Myoblast-mediated gene transfer to the joint

Mesenchymal Stem Cells for Enhanced Healing of the Medial Collateral Ligament of the Knee Joint

Background and Objectives: The medial collateral ligament (MCL) is one of the major supporting ligaments of the knee joint, and MCL injuries are common where excessive valgus loading is applied to the knee joint. Although most MCL injuries can be treated conservatively, healing of the MCL can take several weeks to months. Furthermore, once injured, the biomechanical properties of the healed MCL differ from those of the native MCL, resulting in an increased risk of re-injury and chronic remnant symptoms. Mesenchymal stem cells (MSCs), owing to their therapeutic potential, have been investigated in various musculoskeletal injuries, and some preclinical studies regarding MSC-based approaches in MCL injuries have shown promising results. Despite satisfactory results in preclinical studies, there is still a lack of clinical studies in the orthopedic literature. This article describes the basic knowledge of the MCL, standard treatments for MCL injuries, and recent studies regarding the application of MSCs for enhanced healing of the MCL. MSC-based approaches are expected to be a potential therapeutic option for enhanced healing of the MCL in the future.

Gene therapy approaches for equine osteoarthritis

With an intrinsically low ability for self-repair, articular cartilage injuries often progress to cartilage loss and joint degeneration resulting in osteoarthritis (OA). Osteoarthritis and the associated articular cartilage changes can be debilitating, resulting in lameness and functional disability both in human and equine patients. While articular cartilage damage plays a central role in the pathogenesis of OA, the contribution of other joint tissues to the pathogenesis of OA has increasingly been recognized thus prompting a whole organ approach for therapeutic strategies. Gene therapy methods have generated significant interest in OA therapy in recent years. These utilize viral or non-viral vectors to deliver therapeutic molecules directly into the joint space with the goal of reprogramming the cells' machinery to secrete high levels of the target protein at the site of injection. Several viral vector-based approaches have demonstrated successful gene transfer with persistent therapeutic levels of transgene expression in the equine joint. As an experimental model, horses represent the pathology of human OA more accurately compared to other animal models. The anatomical and biomechanical similarities between equine and human joints also allow for the use of similar imaging and diagnostic methods as used in humans. In addition, horses experience naturally occurring OA and undergo similar therapies as human patients and, therefore, are a clinically relevant patient population. Thus, further studies utilizing this equine model would not only help advance the field of human OA therapy but also benefit the clinical equine patients with naturally occurring joint disease. In this review, we discuss the advancements in gene therapeutic approaches for the treatment of OA with the horse as a relevant patient population as well as an effective and commonly utilized species as a translational model.

Gene Delivery to Joints by Intra-Articular Injection

Most forms of arthritis are incurable, difficult to treat, and a major cause of disability in Western countries. Better local treatment of arthritis is impaired by the pharmacokinetics of the joint that make it very difficult to deliver drugs to joints at sustained, therapeutic concentrations. This is especially true of biologic drugs, such as proteins and RNA, many of which show great promise in preclinical studies. Gene transfer provides a strategy for overcoming this limitation. The basic concept is to deliver cDNAs encoding therapeutic products by direct intra-articular injection, leading to sustained, endogenous synthesis of the gene products within the joint. Proof of concept has been achieved for both in vivo and ex vivo gene delivery using a variety of vectors, genes, and cells in several different animal models. There have been a small number of clinical trials for rheumatoid arthritis (RA) and osteoarthritis (OA) using retrovirus vectors for ex vivo gene delivery and adeno-associated virus (AAV) for in vivo delivery. AAV is of particular interest because, unlike other viral vectors, it is able to penetrate deep within articular cartilage and transduce chondrocytes in situ. This property is of particular importance in OA, where changes in chondrocyte metabolism are thought to be fundamental to the pathophysiology of the disease. Authorities in Korea have recently approved the world's first arthritis gene therapy. This targets OA by the injection of allogeneic chondrocytes that have been transduced with a retrovirus carrying transforming growth factor-β₁ cDNA. Phase III studies are scheduled to start in the United States soon. Meanwhile, two additional Phase I trials are listed on Clinicaltrials.gov , both using AAV. One targets RA by transferring interferon-β, and the other targets OA by transferring interleukin-1 receptor antagonist. The field is thus gaining momentum and promises to improve the treatment of these common and debilitating diseases.

Myoblast Therapy: From Bench to Bedside

Myoblasts are defined as stem cells containing skeletal muscle cell precursors. A decade of experimental work has revealed many properties of myoblasts, including the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity. Early phase clinical trials also showed that myoblast-based therapy is a promising approach for many intractable clinical conditions, including both muscle-related and non-muscle-related diseases. The potential application of myoblast therapy may be in the treatment of genetic muscle diseases, cardiomyocyte damaged heart diseases, and urinary incontinence. This review will provide an overview of myoblast biology, along with discussion of the potential application in clinical medicine. In addition, problems in current myoblast therapy and possible future improvements will be addressed.

