Ex vivo gene therapy with stromal cells transduced with a retroviral vector containing the BMP4 gene completely heals critical size calvarial defect in rats

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

The use of heparin/polycation coacervate sustain release system to compare the bone regenerative potentials of 5 BMPs using a critical sized calvarial bone defect model

Nonunion following bone fracture and segmental bone defects are challenging clinical conditions. To combat this clinical dilemma, development of new bone tissue engineering therapies using biocompatible materials to deliver bone growth factors is desirable. This aim of this study is to use a heparin/polycation coacervate sustained-release platform to compare 5 bone morphogenetic proteins (BMPs) for promoting bone defect healing in a critical sized calvarial defect model. The in vitro 3D osteogenic pellet cultures assays demonstrated that BMPs 2, 4, 6, 7 and 9 all enhanced mineralization in vitro compared to the control group. BMP2 resulted in higher mineralized volume than BMP4 and BMP6. All BMPs and the control group activated the pSMAD5 signaling pathway and expressed osterix (OSX). The binding of BMP2 with coacervate significantly increased the coacervate average particle size. BMP2, 4, 6, & 7 bound to coacervate significantly increased the Zeta potential of the coacervate while BMP9 binding showed insignificant increase. Furthermore, using a monolayer culture osteogenic assay, it was found that hMDSCs cultured in the coacervate BMP2 osteogenic medium expressed higher levels of RUNX2, OSX, ALP and COX-2 compared to the control and BMPs 4, 6, 7 & 9. Additionally, the coacervate complex can be loaded with up to 2 μg of BMP proteins for sustained release. In vivo, when BMPs were delivered using the coacervate sustained release system, BMP2 was identified to be the most potent BMP promoting bone regeneration and regenerated 10 times of new bone than BMPs 4, 6 & 9. BMP7 also stimulated robust bone regeneration when compared to BMPs 4, 6 & 9. The quality of the newly regenerated bone by all BMPs delivered by coacervate is equivalent to the host bone consisting of bone matrix and bone marrow with normal bone architecture. Although the defect was not completely healed at 6 weeks, coacervate sustain release BMPs, particularly BMP2 and BMP7, could represent a new strategy for treatment of bone defects and non-unions.

A Narrative Review of Cell-Based Approaches for Cranial Bone Regeneration

Current cranial repair techniques combine the use of autologous bone grafts and biomaterials. In addition to their association with harvesting morbidity, autografts are often limited by insufficient quantity of bone stock. Biomaterials lead to better outcomes, but their effectiveness is often compromised by the unpredictable lack of integration and structural failure. Bone tissue engineering offers the promising alternative of generating constructs composed of instructive biomaterials including cells or cell-secreted products, which could enhance the outcome of reconstructive treatments. This review focuses on cell-based approaches with potential to regenerate calvarial bone defects, including human studies and preclinical research. Further, we discuss strategies to deliver extracellular matrix, conditioned media and extracellular vesicles derived from cell cultures. Recent advances in 3D printing and bioprinting techniques that appear to be promising for cranial reconstruction are also discussed. Finally, we review cell-based gene therapy approaches, covering both unregulated and regulated gene switches that can create spatiotemporal patterns of transgenic therapeutic molecules. In summary, this review provides an overview of the current developments in cell-based strategies with potential to enhance the surgical armamentarium for regenerating cranial vault defects.

Transplantation of Murine Bone Marrow Stromal Cells under the Kidney Capsule to Secrete Coagulation Factor VIII

Ectopic cell transplantation has been studied as an alternative to whole organ transplantation or as a method to produce secretable proteins for genetic disorders. In this study, bone marrow stromal cells isolated from C57Bl/6 mice were genetically modified to express either lacZ- or B-domain-deleted human factor VIII. In vitro modification of the isolated bone marrow stromal cells was initially performed by transducing increased doses of VSV-G pseudotyped lentiviral vectors expressing lacZ. At a MOI of 25, all of the bone marrow stromal cells were X-gal positive, which maintained their ability to expand and differentiate prior to transplantation into mice. Extremely poor engraftment was observed in the liver, but transplantation of the bone marrow stromal cells expressing lacZ under the kidney capsule resulted in long-term viable X-gal-positive cells for at least 8 weeks (length of study). In vitro expression of human factor VIII was detected in a dose-dependent manner following bone marrow stromal cell with a factor VIII-expressing lentiviral vector. Transplantation of the factor VIII-expressing bone marrow stromal cells under the kidney capsule led to long-term therapeutic expression in the mouse plasma (1–3 ng/ml; n = 4–5 mice/group) for 8 weeks. This study demonstrated that ectopic transplantation of bone marrow stromal cells under the kidney capsule can be effective as a method to express secretable proteins in vivo.

Cationized gelatin hydrogels mixed with plasmid DNA induce stronger and more sustained gene expression than atelocollagen at calvarial bone defects in vivo

Gene transduction of exogenous factors at local sites in vivo is a promising approach to promote regeneration of tissue defects owing to its simplicity and capacity for expression of a variety of genes. Gene transduction by viral vectors is highly efficient; however, there are safety concerns associated with viruses. As a method for nonviral gene transduction, plasmid DNA delivery is safer and simpler, but requires an efficient carrier substance. Here, we aimed to develop a simple, efficient method for bone regeneration by gene transduction and to identify optimal conditions for plasmid DNA delivery at bone defect sites. We focused on carrier substances and compared the efficiencies of two collagen derivatives, atelocollagen, and gelatin hydrogel, as substrates for plasmid DNA delivery in vivo. To assess the efficiencies of these substrates, we examined exogenous expression of green fluorescence protein (GFP) by fluorescence microscopy, polymerase chain reaction, and immunohistochemistry. GFP expression at the bone defect site was higher when gelatin hydrogel was used as a substrate to deliver plasmids than when atelocollagen was used. Moreover, the gelatin hydrogel was almost completely absorbed at the defect site, whereas some atelocollagen remained. When a plasmid harboring bone morphogenic protein 2 was delivered with the substrate to bony defect sites, more new bone formation was observed in the gelatin group than in the atelocollagen group. These results suggested that the gelatin hydrogel was more efficient than atelocollagen as a substrate for local gene delivery and may be a superior material for induction of bone regeneration.

Gene therapy approaches to regenerating bone

Bone formation and regeneration therapies continue to require optimization and improvement because many skeletal disorders remain undertreated. Clinical solutions to nonunion fractures and osteoporotic vertebral compression fractures, for example, remain suboptimal and better therapeutic approaches must be created. The widespread use of recombinant human bone morphogenetic proteins (rhBMPs) for spine fusion was recently questioned by a series of reports in a special issue of The Spine Journal, which elucidated the side effects and complications of direct rhBMP treatments. Gene therapy - both direct (in vivo) and cell-mediated (ex vivo) - has long been studied extensively to provide much needed improvements in bone regeneration. In this article, we review recent advances in gene therapy research whose aims are in vivo or ex vivo bone regeneration or formation. We examine appropriate vectors, safety issues, and rates of bone formation. The use of animal models and their relevance for translation of research results to the clinical setting are also discussed in order to provide the reader with a critical view. Finally, we elucidate the main challenges and hurdles faced by gene therapy aimed at bone regeneration as well as expected future trends in this field.

