Tetracycline transcriptional silencer tightly controls transgene expression after in vivo intramuscular electrotransfer: application to interleukin 10 therapy in experimental arthritis

SilencerDB: a comprehensive database of silencers

Gene regulatory elements, including promoters, enhancers, silencers, etc., control transcriptional programs in a spatiotemporal manner. Though these elements are known to be able to induce either positive or negative transcriptional control, the community has been mostly studying enhancers which amplify transcription initiation, with less emphasis given to silencers which repress gene expression. To facilitate the study of silencers and the investigation of their potential roles in transcriptional control, we developed SilencerDB (http://health.tsinghua.edu.cn/silencerdb/), a comprehensive database of silencers by manually curating silencers from 2300 published articles. The current version, SilencerDB 1.0, contains (1) 33 060 validated silencers from experimental methods, and (ii) 5 045 547 predicted silencers from state-of-the-art machine learning methods. The functionality of SilencerDB includes (a) standardized categorization of silencers in a tree-structured class hierarchy based on species, organ, tissue and cell line and (b) comprehensive annotations of silencers with the nearest gene and potential regulatory genes. SilencerDB, to the best of our knowledge, is the first comprehensive database at this scale dedicated to silencers, with reliable annotations and user-friendly interactive database features. We believe this database has the potential to enable advanced understanding of silencers in regulatory mechanisms and to empower researchers to devise diverse applications of silencers in disease development.

Glucocorticoid-induced leucine zipper governs the therapeutic potential of mesenchymal stem cells by inducing a switch from pathogenic to regulatory Th17 cells in a mouse model of collagen-induced arthritis

OBJECTIVE

Mesenchymal stem cells (MSCs) are potent immunosuppressive cells that have shown promise in the treatment of rheumatoid arthritis (RA). Deciphering the intrinsic characteristics of MSCs that correlate with their biologic activity will facilitate their clinical use. Recently, the role of glucocorticoid-induced leucine zipper (GILZ) in the development of RA has been documented. The aim of this study was to evaluate whether GILZ expression by MSCs may contribute to their therapeutic effect.

METHODS

MSCs were isolated from GILZ-deficient (GILZ(-/-) ) mice and wild-type mice. MSCs (1 × 10(6) cells) were injected twice via the tail vein into mice with collagen-induced arthritis (CIA).

RESULTS

In vitro, we showed that GILZ is a key factor involved in the immunosuppressive potential of MSCs. MSCs derived from GILZ(-/-) mice did not suppress the proliferation of CD4+ T cells and were less efficient than MSCs derived from WT mice in altering Th17 cell polarization. Thus, we investigated the role of GILZ in an experimental model of arthritis and demonstrated that although WT MSCs significantly reduced paw swelling in arthritic mice, GILZ(-/-) MSCs did not. Moreover, the magnitude of the effects of GILZ(-/-) MSCs on Th17 cell frequency was significantly lower than that of WT MSCs. The therapeutic effect of MSCs correlated with the generation of Treg cells bearing the CD4 + RORγt+IL-17(low) IL-10+ signature, and Th17 cell polarization was GILZ dependent.

CONCLUSION

This study demonstrates that GILZ has an essential role in the therapeutic effectiveness of MSCs in arthritis by favoring Th17 cell polarization toward a regulatory phenotype. Therefore, potentiation of GILZ expression in MSCs could represent a means to enhance their therapeutic effect in autoimmune diseases.

PLGA microspheres encapsulating siRNA anti-TNFalpha: efficient RNAi-mediated treatment of arthritic joints

The aim of this study was to investigate potentialities of poly(dl-lactide-co-glycolide) (PLGA) microspheres for the delivery of small interfering RNAs (siRNAs) against tumor necrosis factor α (TNF-α) to achieve prolonged and efficient inhibition of TNF-α for the treatment of rheumatoid arthritis (RA). PLGA microspheres were prepared by a modified multiple emulsion-solvent evaporation method. The formulations were characterized in terms of morphology, mean diameter and siRNAs distribution, encapsulation efficiency, and in vitro release kinetics. The efficiency of this system was then evaluated both in vitro and in vivo using the murine monocytic cell line J774 and a pre-clinical model of RA, respectively. siRNA-encapsulating PLGA microspheres were characterized by a high encapsulation efficiency and a slow and prolonged anti-TNF-α siRNAs. Our results provide evidence that, upon intra-articular administration, PLGA microspheres slowly releasing siRNAs effectively inhibited the expression of TNF-α in arthritic joints. Our system might represent an alternative strategy for the design of novel anti-rheumatic therapies based on the use of RNA interference in RA.

IL-6-dependent PGE2 secretion by mesenchymal stem cells inhibits local inflammation in experimental arthritis

Background

Based on their capacity to suppress immune responses, multipotent mesenchymal stromal cells (MSC) are intensively studied for various clinical applications. Although it has been shown in vitro that the immunomodulatory effect of MSCs mainly occurs through the secretion of soluble mediators, the mechanism is still not completely understood. The aim of the present study was to better understand the mechanisms underlying the suppressive effect of MSCs in vivo, using cells isolated from mice deficient in the production of inducible nitric oxide synthase (iNOS) or interleukin (IL)-6 in the murine model of collagen-induced arthritis.

Principal Findings

In the present study, we show that primary murine MSCs from various strains of mice or isolated from mice deficient for iNOS or IL-6 exhibit different immunosuppressive potential. The immunomodulatory function of MSCs was mainly attributed to IL-6-dependent secretion of prostaglandin E2 (PGE2) with a minor role for NO. To address the role of these molecules in vivo, we used the collagen-induced arthritis as an experimental model of immune-mediated disorder. MSCs effectively inhibited collagen-induced inflammation during a narrow therapeutic window. In contrast to wild type MSCs, IL-6-deficient MSCs and to a lesser extent iNOS-deficient MSCs were not able to reduce the clinical signs of arthritis. Finally, we show that, independently of NO or IL-6 secretion or Treg cell induction, MSCs modulate the host response by inducing a switch to a Th2 immune response.

