN-β-treated mice was significantly lower for 1 month than that observed in the untreated mice. An evaluation of blood-brain barrier (BBB) function, using Evans Blue, showed that injection of pMx-IFN-β suppressed the BBB disruptions normally observed in EAE mice, while BBB disruptions remained evident in the untreated EAE mice. Histological analysis showed fewer invasive inflammatory cells in the spinal cords of the pMx-IFN-β-treated mice than in the spinal cords of the other mice. Serum interferon gamma protein (IFN-γ) concentrations in the pMx-IFN-β-treated mice were significantly lower than that in the untreated mice, indicating that IFN-β gene transfer suppressed the production of IFN-γ from pathogenic T cells. These results indicate that IFN-β transgene expression by single administration of the pMx-IFN-β can be an effective long-term treatment for MS.

Poly (I:C)-DOTAP cationic nanoliposome containing multi-epitope HER2-derived peptide promotes vaccine-elicited anti-tumor immunity in a murine model

In the current study we aimed at developing a vaccine delivery/adjuvant system to enhance anti-tumor immunity against the natural multi-epitope HER2/Neu-derived P5 peptide. Polyriboinosinic: polyribocytidylic acid [Poly (I:C)] is a strong immunoadjuvant able to enhance specific antitumor immunity induced by peptide-based vaccines. Nevertheless, delivering the peptide and adjuvant intracellularly into their target site remains a challenging issue. We hypothesized this barrier could be overcome through the use of a cationic nanoliposome carrier system which can carry and protect the antigen and adjuvant in the extracellular environment and augment the induction of antitumor immunity. P5 was encapsulated in cationic nanoliposomes composed of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP)-Cholesterol either alone or complexed with Poly (I:C). Immunocompetent BALB/c mice were immunized with the formulations 3 times in two-week intervals and the efficiency and type of immune response were then evaluated both in vitro and in vivo. The groups immunized with Lip-P5+PIC (DOTAP-Cholestrol-P5+Poly (I:C)) and Lip+PIC (DOTAP-Cholestrol+Poly (I:C)) enhanced the release of Interferon (IFN)-γ in comparison with other groups. Flow cytometry analysis revealed that Lip-P5+PIC formulation induced the highest level of IFN-γ in CD8(+) lymphocytes. Lip-P5+PIC, Lip+PIC and Lip-P5 (DOTAP-Cholestrol-P5) provided some extent of protection in terms of tumor regression in TUBO tumor mice model during the first 65days post tumor challenge but at the end only the tumors of mice immunized with Lip-P5+PIC were significantly smaller than all other groups. Furthermore, tumors of mice receiving Lip-P5+PIC grew at a significantly slower rate throughout the observation period. Our results showed that the combination of Poly (I:C) and DOTAP with the tumor antigen and without applying additional T-helper epitope induced strong antitumor responses. The observations presented here are of great interest for future vaccine studies.

Kinetic and phenotypic analysis of CD8+ T cell responses after priming with alphavirus replicons and homologous or heterologous booster immunizations

Alphavirus replicons are potent inducers of CD8(+) T cell responses and thus constitute an attractive vaccine vector platform for developing novel vaccines. However, the kinetics and memory phenotype of CD8(+) T cell responses induced by alphavirus replicons are not well characterized. Furthermore, little is known how priming with alphavirus replicons affects booster immune responses induced by other vaccine modalities. We demonstrate here that a single immunization with an alphavirus replicon, administered as viral particles or naked DNA, induced an antigen-specific CD8(+) T cell response that had a sharp peak, followed by a rapid contraction. Administering a homologous boost before contraction had occurred did not further increase the response. In contrast, boosting after contraction when CD8(+) T cells had obtained a memory phenotype (based on CD127/CD62L expression), resulted in maintenance of CD8(+) T cells with a high recall capacity (based on CD27/CD43 expression). Increasing the dose of replicon particles promoted T effector memory (Tem) and inhibited T central memory development. Moreover, infection with a replicating alphavirus induced a similar distribution of CD8(+) T cells as the replicon vector. Lastly, the distribution of T cell subpopulations induced by a DNA-launched alphavirus replicon could be altered by heterologous boosts. For instance, boosting with a poxvirus vector (MVA) favored expansion of the Tem compartment. In summary, we have characterized the antigen-specific CD8(+) T cell response induced by alphavirus replicon vectors and demonstrated how it can be altered by homologous and heterologous boost immunizations.

IMPORTANCE

Alphavirus replicons are promising vaccine candidates against a number of diseases and are by themselves developed as vaccines against, for example, Chikungunya virus infection. Replicons are also considered to be used for priming, followed by booster immunization using different vaccine modalities. In order to rationally design prime-boost immunization schedules with these vectors, characterization of the magnitude and phenotype of CD8(+) T cell responses induced by alphavirus replicons is needed. Here, we demonstrate how factors such as timing and dose affect the phenotypes of memory T cell populations induced by immunization with alphavirus replicons. These findings are important for designing future clinical trials with alphaviruses, since they can be used to tailor vaccination regimens in order to induce a CD8(+) T cell response that is optimal for control and/or clearance of a specific pathogen.