Canine oral mucosal fibroblasts differentiate into osteoblastic cells in response to BMP-2

Several lines of evidence show that transplantation of osteoblastic cells or genetically engineered nonosteogenic cells expressing osteoblast-related genes into bone defects effectively promotes bone regeneration. To extend this possibility, we investigated whether oral mucosal fibroblasts are capable of differentiating into osteoblastic cells by conducting in vitro and in vivo experiments. We investigated the effects of bone morphogenetic protein-2 (BMP-2) on osteoblast differentiation of cultured fibroblasts isolated from canine buccal mucosa. We also transplanted green fluorescence protein (GFP)-expressing fibroblasts with gelatin/BMP-2 complexes into the subfascial regions of athymic mice, and investigated the localization of GFP-positive cells in the ectopically formed bones. The cultured canine buccal mucosal fibroblasts differentiated into osteoblastic cells by increasing their alkaline phosphatase (ALP) activity and Osteocalcin, Runx2, and Osterix mRNA expression levels in response to BMP-2. Transplantation experiments of GFP-expressing oral mucosal fibroblasts with gelatin/BMP-2 complexes revealed that 17.1% of the GFP-positive fibroblasts differentiated into ALP-positive cells, and these cells accounted for 6.2% of total ALP-positive cells in the ectopically formed bone. This study suggests that oral mucosal fibroblasts can differentiate into osteogenic cells in response to BMP-2. Thus, these cells are potential candidates for cell-mediated bone regeneration therapy in dentistry.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mesenchymal stem cells as a potent cell source for bone regeneration

While small bone defects heal spontaneously, large bone defects need surgical intervention for bone transplantation. Autologous bone grafts are the best and safest strategy for bone repair. An alternative method is to use allogenic bone graft. Both methods have limitations, particularly when bone defects are of a critical size. In these cases, bone constructs created by tissue engineering technologies are of utmost importance. Cells are one main component in the manufacture of bone construct. A few cell types, including embryonic stem cells (ESCs), adult osteoblast, and adult stem cells, can be used for this purpose. Mesenchymal stem cells (MSCs), as adult stem cells, possess characteristics that make them good candidate for bone repair. This paper discusses different aspects of MSCs that render them an appropriate cell type for clinical use to promote bone regeneration.

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

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

PEG matrix enables cell-mediated local BMP-2 gene delivery and increased bone formation in a porcine critical size defect model of craniofacial bone regeneration

PURPOSE

This study addressed the suitability of a polyethylene glycol (PEG) matrix as scaffold for cell-mediated local BMP-2 gene transfer in a calvarial critical size defect (CSD) model.

MATERIALS AND METHODS

PEG matrix (degradation time 10 days) and PEG membrane (degradation time 120 days) were used in the pig calvarial model. Cylindrical (1 × 1 cm) CSD (9 per animal; 20 animals) were filled with: (i) HA/TCP, covered by PEG membrane (group 1); (ii) HA/TCP, mixed with PEG matrix (group 2); and (iii) HA/TCP mixed with BMP-2 transfected osteoblasts and PEG matrix (group 3). BMP-2/4 gene transfer: liposomal in vitro transfection of BMP-2/V5-tag fusion-protein. Quantitative histomorphometry (toluidine blue staining) after 2, 4 and 12 weeks assessed bone formation. Semiquantitative immunohistochemistry estimated the expression of BMP-2 and V5-tag.

RESULTS

Group 3 showed significantly higher new bone formation than groups 1, 2 at 4 (P < 0.05) and 12 (P < 0.02) weeks. BMP-2-V5-tag was detected for 4 weeks. BMP-2 expression in group 3 was higher compared to all other groups after 2 and 4 (P < 0.02) weeks.

CONCLUSIONS

The PEG matrix serves as scaffold for cell-mediated BMP-2 gene delivery in guided bone regeneration facilitating cell survival and protein synthesis for at least 4 weeks. Local BMP-2 gene delivery by PEG matrix-embedded cells leads to increased bone formation during critical size defect regeneration.

The comparative effectiveness of demineralized bone matrix, beta-tricalcium phosphate, and bovine-derived anorganic bone matrix on inflammation and bone formation using a paired calvarial defect model in rats

BACKGROUND

In this study, the effectiveness of Iranian Tissue Bank-produced demineralized bone matrix (ITB-DBM), beta-tricalcium phosphate (βTCP), and Bio-Oss(®) (Geistlich Pharma AG, Wolhusen, Switzerland) were evaluated and compared with double controls. The main goal was to measure the amount of new bone formation in the center of defects created in rat calvaria. Another goal was to compare the controls and evaluate the effects of each treatment material on their adjacent untreated (control) defects.

METHODS

In this study, 40 male Wistar rats were selected and divided into four groups, In each group, there were ten rats with two defects in their calvarias; one of them is considered as control and the other one was treated with ITB-DBM (group 1), BIO-OSS (group2), and βTCP (group 3), respectively. But in group 4, both defects were considered as control. The amount of inflammation and new bone formation were evaluated at 4 and 10 weeks. In the first group, one defect was filled with ITB-DBM; in the second group, one defect was filled with Bio-Oss; in the third group, one defect was filled with βTCP; and in the fourth group, both defects were left unfilled. Zeiss microscope (Carl Zeiss AG, Oberkochen, Germany) and Image Tool(®) (version 3.0; University of Texas Health Science Center at San Antonio, San Antonio, TX) software were used for evaluation. SPSS Statistics (IBM Corp, Somers, NY) was used for statistical analysis.

RESULTS

Maximum bone formation at 4 and 10 weeks were observed in the ITB-DBM group (46.960% ± 4.366%, 94.970% ± 0.323%), which had significant difference compared with the other groups (P < 0.001). Ranking second was the Bio-Oss group and third, the βTCP group. Bone formation in the group with two unfilled defects was much more significant than in the other controls beside the Bio-Oss and βTCP after 10 weeks (29.1 ± 2.065, 29.05 ± 1.649), while this group had the least bone formation compared with the other controls at week 4 (2.100% ± 0.758%, 1.630% ± 0.668%, P < 0.001).

CONCLUSION

Overall, the ITB-DBM group showed the best results, although the results for other experimental groups were unfavorable. The authors conclude that human DBM (ITB-DBM) should be offered as an alternative for bone regeneration in animals, such as horses, as well as in humans, especially for jaw reconstruction. In relation to bone regeneration in control defects, the effect of experimental material on controls was apparent during the initial weeks.

Electrospun PLLA nanofiber scaffolds and their use in combination with BMP-2 for reconstruction of bone defects

INTRODUCTION

Adequate migration and differentiation of mesenchymal stem cells is essential for regeneration of large bone defects. To achieve this, modern graft materials are becoming increasingly important. Among them, electrospun nanofiber scaffolds are a promising approach, because of their high physical porosity and potential to mimic the extracellular matrix (ECM).

MATERIALS AND METHODS

The objective of the present study was to examine the impact of electrospun PLLA nanofiber scaffolds on bone formation in vivo, using a critical size rat calvarial defect model. In addition we analyzed whether direct incorporation of bone morphogenetic protein 2 (BMP-2) into nanofibers could enhance the osteoinductivity of the scaffolds. Two critical size calvarial defects (5 mm) were created in the parietal bones of adult male Sprague-Dawley rats. Defects were either (1) left unfilled, or treated with (2) bovine spongiosa, (3) PLLA scaffolds alone or (4) PLLA/BMP-2 scaffolds. Cranial CT-scans were taken at fixed intervals in vivo. Specimens obtained after euthanasia were processed for histology, histomorphometry and immunostaining (Osteocalcin, BMP-2 and Smad5).

RESULTS

PLLA scaffolds were well colonized with cells after implantation, but only showed marginal ossification. PLLA/BMP-2 scaffolds showed much better bone regeneration and several ossification foci were observed throughout the defect. PLLA/BMP-2 scaffolds also stimulated significantly faster bone regeneration during the first eight weeks compared to bovine spongiosa. However, no significant differences between these two scaffolds could be observed after twelve weeks. Expression of osteogenic marker proteins in PLLA/BMP-2 scaffolds continuously increased throughout the observation period. After twelve weeks osteocalcin, BMP-2 and Smad5 were all significantly higher in the PLLA/BMP-2 group than in all other groups.