Significance

Our data indicate that MSCs mediate their immunosuppressive effect via two modes of action: locally, they reduce inflammation through the secretion of anti-proliferative mediators, such as NO and mainly PGE2, and systemically they switch the host response from a Th1/Th17 towards a Th2 immune profile.

In vivo RNAi-mediated silencing of TAK1 decreases inflammatory Th1 and Th17 cells through targeting of myeloid cells

Cells from the mononuclear phagocyte system (MPS) act as systemic and local amplifiers that contribute to the progression of chronic inflammatory disorders. Transforming growth factor-β–activated kinase 1 (TAK1) is a pivotal upstream mitogen-activated protein kinase-kinase-kinase acting as a mediator of cytokine expression. It remains critical to determine in vivo the implication of TAK1 in controlling the innate immune system. Here, we describe a vehicle tailored to selectively deliver siRNAs into MPS cells after intravenous administration, and validate in vivo the potential of the RNAi-mediated TAK1 knock down for immunomodulation. In a mouse model of immune-mediated inflammatory disorder, we show that anti-TAK1 siRNA lipoplexes efficiently alleviate inflammation, severely impair the downstream c-Jun N-terminal kinase and nuclear factor-κB signaling pathways, and decrease the expression of proinflammatory mediators. Importantly, the systemic TAK1 gene silencing decreases the frequency of Th1 and Th17 cells, both mediating autoimmunity in experimental arthritis, demonstrating the immunomodulatory potential of TAK1. Finally, in vitro inhibition of TAK1 in myeloid cells decreases interferon-γ–producing T cells, suggesting that a delivery sys-tem able to target MPS cells and to silence TAK1 impacts on pathogenic T effector cells in autoimmunity.

Adeno-associated virus-mediated IL-10 gene transfer suppresses lacrimal gland immunopathology in a rabbit model of autoimmune dacryoadenitis

PURPOSE

To evaluate the effect of adeno-associated virus (AAV) vector-mediated viral (v)IL-10 gene expression on lacrimal gland (LG) immunopathology and ocular surface disease in a rabbit model of induced autoimmune dacryoadenitis (ID).

METHODS

Autologous peripheral blood lymphocytes, activated in a mixed-cell reaction when cocultured with purified rabbit lacrimal epithelial cells, induce a Sjögren's-like autoimmune dacryoadenitis when injected directly back into the donor animal's inferior LG. Four weeks after disease induction, AAV vector expressing the vIL-10 gene under control of a tetracycline-inducible promoter was injected into the inferior LG of the treatment group (ID/Rx), and doxycycline was fed orally to induce transgene expression. The ID group serving as control also received doxycycline. All LGs were removed 16 weeks after disease induction.

RESULTS

Clinical symptoms showed overall improvement in the ID/Rx group compared with the ID group. Histopathologic examination of the ID group's LG revealed scattered large lymphocytic foci and areas of altered or distorted acini, whereas the ID/Rx group had scattered small lymphocytic foci. The number of CD18(+) cells was almost fivefold lower in the ID/Rx group than in the ID group. Although the total number of RTLA(+) cells did not differ between the groups, the CD4/CD8 ratio was 16-fold smaller in the ID/Rx group.

CONCLUSIONS

Animals with experimentally induced autoimmune dacryoadenitis appeared to benefit from AAV-mediated vIL-10 gene transfer therapy. Quantitative immunohistochemical analysis suggested that the therapy might not have been simply immunosuppressive but rather supported the induction of CD8(+) regulatory cells.

Preclinical characterization of DEKAVIL (F8-IL10), a novel clinical-stage immunocytokine which inhibits the progression of collagen-induced arthritis

Introduction

In this article, we present a comparative immunohistochemical evaluation of four clinical-stage antibodies (L19, F16, G11 and F8) directed against splice isoforms of fibronectin and of tenascin-C for their ability to stain synovial tissue alterations in rheumatoid arthritis patients. Furthermore we have evaluated the therapeutic potential of the most promising antibody, F8, fused to the anti-inflammatory cytokine interleukin (IL) 10.

Methods

F8-IL10 was produced and purified to homogeneity in CHO cells and shown to comprise biological active antibody and cytokine moieties by binding assays on recombinant antigen and by MC/9 cell proliferation assays. We have also characterized the ability of F8-IL10 to inhibit arthritis progression in the collagen-induced arthritis mouse model.

Results

The human antibody F8, specific to the extra-domain A of fibronectin, exhibited the strongest and most homogenous staining pattern in synovial biopsies and was thus selected for the development of a fully human fusion protein with IL10 (F8-IL10, also named DEKAVIL). Following radioiodination, F8-IL10 was able to selectively target arthritic lesions and tumor neo-vascular structures in mice, as evidenced by autoradiographic analysis and quantitative biodistribution studies. The subcutaneous administration route led to equivalent targeting results when compared with intravenous administration and was thus selected for the clinical development of the product. F8-IL10 potently inhibited progression of established arthritis in the collagen-induced mouse model when tested alone and in combination with methotrexate. In preparation for clinical trials in patients with rheumatoid arthritis, F8-IL10 was studied in rodents and in cynomolgus monkeys, revealing an excellent safety profile at doses tenfold higher than the planned starting dose for clinical phase I trials.

Conclusions

Following the encouraging preclinical results presented in this paper, clinical trials with F8-IL10 will now elucidate the therapeutic potential of this product and whether the targeted delivery of IL10 potentiates the anti-arthritic action of the cytokine in rheumatoid arthritis patients.

In vivo gene regulation using tetracycline-regulatable systems

Numerous preclinical studies have demonstrated the efficacy of viral gene delivery vectors, and recent clinical trials have shown promising results. However, the tight control of transgene expression is likely to be required for therapeutic applications and in some instances, for safety reasons. For this purpose, several ligand-dependent transcription regulatory systems have been developed. Among these, the tetracycline-regulatable system is by far the most frequently used and the most advanced towards gene therapy trials. This review will focus on this system and will describe the most recent progress in the regulation of transgene expression in various organs, including the muscle, the retina and the brain. Since the development of an immune response to the transactivator was observed following gene transfer in the muscle of nonhuman primate, focus will be therefore, given on the immune response to transgene products of the tetracycline inducible promoter.

