Characterization of adenovirus-mediated gene transfer in rabbit flexor tendons

Evolving Horizons: Adenovirus Vectors' Timeless Influence on Cancer, Gene Therapy and Vaccines

Efficient and targeted delivery of a DNA payload is vital for developing safe gene therapy. Owing to the recent success of commercial oncolytic vector and multiple COVID-19 vaccines, adenovirus vectors are back in the spotlight. Adenovirus vectors can be used in gene therapy by altering the wild-type virus and making it replication-defective; specific viral genes can be removed and replaced with a segment that holds a therapeutic gene, and this vector can be used as delivery vehicle for tissue specific gene delivery. Modified conditionally replicative-oncolytic adenoviruses target tumors exclusively and have been studied in clinical trials extensively. This comprehensive review seeks to offer a summary of adenovirus vectors, exploring their characteristics, genetic enhancements, and diverse applications in clinical and preclinical settings. A significant emphasis is placed on their crucial role in advancing cancer therapy and the latest breakthroughs in vaccine clinical trials for various diseases. Additionally, we tackle current challenges and future avenues for optimizing adenovirus vectors, promising to open new frontiers in the fields of cell and gene therapies.

New frontiers of tendon augmentation technology in tissue engineering and regenerative medicine: a concise literature review

Tissue banking programs fail to meet the demand for human organs and tissues for transplantation into patients with congenital defects, injuries, chronic diseases, and end-stage organ failure. Tendons and ligaments are among the most frequently ruptured and/or worn-out body tissues owing to their frequent use, especially in athletes and the elderly population. Surgical repair has remained the mainstay management approach, regardless of scarring and adhesion formation during healing, which then compromises the gliding motion of the joint and reduces the quality of life for patients. Tissue engineering and regenerative medicine approaches, such as tendon augmentation, are promising as they may provide superior outcomes by inducing host-tissue ingrowth and tendon regeneration during degradation, thereby decreasing failure rates and morbidity. However, to date, tendon tissue engineering and regeneration research has been limited and lacks the much-needed human clinical evidence to translate most laboratory augmentation approaches to therapeutics. This narrative review summarizes the current treatment options for various tendon pathologies, future of tendon augmentation, cell therapy, gene therapy, 3D/4D bioprinting, scaffolding, and cell signals.

FGF2: a key regulator augmenting tendon-to-bone healing and cartilage repair

Ligament/tendon and cartilage injuries are clinically common diseases that perplex most clinicians. Because of the lack of blood vessels and nerves, their self-repairing abilities are rather poor. Therefore, surgeries are necessary and also widely used to treat ligament/tendon or cartilage injuries. However, after surgery, there are still many problems that affect healing. In recent years, it has been found that exogenous FGF2 plays an important role in the repair of ligament/tendon and cartilage injuries and exerts a synergistic effect with endogenous FGF2. Therefore, FGF2 can be used as a new type of biomolecule to accelerate tendon-to-bone healing and cartilage repair after injury.

Bone morphogenetic protein 4 (BMP4) promotes hepatic glycogen accumulation and reduces glucose level in hepatocytes through mTORC2 signaling pathway

Liver is an important organ for regulating glucose and lipid metabolism. Recent studies have shown that bone morphogenetic proteins (BMPs) may play important roles in regulating glucose and lipid metabolism. In our previous studies, we demonstrated that BMP4 significantly inhibits hepatic steatosis and lowers serum triglycerides, playing a protective role against the progression of non-alcoholic fatty liver disease (NAFLD). However, the direct impact of BMP4 on hepatic glucose metabolism is poorly understood. Here, we investigated the regulatory roles of BMP4 in hepatic glucose metabolism. Through a comprehensive analysis of the 14 types of BMPs, we found that BMP4 was one of the most potent BMPs in promoting hepatic glycogen accumulation, reducing the level of glucose in hepatocytes and effecting the expression of genes related to glucose metabolism. Mechanistically, we demonstrated that BMP4 reduced the hepatic glucose levels through the activation of mTORC2 signaling pathway in vitro and in vivo. Collectively, our findings strongly suggest that BMP4 may play an essential role in regulating hepatic glucose metabolism. This knowledge should aid us to understand the molecular pathogenesis of NAFLD, and may lead to the development of novel therapeutics by exploiting the inhibitory effects of BMPs on hepatic glucose and lipid metabolism.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