CONCLUSION

Electrospun PLLA nanofibers facilitate colonization of bone defects, while their use in combination with BMP-2 also increases bone regeneration in vivo and thus combines osteoconductivity of the scaffold with the ability to maintain an adequate osteogenic stimulus.

Gene Therapy for Cartilage Repair

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

Future of local bone regeneration - Protein versus gene therapy

The most promising attempts to achieve bone regeneration artificially are based on the application of mediators such as bone morphogenetic proteins (BMPs) directly to the deficient tissue site. BMPs, as promoters of the regenerative process, have the ability to induce de novo bone formation in various tissues, and many animal models have demonstrated their high potential for ectopic and orthotopic bone formation. However, the biological activity of the soluble factors that promote bone formation in vivo is limited by diffusion and degradation, leading to a short half-life. Local delivery remains a problem in clinical applications. Several materials, including hydroxyapatite, tricalcium phosphate, demineralised bone matrices, poly-lactic acid homo- and heterodimers, and collagen have been tested as carriers and delivery systems for these factors in a sustained and appropriate manner. Unfortunately these delivery vehicles often have limitations in terms of biodegradability, inflammatory and immunological rejection, disease transmission, and most importantly, an inability to provide a sustained, continuous release of these factors at the region of interest. In coping with these problems, new approaches have been established: genes encoding these growth factor proteins can be delivered to the target cells. In this way the transfected cells serve as local "bioreactors", as they express the exogenous genes and secrete the synthesised proteins into their vicinity. The purpose of this review is to present the different methods of gene versus growth factor delivery in tissue engineering. Our review focuses on these promising and innovative methods that are defined as regional gene therapy and provide an alternative to the direct application of growth factors. Various advantages and disadvantages of non-viral and viral vectors are discussed. This review identifies potential candidate genes and target cells, and in vivo as well as ex vivo approaches for cell transduction and transfection. In explaining the biological basis, this paper also refers to current experimental and clinical applications.

Cranial bone defects: current and future strategies

Bony defects in the craniomaxillofacial skeleton remain a major and challenging health concern. Surgeons have been trying for centuries to restore functionality and aesthetic appearance using autografts, allografts, and even xenografts without entirely satisfactory results. As a result, physicians, scientists, and engineers have been trying for the past few decades to develop new techniques to improve bone growth and bone healing. In this review, the authors summarize the advantages and limitations of current animal models; describe current materials used as scaffolds, cell-based, and protein-based therapies; and lastly highlight areas for future investigation. The purpose of this review is to highlight the major scaffold-, cell-, and protein-based preclinical tools that are currently being developed to repair cranial defects.

Enhanced healing of goat femur-defect using BMP7 gene-modified BMSCs and load-bearing tissue-engineered bone

Segmental defect regeneration is still a clinical challenge. In this study, we investigated the feasibility of bone marrow stromal cells (BMSCs) infected with adenoviral vector containing the bone morphogenetic protein 7 gene (AdBMP7) and load-bearing to enhance bone regeneration in a critically sized femoral defect in the goat model. The defects were implanted with AdBMP7-infected BMSCs/coral (BMP7 group) or noninfected BMSCs/coral (control group), respectively, stabilized with an internal fixation rod and interlocking nails. Bridging of the segmental defects was evaluated by radiographs monthly, and confirmed by biomechanical tests. Much callus was found in the BMP7 group, and nails were taken off after 3 months of implantation, indicating that regenerated bone in the defect can be remodeled by load-bearing, whereas after 6 months in control group. After load-bearing, it is about 5 months; the mechanical property of newly formed bone in the BMP7 group was restored, but 8 months in control group. Our data suggested that the BMP7 gene-modified BMSCs and load-bearing can promote bone regeneration in segmental defects.

Bone regeneration in defects compromised by radiotherapy

Because bone reconstruction in irradiated sites is less than ideal, we applied a regenerative gene therapy method in which a cell-signaling virus was localized to biomaterial scaffolds to regenerate wounds compromised by radiation therapy. Critical-sized defects were created in rat calvariae previously treated with radiation. Gelatin scaffolds containing lyophilized adenovirus encoding BMP-2 (AdBMP-2) or freely suspended AdBMP-2 were transplanted. Lyophilized AdBMP-2 significantly improved bone quality and quantity over free AdBMP-2. Bone mineral density was reduced after radiotherapy. Histological analyses demonstrated that radiation damage led to less bone regeneration. The woven bone and immature marrow formed in the radiated defects indicated that irradiation retarded normal bone development. Finally, we stored the scaffolds with lyophilized AdBMP-2 at -80 degrees C to determine adenovirus stability. Micro-CT quantification demonstrated no significant differences between bone regeneration treated with lyophilized AdBMP-2 before and after storage, suggesting that virus-loaded scaffolds may be convenient for application as pre-made constructs.

Stem cell antigen-1+ cell-based bone morphogenetic protein-4 gene transfer strategy in mice failed to promote endosteal bone formation

BACKGROUND

This study assessed whether a Sca-1+ cell-based ex vivo gene transfer strategy, which has been shown to promote robust endosteal bone formation with a modified fibroblast growth factor-2 (FGF2) gene, can be extended to use with bone morphogenetic protein (BMP)2/4 hybrid gene.

METHODS

Sublethally irradiated recipient mice were transplanted with lentiviral (LV)-BMP2/4-transduced Sca-1+ cells. Bone parameters were monitored by pQCT and microCT. Gene expression was assessed by the real-time reverse transcriptase-polymerase chain reaction.

RESULTS

Recipient mice of LV-BMP2/4-transduced Sca-1+ cells yielded high engraftment and increased BMP4 mRNA levels in marrow cells; but exhibited only insignificant increases in serum and bone alkaline phosphatase activity compared to control mice. pQCT and microCT analyses of femurs showed that, with the exception of small changes in trabecular bone mineral density and cortical bone mineral content in LV-BMP2/4 mice, there were no differences in measured bone parameters between mice of the LV-BMP2/4 group and controls. The lack of large endosteal bone formation effects with the BMP4 strategy could not be attributed to ineffective engraftment or expansion of BMP4-expressing Sca-1+ cells, an inability of the transduced cells to secrete active BMP4 proteins, or to use of the LV-based vector.

CONCLUSIONS

Sca-1+ cell-based BMP4 ex vivo strategy did not promote robust endosteal bone formation, raising the possibility of intrinsic differences between FGF2- and BMP4-based strategies in their ability to promote endosteal bone formation. It emphasizes the importance of choosing an appropriate bone growth factor gene for delivery by this Sca-1+ cell-based ex vivo systemic gene transfer strategy to promote bone formation.

Transport molecules using reverse sequence HIV-Tat polypeptides: not just any old Tat? (WO200808225)

BACKGROUND

Many polycationic cell penetrating peptides (CPPs), alternatively named protein transduction domains, have been used for the efficient intracellular delivery of biologically active agents. Patent WO2008/082885 relates to the properties and proposed biomedical applications of a CPP and putative-related sequences that represent the reverse sequence of a nonapeptide basic domain of the HIV-transactivator protein (Tat) (RRRQRRKKR).

OBJECTIVE

This evaluation critically assesses the reported utility of such transport molecules and the numerous potential embodiments of the invention, in comparison with other recent developments in the field. We also review recent biomedical applications of Tat-derived peptide transporters.

METHODS

The scope of this review includes both Tat-derived peptide transporters and other sequence-related CPPs that are polycationic in nature.

