The adeno-associated virus vector for orthopaedic gene therapy

Synthetic scaffold coating with adeno-associated virus encoding BMP2 to promote endogenous bone repair

Biomaterial scaffolds functionalized to stimulate endogenous repair mechanisms via the incorporation of osteogenic cues offer a potential alternative to bone grafting for the treatment of large bone defects. We first quantified the ability of a self-complementary adeno-associated viral vector encoding bone morphogenetic protein 2 (scAAV2.5-BMP2) to enhance human stem cell osteogenic differentiation in vitro. In two-dimensional culture, scAAV2.5-BMP2-transduced human mesenchymal stem cells (hMSCs) displayed significant increases in BMP2 production and alkaline phosphatase activity compared with controls. hMSCs and human amniotic-fluid-derived stem cells (hAFS cells) seeded on scAAV2.5-BMP2-coated three-dimensional porous polymer Poly(ε-caprolactone) (PCL) scaffolds also displayed significant increases in BMP2 production compared with controls during 12 weeks of culture, although only hMSC-seeded scaffolds displayed significantly increased mineral formation. PCL scaffolds coated with scAAV2.5-BMP2 were implanted into critically sized immunocompromised rat femoral defects, both with or without pre-seeding of hMSCs, representing ex vivo and in vivo gene therapy treatments, respectively. After 12 weeks, defects treated with acellular scAAV2.5-BMP2-coated scaffolds displayed increased bony bridging and had significantly higher bone ingrowth and mechanical properties compared with controls, whereas defects treated with scAAV2.5-BMP2 scaffolds pre-seeded with hMSCs failed to display significant differences relative to controls. When pooled, defect treatment with scAAV2.5-BMP2-coated scaffolds, both with or without inclusion of pre-seeded hMSCs, led to significant increases in defect mineral formation at all time points and increased mechanical properties compared with controls. This study thus presents a novel acellular bone-graft-free endogenous repair therapy for orthotopic tissue-engineered bone regeneration.

Effects of adeno-associated virus-2-mediated human BMP-7 gene transfection on the phenotype of nucleus pulposus cells

Bone morphogenetic protein-7 (BMP-7) was found to stimulate the synthesis of proteoglycans (PGs) and collagen type II. To increase the biological function of the nucleus pulposus (NP) cells, the Ad-hBMP-7 vector was also successfully constructed and transfected NP cells. However, the disadvantages of adenovirus limit the usefulness of the Ad-hBMP7 vector for clinical application. The rAAV2 vector has empirical advantages, especially for clinical use, to transfer exogenous genes into cells. The purpose of this study was to first determine whether a rAAV2-hBMP-7 vector could be used to transfect canine NP cells and effect on the biological functions of canine NP cells. The canine NP cells transfected by the rAAV-BMP7 were assessed semi-quantitatively for BMP-7 expression with real-time PCR and westernbloting. Aggrecan and collagens type I and II secreted by the NP cells were qualitatively assessed at 4, 7, and 14 days post-transfection in the transfection and control groups. We found that rAAV2 can successfully transfer the hBMP-7 gene into canine NP cells. NP cells transfected by the rAAV-hBMP-7 vector express hBMP-7 for at least 14 days. At 7 and 14 days, the expressed hBMP-7 promotes a remarkable and significant accumulation of both proteoglycans (42% and 77% higher than non-transfected cells) (p<0.05) and collagen type II (63% and 94% higher than non-transfected cells) (p<0.05). Thus, we could speculate that the rAAV-based gene delivery technique promotes the expression of proteoglycans and collagen type II of nucleus pulposus cells. Moreover, this technique may be applicable for the future treatment of degenerative disc disease.

Investigation of the peak action wavelength of light-activated gene transduction

Light-activated gene transduction (LAGT) is an approach to localize gene therapy via preactivation of cells with UV light, which facilitates transduction by recombinant adeno-associated virus vectors. Prior studies demonstrated that UVC induces LAGT secondary to pyrimidine dimer formation, while UVA induces LAGT secondary to reactive oxygen species (ROS) generation. However, the empirical UVB boundary of these UV effects is unknown. Thus, we aimed to define the action spectra for UV-induced LAGT independent of DNA damage, and determine an optimal wavelength to maximize safety and efficacy. Results: UV at 288, 311 and 320nm produced significant dose-dependent LAGT effects, of which the maximum (800-fold) was observed with 4kJ/m² at 311nm. Consistent with its robust cytotoxicity, 288nm produced significantly high levels of DNA damage at all doses tested, while 311, 320 and 330nm did not generate pyrimidine dimers and produced low levels of DNA damage detected by comet assay. While 288nm failed to induce ROS, the other wavelengths were effective, with the maximum (10-fold) effect observed with 30 kJ/m² at 311nm. An in vivo pilot study assessing 311nm-induced LAGT of rabbit articular chondrocytes demonstrated a significant 6.6-fold (p<0.05) increase in transduction with insignificant cytotoxicity. Conclusion: 311nm was found to be the optimal wavelength for LAGT based on its superior efficacy at the peak dose, and its broad safety range that is remarkably wider than the other UV wavelengths tested.