Immunomodulation of nanoparticles in nanomedicine applications

Nanoparticles (NPs) have promising applications in medicine. Immune system is an important protective system to defend organisms from non-self matters. NPs interact with the immune system and modulate its function, leading to immunosuppression or immunostimulation. These modulating effects may bring benefits or danger. Compositions, sizes, and surface chemistry, and so forth, affect these immunomodulations. Here we give an overview of the relationship between the physicochemical properties of NPs, which are candidates to be applied in medicine, and their immunomodulation properties.

DNA-aptamer targeting vimentin for tumor therapy in vivo

In recent years, new prospects for the use of nucleic acids as anticancer drugs have been discovered. Aptamers for intracellular targets can regulate cellular functions and cause cell death or proliferation. However, intracellular aptamers have limited use for therapeutic applications due to their low bioavailability. In this work, we selected DNA aptamers to cell organelles and nucleus of cancer cells, and showed that an aptamer NAS-24 binds to vimentin and causes apoptosis of mouse ascites adenocarcinoma cells in vitro and in vivo. To deliver the aptamer NAS-24 inside cells, natural polysaccharide arabinogalactan was used as a carrier reagent. The mixture of arabinogalactan and NAS-24 was injected intraperitonealy for 5 days into mice with adenocarcinoma and inhibited adenocarcinoma growth more effectively than free arabinogalactan or the aptamer alone. The use of aptamers to intracellular targets together with arabinogalactan becomes a promising approach for anticancer therapy.

Sindbis virus replicase-based DNA vaccine construct encoding FMDV-specific multivalent epitope gene: studies on its immune responses in guinea pigs

Foot-and-mouth disease (FMD) is still a perennial global menace affecting livestock health and production. It is imperative to figure out new ways to curb this disease. In this study, a sindbis virus replicase-based DNA vaccine, pSinCMV-Vac-MEG990, encoding a multivalent epitope gene (representing tandemly linked VP1 C-terminal halves of three foot-and-mouth disease virus (FMDV) serotypes) was constructed. In vitro transfection studies in BHK-21 cells revealed that the construct was able to express FMDV-specific antigen but does not overproduce the antigen. Immunization of guinea pigs with the construct at dose rate of 10, 5, 2 and 1 μg per animal through intramuscular route showed significant neutralizing antibody induction at all doses against all serotype tested as compared to non-immunized controls. On viral challenge of guinea pigs 4 week post-immunization with 1000 GPID(50) of FMDV serotype A, it was observed that the immunization not only delayed the appearance and reduced the severity of FMD lesions significantly (P < 0.05) but also provided complete protection in several guinea pigs. In fact, two of six and one of six guinea pigs were completely protected in 10 and 5 μg immunized groups, respectively. These results suggest that the development of the replicase-based DNA vaccine may provide a promising approach as an alternative vaccine strategy for controlling FMD.

Altering an artificial Gagpolnef polyprotein and mode of ENV co-administration affects the immunogenicity of a clade C HIV DNA vaccine

HIV-1 candidate vaccines expressing an artificial polyprotein comprising Gag, Pol and Nef (GPN) and a secreted envelope protein (Env) were shown in recent Phase I/II clinical trials to induce high levels of polyfunctional T cell responses; however, Env-specific responses clearly exceeded those against Gag. Here, we assess the impact of the GPN immunogen design and variations in the formulation and vaccination regimen of a combined GPN/Env DNA vaccine on the T cell responses against the various HIV proteins. Subtle modifications were introduced into the GPN gene to increase Gag expression, modify the expression ratio of Gag to PolNef and support budding of virus-like particles. I.m. administration of the various DNA constructs into BALB/c mice resulted in an up to 10-fold increase in Gag- and Pol-specific IFNγ(+) CD8(+) T cells compared to GPN. Co-administering Env with Gag or GPN derivatives largely abrogated Gag-specific responses. Alterations in the molar ratio of the DNA vaccines and spatially or temporally separated administration induced more balanced T cell responses. Whereas forced co-expression of Gag and Env from one plasmid induced predominantly Env-specific T cells responses, deletion of the only H-2(d) T cell epitope in Env allowed increased levels of Gag-specific T cells, suggesting competition at an epitope level. Our data demonstrate that the biochemical properties of an artificial polyprotein clearly influence the levels of antigen-specific T cells, and variations in formulation and schedule can overcome competition for the induction of these responses. These results are guiding the design of ongoing pre-clinical and clinical trials.