Protection against aminoglycoside-induced ototoxicity by regulated AAV vector-mediated GDNF gene transfer into the cochlea

Since standard aminoglycoside treatment progressively causes hearing disturbance with hair cell degeneration, systemic use of the drugs is limited. Adeno-associated virus (AAV)-based vectors have been of great interest because they mediate stable transgene expression in a variety of postmitotic cells with minimal toxicity. In this study, we investigated the effects of regulated AAV1-mediated glial cell line-derived neurotrophic factor (GDNF) expression in the cochlea on aminoglycoside-induced damage. AAV1-based vectors encoding GDNF or vectors encoding GDNF with an rtTA2s-S2 Tet-on regulation system were directly microinjected into the rat cochleae through the round window at 5 x 10(10) genome copies/body. Seven days after the virus injection, a dose of 333 mg/kg of kanamycin was subcutaneously given twice daily for 12 consecutive days. GDNF expression in the cochlea was confirmed and successfully modulated by the Tet-on system. Monitoring of the auditory brain stem response revealed an improvement of cochlear function after GDNF transduction over the frequencies tested. Damaged spiral ganglion cells and hair cells were significantly reduced by GDNF expression. Our results suggest that AAV1-mediated expression of GDNF using a regulated expression system in the cochlea is a promising strategy to protect the cochlea from aminoglycoside-induced damage.

Inflammation-inducible anti-TNF gene expression mediated by intra-articular injection of serotype 5 adeno-associated virus reduces arthritis

BACKGROUND

The tumor necrosis factor (TNF)-alpha plays a central role in rheumatoid arthritis (RA) and current biotherapies targeting TNF-alpha have a major impact on RA treatment. The long-term safety concerns associated with the repetitive TNF blockade prompt optimization of therapeutic anti-TNF approaches. Since we recently demonstrated that intra-articular gene transfer using a recombinant adeno-associated virus serotype 5 (rAAV5) efficiently transduces arthritic joints, we evaluate its effect on collagen-induced arthritis (CIA) when encoding TNF antagonists.

METHODS

Recombinant AAV5 vectors encoding the human TNFRp55 extracellular domain fused to the Fc region of mice IgG1 (TR1) or a small molecular weight dimeric human TNFRp75 extracellular domain (TR2), under two different promoters, the CMV or a chimeric NF-kappaB-based promoter inducible by inflammation, were injected into mouse CIA joints.

RESULTS

Best protection against arthritis was obtained with the rAAV5 encoding the TR1, as reflected by delayed disease onset, decreased incidence and severity of joint damage. This effect was associated with a transient expression of the anti-TNF agent when expressed under a NF-kappaB-responsive promoter, only detectable during disease flare, while the antagonist expression was rapidly increased and stable when expressed from a CMV promoter. Importantly, using the intra-articular administration of the rAAV5-NF-kappaB-TR1 vector, we observed a striking correlation between local TR1 expression and inflammation.

CONCLUSIONS

These findings strongly support the feasibility of improving the safety of anti-TNF approaches for the treatment of arthritis by local rAAV5-mediated gene expression under an inflammation-responsive promoter, able to provide a limited, transient and therapeutically relevant expression of anti-TNF compounds.

Tet-On Induction with Doxycycline after Gene Transfer in Mice: Sweetening of Drinking Water is not a Good Idea

Gene transfer to skeletal muscle leads to long-term, stable expression of transferred genes. An exiting development is the use of inducible expression systems. Using the inducible Tet-On system, it has been customary to administer doxycycline in drinking water with added sucrose to ameliorate the bitter taste. During a study aiming at regulating electrotransferred genes through the Tet-On system, we observed excessive drinking behavior among mice. Removal of sugar from the drinking water led to normal drinking behavior and most importantly did not affect the level of gene expression. Based on this study, the practice of adding sucrose to drinking water in doxycycline induction studies should be abandoned.

Sensitive and precise regulation of haemoglobin after gene transfer of erythropoietin to muscle tissue using electroporation

Electroporation-based gene transfer (electro gene transfer (EGT)) is gaining increasing momentum, in particular for muscle tissue, where long-term high-level expression is obtainable. Induction of expression using the Tet-On system was previously established; however, attempts to reach a predefined target dose - a prescription, have not been reported. We set three target haemoglobin levels (10, 12 and 14 mmol/l, base level was 8.2 mmol/l) and aimed at them by transferring the erythropoietin (EPO) gene to mouse tibialis cranialis (TC) muscle, and varying (1) DNA amount, (2) muscle mass transfected and (3) induction with the Tet-On system. Results showed that (a) using GFP, luciferase and EPO low DNA amounts were needed. In fact, 0.5 microg of DNA to one TC muscle led to significant Hgb elevation - this amount extrapolates to 1.4 mg of DNA in humans, (b) three prescribers hit the targets with average Hgb of 10.5, 12.0 and 13.7 mmol/l, (c) different approaches could be used, (d) undershooting could be corrected by retransferring, and (e) overshooting could be alleviated by reducing dose of inducer (doxycycline (dox)). In conclusion, this study shows that using EGT to muscle, a preset level of protein expression can be reached. This is of great interest for future clinical use.

