Osteoinduction by ex vivo adenovirus-mediated BMP2 delivery is independent of cell type

A replicating stem-like cell that contributes to bone morphogenetic protein 2-induced heterotopic bone formation

Bone morphogenetic protein 2 (BMP2)‐induced heterotopic bone formation (HBF) starts synchronously from zero upon BMP2 induction, which is advantageous for lineage tracking. The studies reported here in GLAST‐Cre^Ert2:tdTomato red (TR)^floxSTOPflox mice during BMP2‐induced HBF show 78.8 ± 11.6% of chondrocytes and 86.5 ± 1.9% of osteoblasts are TR⁺ after approximately 1 week. Clustering after single‐cell RNAseq resulted in nine cell types, and analysis revealed one as a highly replicating stem‐like cell (RSC). Pseudotiming suggested that the RSC transitions to a mesenchymal stem‐like cell that simultaneously expresses multiple osteoblast and chondrocyte transcripts (chondro‐osseous progenitor [COP]). RSCs and COPs were isolated using flow cytometry for unique surface markers. Isolated RSCs (GLAST‐TR⁺ Hmmr⁺ Cd200⁻) and COPs (GLAST‐TR⁺ Cd200⁺ Hmmr⁻) were injected into the muscle of mice undergoing HBF. Approximately 9% of the cells in heterotopic bone (HB) in mice receiving RSCs were GLAST‐TR⁺, compared with less than 0.5% of the cells in mice receiving COPs, suggesting that RSCs are many times more potent than COPs. Analysis of donor‐derived TR⁺ RSCs isolated from the engrafted HB showed approximately 50% were COPs and 45% were other cells, presumably mature bone cells, confirming the early nature of the RSCs. We next isolated RSCs from these mice (approximately 300) and injected them into a second animal, with similar findings upon analysis of HBF. Unlike other methodology, single cell RNAseq has the ability to detect rare cell populations such as RSCs. The fact that RSCs can be injected into mice and differentiate suggests their potential utility for tissue regeneration.

BMP gene delivery for skeletal tissue regeneration

Musculoskeletal disorders are common and can be associated with significant morbidity and reduced quality of life. Current treatments for major bone loss or cartilage defects are insufficient. Bone morphogenetic proteins (BMPs) are key players in the recruitment and regeneration of damaged musculoskeletal tissues, and attempts have been made to introduce the protein to fracture sites with limited success. In the last 20 years we have seen a substantial progress in the development of various BMP gene delivery platforms for several conditions. In this review we cover the progress made using several techniques for BMP gene delivery for bone as well as cartilage regeneration, with focus on recent advances in the field of skeletal tissue engineering. Some methods have shown success in large animal models, and with the global trend of introducing gene therapies into the clinical setting, it seems that the day in which BMP gene therapy will be viable for clinical use is near.

BMP-2 gene delivery in cell-loaded and cell-free constructs for bone regeneration

To induce osteogenicity in bone graft substitutes, plasmid-based expression of BMP-2 (pBMP-2) has been successfully applied in gene activated matrices based on alginate polymer constructs. Here, we investigated whether cell seeding is necessary for non-viral BMP-2 gene expression in vivo. Furthermore, to gain insight in the role of BMP-producing cells, we compared inclusion of bone progenitor cells with non-osteogenic target cells in gene delivery constructs. Plasmid DNA encoding GFP (pGFP) was used to trace transfection of host tissue cells and seeded cells in a rat model. Transgene expression was followed in both cell-free alginate-ceramic constructs as well as constructs seeded with syngeneic fibroblasts or multipotent mesenchymal stromal cells (MSCs). Titration of pGFP revealed that the highest pGFP dose resulted in frequent presence of positive host cells in the constructs. Both cell-loaded groups were associated with transgene expression, most effectively in the MSC-loaded constructs. Subsequently, we investigated effectiveness of cell-free and cell-loaded alginate-ceramic constructs with pBMP-2 to induce bone formation. Local BMP-2 production was found in all groups containing BMP-2 plasmid DNA, and was most pronounced in the groups with MSCs transfected with high concentration pBMP-2. Bone formation was only apparent in the recombinant protein BMP-2 group. In conclusion, we show that non-viral gene delivery of BMP-2 is a potentially effective way to induce transgene expression in vivo, both in cell-seeded as well as cell-free conditions. However, alginate-based gene delivery of BMP-2 to host cells or seeded cells did not result in protein levels adequate for bone formation in this setting, calling for more reliable scaffold compatible transfection methods.

Osteoinduction by Ex Vivo Nonviral Bone Morphogenetic Protein Gene Delivery Is Independent of Cell Type

Ex vivo nonviral gene delivery of bone inductive factors has the potential to heal bone defects. Due to their inherent role in new bone formation, multipotent stromal cells (MSCs) have been studied as the primary target cell for gene delivery in a preclinical setting. The relative contribution of autocrine and paracrine mechanisms, and the need of osteogenic cells, remains unclear. This study investigates the contribution of MSCs as producer of transgenic bone morphogenetic proteins (BMPs) and to what extent the seeded MSCs participate in actual osteogenesis. Rat-derived MSCs or fibroblasts (FBs) were cotransfected with pBMP-2 and pBMP-6 or pBMP-7 via nucleofection. The bioactivity of BMP products was shown through in vitro osteogenic differentiation assays. To investigate their role in new bone formation, transfected cells were seeded on ceramic scaffolds and implanted subcutaneously in rats. Bone formation was assessed by histomorphometry after 8 weeks. As a proof of principle, we also investigated the suitability of bone marrow-derived mononuclear cells and the stromal vascular fraction isolated from adipose tissue for a one-stage gene delivery strategy. Bone formation was induced in all conditions containing cells overexpressing BMP heterodimers. Constructs seeded with FBs transfected with BMP-2/6 and MSCs transfected with BMP-2/6 showed comparable bone volumes, both significantly higher than controls. Single-stage gene delivery proved possible and resulted in some bone formation. We conclude that bone formation as a result of ex vivo BMP gene delivery can be achieved even without direct osteogenic potential of the transfected cell type, suggesting that transfected cells mainly function as a production facility for osteoinductive proteins. In addition, single-stage transfection and reimplantation of cells appeared feasible, thus facilitating future clinical translation of the method.

[Research of enhanced green fluorescent protein gene transfer with ultrasound-mediated microbubble destruction in bone defects]

Objective

To investigate the effect of ultrasonic irradiation time on enhanced green fluorescent protein (EGFP) gene transfection efficiency and local tissue in bone defects using ultrasound-mediated microbubble destruction.