Transfection of naked nuclear factor-κB decoy oligodeoxynucleotides into liver by rapid portal vein infusion in rats: its effect on ischemia-reperfusion injury of liver

This study was aimed at examining whether rapid portal vein infusion (RPVI) of a small volume of naked oligodeoxynucleotides (ODNs) could be used to transfect sufficient amounts of nuclear factor-κB (NF-κB) decoy ODN into the liver to suppress NF-κB activation during liver ischemia-reperfusion (I/R) injury, in which NF-κB plays a central role in regulating the production of inflammatory cytokines. One milliliter of naked NF-κB decoy ODN solution was administered into the portal vein for a few seconds. Transfection efficacy was examined by labeling the ODN with a fluorescent tag. Activation of NF-κB was investigated by electrophoretic mobility shift assay. Levels of serum liver enzymes and cytokines were measured during liver I/R injury. NF-κB decoy ODN was preferentially incorporated into Kupffer cells and sinusoidal endothelial cells, but not hepatocytes, in the rat liver. Transfected NF-κB decoy ODN suppressed the function of NF-κB in both Kupffer cells and sinusoidal endothelial cells during liver I/R injury, causing significant decreases in serum tumor necrosis factor-α and interleukin-6 levels 3 hr after reperfusion. Although the decrease in serum liver enzymes was not significant, naked NF-κB decoy ODN was successfully incorporated into Kupffer cells and sinusoidal endothelial cells by rapid portal vein infusion, inhibited NF-κB activation in both cells, and suppressed the production of inflammatory cytokines during the early phase of liver I/R injury.

The elucidation of gene transferring mechanism by ultrasound-responsive unmodified and mannose-modified lipoplexes

The development of gene transfection methods enhancing the level of gene expression under simple and low-toxic condition is required for gene therapy in clinical. Our group has developed the ultrasound (US)-mediated gene transfection method using Man-PEG(2000) bubble lipoplexes, which are US-responsive and mannose-modified gene carriers, and succeeded in obtaining the enhanced gene expression in mannose receptor-expressing cells selectively by the gene transfer using Man-PEG(2000) bubble lipoplexes with US exposure in vitro and in vivo. Here, we investigated pDNA transferring mechanism followed by US exposure to unmodified and Man-PEG(2000) bubble lipoplexes, in particular, focused on US exposure timing. Following investigation of intracellular transferring characteristics, a large amount of pDNA was transferred into the cytoplasm followed by US-mediated destruction of bubble lipoplexes in the gene transfer using both bubble lipoplexes with US exposure. Moreover, the effective gene expression was obtained without TNF-α production when US was exposed until 5 min after the addition of bubble lipoplexes. These findings suggest that the gene transfer using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure enables to transfer pDNA into the cytoplasm, and optimized US exposure timing is important to achieve the high level of gene expression and the low level of pro-inflammatory cytokine production.

Role of innate signalling pathways in the immunogenicity of alphaviral replicon-based vaccines

Background

Alphaviral replicon-based vectors induce potent immune responses both when given as viral particles (VREP) or as DNA (DREP). It has been suggested that the strong immune stimulatory effect induced by these types of vectors is mediated by induction of danger signals and activation of innate signalling pathways due to the replicase activity. To investigate the innate signalling pathways involved, mice deficient in either toll-like receptors or downstream innate signalling molecules were immunized with DREP or VREP.

Results

We show that the induction of a CD8⁺ T cell response did not require functional TLR3 or MyD88 signalling. However, IRF3, converging several innate signalling pathways and important for generation of pro-inflammatory cytokines and type I IFNs, was needed for obtaining a robust primary immune response. Interestingly, type I interferon (IFN), induced by most innate signalling pathways, had a suppressing effect on both the primary and memory T cell responses after DREP and VREP immunization.

Conclusions

We show that alphaviral replicon-based vectors activate multiple innate signalling pathways, which both activate and restrict the induced immune response. These results further show that there is a delicate balance in the strength of innate signalling and induction of adaptive immune responses that should be taken into consideration when innate signalling molecules, such as type I IFNs, are used as vaccine adjuvant.

Biodegradable nanoparticles containing TLR3 or TLR9 agonists together with antigen enhance MHC-restricted presentation of the antigen

The effects of intraphagosomal toll-like receptor (TLR) activation on the MHC-restricted presentation of exogenous antigen were examined in dendritic cells (DCs). For phagosomal targeting, nanoparticles containing both a TLR agonist and a model antigen, ovalbumin (OVA), were prepared using biodegradable polymer poly(D,L-lactic acid-co-glycolic acid) and were then opsonized with mouse IgG. After incubating mouse DCs with the nanoparticles, the efficacy of OVA peptide presentation was evaluated using OVA-specific CD8 and CD4 T cells. Inclusion of either the TLR3 agonist poly(I:C) or the TLR9 agonist CpG oligodeoxynucleotides (ODN) significantly increased and prolonged both MHC class I- and class II-restricted OVA presentation. Accordingly, the DCs that phagocytosed the nanoparticles containing poly(I:C) or CpG ODN together with OVA efficiently induced the proliferation of OVA-specific CD8 and CD4 T cells. The potency levels of poly(I:C) and CpG ODN in increasing the MHC-restricted presentation of the exogenous antigen appeared to be similar. A combination of the 2 TLR agonists was synergistic in increasing the MHC class I-restricted, but not the class II-restricted, presentation of exogenous antigen. These results show that IgG-opsonized biodegradable nanoparticles containing both intraphagosomal TLR agonists and antigens can be efficient carrier materials in inducing antigen-specific T cell responses.