A Clinical, Biological, and Biomaterials Perspective into Tendon Injuries and Regeneration

Tendon injury is common and debilitating, and it is associated with long-term pain and ineffective healing. It is estimated to afflict 25% of the adult population and is often a career-ending disease in athletes and racehorses. Tendon injury is associated with high morbidity, pain, and long-term suffering for the patient. Due to the low cellularity and vascularity of tendon tissue, once damage has occurred, the repair process is slow and inefficient, resulting in mechanically, structurally, and functionally inferior tissue. Current treatment options focus on pain management, often being palliative and temporary and ending in reduced function. Most treatments available do not address the underlying cause of the disease and, as such, are often ineffective with variable results. The need for an advanced therapeutic that addresses the underlying pathology is evident. Tissue engineering and regenerative medicine is an emerging field that is aimed at stimulating the body's own repair system to produce de novo tissue through the use of factors such as cells, proteins, and genes that are delivered by a biomaterial scaffold. Successful tissue engineering strategies for tendon regeneration should be built on a foundation of understanding of the molecular and cellular composition of healthy compared with damaged tendon, and the inherent differences seen in the tissue after disease. This article presents a comprehensive clinical, biological, and biomaterials insight into tendon tissue engineering and regeneration toward more advanced therapeutics.

Advances in the healing of flexor tendon injuries

The intrasynovial flexor tendons of the hand are critical for normal hand function. Injury to these tendons can result in absent finger flexion, and a subsequent loss of overall hand function. The surgical techniques used to repair these tendons have improved in the past few decades, as have the postoperative rehabilitation protocols. In spite of these advances, intrasynovial flexor tendon repairs continue to be plagued by postoperative scar formation, which limits tendon gliding and prevents a full functional recovery. This paper describes the current challenges of flexor tendon repair, and evaluates the most recent advances and strategies for achieving an excellent functional outcome.

Distinct effects of platelet-rich plasma and BMP13 on rotator cuff tendon injury healing in a rat model

BACKGROUND

Although platelet-rich plasma (PRP) is used clinically to augment tendon healing, bone morphogenetic protein-13 (BMP13) may provide a better therapeutic avenue to improve early tendon healing and repair.

HYPOTHESIS

Exogenous expression of BMP13 in tenocytes will up-regulate genes involved in tendon healing. Direct delivery of adenovirus-mediated BMP13 (AdBMP13) into the injured rat supraspinatus tendon will increase biomechanical properties.

STUDY DESIGN

Controlled laboratory study.

METHODS

Exogenous expression of BMP13 and the major growth factors in PRP (transforming growth factor-β1 [TGF-β1], vascular endothelial growth factor-A [VEGF-A], and platelet-derived growth factor-BB [PDGF-BB]) was accomplished by using recombinant adenoviral vectors. The expression of tendon- and matrix-associated genes in growth factor-treated tenocytes was analyzed by use of semiquantitative reverse-transcription polymerase chain reaction. A total of 32 rats with supraspinatus defect were divided into 4 groups and injected with adenovirus-containing green fluorescent protein (AdGFP; negative control), PRP, AdBMP13, or PRP+AdBMP13. All rats were sacrificed at 2 weeks after surgery, and tendons were harvested for biomechanical testing and histologic analysis.

RESULTS

BMP13 up-regulated type III collagen expression compared with AdGFP control and PRP growth factors (P < .01). BMP13 and PRP growth factors each up-regulated fibronectin expression (P < .01). There was an increase in stress to failure in each of the 3 treatment groups (P < .05 for PRP; P < .01 for AdBMP13 or PRP+AdBMP13) compared with AdGFP control. AdBMP13 demonstrated higher stress to failure than did the PRPs (P < .01). The addition of PRP did not increase the BMP13-enhanced stress to failure or stiffness. The biomechanical results were further supported by histologic analysis of the retrieved samples.