Targeted gene-and-host progenitor cell therapy for nonunion bone fracture repair

Nonunion fractures present a challenge to orthopedics with no optimal solution. In-vivo DNA electroporation is a gene-delivery technique that can potentially accelerate regenerative processes. We hypothesized that in vivo electroporation of an osteogenic gene in a nonunion radius bone defect site would induce fracture repair. Nonunion fracture was created in the radii of C3H/HeN mice, into which a collagen sponge was placed. To allow for recruitment of host progenitor cells (HPCs) into the implanted sponge, the mice were housed for 10 days before electroporation. Mice were electroporated with either bone morphogenetic protein 9 (BMP-9) plasmid, Luciferase plasmid or injected with BMP-9 plasmid but not electroporated. In vivo bioluminescent imaging indicated that gene expression was localized to the defect site. Microcomputed tomography (µCT) and histological analysis of murine radii electroporated with BMP-9 demonstrated bone formation bridging the bone gap, whereas in the control groups the defect remained unbridged. Population of the implanted collagen sponge by HPCs transfected with the injected plasmid following electroporation was noted. Our data indicate that regeneration of nonunion bone defect can be attained by performing in vivo electroporation with an osteogenic gene combined with recruitment of HPCs. This gene therapy approach may pave the way for regeneration of other skeletal tissues.

Enhancing allograft bone healing through gene therapy

STUDY DESIGN

A review and synopsis of recent literature pertinent to allograft bone healing.

OBJECTIVE

To review the basic principles and primary issues regarding the healing of allograft bone. To review progress made in understanding the molecular mechanisms of healing, and efforts being made to manipulate these processes to enhance healing.

SUMMARY OF BACKGROUND DATA

Bone grafting with both autografts and allografts is a common reconstructive procedure. Failure to heal and catastrophic failure of seemingly healed structural grafts occur. There is currently a great deal of excitement about the potential of bone marrow-derived cells to enhance healing. Gene transfer techniques have been developed which allow the insertion of desired deoxyribonucleic acid-encoded messages into cells. Such messages can result in the production of therapeutic proteins. Gene therapy has been used to enhance the healing of allografts in a murine model.

METHODS

Literature review.

RESULTS

Autografts heal by endochondral ossification at the graft-host interface and by intramembranous bone formation over the surface of the graft. Allografts heal predominately by endochondral ossification at the graft-host interface. The living periosteum of a graft contains progenitor cells that have an important role in graft healing. The addition of bone marrow-derived cells to an allograft does not improve healing unless they are genetically modified to express bone morphogenetic protein 2. Gene therapy to induce expression of several other proteins (VEGF and RANKL, caALK2) can also result in markedly improved allograft healing.

CONCLUSION

Gene therapy techniques can create revitalized allografts in a mouse model. These revitalized grafts heal faster, more completely, more durably, and stronger than allografts.

Effect of transfection strategy on growth factor overexpression by articular chondrocytes

Articular cartilage damage remains an unsolved problem in orthopaedics. Insulin-like growth factor I (IGF-I) and fibroblast growth factor-2 (FGF-2) are anabolic and mitogenic for articular chondrocytes, and are candidates for the application of gene therapy to articular cartilage repair. We tested the hypothesis that the production of IGF-I and FGF-2 can be augmented by modulating vector designs and delivery methods used for gene transfer to articular chondrocytes. We developed a novel adeno-associated virus (AAV)-based plasmid (pAAV) to overexpress IGF-I and FGF-2 cDNAs in adult bovine articular chondrocytes. We found that the pAAV-based vectors generated significantly more growth factor than pcDNA vectors carrying the same cDNAs. Chondrocytes cotransfected with both IGF-I and FGF-2 cDNAs in two separate pAAV plasmids produced significantly more IGF-I and FGF-2 than cells transfected by a single pAAV plasmid carrying both cDNAs in a dicistronic cassette. These data indicate that pAAV vectors are more effective than pcDNA vectors for transfer of IGF-I and FGF-2 genes to articular chondrocytes. They further suggest that cotransfection may be an effective strategy for multiple gene transfer to these cells. These findings may be important in applying growth factor gene transfer to cell-based articular cartilage gene therapy.