Scavenger receptors and their potential as therapeutic targets in the treatment of cardiovascular disease

Scavenger receptors act as membrane-bound and soluble proteins that bind to macromolecular complexes and pathogens. This diverse supergroup of proteins mediates binding to modified lipoprotein particles which regulate the initiation and progression of atherosclerotic plaques. In vascular tissues, scavenger receptors are implicated in regulating intracellular signaling, lipid accumulation, foam cell development, and cellular apoptosis or necrosis linked to the pathophysiology of atherosclerosis. One approach is using gene therapy to modulate scavenger receptor function in atherosclerosis. Ectopic expression of membrane-bound scavenger receptors using viral vectors can modify lipid profiles and reduce the incidence of atherosclerosis. Alternatively, expression of soluble scavenger receptors can also block plaque initiation and progression. Inhibition of scavenger receptor expression using a combined gene therapy and RNA interference strategy also holds promise for long-term therapy. Here we review our current understanding of the gene delivery by viral vectors to cells and tissues in gene therapy strategies and its application to the modulation of scavenger receptor function in atherosclerosis.

Comparison of the type of liposome involving cytokine production induced by non-CpG Lipoplex in macrophages

To improve the transfection efficiency of plasmid DNA (pDNA) into cells, various types of cationic liposome have been used to prepare pDNA/cationic liposome complexes (lipoplexes). It is well-known that lipoplexes induce a large amount of proinflammatory cytokines because unmethylated CpG dinucleotides (CpG motifs) abundantly present in pDNA are recognized by Toll-like receptor-9 (TLR9) expressed in immune cells such as macrophages and dendritic cells. This nonspecific cytokine production is problematic in nonviral gene therapy. Moreover, recent studies have demonstrated that lipoplexes induce not only proinflammatory cytokines but also another type of cytokine, type I interferons (IFNs), irrespective of the frequency of CpG motifs in DNA and the expression of TLR9. To gain more insight into the CpG motif- and TLR9-independent induction of type I IFNs and proinflammatory cytokines by lipoplex, macrophage activation was evaluated in vitro using various cationic liposomes complexed with pDNA containing no CpG motifs. The production of IFN-beta, TNF-alpha and IL-6 by lipoplex was confirmed to be induced independently of the interaction between CpG DNA and TLR9 in macrophages from TLR9-knockout mice. Then, the release of the cytokines, the mRNA expression of Z-DNA binding protein-1 (Zbp1), a cytosolic double-stranded DNA sensor, and the cellular uptake of pDNA were examined in a macrophage-like cell line, RAW264.7. The level of cytokine production and the increase in the Zbp1 mRNA varied depending on the type of cationic liposome used. A good correlation was observed between the cytokine level and the Zbp1 mRNA. A confocal microscopic study using fluorescently labeled pDNA complexes showed that the complexes that released a lot of cytokines showed an enhanced distribution of pDNA-derived fluorescence into the cytosol. These results suggest that different intracellular trafficking derived from the type of liposomes determines the recognition of pDNA by ZBP1 after uptake of lipoplexes by the macrophages, followed by the release of type I IFNs and inflammatory cytokines. The present study demonstrates that cationic liposomes should be selected based on these findings for optimization of DNA-based therapies using lipoplexes.

Dysopsonin activity of serum DNA-binding proteins favorable for gene delivery

Naked DNA is regarded as the safest and simplest method of gene delivery. However, normally intravenously injected naked plasmid DNA is rapidly eliminated from the blood. It has been hypothesized that opsonins, a category of serum DNA-binding proteins (SDBPs), label the injected plasmid DNA as foreign so that it may be recognized and rapidly removed from the bloodstream by liver nonparenchymal cells. Contrary to the hypothesis, our data indicate that some SDBPs across multiple species may have important dysopsonin properties, acting to reduce liver uptake. Formation of SDBP and DNA complexes was observed by agarose gel electrophoresis. An in vivo study involving hepatic artery and portal vein occlusion in a mouse model confirmed the activity of serum diminishing liver uptake of DNA. Data using hydrodynamic gene transfer in the mouse liver and in situ transfection in the mouse lung revealed that serum proteins bound to DNA do not affect the biological activity of the plasmid DNA. We have identified several SDBPs with potential dysopsonin properties. The SDBPs with dysopsonin properties and DNA complexes may be further modified and ultimately be developed into a novel DNA carrier system favorable for systemic gene delivery.

Rapid immunity to vaccination with woodchuck hepatitis virus surface antigen using cationic liposome-DNA complexes as adjuvant

Complexes of cationic liposomes and non-coding DNA (CLDC) have shown promise as vaccine adjuvant. Using the woodchuck animal model of hepatitis B virus (HBV) infection, the immunogenic effects of CLDC were evaluated following vaccination with three doses of woodchuck hepatitis virus surface antigen (WHsAg) adjuvanted with either CLDC or conventional alum and administered intramuscularly (im) or subcutaneously (sc). IM vaccination with WHsAg and CLDC elicited antibodies earlier, in more woodchucks, and with higher titers than WHsAg and alum. After two vaccine doses, antibody titers were higher following im than sc administration. Woodchucks administered two vaccine doses sc received the third vaccine dose im, and antibody responses reached titers comparable to those elicited by im administration. Following the second vaccine dose, im vaccination with WHsAg and CLDC induced T cell responses to WHsAg and selected WHs peptides and expression of the leukocyte surface marker CD8 and of the Th1 cytokines interferon-gamma and tumor necrosis factor alpha in woodchucks. T cell responses and CD8/cytokine expression were diminished in woodchucks from the other groups suggesting that this vaccine regimen induced a skew toward Th1 immune responses. The present study in woodchucks demonstrates that CLDC-adjuvanted WHsAg vaccine administered im resulted in a more rapid induction of humoral and cellular immune responses compared to conventional, alum-adjuvanted WHsAg vaccine. While less rapid, the immune responses following sc administration can prime the im immune responses. This adjuvant activity of CLDC over alum may be beneficial for therapeutic vaccination in chronic HBV infection.