CONCLUSION

Exogenous expression of BMP13 enhances tendon healing more effectively than PRP as assessed by tendon- and matrix-associated gene expression, biomechanical testing, and histologic analysis.

CLINICAL RELEVANCE

While PRP is used in the clinical setting, BMP13 may be explored as a superior biofactor to improve rotator cuff tendon healing and reduce the incidence of retears.

Nanoparticle-mediated delivery of TGF-β1 miRNA plasmid for preventing flexor tendon adhesion formation

Treatment of the disrupted digital flexor tendon is troublesome because of the lack of sufficient healing capacity and the formation of adhesions. Sustained gene delivery may be a promising approach of modulating gene expression in enhancing tendon healing and decreasing adhesions. In this study, a microRNA-based RNAi plasmid was used to specifically silence the expression of TGF-β1 gene associated with scar and adhesion formation in the flexor tendons. The miRNA plasmids were complexed with polylactic-co-glycolic acid (PLGA) nanoparticles to form nanoparticle/TGF-β1 miRNA plasmid (nanoparticle/plasmid) complexes. In vitro and in vivo transfection efficiencies experiments against tenocytes revealed that nanoparticle/plasmid complexes have significantly superior transfection efficiency over the lipofectamine/plasmid complexes. The gene and protein expression associated with adhesion of tendon treated with nanoparticle/plasmid complexes were evaluated by real-time PCR and immunoblotting. The grading of adhesions for tendons treated with nanoparticle/plasmid complexes was less severe than that treated with the nanoparticle/mock plasmid complexes. However, the ultimate strength of repaired tendons treated with nanoparticle/plasmid complexes was significantly lower than that of tendons treated with the nanoparticle/mock plasmid complexes.

Direct FGF-2 gene transfer via recombinant adeno-associated virus vectors stimulates cell proliferation, collagen production, and the repair of experimental lesions in the human ACL

BACKGROUND

Basic fibroblast growth factor (FGF-2) is a powerful stimulator of fibroblast proliferation and type I/III collagen production.

HYPOTHESIS

Overexpression of FGF-2 via direct recombinant adeno-associated virus (rAAV) vector-mediated gene transfer enhances the healing of experimental lesions to the human anterior cruciate ligament (ACL).

STUDY DESIGN

Controlled laboratory study.

METHODS

rAAV vectors carrying a human FGF-2 sequence or the lacZ marker gene were applied to primary human ACL fibroblasts in vitro and to intact or experimentally injured human ACL explants in situ to evaluate the efficacy and duration of transgene expression and the potential effects of FGF-2 treatment upon the proliferative, metabolic, and regenerative activities in these systems.

RESULTS

Sustained, effective dose-dependent lacZ expression was achieved in all systems tested (up to 96% ± 2% in vitro and 80%-85% in situ for at least 30 days). rAAV allowed for continuous FGF-2 production both in vitro and in the intact ACL in situ (32.7 ± 1.4 and 33.1 ± 0.8 pg/mL/24 h, respectively, ie, up to 41-fold more than in the controls at day 30; always P ≤ .001), leading to significantly and durably enhanced levels of proliferation and type I/III collagen production vis-à-vis lacZ (at least 3- and 4-fold increases at day 30, respectively; always P ≤ .001). Most notably, rAAV FGF-2 promoted a significant, long-term production of the factor in experimental ACL lesions (92.7 ± 3.9 pg/mL/24 h, ie, about 5-fold more than in the controls; P ≤ .001) associated with enhanced levels of proliferation and type I/III collagen synthesis (at least 2- and 4-fold increases at day 30, respectively; always P ≤ .001). Remarkably, the FGF-2 treatment allowed for a decrease in the amplitude of such lesions possibly because of the increased expression in contractile α-smooth muscle actin, ligament-specific transcription factor scleraxis, and nuclear factor-κB for proliferation and collagen deposition, which are all markers commonly induced in response to injury.

CONCLUSION

Efficient, stable FGF-2 expression via rAAV enhances the healing of experimental human ACL lesions by activating key cellular and metabolic processes.

