Efficacy of mesenchymal stem cell enriched grafts in an ovine posterolateral lumbar spine model

Comparing the efficacy of adipose-derived and bone marrow-derived cells in a rat model of posterolateral lumbar fusion

Although bone marrow-derived mesenchymal stem cells (BMCs) have been widely used in spinal fusion procedures, adipose-derived stem cells (ASCs) offer a number of advantages as an alternative clinical cell source. This study directly compares the efficacy of ASCs and BMCs from the same donor animals to achieve successful fusion when combined with a clinical-grade bone graft substitute in a rat lumbar fusion model. ASCs and BMCs were isolated from the same Lewis donor rats and grown to passage 2 (P2). Single-level bilateral posterolateral intertransverse process lumbar fusion surgery was performed on syngeneic rats divided into three experimental groups: clinical-grade bone graft substitute alone (CBGS); CBGS+ rat ASCs (rASC); and, CBGS+ rat BMCs (rBMC). Eight weeks postoperatively, fusion was evaluated via micro-CT, manual palpation and histology. In vitro analysis of the osteogenic capacity of rBMCs and rASCs was also performed. Results indicated that the average fusion volume in the rASC group was the largest and was significantly larger than the CBGS group. Although the rASC group displayed the highest fusion rates via micro-CT and manual palpation, this difference was not statistically significant. Cell-seeded grafts showed more histological bone formation than cell-free grafts. P2 rASCs and rBMCs displayed similar in vitro osteogenic differentiation capacities. Overall, this study showed that, when combined with a clinical-grade bone graft substitute in a rat model, rASCs cells yielded the largest fusion masses and comparable fusion results to rBMCs. These results add to growing evidence that ASCs provide an attractive alternative to BMCs for spinal fusion procedures.

MSC therapy in livestock models

Mesenchymal stem cells (MSCs) have great value as therapeutic tools in a wide array of applications in regenerative medicine. The wide repertoire of cell functions regarding tissue regeneration, immunomodulation, and antimicrobial activity makes MSC-based therapy a strong candidate for treatment options in a variety of clinical conditions and should be studied to expand the current breadth of knowledge surrounding their physiological properties and therapeutic benefits. Livestock models are an appropriate resource for testing the efficacy of MSC therapies for their use in biomedical research and can be used to improve both human health and animal agriculture. Agricultural animal models such as pigs, cattle, sheep, and goats have grown in popularity for in vivo research relative to small animal models due to their overlapping similarities in structure and function that more closely mimic the human body. Cutaneous wound healing, bone regeneration, osteoarthritis, ischemic reperfusion injury, and mastitis recovery represent a few examples of the types of disease states that may be investigated in livestock using MSC-based therapy. Although the cost of agricultural animals is greater than small animal models, the information gained using livestock as a model holds great value for human applications, and in some cases, outcompetes the weight of information gained from rodent models. With emerging fields such as exosome-based therapy, proper in vivo models will be needed for testing efficacy and translational practice, i.e., livestock models should be strongly considered as candidates. The potential for capitalizing on areas that have crossover benefits for both agricultural economic gain and improved health of the animals while minimizing the gap between translational research and clinical practice are what make livestock great choices for experimental MSC models.

Comparison of Freshly Isolated Adipose Tissue-derived Stromal Vascular Fraction and Bone Marrow Cells in a Posterolateral Lumbar Spinal Fusion Model

STUDY DESIGN

Rat posterolateral lumbar fusion model.

OBJECTIVE

The aim of this study was to compare the efficacy of freshly isolated adipose tissue-derived stromal vascular fraction (A-SVF) and bone marrow cells (BMCs) cells in achieving spinal fusion in a rat model.

SUMMARY OF BACKGROUND DATA

Adipose tissue-derived stromal cells (ASCs) offer advantages as a clinical cell source compared to bone marrow-derived stromal cells (BMSCs), including larger available tissue volumes and reduced donor site morbidity. While pre-clinical studies have shown that ex vivo expanded ASCs can be successfully used in spinal fusion, the use of A-SVF cells better allows for clinical translation.

METHODS

A-SVF cells were isolated from the inguinal fat pads, whereas BMCs were isolated from the long bones of syngeneic 6- to 8-week-old Lewis rats and combined with Vitoss (Stryker) bone graft substitute for subsequent transplantation. Posterolateral spinal fusion surgery at L4-L5 was performed on 36 female Lewis rats divided into three experimental groups: Vitoss bone graft substitute only (VO group); Vitoss + 2.5 × 106 A-SVF cells/side; and, Vitoss + 2.5 × 106 BMCs/side. Fusion was assessed 8 weeks post-surgery via manual palpation, micro-computed tomography (μCT) imaging, and histology.

RESULTS

μCT imaging analyses revealed that fusion volumes and μCT fusion scores in the A-SVF group were significantly higher than in the VO group; however, they were not significantly different between the A-SVF group and the BMC group. The average manual palpation score was highest in the A-SVF group compared with the BMC and VO groups. Fusion masses arising from cell-seeded implants yielded better bone quality than nonseeded bone graft substitute.

CONCLUSION

In a rat model, A-SVF cells yielded a comparable fusion mass volume and radiographic rate of fusion to BMCs when combined with a clinical-grade bone graft substitute. These results suggest the feasibility of using freshly isolated A-SVF cells in spinal fusion procedures.Level of Evidence: N/A.

Stem Cells and Spinal Fusion

BACKGROUND

This manuscript is a review of the literature investigating the use of mesenchymal stem cells (MSCs) being applied in the setting of spinal fusion surgery. We mention the rates of pseudarthrosis, discuss current bone grafting options, and examine the preclinical and clinical outcomes of utilizing MSCs to assist in successfully fusing the spine.

METHODS

A thorough literature review was conducted to look at current and previous preclinical and clinical studies using stem cells for spinal fusion augmentation. Searches for PubMed/MEDLINE and ClinicalTrials.gov through January 2021 were conducted for literature mentioning stem cells and spinal fusion.

RESULTS

All preclinical and clinical studies investigating MSC use in spinal fusion were examined. We found 19 preclinical and 17 clinical studies. The majority of studies, both preclinical and clinical, were heterogeneous in design due to different osteoconductive scaffolds, cells, and techniques used. Preclinical studies showed promising outcomes in animal models when using appropriate osteoconductive scaffolds and factors for osteogenic differentiation. Similarly, clinical studies have promising outcomes but differ in their methodologies, surgical techniques, and materials used, making it difficult to adequately compare between the studies.

CONCLUSION

MSCs may be a promising option to use to augment grafting for spinal fusion surgery. MSCs must be used with appropriate osteoconductive scaffolds. Cell-based allografts and the optimization of their use have yet to be fully elucidated. Further studies are necessary to determine the efficacy of MSCs with different osteoconductive scaffolds and growth/osteogenic differentiation factors.

LEVEL OF EVIDENCE

3.

Allografts and Spinal Fusion

BACKGROUND

Back pain is a common chief complaint within the United States and is caused by a multitude of etiologies. There are many different treatment modalities for back pain, with a frequent option being spinal fusion procedures. The success of spinal fusion greatly depends on instrumentation, construct design, and bone grafts used in surgery. Bone allografts are important for both structural integrity and providing a scaffold for bone fusion to occur.

METHOD

Searches were performed using terms "allografts" and "bone" as well as product names in peer reviewed literature Pubmed, Google Scholar, FDA-510k approvals, and clinicaltrials.gov.

RESULTS

This study is a review of allografts and focuses on currently available products and their success in both animal and clinical studies.

CONCLUSION

Bone grafts used in surgery are generally categorized into 3 main types: autogenous (from patient's own body), allograft (from cadaveric or living donor), and synthetic. This paper focuses on allografts and provides an overview on the different subtypes with an emphasis on recent product development and uses in spinal fusion surgery.

In vitro and in vivo evaluation of the pH-neutral bioactive glass as high performance bone grafts

Osteogenic and angiogenic properties are two most valued factors for bone grafting materials. Biomedical materials with synergistic promotion effects on these two properties would be highly desirable. In this study, we showed that a recently developed pH-neutral bioactive glass (PSC) possessed such characteristics. Compared to two classical biomaterials, 45S5 bioactive glass and beta-tricalcium phosphate (β-TCP), PSC markedly improved BMSCs' proliferation, migration and mineralization as well as their osteogenic and angiogenic differentiation. In vivo, PSC showed better performance on inducing bone regeneration than both 45S5 and β-TCP, as featured by elevated bone mineral density (BMD) and new bone areas. PSC also significantly promoted new blood vessels formation compared with those in control groups. Furthermore, we revealed that PSC induced osteogenic and angiogenic differentiation of BMSCs through the PI3K/Akt/HIF-1α pathway, which had not been reported before. This synergistic effect of the PI3K/Akt/HIF-1α pathway on osteogenesis and angiogenic differentiation of BMSCs suggested that biomedical materials may promote new bone formation through multiple signal pathways, thus shedding light on the future development of materials with better performance.

