Local high-capacity adenovirus-mediated mCTLA4Ig and mCD40Ig expression prolongs recombinant gene expression in skeletal muscle

Retargeted and detargeted adenovirus for gene delivery to the muscle

We previously selected muscle binding peptides 12.51 and 12.52 from "context-specific" phage display libraries for introduction into adenovirus (Ad) vectors. In this work, these peptides were inserted into the hypervariable region (HVR) 5 loop of the Ad5 hexon protein to display 720 peptides per virions. HVR-12.51 and 12.52 increased transduction of C2C12 cells up to 20-fold when compared to unmodified Ad5. 12.51 increased in vivo muscle transduction 2 to 7-fold over unmodified Ad after intramuscular injection in mice and hamsters. 12.52 did not increase muscle transduction. Notably, insertion of 12.51 into the hexon reduced liver transduction 80-fold when compared to unmodified Ad5 after intravenous injection. Increased muscle transduction in mice translated into increased immune responses after gene-based vaccination. These data suggest there are merits to retargeting and detargeting benefits to modifying the hexons of Ads with peptide ligands.

Adenovirus-Mediated CTLA4Ig or CD40Ig Gene Transfer Delays Pancreatic Islet Rejection in a Rat-to-Mouse Xenotransplantation Model after Systemic but Not Local Expression

Transient costimulation signal blockade of either CD28/CD80–86 interactions and/or CD40/CD154 interactions can prevent islet rejection in some models of both allo- and xenotransplantation. We have used adenoviruses coding for CTLA4Ig or CD40Ig and compared the efficacy of genetic modification of islets to systemic production through either intramuscular (IM) or intravenous (IV) injection of these vectors in a rat-to-mouse islet transplantation model. When gene transfer was performed into islets, a high level of primary nonfunction was induced. Furthermore, transduced functional grafts were rejected with the same kinetics as nontransduced islets. In contrast, IM AdCTLA4Ig and IV AdCD40Ig significantly delayed rejection (mean survival time of 54 ± 26.9 and 67.6 ± 44.9 days, respectively, vs. 24.3 ± 9.7 days for unmodified islets, p < 0.05). Combination of ex vivo AdCTLA4Ig islet transduction and IV AdCD40Ig did not improve graft survival further. In conclusion, islet graft transduction with adenoviruses coding for costimulation inhibitors resulted in local expression with low serum concentrations of CTLA4Ig or CD40Ig and was unable to protect islet xenografts from rejection. In contrast, IM or IV gene transfer resulted in high serum concentrations of these molecules and was highly efficient in prolonging xenograft survival. These results contrast with the efficacy of AdCTLA4Ig we observed in a rat islet allotransplantation model and suggest that islet xenograft rejection might be more difficult to control.

Effect of rapamycin on immunity induced by vector-mediated dystrophin expression in mdx skeletal muscle

Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene. Therapeutic gene replacement of a dystrophin cDNA into dystrophic muscle can provide functional dystrophin protein to the tissue. However, vector-mediated gene transfer is limited by anti-vector and anti-transgene host immunity that causes rejection of the therapeutic protein. We hypothesized that rapamycin (RAPA) would diminish immunity due to vector-delivered recombinant dystrophin in the adult mdx mouse model for DMD. To test this hypothesis, we injected limb muscle of mdx mice with RAPA-containing, poly-lactic-co-glycolic acid (PLGA) microparticles prior to dystrophin gene transfer and analyzed treated tissue after 6 weeks. RAPA decreased host immunity against vector-mediated dystrophin protein, as demonstrated by decreased cellular infiltrates and decreased anti-dystrophin antibody production. The interpretation of the effect of RAPA on recombinant dystrophin expression was complex because of an effect of PLGA microparticles.

Scaffold-free cell sheet injection results in bone formation

We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three-dimensional computed tomography (3D-CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real-time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction.

Migration of dendritic cells from murine skeletal muscle

To better understand the role of dendritic cells (DCs) in skeletal muscle, we investigated the migration of DCs from murine skeletal muscle and compared that to previously studied footpad (FP) DC trafficking. We adoptively transferred carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled mature DCs to syngeneic mice and followed them in various lymphatic tissues at different time points. Injection of DCs into the tibialis anterior muscle resulted in the peak number of CFSE(+) DCs recovered in spleen at 12h, not at 24h, when the largest number of these cells appeared in the draining lymph nodes. Interestingly, this result for adoptive transfer of DCs to skeletal muscle differs with what is previously reported for adoptive transfer to the FP, a result that we also confirmed in parallel studies. These findings could have a significant impact on (1) understanding muscle diseases with immunological complications such as muscular dystrophies and (2) the immunologic effects of treatments for muscle diseases.