[Gene therapy for osteoarticular disorders]

Osteoarticular disorders are the major cause of disability in Europe and North America. It is estimated that rheumatoid arthritis affects 1 % of the population and that more than two third of people over age 55 develop osteoarthritis. Because there are no satisfactory treatments, gene therapy offers a new therapeutic approach. The delivery of cDNA encoding anti-arthritic proteins to articular cells has shown therapeutic efficacy in numerous animal models in vivo. Through the development and the experimental progresses that have been made for both rheumatoid arthritis and osteoarthritis, this review discusses the different gene therapy strategies available today and the safety issues with which they may be associated. Among the different vectors available today, adeno-associated virus seems the best candidate for a direct in vivo gene delivery approach for the treatment of joint disorders.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

Immature Dendritic Cells Suppress Collagen-Induced Arthritis by In Vivo Expansion of CD49b+ Regulatory T Cells

Dendritic cells (DCs) are specialized APCs with an important role in the initiation and regulation of immune responses. Immature DCs (iDCs) reportedly mediate tolerance in the absence of maturation/inflammatory stimuli, presumably by the induction of regulatory T cells. In this study, we show for the first time that repetitive iDC injections trigger the expansion of a novel regulatory population with high immunomodulatory properties, able to protect mice from collagen-induced arthritis. These regulatory T cells are characterized by the expression of the CD49b molecule and correspond to a CD4+ alpha-galactosylceramide/CD1d-nonrestricted T cell population producing IL-10. Adoptive transfer of < 10(5) TCRbeta+ CD49b+ cells isolated from the liver of iDCs-vaccinated mice, conferred a complete protection against arthritis. This protection was associated with an attenuation of the B and T cell response associated with a local secretion of IL-10. Thus, together these data demonstrate that iDCs can expand and activate a novel regulatory population of CD49b+ T cells, with high immunosuppressive potential able to mediate protection against a systemic autoimmune disease.

Activation of invariant NK T cells protects against experimental rheumatoid arthritis by an IL-10-dependent pathway

Invariant natural killer T (iNKT) cells are a unique lymphocyte subtype implicated in the regulation of autoimmunity and a good source of protective Th2 cytokines. Agonist alpha-galactosylceramide (alpha-GalCer) of iNKT cells exert a therapeutical effect in type 1 diabetes. We investigated whether iNKT activation with alpha-GalCer was protective in collagen-induced arthritis (CIA) in DBA/1 mice, a standard model of rheumatoid arthritis. Here, we have shown that in vivo iNKT cell function was altered in DBA/1 mice since stimulation with alpha-GalCer led to decreased IL-4 and IFN-gamma levels in sera, as compared with C57BL/6 mice. alpha-GalCer induced a clear-cut diminution of clinical and histological arthritides. An anti-IL-10 receptor antibody abrogated the protective effect of alpha-GalCer, suggesting a key role for IL-10 in the protection against CIA by activated iNKT cells. Confirming these data, disease protection conferred by alpha-GalCer correlated with the ability of LN CD4+ cells to secrete larger amounts of IL-10. These findings suggest that in CIA susceptibility to autoimmunity is associated with dysfunctions of iNKT cells. Our demonstration that iNKT cell activation by alpha-GalCer remains efficient in CIA-prone DBA/1 mice to provide protective IL-10 suggests that this could be used therapeutically to treat autoimmune arthritis.

Intrasplenic electro-transfer of IL-4 encoding plasmid DNA efficiently inhibits rat experimental allergic encephalomyelitis

Most of the previous studies in which cytokine DNA plasmids were delivered by systemic administration exhibited only marginal therapeutic effects, if any, in the EAE model. One strategy to overcome this limitation would be to determine the optimal delivery route leading to significant beneficial effects both in early (prophylactic) and late (therapeutic) treatments. To address this issue, we directly compared the effects of intrasplenic (i.s.) and intramuscular (i.m.) electro-transfer of interleukin-4 (IL-4) DNA in the rat experimental allergic encephalomyelitis (EAE) model. In the preventive experiment, rats received i.m. (25 or 150 microg) or i.s. (25 microg) administration of IL-4 DNA followed by in vivo electroporation the day before MBP immunization. In the late treatment experiment, rats were treated with i.m. (150 microg) or i.s. (25 microg) administration of IL-4 DNA with electroporation 10 days after MBP immunization. As a control the same amount of vector DNA was used. Macroscopic analysis indicated that the onset of moderate to severe EAE in rats treated with i.s. transfer of 25 microg of IL-4 DNA was prevented on a significant level compared with i.m. 25 microg of the IL-4 DNA transfer group or the control group in the preventive experiments. More importantly, i.s. transfer of 25 microg of IL-4 DNA considerably suppressed the severity of EAE in late treatment experiments while i.m. transfer of 150 microg of IL-4 DNA had little effect. The MBP-specific expression of IFN-gamma from stimulated splenocytes was considerably decreased by the i.s. IL-4 DNA transfer group both in the preventive and therapeutic experiments while i.m. transfer had this effect only in the preventive protocol. Histological analysis showed that spinal cord inflammation was considerably reduced in the i.s. IL-4 DNA transfer group. These data provide the first demonstration that i.s. electro-transfer of IL-4 DNA is more effective both in the prevention and modulation of EAE than i.m. transfer and that i.s. electro-gene transfer may present a new approach to cytokine therapy in autoimmune diseases.

Efficient new cationic liposome formulation for systemic delivery of small interfering RNA silencing tumor necrosis factor α in experimental arthritis

OBJECTIVE

Tumor necrosis factor alpha (TNFalpha) is among the most prominent cytokines in rheumatoid arthritis (RA) and is secreted mainly by macrophages. A direct method for restoring the immunologic balance in RA is use of small interfering RNA (siRNA) for silencing the TNFalpha transcript. The aim of this study was to determine the therapeutic effect of systemic administration of TNFalpha siRNA in an experimental model of RA, optimizing its delivery using new liposome formulations.

METHODS

Murine macrophages were transfected with siRNA targeting TNFalpha, and expression was measured. The therapeutic effect in collagen-induced arthritis (CIA) was assessed after intravenous delivery of TNFalpha siRNA. Delivery was optimized using a carrier DNA for complexation with the cationic liposome RPR209120/DOPE. Levels of TNFalpha and other cytokines were measured in sera and joint tissue-conditioned media. Biodistribution was determined using a fluorescent siRNA.