Evidence of Negative Effects of Defect Size and Older Patient Age by Quantitative CT-Based 3D Image Analysis in Ultraporous Beta-Tricalcium Phosphate Grafted Extremity Bone Defects at One Year

Introduction

Synthetic bone graft materials are commonly used to fill defects after curettage of benign bone lesions. Ultraporous beta tricalcium phosphate (TCP) is a popular synthetic compound used in this situation. Prior clinical studies based on plain X-ray analysis suggest incorporation of TCP is incomplete, even when combined with bone marrow (BMA).

Purpose

The purpose was to analyze volumetric CT-based changes in defects grafted with TCP with/without BMA in a completed prospective RCT to objectively determine (1) relationship between size and age versus TCP incorporation and (2) whether there is an advantage to addition of BMA.

Methods

Twenty-one patients with CT scans at ≥1 year follow-up available for digital analysis (TCP=10, TCP w/BMA =11) form the study population. CT image stacks were evaluated by creating volumetric masks using MIMICS imaging software for total defect, graft remaining, and graft incorporated volumes graft incorporation endpoints.

Results

Overall, there was significant (p=0.0029) negative correlation (r² = 0.38) between defect size and ratio of incorporated bone to defect size. This relationship remained strong (r² = 0.56) particularly for defects > 20 cc but not for smaller defects. Bone width was also a significantly related factor (r² = 0.94), with less graft incorporation in larger bone sites, in part likely due to the linear relationship between defect size and bone width. Relationship with age was complex and closely tied to defect volume. For larger defect volumes, younger patients were more successful at graft incorporation. Although age itself was not an independently significant factor, as defect volume increased, advanced age more negatively impacted new bone formation.

Conclusions

Larger size defect and affected bone and advancing age appear to be important negative factors in synthetic graft incorporation. Results showed no advantage to addition of BMA to TCP.

Intraoperative Construct Preparation: A Practical Route for Cell-Based Bone Regeneration

Stem cell-based bone tissue engineering based on the combination of a scaffold and expanded autologous mesenchymal stem cells (MSCs) represents the current state-of-the-art treatment for bone defects and fractures. However, the procedure of such construct preparation requires extensive ex vivo manipulation of patient's cells to achieve enough stem cells. Therefore, it is impractical and not cost-effective compared to other therapeutic interventions. For these reasons, a more practical strategy circumventing any ex vivo manipulation and an additional surgery for the patient would be advantageous. Intraoperative concept-based bone tissue engineering, where constructs are prepared with easily accessible autologous cells within the same surgical procedure, allows for such a simplification. In this study, we discuss the concept of intraoperative construct preparation for bone tissue engineering and summarize the available cellular options for intraoperative preparation. Furthermore, we propose methods to prepare intraoperative constructs, and review data of currently available preclinical and clinical studies using intraoperatively prepared constructs for bone regenerative applications. We identify several obstacles hampering the application of this emerging approach and highlight perspectives of technological innovations to advance the future developments of intraoperative construct preparation.

Mesenchymal Stem Cell Levels of Human Spinal Tissues

STUDY DESIGN

Systematic review.

OBJECTIVE

The aim of this study was to investigate, quantify, compare, and compile the various mesenchymal stem cell (MSC) tissue sources within human spinal tissues to act as a compendium for clinical and research application.

SUMMARY OF BACKGROUND DATA

Recent years have seen a dramatic increase in academic and clinical understanding of human MSCs. Previously limited to cells isolated from bone marrow, the past decade has illicited the characterization and isolation of human MSCs from adipose, bone marrow, synovium, muscle, periosteum, peripheral blood, umbilical cord, placenta, and numerous other tissues. As researchers explore practical applications of cells in these tissues, the absolute levels of MSCs in specific spinal tissue will be critical to guide future research.

METHODS

The PubMED, MEDLINE, EMBASE, and Cochrane databases were searched for articles relating to the harvest, characterization, isolation, and quantification of human MSCs from spinal tissues. Selected articles were examined for relevant data, categorized according to type of spinal tissue, and when possible, standardized to facilitate comparisons between sites.

RESULTS

Human MSC levels varied widely between spinal tissues. Yields for intervertebral disc demonstrated roughly 5% of viable cells to be positive for MSC surface markers. Cartilage endplate cells yielded 18,500 to 61,875 cells/0.8 mm thick sample of cartilage end plate. Ligamentum flavum yielded 250,000 to 500,000 cells/g of tissue. Annulus fibrosus fluorescence activated cell sorting treatment found 29% of cells positive for MSC marker Stro-1. Nucleus pulposus yielded mean tissue samples of 40,584 to 234,137 MSCs per gram of tissue.

CONCLUSION

Numerous tissues within and surrounding the spine represent a consistent and reliable source for the harvest and isolation of human MSCs. Among the tissues of the spine, the annulus fibrosus and ligamentum flavum each offer considerable levels of MSCs, and may prove comparable to that of bone marrow.

LEVEL OF EVIDENCE

5.

Long-term Radiological and Clinical Outcomes After Using Bone Marrow Mesenchymal Stem Cells Concentrate Obtained With Selective Retention Cell Technology in Posterolateral Spinal Fusion

STUDY DESIGN

Retrospective study.

OBJECTIVE

The aim of this study was to evaluate the long-term clinical and radiological outcomes of the use of bone marrow mesenchymal stem cell concentrate obtained with selective cell retention technology using Cellect with a particular collagen scaffold, Healos for posterolateral spinal fusion.

SUMMARY OF BACKGROUND DATA

With the increasing rate of spinal fusion, the problem of pseudarthrosis, which contributes to recurrent pain with patient disability, is considered to be the most common cause of revision lumbar spine surgery. Intensive research is being carried out to develop an alternative source of bone grafting and improve the spinal fusion rate.

METHODS

A retrospective review of hospital records was performed. Identified patients were contacted to have a clinical and radiological evaluation follow-up. Clinical outcome was evaluated using visual analog scales for the back pain (VAS), Oswestry Disability Index (ODI) scores, and quality of life (EQ-5D) questionnaire. Radiological outcome was evaluated by performing dynamic flexion/extension lateral views and calculation of segmental Cobb angle. Any implant-associated complication was reported. Computed tomography (CT) scans were also performed.

RESULTS

Twenty-one patients were included and all patients achieved successful fusion. The mean difference of the segmental Cobb angle was 0.48° (range 0.3°-0.7°). Computed tomography scans showed solid bilateral fusion with bridging bone (Grade I) in all patients, but solid unilateral fusion with bridging bone (Grade II) was detected for one patient at one level. Patients started to resume working activities within a mean period of 3.5 months. The VAS score for the residual back pain was 4.1 ± 2.1, whereas the ODI was 10.5 ± 5.6 points, and the mean disability index was 21.1%.

CONCLUSION

The use of bone marrow mesenchymal stem cell concentrate obtained with selective cell retention technology could be considered as an effective means for augmenting spinal fusion.

LEVEL OF EVIDENCE

3.

Stem Cells in Spinal Fusion

STUDY DESIGN

Review of literature.

OBJECTIVES

This review of literature investigates the application of mesenchymal stem cells (MSCs) in spinal fusion, highlights potential uses in the development of bone grafts, and discusses limitations based on both preclinical and clinical models.

METHODS

A review of literature was conducted looking at current studies using stem cells for augmentation of spinal fusion in both animal and human models.

RESULTS

Eleven preclinical studies were found that used various animal models. Average fusion rates across studies were 59.8% for autograft and 73.7% for stem cell-based grafts. Outcomes included manual palpation and stressing of the fusion, radiography, micro-computed tomography (μCT), and histological analysis. Fifteen clinical studies, 7 prospective and 8 retrospective, were found. Fusion rates ranged from 60% to 100%, averaging 87.1% in experimental groups and 87.2% in autograft control groups.