Type I interferons inhibit the generation of tumor-associated macrophages

Tumor-associated macrophages (TAM) are very abundant in tumors and are thought to play a major role in promoting tumor growth. The generation of TAM is positively regulated by several cytokines, including colony stimulating factor-1 (CSF-1) and monocyte chemoattractant protein-1 (CCL2). However, endogenous factors that suppress the generation of TAM within tumors have not been previously identified. An earlier study showed that endogenously produced type I interferons (IFN) suppressed tumor growth via their effects on hematopoietic cells rather than through direct effects on tumor cells. Therefore, we used mouse tumor models to investigate the effects of endogenously produced type I IFNs on the generation of TAM. We found using immunohistochemistry and flow cytometry that TAM density was significantly increased in tumors of mice lacking the type I IFN receptor (IFN-alpha/betaR(-/-) mice) compared to wild type mice. Moreover, the increase in TAM density was associated with a significant increase in tumor growth rate and angiogenesis. The phenotype of TAM was similar in IFN-alpha/betaR(-/-) mice and wild type mice and tumors in both mice produced similar amounts of CSF-1 and CCL2. However, in vitro assays indicated that low concentrations of type I IFNs significantly inhibited the generation of bone marrow macrophages in response to CSF-1. These findings indicate that endogenously produced type I IFNs suppress the generation of TAM, which may in turn account for inhibition of tumor growth and angiogenesis.

X4 human immunodeficiency virus type 1 gp120 down-modulates expression and immunogenicity of codelivered antigens

In order to increase the immune breadth of human immunodeficiency virus (HIV) vaccines, strategies such as immunization with several HIV antigens or centralized immunogens have been examined. HIV-1 gp120 protein is a major immunogen of HIV and has been routinely considered for inclusion in both present and future AIDS vaccines. However, recent studies proposed that gp120 interferes with the generation of immune response to codelivered antigens. Here, we investigate whether coimmunization with plasmid-encoded gp120 alters the immune response to other coadministered plasmid encoded antigens such as luciferase or ovalbumin in a mouse model. We found that the presence of gp120 leads to a significant reduction in the expression level of the codelivered antigen in vivo. Antigen presentation by antigen-presenting cells was also reduced and resulted in the induction of weak antigen-specific cellular and humoral immune responses. Importantly, gp120-mediated immune interference was observed after administration of the plasmids at the same or at distinct locations. To characterize the region in gp120 mediating these effects, we used plasmid constructs encoding gp120 that lacks the V1V2 loops (DeltaV1V2) or the V3 loop (DeltaV3). After immunization, the DeltaV1V2, but not the DeltaV3 construct, was able to reduce antigen expression, antigen presentation, and subsequently the immunogenicity of the codelivered antigen. The V3 loop dependence of this phenomenon seems to be limited to V3 loops known to interact with the CXCR4 molecule but not with CCR5. Our study presents a novel mechanism by which HIV-1 gp120 interferes with the immune response against coadministered antigen in a polyvalent vaccine preparation.

Anti-tumor effects of a human VEGFR-2-based DNA vaccine in mouse models

Background

Vascular endothelial growth factor (VEGF) and its receptor, VEGFR-2 (Flk-1/KDR), play a key role in tumor angiogenesis. Blocking the VEGF-VEGFR-2 pathway may inhibit tumor growth. Here, we used human VEGFR-2 as a model antigen to explore the feasibility of immunotherapy with a plasmid DNA vaccine based on a xenogeneic homologue of this receptor.

Methods

The protective effects and therapeutic anti-tumor immunity mediated by the DNA vaccine were investigated in mouse models. Anti-angiogenesis effects were detected by immunohistochemical staining and the alginate-encapsulate tumor cell assay. The mechanism of action of the DNA vaccine was primarily explored by detection of auto-antibodies and CTL activity.

Results

The DNA vaccine elicited a strong, protective and therapeutic anti-tumor immunity through an anti-angiogenesis mechanism in mouse models, mediated by the stimulation of an antigen-specific response against mFlk-1.

Conclusion

Our study shows that a DNA vaccine based on a xenogeneic homologue plasmid DNA induced autoimmunity against VEGFR-2, resulting in inhibition of tumor growth. Such vaccines may be clinically relevant for cancer immunotherapy.

