Adenovirus-mediated gene transfer into tendon and tendon sheath

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.

Boost Tendon/Ligament Repair With Biomimetic and Smart Cellular Constructs

Tendon and ligament are soft connective tissues that play essential roles in transmitting forces from muscle to bone or bone to bone. Despite significant progress made in the field of ligament and tendon regeneration over the past decades, many strategies struggle to recapitulate basic structure-function criteria of native ligament/tendon. The goal here is to provide a fundamental understanding of the structure and composition of ligament/tendon and highlight few key challenges in functional regeneration of these connective tissues. The remainder of the review will examine several biomaterials strategies including biomimetic scaffold with non-linear mechanical behavior, hydrogel patch with anisotropic adhesion and gene-activated scaffold for interactive healing of tendon/ligament. Finally, emerging technologies and research avenues are suggested that have the potential to enhance treatment outcomes of tendon/ligament injuries.

Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part II: treatment options

The treatment of painful chronic tendinopathy is challenging. Multiple non-invasive and tendon-invasive methods are used. When traditional non-invasive treatments fail, the injections of platelet-rich plasma autologous blood or cortisone have become increasingly favored. However, there is little scientific evidence from human studies supporting injection treatment. As the last resort, intra- or peritendinous open or endoscopic surgery are employed even though these also show varying results. This ESSKA basic science committee current concepts review follows the first part on the biology, biomechanics and anatomy of tendinopathies, to provide a comprehensive overview of the latest treatment options for tendinopathy as reported in the literature.

Basic FGF or VEGF gene therapy corrects insufficiency in the intrinsic healing capacity of tendons

Tendon injury during limb motion is common. Damaged tendons heal poorly and frequently undergo unpredictable ruptures or impaired motion due to insufficient innate healing capacity. By basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF) gene therapy via adeno-associated viral type-2 (AAV2) vector to produce supernormal amount of bFGF or VEGF intrinsically in the tendon, we effectively corrected the insufficiency of the tendon healing capacity. This therapeutic approach (1) resulted in substantial amelioration of the low growth factor activity with significant increases in bFGF or VEGF from weeks 4 to 6 in the treated tendons (p < 0.05 or p < 0.01), (2) significantly promoted production of type I collagen and other extracellular molecules (p < 0.01) and accelerated cellular proliferation, and (3) significantly increased tendon strength by 68–91% from week 2 after AAV2-bFGF treatment and by 82–210% from week 3 after AAV2-VEGF compared with that of the controls (p < 0.05 or p < 0.01). Moreover, the transgene expression dissipated after healing was complete. These findings show that the gene transfers provide an optimistic solution to the insufficiencies of the intrinsic healing capacity of the tendon and offers an effective therapeutic possibility for patients with tendon disunion.

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.

Tendon healing in vivo: effect of mannose-6-phosphate on flexor tendon adhesion formation

The purpose of this study was to investigate the preventive effect of mannose-6-phosphate on flexor tendon adhesion formation. From a total of 84 adult New Zealand White rabbits, 36 were randomly divided into 2 groups, the normal saline group and the mannose-6-phosphate group, after anastomosis of the flexor tendons. Tendons were harvested at 4 weeks, and biomechanics testing was conducted. The other 48 rabbits were randomly divided into 2 groups, the normal saline group and the mannose-6-phosphate group, after anastomosis of the flexor tendons, and tendons were harvested at 7, 14, 28, and 56 days and analyzed by in situ hybridization to determine the mRNA expression of transforming growth factor (TGF)-β1 and collagen I. The results of biomechanics testing indicated that mannose-6-phosphate can effectively prevent flexor tendon adhesion formation after anastomonsis. The in situ hybridization examination revealed that TGF-β1 and collagen I mRNA expression in the mannose-6-phosphate group was lower than that in the normal saline group at each time point. Mannose-6-phosphate can effectively inhibit the function of TGF-β1 and prevent adhesion formation after flexor tendon injury.

Mandibular alveolar bony defect repair using bone morphogenetic protein 2-expressing autologous mesenchymal stem cells

BACKGROUND

Mandibular bone regeneration is stepped up by human recombinant bone morphogenetic protein 2 (BMP-2) whose application is also related to limited cementum and periodontal ligament regeneration, local root resorption, and ankylosis. The alveolar bone grafting without traditional autologous bone grafts remains a challenge for plastic surgeons.

METHODS

Bilateral mandibular alveolar and periodontal defects were created over the premolar areas in 9 mature male beagles. The defects were randomly assigned for either the adenovirus BMP-2 (advBMP-2) group with BMP-2-expressing mesenchymal stem cells (MSCs) or the control with MSCs alone. The regenerated periodontal attachment apparatus was evaluated histologically, and the whole regenerated bone volume was scrutinized from three-dimensional computed tomography analysis.

RESULTS

Periodontal apparatus regeneration was significantly better in the advBMP-2 group. New cementum and Sharpey fibers were observed on the denuded root surfaces in the advBMP-2 group, whereas incomplete healing with localized root surface resorption was noted in the control group. Eight weeks after implantation, the advBMP-2 group showed significant increase in bone regeneration than the control one.

CONCLUSIONS

Thus, the use of ex vivo BMP-2-engineered autologous MSCs boosted bone and periodontal apparatus regeneration in mandibular periodontal defects. This de novo approach might be suitable for clinical mandibular bone repair and periodontal apparatus repair.