Bone morphogenetic proteins and tissue engineering: future directions

As long as bone repair and regeneration is considered as a complex clinical condition, the administration of more than one factor involved in fracture healing might be necessary. The effectiveness or not of bone morphogenetic proteins (BMPs) in association with other growth factors and with mesenchymal stem cells in bone regeneration for fracture healing and bone allograft integration is of great interest to the scientific community. In this study we point out possible future developments in BMPs, concerning research and clinical applications.

Biological activation of bone-related biomaterials by recombinant adeno-associated virus vector

Gene therapy is a promising clinical tool that is no longer limited as a method to supplement genetic deficits, but rather is considered reliable for delivering proteins to specific tissues or cells. Recombinant adeno-associated virus (rAAV) vector is one of the most potent gene transfer vehicles. Many biomaterials have been used in reconstructive surgery, but their biological inactivity has limited their use. To overcome shortcomings of available bone-related biomaterials, we investigated the combination of rAAV with biomaterials. Taking advantage of the method of lyophilizing rAAV onto biomaterials, we showed that an rAAV coating successfully induced beta-galactosidase protein expression by rat fibroblasts on hydroxyapatite, beta-tricalcium phosphate, and titanium alloy in vitro. beta-Galactosidase expression was detected for 8 weeks after implantation of rAAV-coated hydroxyapatite into rat back muscles in vivo. A coating of bone morphogenetic protein-2-expressing rAAV induced significant de novo bone formation on hydroxyapatite in rat back muscles. Our study demonstrates that the combination of lyophilized rAAV and biomaterials presents a promising strategy for bone regenerative medicine.

Application of AAV2-mediated bFGF gene therapy on survival of ischemic flaps: effects of timing of gene transfer

Necrosis of surgically transferred flaps is a major problem in reconstructive surgery. We investigated efficacy of a new vector system-adeno-associated viral 2 (AAV2)-mediated bFGF gene transfer to enhance survival of the ischemic flap. Thirty-eight Sprague-Dawley rats were divided into 3 gene therapy groups and 1 nontreated control of 9 or 10 each. 7.5 x 10(10) AAV2-bFGF viral particles were injected to the dorsum of each of the 29 rats; these rats were divided into 3 groups according to the timing of flap elevation. At the time of surgery, 1 week, and 2 weeks after surgery, flaps of 3 x 7 cm were raised. One week after surgery, flap viability was measured. Vascularization and immunohistochemical staining of the bFGF were evaluated of histologic sections. Flap viability was significantly improved by the AAV2-bFGF gene therapy at the time of surgery, and the flaps with the greatest survival area were found in the rats injected with AAV2-bFGF, 2 weeks before surgery. However, flap viability was significantly decreased by the gene therapy 1 week before surgery. Histologically, vascularity was increased in the groups with AAV2-bFGF injection and immunohistochemical staining showed greatly enhanced bFGF expression by gene transfer. The novel approach of AAV2-bFGF gene therapy shows encouraging manifestations in improving survival of flaps when the flaps are prefabricated during or 2 weeks before surgery.

Recent Advances in Gene Delivery for Structural Bone Allografts

In this paper, we review the progress toward developing strategies to engineer improved structural grafting of bone. Three strategies are typically used to augment massive bone defect repair. The first is to engraft mesenchymal stem cells (MSCs) onto a graft or a biosynthetic matrix to provide a viable osteoinductive scaffold material for segmental defect repair. The second strategy is to introduce critical factor(s), for example, bone morphogenetic proteins (BMPs), in the form of bone-derived or recombinant proteins onto the graft or matrix directly. The third strategy uses targeted delivery of therapeutic genes (using viral and nonviral vectors) that either transduce host cells in vivo or stably transduce cells in vitro for subsequent implantation in vivo. We developed a murine femoral model in which allografts can be revitalized via recombinant adeno-associated virus (rAAV) gene transfer. Specifically, allografts coated with rAAV expressing either the constitutively active BMP type I receptor Alk2 (caAlk2), or the angiogenic factor vascular endothelial growth factor (VEGF) combined with the osteoclastogenic factor receptor activator of NF-kappa B ligand (RANKL) have remarkable osteogenic, angiogenic, and remodeling effects that have not been previously documented in healing allografts. Using histomorphometric and micro computed tomography (muCT) imaging we show that rAAV-mediated delivery of caAlk2 induces significant osteoinduction manifested by a mineralized callus on the surface of the allograft, which resembles the healing response of an autograft. We also demonstrate that the rAAV-mediated gene transfer of the combination of VEGF and RANKL can induce significant vascularization and remodeling of processed structural allografts. By contrast, rAAV-LacZ coated allograft controls appeared similar to necrotic allografts and lacked significant mineralized callus, neovascularization, and remodeling. Therefore, innovations in gene delivery offer promising therapeutic approaches for tissue engineering of structural bone substitutes that can potentially have clinical applications in challenging indications.