Methods

Thirty 3-month-old New Zealand rabbits (2.5-3.0 kg in weight) were randomly divided into 5 groups ( n=6) and bone defect models were made on the right ulna. At 10 days after modeling, suspension of microbubbles and EGFP plasmids were locally injected (0.3 mL/kg) and then ultrasound was performed on defect at a frequency of 1 MHz, a intensity of 0.5 W/cm 2, and a duty ratio of 20% for 1, 2, 3, 4, and 5 minutes respectively (in 1, 2, 3, 4, and 5 minutes groups respectively). The survival condition was observed. Rabbits were sacrificed for gross observation at 7 days after transfer. The gene expression was observed by fluorescence staining. HE staining and transmission electron microscopy were used to observe the local tissue damage.

Results

The animals all survived. New soft tissue formed in bone defects area at 1 week after transfer, the surrounding muscle tissue was partly filled in it. Green fluorescence expression was observed in all rabbits. The expression was the strongest in 2 minutes group, and was the weakest in 1 minute group. The absorbance ( A) value showed significant differences when compared 1 minute and 2 minutes groups with other groups ( P<0.05), but no significant difference was found between 3, 4, and 5 minutes groups ( P>0.05). Tissue damage was observed in all groups and it was aggravated with the increase of irradiation time.

Conclusion

EGFP transfection efficiency in bone defect by ultrasound-mediated microbubble destruction is related to irradiation time. EGFP gene can be efficiently transfected without obvious toxicity at 1 MHz, 0.5W/cm 2, and duty ratio of 20% for 2 minutes in bone defects of rabbits.

Progenitors in Peripheral Nerves Launch Heterotopic Ossification

Studies presented here, using a murine model of bone morphogenetic protein type 2 (BMP2)-induced heterotopic ossification (HO) show that the protein initiates HO by signaling through progenitors in the endoneurium of peripheral nerves. In the mouse, these cells were identified in the endoneurium one day after BMP2 induction using antibody against phosphoSMAD (PS) 1, 5, and 8. Studies conducted in a tracking mouse that contains a tamoxifen-regulated Wnt1-Cre recombinase crossed with a td Tomato red (TR) reporter (Wnt1^CreErt :Ai9Tm) confirmed their neural origin. In this model both BMP2 induction and tamoxifen are absolutely required to induce TR. SP7⁺ (osterix⁺ )TR⁺ cells were found in the endoneurium on day 1 and associated with bone on day 7. Quantification of TR⁺ and TR^- cells isolated by fluorescence-activated cell sorting showed that all SP7⁺ cells were found in the TR⁺ population, whereas only about 80% of the TR⁺ cells expressed SP7. Pre-chondrocytes (Sox 9⁺ ) and transient brown fat (tBAT, UCP1⁺ ) also coexpressed TR, suggesting that the progenitor in nerves is multi-potential. The endoneurium of human nerves near the site of HO contained many PS⁺ cells, and SP7⁺ cells were found in nerves and on bone in tissue from patients with HO. Control tissues and nerves did not contain these PS⁺ and SP7⁺ cells. Some osteoblasts on bone from patients with HO were positive for PS, suggesting the continued presence of BMP during bone formation. The data suggests that the progenitors for HO are derived from the endoneurium in both the mouse model of HO and in humans with HO. Stem Cells Translational Medicine 2017;6:1109-1119.

Encapsulation of Adenovirus BMP2-Transduced Cells with PEGDA Hydrogels Allows Bone Formation in the Presence of Immune Response

Gene therapy approaches have been difficult to implement due to pre-existing immunity against the virus used for delivery. To circumvent this problem, a cell-based approach was developed that avoided the use of free virus within the animal. However, even cells transduced in vitro with E1- to E3-deleted adenovirus encoding bone morphogenetic protein 2 (AdBMP2) resulted in the production of virus-neutralizing antibodies in mice. Furthermore, when mice received an intramuscular injection of nonencoding adenovirus (AdEmpty)-transduced cells, AdBMP2-transduced cells were unable to launch bone formation when an intramuscular injection of these BMP2-producing cells was delivered 1 week later. This phenomenon was not observed in NOD/SCID mice, and could be overcome in C57BL/6 mice by encapsulating the adenovirus-transduced cells in a nondegradable hydrogel poly(ethylene glycol) diacrylate (PEGDA). Data collectively suggest that PEGDA hydrogel encapsulation of AdBMP2-transduced cells prevents pre-existing immunity from suppressing BMP2-induced bone formation.

Autologous implantation of BMP2-expressing dermal fibroblasts to improve bone mineral density and architecture in rabbit long bones

Cell-mediated gene therapy may treat bone fragility disorders. Dermal fibroblasts (DFb) may be an alternative cell source to stem cells for orthopedic gene therapy because of their rapid cell yield and excellent plasticity with bone morphogenetic protein-2 (BMP2) gene transduction. Autologous DFb or BMP2-expressing autologous DFb were administered in twelve rabbits by two delivery routes; a transcortical intra-medullar infusion into tibiae and delayed intra-osseous injection into femoral drill defects. Both delivery methods of DFb-BMP2 resulted in a successful cell engraftment, increased bone volume, bone mineral density, improved trabecular bone microarchitecture, greater bone defect filling, external callus formation, and trabecular surface area, compared to non-transduced DFb or no cells. Cell engraftment within trabecular bone and bone marrow tissue was most efficiently achieved by intra-osseous injection of DFb-BMP2. Our results suggested that BMP2-expressing autologous DFb have enhanced efficiency of engraftment in target bones resulting in a measurable biologic response by the bone of improved bone mineral density and bone microarchitecture. These results support that autologous implantation of DFb-BMP2 warrants further study on animal models of bone fragility disorders, such as osteogenesis imperfecta and osteoporosis to potentially enhance bone quality, particularly along with other gene modification of these diseases.

Far-red fluorescence gene reporter tomography for determination of placement and viability of cell-based gene therapies

Non-invasive injectable cellular therapeutic strategies based on sustained delivery of physiological levels of BMP-2 for spinal fusion are emerging as promising alternatives, which could provide sufficient fusion without the associated surgical risks. However, these injectable therapies are dependent on bone formation occurring only at the specific target region. In this study, we developed and deployed fluorescence gene reporter tomography (FGRT) to provide information on in vivo cell localization and viability. This information is sought to confirm the ideal placement of the materials with respect to the area where early bone reaction is required, ultimately providing three dimensional data about the future fusion. However, because almost all conventional fluorescence gene reporters require visible excitation wavelengths, current in vivo imaging of fluorescent proteins is limited by high tissue absorption and confounding autofluorescence. We previously administered fibroblasts engineered to produce BMP-2, but is difficult to determine 3-D information of placement prior to bone formation. Herein we used the far-red fluorescence gene reporter, IFP1.4 to report the position and viability of fibroblasts and developed 3-D tomography to provide placement information. A custom small animal, far-red fluorescence tomography system integrated into a commercial CT scanner was used to assess IFP1.4 fluorescence and to demark 3-D placement of encapsulated fibroblasts with respect to the vertebrae and early bone formation as assessed from CT. The results from three experiments showed that the placement of the materials within the spine could be detected. This work shows that in vivo fluorescence gene reporter tomography of cell-based gene therapy is feasible and could help guide cell-based therapies in preclinical models.