CLINICAL RELEVANCE

This approach has potential value for the development of novel, effective treatments for ligament reconstruction.

Biologics in the management of rotator cuff surgery

The rotator cuff enthesis is not reestablished after a rotator cuff repair. Instead, a scar-mediated healing response occurs at the tendon-bone interface, which is notably weaker than the native enthesis and thus more prone to failure. Biological augmentation through growth factors, AASs, biomimetic scaffolds, or siRNA therapy has the potential to enhance the healing response. The ultimate key, however, is in determining which of these enables a more regenerative healing response of the native tissue rather than enhanced production of scar tissue. In addition, the optimal combination of factors, dosing, and delivery methods remains to be clearly elucidated. Biological augmentation and tissue engineering for tendon healing remains promising, but much work still needs to be done.

Lentiviral-based BMP4 in vivo gene transfer strategy increases pull-out tensile strength without an improvement in the osteointegration of the tendon graft in a rat model of biceps tenodesis

BACKGROUND

The present study aimed to develop a rat model of biceps tenodesis and to assess the feasibility of a lentiviral (LV)-based bone morphogenetic protein (BMP) 4 in vivo gene transfer strategy for healing of biceps tenodesis.

METHODS

A rat model of biceps tenodesis was developed with an interference-fit open surgical technique. A LV vector expressing a BMP4 gene or β-galactosidase (β-gal) control gene was applied to the bone tunnel and the tendon graft before its insertion into the bone tunnel. Osteointegration was assessed by histology and pull-out tensile strength was measured by a biomechanical test suitable for small rat biceps tendon grafts.

RESULTS

Neo-chondrogenesis was seen at the tendon-bone interface of LV-BMP4-treated but not control rats. The LV-BMP4-treated rats showed 32% (p < 0.05) more newly-formed trabecular bone at the tendon-bone junction than the LV-β-gal-treated controls after 3 weeks. However, the sites of neo-chondrogenesis and new bone formation in the LV-BMP4-treated tenodesis were highly spotty. Although the LV-BMP4 strategy did not promote bony integration of the tendon graft, it yielded a 29.5 ± 11.8% (p = 0.066) increase in improvement the pull-out strength of rat biceps tendons compared to the LV-β-gal treatment after 5 weeks.

CONCLUSIONS

Although the LV-BMP4 in vivo gene transfer strategy did not enhance osteointegration of the tendon graft, it yielded a marked improvement in the return of the pull-out strength of the tendon graft. This presumably was largely a result of the bone formation effect of BMP4 that traps or anchors the tendon graft onto the bony tunnel.

Cell- and gene-based approaches to tendon regeneration

Repair of rotator cuff tears in experimental models has been significantly improved by the use of enhanced biologic approaches, including platelet-rich plasma, bone marrow aspirate, growth factor supplements, and cell- and gene-modified cell therapy. Despite added complexity, cell-based therapies form an important part of enhanced repair, and combinations of carrier vehicles, growth factors, and implanted cells provide the best opportunity for robust repair. Bone marrow-derived mesenchymal stem cells provide a stimulus for repair in flexor tendons, but application in rotator cuff repair has not shown universally positive results. The use of scaffolds such as platelet-rich plasma, fibrin, and synthetic vehicles and the use of gene priming for stem cell differentiation and local anabolic and anti-inflammatory impact have both provided essential components for enhanced tendon and tendon-to-bone repair in rotator cuff disruption. Application of these research techniques in human rotator cuff injury has generally been limited to autologous platelet-rich plasma, bone marrow concentrate, or bone marrow aspirates combined with scaffold materials. Cultured mesenchymal progenitor therapy and gene-enhanced function have not yet reached clinical trials in humans. Research in several animal species indicates that the concept of gene-primed stem cells, particularly embryonic stem cells, combined with effective culture conditions, transduction with long-term integrating vectors carrying anabolic growth factors, and development of cells conditioned by use of RNA interference gene therapy to resist matrix metalloproteinase degradation, may constitute potential advances in rotator cuff repair. This review summarizes cell- and gene-enhanced cell research for tendon repair and provides future directions for rotator cuff repair using biologic composites.