VEGF: an essential mediator of both angiogenesis and endochondral ossification

During bone growth, development, and remodeling, angiogenesis as well as osteogenesis are closely associated processes, sharing some essential mediators. Vascular endothelial growth factor (VEGF) was initially recognized as the best-characterized endothelial-specific growth factor, which increased vascular permeability and angiogenesis, and it is now apparent that this cytokine regulates multiple biological functions in the endochondral ossification of mandibular condylar growth, as well as long bone formation. The complexity of VEGF biology is paralleled by the emerging complexity of interactions between VEGF ligands and their receptors. This narrative review summarizes the family of VEGF-related molecules, including 7 mammalian members, namely, VEGF, placenta growth factor (PLGF), and VEGF-B, -C, -D, -E, and -F. The biological functions of VEGF are mediated by at least 3 corresponding receptors: VEGFR-1/Flt-1, VEGFR-2/Flk-1, VEGFR-3/Flt-4 and 2 co-receptors of neuropilin (NRP) and heparan sulfate proteoglycans (HSPGs). Current findings on endochondral ossification are also discussed, with emphasis on VEGF-A action in osteoblasts, chondroblasts, and chondroclasts/osteoclasts and regulatory mechanisms involving oxygen tension, and some growth factors and hormones. Furthermore, the therapeutic implications of recombinant VEGF-A protein therapy and VEGF-A gene therapy are evaluated. Abbreviations used: VEGF, Vascular endothelial growth factor; PLGF, placenta growth factor; NRP, neuropilin; HSPGs, heparan sulfate proteoglycans; FGF, fibroblast growth factor; TGF, transforming growth factor; HGF, hepatocyte growth factor; TNF, tumor necrosis factor; ECM, extracellular matrix; RTKs, receptor tyrosine kinases; ERK, extracellular signal kinases; HIF, hypoxia-inducible factor.

The use of recombinant adeno-associated virus for skeletal gene therapy

OBJECTIVES

To provide a comprehensive literature review describing recent developments of the recombinant adeno-associated virus (rAAV) vector and exploring the therapeutic application of rAAV for bone defects, cartilage lesions and rheumatoid arthritis.

DESIGN

Narrative review.

RESULT

The review outlines the serotypes and genome of AAV, integration and life cycle of the rAAV vectors, the immune response and regulating system for AAV gene therapy. Furthermore, the advancements of rAAV gene therapy for bone growth together with cartilage repair are summarized.

CONCLUSION

Recombinant adeno-associated virus vector is perceived to be one of the most promising vector systems for bone and cartilage gene therapy approaches and further investigations need to be carried out for craniofacial research.

Distribution and expression of recombinant plasmid encoding chicken interleukin-2

A plasmid DNA that encodes chicken interleukin-2 (pCI-ChIL-2-EGFP) was investigated for its distribution and expression after intramuscular (i.m.) injection in chickens. After the i.m. injection, serum distribution was detectable from 2 h post inoculation (p.i.), peaked at 8 h p.i., and disappeared at 7 days p.i. The plasmid DNA was also observed in several organs including heart, liver, lung, spleen, bursa and inoculated muscle at different time points, but at 19 days p.i. the plasmid DNA was not found in any organ except inoculated muscle. Fluorescence of enhanced green fluorescent protein (EGFP) was found in cytoplasm and nucleus of cultured Vero cells, chicken embryo fibroblasts and peripheral blood lymphocytes, which were transfected in vitro with the plasmid DNA or in vivo with Lipofectamine. The expression profile of the fusion gene (ChIL-2-EGFP) in vivo was measured by RT-PCR, ELISA and fluorescence microscopy. The EGFP expression was detected from 8 h p.i. to 14 days p.i. and peaked at 5 days p.i., when the number of EGFP-expression myocytes was about 5% in the injected site. These results demonstrate that intramuscular administration of plasmid DNA leads to widespread distribution and long-term expression in vivo.

Co-expression of sCD40LIg and CTLA4Ig mediated by adenovirus prolonged mouse skin allograft survival

OBJECTIVE

To investigate the role of simultaneous blockade of CD40/CD40L and B7/CD28 pathways in the immune tolerance via co-expression of sCD40LIg and CTLA4Ig mediated by replication-defective adenovirus.

METHODS

Ad-sCD40LIg-IRES(2)-CTLA4Ig, replication-defective adenovirus co-expressing sCD40LIg and CTLA4Ig, was constructed and identified. The co-expression of sCD40LIg and CTLA4Ig was evaluated with confocal laser scanning microscope and Western blotting. Skin transplantations of C57BL/6 to BALB/c mice were performed. PBS, Ad-Shuttle-CMV and Ad-sCD40LIg-IRES(2)-CTLA4Ig were administered. Skin graft survival was monitored and the mRNA expression of both genes was evaluated in the skin allografts.

RESULTS

Ad-sCD40LIg-IRES(2)-CTLA4Ig was constructed successfully and identified. The co-expression of sCD40LIg and CTLA4Ig was identified with confocal laser scanning microscopy and Western blotting. Compared to the skin graft mean survival time (MST) of non-treated group ((5.75+/-0.71) d) or Ad-Shuttle-CMV-treated group ((5.50+/-0.53) d), the skin graft MST was dramatically prolonged in the Ad-sCD40LIg-IRES(2)-CTLA4Ig-treated group ((16.38+/-1.19) d, P<0.001). The mRNA expression of both genes was detected.