RESULTS/CONCLUSION

The patent application indicates that reverse sequence HIV-Tat polypeptides can increase the transdermal delivery of an iodinated mixture of botulinum toxin, albumin and accessory proteins (Neuronox), Medy-Tox, Inc., Seoul, South Korea) as a non-covalent complex. Moreover, the invention also contemplates all variants of the reverse-sequence polypeptide and claims a variety of potential biomedical applications using the reverse sequence peptide as a delivery vector. Unfortunately, in the absence of both rigorous comparative data and toxicological analyses, it is uncertain if these transport molecules offer any advantages compared with many existing and rigorously characterised CPP vector systems.

Marrow stromal cell-based cyclooxygenase 2 ex vivo gene-transfer strategy surprisingly lacks bone-regeneration effects and suppresses the bone-regeneration action of bone morphogenetic protein 4 in a mouse critical-sized calvarial defect model

This study evaluated whether the murine leukemia virus (MLV)-based cyclooxygenase-2 (Cox-2) ex vivo gene-transfer strategy promotes healing of calvarial defects and/or synergistically enhances bone morphogenetic protein (BMP) 4-mediated bone regeneration. Gelatin scaffolds impregnated with mouse marrow stromal cells (MSCs) transduced with MLV-expressing BMP4, Cox-2, or a control gene were implanted into mouse calvarial defects. Bone regeneration was assessed by X-ray, dual-energy X-ray absorptiometry, and histology. In vitro, Cox-2 or prostanglandin E(2) enhanced synergistically the osteoblastic differentiation action of BMP4 in mouse MSCs. In vivo, implantation of BMP4-expressing MSCs yielded massive bone regeneration in calvarial defects after 2 weeks, but the Cox-2 strategy surprisingly did not promote bone regeneration even after 4 weeks. Staining for alkaline phosphatase (ALP)-expressing osteoblasts was strong throughout the defect of animals receiving BMP2/4-expressing cells, but defects receiving Cox-2-expressing cells displayed weak ALP staining along the edge of original intact bone, indicating that the Cox-2 strategy lacked bone-regeneration effects. The Cox-2 strategy not only lacked bone-regeneration effects but also suppressed the BMP4-induced bone regeneration. In vitro coculture of Cox-2-expressing MSCs with BMP4-expressing MSCs in gelatin scaffolds reduced BMP4 mRNA transcript levels, suggesting that Cox-2 may promote BMP4 gene silencing in BMP4-expressing cells, which may play a role in the suppressive action of Cox-2 on BMP4-mediated bone formation. In summary, the Cox-2 ex vivo gene-transfer strategy not only lacks bone-regeneration effects but also suppresses the bone-regeneration action of BMP4 in healing of calvarial defects.

Treatment of rabbit femoral defect by firearm with BMP-4 gene combined with TGF-beta1

BACKGROUND

Firearm bone fractures are difficult to treat compared with general ones as both soft tissue and bone are injured more extensively and severely with contamination in the wound track. The bone morphogenetic protein (BMP) and transforming growth factor (TGF)-beta play an important role in bone fracture healing. Therefore, BMP-4 combined with TGF-beta1 was used to improve and accelerate the repair of rabbit femoral defect resulting from firearm.

METHODS

Femoral defect was made with 0.375 g steel ball fired at 350 m/s. At 6 hours after wounding, the debridement and irrigation were performed, followed by trimming the ends of defected bone at day 7. Plasmid-encoded BMP-4 gene identified in vitro and TGF-beta1 were injected into the tissue of upper and lower parts and the epicenter of the defected area at 2 weeks after wounding, again TGF-beta1 was given at 5 weeks. At 3, 7, 11, and 15 weeks after wounding, the expression of mRNA and protein of BMP-4 were detected by reverse transcription-polymerase chain reaction and Western blot. The activity of alkaline phosphatase and calcium content were measured for describing osteogenetic ability. The course and quality of osteogenesis were determined quantitatively by pathohistological and X-ray examinations.

RESULTS

In vivo BMP-4 mRNA and protein could be continually expressed for 8 weeks. The determination of alkaline phosphatase activity and calcium content showed osteogenetic ability was significantly enhanced by BMP-4 gene combined with TGF-beta1. The pathohistological and X-ray examinations revealed that osteogenetic speed was prominently accelerated, and the quality was improved after the treatment.

CONCLUSION

The repair of rabbit femoral defect resulting from firearm can be significantly improved and accelerated by BMP-4 gene combined with TGF-beta1.

LMP-1 retroviral gene therapy influences osteoblast differentiation and fracture repair: a preliminary study

LIM mineralization protein-1 (LMP-1) is a novel intracellular osteogenic factor associated with bone development that has been implicated in the bone morphogenetic protein (BMP) pathway. This preliminary study evaluated the possibility of LMP-1-based retroviral gene therapy to stimulate osteoblast differentiation in vitro and fracture repair in vivo. A Moloney leukemia virus (MLV)-based retroviral vector to express LMP-1 with a hemagglutinin (HA) tag was developed, and its effects were evaluated on MC3T3-E1 cell differentiation and in the rat femur fracture model. MC3T3-E1 osteoblasts transduced with the MLV-HA-LMP-1 vector demonstrated significantly increased osteoblast marker gene expression (P < 0.05) and mineral deposition compared to control transduced cells. Femoral midshaft fractures were produced in Fischer 344 rats by the three-point bending technique. The MLV-HA-LMP-1 or control vector was applied at the fracture site through percutaneous injections 1 day postfracture. Analysis of fracture healing of 10 MLV-HA-LMP-1-treated and 10 control MLV-beta-galactosidase (beta-gal)-treated animals was completed at 3 weeks by X-ray, peripheral quantitative computed tomography, and histology. MLV-HA-LMP-1-treated animals had 63% more bone mineral content at the fracture site (P < 0.01), 34% greater total hard callus area (P < 0.05), and 45% less cartilage in the fracture callus (P < 0.05) compared to MLV-beta-gal-treated animals. There was no effect of LMP-1 treatment on the density of the hard callus. Immunohistochemistry revealed expression of the LMP-1 transgene in the fracture callus at 21 days postfracture. Immunohistochemistry also revealed that LMP-1 transgene expression did not result in an increase in BMP-4 expression in the fracture callus. Compared to MLV-BMP-4 gene therapy studies, MLV-HA-LMP-1 gene therapy improved bony union of the fracture gap to a greater extent and did not cause heterotopic bone formation. This suggests that LMP-1 may be a better potential candidate for gene therapy for fracture repair than BMP-4. These exciting, albeit preliminary, findings indicate that LMP-1-based gene therapy may potentially be a simple and effective means to enhance fracture repair that warrants further investigation.

Retroviral-mediated gene therapy for the differentiation of primary cells into a mineralizing osteoblastic phenotype

Bone tissue engineering has emerged as a promising strategy for the repair of critical-sized skeletal fractures. However, the clinical application of this approach has been limited by the availability of a robust mineralizing cell source. Non-osteogenic cells, such as skin fibroblasts, are an attractive cell-source alternative because they are easy to harvest from autologous donor skin biopsies and display a high capacity for in vitro expansion. We have recently demonstrated that retroviral gene delivery of the osteoblastic transcription factor Runx2/Cbfa1 promotes osteogenic differentiation in primary dermal fibroblasts cultured in monolayer. Notably, sustained expression of Runx2 was not sufficient to promote functional osteogenesis in these cells, and co-treatment with the steroid hormone dexamethasone was required to induce deposition of biologically-equivalent matrix mineralization. On the basis of these results, we then investigated the osteogenic capacity of these genetically engineered fibroblasts when seeded on polymeric scaffolds in vitro and in vivo. These experiments demonstrated that Runx2-expressing fibroblasts seeded on collagen scaffolds produce significant levels of matrix mineralization after 28 days in vivo implantation in a subcutaneous, heterotopic site. Overall, these results offer evidence that transcription factor-based gene therapy may be a powerful strategy for the conversion of a non-osteogenic cellular phenotype into a mineralizing cell source for bone repair applications. This concept may also be applied to control functional differentiation in a broad range of cell types and tissue engineering applications. The chapter below outlines detailed methods for the isolation and ex vivo genetic modification of primary dermal fibroblasts using retroviral-mediated delivery of the Runx2 transgene in both monolayer culture and three-dimensional scaffolds.