From mysteries to medicines: drug development for fibrodysplasia ossificans progressive

INTRODUCTION

Fibrodysplasia ossificans progressiva (FOP) is the most disabling disorder of skeletal metamorphosis in humans and leads to the formation of a second skeleton of heterotopic bone. Presently, there is no effective treatment.

AREAS COVERED

In this review, the authors discuss heterozygous activating mutations in Activin receptor A, type I/ Activin-like kinase 2 (ACVR1/ALK2), a bone morphogenetic protein (BMP) type I receptor that are the genetic cause of FOP and reveal a promising pharmacologic target in the BMP signaling pathway. Despite these germline mutations, episodic disease activation is induced by soft tissue injury and resultant inflammatory triggers that are dependent on responding progenitor cells and a tissue microenvironment that supports heterotopic ossification.

EXPERT OPINION

Here we review opportunities and challenges for the development of effective therapeutics for FOP. There are many potential approaches that may eventually be used to harness FOP. The long-term treatment of FOP is likely to involve not one, but several concomitant approaches that acknowledge molecular mechanisms involved in the induction and progression of the disease.

Fibrodysplasia ossificans progressiva: mechanisms and models of skeletal metamorphosis

Fibrodysplasia ossificans progressiva (FOP; MIM #135100) is a debilitating genetic disorder of connective tissue metamorphosis. It is characterized by malformation of the great (big) toes during embryonic skeletal development and by progressive heterotopic endochondral ossification (HEO) postnatally, which leads to the formation of a second skeleton of heterotopic bone. Individuals with these classic clinical features of FOP have the identical heterozygous activating mutation (c.617G>A; R206H) in the gene encoding ACVR1 (also known as ALK2), a bone morphogenetic protein (BMP) type I receptor. Disease activity caused by this ACVR1 mutation also depends on altered cell and tissue physiology that can be best understood in the context of a high-fidelity animal model. Recently, we developed such a knock-in mouse model for FOP (Acvr1^R206H/+) that recapitulates the human disease, and provides a valuable new tool for testing and developing effective therapies. The FOP knock-in mouse and other models in Drosophila, zebrafish, chickens and mice provide an arsenal of tools for understanding BMP signaling and addressing outstanding questions of disease mechanisms that are relevant not only to FOP but also to a wide variety of disorders associated with regenerative medicine and tissue metamorphosis.

Transient brown adipocyte-like cells derive from peripheral nerve progenitors in response to bone morphogenetic protein 2

Perineurial-associated brown adipocyte-like cells were rapidly generated during bone morphogenetic protein 2 (BMP2)-induced sciatic nerve remodeling in the mouse. Two days after intramuscular injection of transduced mouse fibroblast cells expressing BMP2 into wild-type mice, there was replication of beta-3 adrenergic receptor(+) (ADRB3(+)) cells within the sciatic nerve perineurium. Fluorescence-activated cell sorting and analysis of cells isolated from these nerves confirmed ADRB3(+) cell expansion and their expression of the neural migration marker HNK1. Similar analysis performed 4 days after BMP2 delivery revealed a significant decrease in ADRB3(+) cells from isolated sciatic nerves, with their concurrent appearance within the adjacent soft tissue, suggesting migration away from the nerve. These soft tissue-derived cells also expressed the brown adipose marker uncoupling protein 1 (UCP1). Quantification of ADRB3-specific RNA in total hind limb tissue revealed a 3-fold increase 2 days after delivery of BMP2, followed by a 70-fold increase in UCP1-specific RNA after 3 days. Expression levels then rapidly returned to baseline by 4 days. Interestingly, these ADRB3(+) UCP1(+) cells also expressed the neural guidance factor reelin. Reelin(+) cells demonstrated distinct patterns within the injected muscle, concentrated toward the area of BMP2 release. Blocking mast cell degranulation-induced nerve remodeling resulted in the complete abrogation of UCP1-specific RNA and protein expression within the hind limbs following BMP2 injection. The data collectively suggest that local BMP2 administration initiates a cascade of events leading to the expansion, migration, and differentiation of progenitors from the peripheral nerve perineurium to brown adipose-like cells in the mouse, a necessary prerequisite for associated nerve remodeling.

Synthesis and inflammatory response of a novel silk fibroin scaffold containing BMP7 adenovirus for bone regeneration

Gene therapy has garnished tremendous awareness for the repair of osseous defects. It exhibits high efficiency gene transfer and osteogenic differentiation potential making it well suitable for the sustained delivery of growth factors to local tissues. In the present study a simplified solution-based in situ biomimetic synthesis method is demonstrated for bone morphogenetic protein 7 (BMP7) adenovirus combined with silk fibroin scaffolds. This scaffold not only provides the three dimensional space for bone ingrowth, but also releases the BMP7 adenovirus which targets its secretion by host cells in vivo. Scaffolds were tested both in vitro for their osteogenic potential as well as in vivo in a critical-size calvarial defect in mice. Scaffolds loaded with bone morphogenetic protein 7 adenovirus (adBMP7) were able to sustain release of adBMP7 for up to 21 days and support cell proliferation and differentiation to bone forming osteoblasts. Calvarial defects treated with scaffolds containing adBMP7 significantly induced new bone formation in vivo. To demonstrate immuno-compatibility with host tissues, IL-2, IL-6 and TNF-α were measured up to 4 weeks post-implantation. Although these scaffolds demonstrated an initial pro-inflammatory response, levels of IL-2, IL-6 and TNF-α returned to baseline control values at either 2 or 4 weeks post-implantation demonstrating long term compatibility for growth factor delivery via gene therapy. The results from the present study indicate the promise of gene delivery scaffold systems for robust, low cost, and high quality bone tissue engineering applications.

Stem cell therapy: a novel & futuristic treatment modality for disaster injuries

Stem cell therapy hold the potential to meet the demand for transplant cells/tissues needed for treating damages resulting from both natural and man-made disasters. Pluripotency makes embryonic stem cells and induced pluripotent stem cells ideal for use, but their teratogenic character is a major hindrance. Therapeutic benefits of bone marrow transplantation are well known but characterizing the potentialities of haematopoietic and mesenchymal cells is essential. Haematopoietic stem cells (HSCs) have been used for treating both haematopoietic and non-haematopoietic disorders. Ease of isolation, in vitro expansion, and hypoimmunogenecity have brought mesenchymal stem cells (MSCs) into limelight. Though differentiation of MSCs into tissue-specific cells has been reported, differentiation-independent mechanisms seem to play a more significant role in tissue repair which need to be addressed further. The safety and feasibility of MSCs have been demonstrated in clinical trials, and their use in combination with HSC for radiation injury treatment seems to have extended benefit. Therefore, using stem cells for treatment of disaster injuries along with the conventional medical practice would likely accelerate the repair process and improve the quality of life of the victim.