CONCLUSION

Ad-sCD40LIg-IRES(2)-CTLA4Ig, a replication-defective adenovirus carrying genes encoding sCD40LIg and CTLA4Ig, was constructed. Simultaneous blockade of CD40/CD40L and B7/CD28 costimulatory pathway mediated by replication-defective adenovirus significantly prolonged skin allograft survival in mice.

Immunomodulation of transgene responses following naked DNA transfer of human factor VIII into hemophilia A mice

A robust humoral immune response against human factor VIII (hFVIII) following naked DNA transfer into immunocompetent hemophilia A mice completely inhibits circulating FVIII activity despite initial high-level hFVIII gene expression. To prevent this undesirable response, we compared transient immunomodulation strategies. Eight groups of mice (n = 4-9 per group) were treated with naked DNA transfer of pBS-HCRHPI-hFVIIIA simultaneously with immunosuppressive reagents that included cyclosporine A (CSA), rapamycin (RAP), mycophenylate mofetil (MMF), a combination of CSA and MMF, a combination of RAP and MMF, a monoclonal antibody against murine CD40 ligand (MR1), recombinant murine Ctla4Ig, and a combination of MR1 and Ctla4Ig. All animals except those receiving only CSA exhibited delayed or absent immune responses against hFVIII. The most effective immunosuppressive regimen, the combination of Ctla4Ig and MR1, prevented inhibitor formation in 8 of 9 animals; the ninth had transient low-titer antibodies. All 9 mice of this group produced persistent, therapeutic levels of hFVIII for more than 6 months. When challenged with the T-dependent antigen bacteriophage Phix174, tolerized mice exhibited normal primary and secondary antibody responses, suggesting that transient immunomodulation to disrupt B/T-cell interaction at the time of plasmid injection effectively promoted long-term immune tolerance specific for hFVIII.

Suppression of inflammation by dexamethasone prolongs adenoviral vector-mediated transgene expression in murine nasal mucosa

CONCLUSION

The results of this study demonstrate that suppression of inflammation by dexamethasone attenuates the host immune response against adenoviral-mediated gene transfection and thereby prolongs transgene expression in murine nasal mucosa.

OBJECTIVES

Gene transfer using a recombinant adenovirus is a good tool for research and clinical applications, but the immune response to adenoviral vectors can induce inflammation and loss of transgene expression in transfected tissues. In this study we investigated the effects of dexamethasone-induced immunosuppression on adenovirus gene transfer in the nasal mucosa of the mouse.

MATERIAL AND METHODS

We administered the recombinant adenovirus Ax1CAlacZ, which encodes Escherichia coli beta-galactosidase (lacZ gene), to the nasal mucosa of mice treated with or without i.p. dexamethasone and evaluated the expression of the lacZ gene on Days 2, 4, 7, 14 and 28. The nasal mucosa was dissected out, and the mRNA level was measured using a LightCycler. The expression of the exogenous beta-galactosidase was detected by means of histochemistry.

RESULTS

Dexamethasone treatment significantly increased the mRNA level compared with that in the controls at Days 4, 7 and 14. Histochemistry showed that the expression of beta-galactosidase protein persisted in the dexamethasone-treated mice at Days 7 and 14 but had diminished almost to nothing in the control group.

Comparison of high-capacity and first-generation adenoviral vector gene delivery to murine muscle in utero

In utero gene delivery could offer the advantage of treatment at an early stage for genetic disorders such as Duchenne muscular dystrophy (DMD) in which the inevitable process of muscle degeneration is already initiated at birth. Furthermore, treatment of fetal muscle with adenoviral (Ad) vectors is attractive because of a high density of Ad receptors, easy vector accessibility due to immaturity of the basal lamina and the possibility of treating stem cells. Previously, we demonstrated the efficient transduction of fetal muscle by high-capacity Ad (HC-Ad) vectors. In this study, we compared HC-Ad and first-generation Ad (FG-Ad) vectors for longevity of lacZ transgene expression, toxicity and induction of immunity after direct vector-mediated in utero gene delivery to fetal C57BL/6 mice muscle 16 days after conception (E-16). The total amount of beta-galactosidase (betagal) expressed from the HC-Ad vector remained stable for the 5 months of the study, although the concentration of betagal decreased due to muscle growth. Higher survival rates that reflect lower levels of toxicity were observed in those mice transduced with an HC-Ad vector as compared to an FG-Ad vector. The toxicity induced by FG-Ad vector gene delivery was dependent on mouse strain and vector dose. Animals treated with either HC-Ad and FG-Ad vectors developed non-neutralizing antibodies against Ad capsid and antibodies against betagal, but these antibodies did not cause loss of vector genomes from transduced muscle. In a mouse model of DMD, dystrophin gene transfer to muscle in utero using an HC-Ad vector restored the dystrophin-associated glycoproteins. Our results demonstrate that long-term transgene expression can be achieved by HC-Ad vector-mediated gene delivery to fetal muscle, although strategies of vector integration may need to be considered to accommodate muscle growth.

