Gene therapy and tissue engineering in orthopaedic surgery

Graded or random - Effect of pore distribution in 3D titanium scaffolds on corrosion performance and response of hMSCs

Researchers agree that the ideal scaffold for tissue engineering should possess a 3D and highly porous structure, biocompatibility to encourage cell/tissue growth, suitable surface chemistry for cell attachment and differentiation, and mechanical properties that match those of the surrounding tissues. However, there is no consensus on the optimal pore distribution. In this study, we investigated the effect of pore distribution on corrosion resistance and performance of human mesenchymal stem cells (hMSC) using titanium scaffolds fabricated by laser beam powder bed fusion (PBF-LB). We designed two scaffold architectures with the same porosities (i.e., 75 %) but different distribution of pores of three sizes (200, 500, and 700 μm). The pores were either grouped in three zones (graded, GRAD) or distributed randomly (random, RAND). Microfocus X-ray computed tomography revealed that the chemically polished scaffolds had the porosity of 69 ± 4 % (GRAD) and 71 ± 4 % (RAND), and that the GRAD architecture had the higher surface area (1580 ± 101 vs 991 ± 62 mm2) and the thinner struts (221 ± 37 vs 286 ± 14 μm). The electrochemical measurements demonstrated that the apparent corrosion rate of chemically polished GRAD scaffold decreased with the immersion time extension, while that for polished RAND was increased. The RAND architecture outperformed the GRAD one with respect to hMSC proliferation (over two times higher although the GRAD scaffolds had 85 % higher initial cell retention) and migration from a monolayer. Our findings demonstrate that the pore distribution affects the biological properties of the titanium scaffolds for bone tissue engineering.

The Holy Grail of Orthopedic Surgery: Mesenchymal Stem Cells-Their Current Uses and Potential Applications

Only select tissues and organs are able to spontaneously regenerate after disease or trauma, and this regenerative capacity diminishes over time. Human stem cell research explores therapeutic regenerative approaches to treat various conditions. Mesenchymal stem cells (MSCs) are derived from adult stem cells; they are multipotent and exert anti-inflammatory and immunomodulatory effects. They can differentiate into multiple cell types of the mesenchyme, for example, endothelial cells, osteoblasts, chondrocytes, fibroblasts, tenocytes, vascular smooth muscle cells, and sarcomere muscular cells. MSCs are easily obtained and can be cultivated and expanded in vitro; thus, they represent a promising and encouraging treatment approach in orthopedic surgery. Here, we review the application of MSCs to various orthopedic conditions, namely, orthopedic trauma; muscle injury; articular cartilage defects and osteoarthritis; meniscal injuries; bone disease; nerve, tendon, and ligament injuries; spinal cord injuries; intervertebral disc problems; pediatrics; and rotator cuff repair. The use of MSCs in orthopedics may transition the practice in the field from predominately surgical replacement and reconstruction to bioregeneration and prevention. However, additional research is necessary to explore the safety and effectiveness of MSC treatment in orthopedics, as well as applications in other medical specialties.

Emerging Applications of Stem Cell and Regenerative Medicine to Sports Injuries

Background:

The treatment of sports-related musculoskeletal injuries with stem cells has become more publicized because of recent reports of high-profile athletes undergoing stem cell procedures. There has been increased interest in defining the parameters of safety and efficacy and the indications for potential use of stem cells in clinical practice.

Purpose:

To review the role of regenerative medicine in the treatment of sports-related injuries.

Study Design:

Review.

Method:

Relevant studies were identified through a PubMed search combining the terms stem cells and cartilage, ligament, tendon, muscle, and bone from January 2000 to August 2013. Studies and works cited in these studies were also reviewed.

Results:

Treatment of sports-related injuries with stem cells shows potential for clinical efficacy from the data available from basic science and animal studies.

Conclusion:

Cell-based therapies and regenerative medicine offer safe and potentially efficacious treatment for sports-related musculoskeletal injuries. Basic science and preclinical studies that support the possibility of enhanced recovery from sports injuries using cell-based therapies are accumulating; however, more clinical evidence is necessary to define the indications and parameters for their use. Accordingly, exposing patients to cell-based therapies could confer an unacceptable risk profile with minimal or no benefit. Continued clinical testing with animal models and clinical trials is necessary to determine the relative risks and benefits as well as the indications and methodology of treatment.