Sensory nerve induced inflammation contributes to heterotopic ossification

Heterotopic ossification (HO), or bone formation in soft tissues, is often the result of traumatic injury. Much evidence has linked the release of BMPs (bone morphogenetic proteins) upon injury to this process. HO was once thought to be a rare occurrence, but recent statistics from the military suggest that as many as 60% of traumatic injuries, resulting from bomb blasts, have associated HO. In this study, we attempt to define the role of peripheral nerves in this process. Since BMP2 has been shown previously to induce release of the neuroinflammatory molecules, substance P (SP) and calcitonin gene related peptide (CGRP), from peripheral, sensory neurons, we examined this process in vivo. SP and CGRP are rapidly expressed upon delivery of BMP2 and remain elevated throughout bone formation. In animals lacking functional sensory neurons (TRPV1(-/-) ), BMP2-mediated increases in SP and CGRP were suppressed as compared to the normal animals, and HO was dramatically inhibited in these deficient mice, suggesting that neuroinflammation plays a functional role. Mast cells, known to be recruited by SP and CGRP, were elevated after BMP2 induction. These mast cells were localized to the nerve structures and underwent degranulation. When degranulation was inhibited using cromolyn, HO was again reduced significantly. Immunohistochemical analysis revealed nerves expressing the stem cell markers nanog and Klf4, as well as the osteoblast marker osterix, after BMP2 induction, in mice treated with cromolyn. The data collectively suggest that BMP2 can act directly on sensory neurons to induce neurogenic inflammation, resulting in nerve remodeling and the migration/release of osteogenic and other stem cells from the nerve. Further, blocking this process significantly reduces HO, suggesting that the stem cell population contributes to bone formation.

Cell-mediated and direct gene therapy for bone regeneration

INTRODUCTION

Bone regeneration is required for the treatment of fracture non/delayed-unions and bone defects. However, most current treatment modalities have limited efficacy, and newer therapeutic strategies, such as gene therapy, have substantial benefit for bone repair and regeneration.

AREAS COVERED

This review discusses experimental and clinical applications of cell-mediated and direct gene therapy for bone regeneration. The review covers literature on this subject from 2000 to February 2012.

EXPERT OPINION

Direct gene therapy using various viral and non-viral vectors of cell-mediated genes has been demonstrated to induce bone regeneration, although use of such vectors has shown some risk in human application. Osteoinductive capability of a number of progenitor cells isolated from bone marrow, fat, muscle and skin tissues, has been demonstrated by genetic modification with osteogenic genes. Cell-mediated gene therapy using such osteogenic gene-expressing progenitor cells has shown promising results in promoting bone regeneration in extensive animal work in recent years.

Cell-based gene therapy for repair of critical size defects in the rat fibula

More than a decade has passed since the first experiments using adenovirus-transduced cells expressing bone morphogenetic protein 2 were performed for the synthesis of bone. Since this time, the field of bone gene therapy has tackled many issues surrounding safety and efficacy of this type of strategy. We present studies examining the parameters of the timing of bone healing, and remodeling when heterotopic ossification (HO) is used for bone fracture repair using an adenovirus gene therapy approach. We use a rat fibula defect, which surprisingly does not heal even when a simple fracture is introduced. In this model, the bone quickly resorbs most likely due to the non-weight bearing nature of this bone in rodents. Using our gene therapy system robust HO can be introduced at the targeted location of the defect resulting in bone repair. The HO and resultant bone healing appeared to be dose dependent, based on the number of AdBMP2-transduced cells delivered. Interestingly, the HO undergoes substantial remodeling, and assumes the size and shape of the missing segment of bone. However, in some instances we observed some additional bone associated with the repair, signifying that perhaps the forces on the newly forming bone are inadequate to dictate shape. In all cases, the HO appeared to fuse into the adjacent long bone. The data collectively indicates that the use of BMP2 gene therapy strategies may vary depending on the location and nature of the defect. Therefore, additional parameters should be considered when implementing such strategies.

Matrix metalloproteinase-9 is a diagnostic marker of heterotopic ossification in a murine model

Heterotopic ossification (HO) is a serious disorder that occurs when there is aberrant bone morphogenic protein (BMP) signaling in soft tissues. Currently, there are no methods to detect HO before mineralization occurs. Yet once mineralization occurs, there are no effective treatments, short of surgery, to reverse HO. Herein, we used in vivo molecular imaging and confirmatory ex vivo tissue analyses of an established murine animal model of BMP-induced HO to show that matrix metalloproteinase-9 (MMP-9) can be detected as an early-stage biomarker before mineralization. Ex vivo analyses show that active MMP-9 protein is significantly elevated within tissues undergoing HO as early as 48 h after BMP induction, with its expression co-localizing to nerves and vessels. In vivo molecular imaging with a dual-labeled near-infrared fluorescence and micro-positron emission tomography (μPET) agent specific to MMP-2/-9 expression paralleled the ex vivo observations and reflected the site of HO formation as detected from microcomputed tomography 7 days later. The results suggest that the MMP-9 is a biomarker of the early extracellular matrix (ECM) re-organization and could be used as an in vivo diagnostic with confirmatory ex vivo tissue analysis for detecting HO or conversely for monitoring the success of tissue-engineered bone implants that employ ECM biology for engraftment.

Human artificial chromosomes for gene delivery and the development of animal models

Random integration of conventional gene delivery vectors such as viruses, plasmids, P1 phage-derived artificial chromosomes, bacterial artificial chromosomes and yeast artificial chromosomes can be associated with transgene silencing. Furthermore, integrated viral sequences can activate oncogenes adjacent to the insertion site resulting in cancer. Various human artificial chromosomes (HACs) exhibit several potential characteristics desired for an ideal gene delivery vector, including stable episomal maintenance and the capacity to carry large genomic loci with their regulatory elements, thus allowing the physiological regulation of the introduced gene in a manner similar to that of native chromosomes. HACs have been generated mainly using either a "top-down approach" (engineered chromosomes), or a "bottom-up approach" (de novo artificial chromosomes). The recent emergence of stem cell-based tissue engineering has opened up new avenues for gene and cell therapies. This review describes the lessons learned and prospects identified mainly from studies in the construction of HACs and HAC-mediated gene expression systems in cultured cells, as well as in animals.

An injectable method for noninvasive spine fusion

BACKGROUND CONTEXT

Bone morphogenetic proteins (BMPs) induce bone formation but are difficult to localize, and subsequent diffusion from the site of interest and short half-life reduce the efficacy of the protein. Currently, spine fusion requires stripping, decortications of the transverse processes, and an autograft harvest procedure. Even in combination with BMPs, clinical spinal fusion has a high failure rate, presumably because of difficulties in localizing sufficient levels of BMP.