CONCLUSIONS

It appears that there is minimal clinical difference between commercially available stem cells and bone marrow aspirates indicating that MSCs may be a good choice in a patient with poor marrow quality. Overcoming morbidity and limitations of autograft for spinal fusion, remains a significant problem for spinal surgeons and further studies are needed to determine the efficacy of stem cells in augmenting spinal fusion.

Bone Marrow Mononuclear Cells Combined with Beta-Tricalcium Phosphate Granules for Alveolar Cleft Repair: A 12-Month Clinical Study

Alveolar cleft is the most common congenital bone defect. Autologous iliac crest bone graft (ICBG) is the most widely adopted procedure for alveolar cleft repair, but the condition is associated with door-site morbidities. For the first time, this study used bone marrow mononuclear cells (BMMNCs) combined with beta-tricalcium phosphate (β-TCP) granules to repair alveolar bone defect. The effectiveness of this technique was compared with autologous ICBG after 12 months of follow-up. The bone formation volume was quantitatively evaluated by three-dimensional computed tomography and computer aided engineering technology. BMMNCs/β-TCP granule grafting was radiographically equivalent to ICBG in alveolar cleft repair. Although considerable resorption was observed up to 6 months after surgery, no significant differences were noted in the Chelsea score and bone formation volume between groups. These finding indicate that BMMNCs/β-TCP grafting is a safe and effective approach for alveolar bone regeneration.

Mesenchymal Stem Cells for the Treatment of Spinal Arthrodesis: From Preclinical Research to Clinical Scenario

The use of spinal fusion procedures has rapidly augmented over the last decades and although autogenous bone graft is the “gold standard” for these procedures, alternatives to its use have been investigated over many years. A number of emerging strategies as well as tissue engineering with mesenchymal stem cells (MSCs) have been planned to enhance spinal fusion rate. This descriptive systematic literature review summarizes the in vivo studies, dealing with the use of MSCs in spinal arthrodesis surgery and the state of the art in clinical applications. The review has yielded promising evidence supporting the use of MSCs as a cell-based therapy in spinal fusion procedures, thus representing a suitable biological approach able to reduce the high cost of osteoinductive factors as well as the high dose needed to induce bone formation. Nevertheless, despite the fact that MSCs therapy is an interesting and important opportunity of research, in this review it was detected that there are still doubts about the optimal cell concentration and delivery method as well as the ideal implantation techniques and the type of scaffolds for cell delivery. Thus, further inquiry is necessary to carefully evaluate the clinical safety and efficacy of MSCs use in spine fusion.

Is lumbar facet fusion biomechanically equivalent to lumbar posterolateral onlay fusion?

OBJECTIVE This study was designed with the following research objectives: 1) to determine the efficacy of facet fusion with recombinant human bone morphogenetic protein-2 (rhBMP-2) on an absorbable collagen sponge (ACS) in an ovine lumbar facet fusion model; 2) to radiographically and histologically compare the efficacy of lumbar facet fusion with rhBMP-2/ACS to facet fusion with an iliac crest bone graft (ICBG); and 3) to biomechanically compare lumbar facet fusion with rhBMP-2/ACS to lumbar posterolateral fusion (PLF) with ICBG. METHODS The efficacies of the 3 treatments to induce fusion were evaluated in an instrumented ovine lumbar fusion model. Eight sheep had 10 cm³/side ICBG placed as an onlay graft for PLF at L2-3. At the adjacent L3-4 level, 0.5 cm³/side ICBG was placed for facet fusion. Finally, 0.5 cm³/side rhBMP-2/ACS (0.43 mg/ml) was placed for facet fusion at L4-5. CT scans were obtained at 2, 4, and 6 months postoperatively with 2 reviewers conducting an evaluation of the 6-month results for all treated spinal levels. All 8 sheep were killed at 6 months, and all posterolateral instrumentation was removed at this time. The spines were then sectioned through L3-4 to allow for nondestructive unconstrained biomechanical testing of the L2-3 and L4-5 segments. All treated spinal levels were analyzed using undecalcified histology with corresponding microradiography. Statistical comparisons were made between the treatment groups. RESULTS The PLF with ICBG (ICBG PLF group) and the rhBMP-2 facet fusion (rhBMP-2 Facet group) treatment groups demonstrated similar levels of stiffness, with the rhBMP-2 Facet group having on average slightly higher stiffness in all 6 loading directions. All 8 levels in the autograft facet fusion treatment group demonstrated CT radiographic and histological fusion. All 8 levels in the rhBMP-2 Facet group showed bilateral CT radiographic and histological fusion. Six of 16 rhBMP-2/ACS-treated facet defects demonstrated small intraosseous hematomas or seromas. Four of the 8 levels (50%) in the ICBG PLF treatment group demonstrated bilateral histological fusion. Three of 8 levels in the ICBG PLF treatment group showed unilateral fusion. One of the 8 levels in the ICBG PLF treatment group demonstrated bilateral histological nonfusion. CONCLUSIONS Both rhBMP-2/ACS and autograft demonstrated 100% efficacy when used for facet fusion in the instrumented ovine model. However, the ICBG PLF treatment group only demonstrated a 50% bilateral fusion rate. Biomechanically, the ICBG PLF and rhBMP-2 Facet groups demonstrated similar stiffness in all 6 loading directions, with the rhBMP-2 Facet group having on average slightly higher stiffness in all directions.

Ovine Mesenchymal Stromal Cells: Morphologic, Phenotypic and Functional Characterization for Osteochondral Tissue Engineering

INTRODUCTION

Knowledge of ovine mesenchymal stromal cells (oMSCs) is currently expanding. Tissue engineering combining scaffolding with oMSCs provides promising therapies for the treatment of osteochondral diseases.

PURPOSE

The aim was to isolate and characterize oMSCs from bone marrow aspirates (oBMSCs) and to assess their usefulness for osteochondral repair using β-tricalcium phosphate (bTCP) and type I collagen (Col I) scaffolds.

METHODS

Cells isolated from ovine bone marrow were characterized morphologically, phenotypically, and functionally. oBMSCs were cultured with osteogenic medium on bTCP and Col I scaffolds. The resulting constructs were evaluated by histology, immunohistochemistry and electron microscopy studies. Furthermore, oBMSCs were cultured on Col I scaffolds to develop an in vitro cartilage repair model that was assessed using a modified International Cartilage Research Society (ICRS) II scale.

RESULTS

oBMSCs presented morphology, surface marker pattern and multipotent capacities similar to those of human BMSCs. oBMSCs seeded on Col I gave rise to osteogenic neotissue. Assessment by the modified ICRS II scale revealed that fibrocartilage/hyaline cartilage was obtained in the in vitro repair model.

CONCLUSIONS

The isolated ovine cells were demonstrated to be oBMSCs. oBMSCs cultured on Col I sponges successfully synthesized osteochondral tissue. The data suggest that oBMSCs have potential for use in preclinical models prior to human clinical studies.

Adverse effect of beta-tricalcium phosphate with zeta potential control in repairing critical defects in rats' calvaria

Objective

To evaluate whether a new biphasic cement composed of calcium sulfate and beta tricalcium phosphate with zeta potential control could induce or lead to bone neoformation in critical defects.

Methods

A critical defect of diameter 8 mm was made in the calvaria of forty male Wistar rats. In the Test Group (n = 20), the defects were filled with cement. In the Control Group (n = 20), the defect was not filled and only coagulum was present. The animals were sacrificed 7, 14, 21 and 42 days after the operation. Calvaria specimens were subjected to microtomography and were then prepared for histological analysis. The analyses included morphological assessment on the histopathology of the repair; comparative morphometric evaluation of the area of formation of bone trabeculae between the groups; and histochemical staining by means of tartrate-resistant phosphatase (TRAP) in order to identify osteoclasts.

Results

Microtomographic images of the defects filled by the cement did not show any decrease in area over the course of postoperative evolution. In the Test Group, the material continued to present a foreign-body response until the last observational periods. Histomorphological analysis showed that there were more significant groupings of giant cells in the Test Group and greater maturity of neoformed bone in the Control Group. Exogenous material was also present. Histomorphometric analysis showed that in the Control Group, the total area of bone neoformation was significantly greater (p = 0.009) and grew progressively. The giant cells presented a positive reaction to TRAP but no osteoclasts were observed.

Conclusion

The ceramic cement did not induce or lead to bone neoformation from the microtomographic or histological point of view.