Patterns of transgene expression and viral clearance from the transplanted liver following ex vivo adenovirus-mediated gene transfer

BACKGROUND/AIMS

In the rat liver transplant model, the liver graft can be transduced ex vivo by adenovirus encoding CTLA-4Ig (AdCTLA-4Ig) to achieve high level of immunosuppression in the liver after transplantation. To characterize the pattern of transgene expression following ex vivo gene transfer to the liver and examine whether immunosuppression would promote adenovirus persistence, we followed the life span of vector DNA and transgene expression in the transplanted liver.

METHODS

Rat liver grafts were perfused ex vivo with adenovirus carrying the reporter gene beta-galactosidase (AdlacZ). The period of transgene expression was assessed at predetermined intervals after transplantation into syngeneic, allogeneic or nude (athymic) recipients. Clearance of vector DNA was assessed by PCR analysis of liver DNA after transplantation.

RESULTS

Graft transduction with AdCTLA-4Ig or systemic cyclosporine treatment effectively abrogated the alloimmune response but did not result in sustained lacZ expression. The course of viral DNA clearance from the liver was also unaffected by immunosuppression as was the implied nucleolytic cleavage of viral DNA.

CONCLUSIONS

In the transplant setting, local expression of CTLA-4Ig or systemic immunosuppression does not solve the problem of viral clearance from the liver. Non-adaptive immune mechanisms may have a significant role in the host response to adenovirus after liver transplantation.

Sustained Muscle Expression of Dystrophin from a High-Capacity Adenoviral Vector with Systemic Gene Transfer of T Cell Costimulatory Blockade

Adenoviral vector (Ad)-mediated gene delivery of normal, full-length dystrophin to skeletal muscle provides a promising strategy for the treatment of Duchenne muscular dystrophy (DMD). However, cellular and humoral immune responses induced by vector gene transfer limit the application of this approach. Blockade of the costimulatory interaction between naïve T cells and antigen-presenting cells has proven to be a successful means to diminish immunity induced by gene transfer. In this study we explore the potential of supplementing dystrophin gene delivery to dystrophin-deficient Dmd mouse skeletal muscle with systemic gene delivery of CTLA4Ig and CD40Ig molecules to effect costimulatory blockade. We found that systemic administration of a high-capacity Ad (HC-Ad) vector carrying murine CTLA4Ig (AdmCTLA4Ig) either alone or codelivered with an HC-Ad vector carrying murine CD40Ig (AdmCD40Ig) provided sustained expression of recombinant full-length murine dystrophin from an HC-Ad vector carrying the dystrophin cDNA (AdmDys). The level of AdmDys vector genomes remained stable in animals cotreated with systemic delivery of vectors carrying molecules to block costimulation. In addition, muscle CD4(+) and CD8(+) T cell infiltrates and Th1 cytokine production by splenocytes were reduced. The production of neutralizing antibody against Ad vector was significantly inhibited in mice receiving systemic codelivery of both AdmCTLA4Ig and AdmCD40Ig, but not in the mice treated with AdmCTLA4Ig alone. The results suggested that coblockade of both CD28/B7 and CD40L/CD40 costimulatory pathways is required for effective inhibition of the Ad vector-induced humoral immune response in Dmd mice, whereas blockade of CD28/B7 alone by murine CTLA4Ig would be sufficient for prolonged dystrophin expression in treated muscle.

Long term transgene expression by hepatocytes transduced with retroviral vectors requires induction of immune tolerance to the transgene

BACKGROUND/AIMS

Gene therapy for inherited liver diseases requires permanent expression of the therapeutic gene. However, in vivo liver transduction with retroviral vectors triggers an immune elimination of transduced hepatocytes. Here we investigated whether immune response could be prevented by treatment with compounds known to induce tolerance in organ transplantation: CTLA4Ig and LF-15-0195.

METHODS

CTLA4Ig was administered either via i.p. injection of the drug or by i.m. injection of recombinant adenoviruses encoding CTLA4Ig. LF-15-0195 was administered i.p. All animals were subjected to partial hepatectomy and received beta-galactosidase retroviral vectors intravenously. Appearance of anti-beta-galactosidase antibodies was monitored and the number of positive hepatocytes was assessed at day 7 and at sacrifice.

RESULTS

No beta-galactosidase antibodies were detected as long as CTLA4Ig was detectable in serum. Short-term treatment with CTLA4Ig induced tolerance in a significant proportion of animals only at high dose (1 mg/kg). Administration of CTLA4Ig adenovectors resulted in prolonged secretion of CTLA4Ig and permanent absence of anti-beta-galactosidase antibodies. LF-15-0915 administration achieved tolerance in some animals.

CONCLUSIONS

In conclusion, manipulation of the immune system at the time of virus delivery using clinically relevant tolerance-inducing protocols is a promising approach to achieve long term expression after retrovirus-mediated gene transfer to the liver.

