Inducible nonviral gene expression in the treatment of osteochondral defects

A tetracycline expression system in combination with Sox9 for cartilage tissue engineering

Cartilage tissue engineering using controllable transcriptional therapy together with synthetic biopolymer scaffolds shows higher potential for overcoming chondrocyte degradation and constructing artificial cartilages both in vivo and in vitro. Here, the potential regulating tetracycline expression (Tet-on) system was used to express Sox9 both in vivo and in vitro. Chondrocyte degradation was measured in vitro and overcome by Soxf9 expression. Experiments confirmed the feasibility of the combined use of Sox9 and Tet-on system in cartilage tissue engineering. Engineered poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) scaffolds were seeded with recombinant chondrocytes which were transfected with Tet-induced Sox9 expression; the scaffolds were implanted under the skin of 8-week-old rats. The experimental group was injected with Dox in the abdomen, while the control group was injected with normal saline. After 4 or 8 days of implantation in vivo, the newly formed pieces of articular chondrocytes were taken out and measured. Dox injection in vivo showed positive effect on recombinant chondrocytes, in which Sox9 expression was up-regulated by an inducible system with specific matrix proteins. The results demonstrate this controllable transcriptional therapy is a potential approach for tissue engineering.

Clinical potential and challenges of using genetically modified cells for articular cartilage repair

Articular cartilage defects do not regenerate. Transplantation of autologous articular chondrocytes, which is clinically being performed since several decades, laid the foundation for the transplantation of genetically modified cells, which may serve the dual role of providing a cell population capable of chondrogenesis and an additional stimulus for targeted articular cartilage repair. Experimental data generated so far have shown that genetically modified articular chondrocytes and mesenchymal stem cells (MSC) allow for sustained transgene expression when transplanted into articular cartilage defects in vivo. Overexpression of therapeutic factors enhances the structural features of the cartilaginous repair tissue. Combined overexpression of genes with complementary mechanisms of action is also feasible, holding promises for further enhancement of articular cartilage repair. Significant benefits have been also observed in preclinical animal models that are, in principle, more appropriate to the clinical situation. Finally, there is convincing proof of concept based on a phase I clinical gene therapy study in which transduced fibroblasts were injected into the metacarpophalangeal joints of patients without adverse events. To realize the full clinical potential of this approach, issues that need to be addressed include its safety, the choice of the ideal gene vector system allowing for a long-term transgene expression, the identification of the optimal therapeutic gene(s), the transplantation without or with supportive biomaterials, and the establishment of the optimal dose of modified cells. As safe techniques for generating genetically engineered articular chondrocytes and MSCs are available, they may eventually represent new avenues for improved cell-based therapies for articular cartilage repair. This, in turn, may provide an important step toward the unanswered question of articular cartilage regeneration.

Gene therapy for intervertebral disk degeneration

Intervertebral disk degeneration is a common and potentially debilitating disease process affecting millions of Americans and other populations each year. Current treatments address resultant symptoms and not the underlying pathophysiology of disease. This has spawned the development of biologic treatments, such as gene therapy, which attempt to correct the imbalance between catabolism and anabolism within degenerating disk cells. The identification of therapeutic genes and development of successful delivery systems have resulted in significant advances in this novel treatment. Continued investigation of the pathophysiology of disk degeneration, however, and safety mechanisms for the application of gene therapy are required for clinical translation.

Gene Therapy for Cartilage Repair

The concept of using gene transfer strategies for cartilage repair originates from the idea of transferring genes encoding therapeutic factors into the repair tissue, resulting in a temporarily and spatially defined delivery of therapeutic molecules to sites of cartilage damage. This review focuses on the potential benefits of using gene therapy approaches for the repair of articular cartilage and meniscal fibrocartilage, including articular cartilage defects resulting from acute trauma, osteochondritis dissecans, osteonecrosis, and osteoarthritis. Possible applications for meniscal repair comprise meniscal lesions, meniscal sutures, and meniscal transplantation. Recent studies in both small and large animal models have demonstrated the applicability of gene-based approaches for cartilage repair. Chondrogenic pathways were stimulated in the repair tissue and in osteoarthritic cartilage using genes for polypeptide growth factors and transcription factors. Although encouraging data have been generated, a successful translation of gene therapy for cartilage repair will require an ongoing combined effort of orthopedic surgeons and of basic scientists.

Physicobiochemical synergism through gene therapy and functional tissue engineering for in vitro chondrogenesis

Mechanical and chemical stimulation have been shown to enhance in vitro chondrogenesis. The aim of this study was to analyze and compare combined physicobiochemical effects. Bovine articular chondrocytes were retrovirally transduced to express bone morphogenetic protein-2 (BMP-2) or left as naïve controls. Cells were seeded in three-dimensional polyurethane scaffolds and further cultured under static conditions or exposed to dynamic compression and shear in a joint-specific bioreactor. Four groups: control (A), load (B), BMP-2-infected (C), and BMP-2-infected plus load (D) were analyzed for DNA and glycosaminoglycan (GAG) content; collagen I, II, and X; aggrecan, (cartilage oligomeric protein (COMP), superficial zone protein, matrix metalloproteinase (MMP)-3; MMP-13 mRNA; histology; and immunohistochemistry at 7, 21, and 35 days post-seeding. Synergistic effects (D) were higher than the sum of the individual treatments (B and C) for GAG/DNA, collagen II, and COMP. Histology revealed a functional organization in D including an intense safranin O staining in C and D superior to that in A and B. Immunostaining for collagen II and aggrecan was detected in C and D and was strongest in D. The results show that both stimuli augment in vitro chondrogenesis better than in controls. Biochemical manipulation proved to be predominantly more effective than load, and synergistic effects were demonstrated.