Retroviral-based gene therapy with cyclooxygenase-2 promotes the union of bony callus tissues and accelerates fracture healing in the rat

BACKGROUND

An in vivo gene therapy strategy was developed to accelerate bone fracture repair.

METHODS

Direct injection of a murine leukemia virus-based vector targeted transgene expression to the proliferating periosteal cells arising shortly after fracture. Cyclooxygenase-2 (Cox-2) was selected because the transgene for its prostaglandin products that promote angiogenesis, bone formation and bone resorption, are all required for fracture healing. The human (h) Cox-2 transgene was modified to remove AU-rich elements in the 3'-untranslated region and to improve protein translation.

RESULTS

In vitro studies revealed robust and sustained Cox-2 protein expression, prostaglandin E(2) and alkaline phosphatase production in rat bone marrow stromal cells and osteoblasts transgenic for the hCox-2 gene. In vivo studies in the rat femur fracture revealed that Cox-2 transgene expression produced bony union of the fracture by 21 days post-fracture, a time when cartilage persisted within the fracture tissues of control animals and approximately 1 week earlier than the healing normally observed in this model. None of the ectopic bone formation associated with bone morphogenetic protein gene therapy was observed.

CONCLUSIONS

This study represents the first demonstration that a single local application of a retroviral vector expressing a single osteoinductive transgene consistently accelerated fracture repair.

Bone regeneration after topical BMP-2-gene delivery in circumferential peri-implant bone defects

OBJECTIVES

The aims of this study were to evaluate the rate of bone formation and osseointegration after topical gene delivery with a liposomal vector system carrying bone morphogenetic protein (BMP)-2 cDNA in combination with a collagen carrier and autologous bone as a carrier in freshly created peri-implant bone defects.

MATERIALS AND METHODS

Eight domestic pigs received nine calvariae defects each (10 x 7 mm). A dental implant was inserted into the centre of each defect. In the test groups, the remaining space was filled with the liposomal vector/BMP-2 complex combined with a collagen carrier (n=18) or an autologous bone graft (n=18). Control groups were collagen only (n=18) and autologous bone graft only (n=18).

RESULTS

There was a significant difference in mineralisation rate in the BMP-2/bone graft (29.9%+/- 4.8 and 68.3%+/- 7.2) and bone graft only (22.6%+/- 2.6 and 49.4%+/- 13.9) groups after 7 and 28 days. Mineralisation values were also significantly higher in the BMP-2/collagen group (21.2%+/- 16.2 and 53.1%+/- 12.5) compared with the collagen-only group (8.2%+/- 7 and 41%+/- 8.1) in two different regions after 28 days. Also the bone-to-implant contact was significantly increased in the BMP-2/bone graft group after 28 days and in the BMP-2/collagen group after 7 and 28 days compared with their control groups.

CONCLUSIONS

The results of this study show a significantly positive effect of liposomal vector/BMP-2 on bone regeneration and osseointegration in bony circumferential peri-implant defects.

Oxysterols enhance osteoblast differentiation in vitro and bone healing in vivo

Oxysterols, naturally occurring cholesterol oxidation products, can induce osteoblast differentiation. Here, we investigated short-term 22(S)-hydroxycholesterol + 20(S)-hydroxycholesterol (SS) exposure on osteoblastic differentiation of marrow stromal cells. We further explored oxysterol ability to promote bone healing in vivo. Osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity, osteocalcin (OCN) mRNA expression, mineralization, and Runx2 DNA binding activity. To explore the effects of osteogenic oxysterols in vivo, we utilized the critical-sized rat calvarial defect model. Poly(lactic-co-glycolic acid) (PLGA) scaffolds alone or coated with 140 ng (low dose) or 1400 ng (high dose) oxysterol cocktail were implanted into the defects. Rats were sacrificed at 6 weeks and examined by three-dimensional (3D) microcomputed tomography (microCT). Bone volume (BV), total volume (TV), and BV/TV ratio were measured. Culture exposure to SS for 10 min significantly increased ALP activity after 4 days, while 2 h exposure significantly increased mineralization after 14 days. Four-hour SS treatment increased OCN mRNA measured after 8 days and nuclear protein binding to an OSE2 site measured after 4 days. The calvarial defects showed slight bone healing in the control group. However, scaffolds adsorbed with low or high-dose oxysterol cocktail significantly enhanced bone formation. Histologic examination confirmed bone formation in the defect sites grafted with oxysterol-adsorbed scaffolds, compared to mostly fibrous tissue in control sites. Our results suggest that brief exposure to osteogenic oxysterols triggered events leading to osteoblastic cell differentiation and function in vitro and bone formation in vivo. These results identify oxysterols as potential agents in local and systemic enhancement of bone formation.

Modifications of the fibroblast growth factor-2 gene led to a marked enhancement in secretion and stability of the recombinant fibroblast growth factor-2 protein

Progress in FGF-2 gene therapy has been hampered by the difficulty in achieving therapeutic levels of FGF-2 secretion. This study tested whether the addition of BMP2/4 hybrid secretion signal to the FGF-2 gene and mutation of cys-70 and cys-88 to serine and asparagine, respectively, would increase the stability and secretion of active FGF-2 protein in mammalian cells using MLV-based vectors. Single or double mutations of cys-70 and cys-88 to ser-70 and asp-88, respectively, markedly increased the amounts of FGF-2 protein in conditioned media and cell lysates, which may be due to glycosylation, particularly at the mutated asp-88 residue. Addition of BMP2/4 secretion signal increased FGF-2 secretion, but also suppressed FGF-2 biosynthesis. The combination of BMP2/4 secretion signal and double cys-70 and cys-88 mutations increased the total amount of secreted FGF-2 protein >60-fold. The modifications did not alter its ability to stimulate cell proliferation and Erk1/2 phosphorylation in marrow stromal cells or its ability to bind heparin in vitro, suggesting that the modified FGF-2 protein was functionally as effective as the unmodified FGF-2. An ex vivo application of rat skin fibroblasts (RSF) transduced with the modified FGF-2 vector in a subcutaneous implant model showed that rats with implants containing cells transduced with the modified FGF-2 vector increased serum FGF-2 level >15-fold, increased growth of the implant, and increased vascularization within the implant, compared to rats that received implants containing beta-galactosidase- or wild-type FGF-2-transduced control cells. This modified vector may be useful in FGF-2 gene therapy investigations.

Lentiviral-mediated BMP-2 gene transfer enhances healing of segmental femoral defects in rats

The objective of the present study was to assess the ability of bone marrow cells expressing BMP-2 created via lentiviral gene transfer to heal a critical sized femoral defect in a rat model. Femoral defects in Lewis rats were implanted with 5x10(6) rat bone marrow stromal cells (RBMSC) transduced with a lentiviral vector containing either the BMP-2 gene (Group I), the enhanced green fluorescent protein (LV-GFP) gene (Group IV), or RBMSC alone (Group V). We also included femoral defects that were treated with BMP-2-producing RBMSC transduced with lentivirus, 8 weeks after infection (Group III), and a group with 1x10(6) RBMSC transduced with a lentiviral vector with the BMP-2 gene (Group II). All defects (10/10) treated in Group I healed at 8 weeks compared with none of the femora in the control groups (Groups IV and V). In Group II, only one out of 10 femora healed. In Group III, 5 out of 10 femora healed. Significantly higher amounts of in vitro BMP-2 protein production were detected in Groups I, II, and III when compared to that of the control groups (p<0.05). Histomorphometric analysis revealed significantly greater total bone volume in defects in Group I and III when compared to control specimens (p<0.003). Biomechanical testing revealed no significant differences in the healed defects in Groups I and III when compared to intact, nonoperated femora with respect to peak torque and torque to failure. Our results indicate that BMP-2-producing RBMSC created through lentiviral gene transfer have the capability of inducing long-term protein production in vitro and producing substantial new bone formation in vivo.