Basic science of bone healing

Bone healing is a complex process that can be influenced by both host and environmental factors. In this article, we review the biology involved in the regeneration of new bone after fracture, and factors influencing bone healing, including diabetes, smoking, NSAID use, and bisphosphonates.

Biologic augmentation of rotator cuff repair

Rotator cuff repair is a common orthopedic procedure. Despite advances in surgical technique, the rotator cuff tendons often fail to heal after surgery. In recent years, a number of biologic strategies have been developed and tested to augment healing after rotator cuff repair. These strategies include allograft, extracellular matrices (ECMs), platelet rich plasma (PRP), growth factors, stem cells, and gene therapy. This chapter reviews the most current research on biologic augmentation of rotator cuff repair using these methods.

Advances in meniscal tissue engineering

Meniscal tears are the most common knee injuries and have a poor ability of healing. In the last few decades, several techniques have been increasingly used to optimize meniscal healing. Current research efforts of tissue engineering try to combine cell-based therapy, growth factors, gene therapy, and reabsorbable scaffolds to promote healing of meniscal defects. Preliminary studies did not allow to draw definitive conclusions on the use of these techniques for routine management of meniscal lesions. We performed a review of the available literature on current techniques of tissue engineering for the management of meniscal tears.

Biologic and pharmacologic augmentation of rotator cuff repairs

As rotator cuff repair techniques have improved, failure of the tendon to heal to the proximal humerus is less likely to occur from weak tendon-to-bone fixation. More likely causes of failure include biologic factors such as intrinsic tendon degeneration, fatty atrophy, fatty infiltration of muscle, and lack of vascularity of the tendons. High failure rates have led to the investigation of biologic augmentation to potentially enhance the healing response. Histologic studies have shown that restoration of the rotator cuff footprint during repair can help reestablish the enthesis. In animal models, growth factors and their delivery scaffolds as well as tissue engineering have shown promise in decreasing scar tissue while maintaining biomechanical strength. Platelet-rich plasma may be a safe adjuvant to rotator cuff repair, but it has not been shown to improve healing or function. Many of these strategies need to be further defined to permit understanding of, and to optimize, the biologic environment; in addition, techniques need to be refined for clinical use.

Age-related variation in cell density of human lumbar intervertebral disc

STUDY DESIGN

changes in cell density of endplate (EP), nucleus pulposus (NP), and anulus fibrosus (AF) during ageing were systematically investigated in defined regions of interest in complete human motion segments.

OBJECTIVES

to elucidate cell density and total cell number in distinct anatomic regions of the intervertebral disc; to test effects of gender, level and age on cell density; and to correlate changes in cell density with histologic signs of disc degeneration.

SUMMARY OF BACKGROUND DATA

the available information on the cell density within intervertebral discs and its age-related changes is sparse. This knowledge, however, is a crucial prerequisite for cell-based tissue engineering approaches of the intervertebral disc.

METHODS

in 49 complete cross-sections from lumbar motion segments (newborn to 86 years) from 22 specimens, cell density was determined by the Abercrombie method in EP, NP, and AF, and total cell number was counted per region of interest.

RESULTS

cell density in EP, NP, and AF decreased significantly from 0 to 16 years with the main changes occuring from 0 to 3 years for NP and AF. No significant variations were observed thereafter. We found a significant correlation of cell density and histologic degeneration score between 0 and 1, but not for scores >1. Gender and disc level did not influence cell density.

CONCLUSION

This study provides data concerning the total number of cells in the various regions of the intervertebral disc for different age groups. This knowledge will be beneficial for cell-based treatment approaches, which may evolve in the future.

Chondrogenic differentiation of bone marrow-derived mesenchymal stem cells: tips and tricks

It is well known that adult cartilage lacks the ability to repair itself; this makes articular cartilage a very attractive target for tissue engineering. The majority of articular cartilage repair models attempt to deliver or recruit reparative cells to the site of injury. A number of efforts are directed to the characterization of progenitor cells and the understanding of the mechanisms involved in their chondrogenic differentiation. Our laboratory has focused on cartilage repair using mesenchymal stem cells and studied their differentiation into cartilage. Mesenchymal stem cells are attractive candidates for cartilage repair due to their osteogenic and chondrogenic potential, ease of harvest, and ease of expansion in culture. However, the need for chondrogenic differentiation is superposed on other technical issues associated with cartilage repair; this adds a level of complexity over using mature chondrocytes. This chapter will focus on the methods involved in the isolation and expansion of human mesenchymal stem cells, their differentiation along the chondrogenic lineage, and the qualitative and quantitative assessment of chondrogenic differentiation.