PURPOSE

The goal was to achieve reliable spine fusion through a single injection of a cell-based gene therapy system without the need for any surgical intervention.

STUDY DESIGN

Eighty-seven immunodeficient (n=44) and immune-competent (n=43) mice were injected along the paraspinous musculature to achieve rapid induction of heterotopic ossification (HO) and ultimately spinal arthrodesis.

METHODS

Immunodeficient and immune-competent mice were injected with fibroblasts, transduced with an adenoviral vector to express BMP2, along the paraspinous musculature. Bone formation was evaluated via radiographs, microcomputed tomography, and biomechanical analysis.

RESULTS

ew bridging bone between the vertebrae and the fusion to adjacent skeletal bone was obtained as early as 2 weeks. Reduction in spine flexion-extension also occurred as early as 2 weeks after injection of the gene therapy system, with greater than 90% fusion by 4 weeks in all animals regardless of their genetic background.

CONCLUSIONS

Injection of our cell-based system into the paraspinous musculature induces spinal fusion that is dependent neither on the cell type nor on the immune status. These studies are the first to harness HO in an immune-competent model as a noninvasive injectable system for clinically relevant spinal fusion and may one day impact human spinal arthrodesis.

Hydrogel microsphere encapsulation of a cell-based gene therapy system increases cell survival of injected cells, transgene expression, and bone volume in a model of heterotopic ossification

Bone morphogenetic proteins (BMPs) are well known for their osteoinductive activity, yet harnessing this capacity remains a high-priority research focus. We present a novel technology that delivers high BMP-2 levels at targeted locations for rapid endochondral bone formation, enhancing our preexisting cell-based gene therapy system by microencapsulating adenovirus-transduced cells in nondegradable poly(ethylene glycol) diacrylate (PEGDA) hydrogels before intramuscular delivery. This study evaluates the in vitro and in vivo viability, gene expression, and bone formation from transgenic fibroblasts encapsulated in PEGDA microspheres. Fluorescent viability and cytotoxicity assays demonstrated >95% viability in microencapsulated cells. ELISA and alkaline phosphatase assays established that BMP-2 secretion and specific activity from microencapsulated AdBMP2-transduced fibroblasts were not statistically different from monolayer. Longitudinal transgene expression studies of AdDsRed-transduced fibroblasts, followed through live animal optical fluorescent imaging, showed that microencapsulated cells expressed longer than unencapsulated cells. When comparable numbers of microencapsulated AdBMP2-transduced cells were intramuscularly injected into mice, microcomputed tomography evaluation demonstrated that the resultant heterotopic bone formation was approximately twice the volume of unencapsulated cells. The data suggest that microencapsulation protects cells and prolongs and spatially distributes transgene expression. Thus, incorporation of PEGDA hydrogels significantly advances current gene therapy bone repair approaches.

Ex vivo gene therapy using autologous dermal fibroblasts expressing hLMP3 for rat mandibular bone regeneration

BACKGROUND

Implantation of autologous skin fibroblasts transduced ex vivo with a replication-defective adenoviral vector, carrying the LIM mineralization protein-3 (Ad-LMP-3), and adsorbed on a hydroxyapatite/collagen (HA/COL) scaffold.

METHODS

Twenty-seven Wistar rats were used. A 5- x 5-mm full-thickness defect was created in the exposed mandible. All animals were randomized into 3 experimental groups: (1) autologous dermal fibroblasts transduced with Ad-LMP-3 and adsorbed on the HA/COL; (2) nontransduced dermal fibroblasts adsorbed on the HA/COL scaffold; and (3) HA/COL scaffold without cells. Three-dimensional micro-CT (3DmicroCT or 3DmuCT) and histological analysis were performed.

RESULTS

Efficient neoosteogenesis was observed in animals treated with LMP-3-expressing cells (group 1) as soon as 4 weeks after surgery. Conversely, nonsignificant bone formation was detected in control animals (groups 2 and 3) at all time points tested.

CONCLUSION

These results suggest that the experimental approach based on transplantation of genetically modified autologous cells could provide an alternative treatment for cranio-maxillo-facial defects. Nonetheless, additional data from the study on larger bone defects must follow to foresee a clinical application in the near future.

Gene therapy for bone healing

Clinical problems in bone healing include large segmental defects, spinal fusions, and the nonunion and delayed union of fractures. Gene-transfer technologies have the potential to aid healing by permitting the local delivery and sustained expression of osteogenic gene products within osseous lesions. Key questions for such an approach include the choice of transgene, vector and gene-transfer strategy. Most experimental data have been obtained using cDNAs encoding osteogenic growth factors such as bone morphogenetic protein-2 (BMP-2), BMP-4 and BMP-7, in conjunction with both nonviral and viral vectors using in vivo and ex vivo delivery strategies. Proof of principle has been convincingly demonstrated in small-animal models. Relatively few studies have used large animals, but the results so far are encouraging. Once a reliable method has been developed, it will be necessary to perform detailed pharmacological and toxicological studies, as well as satisfy other demands of the regulatory bodies, before human clinical trials can be initiated. Such studies are very expensive and often protracted. Thus, progress in developing a clinically useful gene therapy for bone healing is determined not only by scientific considerations, but also by financial constraints and the ambient regulatory environment.

Genetically engineered mesenchymal stem cells: The ongoing research for bone tissue engineering

Bone grafting is crucial in the surgical treatment of bone defects and nonunion fractures. Autogenous bone, allogenous bone, and biomaterial scaffold are three main sources of bone grafts. The biomaterial scaffold, both natural and synthetic, is widely accessible but weak in osteogenic potential. One approach to solve this problem is cell-based bone tissue engineering (BTE), established by growing living osteogenic cells on scaffold in vitro to build up its osteoinducitive capability. Mesenchymal stem cell (MSC) is suitable for use in cell-based BTE, but it remains a considerable challenge to induce MSCs to form solely bone and while preventing MSCs from differentiating into fats, muscles, and possibly neural elements in vivo. Recently, there is a drastic rise in use of genetically engineered MSCs, which can secrete growth factors or alter the transcription level, leading to osteoblast lineage commitment, bone formation, fracture repair, and spinal fusion. In this article, we reviewed the literatures regarding applications of genetically engineered MSCs in BTE. We addressed the currently applicable genes and candidate genes for MSCs modification, transduction efficiency and safety issues of the transfect vectors, and administration routes, and we briefly described in vivo tracking and potential clinical application of the genetically modified MSCs in BTE.

Gene therapy for fracture healing

Traumatic bone defects and nonunion represent a significant source of morbidity and socioeconomic burden in trauma patients. The treatment of these conditions is currently hampered by inadequate therapies. This has prompted a new era of investigation into biologic therapies for augmenting fracture healing. Within this body of research, gene therapy has arisen as a novel and effective method of delivering therapeutic proteins at a site of desired bone regeneration. Gene therapy has shown tremendous potential in preclinical studies of fracture healing, but to date, no clinical trials have occurred. This article reviews the scientific basis for gene therapy in fracture healing, provides an overview of important preclinical studies that have been performed to date, and discusses the current barriers and future directions of gene therapy as it applies to fracture healing.