Allogeneic mesenchymal precursor cells (MPCs) combined with an osteoconductive scaffold to promote lumbar interbody spine fusion in an ovine model

BACKGROUND

Advances in immunomagnetic cell sorting have enabled isolation and purification of pleuripotent stem cells from marrow aspirates and have expanded stem cell therapies to include allogeneic sources.

PURPOSE

This study aimed to determine the safety and efficacy of allogeneic mesenchymal precursor cells (MPCs) combined with an osteoconductive scaffold in lumbar interbody spinal fusion using an ovine model.

STUDY DESIGN

Thirty-two skeletally mature ewes underwent a single-level interbody fusion procedure using a Polyetheretherketone fusion cage supplemented with either iliac crest autograft (AG) or an osteconductive scaffold (Mastergraft Matrix, Medtronic, Memphis, TN, USA) with 2.5×10(6) MPCs, 6.25×10(6) MPCs, or 12.5×10(6) MPCs.

METHODS

Plain radiographs and computed tomography scans were scored for bridging bone at multiple points during healing and at necropsy. The biomechanical competency of fusion was scored by manual palpation and quantified using functional radiographs at necropsy. Postnecropsy histopathology and histomorphometric analysis assessed the local response to MPC treatment and quantified the volume and connectivity of newly formed bridging bone. Safety was assessed by serum biochemistry, hematology, and organ histopathology.

RESULTS

Mesenchymal precursor cell treatment caused no adverse systemic or local tissue responses. All analyses indicated MPCs combined with an osteoconductive scaffold achieved similar or better fusion success as AG treatment after 16 weeks, and increasing the MPC dose did not enhance fusion. Manual palpation of the fusion site indicated more than 75% of MPC-treated and 65% of AG-treated animals achieved rigid fusion, which was corroborated with functional radiography. Computed tomography fusion scores indicated all animals in the MPC- and AG-treatment groups were fused at 16 weeks, yet X-ray scores indicated only 67% of the AG-treated animals were fused. Histomorphometry analyses showed equivalent outcomes for fusion connectivity and bony fusion area for MPC- and AG-treated groups. Approximately 6% residual graft material remained in the MPC-treated fusion sites at 16 weeks.

CONCLUSIONS

Adult allogeneic MPCs delivered using an osteoconductive scaffold were both safe and efficacious in this ovine spine interbody fusion model. These results support the use ofallogeneic MPCs as an alternative to AG for lumbar interbody spinal fusion procedures.

Enhanced osteogenic differentiation and biomineralization in mouse mesenchymal stromal cells on a β-TCP robocast scaffold modified with collagen nanofibers

B-TCP robocast scaffolds modified with collagen nanofibers promote osteoblastic differentiation and biomineralization of mMSCs.

Bone marrow-derived mesenchymal stem cells assembled with low-dose BMP-2 in a three-dimensional hybrid construct enhances posterolateral spinal fusion in syngeneic rats

BACKGROUND CONTEXT

The combination of potent osteoinductive growth factor, functional osteoblastic cells, and osteoconductive materials to induce bone formation is a well-established concept in bone tissue engineering. However, supraphysiological dose of growth factor, such as recombinant human bone morphogenetic protein 2 (rhBMP-2), which is necessary in contemporary clinical application, have been reported to result in severe side effects.

PURPOSE

We hypothesize that the synergistic osteoinductive capacity of low-dose bone morphogenetic protein 2 (BMP-2) combined with undifferentiated bone marrow-derived stromal cells (BMSCs) is comparable to that of osteogenically differentiated BMSCs when used in a rodent model of posterolateral spinal fusion.

STUDY DESIGN/SETTING

A prospective study using a rodent model of posterolateral spinal fusion was carried out.

PATIENT SAMPLE

Thirty-six syngeneic Fischer rats comprised the patient sample.

METHODS

Six groups of implants were evaluated as follows (n=6): (1) 10 µg BMP-2 with undifferentiated BMSCs; (2) 10 µg BMP-2 with osteogenic-differentiated BMSCs; (3) 2.5 µg BMP-2 with undifferentiated BMSCs; (4) 2.5 µg BMP-2 with osteogenic-differentiated BMSCs; (5) 0.5 µg BMP-2 with undifferentiated BMSCs; and (6) 0.5 µg BMP-2 with osteogenic-differentiated BMSCs. Optimal in vitro osteogenic differentiation of BMSCs was determined by quantitative real-time polymerase chain reaction (qRT-PCR) gene analysis whereas in vivo bone formation capacity was evaluated by manual palpation, micro-computed tomography, and histology.

RESULTS

Rat BMSCs cultured in fibrin matrix that was loaded into the pores of medical-grade poly epsilon caprolactone tricalcium phosphate scaffolds differentiated toward osteogenic lineage by expressing osterix, runt-related transcription factor 2, and osteocalcium mRNA when supplemented with dexamethasone, ascorbic acid, and β-glycerophosphate. Whereas qRT-PCR revealed optimal increase in osteogenic genes expression after 7 days of in vitro culture, in vivo transplantation study showed that pre-differentiation of BMSCs before transplantation failed to promote posterolateral spinal fusion when co-delivered with low-dose BMP-2 (1/6 or 17% fusion rate). In contrast, combined delivery of undifferentiated BMSCs with low-dose BMP-2 (2.5 µg) demonstrated significantly higher fusion rate (4/6 or 67%) as well as significantly increased volume of new bone formation (p<.05).

CONCLUSION

In summary, this study supports the combination of undifferentiated BMSCs and low-dose rhBMP-2 for bone tissue engineering construct.

Tethering of Epidermal Growth Factor (EGF) to Beta Tricalcium Phosphate (βTCP) via Fusion to a High Affinity, Multimeric βTCP-Binding Peptide: Effects on Human Multipotent Stromal Cells/Connective Tissue Progenitors

Transplantation of freshly-aspirated autologous bone marrow, together with a scaffold, is a promising clinical alternative to harvest and transplantation of autologous bone for treatment of large defects. However, survival proliferation, and osteogenic differentiation of the marrow-resident stem and progenitor cells with osteogenic potential can be limited in large defects by the inflammatory microenvironment. Previous studies using EGF tethered to synthetic polymer substrates have demonstrated that surface-tethered EGF can protect human bone marrow-derived osteogenic stem and progenitor cells from pro-death inflammatory cues and enhance their proliferation without detriment to subsequent osteogenic differentiation. The objective of this study was to identify a facile means of tethering EGF to clinically-relevant βTCP scaffolds and to demonstrate the bioactivity of EGF tethered to βTCP using stimulation of the proliferative response of human bone-marrow derived mesenchymal stem cells (hBMSC) as a phenotypic metric. We used a phage display library and panned against βTCP and composites of βTCP with a degradable polyester biomaterial, together with orthogonal blocking schemes, to identify a 12-amino acid consensus binding peptide sequence, LLADTTHHRPWT, with high affinity for βTCP. When a single copy of this βTCP-binding peptide sequence was fused to EGF via a flexible peptide tether domain and expressed recombinantly in E. coli together with a maltose-binding domain to aid purification, the resulting fusion protein exhibited modest affinity for βTCP. However, a fusion protein containing a linear concatamer containing 10 repeats of the binding motif the resulting fusion protein showed high affinity stable binding to βTCP, with only 25% of the protein released after 7 days at 37oC. The fusion protein was bioactive, as assessed by its abilities to activate kinase signaling pathways downstream of the EGF receptor when presented in soluble form, and to enhance the proliferation of hBMSC when presented in tethered form on commercial βTCP bone regeneration scaffolds.