Stem cells for the treatment of skeletal muscle injury

Skeletal muscle injuries are extremely common, accounting for up to 35%-55% of all sports injuries and quite possibly affecting all musculoskeletal traumas. These injuries result in the formation of fibrosis, which may lead to the development of painful contractures, increases patients' risk for repeat injuries, and limits their ability to return to a baseline or pre-injury level of function. The development of successful therapies for these injuries must consider the pathophysiology of these musculoskeletal conditions. We discuss the direct use of muscle-derived stem cells and some key cell population dynamics as well as the use of clinically applicable modalities that may enhance the local supply of stem cells to the zone of injury by promoting angiogenesis.

Gene therapy applications for fracture-healing

Biologic therapies to promote fracture-healing such as use of bone morphogenetic proteins (BMPs) are being increasingly employed in multiple clinical scenarios. However, it has been challenging to design therapies that deliver sufficient quantities of protein over a sustained time period. A potential solution is the application of gene therapy that transfers genetic information to host cells at the fracture site, resulting in the continuous and localized production of the desired proteins. This approach has demonstrated tremendous potential in preclinical animal models of fracture-healing. This article will review the current state of gene therapy approaches to fracture-healing with an emphasis on potential clinical applications.

Tissue engineering of tendons and ligaments by human bone marrow stromal cells in a liquid fibrin matrix in immunodeficient rats: results of a histologic study

INTRODUCTION

The original complex structure and mechanical properties are not fully restored after ligament and tendon injuries. Due to their high proliferation rate and differentiation potential, Bone Marrow Stromal Cells (BMSC) are considered to be an ideal cell source for tissue engineering to optimize the healing process. Ideal matrices for tissue engineering of ligaments and tendons should allow for homogenous cell seeding and offer sufficient stability.

MATERIAL AND METHODS

A mixture of human BMSC and liquid fibrin glue was injected into a standardized full-thickness window defect of the patellar tendon of immunodeficient rats (BMSC group). The histology of the tissue was analysed 10 and 20 days postoperatively and compared to four control groups. These groups consisted of a cohort with a mixture of human fibroblasts and fibrin glue, fibrin glue without cells, a defect group without treatment, and a group with uninjured patellar tendon tissue.

RESULTS

Tendon defects in the BMSC group revealed dense collagen fibres and spindle-shaped cells, which were mainly orientated along the loading axis. Histologic sections of the control groups, especially of untreated defects and of defects filled with fibrin glue only, showed irregular patterns of cell distribution, irregular formed cell nucleoli and less tissue maturation. Compared to healthy tendon tissue, higher numbers of cells and less intense matrix staining was observed in the BMSC group. No ectopic bone or cartilage formation was observed in any specimen.

CONCLUSIONS

Injection of human BMSC in a fibrin glue matrix appears to lead to more mature tissue formation with more regular patterns of cell distribution. Advantages of this "in-vivo" tissue engineering approach are a homogenous cell-matrix mixture in a well-known and approved biological matrix, and simple, minimally-invasive application by injection.

Stab incision for inducing intervertebral disc degeneration in the rat

STUDY DESIGN

The degenerative response of rat tail and lumbar intervertebral discs to a stab incision was evaluated.

OBJECTIVE

To examine and compare the postinjury degenerative response of lumbar and tail discs.

SUMMARY OF BACKGROUND DATA

Although successful in larger animals, a stab incision for inducing disc degeneration in rats has not been evaluated. Rodents are desirable models for disc repair studies due to their low cost, ease of care, and fast healing times.

METHODS

Lumbar and tail discs were exposed surgically and stabbed with a number 11 blade. Disc architecture, levels of IL-1beta, IL-6, and TNF-alpha, and biomechanical properties were analyzed. A functional disability secondary to multilevel lumbar disc injury was quantified and compared with that of rats undergoing sham surgery.

RESULTS

Histologic evaluation of stabbed tail discs demonstrated a nucleus pulposus size decrease, anular collagen layer disorganization, and cellular metaplasia of anular fibroblasts to chondrocyte-appearing cells. Besides the continued presence of the stab injury tract, few changes were observed in the lumbar disc histology. Cytokine measurements indicated a transient peak in IL-1beta in tail discs 4 days following injury. No significant changes in IL-1beta, IL-6, or TNF-alpha were measured. No significant differences in biomechanical properties were observed between stab injury and sham surgery discs. Yet, despite insignificant differences in histologic, cytochemical, or biomechanical properties in the lumbar discs, the rats with lumbar stab injury had a significant decrease in walking ability 28 days after surgery.