RESULTS

In vitro, TNFalpha siRNA efficiently and specifically modulated the expression of TNFalpha at both the messenger RNA and protein levels. In vivo, complete cure of CIA was observed when TNFalpha siRNA was administered weekly, complexed with the liposome and combined with carrier DNA. Inhibition (50-70%) of articular and systemic TNFalpha secretion was detected in the siRNA-injected groups, which correlated with a decrease in the levels of interleukin-6 and monocyte chemotactic protein 1. The main organs targeted by siRNA were the liver and spleen; the addition of liposome RPR209120 and carrier DNA significantly increased organ uptake.

CONCLUSION

We demonstrated the efficiency of systemic delivery of siRNA designed to silence TNFalpha in CIA, using a liposome carrier system as a way to address the methodologic limitations in vivo.

A comparative study on intra-articular versus systemic gene electrotransfer in experimental arthritis

BACKGROUND

Electric pulse mediated gene transfer has been applied successfully in vivo for increasing naked DNA administration in various tissues. To achieve non-viral gene transfer into arthritic joint tissue, we investigated the use of electrotransfer (ET). Because anti-inflammatory cytokine strategies have proven efficient in experimental models of arthritis, we compared the therapeutic efficiency of local versus systemic delivery of the interleukin-10 (IL-10) using in vivo ET.

METHODS

A plasmid vector expressing IL-10 was transferred into DBA/1 mouse knee joints by ET with 12 pulses of variable duration and voltage. The kinetics of transgene expression were analyzed by specific enzyme-linked immunosorbent assay (ELISA) in sera and knees. Optimal conditions were then used to deliver increasing amounts of IL-10 plasmid intra-articularly (i.a.) in the collagen-induced arthritis (CIA) mouse model. The therapeutic efficiency was compared with the potency of intra-muscular (i.m.) ET.

RESULTS

Following i.a. ET, local IL-10 secretion peaked on day 7 and dropped 2 weeks after. A second ET produced the same kinetics without enhancing gene transfer efficiency, while transgene was still detected in injected muscles 4 weeks after ET. Only the i.m. ET of 25 microg of IL-10 significantly inhibited all the clinical and biological features of arthritis. The i.a. ET only showed mild improvement of arthritis when 100 microg of IL-10 plasmid were electrotransfered weekly from day 18 following arthritis induction.

CONCLUSIONS

The present results suggest that gene transfer into arthritic joints by ET is an effective means to deliver anti-inflammatory cytokines. However, short duration of transgene expression impedes a significant effect for the treatment of arthritis, making i.m. ET more potent than i.a. ET for clinical benefit in CIA.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Early events of electroporation-mediated intramuscular DNA vaccination potentiate Th1-directed immune responses

BACKGROUND

Application of electrical pulses after DNA injection into muscle increases expression of the encoded genes, and is shown to improve antigen-specific immune responses when used for DNA vaccination. In addition, electroporation causes tissue injury and inflammatory reactions. Together with immune stimulatory motifs in the injected DNA these factors may potentiate the immune response by acting as adjuvants for the antigen. Here, we have examined the role of these factors in promoting the efficiency of DNA vaccination.

METHODS

We injected a plasmid DNA vector containing the gene Ag85B from M. tuberculosis into mouse quadriceps muscles followed by electroporation. Ag85B was under control of a Tet-responsive promoter, and was expressed either immediately or up to 28 days later by administrating doxycycline to the mice. Delayed expression was combined with injection of non-coding DNA or saline with or without electroporation to examine the ability of these factors to enhance the Ag85B-specific antibody response in the blood and cellular responses in the spleen. Blood samples were analysed with ELISA, while the number of Ag85B-specific IFN-gamma- and IL-4-producing spleenocytes was analysed with ELISpot.

RESULTS

Delaying Ag85B expression by 5 or 28 days caused lower anti-Ag85B-specific IgG2a levels. In contrast, the IgG1 antibody response was not significantly affected. Injection of non-coding DNA followed by electroporation moderately increased the IgG2a response. Delaying the Ag85B expression by 28 days reduced the average number of Ag85B-specific IFN-gamma-producing spleenocytes by over 60%. No significant change in the number of IL-4-producing Ag85B-specific spleenocytes was observed.

CONCLUSIONS

These results suggest that DNA and electroporation per se may act as good adjuvants in promoting efficient Th1-directed responses during DNA vaccination.

Kinetic of transgene expression after electrotransfer into skeletal muscle: Importance of promoter origin/strength

We determined over a 3-week period some of the factors that may influence the kinetic of gene expression following in vivo gene electrotransfer. Histochemical analysis of beta-galactosidase and biochemical analysis of luciferase expressions were used to determine reporter gene activity in the Tibialis anterior muscles of young Sprague-Dawley male rats. Transfection efficiency peaked 5 days after gene electrotransfer and then exponentially decreased to reach non-detectable levels at day 28. Reduction of muscle damage by decreasing the amount of DNA injected or the cumulated pulse duration did not improve the kinetic of gene expression. Electrotransfer of luciferase expression plasmids driven either by viral or mammalian promoters rather show that most of the decrease in transgene expression was related to promoter origin/strength. By regulating the amount of transgene expression, the promoter origin/strength could modulate the immune response triggered against the foreign protein and ultimately the kinetic of transgene expression.

Targeted gene therapy of autoimmune diseases: advances and prospects

Idealized gene therapy of autoimmune diseases would mean getting the right drug to the right place at the right time to affect the right mechanism of action. In other words, a specific gene therapy strategy needs to have functional, spatial and temporal specificity. Functional specificity implies targeting the cellular, molecular and/or genetic mechanisms relevant to the disease, without affecting nondiseased organs or tissues through mechanisms that cause adverse effects. Spatial specificity means the delivery of the therapeutic agent exclusively to sites and cells that are relevant to the disease. Temporal specificity is, in principle, synonymous with controlled on-demand expression of the therapeutic gene and thus represents a major safety feature. This article reviews recent advances in strategies to use gene therapy in the treatment of autoimmune diseases.