Tissue engineered biological augmentation for tendon healing: a systematic review

INTRODUCTION

Tendon injuries give rise to significant morbidity. In the last few decades, several techniques have been increasingly used to optimize tendon healing.

SOURCES OF DATA

We performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL and Embase databases using various combinations of the commercial names of each scaffold and the keywords 'tendon', 'rotator cuff', 'supraspinatus tendon', 'Achilles tendon', 'growth factors', 'cytokines', 'gene therapy', 'tissue engineering', 'mesenchymal' and 'stem cells' over the years 1966-2009. All articles relevant to the subject were retrieved, and their bibliographies were hand searched for further references in the context to tissue-engineered biological augmentation for tendon healing.

AREAS OF AGREEMENT

Several new techniques are available for tissue-engineered biological augmentation for tendon healing, growth factors, gene therapy and mesenchimal stem cells.

AREAS OF CONTROVERSY

Data are lacking to allow definitive conclusions on the use of these techniques for routine management of tendon ailments.

GROWING POINTS

The emerging field of tissue engineering holds the promise to use new techniques for tendon augmentation and repair. Preliminary studies support the idea that these techniques can provide an alternative for tendon augmentation with great therapeutic potential.

AREAS TIMELY FOR DEVELOPING RESEARCH

The optimization strategies discussed in this article are currently at an early stage of development. Although these emerging technologies may develop into substantial clinical treatment options, their full impact needs to be critically evaluated in a scientific fashion.

Adenoviral-mediated gene transfer of human bone morphogenetic protein-13 does not improve rotator cuff healing in a rat model

BACKGROUND

Rotator cuff tendon-to-bone healing occurs by formation of a scar tissue interface after repair, which makes it prone to failure. Bone morphogenetic protein-13 (BMP-13) has been implicated in tendon and cartilage repair, and thus may augment rotator cuff repairs. The purpose of this study was to determine if the application of mesenchymal stem cells (MSCs) transduced with BMP-13 could improve regeneration of the tendon-bone insertion site in a rat rotator cuff repair model.

HYPOTHESIS

Mesenchymal stem cells genetically modified to overexpress BMP-13 will improve rotator cuff healing based on histologic and biomechanical outcomes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty Lewis rats underwent unilateral detachment and repair of the supraspinatus tendon and 10 rats were used for MSC harvest. Animals were randomized into 2 groups (30 animals/group). The experimental group received 10⁶ MSCs transduced with adenoviral-mediated gene transfer of human BMP-13 (Ad-BMP-13). The second group received untransduced MSCs. Fifteen animals in each group were sacrificed at 2 and 4 weeks. At each time point, 12 animals were allocated for biomechanical testing, and 3 for histomorphometric analysis.

RESULTS

There were no differences in the amount of new cartilage formation or collagen fiber organization between groups at either time point. There were also no differences in the biomechanical strength of the repairs, the cross-sectional area, peak stress at failure, or stiffness.

CONCLUSION

Application of MSCs genetically modified to overexpress BMP-13 did not improve healing in a rat model of rotator cuff repair.

CLINICAL RELEVANCE

Further studies are needed to evaluate various growth factors and combinations of growth factors to determine the optimal factor for the biologic augmentation of rotator cuff repairs.

Stem cells genetically modified with the developmental gene MT1-MMP improve regeneration of the supraspinatus tendon-to-bone insertion site

BACKGROUND

Rotator cuffs heal through a scar tissue interface after repair, which makes them prone to failure. Membrane type 1 matrix metalloproteinase (MT1-MMP) is upregulated during embryogenesis in areas that develop into tendon-bone insertion sites.

HYPOTHESIS

Bone marrow-derived stem cells in the presence of the developmental signal from MT1-MMP will drive the healing process toward regeneration and away from scar formation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty Lewis rats underwent unilateral detachment and repair of the supraspinatus tendon. Thirty animals received mesenchymal stem cells (MSCs) in a fibrin glue carrier, and 30 received adenoviral MT1-MMP (Ad-MT1-MMP)-transduced MSCs. Animals were sacrificed at 2 weeks and 4 weeks and evaluated for the presence of fibrocartilage and collagen fiber organization at the insertion. Biomechanical testing was performed to determine the structural and material properties of the repaired tissue. Statistical analysis was performed with a Wilcoxon rank-sum test with significance set at P = .05.