Repair of large cranial defects by hBMP-2 expressing bone marrow stromal cells: comparison between alginate and collagen type I systems

Despite a wide range of available sources for bone repair, significant limitations persist. To bioengineer bone, we have previously transferred adenovirus-mediated human BMP-2 gene into autologous bone marrow stromal cells (MSC). We have successfully repaired large, full thickness, cranial defects using this approach. We report now the effectiveness of various hydrogels as the scaffold for this type of bone regeneration, comparing specifically alginate with Type I collagen. Cultured MSC of miniature swine were infected with BMP-2 or beta-gal adenovirus 7 days before implantation. These cells were mixed with alginate, ultrapure alginate, alginate-RGD, or type I collagen to fabricate the MSC/biomaterial constructs. The results of cranial bone regeneration were assessed by gross examination, histology, 3D CT, and biomechanical tests at 6 weeks and 3 months after implantation. We found that the BMP-2 MSC/collagen type I construct, but not the beta-gal control, effectively achieved nearly complete repair of the cranial defects. No bone regeneration was observed with the other hydrogels. Biomechanical testing showed that the new bone strength was very close and only slightly inferior to that of normal cranial bone. Controlling for the integration of stem cells and ex vivo gene transfer, the alginate scaffolds has a significant negative impact on the success of the construct. Our study demonstrates better bone regeneration by collagen type I over alginate. This may have therapeutic implications for tissue engineered bone repair.

Effects of antisense transforming growth factor-beta1 gene transfer on the biological activities of tendon sheath fibroblasts

Recent studies have shown the importance of transforming growth factor-beta (TGF-beta) in flexor tendon wound healing. Decreased adhesion formation and increased range of motion after the administration of TGF-beta antibodies after tendon repair have been shown. But TGF-beta antibodies have a short biologic half-life, and continuous supplementation of exogenous TGF-beta antibodies is not practical. Transfer of growth factor genes to tenocytes provides an alternative to protein therapeutics, and a gene therapy approach will prolong the availability of therapeutic proteins.We investigated the biological activities effects of rabbit tendon sheath fibroblasts transfected by antisense TGF-beta1 gene. Tendon sheath fibroblasts were isolated from New Zealand white rabbits and transfected by antisense TGF-beta1 gene with Lipofectin (Invitrogen, Carlsbad, California). Reverse transcription polymerase chain reaction was used to measure collagen I, collagen III, and TGF-beta1 expression, and Western blot was used to measure collagen protein I expression in tendon sheath fibroblasts after being transfected by antisense TGF-beta1 gene. Reverse transcription polymerase chain reaction displayed that tendon sheath fibroblasts transfected with antisense TGF-beta1 gene showed marked decrease collagen I, collagen III, and TGF-beta1 mRNA expression. Western blot showed that tendon sheath fibroblasts transfected with antisense TGF-beta1 gene showed marked decrease expression of collagen I protein, and there was significant difference compared with the untransfected and empty transfected groups (P<.01). Tendon sheath fibroblasts can transfect with antisense TGF-beta1 gene successfully and can decrease production of collagen I, collagen III, and TGF-beta1, which were factors of tendon adhere formation.

Large-scale bicortical skull bone regeneration using ex vivo replication-defective adenoviral-mediated bone morphogenetic protein-2 gene-transferred bone marrow stromal cells and composite biomaterials

OBJECTIVE

Bone marrow stromal cells (BMSCs) have great potential in bone repair. We developed an animal model to test the hypothesis that ex vivo gene transfer of human bone morphogenetic protein (BMP)-2 to BMSCs via a replication-defective (E1A-deleted) adenovirus vector (AdV) with appropriate biopolymers would enhance autologous bone formation during repair of a large-scale skull defect.

METHODS

Eighteen miniature swine were treated with AdV BMP-2-transduced BMSCs in biopolymer (group 1), BMSCs in biopolymer (group 2), or biopolymer alone (group 3). After 6 months, the swine were killed, and the skull repair was examined by gross pictures, histology, 3-dimensional computed tomography, and biomechanical study.

RESULTS

Group 1 showed complete solid bone formation after 6 months, and hematoxylin and eosin staining demonstrated the presence of mature, woven, well-mineralized bone. Computed tomography showed wholesome repair of the skull defect. Statistical analysis demonstrated a significant difference in bone thickness between groups 1 and 2. Biomechanical testing showed a statistically significant difference in the stiffness of new bone formed in group 1 compared with group 2.

CONCLUSION

The Ad5 E1A-deleted AdV may be the optimal starting vector in ex vivo gene therapy for benign skeletal diseases. Additionally, the use of the gelatin/tricalcium phosphate ceramic/glutaraldehyde biopolymer with AdV BMP-2 gene transfer strongly enhances the bony healing of critical-size bicortical craniofacial defects. This method can be used by modifying the delivery of constructs to malunion treatment, in regional osteoporosis therapy, and spinal fusion.