CTLA4Ig delivered by high-capacity adenoviral vector induces stable expression of dystrophin in mdx mouse muscle

Adenoviral (Ad) vector-mediated gene delivery of normal, full-length dystrophin to skeletal muscle provides a promising strategy for the treatment of Duchenne muscular dystrophy (DMD), an X-linked recessive, dystrophin-deficient muscle disease. Studies in animal models suggest that successful DMD gene therapy by Ad vector-mediated gene transfer would be precluded by cellular and humoral immune responses induced by vector capsid and transgene proteins. To address the immunity induced by Ad vector-mediated dystrophin gene delivery to dystrophic muscle, we developed high-capacity adenoviral (HC-Ad) vectors expressing mouse dystrophin driven by the muscle creatine kinase promoter (AdmDys) and mCTLA4Ig (AdmCTLA4Ig) individually, or together from one vector (AdmCTLA4Ig/mDys). We found stable expression of dystrophin protein in the tibialis anterior muscles of mdx mice, coinjected with AdmCTLA4Ig and AdmDys, or injected alone with AdmCTLA4Ig/mDys, whereas the expression of dystrophin protein in the control group coinjected with AdmDys and an empty vector decreased by at least 50% between 2 and 8 weeks after administration. Additionally, we observed reductions in Ad vector-induced Th1 and Th2 cytokines, Ad vector-specific cytotoxic T lymphocyte activation and neutralizing anti-Ad antibodies in both experimental groups that received a mCTLA4Ig-expressing vector as compared to the control group. This study demonstrates that the coexpression of mCTLA4Ig and dystrophin in skeletal muscle provided by HC-Ad vector-mediated gene transfer can provide stable expression of dystrophin in immunocompetent, adult mdx mouse muscle and applies a potentially powerful strategy to overcome adaptive immunity induced by Ad vector-mediated dystrophin gene delivery toward the ultimate goal of treatment for DMD.

Blocking B7 and CD40 co-stimulatory molecules decreases antiviral T cell activity

Inhibition of co-stimulatory signals for T cells by interrupting CD80/CD86-CD28 and CD40-CD154 interactions is a promising approach to prevent transplant rejection and to induce graft tolerance. However, this tolerizing treatment might affect T cell reactivity towards all the antigens to which the immune system is exposed during treatment. We addressed the question whether such inhibition of co-stimulatory ligands on human antigen presenting cells (APC) would affect T cell reactivity against a virus. This was tested in an in vitro system with freshly isolated human monocytes transduced with adenovirus (ad) containing either murine interferon-gamma (mIFN-gamma) or green fluorescent protein (GFP) as marker transgene. T cells co-cultured with transduced monocytes proliferated and produced cytokines. These 'primed' T cells had strong antiviral activity as they subsequently killed ad/GFP-transduced monocytes and reduced mIFN-gamma accumulation in coculture with ad/mIFN-transduced monocytes. However, if priming had occurred in the presence of blocking anti-CD40/CD80/CD86 MoAbs, generation of this antiviral activity was completely prevented. Moreover, T cells primed in the absence of co-stimulatory cells failed to proliferate upon restimulation with adenovirus-transduced monocytes. The results confirm that co-stimulatory signals from APC are required for efficient induction of antiviral T cell activity and point to a potential infectious risk of blocking co-stimulatory signals.

Osteogenesis in rats induced by a novel recombinant helper-dependent bone morphogenetic protein-9 (BMP-9) adenovirus

BACKGROUND

Although recombinant first-generation BMP adenoviruses can induce ectopic bone formation in immune deficient animals, the osteoinductive activity of these BMP vectors is reduced in immune competent animals. Helper-dependent adenoviral vectors have been developed to decrease the immune response and, therefore, increase gene expression in immune competent animals compared with first-generation vectors. In the present study, the osteoinductive activity of a helper-dependent GFP and BMP-9 adenoviral vector (ADGBMP9) was evaluated in vitro and in vivo.

METHODS

Initially, purified ADGBMP9 was used to transduce human mesenchymal stem cells (hMSCs) and the alkaline phosphatase activity was determined as a measure of osteogenic activity. The vector was then injected into the thigh muscle of athymic nude and Sprague-Dawley rats, and CT scans and histology were subsequently used to assess bone formation.

RESULTS

In vitro, ADGBMP9 was capable of inducing alkaline phosphatase expression in hMSCs. In vivo in athymic nude and Sprague Dawley rats, ADGBMP9 initiated the process of bone formation 3 days after percutaneous injection into the thigh musculature. The rats demonstrated intramuscular ectopic ossification in CT scans as early as day 9 post viral injection and ultimately formed significant amounts of ectopic bone. Histologically, the induced bone was formed via normal endochondral mechanisms.

CONCLUSIONS

A helper-dependent adenoviral vector containing the BMP-9 and GFP genes has significant osteoinductive activity in both athymic nude and immune competent rats. Additional direct and ex vivo BMP gene therapy studies are required to assess the vector's activity in more animal models.