Tendon Healing In Vitro: Adeno-Associated Virus-2 Effectively Transduces Intrasynovial Tenocytes with Persistent Expression of the Transgene, but Other Serotypes Do Not

BACKGROUND

Transfer of exogenous growth factor genes to injured tendons offers a promising method for strengthening tendon repairs. Adeno-associated virus vectors have advantages of being both nonpathogenic and nontoxic. The authors explored the efficiency of transduction of intrasynovial tenocytes with different serotypes of adeno-associated virus (AAV) and the persistency of its expression of a growth factor transgene.

METHODS

Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed to 82 wells in eight culture plates and to 30 culture dishes. The tenocytes in the wells were treated with AAV1, AAV2, AAV3, AAV4, AAV5, AAV7, and AAV8 vectors containing the lacZ gene, and plasmid vectors (pCMVbeta-lacZ). The tenocytes were stained with in situ beta-galactosidase 5 days later. The basic fibroblast growth factor (bFGF) gene was cloned to the AAV2 vector to construct the AAV2-bFGF vector, which transduced tenocytes in culture dishes. Expression of the transgene was measured over 3 weeks and analyzed statistically.

RESULTS

AAV2 effectively delivered exogenous genes to proliferating intrasynovial tenocytes. In contrast, other tested adeno-associated viruses transduced tenocytes minimally or not at all. The efficiency of gene transfer by AAV2, indicated by the percentage of cells with positive beta-galactosidase staining, was significantly greater than that by a plasmid vector (p = 0.001). Expression of the bFGF gene in tenocytes transduced with the AAV2-bFGF was significantly higher than that in the control over the 3-week period (p < 0.01).

CONCLUSIONS

Gene transfer to tenocytes by AAV2 is more efficient than that by a plasmid vector. However, other adeno-associated virus serotypes cannot effectively transduce tenocytes. The bFGF gene can be delivered to intrasynovial tenocytes by the AAV2 vector effectively, and the gene transfer significantly increases expression of bFGF gene over 3 weeks.

Virus-based gene therapy strategies for bone regeneration

Gene therapy has emerged as a promising strategy for the repair and regeneration of damaged musculoskeletal tissues. Application of this paradigm to bone healing has shown enhanced efficacy in preclinical animal studies compared to conventional bone grafting approaches. This review discusses current and emerging virus-based genetic engineering strategies for the delivery of therapeutic molecules which promote skeletal regeneration. Viral gene delivery vectors are discussed in the context of bone repair in order to illustrate the challenges and applications of these methods with tissue-specific examples. Moreover the concepts discussed can be broadly applied to promote healing in a wide range of tissues. We also present important considerations involved in the application of these gene therapy techniques to a variety of osteogenic (e.g. bone marrow-derived cells) and non-osteogenic (e.g. fibroblasts and skeletal myoblasts) cell types. Criteria for the selection of regenerative molecules with soluble versus intracellular modes of action and emerging combinatorial approaches are also discussed. Overall, gene transfer technologies have the potential to overcome limitations associated with existing bone grafting approaches and may enable investigators to design therapies which more closely mimic the complex spatial and temporal cascade of proteins involved in endogenous bone development and repair.

Tissue reactions of adenoviral, adeno-associated viral, and liposome-plasmid vectors in tendons and comparison with early-stage healing responses of injured flexor tendons

PURPOSE

Delivery of growth factor genes that may substantially increase the healing rate of injured digital flexor tendons is a new application of gene therapy. Adenoviral, adeno-associated viral (AAV), and liposome-plasmid vectors have been used to deliver genes to tendons, but the tendon reactions to these vectors--particularly in contrast to the healing responses in the injured tendons--were unknown. This study was designed to compare the tissue reactions of the earlier-mentioned vectors in tendons with the healing responses of injured flexor tendons.

METHODS

Forty-two flexor digitorum profundus tendons of 6 New Zealand white rabbits were used. Eighteen tendons were divided into 3 groups of 6 each and injected with different vectors: adenoviral vector, AAV2-luciferase vector, or pCMV-beta vector with liposome. Another 12 tendons were cut and repaired. At 3, 7, and 14 days, the tendons were harvested and stained with hematoxylin and eosin. Normal flexor tendons were harvested as controls.

RESULTS

The tissue reactions of the liposome-plasmid vector in tendons were the most prominent among the 3 vectors tested. The adenoviral vector elicited a moderate degree of tissue reaction. The AAV2 vector caused remarkable reactions in epitenon but almost no reactions in endotenon. Early-stage tissue reactions were more robust in the injured tendons. Compared with early-stage inflammatory and healing responses, the reactions elicited by these vectors were less severe.