Evaluation of posterolateral lumbar fusion in sheep using mineral scaffolds seeded with cultured bone marrow cells

The objective of this study is to investigate the efficacy of hybrid constructs in comparison to bone grafts (autograft and allograft) for posterolateral lumbar fusion (PLF) in sheep, instrumented with transpedicular screws and bars. Hybrid constructs using cultured bone marrow (BM) mesenchymal stem cells (MSCs) have shown promising results in several bone healing models. In particular, hybrid constructs made by calcium phosphate-enriched cells have had similar fusion rates to bone autografts in posterolateral lumbar fusion in sheep. In our study, four experimental spinal fusions in two animal groups were compared in sheep: autograft and allograft (reference group), hydroxyapatite scaffold, and hydroxyapatite scaffold seeded with cultured and osteoinduced bone marrow MSCs (hybrid construct). During the last three days of culture, dexamethasone (dex) and beta-glycerophosphate (β-GP) were added to potentiate osteoinduction. The two experimental situations of each group were tested in the same spinal segment (L4–L5). Spinal fusion and bone formation were studied by clinical observation, X-ray, computed tomography (CT), histology, and histomorphometry. Lumbar fusion rates assessed by CT scan and histology were higher for autograft and allograft (70%) than for mineral scaffold alone (22%) and hybrid constructs (35%). The quantity of new bone formation was also higher for the reference group, quite similar in both (autograft and allograft). Although the hybrid scaffold group had a better fusion rate than the non-hybrid scaffold group, the histological analysis revealed no significant differences between them in terms of quantity of bone formation. The histology results suggested that mineral scaffolds were partly resorbed in an early phase, and included in callus tissues. Far from the callus area the hydroxyapatite alone did not generate bone around it, but the hybrid scaffold did. In nude mice, labeled cells were induced to differentiate in vivo and monitored by bioluminescence imaging (BLI). Although the cultured MSCs had osteogenic potential, their contribution to spinal fusion when seeded in mineral scaffolds, in the conditions disclosed here, remains uncertain probably due to callus interference with the scaffolds. At present, bone autografts are better than hybrid constructs for posterolateral lumbar fusion, but we should continue to seek better conditions for efficient tissue engineering.

Cellular bone matrices: viable stem cell-containing bone graft substitutes

BACKGROUND CONTEXT

Advances in the field of stem cell technology have stimulated the development and increased use of allogenic bone grafts containing live mesenchymal stem cells (MSCs), also known as cellular bone matrices (CBMs). It is estimated that CBMs comprise greater than 17% of all bone grafts and bone graft substitutes used.

PURPOSE

To critically evaluate CBMs, specifically their technical specifications, existing published data supporting their use, US Food and Drug Administration (FDA) regulation, cost, potential pitfalls, and other aspects pertaining to their use.

STUDY DESIGN

Areview of literature.

METHODS

A series of Ovid, Medline, and Pubmed-National Library of Medicine/National Institutes of Health (www.ncbi.nlm.nih.gov) searches were performed. Only articles in English journals or published with English language translations were included. Level of evidence of the selected articles was assessed. Specific technical information on each CBM was obtained by direct communication from the companies marketing the individual products.

RESULTS

Five different CBMs are currently available for use in spinal fusion surgery. There is a wide variation between the products with regard to the average donor age at harvest, total cellular concentration, percentage of MSCs, shelf life, and cell viability after defrosting. Three retrospective studies evaluating CBMs and fusion have shown fusion rates ranging from 90.2% to 92.3%, and multiple industry-sponsored trials are underway. No independent studies evaluating spinal fusion rates with the use of CBMs exist. All the commercially available CBMs claim to meet the FDA criteria under Section 361, 21 CFR Part 1271, and are not undergoing FDA premarket review. The CBMs claim to provide viable MSCs and are offered at a premium cost. Numerous challenges exist in regard to MSCs' survival, function, osteoblastic potential, and cytokine production once implanted into the intended host.

CONCLUSIONS

Cellular bone matrices may be a promising bone augmentation technology in spinal fusion surgery. Although CBMs appear to be safe for use as bone graft substitutes, their efficacy in spinal fusion surgery remains highly inconclusive. Large, nonindustry sponsored studies evaluating the efficacy of CBMs are required. Without results from such studies, surgeons must be made aware of the potential pitfalls of CBMs in spinal fusion surgery. With the currently available data, there is insufficient evidence to support the use of CBMs as bone graft substitutes in spinal fusion surgery.

Human perivascular stem cell-based bone graft substitute induces rat spinal fusion

Adipose tissue is an attractive source of mesenchymal stem cells (MSCs) because of its abundance and accessibility. We have previously defined a population of native MSCs termed perivascular stem cells (PSCs), purified from diverse human tissues, including adipose tissue. Human PSCs (hPSCs) are a bipartite cell population composed of pericytes (CD146+CD34-CD45-) and adventitial cells (CD146-CD34+CD45-), isolated by fluorescence-activated cell sorting and with properties identical to those of culture identified MSCs. Our previous studies showed that hPSCs exhibit improved bone formation compared with a sample-matched unpurified population (termed stromal vascular fraction); however, it is not known whether hPSCs would be efficacious in a spinal fusion model. To investigate, we evaluated the osteogenic potential of freshly sorted hPSCs without culture expansion and differentiation in a rat model of posterolateral lumbar spinal fusion. We compared increasing dosages of implanted hPSCs to assess for dose-dependent efficacy. All hPSC treatment groups induced successful spinal fusion, assessed by manual palpation and microcomputed tomography. Computerized biomechanical simulation (finite element analysis) further demonstrated bone fusion with hPSC treatment. Histological analyses showed robust endochondral ossification in hPSC-treated samples. Finally, we confirmed that implanted hPSCs indeed differentiated into osteoblasts and osteocytes; however, the majority of the new bone formation was of host origin. These results suggest that implanted hPSCs positively regulate bone formation via direct and paracrine mechanisms. In summary, hPSCs are a readily available MSC population that effectively forms bone without requirements for culture or predifferentiation. Thus, hPSC-based products show promise for future efforts in clinical bone regeneration and repair.

Lumbar spinal fusion with β-TCP granules and variable Escherichia coli-derived rhBMP-2 dose

BACKGROUND CONTEXT

The ideal tissue-engineered solution for any bone graft substitute is to assist in the rapid formation of bone and facilitate fusion.

PURPOSE

The present study aims to evaluate this E-BMP-2 (Escherichia coli-derived human bone morphogenetic protein-2) in ovine posterolateral lumbar fusion (PLF) to examine the influence of dose and overall performance in a model with similar graft size and diffusive challenges to the human.

STUDY DESIGN/SETTING

In vivo large animal model study.

METHODS

An adult ovine PLF was performed in 30 animals with groups of E-BMP-2 with a beta-tricalcium phosphate (β-TCP) carrier at three different dosages, β-TCP alone, and autograft from the iliac crest. The fusions were assessed by radiography (X-ray and microcomputed tomography), mechanical testing, and hard-tissue histology with bone labels at 6, 8, and 10 weeks along with routine paraffin histology at 12 weeks.

RESULTS

Results showed increasing new bone and fusion rate with E-BMP-2 dose, whereas β-TCP alone was largely resorbed and did not achieve fusion in this model at 12 weeks. Autograft showed similar grading for the amount of bone between the transverse processes but a lower fusion rate than β-TCP/E-BMP-2 groups. Bone labels revealed new bone formation at all time points for the E-BMP2 groups, whereas the autograft group showed active bone formation at 10 weeks. Beta-tricalcium phosphate displayed reliable incorporation into the decorticated host bone, whereas limited new bone was found between the transverse processes. At the center of the fusion mass, increased E-BMP-2 dose led to increased incorporation of β-TCP by new bone.

CONCLUSIONS

These results suggest that E-BMP-2 was capable of producing posterolateral fusion in the ovine model that is equal to or superior to autologous graft in terms of fusion rate and mechanical strength. E-BMP-2 dose had considerable influence on β-TCP granule resorption.

Repair of orbital bone defects in canines using grafts of enriched autologous bone marrow stromal cells

Backgroud

Bone tissue engineering is a new approach for the repair of orbital defects. The aim of the present study was to explore the feasibility of tissue-engineered bone constructed using bone marrow stromal cells (BMSCs) that were rapidly isolated and concentrated from bone marrow (BM) by the red cell lysis method, then combined with β-tricalcium phosphate (β-TCP) to create grafts used to restore orbital bone defects in canines.

Methods

In the experimental group, grafts were constructed using BMSCs obtained by red cell lysis from 20 ml bone marrow, combined with β-TCP and BM via the custom-made stem cell-scaffold device, then used to repair 10 mm diameter medial orbital wall bony defects in canines. Results were compared with those in groups grafted with BM/β-TCP or β-TCP alone, or with defects left untreated as controls. The enrichment of BMSCs and nucleated cells (NCs) in the graft was calculated from the number in untreated bone marrow and in suspensions after red cell lysis. Spiral computed tomography (CT) scans were performed 1, 4, 12 and 24 weeks after implantation in all groups. Gross examination, micro-CT and histological measurements were performed 24 weeks after surgery. The results were analyzed to evaluate the efficacy of bone repair.