Electric pulse-mediated gene delivery to various animal tissues

Electroporation designates the use of electric pulses to transiently permeabilize the cell membrane. It has been shown that DNA can be transferred to cells through a combined effect of electric pulses causing (1) permeabilization of the cell membrane and (2) an electrophoretic effect on DNA, leading the polyanionic molecule to move toward or across the destabilized membrane. This process is now referred to as DNA electrotransfer or electro gene transfer (EGT). Several studies have shown that EGT can be highly efficient, with low variability both in vitro and in vivo. Furthermore, the area transfected is restricted by the placement of the electrodes, and is thus highly controllable. This has led to an increasing use of the technology to transfer reporter or therapeutic genes to various tissues, as evidenced from the large amount of data accumulated on this new approach for non-viral gene therapy, termed electrogenetherapy (EGT as well). By transfecting cells with a long lifetime, such as muscle fibers, a very long-term expression of genes can be obtained. A great variety of tissues have been transfected successfully, from muscle as the most extensively used, to both soft (e.g., spleen) and hard tissue (e.g., cartilage). It has been shown that therapeutic levels of systemically circulating proteins can be obtained, opening possibilities for using EGT therapeutically. This chapter describes the various aspects of in vivo gene delivery by means of electric pulses, from important issues in methodology to updated results concerning the electrotransfer of reporter and therapeutic genes to different tissues.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.

Internal ribosome entry site structural motifs conserved among mammalian fibroblast growth factor 1 alternatively spliced mRNAs

Fibroblast growth factor 1 (FGF-1) is a powerful angiogenic factor whose gene structure contains four promoters, giving rise to a process of alternative splicing resulting in four mRNAs with alternative 5' untranslated regions (5' UTRs). Here we have identified, by using double luciferase bicistronic vectors, the presence of internal ribosome entry sites (IRESs) in the human FGF-1 5' UTRs, particularly in leaders A and C, with distinct activities in mammalian cells. DNA electrotransfer in mouse muscle revealed that the IRES present in the FGF-1 leader A has a high activity in vivo. We have developed a new regulatable TET OFF bicistronic system, which allowed us to rule out the possibility of any cryptic promoter in the FGF-1 leaders. FGF-1 IRESs A and C, which were mapped in fragments of 118 and 103 nucleotides, respectively, are flexible in regard to the position of the initiation codon, making them interesting from a biotechnological point of view. Furthermore, we show that FGF-1 IRESs A of murine and human origins show similar IRES activity profiles. Enzymatic and chemical probing of the FGF-1 IRES A RNA revealed a structural domain conserved among mammals at both the nucleotide sequence and RNA structure levels. The functional role of this structural motif has been demonstrated by point mutagenesis, including compensatory mutations. These data favor an important role of IRESs in the control of FGF-1 expression and provide a new IRES structural motif that could help IRES prediction in 5' UTR databases.

Protection against collagen-induced arthritis by electrotransfer of an expression plasmid for the interleukin-4

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease, leading to cartilage and bone destruction. We investigated whether the electrotransfer of IL-4 DNA could regulate the disease progress of murine collagen-induced arthritis (CIA). The maximum serum level of mIL-4 was measured by 340 pg/ml on day 1 following DNA transfer. The onset of severe CIA and the degree of synovitis and cartilage erosion were significantly reduced in mice treated with IL-4 DNA (P<0.05). The beneficial effect of IL-4 gene transfer lasted for at least 17 days subsequent to treatment. The expression of IL-1beta was considerably decreased in the paws by IL-4 DNA transfer (P<0.01). On the contrary, the ratio of TIMP2 to MMP2 significantly increased in the IL-4 DNA-treated group (P<0.01). These data demonstrated that electroporation-mediated gene transfer could provide a new approach as an IL-4 therapy for autoimmune arthritis.

Electroporation for gene transfer to skeletal muscles: current status

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.

HLA-A*0201-restricted cytolytic responses to the rtTA transactivator dominant and cryptic epitopes compromise transgene expression induced by the tetracycline on system

The tetracycline-controlled transcription system (Tet-on) is widely used to regulate gene expression in mammalian cells. In gene therapy applications, immune responses to Tet-on proteins such as the rtTA transcription factor have been reported, raising concerns about their occurrence in humans. To monitor the HLA class I cytolytic responses against Tet-on regulators, we characterized the immunogenic CD8+ epitopes within rtTA and tTS regulators using HLA-A*0201 class I transgenic mice. Epitope prediction programs, HLA-A*0201 binding assays, and peptide immunization were used to select a set of immunogenic peptides within rtTA and tTS sequences. To identify further the rejection epitopes, we expressed Tet-on protein components in vivo and found a single dominant rtTA186 CTL epitope in the rtTA tetracycline repressor domain. Target cells expressing rtTA were susceptible to CTL lysis, and rtTA expression compromised muscle transgene engraftment. To reduce the occurrence of immune responses to rtTA protein, we mutated the dominant rtTA186 epitope and found that this leads to the appearance of subdominant epitopes. As a result, we think that an epitope modification strategy is not applicable to blunt the immune response in this model. Moreover, the identification of HLA-A*0201 rtTA epitopes allowed us to demonstrate here that the delivery of the Tet-on system with weakly immunogenic rAAV vectors does not trigger primary CTL responses in mice, in contrast to DNA transfer. Altogether, the existence of HLA-A*0201 rtTA epitopes may lead to the occurrence of immune responses depending on vectors and local inflammation in gene therapy applications involving rtTA-based regulatory systems.

Gene therapy in animal models of rheumatoid arthritis: are we ready for the patients?

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints, with progressive destruction of cartilage and bone. Anti-tumour necrosis factor-α therapies (e.g. soluble tumour necrosis factor receptors) ameliorate disease in 60–70% of patients with RA. However, the need for repeated systemic administration of relatively high doses in order to achieve constant therapeutic levels in the joints, and the reported side effects are downsides to this systemic approach. Several gene therapeutic approaches have been developed to ameliorate disease in animal models of arthritis either by restoring the cytokine balance or by genetic synovectomy. In this review we summarize strategies to improve transduction of synovial cells, to achieve stable transgene expression using integrating viruses such as adeno-associated viruses, and to achieve transcriptionally regulated expression so that drug release can meet the variable demands imposed by the intermittent course of RA. Evidence from animal models convincingly supports the application of gene therapy in RA, and the feasibility of gene therapy was recently demonstrated in phase I clinical trials.