Nonviral gene transfer to human meniscal cells. Part I: transfection analyses and cell transplantation to meniscus explants

PURPOSE

Our aim was to evaluate whether nonviral vectors can genetically modify primary human juvenile and adult meniscal fibrochondrocytes at low toxicity in vitro and to test the hypothesis that transfected human meniscal fibrochondrocytes transplanted into longitudinal defects and onto human medial meniscus explant cultures are capable of expressing transgene products in vitro.

METHODS

Eighteen nonviral gene transfer systems were examined to identify the best suited method for an efficient transfection of primary cultures of juvenile and adult human meniscal fibrochondrocytes using luciferase and lacZ reporter gene constructs and then transplanted to meniscus explant cultures.

RESULTS

Gene transfer systems FuGENE 6, GeneJammer, TurboFectin 8, calcium phosphate co-precipitates and GeneJuice led to minimal toxicity in both cell types. Nanofectin 2 and JetPEI resulted in maximal luciferase activity in both cell types. Maximal transfection efficiency based on X-gal staining following lacZ gene transfer was achieved using Lipofectamine 2000, revealing a mean transfection efficiency of 8.6 % in human juvenile and of 8.4 % in adult meniscal fibrochondrocytes. Transfected, transplanted meniscal fibrochondrocytes adhered to the meniscal tissue and continued to express the transgene for at least five days following transfection.

CONCLUSIONS

Nonviral gene transfer systems are safe and capable of transfecting both juvenile and adult human meniscal fibrochondrocytes, which, when transplanted to meniscal tissue in vitro, permit the expression of selected transgenes to be maintained. These results are of value for combining gene therapy and cell transplantation approaches as a means to enhance meniscal repair.

Chondrogenesis of myoblasts in biodegradable poly-lactide-co-glycolide scaffolds

Myoblasts are considered to be an alternative cell source for cell-based meniscal repair due to their multiple differentiation potentials. This study addresses the chondrogenic differentiation of myoblasts seeded into poly-lactide-co-glycolide (PLGA) scaffolds following implantation in a subcutaneous pocket of nude mice. Canine myoblasts isolated from a Beagle were expanded and seeded into PLGA scaffolds and cultured in cartilage-derived morphogenetic protein-2 (CDMP-2) and transforming growth factor-β1 (TGF-β1)-containing medium for 2 weeks in vitro. The constructs were implanted into a subcutaneous pocket of 24 combined immunodeficiency mice and harvested after 8 and 12 weeks, respectively. Hematoxylin and eosin staining of the sections of the engineered cartilage at 8 and 12 weeks revealed the regeneration of fibrocartilage. Immunohistochemical staining confirmed a similar distribution of collagen type Ⅱ in the engineered cartilage as the normal meniscus. At 12 weeks, expression of mRNAs for type Ⅰ collagen, type Ⅱ collagen and aggrecan was detected by RT-PCR. The compressive moduli of engineered cartilage reached 85.72% of the normal meniscus at 12 weeks, with a high level of glycosaminoglycan (GAG) content (no statistical difference from normal). Myoblast-seeded PLGA scaffolds express a stable chondrogenic phenotype in a heterotopic model of cartilage transplantation and represent a suitable tool for tissue engineering of cartilage.

Role of angiogenesis after muscle derived stem cell transplantation in injured medial collateral ligament

We performed this study to investigate the therapeutic role of vascular endothelial growth factor (VEGF) in medial collateral ligament (MCL) healing. Murine muscle derived stem cells (MDSCs) obtained via the preplate technique were retrovirally transduced to express: (1) VEGF and nLacZ (MDSC-VEGF), (2) soluble fms-like tyrosine kinase-1 (sFLT1, a VEGF-specific antagonist) and nLacZ (MDSC-sFLT1), and (3) nLacZ (MDSC-nLacZ). After transecting the MCL of immunodeficient rats, 5 × 10(5)  cells of each of the transduction groups list above were transplanted into the MCL injury site. A control group was injected with phosphate-buffered saline (PBS) only. Immunohistochemical staining demonstrated that there were more Isolectin B4 and β-galactosidase double positive cells in the rats transplanted with MDSC-VEGF transduced cells than the other groups at week 1. Capillary density was significantly higher in the MDSC-VEGF group than the other groups at week 2; however, there were no significant differences in the biomechanical assessment between the MDSC-VEGF and MDSC-nLacZ groups. On the other hand, the MDSC-sFLT1 group revealed a lower capillary density than the other two groups and the functional ligament healing of the MDSC-sFLT1 group was significantly decreased compared to the other groups when assessed biomechanically. The findings of the present study suggest that angiogenesis plays a critical role in the healing process of injured MCL.

Autologous transplantation of culture-born myofibroblasts into intact and injured rabbit ligaments

PURPOSE

The myofibroblast, a contractile fibroblastic cell expressing α-smooth muscle actin (α-SMA), has been reported to play a role in ligament healing. The aim of this study was to evaluate the feasibility of transplanting culture-derived myofibroblasts in injured rabbit medial collateral ligaments (MCL) and in intact anterior cruciate ligaments (ACL).

METHODS

Fibroblasts isolated from the iliotibial band were cultured in the presence of transforming growth factor beta-1 (TGF-β1) for five days and analysed for α-SMA expression. In a concentration of TGF-β1 ≥ 10 ng/ml, the differentiation rate into myofibroblast was 90%. After labelling with PKH26, α-SMA -positive cells were transplanted in intact ACL and in injured MCL of ten rabbits.