Remodeling of murine intrasynovial tendon adhesions following injury: MMP and neotendon gene expression

Tendon injury frequently results in the formation of adhesions that reduce joint range of motion. To study the cellular, molecular, and biomechanical events involved in intrasynovial tendon healing and adhesion formation, we developed a murine flexor tendon healing model in which the flexor digitorum longus (FDL) tendon of C57BL/6 mice was transected and repaired using suture. This model was used to test the hypothesis that murine flexor tendons heal with differential expression of matrix metalloproteases (MMPs), resulting in the formation of scar tissue as well as the subsequent remodeling of scar and adhesions. Healing tendons were evaluated by histology, gene expression via real-time RT-PCR, and in situ hybridization, as well as biomechanical testing to assess the metatarsophalangeal (MTP) joint flexion range of motion (ROM) and the tensile failure properties. Tendons healed with a highly disorganized fibroblastic tissue response that was progressively remodeled through day 35 resulting in a more organized pattern of collagen fibers. Initial repair involved elevated levels of Mmp-9 at day 7, which is associated with catabolism of damaged collagen fibers. High levels of Col3 are consistent with scar tissue, and gradually transition to the expression of Col1. Scleraxis expression peaked at day 7, but the expression was limited to the original tendon adjacent to the injury site, and no expression was present in granulation tissue involved in the repair response. The MTP joint ROM with standardized force on the tendon was decreased on days 14 and 21 compared to day 0, indicating the presence of adhesions. Peak expressions of Mmp-2 and Mmp-14 were observed at day 21, associated with tendon remodeling. At day 28, two genes associated with neotendon formation, Smad8 and Gdf-5, were elevated and an improvement in MTP ROM occurred. Tensile strength of the tendon progressively increased, but by 63 days the repaired tendons had not reached the tensile strength of normal tendon. The murine model of primary tendon repair, described here, provides a novel mechanism to study the tendon healing process, and further enhances the understanding of this process at the molecular, cellular, and biomechanical level.

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.

Twenty-five years of tendon and ligament research

Twenty-five years ago, the Journal of Orthopaedic Research published its first volume, which included five articles covering topics in tendon and ligament research. Since then, the body of tendon and ligament research has continued to increase exponentially. This review summarizes major advancements in tendon and ligament research since the initial publication of this journal. The purpose of this article is not to provide an in-depth review of all of tendon and ligament research, but instead to provide a concise literature review of some of the major and recurring areas of research. The general topics covered over the last 25 years include tissue properties, tendinopathy, healing, and engineered scaffolds.

Periodontal regeneration using ex vivo autologous stem cells engineered to express the BMP-2 gene: an alternative to alveolaplasty

The regeneration of the periodontal attachment apparatus remains clinically challenging because of the involvement of three tissue types and the complexity of their relationship. Human recombinant bone morphogenic protein-2 (rhBMP-2) can accelerate the regeneration of bone and cementum and the insertion of periodontal ligament fibers but may lead to a deranged periodontal relationship, ankylosis and root resorption.This study evaluated a novel approach to regeneration of the periodontal attachment apparatus using a combination of ex vivo autologous bone marrow mesenchymal stem cells (MSCs) engineered by replication-defective adenovirus to express the BMP-2 gene and Pluronic F127 (PF127). Twenty-four periodontal defects were surgically created in 12 New Zealand white rabbits and randomly assigned to three experimental groups with MSCs: the advBMP-2 group; the advbetagal group; the MSC group and one control group: PF127 only. The regenerated periodontal attachment apparatus was assessed histologically and the total regenerated bone volume was calculated from three-dimensional computed tomography analysis.This approach regenerated not only cementum with Sharpey's fiber insertion, but also statistically significant quantities of bone, re-establishing a more normal relationship among the components of the regenerated periodontal attachment apparatus, which is beneficial for the maintenance of periodontal health.Ex vivo gene transfer using stem cells as vectors may provide an advantage of slower BMP-2 release, increasing cementogenesis. There is regeneration of the periodontal attachment apparatus, whereas direct usage of the protein (rhBMP-2) yields unhinged periodontal relationship. Thus, this approach may represent an alternative means for periodontal alveolar bone graft in clinical settings.

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.

IN VITRO TRANSPLANTATION OF GENETICALLY MODIFIED CELLS TO THE TENDON SURFACE

The objective of this paper was to study in vitro transfection of tendon cells and adherence of transfected cells to different tendon surfaces. Achilles tendon fibroblasts from 2-month-old New Zealand white rabbits were cultured to confluence, after which the cells were transfected by an adenovirus carrying either the β-galactosidase reporter gene or the green fluorescent protein (GFP) gene at multiplicities of infection (MOIs) of 50, 100, or 500. Two days later, the cells were transplanted onto the surfaces of rabbit Achilles, peroneus brevis, flexor profundus, and extensor longus tendons. The tendons were assessed by X-gal staining after 9 days, and by GFP fluorescence at 7, 14, and 21 days. Twenty percent to 50% of the treated cells stained for β-galactosidase at an MOI of 500. The GFP-labeled cells showed nearly 100% fluorescence at an MOI of 50. No positive cells were visible in the control group. The β-galactosidase and GFP-expressing cells remained viable for as long as 3 weeks. It is possible to introduce foreign genes into rabbit tendon cells, transplant the cells onto tendon surfaces, and maintain viability of the cell/tendon construct for several weeks.