Results

The number of NCs and of colony-forming units within the scaffolds were increased 54.8 times and 53.4 times, respectively, compared with untreated bone marrow. In the BMSC-BM/β-TCP group, CT examination revealed that the scaffolds were gradually absorbed and the bony defects were restored. Micro-CT and histological examination confirmed that the implantations led to good repair of the defects, with 6 out 8 orbital defects completely restored in the experimental group, while by contrast, the grafts in the control groups did not fully repair the bony defects, a difference which was statistically significant (p < 0.05).

Conclusions

Tissue-engineered bone, constructed using BMSCs isolated by red cell lysis of BM, can restore critical-sized orbital wall defects in canines.

Stem cells in preclinical spine studies

BACKGROUND CONTEXT

The recent identification and characterization of mesenchymal stem cells have introduced a shift in the research focus for future technologies in spinal surgery to achieve spinal fusion and treat degenerative disc disease. Current and past techniques use allograft to replace diseased tissue or rely on host responses to recruit necessary cellular progenitors. Adult stem cells display long-term proliferation, efficient self-renewal, and multipotent differentiation.

PURPOSE

This review will focus on two important applications of stem cells in spinal surgery: spine fusion and the management of degenerative disc disease.

STUDY DESIGN

Review of the literature.

METHODS

Relevant preclinical literature regarding stem cell sources, growth factors, scaffolds, and animal models for both osteogenesis and chondrogenesis will be reviewed, with an emphasis on those studies that focus on spine applications of these technologies.

RESULTS

In both osteogenesis and chondrogenesis, adult stem cells derived from bone marrow or adipose show promise in preclinical studies. Various growth factors and scaffolds have also been shown to enhance the properties and eventual clinical potential of these cells. Although its utility in clinical applications has yet to be proven, gene therapy has also been shown to hold promise in preclinical studies.

CONCLUSIONS

The future of spine surgery is constantly evolving, and the recent advancements in stem cell-based technologies for both spine fusion and the treatment of degenerative disc disease is promising and indicative that stem cells will undoubtedly play a major role clinically. It is likely that these stem cells, growth factors, and scaffolds will play a critical role in the future for replacing diseased tissue in disease processes such as degenerative disc disease and in enhancing host tissue to achieve more reliable spine fusion.

Adverse reactions of artificial bone graft substitutes: lessons learned from using tricalcium phosphate geneX®

BACKGROUND

Artificial bone graft substitutes are widely used to fill bony defects after curettage of benign tumors. We sought to evaluate the efficacy of one such bone graft substitute, geneX®, which contains tricalcium phosphate and calcium sulphate; however, during the course of this study we observed a high number of complications.

QUESTIONS/PURPOSES

The primary aim of this prospective series was assessment of the effectiveness of geneX® concerning resorption profile and bone healing and remodeling after surgery. We present the types and frequencies of complications observed in patients treated for bone tumors by curettage and filling the defect using geneX®.

METHODS

We planned to study 40 patients; however, after enrollment of the first 31 patients, the study was stopped as a result of serious complications. There were 20 female and 11 male patients with a mean age at surgery of 40 years (range, 6–71 years). Plain radiographs were obtained at different intervals during followup and CT scans were obtained 6 and 12 months postoperatively. Complications were assessed using a 5-point scale according to Goslings and Gouma.

RESULTS

Five of the 31 patients (16%) had complications develop after surgery. In three cases, a sterile inflammation adjacent to the geneX® occurred, with delayed wound healing in two patients and local pain. In the third patient, geneX® produced moderate to severe skin damage in the area of the scar, needing revision surgery. In two other patients, inflammatory cystic formations developed in the soft tissues with sizes up to 15 cm, which gradually reduced in size with time. Overall, there were four Grade 1 complications and one Grade 2 according to Goslings and Gouma.

CONCLUSIONS

We concluded from this series of patients that geneX® causes soft tissue inflammation and pain with its use. Based on this experience we believe that this type of bone substitute should not be used in the treatment of bony defects.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Allogeneic mesenchymal progenitor cells for posterolateral lumbar spine fusion in sheep

BACKGROUND CONTEXT

Osteoconductive porous ceramic bone graft materials supplemented with mesenchymal precursor cells (MPC) derived from autologous bone marrow aspirates have been shown to stimulate successful interbody and posterolateral spine fusion in preclinical models. Recent advances in immunomagnetic cell sorting have enabled purification and isolation of pluripotent stem cells from marrow aspirates and have expanded stem cell technology to allogeneic cell sources. Allogeneic MPC technology combined with appropriate synthetic biomaterial carriers could provide both the osteogenic and osteoconductive components needed for successful posterolateral spine fusion without the need for autologous bone harvest or expensive recombinant protein technology.

PURPOSE

To determine the safety and efficacy of a hydroxyapatite:tricalcium phosphate graft material supplemented with allogeneic mesenchymal precursor cells in posterolateral lumbar spine fusion using an ovine model.

STUDY DESIGN

Skeletally mature ewes underwent single-level instrumented posterolateral lumbar spine fusion using either autograft (AG), hydroxyapatite:tricalcium phosphate carrier (CP), or CP supplemented with allogeneic mesenchymal progenitor cells (MPCs). Three doses of MPCs were evaluated: 25 × 10⁶ cells (low dose, LD), 75 × 10⁶ cells (mid dose, MD), and 225 × 10⁶ cell (high dose, HD). Animals survived for either 4 or 9 months.

METHODS

Plain radiographs were acquired and scored for bridging bone at regular intervals during healing to monitor fusion development. Hematology, coagulation, and serum chemistry were monitored at regular intervals throughout the study to monitor animal health. After necropsy, computed tomography, high-resolution radiography, biomechanical testing, organ pathology, bone histopathology, and bone histomorphometry were conducted to monitor the safety and ascertain the efficacy of MPC treatment.

RESULTS

MPC treatment in this spine fusion model resulted in no observed adverse systemic or local tissue responses. Radiographically, fusion scores for MPC-treated animals were uniformly higher compared with those treated with carrier alone (CP) after 3 months and continued the same trend throughout 9 month of healing. Quantitative computed tomography confirmed better connectivity of the fusion for MPC treatment groups compared with CP. Biomechanical analyses were not able to differentiate between treatment groups. Histomorphometry results confirmed radiographic and quantitative computed tomography results; cell-supplemented treatment groups and autograft had equivalent amounts of bone within the fusion mass and less bony fusion tissue was found within the fusion mass in specimens from the CP treatment group. No conclusive effects of cell dose of fusion efficacy were noted.

CONCLUSIONS

Adult allogeneic mesenchymal precursor cells delivered via a hydroxyapatite:tricalcium phosphate carrier were both safe and efficacious in this ovine spine fusion model. Results from this preclinical study support that allogeneic mesenchymal precursor cells produced fusion efficacy similar to that achieved using iliac crest autograft, thereby providing a safe and viable option to achieve successful posterolateral spine fusion.

Spinal fusion in the next generation: gene and cell therapy approaches

Bone fusion represents a challenge in the orthopedics practice, being especially indicated for spine disorders. Spinal fusion can be defined as the bony union between two vertebral bodies obtained through the surgical introduction of an osteoconductive, osteoinductive, and osteogenic compound. Autogenous bone graft provides all these three qualities and is considered the gold standard. However, a high morbidity is associated with the harvest procedure. Intensive research efforts have been spent during the last decades to develop new approaches and technologies for successful spine fusion. In recent years, cell and gene therapies have attracted great interest from the scientific community. The improved knowledge of both mesenchymal stem cell biology and osteogenic molecules allowed their use in regenerative medicine, representing attractive approaches to achieve bone regeneration also in spinal surgery applications. In this review we aim to describe the developing gene- and cell-based bone regenerative approaches as promising future trends in spine fusion.

Tissue engineering strategies in spinal arthrodesis: the clinical imperative and challenges to clinical translation

Skeletal disorders requiring the regeneration or de novo production of bone present considerable reconstructive challenges and are one of the main driving forces for the development of skeletal tissue engineering strategies. The skeletal or mesenchymal stem cell is a fundamental requirement for osteogenesis and plays a pivotal role in the design and application of these strategies. Research activity has focused on incorporating the biological role of the mesenchymal stem cell with the developing fields of material science and gene therapy in order to create a construct that is not only capable of inducing host osteoblasts to produce bone, but is also osteogenic in its own right. This review explores the clinical need for reparative approaches in spinal arthrodesis, identifying recent tissue engineering strategies employed to promote spinal fusion, and considers the ongoing challenges to successful clinical translation.