RESULTS

Survival of PKH-26+ cells was seen in all intact and damaged ligaments one day after injection. The density of PKH-26+ cells had decreased at seven days postinjection in both ligaments. Double-positive PKH-26+/α-SMA+ cells were only observed in injured MCL at seven days postinjection. Moreover, we found that genetically modified fibroblasts differentiate into myofibroblasts and can be transplanted into ligaments.

CONCLUSIONS

Our data demonstrate that culture-born myofibroblasts survive and maintain α-SMA expression up to one week after transplantation. This study provides the first insight into the feasibility of transplanted mechanically active cells for ligament reconstruction.

Repair of meniscal defect using an induced myoblast-loaded polyglycolic acid mesh in a canine model

Defects of the meniscus greatly alter knee function and predispose the joint to degenerative changes. The purpose of this study was to test a recently developed cell-scaffold combination for the repair of a critical-size defect in the canine medial meniscus. A bilateral, complete resection of the anterior horn of the medial meniscus was performed in 18 Beagle canines. A PLGA scaffold was implanted into the defect of one knee of 6 canines and the contralateral defect was left untreated. Scaffolds loaded with autologous myoblasts and cultured in a chondrogenic medium for 14 days were implanted in a second series of 12 canines. Empty scaffolds were implanted in the contralateral knees. Menisci were harvested at 12 weeks. Untreated defects had a muted fibrous healing response. Defects treated with cell-free implants also showed predominantly fibrous tissue, whereas fibrocartilage was present in several scaffolds. The thickness of the repair tissue after treatment with cell-free scaffolds was significantly greater compared to the controls (p<0.05). Pre-cultured implants integrated with the host tissue, and 9 of 12 contained meniscus-like fibrocartilage when compared to 2 of the 12 controls (p<0.05). The thickness of the pre-cultured implant repair tissue was greater compared to the controls (p<0.05). This study demonstrates the repair of a critical size meniscal defect using a stem cell and scaffold-based tissue engineering approach.

Terminal differentiation is not a major determinant for the success of stem cell therapy - cross-talk between muscle-derived stem cells and host cells

We have found that when muscle-derived stem cells (MDSCs) are implanted into a variety of tissues only a small fraction of the donor cells can be found within the regenerated tissues and the vast majority of cells are host derived. This observation has also been documented by other investigators using a variety of different stem cell types. It is speculated that the transplanted stem cells release factors that modulate repair indirectly by mobilizing the host's cells and attracting them to the injury site in a paracrine manner. This process is loosely called a 'paracrine mechanism', but its effects are not necessarily restricted to the injury site. In support of this speculation, it has been reported that increasing angiogenesis leads to an improvement of cardiac function, while inhibiting angiogenesis reduces the regeneration capacity of the stem cells in the injured vascularized tissues. This observation supports the finding that most of the cells that contribute to the repair process are indeed chemo-attracted to the injury site, potentially through host neo-angiogenesis. Since it has recently been observed that cells residing within the walls of blood vessels (endothelial cells and pericytes) appear to represent an origin for post-natal stem cells, it is tempting to hypothesize that the promotion of tissue repair, via neo-angiogenesis, involves these blood vessel-derived stem cells. For non-vascularized tissues, such as articular cartilage, the regenerative property of the injected stem cells still promotes a paracrine, or bystander, effect, which involves the resident cells found within the injured microenvironment, albeit not through the promotion of angiogenesis. In this paper, we review the current knowledge of post-natal stem cell therapy and demonstrate the influence that implanted stem cells have on the tissue regeneration and repair process. We argue that the terminal differentiation capacity of implanted stem cells is not the major determinant of the cells regenerative potential and that the paracrine effect imparted by the transplanted cells plays a greater role in the regeneration process.

Chondrogenesis of synovium-derived mesenchymal stem cells in gene-transferred co-culture system

A co-culture strategy has been developed in this study wherein rabbit synovial mesenchymal stem cells (SMSCs) are co-cultured with growth factor (GF) transfected articular chondrocytes. Toward this end, both SMSCs and early passage rabbit articular chondrocytes that had been adenovirally transduced with transforming growth factor-beta 3 (TGF-beta3) gene were separately encapsulated in alginate beads and co-cultured in the same pool of chondrogenic medium. The chondrocytes act as transfected companion cells (TCCs) providing GF supply to induce chondrogenic differentiation of SMSCs that play the role of therapeutic progenitor cells (TPCs). Against the same TCC based TGF-beta3 release profile, the co-culture was started at different time points (Day 0, Day 10 and Day 20) but made to last for identical periods of exposure (30 days) so that the exposure conditions could be optimized in terms of initiation and duration. Transfection of TCCs prevents the stem cell based TPCs from undergoing the invasive procedure. It also prevents unpredictable complications in the TPCs caused by long-term constitutive over-expression of a GF. The adenovirally transfected TCCs exhibit a transient GF expression which results in a timely termination of GF supply to the TPCs. The TCC-sourced transgenic TGF-beta3 successfully induced chondrogenesis in the TPCs. Real-time PCR results show enhanced expression of cartilage markers and immuno/histochemical staining for Glycosaminoglycans (GAG) and Collagen II also shows abundant extracellular matrix (ECM) production and chondrogenic morphogenesis in the co-cultured TPCs. These results confirm the efficacy of directing stem cell differentiation towards chondrogenesis and cartilage tissue formation by co-culturing them with GF transfected chondrocytes.