Tendon and ligament engineering in the adult organism: mesenchymal stem cells and gene-therapeutic approaches

Tendons and ligaments are elastic collagenous tissues with similar composition and hierarchical structure, contributing to motion. Their strength is related to the number and size of the collagen fibrils. Collagen fibrils increase in size during development and in response to increased physical demands or training. Tendon disorders are commonly seen in clinical practice and give rise to significant morbidity. Treatment is difficult and patients often suffer from the symptoms for quite a long time. Despite remodelling, the biochemical and mechanical properties of healed tendon tissue never match those of intact tendon. The prerequisite for focussed treatment strategies in the future will be an improved understanding of the molecular events both in the embryo and contributing to regeneration in the adult organism. Novel approaches include the local delivery of growth factors, stem- and tendon-cell-derived therapy, the application of mechanical load and gene-therapeutic approaches based on vehicles encoding selected factors, or combinations of these. Important factors are proteins of the extracellular matrix like the metalloproteinases, growth factors like the bone morphogenetic proteins but also intracellular signalling mediator proteins, such as the Smads and transcription factors from the helix-loop-helix and other families. In this review, we focus specifically on such molecular approaches based on mesenchymal stem cells.

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.

Tendon and ligament engineering: from cell biology to in vivo application

Tendons and ligaments are related connective tissues that join muscle to bone and bone to bone, respectively. Tendon and ligament injuries are widely distributed clinical problems in society and while healing of such disorders can occur, the original biological properties of the tissue do not return to normal. In this review, recent work on tendon and ligament development and the use of growth factors for successful cellular therapy of tendon and ligament disorders are discussed. In addition, anti-inflammatory concepts for the treatment of tendon and ligament injuries and recent developments in stem cell engineering for tendon and ligament tissues are examined. Lastly, gene transfer strategies for therapeutic applications to heal tendon and ligament disorders are reviewed.

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.

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.

Tendon tissue engineering and gene transfer: the future of surgical treatment

Technologic improvements in the field of tissue engineering are leading to new potential developments in the currently used approaches to treat tendon injuries including difficult clinical scenarios such as zone II flexor tendon injuries of the hand and the mutilated hand with extensive tendon defects. A combination of mesenchymal (adult stem) cells, growth factors, and bioresorbable polymers can provide a solution for the treatment of difficult tendon injuries. Extensive research is needed to show that the extracellular matrix produced in response to the cell/growth factor/polymer composites in vivo is effective and functional as a regenerate tissue. Further exciting advances are foreseen in cell-based genetic engineering with the transfer of DNA to the site of tendon lacerations. These treatment modalities require improved safety precautions to reduce the risks and enhance the benefits of gene therapy.

Musculoskeletal gene therapy and its potential use in the treatment of complicated musculoskeletal infection

Tissue repair is a major issue in orthopedics. Many musculoskeletal tissues, including cartilage, meniscus, and the anterior cruciate ligament, heal poorly after injury. Recent studies have led to the identification of numerous growth factors and other gene products that can promote the regeneration of damaged musculoskeletal tissues. In the last century, the discovery and evolving use of antibiotics has significantly decreased the prevalence and severity of infectious diseases. In many orthopedic scenarios, however, treatment of infections can be difficult, and often involves a prolonged course of antibiotics with concomitant surgical interventions and loss of tissue. Although studies have demonstrated the successful transfer of target genes and the associated manipulation of the musculoskeletal tissue environment, researchers have made few attempts designed to use gene therapy to treat infectious musculoskeletal diseases in animal models. Before it is possible to use gene-based approaches to treat such diseases effectively, researchers must perform more studies to investigate the potential problems that may arise when using gene therapy in an infectious environment.

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.

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.

The use of growth factors on tendon injuries

Tendon injuries continue to be a vexing clinical problem faced by the upper extremity surgeon. These injuries often lead to disability and dissatisfaction for both the patient and treating physician. Advances throughout the century have focused largely on improvements in surgical techniques and therapy protocols. Recently, attention has been turned to the biologic pathways by which tendons heal and the growth factors involved in this process have been identified. There is great hope that these growth factors may one day be used to treat tendon injuries. This article provides a summary of the use of growth factors on tendon injuries including contemporary research, delivery methods, and future directions in this field.

The future of flexor tendon surgery

Clinical outcomes following flexor tendon repair have made significant improvements in the last 50 years. In that time standard treatment has evolved from secondary grafting to primary repair with postoperative rehabilitation protocols. Unfortunately, excellent results are not yet attained universally following treatment. Improving understanding of tendon healing at the cellular, molecular, and genetic levels will likely enable surgeons to modulate the normal repair process. We now look toward biologic augmentation of flexor tendon repairs to address the problems of increasing tensile strength while reducing adhesion formation following injury and operative repair.

Tendon healing in vitro: modification of tenocytes with exogenous vascular endothelial growth factor gene increases expression of transforming growth factor beta but minimally affects expression of collagen genes

PURPOSE

It is not clear how the transfer of exogenous growth factor genes to tenocytes affects collagen production. An increase in collagen production enhances the repair but an increase in growth factors that stimulate tissue fibrosis may cause adhesion. Gene therapy is a new way to regulate tendon healing but it has been explored rarely. We genetically modified tenocytes with the vascular endothelial growth factor (VEGF) gene and investigated the expression of the genes for collagen production in an in vitro model of the proliferating tenocytes.