Bone marrow-derived mesenchymal stem cells for regenerative medicine in craniofacial region

The craniofacial region contains many specified tissues including bone, cartilage, muscle, blood vessels and neurons. Defect or dysfunction of the craniofacial tissue after post-cancer ablative surgery, trauma, congenital malformations and progressive deforming skeletal diseases has a huge influence on the patient's life. Therefore, functional reconstruction of damaged tissues is highly expected. Bone marrow-derived mesenchymal stem cells (BMMSCs) are one of the most well characterized postnatal stem cell populations, and considered to be utilized for cell-based clinical therapies. Here, the current understanding and the potential applications in craniofacial tissue regeneration of BMMSCs are reviewed, and the current limitations and drawbacks are also discussed.

Virus-based gene therapy strategies for bone regeneration

Gene therapy has emerged as a promising strategy for the repair and regeneration of damaged musculoskeletal tissues. Application of this paradigm to bone healing has shown enhanced efficacy in preclinical animal studies compared to conventional bone grafting approaches. This review discusses current and emerging virus-based genetic engineering strategies for the delivery of therapeutic molecules which promote skeletal regeneration. Viral gene delivery vectors are discussed in the context of bone repair in order to illustrate the challenges and applications of these methods with tissue-specific examples. Moreover the concepts discussed can be broadly applied to promote healing in a wide range of tissues. We also present important considerations involved in the application of these gene therapy techniques to a variety of osteogenic (e.g. bone marrow-derived cells) and non-osteogenic (e.g. fibroblasts and skeletal myoblasts) cell types. Criteria for the selection of regenerative molecules with soluble versus intracellular modes of action and emerging combinatorial approaches are also discussed. Overall, gene transfer technologies have the potential to overcome limitations associated with existing bone grafting approaches and may enable investigators to design therapies which more closely mimic the complex spatial and temporal cascade of proteins involved in endogenous bone development and repair.

Nell-1-induced bone regeneration in calvarial defects

Many craniofacial birth defects contain skeletal components requiring bone grafting. We previously identified the novel secreted osteogenic molecule NELL-1, first noted to be overexpressed during premature bone formation in calvarial sutures of craniosynostosis patients. Nell-1 overexpression significantly increases differentiation and mineralization selectively in osteoblasts, while newborn Nell-1 transgenic mice significantly increase premature bone formation in calvarial sutures. In the current study, cultured calvarial explants isolated from Nell-1 transgenic newborn mice (with mild sagittal synostosis) demonstrated continuous bone growth and overlapping sagittal sutures. Further investigation into gene expression cascades revealed that fibroblast growth factor-2 and transforming growth factor-beta1 stimulated Nell-1 expression, whereas bone morphogenetic protein (BMP)-2 had no direct effect. Additionally, Nell-1-induced osteogenesis in MC3T3-E1 osteoblasts through reduction in the expression of early up-regulated osteogenic regulators (OSX and ALP) but induction of later markers (OPN and OCN). Grafting Nell-1 protein-coated PLGA scaffolds into rat calvarial defects revealed the osteogenic potential of Nell-1 to induce bone regeneration equivalent to BMP-2, whereas immunohistochemistry indicated that Nell-1 reduced osterix-producing cells and increased bone sialoprotein, osteocalcin, and BMP-7 expression. Insights into Nell-1-regulated osteogenesis coupled with its ability to stimulate bone regeneration revealed a potential therapeutic role and an alternative to the currently accepted techniques for bone regeneration.

The use of tissue-engineered bone with human bone morphogenetic protein-4-modified bone-marrow stromal cells in repairing mandibular defects in rabbits

In this study, the capacity of hBMP-4 gene therapy combined with tissue-engineering techniques to improve the repair of mandibular osseous defects in rabbits was explored. A mammalian plasmid vector expressing enhanced green fluorescent protein-human bone morphogenetic protein-4 (pEGFP-hBMP-4) was initially constructed through subcloning techniques. Bone-marrow stromal cells (bMSCs) from New Zealand White rabbits were cultured and either transfected with pEGFP-hBMP-4 or pEGFP, or left untransfected in vitro. Once the transfer efficiency was determined through the expression of EGFP, cells from the three groups were combined with natural non-organic bone (NNB) at a concentration of 50 x 10(6)cells/ml and placed in 15 mm x 6 mm bilateral, full-thickness, mandibular defects surgically made in 12 rabbits. Together with NNB control, there were six samples per group. Four weeks after surgery, the implants were harvested and evaluated histomorphologically. Under optimal experimental conditions, gene transfer efficiency reached a maximum of 38.2+/-9.4%. While the percentage of new bone area in the NNB control group was 8.8+/-3.1%, in the untransfected bMSC group 22.5+/-8.2%, and in the pEGFP group 18.1+/-9.0%, a significantly higher amount of 32.5+/-6.1% was observed in the pEGFP-hBMP-4 group. These results suggest that transfection of bMSCs with hBMP-4 enhances their inherent osteogenic capacity for maxillofacial bone tissue-engineering applications.

Evaluation of permissiveness and cytotoxic effects in equine chondrocytes, synovial cells, and stem cells in response to infection with adenovirus 5 vectors for gene delivery

OBJECTIVE

To evaluate host cell permissiveness and cytotoxic effects of recombinant and modified adenoviral vectors in equine chondrocytes, synovial cells, and bone marrow-derived mesenchymal stem cells (BMD-MSCs).

SAMPLE POPULATION

Articular cartilage, synovium, and bone marrow from 15 adult horses.

PROCEDURES

Equine chondrocytes, synovial cells, and BMD-MSCs and human carcinoma (HeLa) cells were cultured and infected with an E-1-deficient adenovirus vector encoding the beta-galactosidase gene or the green fluorescent protein gene (Ad-GFP) and with a modified E-1-deficient vector with the arg-gly-asp capsid peptide insertion and containing the GFP gene (Ad-RGD-GFP). Percentages of transduced cells, total and transduced cell counts, and cell viability were assessed 2 and 7 days after infection.

RESULTS

-Permissiveness to adenoviral vector infection was significantly different among cell types and was ranked in decreasing order as follows: HeLa cells > BMD-MSCs > chondrocytes > synovial cells. Morphologic signs of cytotoxicity were evident in HeLa cells but not in equine cells. Numbers of transduced cells decreased by day 7 in all cell types except equine BMD-MSCs. Transduction efficiency was not significantly different between the Ad-GFP and Ad-RGD-GFP vectors.

CONCLUSION AND CLINICAL RELEVANCE

Sufficient gene transfer may be achieved by use of an adenovirus vector in equine cells. High vector doses can be used in equine cells because of relative resistance to cytotoxic effects in those cells. Greater permissiveness and sustained expression of transgenes in BMD-MSCs make them a preferential cell target for gene therapy in horses.

Superior Effect of MD05, Beta-Tricalcium Phosphate Coated With Recombinant Human Growth/Differentiation Factor-5, Compared to Conventional Bone Substitutes in the Rat Calvarial Defect Model

BACKGROUND

MD05 consists of beta-tricalcium phosphate (beta-TCP) coated with recombinant human growth/differentiation factor-5 (rhGDF-5) and is under evaluation as an osteoinductive and osteoconductive bone graft material for use in dental and maxillofacial applications. The objective of this study was to compare the bone regenerative properties of MD05 with those of conventional commercially available bone substitutes.