Mesenchymal stem cell-based therapy: a new paradigm in regenerative medicine

Mesenchymal stem cells (MSCs), adherent fibroblastoid cells, present in bone marrow and many other tissues can be easily isolated and expanded in vitro. They are capable of differentiating into different cell types such as osteoblasts, chondrocytes, adipocytes, cardiomyocytes, hepatocytes, endothelial cells and neuronal cells. Such immense plasticity coupled with their ability to modulate the activity of immune cells makes them attractive for stem cell-based therapy aimed at treating previously incurable disorders. Preclinical studies have reported successful use of MSCs for delivering therapeutic proteins and repairing defects in a variety of disease models. These studies highlighted the in vivo potential of MSCs and their ability to home to injury sites and modify the microenvironment by secreting paracrine factors to augment tissue repair. Their therapeutic applicability has been widened by genetic modification to enhance differentiation and tissue targeting, and use in tissue engineering. Clinical trials for diseases such as osteogenesis imperfecta, graft-versus-host disease and myocardial infarction have shown some promise, demonstrating the safe use of both allogeneic and autologous cells. However, lack of knowledge of MSC behaviour and responses in vitro and in vivo force the need for basic and animal studies before heading to the clinic. Contrasting reports on immunomodulatory functions and tumorigenicity along with issues such as mode of cell delivery, lack of specific marker, low survival and engraftment require urgent attention to harness the potential of MSC-based therapy in the near future.

Comparison of osteogenic potentials of BMP4 transduced stem cells from autologous bone marrow and fat tissue in a rabbit model of calvarial defects

We compared bone marrow stem cells (BMSCs) and adipose-derived stem cells (ADSCs) of adult rabbits under identical conditions in terms of their culture characteristics, proliferation capacity, osteogenic differentiation potentials induced by adenovirus-containing bone morphogenetic protein 4 (Ad-BMP4) in vitro, and capacity to repair calvarial defects in the rabbit model by autologous transplantation ex vivo. According to the results of growth curve, cell cycle, and telomerase activity analysis, ADSCs possess a higher proliferation potential. Both of the Ad-BMP4 transduced MSCs expressed BMP4 mRNA and protein and underwent osteogenic differentiation. Up-regulated mRNA expression of all osteogenic genes was observed in differentiated BMSCs and ADSCs, but with different patterns confirmed by real-time RT-PCR. Deposition of calcified extracellular matrix was significantly greater in differentiated ADSCs compared with differentiated BMSCs. X-ray and histological examination indicated significant bone regeneration in the calvarial defects transplanted with Ad-BMP4 transduced autologous MSCs compared to the control groups. There was no significant difference in new bone formation in Ad-BMP4 transduced MSCs based on quantitative digital analysis of histological sections. The use of ADSCs often resulted in the growth of fat tissue structures in the control groups, and the fat tissue structures were not seen with BMSC cells. Our data demonstrate that BMP4 can be potently osteoinductive in vivo, resulting in bone repair. ADSCs may be an attractive alternative to BMSCs for bone tissue engineering under appropriate stimuli. But the easy adipogenic differentiation needs to be considered when choosing adipose tissue for specific clinical application.

Orthopedic gene therapy in 2008

Orthopedic disorders, although rarely fatal, are the leading cause of morbidity and impose a huge socioeconomic burden. Their prevalence will increase dramatically as populations age and gain weight. Many orthopedic conditions are difficult to treat by conventional means; however, they are good candidates for gene therapy. Clinical trials have already been initiated for arthritis and the aseptic loosening of prosthetic joints, and the development of bone-healing applications is at an advanced, preclinical stage. Other potential uses include the treatment of Mendelian diseases and orthopedic tumors, as well as the repair and regeneration of cartilage, ligaments, and tendons. Many of these goals should be achievable with existing technologies. The main barriers to clinical application are funding and regulatory issues, which in turn reflect major safety concerns and the opinion, in some quarters, that gene therapy should not be applied to nonlethal, nongenetic diseases. For some indications, advances in nongenetic treatments have also diminished enthusiasm. Nevertheless, the preclinical and early clinical data are impressive and provide considerable optimism that gene therapy will provide straightforward, effective solutions to the clinical management of several common debilitating disorders that are otherwise difficult and expensive to treat.

Preparation and ectopic osteogenesis in vivo of scaffold based on mineralized recombinant human-like collagen loaded with synthetic BMP-2-derived peptide

The ideal bone graft material must be biocompatible, biodegradable, osteoconductive and osteoinductive. In this study, a new biomimetic scaffold based on mineralized recombinant collagen, nano-hydroxyapatite/recombinant human-like collagen/poly(lactic acid) (nHA/RHLC/PLA), was prepared and the synthetic P24 peptide derived from BMP-2 was introduced into the porous nHA/RHLC/PLA scaffold to improve its osteoinductive property. The nHA/RHLC/PLA implants loaded with 3 mg, 2 mg, 1 mg and 0 mg P24 peptide were implanted subcutaneously into rats. At the 4th, 8th and 12th weeks after implantation, the rats were sacrificed in batch and the samples were harvested. Their osteogenic capability was detected by CT scan and histological observation. The results indicated that the osteogenic capability of 3 mg, 2 mg and 1 mg of the P24 peptide was superior to the implants without the P24 peptide. There was no significant difference between implants with 3 mg and 2 mg P24 peptide, but the osteogenic capability of the two dosage groups was significantly better than that of the 1 mg group. It was concluded that BMP-2-derived peptide can increase the osteoinduction of nHA/RHLC/PLA scaffold and the P24 peptide induced new bone formation in a dose-dependent manner. The nHA/RHLC/PLA scaffold loaded with the synthetic BMP-2-derived peptide is a kind of ideal scaffold material for bone tissue engineering.

Ex vivo-transduced autologous skin fibroblasts expressing human Lim mineralization protein-3 efficiently form new bone in animal models

Local gene transfer of the human Lim mineralization protein (LMP), a novel intracellular positive regulator of the osteoblast differentiation program, can induce efficient bone formation in rodents. To develop a clinically relevant gene therapy approach to facilitate bone healing, we have used primary dermal fibroblasts transduced ex vivo with Ad.LMP-3 and seeded on a hydroxyapatite/collagen matrix prior to autologous implantation. Here, we demonstrate that genetically modified autologous dermal fibroblasts expressing Ad.LMP-3 are able to induce ectopic bone formation following implantation of the matrix into mouse triceps and paravertebral muscles. Moreover, implantation of the Ad.LMP-3-modified dermal fibroblasts into a rat mandibular bone critical size defect model results in efficient healing, as determined by X-rays, histology and three-dimensional microcomputed tomography (3DmuCT). These results demonstrate the effectiveness of the non-secreted intracellular osteogenic factor LMP-3 in inducing bone formation in vivo. Moreover, the utilization of autologous dermal fibroblasts implanted on a biomaterial represents a promising approach for possible future clinical applications aimed at inducing new bone formation.