METHODS

Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed randomly to 25 dishes. The tenocytes in the experimental dishes (n = 9) were treated for 12 hours with plasmid containing the VEGF complementary deoxyribonucleic acid and then were cultured for 5 days; the tenocytes in the control dishes (n = 8) did not receive the exogenous gene. Tenocytes in the other dishes received exogenous platelet-derived growth factor (PDGF) gene for comparison of the effects of VEGF gene therapy. Efficiency of the gene transfer was evaluated by presence of the transgene in the tenocytes which was detected by reverse transcription polymerase chain reactions. Levels of expression of types I and III collagen and transforming growth factor (TGF)-beta genes were determined by quantitative analysis of the products of reverse transcription polymerase chain reactions.

RESULTS

Expression of the TGF-beta gene increased significantly in the cells treated with exogenous VEGF cDNA. Expression of type I and III collagen genes by tenocytes was affected minimally by transfer of the VEGF gene to the tenocytes and was significantly weaker than that stimulated by PDGF gene therapy. Efficient gene transfer was confirmed by the presence of the VEGF complementary deoxyribonucleic acid in the tenocytes receiving the transferred gene.

CONCLUSIONS

Transfer of exogenous VEGF gene has very limited effects on the promotion of collagen production in the proliferating tenocytes. This study suggests that VEGF gene therapy is not as beneficial as PDGF gene therapy to tendon healing and may increase the activities of TGF-beta that are associated with adhesion formations.

Adenovirus-mediated gene transfer of growth and differentiation factor-5 into tenocytes and the healing rat Achilles tendon

Growth and differentiation factor-5 (GDF-5) is known to induce tendon tissue and stimulate tendon healing. The hypothesis was that adenoviral GDF-5 transfer leads to transitory transgene expression and improves Achilles tendon healing. In vitro experiments were first performed with rat tenocytes. Transgene expression was evaluated by RT-PCR, Western blotting and GDF-5-ELISA. In vivo virus dosage and transgene expression were examined by a marker gene transfer (LacZ and luciferase). In the main experiment in 131 rats, adenovirus particles (3 x 10(10)) were injected into transected Achilles tendons. The time course of GDF-5 mRNA expression was assessed by real-time RT-PCR. Histology and biomechanical testing were used to evaluate tendon healing and tensile strength. In vitro GDF-5 was secreted with a maximum after 2 weeks (330 ng GDF-5/10(6) cells per 24 hr). In vivo GDF-5 transgene expression showed a maximum at 4 weeks. At 8 weeks, GDF-5 specimens were thicker (p<0.05) with a trend to higher strength (p=0,064). Histology showed greater cartilage formation in type II collagen stains than in controls. Injection of adenovirus particles successfully can deliver the GDF-5 gene in healing tendons and leads to thicker tendon regenerates after 8 weeks. This technique might become a new approach for nonsurgical treatment of tendon injuries.

Characterization of adenovirus-mediated gene transfer in rabbit flexor tendons

PURPOSE

Adenoviral vector-based gene therapy is a promising technique for the delivery of growth factors to tendons. The objective of this study was to determine whether rabbit flexor tendons could be transduced effectively by adenoviral vectors and whether the introduction of adenoviral vectors would cause a notable local inflammatory response.

METHODS

Recombinant adenoviruses expressing green fluorescent protein (AdGFP) or BMP-13 (AdBMP-13) were constructed and 3 different viral titers (1 x 10(7), 1 x 10(8), and 1 x 10(9)) were tested in this study. The second through fifth tendons of the forepaws and hindpaws of a New Zealand white rabbit were identified surgically and injected with different viral titers of adenoviruses. The fifth tendon was used as a control. The tendons were harvested 12 days after surgery. The retrieved tendons were sectioned to measure transgene expression, as well as for histologic evaluation.

RESULTS

At all tested viral titers an efficient dose-dependent transgene expression was detected in all samples at 12 days after injection. At the highest dose the injection sites were notable for lymphocytic infiltration, suggesting that injected adenoviral vectors can illicit some local inflammatory response. Lymphocytic infiltration was much less apparent, however, in the tendons injected with lower titers of adenoviral vectors. There was no evidence of a massive inflammatory response and/or cell death.

CONCLUSIONS

Our findings show that adenovirus-based gene therapy is an efficient means of gene delivery to rabbit flexor tendons. Transduction efficiency of transgenes was dose dependent across the tested titers, although adenovirus-induced inflammation was notable only at the highest titer. This indicates that efficient gene transfer without notable local inflammatory response may be achieved by using the lower titers. Although adenovirus-induced inflammation can be minimized by using lower viral titers, its impact on adhesion formation in the long term remains unknown.

Tendon healing in vitro: genetic modification of tenocytes with exogenous PDGF gene and promotion of collagen gene expression

PURPOSE

Promotion of collagen production can increase tendon healing strength and reduce repair ruptures. Transfer of an exogenous growth factor gene to tenocytes of intrasynovial tendons may enhance the capacity of cells to produce collagen. We transferred the platelet-derived growth factor B (PDGF-B) gene to tenocytes and investigated its effects on the expression of the PDGF gene and the type I collagen gene in an in vitro tenocyte culture model.