CONCLUSIONS

The 3 gene delivery systems tested elicit less severe tissue reactions in flexor tendons compared with early-stage inflammatory changes in injured tendons. Adenoviral and AAV vectors elicit less severe tissue reactions than liposome-plasmid vectors. The AAV2 vector appears to cause almost no reaction in endotenon. In terms of tissue reactions, the adenoviral and AAV2 vectors, in particular AAV2, are suitable gene delivery systems for future gene transfer to the tendon in vivo.

Local gene transfer to calcified tissue cells using prolonged infusion of a lentiviral vector

Gene transfer using viral vectors offers the potential for the sustained expression of proteins in specific target tissues. However, in the case of calcified tissues, in vivo delivery remains problematic because of limited accessibility. The aim of this study was to test the efficiency of lentiviral vectors (LVs) on osteogenic cells in vitro, and determine the feasibility of directly transducing resident bone cells in vivo. LVs encoding for green fluorescent protein (GFP) and ameloblastin (AMBN), a protein associated with mineralization not reported in bone, were generated. The transduction efficiency of the LVs was evaluated using the MC3T3 cell line and primary calvaria-derived osteogenic cells. For in vivo delivery, the LVs were infused using osmotic minipumps through holes created in the bone of the rat hemimandible and tibia. The production of GFP and AMBN in vitro and in vivo was monitored using fluorescence microscopy. Both transgenes were expressed in MC3T3 and primary osteogenic cells. In vivo, GFP was detected at the infusion site and fibroblast-like cells, osteoblasts, osteocytes and osteoclasts expressed AMBN. Our data demonstrate, for the first time, that primary osteogenic cells are efficiently transduced with LVs and that their infusion is advantageous for locally delivering DNA to bone cells.

Repair of articular cartilage defect by intraarticular administration of basic fibroblast growth factor gene, using adeno-associated virus vector

The objective of this study was to establish the potency of adeno-associated virus (AAV) as a viral vector to transport the basic fibroblast growth factor (bFGF) gene into synovial tissue, and to evaluate the consequent repair of articular cartilage defects. In the in vitro study, LacZ- and bFGF-encoding genes were transduced into rabbit synoviocytes by recombinant adeno-associated virus (AAV) vector, and the cells were cultured for 2 weeks. The percentage of successfully transduced LacZ-positive cells was assessed by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining, and the concentration of bFGF in the culture supernatant was confirmed by bFGF-specific enzyme-linked immunosorbent assay. In the in vivo study, 12- to 14-week-old Japanese white rabbits (all female) were used. AAV-bFGF was administered into an artificially created full-thickness defect (5 mm in diameter and 3 mm deep) in the patellar groove of the distal femur. Cartilage repair was subsequently monitored at 4, 8, and 12 weeks, by macroscopic and histological examination, and results were graded on the basis of semiquantitative scores. lacZ gene expression in synoviocytes reached more than 93% within the first 2 weeks, and the mean bFGF concentration in the culture supernatant of the bFGF gene-transduced group was significantly increased (p < 0.01). Semiquantitative macroscopic and histological assessment indicated that the average score was significantly better in the bFGF-transduced group throughout the observation period, suggesting better cartilage repair. These results demonstrate that gene transfer into synoviocytes, using the AAV vector, was a potent method of gene transduction. Moreover, after intraarticular administration of AAV-bFGF, constant expression of bFGF in the knee joints resulted in substantial cartilage regeneration that, with further long-term study, could possibly merit consideration for clinical application.

Biological effects of rAAV-caAlk2 coating on structural allograft healing

Structural bone allografts often fracture due to their lack of osteogenic and remodeling potential. To overcome these limitations, we utilized allografts coated with recombinant adeno-associated virus (rAAV) that mediate in vivo gene transfer. Using beta-galactosidase as a reporter gene, we show that 4-mm murine femoral allografts coated with rAAV-LacZ are capable of transducing adjacent inflammatory cells and osteoblasts in the fracture callus following transplantation. While this LacZ vector had no effect on allograft healing, bone morphogenetic protein signals delivered via rAAV-caAlk2 coating induced endochondral bone formation directly on the cortical surface of the allograft by day 14. By day 28 there was evidence of remodeling of the new woven bone and massive osteoclastic resorption of the cortical surface of the rAAV-caAlk2-coated allografts only. Micro-CT analysis of rAAV-LacZ- vs rAAV-caAlk2-coated allografts after 42 days of healing demonstrated a significant increase in new bone formation (0.67 +/- 0.21 vs 2.49 +/- 0.40 mm(3); P < 0.005). Furthermore, the 3D micro-CT images of femurs grafted with rAAV-Alk2-coated allografts provided the first evidence that complete bridging of bone around a cortical allograft is possible. These results indicate that cell-free, rAAV-coated allografts have the potential to revitalize in vivo following transplantation.