Administrations of peripheral blood CD34-positive cells contribute to medial collateral ligament healing via vasculogenesis

Neoangiogenesis is a key process in the initial phase of ligament healing. Adult human circulating CD34+ cells, an endothelial/hematopoietic progenitor-enriched cell population, have been reported to contribute to neoangiogenesis; however, the therapeutic potential of CD34+ cells for ligament healing is still unclear. Therefore, we performed a series of experiments to test our hypothesis that ligament healing is supported by CD34+ cells via vasculogenesis. Granulocyte colony-stimulating factor-mobilized peripheral blood (GM-PB) CD34+ cells with atelocollagen (CD34+ group), GM-PB mononuclear cells (MNCs) with atelocollagen (MNC group), or atelocollagen alone (control group) was locally transplanted after the creation of medial collateral ligament injury in immunodeficient rats. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical staining at the injury site demonstrated that molecular and histological expression of human-specific markers for endothelial cells was higher in the CD34+ group compared with the other groups at week 1. Endogenous effect, assessed by capillary density and mRNA expression of vascular endothelial growth factor, was significantly higher in CD34+ cell group than the other groups. In addition to the observation that, as assessed by real-time RT-PCR, gene expression of ligament-specific marker was significantly higher in the CD34+ group than in the other groups, ligament healing assessed by macroscopic, histological, and biomechanical examination was significantly enhanced by CD34+ cell transplantation compared with the other groups. Our data strongly suggest that local transplantation of circulating human CD34+ cells may augment the ligament healing process by promoting a favorable environment through neovascularization.

Gene therapy for cartilage defects

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

Gene therapy as a therapeutic approach for the treatment of rheumatoid arthritis: innovative vectors and therapeutic genes

In recent years, significant progress has been made in the treatment of rheumatoid arthritis (RA). In addition to conventional therapy, novel biologicals targeting tumour necrosis factor-alpha have successfully entered the clinic. However, the majority of the patients still has some actively inflamed joints and some patients suffer from side-effects associated with the high systemic dosages needed to achieve therapeutic levels in the joints. In addition, due to of the short half-life of these proteins there is a need for continuous, multiple injections of the recombinant protein. An alternative approach might be the use of gene transfer to deliver therapeutic genes locally at the site of inflammation. Several viral and non-viral vectors are being used in animal models of RA. The first gene therapy trials for RA have already entered the clinic. New vectors inducing long-term and regulated gene expression in specific tissue are under development, resulting in more efficient gene transfer, for example by using distinct serotypes of viral vectors such as adeno-associated virus. This review gives an overview of some promising vectors used in RA research. Furthermore, several therapeutic genes are discussed that could be used for gene therapy in RA patients.

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.

Stem cells as vehicles for orthopedic gene therapy

Adult stem cells reside in adult tissues and serve as the source for their specialized cells. In response to specific factors and signals, adult stem cells can differentiate and give rise to functional tissue specialized cells. Adult mesenchymal stem cells (MSCs) have the potential to differentiate into various mesenchymal lineages such as muscle, bone, cartilage, fat, tendon and ligaments. Adult MSCs can be relatively easily isolated from different tissues such as bone marrow, fat and muscle. Adult MSCs are also easy to manipulate and expand in vitro. It is these properties of adult MSCs that have made them the focus of cell-mediated gene therapy for skeletal tissue regeneration. Adult MSCs engineered to express various factors not only deliver them in vivo, but also respond to these factors and differentiate into skeletal specialized cells. This allows them to actively participate in the tissue regeneration process. In this review, we examine the recent achievements and developments in stem-cell-based gene therapy approaches and their applications to bone, cartilage, tendon and ligament tissues that are the current focus of orthopedic medicine.

In Vivo Evaluation of Gene Therapy Vectors in Ex Vivo-Derived Marrow Stromal Cells for Bone Regeneration in a Rat Critical-Size Calvarial Defect Model

Cells genetically modified to produce osteoinductive factors have potential for use in enhancing bone regeneration for reconstructive applications. Genetic modification of cells can be accomplished by a variety of gene therapy vectors. In this study we evaluated the ex vivo genetic modification of rat marrow stromal cells (MSCs) by adenoviral, retroviral, and cationic lipid vectors containing the gene for human bone morphogenetic protein 2 (hBMP-2). We investigated both the in vitro and in vivo osteogeneic potential of MSCs modified by each vector. In vitro, we found that only MSCs modified with the adenoviral vector produced detectable hBMP-2 and demonstrated a statistically significant increase in endogenous alkaline phosphatase activity indicative of osteogeneic differentiation. We further investigated the ability of genetically modified MSCs seeded on a titanium mesh scaffold to facilitate bone formation in vivo. In an orthotopic critical-size defect created in the rat cranium, bone formation was observed in all conditions with MSCs modified by the adenoviral vector demonstrating a small but statistically significant increase in bone formation relative to the other vectors and control. Implants in an ectopic location demonstrated minimal bone formation relative to the orthotopic location, with MSCs modified with cationic lipids forming less bone than the other vectors and control. Our results show that MSCs genetically modified with adenovirus containing the hBMP-2 gene had enhanced osteogeneic capacity relative to unmodified MSCs or MSCs modified by the other vectors. This study was the first to compare three different gene therapy vectors for the genetic modification of cells to produce osteoinductive factors for the purpose to enhance bone regeneration.