METHODS

Tenocytes obtained from explant cultures of rat intrasynovial tendons were treated for 12 hours with the plasmid containing the PDGF complementary deoxyribonucleic acid (cDNA) with liposome and were then cultured for 6 additional days. The control tenocytes did not receive the exogenous gene and liposome. Efficiency of the gene transfer was evaluated by using reverse transcription polymerase chain reactions (RT-PCR) to detect the presence of the transferred gene in the tenocytes. Enhancement of the expression of the target gene was assessed by RT-PCR with primers effective to amplify both internal and transferred genes. Expression of the type I collagen gene was determined by quantitative analysis of the products of RT-PCR.

RESULTS

Levels of expression of the type I collagen gene by tenocytes were increased significantly by transfer of the exogenous PDGF gene to the tenocytes. Efficiency of the gene transfer was confirmed by the presence of exogenous PDGF cDNA in the tenocytes receiving the transferred gene. Expression of the PDGF gene increased significantly in the cells treated with exogenous PDGF cDNA.

CONCLUSIONS

Exogenous PDGF genes can be transferred effectively into intrasynovial tenocytes and the transfer increases significantly the expression of genes for PDGF and type I collagen. Transfer of the PDGF gene may offer a novel way of effectively promoting healing of intrasynovial flexor tendons. The findings warrant future in vivo study to test the effectiveness of gene therapy to promote flexor tendon healing.

Clinical implications of growth factors in flexor tendon wound healing

Recent research has focused on the role of growth factors in flexor tendon wound healing. These basic science reports have described the identification and quantification of various growth factors in in vitro and in vivo models. Although these reports have begun to piece together the cascade of events involved in flexor tendon wound healing, the clinical relevance for the practicing hand surgeon is unclear. Growth factors are cell-secreted proteins that regulate cellular functions. These growth factors are involved in cell differentiation and growth, including the normal processes of development and tissue repair. Several growth factors recently have been identified as playing roles in tendon healing including vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-beta). In addition, the transcription factor NF-kappaB has been implicated in the signaling pathways of these growth factors. The purpose of this article is to describe what is known about the molecular basis of flexor tendon wound healing, to review the most commonly studied growth factors, and to summarize likely clinical applications of these growth factors to flexor tendon repair.

Cranial repair using BMP-2 gene engineered bone marrow stromal cells

BACKGROUND

Bone grafts, allografts, and biocompatible artificial bone substitutes all have their shortcomings when used for the repair of cranial bone defects. Tissue engineered bone shows promise as an alternative for the repair of these defects.

MATERIALS AND METHODS

Rabbit bone marrow mesenchymal stromal cells (MSCs) were separated from iliac crest aspirates and expanded in a monolayer culture 1 month before implantation. These MSCs were then infected with replication-defective adenovirus-human BMP-2 genes 1 week before implantation. Bilateral critical-size cranial defects were created in the animal with removal of osteoinductive periosteum and dura. MSCs were mixed with alginate UP (ultrapure) to form MSC/polymer construct. MSCs used for the control site were infected with adenovirus beta-galactosidase (beta-gal). After 1 week, 6 weeks, and 3 months, five rabbits from each experimental group were sacrificed and the cranial defect site was examined by histology study.

RESULTS

Near-complete repair of the large size cranial defects using the tissue engineered MSC/alginate construct was observed. The H&E stain and von Kossa's staining should better regenerate bone at the experiment site. A statistically significant difference in bone formation was noted by 3D CT imaging at 3 months post-BMP-2 treatment of the cranial defects (0.79 +/- 0.06 versus 0.47 +/- 0.05 cm(2), P < 0.001) but not at 6 weeks (0.36 +/- 0.04 versus 0.33 +/- 0.03 cm(2), P = 0.347).

CONCLUSIONS

Near-complete repair of large cranial defects can be achieved using tissue engineered bone. The use of newly developed polymers as well as the integration of the stem cell concept with gene medicine is necessary to attain this goal.

Gene intervention in ligament and tendon: current status, challenges, future directions

Ligament and tendon injuries are common clinical problems. Healing of these tissues occurs, but their properties do not return to normal. This predisposes to recurrent injuries, instability and arthritis, loss of motion and weakness. Gene therapy offers a novel approach to the repair of ligaments and tendons. Introduction of genes into ligaments and tendons using vectors has been successful. Marker genes and therapeutic genes have been introduced into both tissues with evidence of corresponding functional alterations. In addition, gene transfer has been used to manipulate the healing environment, opening the possibility of gene transfer to investigate ligament and tendon development and homeostasis, in addition to using this technology therapeutically. Several factors modulate the 'success' of gene transfer in these tissues.

Animal models of tendon and ligament injuries for tissue engineering applications

Animal modeling continues to be an important component to the critical evaluation of new techniques to treat tendon and ligament injuries. Appropriate choice and analysis of these models is essential. Factors that should be considered in assessing a potential model include the tissue type (ligament versus tendon and intrasynovial versus extrasynovial), the type of injury to be modeled, the techniques of measuring the response to treatment, the ease of comparison to previously published models and finally, the ease of translation to human trials and eventually to clinical usage.

Adenovirus mediated BMP-13 gene transfer induces chondrogenic differentiation of murine mesenchymal progenitor cells

Chondrogenic/osteogenic differentiation of a mesenchymal progenitor stimulated by BMP-13 (CDMP-2) was studied. C3H10T1/2 cells were transduced by an adenoviral construct containing BMP-13 or BMP-2. BMP-13 supported chondrogenesis but not terminal differentiation, whereas BMP-2 stimulated endochondral ossification. The studies show that BMP-13 may fail to support terminal chondrocyte differentiation.