Adeno-associated virus-mediated bone morphogenetic protein-4 gene therapy for in vivo bone formation

Adeno-associated virus (AAV) is so far the most valuable vehicle for gene therapy because it has no association with immune response and human disease. The present study was conducted to investigate the feasibility of AAV-mediated BMP4 gene transfer for bone formation. In vitro study suggested that AAV-BMP4 vectors could transduce myoblast C2C12 cells and produce osteogenic BMP4. In vivo study demonstrated that new bone formation could be induced by direct injection of AAV-BMP4 into the skeletal muscle of immunocompetent rats. Histological analysis revealed that the newly formed bone was induced through endochondral mechanism. Immunohistochemical staining further demonstrated that AAV-BMP4 gene delivery could mediate long-term transduction, and the involvement of BMP4 expression was responsible for the endochondral ossification. This study is, to our knowledge, the first report in the field of AAV-based BMP gene transfer and should be promising for clinical orthopaedic applications.

Gene therapy for new bone formation using adeno-associated viral bone morphogenetic protein-2 vectors

Previous reports have suggested that bone morphogenetic protein (BMP) gene therapy could be applied for in vivo bone regeneration. However, these studies were conducted either using immunodeficient animals because of immunogenicity of adenovirus vectors, or using ex vivo gene transfer technique, which is much more difficult to handle. Adeno-associated virus (AAV) is a replication-defective virus without any association with immunogenicity and human disease. This study was conducted to investigate whether orthotopic new bone formation could be induced by in vivo gene therapy using AAV-based BMP2 vectors. To test the feasibility of this approach, we constructed an AAV vector carrying human BMP2 gene. Mouse myoblast cells (C2C12) transduced with this vector could produce and secrete biologically active BMP2 protein and induce osteogenic activity, which was confirmed by ELISA and alkaline phosphatase activity assay. For in vivo study, AAV-BMP2 vectors were directly injected into the hindlimb muscle of immunocompetent Sprague-Dawley rats. Significant new bone under X-ray films could be detected as early as 3 weeks postinjection. The ossification tissue was further examined by histological and immunohistochemical analysis. This study is, to our knowledge, the first to establish the feasibility of AAV-based BMP2 gene therapy for endochondral ossification in immunocompetent animals.

Gene therapy progress and prospects: adenoviral vectors

In September 1999, the perceptions of the use of adenoviral (Ad) vectors for gene therapy were altered when a patient exposed via the hepatic artery to a high dose of adenoviral vector succumbed to the toxicity related to vector administration. Appropriately, concerns were raised about continued use of the Ad vector system and, importantly, there were increased efforts to more fully understand the toxicity. Today it is recognized that there is no ideal vector system, and that while Ad vectors are not suitable for all applications, the significant advantages over other vector systems including efficient transduction of a variety of cell types, both quiescent and dividing, make it optimal for certain applications. These include protocols where high levels of short-term expression are sufficient to provide a therapeutic benefit. Potential target applications include therapeutic angiogenesis, administration into immune-privileged sites such as the CNS, or treatments where the adjuvant effect of adenovirus can be of benefit such as cancer vaccines. Broader applicability of Ad vectors will require resolution of toxicity issues. This review will therefore focus on studies conducted over the last 2 years that have advanced our understanding of the toxicity associated with Ad vectors, studies that have employed methods to reduce toxicity and improvements in Ad vectors themselves that will reduce toxicity by one of several mechanisms. These mechanisms include retargeting vector to the tissue of interest, minimizing or eliminating viral gene expression that is thought to result in loss of transduced cells, or by methods that seek to reduce the vector dose required for therapeutic benefit. An area where there remains significant room for improvement is when readministration of vector is required because transgene expression has decreased to background levels.

Persistent hepatic expression of human apo A-I after transfer with a helper-virus independent adenoviral vector