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.

The influence of the stable expression of BMP2 in fibrin clots on the remodelling and repair of osteochondral defects

Growth factors like BMP2 have been tested for osteochondral repair, but transfer methods used until now were insufficient. Therefore, the aim of this study was to analyse if stable BMP2 expression after retroviral vector (Bullet) transduction is able to regenerate osteochondral defects in rabbits. Fibrin clots colonized by control or BMP2-transduced chondrocytes were generated for in vitro experiments and implantation into standardized corresponding osteochondral defects (n=32) in the rabbit trochlea. After 4 and 12 weeks repair tissue was analysed by histology (HE, alcian-blue, toluidine-blue), immunohistochemistry (Col1, Col2, aggrecan, aggrecan-link protein), ELISA (BMP2), and quantitative RT-PCR (BMP2, Col1, Col2, Col10, Cbfa1, Sox9). In vitro clots were also analysed by BMP2-ELISA, histology (alcian-blue), quantitative RT-PCR and in addition by electron microscopy. BMP2 increased Col2 expression, proteoglycan production and cell size in vitro. BMP2 transduction by Bullet was efficient and gene expression was stable in vivo over at least 12 weeks. Proteoglycan content and ICRS-score of repair tissue were improved by BMP2 after 4 and 12 weeks and Col2 expression after 4 weeks compared to controls. However, in spite of stable BMP2 expression, a complete repair of osteochondral defects could not be demonstrated. Therefore, BMP2 is not suitable to regenerate osteochondral lesions completely.

A feasibility study of computer-assisted bone graft implantation for tissue-engineered replacement of the human ankle joint

OBJECTIVE

Computer-assisted graft implantation may contribute to achieving biological joint replacement in the future. The purpose of this experimental study was to evaluate the feasibility and accuracy of a series of computer-assisted graft implantations into human cadaver ankle joints.

METHODS

Three-dimensional graft models of virtually planned corresponding tibial and talar defects were created from bovine cancellous bone. A platform for computer-assisted surgery (CAS) was set up to implant the grafts. Registration was performed by pair-point matching with anatomical landmarks. In the case of insufficient registration accuracy, artificial landmarks were used for registration. Eight grafts (four tibial, four talar) were implanted in four human cadaver ankle joints. Postoperative CT was used for outcome analysis. The following criteria of accuracy were defined: macroscopic quality of implant fit; quality of the sagittal and coronar joint surface; and quality of the undersurface of the graft in relation to the base of the defect.

RESULTS

No technical complications were observed during computer-assisted graft implantation. Clinically acceptable accuracy was achieved in 6 of 8 graft implantations, with implant failure occurring at the tibial and talar location in one ankle joint. In total, 25 of 32 criteria of accuracy were achieved: 6/8 for macroscopic implant fit; 5/8 for quality of the sagittal joint surface; 7/8 for quality of the coronar joint surface; and 7/8 for quality of the undersurface of the graft. Registration with anatomical landmarks did not achieve sufficient accuracy in 4 of 8 cases, whereas registration with artificial landmarks was successful in all these cases.

CONCLUSIONS

We demonstrated the feasibility and accuracy of computer-assisted graft implantation for tissue-engineered replacement of the human ankle joint. However, we cannot recommend the present type of registration by pair-point matching with anatomical landmarks due to the considerable inaccuracies. The focus should be on the improvement of non-invasive registration techniques and methods for evaluating postoperative outcome.

Safety assessment of intradiscal gene therapy II: effect of dosing and vector choice

STUDY DESIGN

Clinical, biochemical, and histologic analysis was performed after in vivo delivery of cDNA encoding various anabolic cytokines and marker genes to the lumbar epidural space of New Zealand white rabbits, using both adenoviral and adeno-associated viral vectors.

OBJECTIVE

To mimic errant or misplaced doses of gene therapy to better ascertain the potential risks associated with alternative vectors and transgene products with regard to their application to problems of the intervertebral disc.

SUMMARY OF BACKGROUND DATA

Work done with several anabolic cytokines including bone morphogenic proteins and transforming growth factors, has demonstrated the potential of gene therapy. Recently, data has been published demonstrating that improperly dosed or delivered adenoviral-mediated gene therapy within the subarachnoid space can result in significant morbidity in rabbits. There are currently no studies examining the effect of these errors within the epidural space or using an adeno-associated viral (AAV) vector.