Transfer of human artificial chromosome vectors into stem cells

Human chromosome fragments and human artificial chromosomes (HAC) represent feasible gene delivery vectors via microcell-mediated chromosome transfer. Strategies to construct HAC involve either 'build up' or 'top-down' approaches. For each approach, techniques for manipulating HAC in donor cells in order to deliver HAC to recipient cells are required. The combination of chromosome fragments or HAC with microcell-mediated chromosome transfer has facilitated human gene mapping and various genetic studies. The recent emergence of stem cell-based tissue engineering has opened up new avenues for gene and cell therapies. The task now is to develop safe and effective vectors that can deliver therapeutic genes into specific stem cells and maintain long-term regulated expression of these genes. Although the transfer-efficiency needs to be improved, HAC possess several characteristics that are required for gene therapy vectors, including stable episomal maintenance and the capacity for large gene insets. HAC can also carry genomic loci with regulatory elements, which allow for the expression of transgenes in a genetic environment similar to the natural chromosome. This review describes the lessons and prospects learned, mainly from recent studies in developing HAC and HAC-mediated gene expression in embryonic and adult stem cells, and in transgenic animals.

Efficient and rapid osteoinduction in an immune-competent host

Osteoinductive systems to induce targeted rapid bone formation hold clinical promise, but development of technologies for clinical use that must be tested in animal models is often a difficult challenge. We previously demonstrated that implantation of human cells transduced with Ad5F35BMP2 to express high levels of bone morphogenetic protein-2 (BMP2) resulted in rapid bone formation at targeted sites. Inclusion of human cells in this model precluded us from testing this system in an immune-competent animal model, thus limiting information about the efficacy of this approach. Here, for the first time we demonstrate the similarity between BMP2-induced endochondral bone formation in a system using human cells in an immune-incompetent mouse and a murine cell-based BMP2 gene therapy system in immune-competent animals. In both cases the delivery cells are rapidly cleared, within 5 days, and in neither case do they appear to contribute to any of the structures forming in the tissues. Endochondral bone formation progressed through a highly ordered series of stages that were both morphologically and temporally indistinguishable between the two models. Even longterm analysis of the heterotopic bone demonstrated similar bone volumes and the eventual remodeling to form similar structures. The results suggest that the ability of BMP2 to rapidly induce bone formation overrides contributions from either immune status or the nature of delivery cells.

Oxygen Tension Directs Chondrogenic Differentiation of Myelo-Monocytic Progenitors During Endochondral Bone Formation

Synthesis of bone requires both essential progenitors to form the various structures and the correct microenvironment for their differentiation. To identify these factors, we have used a system that exploits bone morphogenetic protein's ability to induce endochondral bone formation rapidly. One of the earliest events observed was the influx and proliferation of fibroblastic cells that express both vascular smooth muscle cell markers, alpha smooth muscle actin (alpha SMA), smooth muscle myosin heavy chain, and the monocytic marker CD68. The expression of these factors was lost by days 4 to 5, coincident with the up-regulation of Sox9 and the appearance of chondrocytes. Studies with a cyclization recombination (Cre)/lox system, in which a myeloid-specific promoter driving Cre recombinase can irreversibly unblock expression of beta-galactosidase only in cells of myeloid origin, showed specific activity in the newly formed chondrocytes. These results suggest that early chondrocyte progenitors are of myeloid origin. Simultaneous with this recruitment, we determined that a numbers of these cells were in a hypoxic state, indicative of a low-oxygen environment. The cells in the hypoxic regions were undergoing chondrogenesis, whereas cells in adjacent normoxic regions appeared to be assembling into new vessels, suggesting that the oxygen microenvironment is critical for establishment of the cartilage.

Hypoxic adipocytes pattern early heterotopic bone formation

The factors contributing to heterotopic ossification, the formation of bone in abnormal soft-tissue locations, are beginning to emerge, but little is known about microenvironmental conditions promoting this often devastating disease. Using a murine model in which endochondral bone formation is triggered in muscle by bone morphogenetic protein 2 (BMP2), we studied changes near the site of injection of BMP2-expressing cells. As early as 24 hours later, brown adipocytes began accumulating in the lesional area. These cells stained positively for pimonidazole and therefore generated hypoxic stress within the target tissue, a prerequisite for the differentiation of stem cells to chondrocytes and subsequent heterotopic bone formation. We propose that aberrant expression of BMPs in soft tissue stimulates production of brown adipocytes, which drive the early steps of heterotopic endochondral ossification by lowering oxygen tension in adjacent tissue, creating the correct environment for chondrogenesis. Results in misty gray lean mutant mice not producing brown fat suggest that white adipocytes convert into fat-oxidizing cells when brown adipocytes are unavailable, providing a compensatory mechanism for generation of a hypoxic microenvironment. Manipulation of the transcriptional control of adipocyte fate in local soft-tissue environments may offer a means to prevent or treat development of bone in extraskeletal sites.

Endochondral Bone Formation from Hydrogel Carriers Loaded with BMP2-transduced Cells

The success of ex vivo viral gene therapy systems for promoting bone formation could be improved through the development of systems to spatially localize gene expression. Towards this goal, we have encapsulated adenovirus-transduced human diploid fetal lung fibroblasts (MRC-5) expressing bone morphogenetic protein-type 2 (BMP-2) within non-degradable poly(ethylene glycol)-diacrylate (PEG-DA) hydrogels and implanted these intramuscularly to promote endochondral bone formation. To optimize BMP-2 secretion, the molecular weight of the polymers and cell densities were varied. Polymers with molecular weights of 6, 10, and 20 kDa were used to prepare hydrogels containing 1, 5, or 10 million transduced cells. The results showed that 10 million transduced fibroblasts that was the maximum number of cells feasible for encapsulation within PEG-DA 10 and 20 kDa hydrogels produced the highest amount of secreted BMP-2 protein. Encapsulation of MRC-5 and transduced fibroblasts resulted in 71 and 58% cell viability, respectively. The bioactivity of secreted BMP-2 protein from the hydrogels was confirmed with an alkaline phosphatase assay. Micro-CT of the lower limb muscles of NOD/SCID mice following implantation with hydrogels showed 39.5 +/- 25.0 mm3 mineralized tissue and 31.8 +/- 7.8 mm3 for the cell-injected mice, and the bone was localized to the hydrogel surfaces. Histology revealed bone as well as cartilage for both hydrogel implanted and cell-injected animals.