Premature stop codons involved in muscular dystrophies show a broad spectrum of readthrough efficiencies in response to gentamicin treatment

The suppression levels induced by gentamicin on premature stop codons, caused by primary nonsense mutations found in muscular dystrophy patients, were assessed using a very sensitive dual reporter gene assay. Results show that: (i) the effect of gentamicin on readthrough is similar in cultured cells and in vivo in murine skeletal muscle; (ii) a wide variability of readthrough efficiency is obtained, depending on the mutation tested; (iii) due to the complexity of readthrough regulation, efficiency cannot be predicted by the nucleotide context of the stop codon; (iv) only a minority of premature stop codons found in patients show a significant level of readthrough, and would thus be amenable to this pharmacological treatment, given our present understanding of the problem. These results probably provide an explanation for the relative failure of clinical trials reported to date using gentamicin to treat diseases due to premature stop codons, and emphasize that preliminary assays in cell culture provide valuable information concerning the potential efficiency of pharmacological treatments.

Evidence of antiangiogenic and antimetastatic activities of the recombinant disintegrin domain of metargidin

Metargidin, a transmembrane protein of the adamalysin family, and integrins, e.g., alpha5beta1 and alphav, are preferentially expressed on endothelial cells on angiogenesis. Furthermore, metargidin interacts with these integrins via its disintegrin domain. In this study, recombinant human disintegrin domain (RDD) was produced in Escherichia coli by subcloning its cDNA into the pGEX-2T vector, and the effect of purified RDD on different steps of angiogenesis was evaluated. At concentrations of 2-10 micro g/ml, RDD exhibited inhibitory activities in a variety of in vitro functional assays, including endothelial cell proliferation and adhesion on the integrin substrates fibronectin, vitronectin, and fibrinogen. RDD (10 micro g/ml) totally abrogated endothelial cell migration and blocked most capillary formation in a three-dimensional fibrin gel. To test RDD efficacy in vivo, the RDD gene inserted into pBi vector containing a tetracycline-inducible promoter was electrotransferred into nude mouse muscle. RDD was successfully synthesized by muscle cells in vivo as shown by immunolabeling and Western blotting. In addition, 78% less MDA-MB-231 tumor growth, associated with strong inhibition of tumor angiogenesis, was observed in athymic mice bearing electrotransferred RDD. Moreover, in the presence of RDD, 74% fewer B16F10 melanoma lung metastases were found in C57BL/6 mice. Taken together, these results identified this RDD as a potent intrinsic inhibitor of angiogenesis, tumor growth, and metastasis, making it a promising tool for use in anticancer treatment.

Regulation of transgene expression in muscles by ultrasound-mediated hyperthermia

Heat-sensitive transgene expression systems have been proposed recently for use in gene therapy to enable both spatial and temporal control of the gene activity. The transgene was put under the control of HSP-related promoters and could be turned on by external heat treatment. While the 'heat activation' phenomenon of the HSP-related promoters in vitro had been well documented, the detailed time response and temporal regulation profile in vivo were not fully understood. We reported here the regulation of transgene luciferase expression in vivo in muscles using a custom-built ultrasound-mediated hyperthermia instrument. The effects of different heating parameters and treatment regimens were evaluated. Optimal activation of gene expression was found at 39 degrees C. Significant tissue damage was observed at 41 degrees C and above, which directly correlated with the greatly reduced gene expression. The gene constructs remained stable and silent in muscle cells, and could be turned on at a later time without losing much activity. Repeated activation was also possible, but required heat treatment at a higher temperature to overcome thermotolerance.

Electrotransfer of human IL-1Ra into skeletal muscles reduces the incidence of murine collagen-induced arthritis

BACKGROUND

It has previously been demonstrated that high levels of gene expression in skeletal muscles can be achieved after direct in vivo electrotransfer of naked plasmid DNA. The purpose of this study is to examine the potential of in vivo electroporation of plasmid DNA encoding human IL-1Ra for the prevention of murine collagen-induced arthritis (CIA).

METHODS

DBA/1 mice were injected in gastrocnemius muscles with plasmid DNA followed by in vivo electroporation. To uncover the optimum conditions of gene transfer, various electric field strengths and different amounts of plasmid DNA were applied. Calf muscles around the injected areas were investigated with histological methods for damage to muscle tissue. The levels of human IL-1Ra expression in the injected area and also in the serum were determined with ELISA for human IL-1Ra. Based on these data, the effects of electrotransfer of plasmid DNA were tested using the murine CIA model. DBA/1 mice were immunized with bovine collagen type II at the base of the tail. On day 21, mice were given a booster injection with the same antigen. Mice were divided into two groups on day 26. One group of mice received plasmid containing the IL-1Ra cDNA sequence, while control mice were given plasmid lacking the IL-1Ra coding sequence. The incidence of arthritis was evaluated by macroscopic analysis, histological analysis, and the levels of inflammatory cytokines.

RESULTS

IL-1Ra expression increased as a function of the electrical field strength and the amount of DNA. 200 V/cm (eight pulses; 20 ms per pulse; 1 Hz) and 15 microg of plasmid DNA per mouse were found to be optimum for gene transfer. After in vivo electroporation, gene expression in both muscle and serum increased gradually, reaching a peak value on day 10. Significant levels of human IL-1Ra expression were maintained for 20 days. Macroscopic analysis showed that the onset of CIA was significantly inhibited by direct electrotransfer of plasmid DNA encoding human IL-1Ra. Histological analysis of knee joints showed that the incidence of arthritis in knee joints was also prevented. The levels of mouse IL-1beta and IL-12 in paws were significantly lower in the group treated with IL-1Ra than those in the control group.