Gene transfer as a future therapy for rheumatoid arthritis

Inhibiting key pathogenic processes within the rheumatoid synovium is a most attractive goal to achieve, and the number of potential intra- and extracellular pathways operative in rheumatoid arthritis (RA) that could be used for a gene therapy strategy is increasing continuously. Gene transfer or gene therapy might also be one of the approaches to solve the problem of long-term expression of therapeutic genes, in order to replace the frequent application of recombinant proteins, in the future. However, at present, gene therapy has not reached a realistic clinical stage, which is mainly due to severe side effects in humans, the complexity of RA pathophysiology and the current state of available gene transfer techniques. On the other hand, novel gene delivery systems are not restricted to vectors or certain types of cells, as mobile cells including macrophages, dendritic cells, lymphocytes and multipotent stem cells can also be used as smart gene transfer vehicles. Moreover, the observation in animal models that application of viral vectors into a joint can exert additional therapeutic effects in nearby joints might also facilitate the transfer from animal to human gene therapy. Future strategies will also examine the potential of novel long-term expression vectors such as lentiviruses and cytomegalovirus (CMV)-based viruses as a basis for future clinical trials in RA.

Dynamics of the early immune cellular reactions after myogenic cell transplantation

The role of immune cells in the early donor cell death/survival following myoblast transplantation is confusing, one of the reasons being the lack of data about the immune reactions following cell transplantation. We used outbred mice as hosts for transplantation of primary cultured muscle cells and T-antigen-immortalized myoblasts. The host muscles were analyzed 1 h to 7 days after cell injection. No net loss of the donor primary cultured cell population was observed in this period. The immune cellular reaction in this case was: 1) a brief (<48 h) neutrophil invasion; 2) macrophage infiltration from days 1 to 7; 3) a specific response involving CTL and few NK cells (days 6 and 7), preceded by a low CD4+ cell infiltration starting at day 3. In contrast, donor-immortalized myoblasts completely disappeared during the 7-day follow-up. In this case, an intense infiltration of CTL and macrophages, with moderate CD4+ infiltration and lower amounts of NK cells, was observed starting at day 2. The nonspecific immune response at days 0 and 1 was similar for both types of donor cells. The present observations set a basis to interpret the role of immune cells on the early death/survival of donor cells following myoblast transplantation.

Autologous chondrocyte implantation and osteochondral cylinder transplantation in cartilage repair of the knee joint. A prospective, comparative trial

BACKGROUND

Current methods used to restore the joint surface in patients with localized articular cartilage defects include transplantation of an autologous osteochondral cylinder and implantation of autologous chondrocytes. The purpose of this study was to evaluate the clinical and histological outcomes of these two techniques.

METHODS

We performed a prospective clinical study to investigate the two-year outcomes in forty patients with an articular cartilage lesion of the femoral condyle who had been randomly treated with either transplantation of an autologous osteochondral cylinder or implantation of autologous chondrocytes. Biopsy specimens from representative patients of both groups were evaluated with histological staining, immunohistochemistry, and scanning electron microscopy.

RESULTS

According to the postoperative Lysholm score, the recovery after autologous chondrocyte implantation was slower than that after osteochondral transplantation at six months (p < or = 0.015), twelve months (p < or = 0.001), and twenty-four months (p < or = 0.012). On the basis of the Meyers score and the Tegner activity score, the results were equally good with the two methods two years after treatment. Histomorphological evaluation of biopsy specimens within two years after autologous chondrocyte implantation demonstrated a complete, mechanically stable resurfacing of the defect in all patients. The tissue consisted mainly of fibrocartilage, while localized areas of hyaline-like regenerative cartilage could be detected close to the subchondral bone. Although a gap remained at the site of the transplantation in all five biopsy specimens examined as long as two years after osteochondral cylinder transplantation, histomorphological analysis and scanning electron microscopy revealed no differences between the osteochondral transplants and the surrounding original cartilage.

CONCLUSIONS

Both treatments resulted in a decrease in symptoms. However, the improvement provided by the autologous chondrocyte implantation lagged behind that provided by the osteochondral cylinder transplantation. Histologically, the defects treated with autologous chondrocyte implantation were primarily filled with fibrocartilage, whereas the osteochondral cylinder transplants retained their hyaline character, although there was a persistent interface between the transplant and the surrounding original cartilage. Limitations of our study included the small number of patients, the relatively short (two-year) follow-up, and the absence of a control group.