RESULTS

There were no differences between the Ad-MT1-MMP and MSC groups in any outcome variable at 2 weeks. At 4 weeks, the Ad-MT1-MMP group had more fibrocartilage (P = .05), higher ultimate load to failure (P = .01), higher ultimate stress to failure (P = .005), and higher stiffness values (P = .02) as compared with the MSC group.

CONCLUSION

Mesenchymal stem cells genetically modified to overexpress the developmental gene MT1-MMP can augment rotator cuff healing at 4 weeks by the presence of more fibrocartilage at the insertion and improved biomechanical strength.

CLINICAL RELEVANCE

Biologic augmentation of repaired rotator cuffs with MT1-MMP-transduced MSCs may reduce the incidence of retears. However, further studies are needed to determine if this remains safe and effective in larger models.

Effect of interleukin-10 overexpression on the properties of healing tendon in a murine patellar tendon model

PURPOSE

Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine shown to inhibit scar formation in fetal wound healing. The role of IL-10 in adult tendon healing and scar formation, however, remains unknown. The objective of this study is to investigate the effect of IL-10 overexpression on the properties of adult healing tendon using a well-established murine model of tendon injury and a lentiviral-mediated method of IL-10 overexpression.

METHODS

A murine model of patellar tendon injury was used and animals divided into 3 groups. Mice received bilateral patellar tendon injections with a lentiviral vector containing an IL-10 transgene (n = 34) or no transgene (n = 34). Control mice (n = 34) received injections of sterile saline. All animals then were subjected to bilateral, central patellar tendon injuries 2 days after injection and were killed at 5, 10, 21, and 42 days after injury. IL-10 content was analyzed by immunohistochemistry (n = 4/group). Tendon healing was evaluated by histology (n = 4/group) and biomechanical analysis (n = 10/group).

RESULTS

Overexpression of IL-10 in patellar tendon was confirmed after injection of the lentiviral vector. IL-10 immunostaining was increased at day 10 in the IL-10 group relative to that in controls. Histologically, there was no significant difference in angular deviation between groups at day 21, but a trend toward decreased angular deviation in controls relative to that in empty vector group mice was seen at day 42. Biomechanically, the IL-10 group showed significantly increased maximum stress at day 42 relative to that in controls. Percent relaxation showed a trend toward an increase at day 10 and a significant increase at day 42 in the IL-10 group relative to that in controls.

CONCLUSIONS

This study demonstrates successful gene transfer of IL-10 into adult murine patellar tendon using a lentiviral vector. Although the effects of overexpression of IL-10 on adult tendon healing have not yet been fully elucidated, the current study may help to further clarify the mechanisms of tendon injury and repair.

Adeno-associated virus-2-mediated bFGF gene transfer to digital flexor tendons significantly increases healing strength. an in vivo study

BACKGROUND

Treatment of the disrupted intrasynovial flexor tendon is troublesome and can be complicated by the rupture of weak repairs and the formation of adhesions. The central issue underlying the unsatisfactory outcomes is the lack of sufficient healing capacity, which prohibits aggressive postoperative tendon motion. Transfer of genes that are critical to healing by means of an efficient vector system offers a promising way of strengthening the repair. The purpose of the present study was to transfer the basic fibroblast growth factor gene through the adeno-associated viral-2 vector to injured digital flexor tendons and to investigate its effects on the healing strength of the tendon and on adhesion formation in a clinically relevant injury model.

METHODS

One hundred and twenty-eight long toes from sixty-four white leghorn chickens were used. The flexor digitorum profundus tendons were cut completely in the digital sheath area and were repaired with the modified Kessler method. In Group 1, a total of 2 x 10(9) particles of adeno-associated viral vector harboring the basic fibroblast growth factor gene were injected into both ends of the cut tendon. In Group 2, the same amount of adeno-associated viral vector carrying the luciferase gene was injected. In Group 3 (the non-injection control group), the tendons were sutured without any injection. At the end of two, four, eight, and twelve weeks, the toes were harvested and the tendons were tested for determination of the load-to-failure strength. At the end of eight and twelve weeks, the energy required to flex the toes was tested. The morphology regarding healing status and adhesions around the tendon were evaluated at two, four, eight, and twelve weeks.