METHODS

Full-thickness, 6-mm diameter, calvarial critical-size defects (two per animal) were created in adult Sprague-Dawley rats. Groups of rats were implanted with the following: 1) MD05; 2) bovine bone mineral; 3) bovine bone mineral with collagen; 4) bovine bone mineral with synthetic peptide, 5) beta-TCP (from two different manufacturers); or 6) no filling material (sham controls). Blinded macroscopic analysis, histopathologic analysis, and histomorphometric analysis were carried out 6 weeks after implantation.

RESULTS

New bone formation assessed histomorphometrically was about five times greater with MD05 than with the other bone substitutes tested, and bone repair was well advanced in MD05-filled defects after 6 weeks. The extent of fibrous tissue and residual implant were significantly lower in the MD05 group. In contrast to the other materials, the use of MD05 was associated with the complete osseous bridging of the defect and with the presence of normal bone marrow. The osteoinductive effect of rhGDF-5 was apparent from the more pronounced bone ingrowth observed with MD05 compared to the beta-TCP carrier alone. All implants showed good biocompatibility.

CONCLUSION

MD05 achieved superior bone regeneration compared to conventional materials and is a promising new bone substitute for dental and maxillofacial applications.

Potential of mesenchymal stem cells in gene therapy approaches for inherited and acquired diseases

The intriguing biology of stem cells and their vast clinical potential is emerging rapidly for gene therapy. Bone marrow stem cells, including the pluripotent haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and possibly the multipotent adherent progenitor cells (MAPCs), are being considered as potential targets for cell and gene therapy-based approaches against a variety of different diseases. The MSCs from bone marrow are a promising target population as they are capable of differentiating along multiple lineages and, at least in vitro, have significant expansion capability. The apparently high self-renewal potential makes them strong candidates for delivering genes and restoring organ systems function. However, the high proliferative potential of MSCs, now presumed to be self-renewal, may be more apparent than real. Although expanded MSCs have great proliferation and differentiation potential in vitro, there are limitations with the biology of these cells in vivo. So far, expanded MSCs have failed to induce durable therapeutic effects expected from a true self-renewing stem cell population. The loss of in vivo self-renewal may be due to the extensive expansion of MSCs in existing in vitro expansion systems, suggesting that the original stem cell population and/or properties may no longer exist. Rather, the expanded population may indeed be heterogeneous and represents several generations of different types of mesenchymal cell progeny that have retained a limited proliferation potential and responsiveness for terminal differentiation and maturation along mesenchymal and non-mesenchymal lineages. Novel technology that allows MSCs to maintain their stem cell function in vivo is critical for distinguishing the elusive stem cell from its progenitor cell populations. The ultimate dream is to use MSCs in various forms of cellular therapies, as well as genetic tools that can be used to better understand the mechanisms leading to repair and regeneration of damaged or diseased tissues and organs.

Gene-enhanced tissue engineering for dental hard tissue regeneration: (1) overview and practical considerations

Gene-based therapies for tissue regeneration involve delivering a specific gene to a target tissue with the goal of changing the phenotype or protein expression profile of the recipient cell; the ultimate goal being to form specific tissues required for regeneration. One of the principal advantages of this approach is that it provides for a sustained delivery of physiologic levels of the growth factor of interest.

This manuscript will review the principals of gene-enhanced tissue engineering and the techniques of introducing DNA into cells. Part 2 will review recent advances in gene-based therapies for dental hard tissue regeneration, specifically as it pertains to dentin regeneration/pulp capping and periodontal regeneration.

Endowing human adenovirus serotype 5 vectors with fiber domains of species B greatly enhances gene transfer into human mesenchymal stem cells

Bone marrow-derived human mesenchymal stem cells (hMSCs) lack the Coxsackie-adenovirus (Ad) receptor and thus are poorly transduced by vectors based on human Ad serotype 5 (Ad5). We investigated whether this problem could be overcome by using tropism-modified Ad5 vectors carrying fiber shaft domains and knobs of different human species B Ads (Ad5FBs). To allow quantitative analyses, these vectors coded for the enhanced green fluorescent protein (eGFP). Transgene expression analysis showed superior transduction of hMSCs by all Ad5FBs tested as compared with conventional Ad5 vectors. This was evident both by the frequency of eGFP-positive cells and by the eGFP level per cell. Highly efficient transduction of hMSCs, with limited variability between cells from different donors, was achieved with vectors displaying fiber domains of Ad serotypes 50, 35, and 16. These findings could not be reconciled with the very low levels of CD46, a recently identified receptor for species B Ads, on hMSCs, suggesting that AdFBs probably use receptors other than CD46 to enter these cells. We further observed that high eGFP levels were maintained in replication-restricted hMSCs for more than 30 days. In dividing hMSCs, foreign DNA delivered by Ad5FBs was expressed in a large fraction of the cells for approximately 3 weeks without compromising their replication capacity. Importantly, the transduced hMSCs retained their capacity to differentiate into adipocytes and osteoblasts when exposed to the appropriate stimuli.

Direct percutaneous gene delivery to enhance healing of segmental bone defects

BACKGROUND

Healing of segmental bone defects can be induced experimentally with genetically modified osteoprogenitor cells, an ex vivo strategy that requires two operative interventions and substantial cost. Direct transfer of osteogenic genes offers an alternative, clinically expeditious, cost-effective approach. We evaluated its potential in a well-established, critical-size, rat femoral defect model.

METHODS

A critical-size defect was created in the right femur of forty-eight skeletally mature Sprague-Dawley rats. After twenty-four hours, each defect received a single, intralesional, percutaneous injection of adenovirus carrying bone morphogenetic protein-2 (Ad.BMP-2) or luciferase cDNA (Ad.luc) or it remained untreated. Healing was monitored with weekly radiographs. At eight weeks, the rats were killed and the femora were evaluated with dual-energy x-ray absorptiometry, micro-computed tomography, histological analysis, histomorphometry, and torsional mechanical testing.

RESULTS

Radiographically, 75% of the Ad.BMP-2-treated femora showed osseous union. Bone mineral content was similar between the Ad.BMP-2-treated femora (0.045 +/- 0.020 g) and the contralateral, intact femora (0.047 +/- 0.003 g). Histologically, 50% of the Ad.BMP-2-treated defects were bridged by lamellar, trabecular bone; the other 50% contained islands of cartilage. The control (Ad.luc-treated) defects were filled with fibrous tissue. Histomorphometry demonstrated a large difference in osteogenesis between the Ad.BMP-2 group (mean bone area, 3.25 +/- 0.67 mm(2)) and the controls (mean bone area, 0.65 +/- 0.67 mm(2)). By eight weeks, the Ad.BMP-2-treated femora had approximately one-fourth of the strength (mean, 0.07 +/- 0.04 Nm) and stiffness (mean, 0.5 +/- 0.4 Nm/rad) of the contralateral femora (0.3 +/- 0.08 Nm and 2.0 +/- 0.5 Nm/rad, respectively).

CONCLUSIONS

A single, percutaneous, intralesional injection of Ad.BMP-2 induces healing of critical-size femoral bone defects in rats within eight weeks. At this time, the repair tissue is predominantly trabecular bone, has normal bone mineral content, and has gained mechanical strength.