Mucosal immunotherapy for protection from pneumonic infection with Francisella tularensis

Previous studies have demonstrated that systemically administered immunotherapy can protect mice from systemic challenge with the bacterial pathogen Francisella tularensis. However, for protection from inhalational challenge with this bacterium, we wondered if mucosally administered immunotherapy might be more effective. Therefore, we administered cationic liposome-DNA complexes (CLDC), which are potent activators of innate immunity, intranasally (i.n.) and assessed the effectiveness of protection from lethal inhalational challenge with F. tularensis. We found that pretreatment by i.n. administration of CLDC 24h prior to bacterial challenge elicited nearly complete protection of BALB/c mice from lethal challenge with F. tularensis LVS strain. We also observed that mucosal CLDC immunotherapy provided a statistically significant increase in survival time in mice challenged with the highly virulent F. tularensis Schu4 strain. Protection was associated with a significant reduction in bacterial burden in the lungs, liver, and spleen. Mucosal administration of CLDC elicited significantly increased expression of IL-12, IFN-gamma, TNF-alpha, IFN-beta and IFN-alpha genes in the lung as detected by real-time quantitative PCR. In vitro treatment of F. tularensis infected macrophages with CLDC-elicited cytokines also significantly suppressed intracellular replication of F. tularensis in infected macrophages. In vivo, depletion of NK cells prior to administration of CLDC completely abolished the protective effects of CLDC immunotherapy. CLDC-elicited protection was also dependent on induction of IFN-gamma production in vivo. We conclude therefore that activation of local pulmonary innate immune responses is capable of eliciting significant protection from inhalational exposure to a virulent bacterial pathogen.

A biotechnological product and its potential as a new immunomodulator for treatment of animal phlebovirus infection: Punta Toro virus

Intracellular pathogens with widespread drug-resistance contribute substantially to the increasing rates in morbidity and mortality due to emerging and reemerging diseases. Thus, the development of new drugs, including those that can enhance the immune response, is urgently needed. The immunomodulator, P-MAPA, a proteinaceous aggregate of ammonium and magnesium phospholinoleate-palmitoleate anhydride derived from Aspergillus oryzae, have been shown to induce antitumor activities. The ability of this compound to elicit protective immunity against viral infections has not been fully explored. Here, we report findings on the use of P-MAPA as an antiviral agent in a mouse model of acute phleboviral (Punta Toro virus) disease. A dose administered i.p. 24h post-infectious challenge (100mg/kg dose of P-MAPA) was remarkably effective at preventing death due to Punta Toro virus infection. This dose also reduced systemic viral burden and liver discoloration assayed on day 3 of infection. Taken together, our findings indicate that non-specific immunotherapy with P-MAPA appears to be an effective treatment for blocking Punta Toro virus-induced disease and suggest that further exploration with other viral disease models is warranted.

Biological gene delivery vehicles: beyond viral vectors

Gene therapy covers a broad spectrum of applications, from gene replacement and knockdown for genetic or acquired diseases such as cancer, to vaccination, each with different requirements for gene delivery. Viral vectors and synthetic liposomes have emerged as the vehicles of choice for many applications today, but both have limitations and risks, including complexity of production, limited packaging capacity, and unfavorable immunological features, which restrict gene therapy applications and hold back the potential for preventive gene therapy. While continuing to improve these vectors, it is important to investigate other options, particularly nonviral biological agents which include bacteria, bacteriophage, virus-like particles (VLPs), erythrocyte ghosts, and exosomes. Exploiting the natural properties of these biological entities for specific gene delivery applications will expand the repertoire of gene therapy vectors available for clinical use. Here, we review the prospects for nonviral biological delivery vehicles as gene therapy agents with focus on their unique evolved biological properties and respective limitations and potential applications. The potential of these nonviral biological entities to act as clinical gene therapy delivery vehicles has already been shown in clinical trials using bacteria-mediated gene transfer and with sufficient development, these entities will complement the established delivery techniques for gene therapy applications.

Radioprotection in vitro and in vivo by minicircle plasmid carrying the human manganese superoxide dismutase transgene

Manganese superoxide dismutase plasmid liposomes (MnSOD-PL) confer organ-specific in vivo ionizing irradiation protection. To prepare for potential intravenous clinical trials of systemic MnSOD-PL for radioprotection in humans, plasmid and bacterial sequences were removed and a new minicircle construct was tested. Minicircle MnSOD was purified and then cotransfected into 32D cl 3 murine interleukin-3-dependent hematopoietic progenitor cells along with another plasmid carrying the neo gene. Cells were selected in G418 (50 microg/ml) and cloned by limiting dilution. Biochemical analysis of minicircle MnSOD-transfected cells showed an MnSOD biochemical activity level of 5.8 +/- 0.5 U/mg compared with 2.7 +/- 0.1 U/mg for control 32D cl 3 cells (p = 0.0039). 32D-mc-MnSOD cells were as radioresistant as full-length MnSOD-PL transgene-expressing 2C6 cells, relative to 32D cl 3 parent cells, with an increased shoulder on the radiation survival curve (n = 4.8 +/- 0.2 and n = 4.6 +/- 0.2, respectively, compared with 1.5 +/- 0.5 for 32D cl 3 cells; p = 0.007). C57BL/6NHsd mice received intraoral mc-MnSOD-PL, mc-DsRed-PL control, full-length MnSOD-PL, or blank-PL and then were irradiated 24 hr later with 31 Gy to the esophagus. Mice receiving mc-MnSOD-PL showed increased survival compared with control mice or mice treated with mc-DsRed-PL (p = 0.0003 and 0.039, respectively), and comparable to full-length MnSOD-PL. Intravenous, systemic administration of mc-MnSOD-PL protected mice from total body irradiation (9.75 Gy). Therefore, minicircle DNA containing the human MnSOD transgene confers undiminished radioprotection in vitro and in vivo.