INTRODUCTION

Bone morphogenetic protein (BMP)-13 is a member of the transforming growth factor beta (TGF-beta) superfamily of growth factors. Although the biological functions of BMP-13 remain poorly understood, continued postnatal expression of BMP-13 in articular cartilage suggests that this protein may function in an autocrine/paracrine fashion to regulate growth and maintenance of articular cartilage. The purpose of this study was to elucidate the role of BMP-13 in chondrogenic differentiation.

MATERIALS AND METHODS

Replication-deficient adenoviruses carrying human BMP-13 (Adv-hBMP13), bacterial beta-galactosidase (Adv-beta gal), and human BMP-2 (Adv-hBMP2) were constructed. Murine mesenchymal progenitor cells (C3H10T1/2) were transduced with these vectors, and differentiation to the chondrogenic lineage was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR), biochemical, and histological analyses.

RESULTS AND CONCLUSIONS

Our findings revealed that hBMP-13 transduced cells differentiated into round cells that stained with Alcian blue. Analysis of gene expression in hBMP-13-transduced cells demonstrated presence of cartilage-specific markers, absence of hypertrophic chondrocyte specific markers, and upregulation of proteoglycan biosynthesis. In particular, hBMP-13-transduced cells had significantly less and delayed expression of alkaline phosphatase activity and calcium mineral accumulation than hBMP-2-transduced cells. Except for BMPR-IB/ALK-6, expression of BMP receptors was identified constitutively in C3H10T1/2 cells and was not affected by the presence of either of the BMPs. In summary, hBMP-13, while stimulating chondrogenesis, failed to support differentiation to hypertrophic chondrocytes and endochondral ossification similar to hBMP-2. Thus, this may prove to be a useful strategy for cell-based regeneration of articular cartilage.

Ex Vivo Gene Therapy in Autologous Critical-Size Craniofacial Bone Regeneration

In therapeutic bone repairs, autologous bone grafts, conventional or vascularized allografts, and biocompatible artificial bone substitutes all have their shortcomings. The bone formed from peptides [recombinant human bone morphogenetic proteins (BMPs)], demineralized bone powder, or a combination of both is small in size. Tissue engineering may be an alternative for cranial bone repair. In this study, the authors developed an animal model to test the hypothesis that replication-defective, adenovirus-mediated human BMP-2 gene transfer to bone marrow stromal cells enhances the autologous bone formation for repairing a critical-size craniofacial defect. The mesenchymal stromal cells of miniature swine were separated from the iliac crest aspirate and expanded in monolayer culture 1 month before implantation. The cultured mesenchymal stromal cells were infected with recombinant, replication-defective human adenovirus BMP-2, 7 days before implantation. Bilateral 2 x 5-cm2 cranial defects were created, leaving no osteogenic periosteum and dura behind. Mesenchymal stromal cells at 5 x 10(7)/ml were mixed with collagen type I to form mesenchymal stromal cell/polymer constructs. Mesenchymal stromal cells used for the control site were infected with adenovirus beta-Gal under the same conditions. After 6 weeks and 3 months, 10 miniature swine were euthanized and the cranium repair was examined. Near-complete repair of the critical-size cranial defect by tissue-engineered mesenchymal stromal cell/collagen type I construct was observed. The new bone formation area (in square centimeters) measured by three-dimensional computed tomography demonstrated that the improvement from 6 weeks to 3 months was significantly greater on the experimental side than on the control side (2.15 cm2 versus 0.54 cm2, p < 0.001) and significantly greater at 3 months than at 6 weeks (2.13 cm2 versus 0.52 cm2, p < 0.001). The difference between the experimental and control groups was significant at 3 months (mean difference, 2.13 cm2; p < 0.001). The maximal compressive strength of the new bone was similar to that of the normal cranial bone when evaluated by biomechanical testing (cranium bone versus tissue-engineered bone, 88.646 +/- 5.121 MPa versus 80.536 +/- 19.302 MPa; p = 0.227). Adenovirus was absent from all constructs by immunochemical staining at 6 weeks and 3 months after implantation. The successful repair of cranial defects in this experiment demonstrates the efficacy of the integration of the autologous stem cell concept, gene medicine, and polymers in producing tissue-engineered bone.

Ex vivo gene therapy in autologous bone marrow stromal stem cells for tissue-engineered maxillofacial bone regeneration

This study examines the clinical relevance of tissue engineering integrating gene therapy and polymer science to bone regeneration. Bilateral maxillary defects (3 x 1.2 cm(2)) in 20 miniature swine were bridged with a bioresorbable internal splint. Constructs were created using ex vivo adenovirus bone morphogenetic protein (BMP)-2-mediated gene transfer to the expanded bone marrow mesenchymal stem cells (MSCs) 7 days before implantation. Controls were performed using adenovirus beta-galactosidase. The BMP-2 cell/construct displayed white solid bone formation after 3 months. Meanwhile, the hematoxylin and eosin and Von Kossa stains demonstrated exhibited mature woven bone with good mineralization. Additionally, three-dimensional computer tomography imaging revealed a nearly complete infraorbital rim repair. Quantitative analysis demonstrated a significant difference (P<0.001) in bone formation. Finally, biomechanical testing revealed no statistically significant difference in the maximal compressive strength of new bone formed by BMP-2 cell constructs and the normal maxilla. The data evidenced de novo bone formation capable of sustaining axial compressive loads. The measurement results showed that ex vivo replication defective adenovirus-mediated human BMP-2 gene transfer to MSCs enhances autologous bone formation in the repair of maxillary defects.