METHODS

Using either adenoviral or AAV vectors, complementary DNA (cDNA) encoding anabolic cytokines bone morphogenic protein-2 (BMP-2) and transforming growth factor-beta 1 and marker proteins LacZ and green fluorescent protein were injected into the epidural space of 37 New Zealand white rabbits at the L5/6 level. Rabbits were then observed clinically for up to 6 weeks, after which the rabbits were sacrificed in order to perform a comprehensive biochemical and histologic analysis.

RESULTS

Following adenoviral-mediated delivery of anabolic cytokine cDNA, up to eighty percent of rabbits demonstrated significant clinical, biochemical, and histologic morbidity. Conversely, AAV-mediated delivery of any cDNA and adenoviral-mediated delivery of marker protein cDNA resulted in no clinical, histologic, or biochemical morbidity.

CONCLUSION

Properly dosed and directed gene therapy seems to be both safe and potentially efficacious. This study suggests that side effects of gene therapy may be due to a combination of dosing, transgene product, and vector choice, and that newer AAV vectors may reduce these side-effects and decrease the risk of this technology.

Gene therapy used for tissue engineering applications

This review highlights the advances at the interface between tissue engineering and gene therapy. There are a large number of reports on gene therapy in tissue engineering, and these cover a huge range of different engineered tissues, different vectors, scaffolds and methodology. The review considers separately in-vitro and in-vivo gene transfer methods. The in-vivo gene transfer method is described first, using either viral or non-viral vectors to repair various tissues with and without the use of scaffolds. The use of a scaffold can overcome some of the challenges associated with delivery by direct injection. The ex-vivo method is described in the second half of the review. Attempts have been made to use this therapy for bone, cartilage, wound, urothelial, nerve tissue regeneration and for treating diabetes using viral or non-viral vectors. Again porous polymers can be used as scaffolds for cell transplantation. There are as yet few comparisons between these many different variables to show which is the best for any particular application. With few exceptions, all of the results were positive in showing some gene expression and some consequent effect on tissue growth and remodelling. Some of the principal advantages and disadvantages of various methods are discussed.

Tissue-Engineering zur Knorpelreparatur verbessert durch Gentransfer

Cartilage tissue engineering is the creation of functional substitutes of native articular cartilage in bioreactors by attaching chondrogenic cells to polymer scaffolds. One limitation of tissue engineering is the delivery of regulatory signals to cells according to specific temporal and spatial patterns. Using gene transfer techniques, polypeptide growth factor genes such as the human insulin-like growth factor I (IGF-I) gene can be transferred into chondrocytes. When these modified cells are used for cartilage tissue engineering, the resulting cartilaginous constructs have improved structural and functional characteristics compared to constructs based on nonmodified cells. The combination of cartilage tissue engineering with overexpression of potential therapeutic genes using gene transfer technologies provides a basis for the development of novel molecular therapies for the repair of cartilage defects.

Gene therapy for cartilage defects

Focal defects of articular cartilage are an unsolved problem in clinical orthopaedics. These lesions do not heal spontaneously and no treatment leads to complete and durable cartilage regeneration. Although the concept of gene therapy for cartilage damage appears elegant and straightforward, current research indicates that an adaptation of gene transfer techniques to the problem of a circumscribed cartilage defect is required in order to successfully implement this approach. In particular, the localised delivery into the defect of therapeutic gene constructs is desirable. Current strategies aim at inducing chondrogenic pathways in the repair tissue that fills such defects. These include the stimulation of chondrocyte proliferation, maturation, and matrix synthesis via direct or cell transplantation-mediated approaches. Among the most studied candidates, polypeptide growth factors have shown promise to enhance the structural quality of the repair tissue. A better understanding of the basic scientific aspects of cartilage defect repair, together with the identification of additional molecular targets and the development of improved gene-delivery techniques, may allow a clinical translation of gene therapy for cartilage defects. The first experimental steps provide reason for cautious optimism.

Gene therapy for disc repair

BACKGROUND CONTEXT

Recent advances in our understanding of the biologic makeup and environment of the intervertebral disc (IVD) have led to increased interest in the development of novel treatments for disc degeneration. Certain genes found to alter rates of matrix synthesis and catabolism within the disc have provided targets for scientists seeking to alter the balance between the two. To this end, gene therapy has emerged as a potential therapeutic option, and recent research efforts have yielded very promising results.

PURPOSE

To update and consolidate information regarding the recent advances in gene therapy and its application to IVD degeneration.

STUDY DESIGN/SETTING

Review of recent and ongoing research in the field of gene therapy, particularly regarding its application to the treatment of IVD degeneration.

METHODS

Literature review.

RESULTS

With its unique ability to provide sustained delivery of potentially therapeutic agents, gene therapy has shown much promise with regard to the treatment of IVD degeneration. There have been many exciting developments such as safer and more reliable vector constructs, favorable results using therapeutic transgenes in disc cells both in vitro and in vivo, and improvement in transgene regulation, and investigators continue to explore ways in which gene therapy can become a powerful tool in the future treatment of disc degeneration.

CONCLUSIONS

With continued perseverance and dedication, many advances have been made in the application of gene therapy to the IVD, and it continues to demonstrate great potential to become a powerful tool in the future treatment of disc degeneration.