CONCLUSIONS

These results demonstrate that direct electrotransfer of plasmid containing the human IL-1Ra cDNA sequence to skeletal muscle can reduce the incidence of CIA in mice.

Inhibition of established collagen-induced arthritis with a tumour necrosis factor-alpha inhibitor expressed from a self-contained doxycycline regulated plasmid

Tumor necrosis factor (TNF)-alpha is produced by cells of the immune system and is a key mediator in immune and inflammatory reactions. Through interaction with widely expressed receptors (TNF receptor 1 and TNF receptor 2), TNF-alpha is able to orchestrate the expression of a range of downstream proinflammatory molecules. Over the past decade novel biologics that inhibit TNF-alpha have been developed as extremely effective treatments for rheumatoid arthritis. Structurally, these biologics are antibodies, or TNF receptors on an antibody backbone that bind TNF-alpha directly and are delivered to patients by repeated injection. Gene therapy offers an improved approach to delivering biologics as a single administration of their encoding genetic material. In the present study we demonstrate the therapeutic effect of a small molecular weight dimeric TNF receptor 2 (dTNFR) constitutively expressed from plasmid DNA, delivered intramuscularly with electroporation, after disease onset in a collagen-induced arthritis model. Regulated promoters that enable the production of a transgene to be controlled are more suited to the application of gene therapy in the clinic. Regulated expression of dTNFR from the plasmid pGTRTT was also therapeutic in the mouse collagen-induced arthritis model when the inducer doxycycline was also administered, whereas no therapeutic effect was observed in the absence of doxycycline. The therapeutic effect of dTNFR expressed from a constitutive or regulated plasmid was dependent on the degree of disease activity at the time of DNA injection. The observations of this study are considered with regard to the disease model, the magnitude of gene regulation, and the path to clinical application.

Coelectrotransfer to skeletal muscle of three plasmids coding for antiangiogenic factors and regulatory factors of the tetracycline-inducible system: tightly regulated expression, inhibition of transplanted tumor growth, and antimetastatic effect

We describe an approach employing intramuscular plasmid electrotransfer to deliver secretable forms of K1-5 and K1-3-HSA (a fusion of K1-3 with human serum albumin), which span, respectively, five and three of the five kringle domains of plasminogen. A tetracycline-inducible system (Tet-On) composed of three plasmids coding, respectively, for the transgene, the tetracycline transcriptional activator rtTA, and the silencer tTS was employed. K1-3-HSA and K1-5, produced from C2C12 muscle cells, were found to inhibit endothelial cell (HMEC-1) proliferation by 30 and 51%, respectively. In vivo, the expression of the transgene upon doxycycline stimulation was rapid, stable, and tightly regulated (no background expression) and could be maintained for at least 3 months. Blood half-lives of 2.1 and 3.7 days were found for K1-5 and K1-3-HSA, respectively. The K1-5 protein was secreted from muscle into blood at a level of 45 ng/ml, which was sufficient to inhibit MDA-MB-231 tumor growth by 81% in nude mice and B16-F10 melanoma cell lung invasion in C57BL/6 mice by 73%. PECAM-1 immunostaining studies revealed modest tumor vasculature in mice expressing K1-5. In contrast, K1-3-HSA, although secreted into blood at much higher level (250 ng/ml) than K1-5, had no effect on tumor growth.

Gene regulation by tetracyclines. Constraints of resistance regulation in bacteria shape TetR for application in eukaryotes

The Tet repressor protein (TetR) regulates transcription of a family of tetracycline (tc) resistance determinants in Gram-negative bacteria. The resistance protein TetA, a membrane-spanning H+-[tc.M]+ antiporter, must be sensitively regulated because its expression is harmful in the absence of tc, yet it has to be expressed before the drugs' concentration reaches cytoplasmic levels inhibitory for protein synthesis. Consequently, TetR shows highly specific tetO binding to reduce basal expression and high affinity to tc to ensure sensitive induction. Tc can cross biological membranes by diffusion enabling this inducer to penetrate the majority of cells. These regulatory and pharmacological properties are the basis for application of TetR to selectively control the expression of single genes in lower and higher eukaryotes. TetR can be used for that purpose in some organisms without further modifications. In mammals and in a large variety of other organisms, however, eukaryotic transcriptional activator or repressor domains are fused to TetR to turn it into an efficient regulator. Mechanistic understanding and the ability to engineer and screen for mutants with specific properties allow tailoring of the DNA recognition specificity, the response to inducer tc and the dimerization specificity of TetR-based eukaryotic regulators. This review provides an overview of the TetR properties as they evolved in bacteria, the functional modifications necessary to transform it into a convenient, specific and efficient regulator for use in eukaryotes and how the interplay between structure--function studies in bacteria and specific requirements of particular applications in eukaryotes have made it a versatile and highly adaptable regulatory system.

Gene transfer as a future therapy for rheumatoid arthritis

Inhibiting key pathogenic processes within the rheumatoid synovium is a most attractive goal to achieve, and the number of potential intra- and extracellular pathways operative in rheumatoid arthritis (RA) that could be used for a gene therapy strategy is increasing continuously. Gene transfer or gene therapy might also be one of the approaches to solve the problem of long-term expression of therapeutic genes, in order to replace the frequent application of recombinant proteins, in the future. However, at present, gene therapy has not reached a realistic clinical stage, which is mainly due to severe side effects in humans, the complexity of RA pathophysiology and the current state of available gene transfer techniques. On the other hand, novel gene delivery systems are not restricted to vectors or certain types of cells, as mobile cells including macrophages, dendritic cells, lymphocytes and multipotent stem cells can also be used as smart gene transfer vehicles. Moreover, the observation in animal models that application of viral vectors into a joint can exert additional therapeutic effects in nearby joints might also facilitate the transfer from animal to human gene therapy. Future strategies will also examine the potential of novel long-term expression vectors such as lentiviruses and cytomegalovirus (CMV)-based viruses as a basis for future clinical trials in RA.