RESULTS

The ultimate strength of repaired tendons that had been treated with adeno-associated viral vector-basic fibroblast growth factor was significantly greater than that of tendons that had been treated with the sham vector or simple repair both during the early healing period (two weeks, p < 0.01; four weeks, p < 0.01) and a later period (eight weeks, p < 0.05). At four weeks, the strength of tendons that had been treated with adeno-associated viral vector-basic fibroblast growth factor (8.9 +/- 1.9 N) was significantly greater than that of tendons that had been treated with sham vector (6.1 +/- 1.0 N) (p < 0.01) or simple suture (5.7 +/- 1.1 N) (p < 0.001). Statistically, the grading of adhesions was the same among all three groups at four and eight weeks, but at twelve weeks it was significantly less severe for tendons that had been treated with adeno-associated viral vector-basic fibroblast growth factor than for those that had been treated with simple suture (p < 0.05). The energy that was required to flex the toes after treatment with adeno-associated viral vector-basic fibroblast growth factor was not increased at eight or twelve weeks compared with that in the controls.

CONCLUSIONS

The present study demonstrates that basic fibroblast growth factor gene transfer to digital flexor tendons by means of adeno-associated viral vector-2 significantly increases healing strength during the critical tendon healing period but does not increase adhesion formation.

Freeze-dried tendon allografts as tissue-engineering scaffolds for Gdf5 gene delivery

Tendon reconstruction using grafts often results in adhesions that limit joint flexion. These adhesions are precipitated by inflammation, fibrosis, and the paucity of tendon differentiation signals during healing. In order to study this problem, we developed a mouse model in which the flexor digitorum longus (FDL) tendon is reconstructed using a live autograft or a freeze-dried allograft, and identified growth and differentiation factor 5 (Gdf5) as a therapeutic target. In this study we have investigated the potential of rAAV-Gdf5 -loaded freeze-dried tendon allografts as "therapeutically endowed" tissue-engineering scaffolds to reduce adhesions. In reporter gene studies we have demonstrated that recombinant adeno-associated virus (rAAV)-loaded tendon allografts mediate efficient transduction of adjacent soft tissues, with expression peaking at 7 days. We have also demonstrated that the rAAV-Gdf5 vector significantly accelerates wound healing in an in vitro fibroblast scratch model and, when loaded onto freeze-dried FDL tendon allografts, improves the metatarsophalangeal (MTP) joint flexion to a significantly greater extent than the rAAV-lacZ controls do. Collectively, our data demonstrate the feasibility and efficacy of therapeutic tendon allograft processing as a novel paradigm in tissue engineering in order to address difficult clinical problems such as tendon adhesions.

BMP-14 gene therapy increases tendon tensile strength in a rat model of Achilles tendon injury

BACKGROUND

Molecular and cellular-based enhancements of healing combined with conventional methods may yield better outcomes after the surgical management of tendon injury. We examined the histological and biomechanical effects of adenovirus-mediated transgene expression of bone morphogenetic protein-14 (BMP-14) on healing in a rat Achilles tendon laceration model. Specifically, we hypothesized that this delivery system for gene therapy would hasten the restoration of the normal histological appearance and tensile strength of a surgically repaired tendon.

METHODS

The right Achilles tendon of ninety male Sprague-Dawley rats was transected, repaired, and immediately infected with adenovirus expressing either the gene for green fluorescent protein (AdGFP) or the gene for human BMP-14 and green fluorescent protein (AdBMP-14). A sham control group received no viral-mediated infection after repair. Animals from each of the three groups were killed at one, two, and three weeks after surgery. The retrieved tendons were inspected, examined under light and fluorescent microscopy, and tested to determine their tensile strength.