Current application of β-tricalcium phosphate composites in orthopaedics

Presently, bioceramic materials have been extensively used in spinal surgery as bone grafts; however, there are some limitations for bioceramic materials. Calcium sulfate is rapidly absorbed in vivo, the degradation of which often occurs prior to the formation of new bones. Hydroxyapatite (HA) is hardly absorbed, which blocks the formation of new bones and remodeling, and results in poor local stability or permanent stress concentration. Only β-tricalcium phosphate (β-TCP) is relatively balanced between scaffold absorption and bone formation. And it is a good biodegradable ceramic material that could supply a large quantity of calcium ion and sulfate ion as well as scaffold structure for bone regeneration. However, the problem of single β-TCP is lack of osteoinductivity and osteogenicity, which restricts its application. Therefore β-TCP composite materials have been used in the field of orthopaedics in recent decades, which fully use excellent properties of other bone repairing materials, such as biodegradability, osteoinductivity, osteogenicity and osteoconductivity. These materials make up for the deficiencies of single β-TCP and endow β-TCP with more biological and physical properties.

Intraoperative stem cell therapy

Stem cells hold significant promise for regeneration of tissue defects and disease-modifying therapies. Although numerous promising stem cell approaches are advancing in clinical trials, intraoperative stem cell therapies offer more immediate hope by integrating an autologous cell source with a well-established surgical intervention in a single procedure. Herein, the major developments in intraoperative stem cell approaches, from in vivo models to clinical studies, are reviewed, and the potential regenerative mechanisms and the roles of different cell populations in the regeneration process are discussed. Although intraoperative stem cell therapies have been shown to be safe and effective for several indications, there are still critical challenges to be tackled prior to adoption into the standard surgical armamentarium.

The Utility of Allograft Mesenchymal Stem Cells for Spine Fusion: A Literature Review

More than 50% of patients complain of postoperative donor site morbidity following iliac crest bone graft harvest, and recent discoveries have identified adverse outcomes following bone morphogenetic protein use in spine fusion. This has led the spine community to turn toward alternative methods to promote fusion following spine surgery. The present article reviews numerous studies that have shown the osteogenic potential of mesenchymal stem cells (MSCs). MSCs have been used with both in vitro and in vivo models and have involved animal studies ranging from rats to macaque monkeys to successfully induce bone regeneration in lesions of the tibia and spine. There is no fear of graft rejection, as there may be with other allograft materials, because neither undifferentiated nor differentiated MSCs elicit lymphocyte response when transplanted; they tend to alter the cytokine profile to an anti-inflammatory state. Early clinical trials are underway with various commercially available MSC formulations. Although there is much enthusiasm, it is integral that the spine surgery community carefully evaluate the use of MSCs in spine fusion through well-designed and executed studies to determine the efficacy and safety profiles in spine surgery patients.

Characterization, GFP gene Nucleofection, and allotransplantation in injured tendons of ovine amniotic fluid-derived stem cells

Amniotic fluid has drawn increasing attention in the recent past as a cost-effective and accessible source of fetal stem cells. Amniotic fluid-derived mesenchymal stem cells (AFMSCs) that display high proliferation rate, large spectrum of differentiation potential, and immunosuppressive features are considered optimal candidates for allogeneic repair of mesenchymal damaged tissues. In this study, ovine AFMSCs (oAFMSCs) isolated from 3-month-old sheep fetuses were characterized for their proliferation rate, specific surface antigen and pluripotency marker expression, genomic stability, and mesenchymal lineage differentiation during their in vitro expansion (12 passages) and after nucleofection. The high proliferation rate of oAFMSCs gradually decreased during the first six subculture passages while the expression of surface molecules (CD29, CD58, CD166) and of pluripotency-associated markers (OCT4, TERT, NANOG, SOX2), the in vitro osteogenic differentiation potential, and a normal karyotype were maintained. Afterwards, oAFMSCs were nucleofected with a selectable plasmid coding for green fluorescent protein (GFP) using two different programs, U23 and C17, previously optimized for human mesenchymal stem cells. Transfection efficiencies were ∼63% and ∼37%, while cell recoveries were ∼10% and ∼22%, respectively. Nucleofected oAFMSCs expressing the GFP transgene conserved their pluripotency marker profile and retained a normal karyotype and the osteogenic differentiation ability. Seven single clones with a GFP expression ranging from 80% to 97% were then isolated and expanded over 1 month, thus providing stably transfected cells with long-term therapeutic potential. The in vivo behavior of GFP-labeled oAFMSCs was tested on a previously validated preclinical model of experimentally induced Achille's tendon defect. The allotransplanted oAFMSCs were able to survive within the host tissue for 1 month enhancing the early phase of tendon healing as indicated by morphological and biomechanical results. Altogether these data suggest that genetically modified oAFMSCs might represent a valuable tool for in vivo preclinical studies in a highly valid translational model.

Goat bone tissue engineering: comparing an intramuscular with a posterolateral lumbar spine location

The aim of this study was to investigate the effect of implant location on bone formation in goats using autologous bone marrow-derived stromal cells in porous calcium phosphate scaffolds. Intramuscular locations were compared to posterolateral spine fusion locations in eight goats. As scaffolds, we used biphasic calcium phosphate porous blocks of 5 x 5 x 5 mm. Cell-seeded implants were compared to empty controls. Bone marrow-derived stromal cells were seeded at 8 million cells per cm(3) scaffold and cultured for 1 week. The follow-up time was 12 weeks. Fluorochromes were administered intravenously at 4, 6, and 8 weeks. Ectopic implants showed 21 +/- 3.6% bone formation for the cell seeded and 2.0 +/- 3.0% for the controls (p < 0.001). Paraspinal implants, however, showed 0.10 +/- 0.13% in the cell seeded compared to 0.023 +/- 0.027% in the control group (p = 0.09). A benefit of the cells was only found in the area closest to the paraspinal muscles (p < 0.01). Bone formation in the control samples was of later onset compared to the cell-seeded implants. In conclusion, cell-based bone tissue engineering in an ectopic environment was clearly effective. Similar constructs implanted in a posterolateral spine fusion location hardly showed any effect.

Comparative assessment of the osteoconductive properties of different biomaterials in vivo seeded with human or ovine mesenchymal stem/stromal cells

Mesenchymal stromal/stem cells (MSC), when used in combination with biomaterial scaffolds, have been shown to contribute at varying efficiencies to bone and cartilage regeneration in preclinical large animal models and human clinical trials. In an orthopedic context, identification of the optimal scaffold, which is capable of inducing tissue regeneration, has been the subject of numerous studies. In the present study, we show that ex vivo-expanded MSC from human and ovine bone marrow display similar phenotypic properties, but exhibit differences in their ability to form bone in vivo when transplanted with different biocompatible scaffold composites. We found that the ovine MSC formed ectopic bone on all scaffolds tested with the exception of collagen-based demineralized bone matrix. In contrast, human MSC in general formed less bone and only on those biomaterials composed of ceramic particles containing at least 15% hydroxyapatite. This study demonstrates the differences in bone formation potential between human and ovine MSC in vivo based on the osteoconductive properties of different bioscaffolds currently being used for orthopedic clinical applications.

Heat shock protein-90 beta is expressed at the surface of multipotential mesenchymal precursor cells: generation of a novel monoclonal antibody, STRO-4, with specificity for mesenchymal precursor cells from human and ovine tissues

Mesenchymal stromal cells (MSCs) and their precursor cells (MPCs) can proliferate and differentiate into multiple mesodermal and some ectodermal and endodermal tissues. Culture-expanded MSCs are currently being evaluated as a possible cell therapy to replace/repair injured or diseased tissues. While a number of mAb reagents with specificity to human MSCs, including STRO-1, STRO-3 (BLK ALP), CD71 (SH2, SH3), CD106 (VCAM-1), CD166, and CD271, have facilitated the isolation of purified populations of human MSCs from primary tissues, few if any mAb reagents have been described that can be used to isolate equivalent cells from other species. This is of particular relevance when assessing the tissue regenerative efficacy of MSCs in large immunocompetent, preclinical animal models of disease. In light of this, we sought to generate novel monoclonal antibodies (mAb) with specific reactivity against a cell surface molecule that is expressed at high levels by MSCs from different species. Using CD106 (VCAM-1)-selected ovine MSCs as an immunogen, mAb-producing hybridomas were selected for their reactivity to both human and ovine MSCs. One such hybridoma, termed STRO-4, produced an IgG mAb that reacted with <5% of human and ovine bone marrow (BM) mononuclear cells. As a single selection reagent, STRO-4 mAb was able to enrich colony-forming fibroblasts (CFU-F) in both human and ovine BM by 16- and 8-folds, respectively. Cells isolated with STRO-4 exhibited reactivity with markers commonly associated with MSCs isolated by plastic adherence including CD29, CD44, and CD166. Moreover, when placed in inductive culture conditions in vitro, STRO-4(+) MSCs exhibited multilineage differentiation potential and were capable of forming a mineralized matrix, lipid-filled adipocytes, and chondrocytes capable of forming a glycosaminoglycan-rich matrix. Biochemical analysis revealed that STRO-4 identified the beta isoform of heat shock protein-90 (Hsp90beta). In addition to identifying an antibody reagent that identifies a highly conserved epitope expressed by MSCs from different species, our study also points to a potential role for Hsp90beta in MSC biology.