Cancer vaccines: accomplishments and challenges

Advancements in knowledge in diverse fields of science, including genetics, cell biology, molecular biology and biochemistry, have shed light on the origins of cancer and cell intrinsic properties that allow it to grow, invade and metastasize. Many therapies currently in use or under development are based on this knowledge. Advances in immunology, on the other hand, have shed light on how the host responds to these malignant properties of cancer. Based on that knowledge, immunotherapy, in particular vaccines directed at improving the host response against cancer, is being developed as an alternative therapeutic approach. In this review, we address main issues that have driven development of cancer vaccines and the challenges that have been met and/or are anticipated.

Cationic liposomal lipids: from gene carriers to cell signaling

Cationic lipids are positively charged amphiphilic molecules which, for most of them, form positively charged liposomes, sometimes in combination with a neutral helper lipid. Such liposomes are mainly used as efficient DNA, RNA or protein carriers for gene therapy or immunization trials. Over the past decade, significant progress has been made in the understanding of the cellular pathways and mechanisms involved in lipoplex-mediated gene transfection but the interaction of cationic lipids with cell components and the consequences of such an interaction on cell physiology remains poorly described. The data reported in the present review provide evidence that cationic lipids are not just carriers for molecular delivery into cells but do modify cellular pathways and stimulate immune or anti-inflammatory responses. Considering the wide number of cationic lipids currently available and the variety of cellular components that could be involved, it is likely that only a few cationic lipid-dependent functions have been identified so far.

Liposome-nucleic acid immunotherapeutics

Cationic liposome-nucleic acid complexes, which were originally developed for use as non-viral gene delivery vectors, may now have an equally important application as immunotherapeutic drugs. Recent studies have highlighted the ability of cationic liposomes to potently activate the innate immune system when used to deliver certain Toll-like receptor (TLR) agonists. The immune-enhancing properties of cationic liposomes have been most clearly demonstrated when combined with nucleic acid agonists for endosomally located TLRs, including TLR3, TLR7/8 and TLR9. Immune potentiation by cationic liposomes likely results from the combined effects of endosomal targeting, protection of nucleic acids from extracellular degradation, and from signaling via newly identified cytoplasmic receptors for nucleic acids. The potent innate immune stimulatory properties of liposome-nucleic acid complexes make them particularly attractive as non-specific immunotherapeutics and as vaccine adjuvants. Liposome-nucleic acid complexes have demonstrated impressive anticancer activity in a number of different animal tumor models. Moreover, liposome-nucleic acid complexes have also been shown to be effective for immunotherapy of acute viral and bacterial infections, as well as chronic fungal infections. When used as vaccine adjuvants, liposome-nucleic acid complexes target antigens for efficient uptake by dendritic cells and are particularly effective in eliciting CD8(+) T-cell responses to protein antigens. Thus, liposome-nucleic acid complexes form a potent and versatile immunotherapeutic platform.

Non-coding pDNA bearing immunostimulatory sequences co-entrapped with leishmanial antigens in cationic liposomes elicits almost complete protection against experimental visceral leishmaniasis in BALB/c mice

The difficulty in making successful vaccines against leishmaniasis is partly due to lack of an appropriate adjuvant. Non-coding plasmid DNA (pDNA) bearing immunostimulatory sequences (ISS) is a potent activator of innate immunity, and can thus act as an adjuvant with vaccine antigen. We therefore evaluated the efficacy of pDNA and soluble leishmanial antigens (SLA) to protect against challenge with Leishmania donovani infection. We demonstrate that immunomodulatory activity of pDNA, which potentiated a Th1 immune responses, led to enhanced protection with SLA. Importantly, adding cationic liposomes as vehicle to the antigen, with pDNA either complexed or entrapped within, significantly increased the potentiating effect of pDNA. Further, comparison of the two vaccine formulations demonstrated an impressive increase in the protective efficacy up to two folds when both antigen and pDNA were within the vehicle. Thus, these studies establish the utility of non-coding pDNA bearing ISS as strong promoters of vaccine potency of liposomal antigens especially when co-entrapped with the antigen in cationic liposomes.

Effects of type I interferons on the adjuvant properties of plasmid granulocyte-macrophage colony-stimulating factor in vivo

While administration of granulocyte-macrophage colony-stimulating factor (GM-CSF) can induce the local recruitment of activated antigen-presenting cells at the site of vaccine inoculation, this cellular recruitment is associated with a paradoxical decrease in local vaccine antigen expression and vaccine-elicited CD8+ T-cell responses. To clarify why this cytokine administration does not potentiate immunization, we examined the recruited cells and expressed inflammatory mediators in muscles following intramuscular administration of plasmid GM-CSF in mice. While large numbers of dendritic cells and macrophages were attracted to the site of plasmid GM-CSF inoculation, high concentrations of type I interferons were also detected in the muscles. As type I interferons have been reported to damp foreign gene expression in vivo, we examined the possibility that these local innate mediators might decrease plasmid DNA expression and therefore the immunogenicity of plasmid DNA vaccines. In fact, we found that coadministration of an anti-beta interferon monoclonal antibody with the plasmid DNA immunogen and plasmid GM-CSF restored both the local antigen expression and the CD8+ T-cell immunogenicity of the vaccine. These data demonstrate that local innate immune responses can change the ability of vaccines to generate robust adaptive immunity.