CONCLUSIONS

Tail disc stab injury was successful in creating morphologic signs of degeneration and transient high concentrations of IL-1beta. However, the degenerative response in the lumbar discs was much slower, suggesting that site-specific factors, such as increased stability due to posterior elements and torso musculature, helped facilitate healing. Yet, functional assessment indicated that the rats were partially disabled by multiple lumbar injuries.

Tissue engineering in musculoskeletal problems related to haemophilia

This article is a review of how advances in tissue engineering can be applied to the musculoskeletal pathology of patients with haemophilia. This article will also explain the theory that the deterioration of joints in patients with haemophilia is due to biological and mechanical causes. Current concepts of tissue engineering would be to replace the degenerated and damaged tissue by live cells, using them as a biological implant. However, before these new technologies are applied, an appropriate control of their indication and results is required.

Regional gene therapy for full-thickness articular cartilage lesions using naked DNA with a collagen matrix

A novel gene therapy approach for treating damaged cartilage is proposed that involves placing endotoxin-free cDNA containing the gene for bone morphogenetic protein-2 (BMP-2) in type I collagen sponges and then transferring the naked plasmid DNA construct to the injury site. A full-thickness cartilaginous defect in rabbits implanted with plasmid containing a marker gene (beta-galactosidase) showed expressed protein as detected by immunostaining. At 1 week postimplantation, mesenchymal cells subjacent to the defect had incorporated the implanted naked plasmid DNA and, once transfected, served as local bioreactors, transiently producing the gene product. Plasmids containing the gene for BMP-2 implanted in collagen sponges in cartilage lesions stimulated hyalinelike articular cartilage repair at 12 weeks postimplantation, nearly equivalent in quality to that induced by collagen sponges with recombinant BMP-2 protein. Our approach circumvents the risks of inflammation and immunogenic response associated with the use of viral vectors. Naked plasmid DNA as a vehicle for transferring therapeutic genes has been shown to be effective in a therapeutic model within rabbit articular cartilage and appears to be safe and cost effective.

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.

Lateral compartment osteoarthritis of the knee after meniscectomy treated by the transplantation of tissue-engineered cartilage and osteochondral plug

Management of osteoarthritis of the knee after meniscectomy has been challenging, especially for young patients, because articular cartilage has very poor healing capacity because of its lack of vessels, nerve supply, and isolation from systemic regulation. Osteoarthritic lesions often involve both femoral and tibial cartilage, requiring treatments for both lesions. We report the case of a 14-year-old girl with lateral compartment osteoarthritis of the knee after a total meniscectomy of the discoid meniscus, who was successfully treated by the transplantation of both tissue-engineered cartilage made ex vivo for a femoral lesion and an autologous osteochondral plug for a tibial lesion. We treated both femoral and tibial cartilage defects simultaneously with this procedure. We confirmed cartilaginous regeneration in both femoral and tibial lesions at second-look arthroscopy. This procedure is one option to prevent further development of osteoarthritis in young patients.

Biologic approaches to articular cartilage surgery: future trends

The treatment of unicompartmental osteoarthritis and focal chondral pathologic conditions in the knee in active aging athletes has captured the interest of patients, clinicians, basic scientists, and medical industry researchers. Most would agree that a biologic solution to treating hyaline cartilage injuries and degeneration would be optimal over prosthetic joint arthroplasty. Articular cartilage resurfacing techniques and biologic surgical methods continue to evolve and have gained more acceptance in orthopedic practice. A consensus exists for the ultimate goal of achieving a more predictable and durable result after surgical tissue repair or regeneration. Numerous promising approaches are now on the horizon and although the final word is far from in, the integration of many of the anticipated advances in molecular medicine, biomedical engineering, polymer chemistry, cell biology, and clinical orthopedics contributes to an exciting and rapidly evolving field. This article reviews the current concepts of the biologic approach to articular cartilage pathologic conditions and discusses future trends and novel technologies.