Human artificial chromosome vectors meet stem cells: new prospects for gene delivery

The recent emergence of stem cell-based tissue engineering has now opened up new venues for gene therapy. The task now is to develop safe and effective vectors that can deliver therapeutic genes into specific stem cell lines and maintain long-term regulated expression of these genes. Human artificial chromosomes (HACs) possess several characteristics that require gene therapy vectors, including a stable episomal maintenance, and the capacity for large gene inserts. HACs can also carry genomic loci with regulatory elements, thus allowing for the expression of transgenes in a genetic environment similar to the chromosome. Currently, HACs are constructed by a two prone approaches. Using a top-down strategy, HACs can be generated from fragmenting endogenous chromosomes. By a bottom-up strategy, HACs can be created de novo from cloned chromosomal components using chromosome engineering. This review describes the current advances in developing HACs, with the main focus on their applications and potential value in gene delivery, such as HAC-mediated gene expression in embryonic, adult stem cells, and transgenic animals.

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.

Rat adipose-derived stromal cells expressing BMP4 induce ectopic bone formation in vitro and in vivo

AIM

Bone morphogenetic protein 4 (BMP4) is one of the main local contributing factors in callus formation in the early phase of fracture healing. Adipose-derived stromal cells (ADSC) are multipotent cells. The present study was conducted to investigate the osteogenic potential of ADSC when exposed to adenovirus containing BMP4 cDNA (Ad-BMP4).

METHODS

ADSC were harvested from Sprague-Dawley rats. After exposure to Ad-BMP4, ADSC were assessed by alkaline phosphatase activity (ALP) assay, RT-PCR and von Kossa staining. BMP4 expression was assessed by RT-PCR, immunofluorescence and Western blot analysis. ADSC transduced with Ad-BMP4 were directly injected into the hind limb muscles of athymic mice. ADSC Ad-EGFP(enhanced green fluorescence protein) served as controls. All animals were examined by X-ray film and histological analysis.

RESULTS

The expression of BMP4 was confirmed at both mRNA and protein levels. The expression of the osteoblastic gene, ALP activity and von Kossa staining confirmed that ADSC transduced with Ad-BMP4 underwent rapid and marked osteoblast differentiation, whereas ADSC transduced with Ad-EGFP and cells left alone displayed no osteogenic differentiation. X-ray and histological examination confirmed new bone formation in athymic mice transplanted with ADSC transduced with Ad-BMP4.

CONCLUSION

Our data demonstrated successful osteogenic differentiation of ADSC transduced with Ad-BMP4 in vitro and in vivo. ADSC may be an ideal source of mesenchyme lineage stem cells for gene therapy and tissue engineering.

A new group B adenovirus receptor is expressed at high levels on human stem and tumor cells

CD46 is used by human group B adenoviruses (Ads) as a high-affinity attachment receptor. Here we show evidence that several group B Ads utilize an additional receptor for infection of human cells, which is different from CD46. We tentatively named this receptor receptor X. Competition studies with unlabeled and labeled Ads, recombinant Ad fiber knobs, and soluble CD46 and CD46 antibodies revealed three different subgroups of group B Ads, in terms of their receptor usage. Group I (Ad16, -21, -35, and -50) nearly exclusively uses CD46. Group II (Ad3, -7p, and -14) utilizes receptor X and not CD46. Group III (Ad11p) uses both CD46 and the alternative receptor X. Interaction of group II and III Ads with receptor X occurs via the fiber knob. Receptor X is an abundantly expressed glycoprotein that interacts with group II and III Ads at relatively low affinity in a Ca(2+)-dependent manner. This receptor is expressed at high levels on human mesenchymal and undifferentiated embryonic stem cells, as well as on human cancer cell lines. These findings have practical implications for stem cell and gene therapy.

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.

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.

Nucleofection-BasedEx VivoNonviral Gene Delivery to Human Stem Cells as a Platform for Tissue Regeneration

There are several gene therapy approaches to tissue regeneration. Although usually efficient, virusbased approaches may elicit an immune response against the viral proteins. An alternative approach, nonviral transfer, is safer, and can be controlled and reproduced. We hypothesized that in vivo bone formation could be achieved using human mesenchymal stem cells (hMSCs) nonvirally transfected with the human bone morphogenetic protein-2 (hBMP-2) or -9 (hBMP-9) gene. Human MSCs were transfected using nucleofection, a unique electropermeabilization-based technique. Postnucleofection, cell viability was 53.6 +/- 2.5% and gene delivery efficiency was 51% to 88% (mean 68.2 +/- 4.1%), as demonstrated by flow cytometry in enhanced green fluorescent protein (EGFP)-nucleofected hMSCs. Transgene expression lasted longer than 14 days and was very low 21 days postnucleofection. Both hBMP-2- and hBMP-9-nucleofected hMSCs in culture demonstrated a significant increase in calcium deposition compared with EGFP-nucleofected hMSCs. Human BMP-2- and hBMP-9-nucleofected hMSCs transplanted in ectopic sites in NOD/SCID mice induced bone formation 4 weeks postinjection. We conclude that in vivo bone formation can be achieved by using nonvirally nucleofected hMSCs. This could lead to a breakthrough in the field of regenerative medicine, in which safer, nonviral therapeutic strategies present a very attractive alternative.

In vitro and in vivo induction of bone formation based on ex vivo gene therapy using rat adipose-derived adult stem cells expressing BMP-7

BACKGROUND

Adipose-derived adult stem (ADAS) cells are multipotent cells capable of differentiating into osteoblasts, adipocytes and chondrocytes. The aim of this study was to determine whether BMP-7-expressing ADAS cells would elicit bone formation invitro and in vivo.

METHODS

ADAS cells were harvested from Lewis rats and transduced with adenovirus carrying the recombinant human bone morphogenetic protein-7 (Ad-BMP-7) gene. Untransduced cells and cells transduced with adenovirus carrying the enhanced green fluorescence protein (Ad-EGFP) gene served as controls. BMP-7 expression was assessed by RT-PCR, immunofluorescence on day 1, and Western blot on days 4, 8 and 12. Alkaline phosphatase (ALP) activity was assayed on days 2, 4, 6, 8, 10 and 12. Osteocalcin production and bone nodule formation were detected by immunohistochemistry and von Kossa stain on day 12. A total of 1 x 10(6) cells mixed with type I collagen were implanted into the subcutaneous pocket in Lewis rat and subjected to histologic analysis 1, 2 and 4 weeks post-implantation.

RESULTS

The Ad-BMP-7-transduced ADAS cells expressed BMP-7 at both mRNA and protein levels. ALP activity was detected in Ad-BMP-7-transduced cells from day 2 to day 12, peaking on day 8. Osteocalcin production and matrix mineralization further confirmed that these cells differentiated into osteoblasts and induced bone formation in vitro. Histologic examination revealed that implantation of BMP-7-expressing ADAS cells could induce new bone formation in vivo.

DISCUSSION

ADAS cells would be a promising source of adult autologous stem cells for BMP gene therapy and tissue engineering.