Tendon healing in vitro: bFGF gene transfer to tenocytes by adeno-associated viral vectors promotes expression of collagen genes

PURPOSE

Adeno-associated virus-mediated gene transfer is promising in the delivery of genes to tendons because this vector stimulates few adverse tissue reactions. Basic fibroblast growth factor (bFGF) promotes collagen production in healing tendons. We transferred the exogenous bFGF gene to proliferating tenocytes by adeno-associated viral (AAV) vectors and investigated its effects on the expression of the collagen genes in an in vitro tenocyte model.

METHODS

AAV2 vectors harboring the rat bFGF gene were constructed. Tenocytes were obtained from explant cultures of rat intrasynovial tendons and were distributed into 21 culture dishes and 8 wells. Tenocytes in 7 dishes were treated with AAV2 bFGF for 3 hours and then were cultured for 10 days. Tenocytes in 14 dishes (sham vector and nontreatment controls) did not receive the transgene. Efficiency of the gene transfer was evaluated by in situ beta-galactosidase staining in 8 wells after treatment with AAV2 lacZ. Expression of the target genes was assessed by reverse-transcription polymerase chain reactions with primers specifically amplifying the target genes. Expression of bFGF and type I and III collagen genes was determined by quantitative analysis of the polymerase chain reaction products.

RESULTS

Positive beta-galactosidase staining confirmed the effectiveness of AAV2-mediated gene delivery to tenocytes. The level of expression of the bFGF gene was increased significantly after gene transfer. Levels of expression of type I and III collagen genes after transfer of the exogenous bFGF gene were increased significantly compared with those in the cells treated with sham vectors or in nontreatment controls.

CONCLUSIONS

Delivery of exogenous bFGF gene to tenocytes can increase significantly the levels of expression of the bFGF and type I and III collagen genes. AAV2 vectors provide a novel method for delivering growth factor genes to tenocytes. These findings warrant future in vivo study of the delivery of genes pertinent to tendon healing through AAV2-based gene therapy to enhance repairs of injured flexor tendons.

Adeno-associated virus-mediated bone morphogenetic protein-7 gene transfer induces C2C12 cell differentiation into osteoblast lineage cells

AIM

To investigate the effects of bone morphogenetic protein-7 (BMP7)-expressing recombinant adeno-associated virus (AAV) vector on the differentiation of C2C12 cells.

METHODS

AAV-BMP7 was packaged by infecting the stable cell clone BHK-21 (integrated with recombinant AAV vector plasmid pSNAV-BMP7) with recombinant herpes simplex virus type 1, which expresses AAV-2 Rep and Cap and possesses AAV packaging functions. Following infection with AAV-BMP7 at multiplicities of infection of 1 x 10(5) vector genomes per cell and subsequent culture, C2C12 cells were assessed qualitatively for BMP7 production, alkaline phosphatase activity, osteocalcin production and Cbfal and MyoD expression.

RESULTS

C2C12 cells transduced with AAV-BMP7 could produce BMP7 protein until d 28. Alkaline phosphatase in the cultured C2C12 cell lysate was elevated. Secreted osteocalcin in the culture medium was detectable at d 12 and Cbfal mRNA expression level was upregulated, coinciding with downregulation of MyoD in a temporal manner.

CONCLUSION

The present in vitro study demonstrated that AAV-BMP7 could infect and efficiently convert C2C12 cells from myoblasts into osteoblast lineage cells.

Deletion of iNOS gene impairs mouse fracture healing

Nitric oxide (NO) is a signaling molecule synthesized from l-arginine by nitric oxide synthases (NOSs). NOS isoforms are either constitutive (endothelial NOS [eNOS] and neuronal NOS [nNOS]) or inducible NOS (iNOS). Previously, our group has reported that NO is expressed during and modulates fracture healing. In this study, we evaluated the specific contribution of iNOS to fracture healing by using iNOS gene therapy in iNOS-deficient mice. Twelve-week-old female wild-type mice and iNOS-KO mice had a right femoral midshaft osteotomy fixed with an intramedullary 0.5-mm-diameter needle. A gelatine sponge was implanted across the fracture site. The gelatine sponge received either Ad5-CMViNOS (in iNOS-deficient mice; n=16) or Ad5-CMVempty (in wild-type mice; n=15, and iNOS-deficient mice; n=15) at a dose of 10(7) pfu. Mice were sacrificed at day 14, and their right and left hind limbs were harvested. Cross-sectional area (CSA) was determined by measuring the callus diameter across the mediolateral and anteroposterior plane using a vernier caliper. Specimens were loaded to failure torsionally in a biaxial INSTRON testing system, and maximum torque, torsional stiffness, and maximal and total energy were determined. Deletion of the iNOS gene decreased the total and maximum energy absorption of the healing femoral fracture by 30% and by 70% (P<0.01), respectively, in comparison to the wild-type mice. This reduction in energy absorption was reversed by iNOScDNA administration via adenovirus vector. Furthermore, iNOScDNA caused an increase in torsional failure by 20% (P=0.01) in comparison to iNOS(-/-) mice that did not receive the iNOScDNA. There were no significant differences in the biomechanical properties of intact femora. These data indicate that iNOS is important in mouse fracture healing. However, the clinical utility of NOS gene therapy to enhance fracture healing will need further evaluation.