Muscle cell-mediated gene delivery to the rotator cuff

Rotator cuff lesions are one of the most common causes of upper extremity disability. Surgical therapy addresses mostly the extrinsic etiology, but not intrinsic factors such as aging, structural changes, low vascularity, and inflammatory processes. In this study, genetically engineered, highly purified muscle-derived cells (MDCs) were characterized and injected into the supraspinatus tendons of nude rats. The injected cells were monitored for 3 weeks. In vitro, the engineered, highly purified MDCs do not express vimentin; 98% of them are positive for the beta-galactosidase marker gene, and 99% hybridize with the specific pancentromeric mouse probe. beta-Galactosidase marker gene expression of the injected cells was detected up to 21 days. From day 7 after injection, the cell nuclei became spindle shaped, cells were integrated into the tendon collagen bundles, and the cells showed differentiation into vimentin-expressing fibroblastic cells. The results indicate that the rotator cuff tendon matrix and its original cellular components modulated the injected MDCs toward a fibroblastic phenotype. The compatibility and ability of MDCs to differentiate into other cell lineages, such as fibroblasts, might have high potential utility in tissue-engineering applications for tendon healing. This approach facilitates the application of muscle-derived progenitor cells and ex vivo gene therapy for the treatment of rotator cuff lesions.

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.

Fate of donor bone marrow cells in medial collateral ligament after simulated autologous transplantation

A potential strategy to enhance ligament healing by transplantation of mesenchymal stem cells (MSCs), which are demonstrated to differentiate into fibroblast-like cells in vitro, is presented. The objective of this study was to follow transplanted nucleated cells from bone marrow, which contain MSCs, in the healing medial collateral ligament (MCL) over time, and to examine their phenotype and survivability. It was hypothesized that MSCs in nucleated cells from bone marrow would differentiate into fibroblast-like cells in the healing ligament following adaptation to the environment. The transplantation model employed in this study eliminates the immune response to a donor by the recipient using a transgenic rat (donor), which does not produce foreign protein from transgenes, and its wild-type rat (recipient) in order to simulate autologous transplantation. The MCL of the wild-type rat was ruptured, where 1 x 10(6) nucleated cells of bone marrow from the transgenic rat were injected. The transgenes in transplanted nucleated cells were detected throughout the healing MCL for 28 days by in situ hybridization. At 3 days, many donor cells were evident in the injury site and fascial pocket, and some were found in the midsubstance. Morphologically, transplanted cells with elongated nuclei were found at the ruptured edge of the midsubstance and surface of the unruptured site after 3 days. At 28 days, these cells continued to survive in the healing MCL. Their shapes were similar to those of surrounding recipient MCL fibroblasts. Thus, transplanted cells might differentiate into fibroblasts. Therefore, it was demonstrated that there is a potential for nucleated cells from bone marrow to serve as a vehicle for therapeutic molecules as well as to be a source in enhancing healing of ligaments.

Gene therapy and tissue engineering for urologic dysfunction: status and prospects

This article reviews the recent advances in gene therapy and tissue engineering for urologic dysfunction. Although the number of gene therapy-based clinical trials has increased dramatically in the field of urologic oncology, such trials are still few within the neurourologic field. Recently, new biologic approaches employing growth factors have been utilized to treat various pathological conditions. Among them, transfer of genes such as those encoding growth factors represents a promising way to deliver therapeutic proteins to malfunctioning tissues, which leads to the improvement of organ function. Tissue engineering, which may eventually be combined with gene therapy, also offers the potential to create new functional genitourinary tissue for regeneration and replacement of tissue lost as a consequence of disease. Thus, both tissue engineering and gene therapy may hold promising new solutions in the urologic field.

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.

Ex vivo gene transfer in the years to come

Synovial fibroblasts (SFs) have become a major target for ex vivo gene transfer in rheumatoid arthritis (RA), but efficient transduction of RA-SFs still is a major problem. The low proliferation rate and heterogeneity of RA-SFs, together with their lack of highly specific surface receptors, have hampered a more extensive application of this technique. Improving transduction protocols with conventional viral vectors, therefore, as well as developing novel strategies, such as alternative target cells, and novel delivery systems constitute a major challenge. Recent progress in this field will lead to the achievement of high transgene expression, and will facilitate the use of gene transfer in human trials.

Gene therapy and tissue engineering in orthopaedic surgery

A new biologic era of orthopaedic surgery has been initiated by basic scientific advances that have resulted in the development of gene therapy and tissue engineering approaches for treating musculoskeletal disorders. The terminology, fundamental concepts, and current research in this burgeoning field must be understood by practicing orthopaedic surgeons. Different gene therapy approaches, multiple gene vectors, a multitude of cytokines, a growing list of potential scaffolds, and putative stem cells are being studied. Gene therapy and tissue engineering applications for bone healing, articular disorders, intervertebral disk pathology, and skeletal muscle injuries are being explored. Innovative methodologies that ensure patient safety can potentially lead to many new treatment strategies for musculoskeletal conditions.

Muscle-based gene therapy and tissue engineering for the musculoskeletal system

The recent expansion of molecular biology techniques has opened the gates for a rapid advancement in our knowledge of disease mechanisms. These techniques, in addition to advances in cell biology and polymer chemistry, are resulting in novel approaches to treating musculoskeletal disorders. Surgeons, who have traditionally used the tools of excision and reconstruction to treat patients, might now serve as surgical 'gardeners', who create microenvironments that are conducive for tissue regeneration. This review will update readers on the principles and current advances in muscle-based gene therapy and tissue engineering for the musculoskeletal system.