RESULTS

Tendons transduced with BMP-14 exhibited less visible gapping, a greater number of neotenocytes at the site of healing, and 70% greater tensile strength than did either those transduced with GFP or the sham controls at two weeks after repair. Histological examination revealed no inflammatory response to the adenovirus in tendons transduced with BMP-14 or GFP. No ectopic bone or cartilage formed in the tendons transduced with BMP-14.

CONCLUSIONS

Adenovirus-mediated gene therapy with BMP-14 expedites tendon-healing in this animal model. No adverse immunological response to the adenoviral vector was detected in the host tissue, and the local production of BMP-14 did not induce unwelcome bone or cartilage formation within the healing tendon.

CLINICAL RELEVANCE

The results of this animal study suggest that gene therapy with BMPs may improve the capacity of injured musculoskeletal tissue to heal.

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.

Molecular therapy of the intervertebral disc

Disc degeneration is the loss of the normal nucleus pulposus disc matrix to a more fibrotic and less cartilaginous structure. This change in disc micro-anatomy can be associated with pain and deformity, however, prevention and treatment options of disc degeneration are currently limited. Much research is going on to understand intervertebral discs at a molecular/ cellular level in hopes of creating clinically applicable options for treating disc degeneration. This review article will give insight into the current and developing status of treating intervertebral disc degeneration from a molecular standpoint.

[Role of gene therapy in trauma and orthopedic surgery]

Modern molecular and genetic technologies enable the modification of a cellular genome through transfer of specific genes. The various procedures alter specific cell functions, which allow the transfected cell to produce any encoded transgene information. The transfected cell then synthesizes proteins that are normally not produced or only in very small amounts. Numerous animal studies have demonstrated that gene therapy may support and accelerate the healing and regeneration of specific tissues such as skin, tendons, cartilage, and bones. Currently, further animal studies are evaluating new vectors with reduced immunogenicity in the continuous effort to improve the efficacy and safety of gene transfer. In the forthcoming decade we expect gene therapy to have an important influence on the treatment of fractures, cartilage lesions, and infection.

Gene-mediated osteogenic differentiation of stem cells by bone morphogenetic proteins-2 or -6

Bone marrow-derived mesenchymal stem cells (BMDMSC) hold promise for targeted osteogenic differentiation and can be augmented by delivery of genes encoding bone morphogenetic proteins (BMP). The feasibility of promoting osteogenic differentiation of BMDMSC was investigated using two BMP genes in monolayer and three-dimensional alginate culture systems. Cultured BMDMSC were transduced with E1-deleted adenoviral vectors containing either human BMP2 or BMP6 coding sequence under cytomegalovirus (CMV) promoter control [17:1 multiplicities of infection (moi)] and either sustained in monolayer or suspended in 1 mL 1.2% alginate beads for 22 days. Adenovirus (Ad)-BMP-2 and Ad-BMP-6 transduction resulted in abundant BMP-2 and BMP-6 mRNA and protein expression in monolayer culture and BMP-2 protein expression in alginate cultures. Ad-BMP-2 and Ad-BMP-6 transduced BMDMSC in monolayer had earlier and robust alkaline phosphatase-positive staining and mineralization and were sustained for a longer duration with better morphology scores than untransduced or Ad-beta-galactosidase-transduced cells. Ad-BMP-2- and, to a lesser degree, Ad-BMP-6-transduced BMDMSC suspended in alginate demonstrated greater mineralization than untransduced cells. Gene expression studies at day 2 confirmed an inflammatory response to the gene delivery process with upregulation of interleukin 8 and CXCL2. Upregulation of genes consistent with response to BMP exposure and osteogenic differentiation, specifically endochondral ossification and extracellular matrix proteins, occurred in BMP-transduced cells. These data support that transduction of BMDMSC with Ad-BMP-2 or Ad-BMP-6 can accelerate osteogenic differentiation and mineralization of stem cells in culture, including in three-dimensional culture. BMP-2-transduced stem cells suspended in alginate culture may be a practical carrier system to support bone formation in vivo. BMP-6 induced a less robust cellular response than BMP-2, particularly in alginate culture.

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.