A calcium phosphate-based gene delivery system

Although nonviral vectors have lower transfection efficiency than viral vectors, the excellent safety profile of nonviral vectors is appealing for gene therapy. An efficient, simple nonviral vector gene delivery system has been designed that includes plasmid DNA-calcium phosphate precipitates (pDNA-CaP) and porous collagen spheres (Cultispherestrade mark). The hypothesis for this study was the pDNA-CaP would achieve efficient plasmid DNA transfection and the porous collagen spheres would provide a suitable delivery carrier system for three-dimensional (3D) administration. To test the hypothesis, plasmid DNA including the LacZ reporter gene encoding beta-galactosidase was precipitated with CaP to form particles of compacted LacZ-CaP and delivered directly or by Cultispherestrade mark to cells in vitro. The transfection efficiency was determined by beta-galactosidase gene expression. Results indicated that pLacZ-CaP promoted 25-84% of transfection efficiency in a broad cell line spectrum and in flexible experimental conditions. Maximum transfection efficiency was achieved by having mostly nano-sized partles (50-200 nm in diameter) of pDNA-CaP precipitates. Seeding density of 0.7-4 x 10(4) cells/cm2 provided sufficient transfection efficiency, and storage of pDNA-CaP at 4 degrees C was most efficient to preserve transfection efficacy for up to 3 days. The pDNA-CaP worked well in the presence of serum and serum-free conditions and was less cytotoxic than the liposomes. Cultispherestrade mark carrying plasmid LacZ-CaP was an effective 3D system for gene delivery. The technique described here is a simple and safe procedure to deliver genes, and may have application to regenerate bone and other tissues.

Scaffold-based bone engineering by using genetically modified cells

The first generation of clinically applied tissue engineering concepts in the area of skin, cartilage and bone marrow regeneration was based on the isolation, expansion and implantation of cells from the patient's own tissue. Although successful in selective treatments, tissue engineering needs to overcome major challenges to allow widespread clinical application with predictable outcomes. One challenge is to present the cells in a matrix to the implantation site to allow the cells to survive the wound healing contraction forces, tissue remodeling in certain tissues such as bone and biomechanical loading. Hence, several tissue engineering strategies focus on the development of load-bearing scaffold/cell constructs. From a cell source point of view, bone engineers face challenges to isolate and expand cells with the highest potential to form osseous tissue along with harvesting tissue without extensive donor site morbidity. A major hurdle to tissue engineering is de-differentiation and limited ability to control cell phenotype following in vitro expansion. Due to early successes with genetic engineering, bone tissue engineers have used different strategies to genetically alter various types of mesenchymal cells to enhance the mineralization capacity of tissue-engineered scaffold/cell constructs. Although the development of multi-component scaffold/osteogenic cell constructs requires a combination of interdisciplinary research strategies, the following review is limited to describe the general aspects of bone engineering and to present overall directions of technology platforms, which include a genetic engineering component. This paper reviews the most recent work in the field and discusses the concepts developed and executed by a collaborative effort of the multi-disciplinary teams of the two authors.

Biologic strategies for the therapy of intervertebral disc degeneration

Recent advances in tissue engineering have led to promising new approaches for the biologic treatment of disc degeneration. At present, there is no effective therapy for disc degeneration, a condition which results in large healthcare and socio-economic costs. This article will examine the current approaches used in biologic therapies for disc degeneration, including cell-based tissue engineering, gene therapy and the application of mesenchymal stem cells, and discuss their therapeutic potential, as demonstrated in animal models and experimental studies to date.

Modulation of chondrocytic properties of fat-derived mesenchymal cells in co-cultures with nucleus pulposus

Human subcutaneous fat-derived mesenchymal cells recently have been shown to have the potential to differentiate in vitro into a variety of cell types, including adipocytes, osteoblasts, chondrocytes, and myoblasts. This effect suggests that fat tissue may serve as an abundant and easily acquired source of multipotent cells for tissue engineering. The multipotential characteristics of fat-derived mesenchymal cells from the inguinial fat pad of rabbit have not been clearly defined. In this study we have isolated a population of mesenchymal cells from inguinal fat from adult New Zealand white rabbits. The cells that were maintained under various differentiation conditions were shown to differentiate in vitro into adipocytes, osteoblasts, or chondrocytes; this differentiation was demonstrated using gene expression for tissue-specific proteins. We also co-cultured the cells with intervertebral disk tissue from the nucleus pulpous or from the annulus fibrosus. The fat-derived cells co-cultured with nucleus pulposus showed an increase in expression of type II collagen and aggrecan genes, compared with cells in alginate alone and cells co-cultured with annulus fibrosus. The data suggest that the fat-derived mesenchymal cells responded to soluble mediators from the disk. Future studies on intervertebral disk reconstruction could be based on our findings with fat-derived multipotential cells from the inguinal region of the rabbit that were co-cultured with disk tissue and may prove useful in tissue engineering strategies.