Innate immune response induced by gene delivery vectors

Gene therapy is a clinical strategy that has the potential to treat an array of genetic and nongenetic diseases. Vectors for gene transfer are the essential tools of gene therapy. For gene therapy to be successful, an appropriate amount of the therapeutic gene must be delivered into the target cells without substantial toxicity. A major limitation of the use of gene therapy vectors is the innate immune responses triggered by systemic administration of such vectors. It is essential to overcome vector-mediated innate immune responses, such as production of inflammatory cytokines, the maturation of antigen-presenting cells and tissue damage, because the induction of these responses not only shortens the period of gene expression but also leads to serious side effects. Viral vectors (for example, adenovirus (Ad) vectors) have been assumed to be more potent in inducing innate immune responses in spite of their high transduction efficiency since they contain pathogenic proteins. However, recent studies have demonstrated that not only viral vectors but also nonviral vectors, such as lipoplex (liposome/plasmid DNA complex), can induce innate immune responses. Indeed, nonviral vectors including lipoplex induce comparable or larger levels of innate immune response than viral vectors. In this review, we present an overview of the innate immune responses induced by Ad vector and lipoplex, which are used primarily for in vivo gene transfer.

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.

DNA and its cationic lipid complexes induce CpG motif-dependent activation of murine dendritic cells

Unmethylated CpG motifs in bacterial DNA, but not in vertebrate DNA, are known to trigger an inflammatory response of antigen-presenting cells (APC). In this study, we investigated the cytokine release from murine dendritic cells (DC) by the addition of various types of DNA in the free or complexed form with cationic lipids. Naked plasmid DNA and Escherichia coli DNA with immunostimulatory unmethylated CpG motifs induced pro-inflammatory cytokine secretion from granulocyte-macrophage colony-stimulating factor (GM-CSF)-cultured bone marrow-derived DC and the DC cell-line, DC2.4 cells, though vertebrate calf thymus DNA (CT DNA) with less CpG motifs did not. These characteristics differed from mouse peritoneal resident macrophages that do not respond to any naked DNA. The amount of cytokines released from the DC was significantly increased by complex formation with cationic lipids when CpG-motif positive DNAs were used. Unlike murine macrophages or Flt-3 L cultured DC, GM-CSF DC did not release inflammatory cytokines in response to the addition of CT DNA/cationic lipid complex, suggesting that the activation is completely dependent on CpG motifs. Taken together, the results of the present study demonstrate that murine DC produce pro-inflammatory cytokines upon stimulation with CpG-containing DNAs and the responses are enhanced by cationic lipids. These results also suggest that DC are the major cells that respond to naked CpG DNA in vivo, although both DC and macrophages will release inflammatory cytokines after the administration of a DNA/cationic lipid complex.

Gene therapy progress and prospects: non-viral gene therapy by systemic delivery

Non-viral vectors continue to be an attractive alternative to viral vectors due to their safety, versatility and ease of preparation and scale-up. Over the past few years, investigators have been successful in developing gene carriers that can be targeted to the disease site. Several different delivery vectors for systemic use have been developed by different groups for plasmid DNA and oligonucleotide. Most of them are designed for targeted tumor therapy. The mechanism of inflammatory toxicity, the major toxicity of cationic lipoplex, has been studied and managed. In this review, we focus on the progress made over the last 2 years. We also discuss some future prospects for gene delivery.

Vaccination with liposome--DNA complexes elicits enhanced antitumor immunity

Cationic liposomes have been shown to potentiate markedly the ability of plasmid DNA to activate innate immune responses. We reasoned therefore that liposome-DNA complexes (LDC) could be used to produce more effective plasmid DNA vaccines for cancer. To test this hypothesis, tumor-bearing mice were vaccinated with conventional plasmid DNA vaccines or with LDC vaccines encoding model tumor antigens and CD8(+) T-cell responses and antitumor activity were assessed. We found that although plasmid DNA vaccines generated large increases in antigen-specific CD8(+) T cells, they failed to elicit significant antitumor immunity. In contrast, LDC vaccines elicited large numbers of antigen-specific CD8(+) T cells and also generated significant antitumor activity against established tumors. The antitumor activity elicited by immunization with LDC vaccines was mediated primarily by CD8(+) T cells. Studies of the interaction of LDC with antigen-presenting cells found that LDC triggered dendritic cell production of interleukin-12 and interferon (IFN)-gamma production by natural killer cells in vivo. Activation by LDC was also accompanied by upregulation of costimulatory molecule expression. These findings suggest that by concurrently activating strong systemic innate immune responses and generating cytotoxic T-lymphocyte responses, LDC may be used to increase the effectiveness of therapeutic plasmid DNA vaccination for cancer.