Anticytokine gene therapy of autoimmune diseases

Viral and nonviral gene therapy vectors have been successfully employed to deliver inflammatory cytokine inhibitors (anticytokines), or anti-inflammatory cytokines, such as transforming growth factor beta-1 (TGF-beta 1), which protect against experimental autoimmune diseases. These vectors carry the relevant genes into a variety of tissues, for either localised or systemic release of the encoded protein. Administration of cDNA encoding soluble IFN-gamma receptor (IFN-gamma R)/IgG-Fc fusion proteins, soluble TNF-alpha receptors, or IL-1 receptor antagonist (IL-1ra), protects against either lupus, various forms of arthritis, autoimmune diabetes, or other autoimmune diseases. These inhibitors, unlike many cytokines, have little or no toxic potential. Similarly, TGF-beta 1 gene therapy protects against numerous forms of autoimmunity, though its administration entails more risk than anticytokine therapy. We have relied on the injection of naked plasmid DNA into skeletal muscle, with or without enhancement of gene transfer by in vivo electroporation. Expression plasmids offer interesting advantages over viral vectors, since they are simple to produce, non-immunogenic and nonpathogenic. They can be repeatedly administered and after each treatment the encoded proteins are produced for relatively long periods, ranging from weeks to months. Moreover, soluble receptors which block cytokine action, encoded by gene therapy vectors, can be constructed from non-immunogenic self elements that are unlikely to be neutralised by the host immune response (unlike monoclonal antibodies [mAbs]), allowing long-term gene therapy of chronic inflammatory disorders.

Treatment of osteochondral injuries. Genetic engineering

Articular cartilage injuries are commonly encountered problems in sports medicine and orthopaedics. The treatment of chondral and osteochondral lesions, which possess only a very limited potential for healing, still represents a great challenge to clinicians and to scientists. Experimental investigations reported over the last 20 years have shown that a variety of methods, including implantation of periosteum, perichondrium, artificial matrices, growth factors, and transplanted cells, can stimulate formation of new cartilage. Genetic engineering--a combination of gene transfer techniques and tissue engineering--will facilitate new approaches to the treatment of articular cartilage injuries.

Gene therapy of autoimmune diseases with vectors encoding regulatory cytokines or inflammatory cytokine inhibitors

Gene therapy offers advantages for the immunotherapeutic delivery of cytokines or their inhibitors. After gene transfer, these mediators are produced at relatively constant, non-toxic levels and sometimes in a tissue-specific manner, obviating limitations of protein administration. Therapy with viral or nonviral vectors is effective in several animal models of autoimmunity including Type 1 diabetes mellitus (DM), experimental allergic encephalomyelitis (EAE), systemic lupus erythematosus (SLE), colitis, thyroiditis and various forms of arthritis. Genes encoding transforming growth factor beta, interleukin-4 (IL-4) and IL-10 are most frequently protective. Autoimmune/ inflammatory diseases are associated with excessive production of inflammatory cytokines such as IL-1, IL-12, tumor necrosis factor alpha (TNFalpha) and interferon gamma (IFNgamma). Vectors encoding inhibitors of these cytokines, such as IL-1 receptor antagonist, soluble IL-1 receptors, IL-12p40, soluble TNFalpha receptors or IFNgamma-receptor/IgG-Fc fusion proteins are protective in models of either arthritis, Type 1 DM, SLE or EAE. We use intramuscular injection of naked plasmid DNA for cytokine or anticytokine therapy. Muscle tissue is accessible, expression is usually more persistent than elsewhere, transfection efficiency can be increased by low-voltage in vivo electroporation, vector administration is simple and the method is inexpensive. Plasmids do not induce neutralizing immunity allowing repeated administration, and are suitable for the treatment of chronic immunological diseases.

Progress in myoblast transplantation: a potential treatment of dystrophies

Myoblast transplantation (MT) consists of injecting normal or genetically modified myogenic cells into muscles, where they are expected to fuse and form mature fibers. As an experimental approach to treat severe genetic muscle diseases, MT was tested in dystrophic patients at the beginning of the 1990s. Although these early clinical trials were unsuccessful, MT has progressed through the research on animal models. Many factors that may condition the success of MT were identified in the last years. The present review updates our knowledge on MT and describes the different problems that have limited its success. Factors that were first underestimated, like the specific immune response after MT, are presently well characterized. Destruction of the hybrid fibers by activated T-lymphocytes and production of antibodies against the transplanted myoblasts take place after MT and are responsible for the graft rejection. The choice of the immunosuppression seems to be very important, and FK506 is the best agent known to allow the best results after MT. Under FK506 immunosuppression, very efficient MT were obtained both in mice and monkeys. Moreover, in dystrophic mice it was demonstrated that MT ameliorates some phenotypical characteristics of the disease. The improvement of the survival of the transplanted cells and the increase of their migration into the injected tissue are presently under investigation. Some of the present research is directed also to bypass the immunosuppression by using the patient's own cells for MT. In this sense, efforts are conducted to introduce the normal gene into the patient's myoblasts before MT and to improve the ability of these cells to proliferate in vitro. Micros. Res. Tech. 48:213-222, 2000.