Remodeling of cortical bone allografts mediated by adherent rAAV-RANKL and VEGF gene therapy

Structural allograft healing is limited because of a lack of vascularization and remodeling. To study this we developed a mouse model that recapitulates the clinical aspects of live autograft and processed allograft healing. Gene expression analyses showed that there is a substantial decrease in the genes encoding RANKL and VEGF during allograft healing. Loss-of-function studies showed that both factors are required for autograft healing. To determine whether addition of these signals could stimulate allograft vascularization and remodeling, we developed a new approach in which rAAV can be freeze-dried onto the cortical surface without losing infectivity. We show that combination rAAV-RANKL- and rAAV-VEGF-coated allografts show marked remodeling and vascularization, which leads to a new bone collar around the graft. In conclusion, we find that RANKL and VEGF are necessary and sufficient for efficient autograft remodeling and can be transferred using rAAV to revitalize structural allografts.

Repair of articular cartilage defect by autologous transplantation of basic fibroblast growth factor gene-transduced chondrocytes with adeno-associated virus vector

OBJECTIVE

To examine the effects of basic fibroblast growth factor (bFGF) gene-transduced chondrocytes on the repair of articular cartilage defects.

METHODS

LacZ gene or bFGF gene was transduced into primary isolated rabbit chondrocytes with the use of a recombinant adeno-associated virus (AAV) vector. These gene-transduced chondrocytes were embedded in collagen gel and transplanted into a full-thickness defect in the articular cartilage of the patellar groove of a rabbit. The efficiency of gene transduction was assessed according to the percentage of LacZ-positive cells among the total number of living cells. The concentration of bFGF in the culture supernatant was measured by enzyme-linked immunosorbent assay to confirm the production by bFGF gene-transduced chondrocytes. At 4, 8, and 12 weeks after transplantation, cartilage repair was evaluated histologically and graded semiquantitatively using a histologic scoring system ranging from 0 (complete regeneration) to 14 (no regeneration) points.

RESULTS

LacZ gene expression by chondrocytes was maintained until 8 weeks in >85% of the in vitro population. LacZ-positive cells were found at the transplant sites for at least 4 weeks after surgery. The mean concentration of bFGF was significantly increased in bFGF gene-transduced cells compared with control cells (P < 0.01). Semiquantitative histologic scoring indicated that the total score was significantly lower in the bFGF-transduced group than in the control group throughout the observation period.

CONCLUSION

These results demonstrated that gene transfer to chondrocytes by an ex vivo method was established with the AAV vector, and transplantation of bFGF gene-transduced chondrocytes had a clear beneficial effect on the repair of rabbit articular cartilage defects.

Light-activated gene transduction of recombinant adeno-associated virus in human mesenchymal stem cells

Deficiencies in skeletal tissue repair and regeneration lead to conditions like osteoarthritis, osteoporosis and degenerative disc disease. While no cure for these conditions is available, the use of human bone marrow derived-mesenchymal stem cells (HuMSCs) has been shown to have potential for cell-based therapy. Furthermore, recombinant adeno-associated viruses (rAAV) could be used together with HuMSCs for in vivo or ex vivo gene therapy. Unfortunately, the poor transduction efficiency of these cells remains a significant obstacle. Here, we describe the properties of ultraviolet (UV) light-activated gene transduction (LAGT) with rAAV in HuMSCs, an advance toward overcoming this limitation. Using direct fluorescent image analysis and real-time quantitative PCR to evaluate enhanced green fluorescent protein (eGFP) gene expression, we found that the optimal effects of LAGT with limited cytotoxicity occurred at a UV dose of 200 J/m(2). Furthermore, this UV irradiation had no effect on either the chondrogenic or osteogenic potential of HuMSCs. Significant effects of LAGT in HuMSCs could be detected as early as 12 h after exposure and persisted over 21 days, in a time and energy-dependent manner. This LAGT effect was maintained for more than 8 h after irradiation and required only a 10-min exposure to rAAV after UV irradiation. Finally, we show that the production of secreted TGFbeta1 protein from rAAV-TGFbeta1-IRES-eGFP infected to HuMSCs is highly inducible by UV irradiation. These results demonstrate that LAGT combined with rAAV is a promising procedure to facilitate gene induction in HuMSCs for human gene therapy.