New therapies in tendon reconstruction

Despite the use of various types of grafts, no surgical treatment currently exists to restore a tendon to its normal condition. Tissue engineering techniques are being used to develop therapies for tendon reconstruction. Biologic and synthetic scaffolds can both repair tendon defects and improve healing by allowing for the regeneration of the tendon's natural biologic composition to restore its mechanical capacity. This process can be further enhanced through augmentation methods such as cell seeding, growth factor implantation, and gene therapy.

In vivo gene delivery to articular chondrocytes mediated by an adeno-associated virus vector

PURPOSES

(1) To investigate the efficiency of direct in vivo adeno-associated virus (AAV) vector-mediated gene transduction to chondrocytes in relation to normal and injured articular cartilage. (2) To evaluate the effects of ultra-violet light-activated gene transduction (LAGT) in chondrocytes in vivo. (3) To determine dissemination of active rAAV vector after intra-articular administration.

METHODS

Rabbit knees with either normal or injured cartilage received an intra-articular injection with 1.5x10(12) infectious rAAV-eGFP particles. The right knees received rAAV-eGFP alone, whereas the left knees were given LAGT-treatment. The transduction efficiencies were determined at 1 and 3 weeks after infection by fluorescence-activated cell scanning. The occurrence of active shedding was monitored in serum and various tissues.

RESULTS

After 1 week, 7% of the chondrocytes in normal cartilage were transduced by direct rAAV transduction technique. Chondrocytes in cartilage defects demonstrated higher transduction rates compared to chondrocytes in normal cartilage. LAGT increased the cellular eGFP expression in the internal zones to 12%, but did not have any effect in the external zones in defects. Finally, infectious particles were not detected in either serum or tissue samples.

CONCLUSIONS

Direct rAAV-mediated gene transfer in vivo to articular chondrocytes is possible. LAGT improves rAAV transduction of chondrocytes in vivo but appears to have a very limited range of effect induction. Expression of eGFP was not determined in other tissues than synovium and cartilage in the treated joints.

In vivo bioluminescent imaging of virus-mediated gene transfer and transduced cell transplantation in the intervertebral disc

STUDY DESIGN

Work presented here used a small animal model to demonstrate the feasibility and usefulness of in vivo bioluminescent imaging to studying degenerative disc disease.

OBJECTIVES

To determine the utility of in vivo bioluminescent imaging to monitor the temporal and spatial expression of genetically modified cells within the intervertebral disc of a rodent model.

SUMMARY OF THE BACKGROUND DATA

Noninvasive imaging of genetically engineered cells in the spine has the advantage of allowing events to be tracked without killing the animal and can be used to follow the time course of a particular therapy. Results are presented on the use of Sprague-Dawley rats in experimental studies in which the luciferase reporter gene was delivered to the lumbar intervertebral disc through adenovirus-mediated or cell-based transfer techniques to demonstrate the feasibility to monitor gene expression noninvasively over time.

METHODS

Tissue culture, disc surgery, and in vivo bioluminescent imaging were used. The intervertebral disc of the rat was either injected in situ with an adenovirus containing the luciferase reporter gene or implanted with fat, bone marrow or intervertebral disc cells transduced ex vivo and contained in a bioresorbable carrier. Results were assessed with in vivo bioluminescent imaging at several time points.

CONCLUSION

Data from 11 animals were obtained with imaging up to 14 days. To our knowledge, this is the first description of in vivo bioluminescence imaging to study spinal conditions. We have characterized the relative expression of three cell types transduced with the Ad-luc virus by ex vivo transfection followed by cell implantation in the rat spine and compared them to one another and to direct infection of Ad-luc adenovirus in situ. Our results demonstrate the feasibility of tracing genetically altered cells in the spine. This technique has the potential to be used to noninvasively track the fate and expression of therapeutic genes within the spine of small animals used in disc research.

Cell-based tissue engineering for the intervertebral disc: in vitro studies of human disc cell gene expression and matrix production within selected cell carriers

BACKGROUND CONTEXT

Little is known about how disc cells attach, proliferate and form extracellular matrix (ECM) within carrier materials. Such information is needed to help formulate criteria for successful cell-carrier interactions in tissue engineering.