Tissue engineering of ligament and tendon healing

Ligaments and tendons are bands of dense connective tissue that mediate normal joint movement and stability. Injury to these structures may result in significant joint dysfunction because they either heal by production of inferior matrix or do not heal at all. The process of ligament and tendon healing is complex and the roles of cellular and biochemical mediators continue to be elucidated. The expression of growth factors and growth factor receptors is modulated after injury, and cells from healing tissues are responsive to growth factors. Tissue engineering offers the potential to improve the quality of ligaments and tendons during the healing process. The concept is based on the manipulation of cellular and biochemical mediators to affect protein synthesis and improve tissue remodeling. Recently, novel techniques such as application of growth factors, gene transfer techniques, and cell therapy have shown promise and may become effective biologic therapies in the future. Many groups have been successful in introducing marker and therapeutic genes into ligaments and tendons. Cell therapy involves the introduction of mesenchymal progenitor cells as a pluripotent cell source into the healing environment. The combination of cell therapy with growth factor application via gene transfer offers new avenues to improve ligament and tendon healing.

Genetically augmented tissue engineering of the musculoskeletal system

Recent advances in gene transfer technology permit the design of strategies to improve the outcome of orthopaedic tissue engineering by genetic means. Using ex vivo and in vivo strategies, genes have been transferred successfully to, and expressed within, numerous tissues of the musculoskeletal system, including articular cartilage, meniscus, intervertebral disc, bone, tendon, ligament, synovium, and muscle. With these technologies, various genes encoding modulatory species of ribonucleic acid or proteins such as growth factors, receptors, and transcription factors could be used in the context of genetically augmented tissue engineering. Proof of principle has been established in numerous animal models, and a human protocol for the transfer of genes to synovium already is underway. Progress so far permits cautious optimism of a successful outcome to these pursuits.

Direct-, fibroblast- and myoblast-mediated gene transfer to the anterior cruciate ligament

The anterior cruciate ligament (ACL) has poor capabilities of healing. Maturation or "ligamentization" of the ACL following autograft or allograft reconstruction has been found slow and remains under investigation. In vitro and in vivo studies have shown that platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), and epidermal growth factor (EGF) have the potential to improve ligament healing. Gene therapy approaches may represent a new alternative in delivering these specific growth factors to the ACL. The aim of this study was to investigate the feasibility of three different gene therapy approaches (direct-, fibroblast-, and myoblast-mediated gene transfer) to the ACL. Rabbit myoblasts and ACL-fibroblasts were transduced with 5 x 10(7) recombinant adenoviral particles carrying the LacZ reporter gene (MOI = 50). Myoblasts and fibroblasts (1 x 10(6)) were each injected into the right ACL of 10 adult rabbits; direct injection of 5 x 10(7) adenoviral particles was performed in 10 other rabbits. The left side was used as sham. The beta-galactosidase production was revealed using the LacZ histochemical technique. The transduced fibroblasts and myoblasts were found in the ligament tissue and in the synovial tissue surrounding the ACL at 4, 7, 14, and 21 days postinjection. The myoblasts fused and formed myotubes in the ligament. The direct approach also allowed the transfer of the marker gene in the ligament at 4, 7, 21, and 42 days postinjection. X-gal staining revealed no expression of beta-galactosidase in the sham ligament. The presence of cells expressing the marker gene in the ACL opens up the possibility of delivering proteins (i.e., PDGF, TGF-beta, and EGF) capable of improving ACL healing and graft maturation. Furthermore, engineered myoblasts may mediate and accelerate the intraligament neovascularization. This new technology based on gene therapy and tissue engineering may allow a persistent expression of selected growth factors to enhance ACL healing following injury.

Use of muscle cells to mediate gene transfer to the bone defect

Segmental bone defects and nonunions are relatively common problems facing all orthopaedic surgeons. Osteogenic proteins, i.e., BMP-2, can promote bone healing in segmental bone defects. However, a large quantity of the human recombinant protein is needed to enhance the bone healing potential. Cell mediated gene therapy in the bone defect can allow a sustained expression of the osteogenic proteins and further enhance bone healing. Muscle cells can be easily isolated and cultivated, and they are known to be an efficient gene delivery vehicle to muscle and nonmuscle tissues. Furthermore, they are capable of transforming into osteoblasts when stimulated by BMP-2. Thus, the utilization of muscle cells as the gene delivery vehicle to a bone defect would be an important step in establishing a less invasive treatment for non-unions and segmental bone defects. Muscle cells were transduced when the adenoviral-lacZ vector and injected into the bone defect and the muscles surrounding the defect. Expression of the marker gene was visualized 7 days after the injection, both macroscopically and microscopically, using lacZ histochemistry. The lacZ expressing cells in the defect tissue were also stained for desmin, a muscle specific marker, indicating the presence of muscle cells that have fused into myofibers in this nonmuscle bone defect area. With successful myoblast mediated gene delivery into the segmental bone defect, future experiments would focus on delivering viral vectors expressing osteogenic proteins to eventually improve bone healing postinjury.