Light-activated gene transduction enhances adeno-associated virus vector-mediated gene expression in human articular chondrocytes

OBJECTIVE

To evaluate the effects of ultraviolet (UV) light as an adjuvant for recombinant adeno-associated virus (rAAV) transduction in human articular chondrocytes.

METHODS

Primary articular chondrocytes and immortalized chondrocytes (tsT/AC62) were exposed to various doses of UV light (0-1,000 J/m(2)) and infected at various multiplicities of infection (MOIs) with rAAV containing the enhanced green fluorescent protein (EGFP) gene. Cells were analyzed for viability and EGFP expression by fluorescence-activated cell sorting on days 2, 4, and 8 following infection. To evaluate the transduction efficiency in intact articular cartilage, full-thickness explants were exposed to UV light (0-200 J/m(2)), infected with rAAV-eGFP, and analyzed for transduction via immunohistochemistry.

RESULTS

Toxicity from UV exposure was observed at doses > or =500 J/m(2) and > or =200 J/m(2) in primary and immortalized chondrocyte cultures, respectively. Transduction efficiency was dependent on the UV dose, MOI, and time. In the cell line, the adjuvant effect of UV on the percentage of cells transduced was modest, but 100 J/m(2) increased the mean fluorescence intensity (MFI) of the transduced cells 4-fold. In contrast, UV treatment had a profound effect on the transduction efficiency of primary chondrocytes, which reached approximately 100% after exposure to 100 J/m(2) of UV light and 10(3) MOIs for 8 days. Under the same conditions, 200 J/m(2) of UV light enhanced the MFI 7-fold. In cartilage explants, there was no difference in the number of transduced chondrocytes at the edge of the explants in the superficial, intermediate, or basal zones; however, 200 J/m(2) of UV light increased the transduction efficiency 2-fold at a low MOI. In the center of the explants, the superficial chondrocytes were efficiently transduced; those in the intermediate and basal zones could not be efficiently transduced under any condition. In the superficial chondrocytes, a low MOI and 200 J/m(2) of UV light increased the transduction efficiency 3-fold (to 100%).

CONCLUSION

UV light at doses of up to 200 J/m(2) (which do not significantly affect cell viability) significantly enhances the transduction efficiency and expression of the transduced gene in cultures of rAAV-infected primary chondrocytes and in chondrocytes in the superficial zone of intact articular cartilage. These findings support the concept that UV-activated gene transduction could be used as an adjuvant for in vivo rAAV articular cartilage gene therapy with low viral titers to prevent and/or treat arthritis.

Viral interleukin-10 gene inhibition of inflammation, osteoclastogenesis, and bone resorption in response to titanium particles

OBJECTIVE

To evaluate the potential of viral interleukin-10 (vIL-10) gene therapy as an approach to prevent wear debris-induced inflammation, osteoclastogenesis, and bone resorption as it relates to periprosthetic osteolysis in patients with total joint replacements.

METHODS

Replication-defective adenovirus vectors expressing vIL-10 (AdvIL-10) or LacZ (AdLacZ) target genes were used to transduce fibroblast-like synoviocytes (FLS) in vitro, and the effects of these cells on wear debris-induced proinflammatory cytokine production and receptor activator of nuclear factor kappaB ligand + macrophage colony-stimulating factor splenocyte osteoclastogenesis were assessed by enzyme-linked immunosorbent assay and tartrate-resistant acid phosphatase assay. The effects of AdvIL-10 administration on wear debris-induced osteolysis in vivo were analyzed using the mouse calvaria model, in which AdLacZ was used as the control.

RESULTS

In the presence of AdLacZ-infected FLS, titanium particle-stimulated macrophages exhibited a marked increase in secretion of tumor necrosis factor alpha (TNFalpha) (6.5-fold), IL-6 (13-fold), and IL-1 (5-fold). Coculture with AdvIL-10-transduced FLS suppressed cytokine secretion to basal levels, while addition of an anti-IL-10 neutralizing antibody completely blocked this effect. The vIL-10-transduced FLS also inhibited osteoclastogenesis 10-fold in an anti-IL-10-sensitive manner. In vivo, titanium implantation resulted in a 2-fold increase in osteoclasts (P < 0.05) and in a 2-fold increase in sagittal suture area (P < 0.05). This increase over control levels was completely blocked in mice receiving intraperitoneal injections of AdvIL-10, all of whom had measurable serum vIL-10 levels for the duration of the experiment. Immunohistochemistry demonstrated reduced cyclooxygenase 2 and TNFalpha expression in AdvIL-10-infected animals.

CONCLUSION

This study demonstrates that gene delivery of vIL-10 inhibits 3 processes critically involved in periprosthetic osteolysis: 1) wear debris-induced proinflammatory cytokine production, 2) osteoclastogenesis, and 3) osteolysis.