Nell-1 induced bone formation within the distracted intermaxillary suture

Maxillary bone deficiencies, such as cleft palate and underdeveloped maxilla that require bone graft or regeneration after orthopedic or surgical expansion, pose a significant biomedical burden. Nell-1 is a secreted molecule that possesses chordin-like domains and induces cranial suture bone growth and osteoblast differentiation. To accelerate bone formation in acutely distracted palatal sutures, rat organ cultures were stimulated with Nell-1 or BMP-7 for 8 days in vitro. We hypothesized that Nell-1 stimulation to the distracted palatal suture would accelerate bone formation. Distracted palates of 4-week-old male rats were maintained in an organ culture system, and tissue was either unstimulated or stimulated with Nell-1 or BMP-7 for 8 days. MicroCT was conducted to quantitate bone formation, while alcian blue staining was conducted for cartilage localization. Immunohistochemistry of Sox9 for chondrocyte proliferation, type X collagen for hypertrophic cartilage in endochondral bone formation, and bone sialoprotein for bone formation was conducted to characterize the cellular mechanism of newly developed tissues. Distracted palates cultured in the presence of Nell-1 or BMP-7 produced statistically significantly (P < 0.05) more bone and cartilage within the intermaxillary suture, relative to unstimulated control samples. While both BMP-7 and Nell-1 induced similar bone formation in the distracted suture, BMP-7 induced both chondrocyte proliferation and differentiation, while Nell-1 accelerated chondrocyte hypertrophy and endochondral bone formation. While both Nell-1 and BMP-7 are effective in forming bone in the distracted palatal suture, they are suggested to have distinctively different mechanisms. The ability of Nell-1 to accelerate bone formation within the palate suture demonstrates the versatility of Nell-1 within the craniofacial complex as well as an exciting advance in palate suture defect healing.

Growth factor delivery for bone tissue repair: an update

Growth factors (GFs) are endogenous proteins capable of acting on cell-surface receptors and directing cellular activities involved in the regeneration of new bone tissue. The specific actions and long-term effects of GFs on bone-forming cells have resulted in exploration of their potential for clinical bone repair. The concerted efforts have led to the recent approval of two GFs, bone morphogenetic protein-2 and osteogenic protein-1, for clinical bone repair, and human parathryroid hormone (1-34) for augmentation of systemic bone mass. This review provides a selective summary of recent (2001-2004) attempts for GF delivery in bone tissue regeneration. First, a summary of non-human primate studies involving local regeneration and repair is provided, with special emphasis on the range of biomaterials used for GF delivery. Next, efforts to administer GFs for systemic augmentation of bone tissue are summarised. Finally, an alternative means of GF delivery, namely the delivery of genes coding for osteogenic proteins, rather than the delivery of the proteins, is summarised from rodent models. To conclude, future avenues of research considered promising to enhance the clinical application of GFs are discussed.

[Regenerative medicine and plastic surgery]

Regenerative medicine recently evolved as a new medical field that includes tissue engineering, cell/system biology, nanotechnology, pharmacology, stem-cell biology, and bioengineering. Regenerative medicine targets new forms of therapy to promote and support the intrinsic, autologous, regenerative potential of human biological systems. All fields of surgery have profited from these developments, and spectacular experimental results and clinical benefits have been obtained. Plastic surgery has shown interest in regenerative medicine due to its focus on reconstructive surgery. Early on, several interdisciplinary experimental working groups were founded including plastic surgery. This overview takes a closer look at common experimental and clinical results of regenerative medicine and plastic surgery.

Lentivirus-mediated gene transfer induces long-term transgene expression of BMP-2 in vitro and new bone formation in vivo

We examined the potential of ex vivo gene therapy to enhance bone repair using lentiviral vectors encoding either enhanced green fluorescent protein (EGFP) as a reporter gene or bone morphogenetic protein-2 (BMP-2) downstream of either the cytomegalovirus immediate early (CMV) promoter or the murine leukemia virus long terminal repeat (RhMLV) promoter derived from a murine retrovirus adapted to replicate in a rhesus macaque. In vitro, rat bone marrow stromal cells (BMSCs) transduced with Lenti-CMV-EGFP or Lenti-RhMLV-EGFP demonstrated over 90% transduction efficiency at 1 week and continued to demonstrate stable expression for 8 weeks. ELISA results demonstrated that lentivirus-mediated gene transfer into BMSCs induced stable BMP-2 production in vitro for 8 weeks. Increased EGFP and BMP-2 production was noted with the RhMLV promoter. In addition, we implanted BMSCs transduced with Lenti-RhMLV-BMP-2 into a muscle pouch in the hind limbs of severe combined immune deficient mice. Robust bone formation was noted in animals that received Lenti-RhMLV-BMP-2 cells at 3 weeks. These results demonstrate that lentiviral vectors expressing BMP-2 can induce long-term gene expression in vitro and new bone formation in vivo under the control of the RhMLV promoter. Prolonged gene expression may be advantageous when developing tissue engineering strategies to repair large bone defects.

Repairing of goat tibial bone defects with BMP-2 gene-modified tissue-engineered bone

Bone defects larger than a critical size are major challenges in orthopedic medicine. We combined tissue-engineered bone and gene therapy to provide osteoprogenitor cells, osteoinductive factors, and osteo-conductive carrier for ideal bone regeneration in critical-sized bone defects. Goat diaphyseal bone defects were repaired with tissue and genetically engineered bone implants, composed of biphasic calcined bone (BCB) and autologous bone marrow derived mesenchymal stem cells (BMSC) transduced with human bone morphogenetic protein-2 (hBMP-2). Twenty six goats with tibial bone defects were divided into groups receiving implants by using a combination of BCB and BMSCs with or without the hBMP-2 gene. In eight goats that were treated with BCB that contained hBMP-2 transduced BMSC, five had complete healing and three showed partial healing. Goats in other experimental groups had only slight or no healing. Furthermore, the area and biochemical strength of the callus in the bone defects were significantly better in animals treated with genetically engineered implants. We concluded that the combination of genetic and tissue engineering provides an innovative way for treating critical-sized bone defects.

Bone Regeneration in Cranial Defects Previously Treated with Radiation

OBJECTIVES/HYPOTHESIS

Bone reconstruction in the head and neck region is frequently performed in the context of previous radiation treatment. Thus, the effectiveness of tissue engineering approaches for regenerating bone in radiated defects needs to be determined before considering application to patients. Incomplete healing is described when using osteoinductive protein therapy alone for bone defects previously treated with radiation. We hypothesized that a different approach using ex vivo gene therapy can heal these severely compromised defects.

STUDY DESIGN

Animal study using Fisher rats.

METHODS

Two weeks before surgery, rats received either no radiation or a 12 Gray radiation dose to the calvarium. Syngeneic dermal fibroblasts were transduced ex vivo using an adenoviral vector containing the cDNA for bone morphogenetic protein (BMP)-7. Critical-sized calvarial defects were created, and either a transduced cell-seeded scaffold or an autologous bone graft was placed into the defect. Nonradiated defects were harvested 4 weeks later for both groups. Radiated defects treated with bone grafts were harvested at 4 weeks, and those treated with gene therapy were harvested either at 4 or 8 weeks. Gross inspection and histology were used to evaluate wound healing.

RESULTS

None of the bone grafts had gross or histologic evidence of healing at the wound margins. The nonradiated gene therapy treated defects revealed gross and histologic near-100% bone regeneration by 4 weeks after surgery. By gross inspection, the radiated defects had soft tissue admixed with islands of bone at both 4 and 8 weeks. The histologic appearance revealed areas of dense bone in a nonconfluent pattern admixed with adjacent cells having the morphologic appearance of hypertrophic chondrocytes, suggesting continued endochondral ossification.

CONCLUSIONS

Preoperative radiation significantly impairs the ability of BMP-7 ex vivo gene therapy to heal rat critical-sized cranial defects. This finding has significant implications for translating this tissue engineering approach to patients with cancer-related segmental bone defects.