Gene transfer with 'gutted' vectors is associated with persistent transgene expression and absence of hepatotoxicity, but the requirement of helper viruses hampers efficient production and leads to contamination of viral batches with these helper-viruses. In the present study, gene transfer with a helper-virus independent E(1)/E(3)/E(4)-deleted adenoviral vector induced persistent expression of human apo A-I (200 +/- 16 mg/dl at day 35, 190 +/- 15 mg/dl at 4 months, 170 +/- 16 mg/dl at 6 months) and stable transgene DNA levels (3.5 +/- 0.60 at day 35, 3.3 +/- 0.39 at 4 months, 3.1 +/- 0.47 mg/dl at 6 months) in C57BL/6 mice in the absence of significant toxicity. The vector contained the 1.5 kb human alpha(1)-antitrypsin promoter in front of the genomic human apo A-I sequence and four copies of the human apo E enhancer (hAAT.gA-I.4xapoE) and was deleted in E(1), E(3) and E(4). Reintroduction of E(4) ORF 3 and E(4) ORF 4 in the viral backbone caused a more than four-fold decline of transgene DNA between day 35 and 4 months after transfer both in wild-type and in C57BL/6 SCID and C57BL/6 Rag-1(-/-) mice, indicating that the effect of E(4) ORF 3 and E(4) ORF 4 is independent of a cellular immune response against viral epitopes. Co-injection of an E(1)-deleted vector containing no expression cassette and the E(1)/E(3)/E(4)-deleted vector containing the hAAT.gA-I.4xapoE expression cassette indicated that E(4) gene products destabilize transgene DNA in trans. Gene transfer with an E(1)/E(3)/E(4)-deleted vector containing only E(4) ORF 3 and the hAAT.gA-I.4xapoE expression cassette was associated with transgene DNA decline, but not with hepatotoxicity, indicating that transgene DNA persistence and hepatotoxicity are dissociated processes. After transfer with E(1)/E(3)/E(4)-deleted vectors containing expression cassettes with a different promoter or a different position of the apo E enhancers, transgene DNA levels were less stable than after transfer with the vector containing hAAT.gA-I.4xapoE, indicating that the expression cassette is an important determinant of episomal stability. In conclusion, gene transfer with an E(1)/E(3)/E(4)-deleted vector containing the hAAT.gA-I.4xapoE expression cassette induces persistent expression of human apo A-I in the absence of hepatotoxicity. Transgene DNA turnover is independent of an adaptive cellular immune response against viral epitopes and of hepatotoxicity. E(1)/E(3)/E(4)-deleted vectors containing transgenes under control of the hAAT promoter in combination with four copies of the human apo E enhancer may be suitable for hepatocyte-specific overexpression of transgenes after gene transfer. doi:10.1038/sj.gt.3301824

In vivo new bone formation by direct transfer of adenoviral-mediated bone morphogenetic protein-4 gene

Previous studies have demonstrated that bone morphogenetic protein-4 (BMP4) could participate in vivo endochondral ossification and is one of the main local contributing factors in the early stage of fracture healing. To investigate the effectiveness of BMP4 gene transfer, we constructed an adenoviral vector, Ad-BMP4, and evaluated its osteoinduction activity both in vitro and in vivo. In vitro study suggested that this vector could efficiently transduce mouse myoblast C2C12 cells and produce osteogenic BMP4 protein, as confirmed by immunofluorescence analysis and alkaline phosphatase activity assay. For in vivo study, Ad-BMP4 was directly injected into the hind limb muscles of male athymic nude rats. Visible new bone formation under X-ray films could be detected as early as three weeks post-injection. The bone tissue was further analyzed by histological staining and revealed a typical remodeled bone structure. In conclusion, this study is the first to establish the feasibility of adenovirus-based BMP4 gene therapy for bone regeneration.

Experimental and therapeutic approaches to muscular dystrophies

PURPOSE OF REVIEW

Most patients suffering from muscular dystrophies can now obtain a precise diagnosis of their underlying molecular defect, but no efficient treatment to prevent disability and death. This review summarizes recent progress towards developing efficient treatments for these severe diseases.

RECENT FINDINGS

Different levels of progress have been achieved in three main approaches: gene therapy, cell therapy and pharmacological therapy. Gene therapy has progressed by improving different vectors for gene delivery. Adenoviruses (mainly high capacity versions) and adeno-associated viruses were the most explored viral vectors. Progress was made in understanding the factors needed for an efficient transfection of muscle. An understanding of protein structure and function in muscular dystrophies has allowed elegant examples of protein engineering as a way of gene therapy. Non-viral vectors for gene transfer, targeted gene modification and transcription modulation have also been explored recently. Cell therapy (myogenic-cell transplantation) progressed in understanding myoblast transplantation in primates for human applications, evaluating protocols for the control of graft rejection, understanding the biology of donor myogenic cells, and searching for alternative sources of donor cells. Three clinical trials using pharmacological approaches (anabolic agents and gentamicin) show very poor or negative results. Other pharmacological approaches (upregulation of alternative therapeutic proteins) are still being researched in mice.

SUMMARY

This panoply of experimental approaches covered all the current possibilities of attacking the problem of treating muscular dystrophies. It is expected that one or more will progress to provide efficient tools for the ultimate clinical goal: to prolong function and life in severe muscular dystrophy patients.