PURPOSE

To compare proliferation, ECM production and gene expression in annulus cells cultured in a variety of cell carrier materials with potential application in tissue engineering of the disc.

STUDY DESIGN

Human intervertebral disc cells from the annulus were used in a prospective study of proliferation, ECM production and gene expression within selected cell carriers.

METHODS

Annulus cells from discs of 29 individuals were tested in collagen sponge, collagen gel, agarose, alginate or fibrin gel formulations. In situ hybridization assessed ECM gene expression of Types I and II collagen, aggrecan and chondroitin-6 sulfotransferase. Cell proliferation, cell shape, attachment and ECM production were evaluated.

RESULTS

Collagen sponges provided the best microenvironment for disc cell ECM production and gene expression. Although collagen gels often could support good cell growth, such constructs did not result in either abundant ECM production or ECM gene expression, as shown by in situ hybridization. Growth and ECM production and gene expression in alginate, agarose and fibrin microenvironments were inferior.

CONCLUSIONS

Tissue engineering techniques open new therapeutic possibilities for use of autologous disc cells, but fundamental questions on how these cells interact with cell carriers are unexplored. Results provide novel data on disc cell gene expression within diverse microenvironments. The collagen sponge proved to be a superior microenvironment.

Bone graft substitutes

A better understanding of the biology of fracture healing and an increasing awareness of the limitations and potential complications of autogenous bone graft harvest have combined to foster a burgeoning interest in the development of bone graft substitutes. A few of these materials have been available for more than a decade, and many more should become available in the near future. The characteristics of the ideal bone graft substitute may vary considerably depending on the intended site of application and the clinical setting in which it is used. Knowledge of the available alternatives is a necessary prerequisite to informed decision making.

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.

Recent advances in disc cell biology

STUDY DESIGN

There have been many advances over the past decade in understanding and experimentally modulating biologic aspects of intervertebral disc cell function. An overview of the current state of this biologic research is presented.

OBJECTIVES

To provide clinicians with a review of important recent advances in biologic studies of the disc and their implications for potential disc therapies.

SUMMARY OF BACKGROUND DATA

Historically, anatomic, biochemical, radiologic, and biomechanical studies of the intervertebral disc formed the foundation on which our understanding of disc function was built. Magnetic resonance imaging techniques that allowed viewing of soft tissue components of the disc further advanced imaging capabilities.

METHODS

Recent publications are reviewed.

RESULTS

Experimental approaches over the past decade have enabled researchers to look more critically at disc cell function. This is important because disc cell function produces the extracellular matrix components of the disc, which, in turn, shape the disc's subsequent physiologic and biomechanical functions. New approaches to the study of disc cell function, methods to manipulate disc cells, studies of intact discs and disc nutrition, vertebral endplate structure and function, tissue engineering, gene therapy, and the potential of stem cells in disc therapy are reviewed and discussed.

CONCLUSIONS

Many believe that disc degeneration has a cellular basis. New research is helping us better understand healthy, aging, and degenerating discs. Modern methods to manipulate and modulate disc cell function open exciting and challenging new therapeutic possibilities for future biologic treatments of disc degeneration.

The SH-3 and SH-4 antibodies recognize distinct epitopes on CD73 from human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are pluripotent cells in the bone marrow that have the capacity to differentiate along a number of connective tissue lineages, including cartilage, bone, adipose tissue, and stroma. The SH-3 and SH-4 monoclonal antibodies recognize epitopes present on the surface of human MSCs. This study describes the isolation and characterization of the antigen that is recognized by these antibodies. A protein of molecular weight approximately 67 kDa was immunoprecipitated from a solubilized membrane preparation of human MSCs using the SH-3 antibody. Analysis of peptides derived from this protein by mass spectrometry and sequencing identified it as CD73 (ecto-5'-nucleotidase). The SH-4 antibody was also shown to react with purified bovine CD73 by immunoblotting, but the SH-3 antibody failed to react with the bovine protein. These results indicate that both SH-3 and SH-4 epitopes are present on CD73, but they are distinct. CD73, present in lymphoid tissue, plays a role in the activation of B-lymphocytes and in signal transduction in the hematopoietic compartment of bone marrow. The role that CD73 may play in bone marrow stromal interactions and in the differentiation of MSCs is discussed.