Natural bone collagen scaffold combined with autologous enriched bone marrow cells for induction of osteogenesis in an ovine spinal fusion model

Autologous bone graft, the standard of bone grafting in achieving spinal fusion, is associated with several limitations and complications. The use of bone marrow cells (BMCs) as a potential cell source for spinal fusion, combined with a suitable scaffold to promote bone formation, may be a better choice. The aims of this study were to evaluate the efficacy of natural bone collagen scaffold (NBCS) combined with autologous-enriched BMCs for induction of osteogenesis in vitro and in vivo. Ovine-enriched BMCs were co-cultured with NBCS for 1, 2, 3, and 4 weeks to investigate whether NBCS would support the population expansion and differentiation of enriched BMCs. Using an ovine interbody fusion model, NBCS seeded with autologous enriched BMCs was implanted into the lumbar disc space. Fusion outcomes were compared with the use of the autograft, NBCS without BMCs, and BMCs without NBCS. In vitro results demonstrated that NBCS facilitated the population expansion and differentiation of ovine-enriched BMCs, promoting the expression of collagen type I and the formation of a mineralized matrix. The use of NBCS combined with enriched BMCs in vivo enhanced the spinal fusion rate (6 of 6 at 10 week) (p < 0.05), the biomechanical stiffness of fusion masses, and bone volume at the fusion site (p < 0.05). Histological findings also revealed that a combination of NBCS and BMCs induced new bone formation that integrated well with host bone tissue. In conclusion, NBCS is an effective scaffold that supports ovine-enriched BMCs. The combination of NBCS and BMCs may be a useful alternative for autograft in induction of spinal fusion.

Beta tricalcium phosphate: observation of use in 100 posterolateral lumbar instrumented fusions

BACKGROUND

Beta tricalcium phosphate (B-TCP) is increasingly used to supplement lamina autograft to perform posterolateral lumbar-instrumented arthrodesis.

PURPOSE

To determine the radiographic arthrodesis and pseudarthrosis rates after multisegment lumbar laminectomies and one- or two-segment posterolateral instrumented fusion using lamina autograft and an artificial bone graft expander B-TCP (Vitoss; Orthovita, Malvern, PA, USA).

STUDY DESIGN/SETTING

To document radiographic arthrodesis/pseudarthrosis rates using lamina autograft and B-TCP.

PATIENT SAMPLE

One hundred patients with lumbar spinal stenosis underwent multisegment laminectomies (average 3.6 segments) and one- (78 patients) or two- (22 patients) segment posterolateral instrumented arthrodesis.

OUTCOME MEASURES

Two-year postoperative outcomes were assessed using Short-Form 36 questionnaires.

METHODS

The arthrodesis mass consisted of lamina autograft and B-TCP. Two independent neuroradiologists, using both dynamic X-rays and 2D-CT studies performed 3, 4.5, 6, and up to 12 months postoperatively, documented radiographic arthrodesis progression.

RESULTS

One-segment arthrodesis was performed in 79 patients; 74 (93.7%) were radiographically fused "early" (6.5 postoperative months), 2 (2.5%) fused "late" (6.5-12 months), and 3 (3.8%) exhibited pseudarthrosis. Two-segment arthrodesis was performed in 21 patients; 14 (66.7%) radiographically fused "early," 5 (23.8%) fused "late," and 2 (9.5%) exhibited pseudarthrosis. Although chi-square analyses revealed a significant increase in the number of "late" radiographic fusions occurring for patients undergoing two-level arthrodesis, no significant difference in radiographic pseudarthrosis rates was noted between the two patient populations. In both groups, Short-Form 36 questionnaires revealed nearly comparable maximal improvement on seven of eight Health Scales by the second postoperative year.

CONCLUSIONS

At 6.5 months after multisegment lumbar laminectomies with posterolateral instrumented lumbar arthrodesis using lamina autograft/B-TCP, more one-segment (93.7%) versus two-segment (66.7%) radiographic arthrodesis occurred. By 1 year after operation, there was no significant difference in fusion rates between one- and two-segment radiographic arthrodeses.

Mesenchymal stem cell and gene therapies for spinal fusion

THE IDEAL GRAFT material to promote spinal fusion should possess osteoconductive, osteoinductive, and osteogenic properties. Although autogenous bone graft has all three qualities and is the standard for comparison, research has focused on finding alternatives that have similar efficacy but not the morbidities associated with graft donor sites. Efforts have focused on various osteoconductive scaffolds and introduction of osteoinductive proteins, including bone morphogenetic protein. Recently, interest in using osteoprogenitor cells, or osteogenesis, for spinal fusion has increased. Bone marrow aspiration allows the introduction of mesenchymal stem cells and ultimately osteoblasts to promote fusion. Preclinical studies suggest that the addition of osteoprogenitor cells to various osteoconductive materials results in a fusion rate similar to that of autograft. There is growing recognition that local gene therapy has the benefit of delivering therapeutic genes that encode novel osteoinductive proteins. Gene delivery offers an alternative to local implantation of recombinant protein, which typically requires high doses of the protein to result in a sufficient osteoinductive response. The findings of animal studies demonstrate that gene therapy results in sustained and regulated production of desired osteoinductive proteins and is efficacious in promoting spinal fusion; however, before treatment in humans can be undertaken, obstacles such as the safety profile, host immune response, transfection rates with insufficient transgene expression, and imprecise control of the timing of transgene expression must be overcome. In this review, the authors summarize the latest research efforts under way to promote spinal fusion with osteoprogenitor cells and gene therapy and discuss the clinical implications of these treatments.

Chemical engineering of mesenchymal stem cells to induce a cell rolling response

Covalently conjugated sialyl Lewis X (SLeX) on the mesenchymal stem cell (MSC) surface through a biotin-streptavidin bridge imparts leukocyte-like rolling characteristics without altering the cell phenotype and the multilineage differentiation potential. We demonstrate that the conjugation of SLeX on the MSC surface is stable, versatile, and induces a robust rolling response on P-selectin coated substrates. These results indicate the potential to increase the targeting efficiency of any cell type to specific tissue.

Characterisation and developmental potential of ovine bone marrow derived mesenchymal stem cells

Since discovery, significant interest has been generated in the potential application of mesenchymal stem cells or multipotential stromal cells (MSC) for tissue regeneration and repair, due to their proliferative and multipotential capabilities. Although the sheep is often used as a large animal model for translating potential therapies for musculoskeletal injury and repair, the characteristics of MSC from ovine bone marrow have been inadequately described. Histological and gene expression studies have previously shown that ovine MSC share similar properties with human and rodents MSC, including their capacity for clonogenic growth and multiple stromal lineage differentiation. In the present study, ovine bone marrow derived MSCs positively express cell surface markers associated with MSC such as CD29, CD44 and CD166, and lacked expression of CD14, CD31 and CD45. Under serum-deprived conditions, proliferation of MSC occurred in response to EGF, PDGF, FGF-2, IGF-1 and most significantly TGF-alpha. While subcutaneous transplantation of ovine MSC in association with a ceramic HA/TCP carrier into immunocomprimised mice resulted in ectopic osteogenesis, adipogenesis and haematopoietic-support activity, transplantation of these cells within a gelatin sponge displayed partial chondrogenesis. The comprehensive characterisation of ovine MSC described herein provides important information for future translational studies involving ovine MSC.