Systemic delivery of a high-capacity adenoviral vector expressing mouse CTLA4Ig improves skeletal muscle gene therapy

Adenoviral vectors (AdV) are promising vectors for gene transfer of skeletal muscle. To alleviate humoral and cellular immune responses that limit successful gene transfer, the present study determined the route of administration of AdmCTLA4Ig (an adenovirus that encodes a fusion protein of mouse cytotoxic T lymphocyte-associated protein 4 (CTLA4) and the Fc protion of immunoglobulin G (IgG), CTLA4Ig) that provided optimal AdV-mediated immunosuppression. AdmCTLA4Ig was administered either intramuscularly (i.m.), intravenously (i.v.), or in the footpad (f.p.) of mice that simultaneously received an i.m. injection of an AdV encoding enhanced green fluorescent protein (AdEGFP). EGFP expression in muscle and serum levels of CTLA4Ig were higher in the i.v. and f.p. groups than the i.m. group 30 days after treatment. The i.v. and f.p. groups showed lower levels of CD4(+) and CD8(+) T-cell infiltration and decreased interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) production by splenocytes. The T helper cell (Th) 2 cytokine, interleukin 4 (IL-4), was increased 30 days after treatment in the i.v. group. Neutralizing antibodies to AdV were lower in the i.v. and f.p. groups, whereas total antibodies to AdV and EGFP were lower only in the f.p. group. Our results suggest that the optimal route of administration of AdmCTLA4Ig is i.v., providing at least 2 months of stable transgene expression in muscle. The inhibition of the cellular immune response, especially the Th1 response, appeared to play a critical role in prolonging transgene expression. These results suggest that AdV-mediated delivery of targeted immune suppression will be a useful adjunct to muscle gene delivery.

Immune response to full-length dystrophin delivered to Dmd muscle by a high-capacity adenoviral vector

Adenoviral vector-mediated gene transfer to skeletal muscle is a promising potential treatment for Duchenne muscular dystrophy. However, the immunological response to viral antigens and the therapeutic protein expressed by the delivered gene could prevent effective treatment. In this study, we investigated the immune response induced by adenoviral and dystrophin antigens presented by high-capacity adenoviral vector-mediated dystrophin and beta-galactosidase delivery to skeletal muscle of a mouse model that is both dystrophin-deficient and lacZ transgenic. Direct intramuscular gene delivery of the high-capacity adenoviral vector encoding full-length murine dystrophin resulted in stable expression of recombinant dystrophin for 5 months in mice treated as neonates and for 4 weeks in mice treated as adults. We observed neutralizing antibody to adenoviral antigens only in mice treated as adults and not in mice treated as neonates. This suggested that adenoviral antigens were only presented at the time of vector administration when the neonatal immune system was not yet mature. In contrast, antibodies to dystrophin were observed both in mice treated as neonates and in mice treated as adults. The development of an anti-dystrophin antibody response in mice treated with the high-capacity adenoviral vector as neonates suggested that dystrophin antigens were presented to the immune system at a time remote from the gene delivery, when the immune system was mature. Interestingly, an antibody response against beta-galactosidase developed late in the course of mice treated with the high-capacity adenoviral vector as neonates, suggesting a loss of tolerance to beta-galactosidase, a self-antigen in these transgenic mice. Our results suggest that future human trials of dystrophin gene delivery will need to address the potential for immunity induced by ongoing segmental degeneration of partially treated muscle fibers and presentation of recombinant dystrophin antigens in the context of a Duchenne muscular dystrophy patient.

Dangerous liaisons: the role of "danger" signals in the immune response to gene therapy

Recent studies in gene transfer suggest that the innate immune system plays a significant role in impeding gene therapy. In this review, we examine factors that might influence the recruitment and activation of the innate system in the context of gene therapy. We have adopted a novel model of immunology that contends that the immune system distinguishes not between self and nonself, but between what is dangerous and what is not dangerous. In taking this perspective, we provide an alternative and complementary insight into some of the failures and successes of current gene therapy protocols.

Prolonged blockade of CD40-CD40 ligand interactions by gene transfer of CD40Ig results in long-term heart allograft survival and donor-specific hyporesponsiveness, but does not prevent chronic rejection

Previous work on blockade of CD40-CD40 ligand interaction in mice and primates with anti-CD40 ligand mAbs has resulted in a moderate prolongation of allograft survival without the development of true allograft tolerance. In this study, we show in rats that adenovirus-mediated gene transfer of CD40Ig sequences into the graft resulted in prolonged (>200 days) expression of CD40Ig and in long-term (>300 days) survival. Recipients expressing CD40Ig displayed strongly (>90%) inhibited mixed leukocyte reactions and alloantibody production at early (days 5 and 17) and late time points (>100 day) after transplantation, but showed limited inhibition of leukocyte infiltration and cytokine production as evaluated by immunohistology at early time points (day 5). Recipients of long-surviving hearts showed donor-specific hyporesponsiveness since acceptance of second cardiac allografts was donor specific. Nevertheless, long-term allografts (>100 days) displayed signs of chronic rejection vasculopathy. Occluded vessels showed leukocyte infiltration, mainly composed of CD4(+) and CD8(+) cells, macrophages, and mast cells. These recipients also showed antidonor CTL activity. Recipients expressing CD40Ig did not show nonspecific immunosuppression, as they were able to mount anticognate immune responses that were partially inhibited at early time points and were normal thereafter. We conclude that gene transfer-mediated expression of CD40Ig resulted in a highly efficient inhibition of acute heart allograft rejection in rats. This treatment induced donor-specific inhibition of certain alloreactive mechanisms in the short-, but not the long-term, which resulted in long-term survival of allografts concomitant with the development of chronic rejection.