Tissue engineering of flexor tendons

Despite technical advances in suture methods and rehabilitation protocols, challenges remain in the field of flexor tendon repair. This article reviews the state-of-the-art research in the tissue engineering of flexor tendons. These early published data will hopefully lay the foundation for molecular methods and materials that can be used to reconstruct tendons to restore normal form and function in the hand.

Gene therapy and tissue engineering for sports medicine

Sports injuries usually involve tissues that display a limited capacity for healing. The treatment of sports injuries has improved over the past 10 to 20 years through sophisticated rehabilitation programs, novel operative techniques, and advances in the field of biomechanical research. Despite this considerable progress, no optimal solution has been found for treatment of various sports-related injuries, including muscle injuries, ligament and tendon ruptures, central meniscal tears, cartilage lesions, and delayed bone fracture healing. New biological approaches focus on the treatment of these injuries with growth factors to stimulate and hasten the healing process. Gene therapy using the transfer of defined genes encoding therapeutic proteins represents a promising way to efficiently deliver suitable growth factors into the injured tissue. Tissue engineering, which may eventually be combined with gene therapy, may potentially result in the creation of tissues or scaffolds for regeneration of tissue defects following trauma. In this article we will discuss why gene therapy and tissue engineering are becoming increasingly important in modern orthopaedic sports medicine practice. We then will review recent research achievements in the area of gene therapy and tissue engineering for sports-related injuries, and highlight the potential clinical applications of this technology in the treatment of patients with musculoskeletal problems following sports-related injuries.

Engineered allogeneic mesenchymal stem cells repair femoral segmental defect in rats

Bone marrow derived mesenchymal stem cells (MSC) have been shown to be progenitor cells for mesenchymal tissues. These cells may also provide a potential therapy for bone repair. Our previous studies showed that MSC engineered with the gene for bone morphogenetic protein 2 (BMP-2), a growth factor for bone cells, were capable of differentiating into osteoblast lineage and inducing autologous bone formation in several animal models. Culturing individual MSC for autologous implantation, however, remains problematic. The number of human MSC with osteogenic potential decreases with age, and, in certain diseases, the patient's marrow may be damaged or the healthy cells reduced in number. In this study, we used rats with a femoral segmental defect to investigate whether allogeneic BMP-2 engineered MSC would facilitate bone healing. We show that BMP-2 engineered allogeneic MSC can repair critical bone defects to the same degree as rats treated with BMP-2 engineered autologous MSC, if the allogeneic group receives short-term treatment with immunosuppressant FK506. We also show that allogeneic gene transferred MSC are directly involved in bone repair, in addition to acting as gene deliverers.

What advice should we give to athletes postconcussion?

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Response of donor and recipient cells after transplantation of cells to the ligament and tendon

The mechanical properties of healing ligaments and tendons are not comparable to those of normal tissue. To improve the quality of the ligament healing, therapeutic strategies include gene transfer or placement of mesenchymal stem cells at the healing site. Studies show that marker genes, growth factors, and antisense oligonucleotides can be delivered to both normal and healing ligaments and tendons by gene transfer. Cells with and without genetic modification have been successfully transplanted to ligaments and tendons and remain viable. Tendon healing can be improved using collagen gel implants seeded with autologous mesenchymal stem cells. Even though these early results are encouraging, more work is required regarding the response of the recipient site to donor cells or vectors.

Genetic engineering of meniscal allografts

Allograft meniscal transplantation represents one of the few available treatment options after menisectomy. Despite acceptable early results, a considerable controversy exists with regard to poor graft regeneration, shrinkage and biomechanical failure of transplanted menisci. Transfer of specific growth factor genes may improve the regeneration process of meniscal allografts. The aim of this study was to investigate the feasibility of gene transfer in meniscal allografts in rabbits. Four different viral vectors encoding marker genes, including lacZ, luciferase, and green fluorescence protein were used to investigate viral transduction in 50 lapine menisci for 4 weeks in vitro. Subsequently, 16 unilateral meniscus replacements were performed with ex vivo retrovirally transduced meniscal allografts, and the expression of the lacZ gene was examined histologically at 2, 4, 6, and 8 weeks after transplantation. Gene expression in the superficial cell layers of the menisci can be detected for up to 4 weeks in vitro, but the level of gene transfer declined over time. The transduction with retrovirus showed better persistence and deep penetration of the menisci with infected cells. In vivo, declining numbers of beta-galactosidase-positive cells were also detected in retrovirally transduced allografts up to 8 weeks. Consistently, transduced cells were found at the menisco-synovial junction of the transplants and in deeper layers of the menisci. There was no evidence of cellular immune response in the transduced transplants. This investigation showed a prospective for growth factor delivery in auto- and allografts. In further experiments, vectors expressing therapeutic proteins such as growth factors will be investigated to assess their potential to improve remodeling and healing of meniscal allografts.