Endothelial progenitor and mesenchymal stem cell-derived cells persist in tissue-engineered patch in vivo: application of green and red fluorescent protein-expressing retroviral vector

Characterisation of ovine bone marrow-derived stromal cells (oBMSC) and evaluation of chondrogenically induced micro-pellets for cartilage tissue repair in vivo

Abstract

Bone marrow stromal cells (BMSC) show promise in cartilage repair, and sheep are the most common large animal pre-clinical model.

Objective

The objective of this study was to characterise ovine BMSC (oBMSC) in vitro, and to evaluate the capacity of chondrogenic micro-pellets manufactured from oBMSC or ovine articular chondrocytes (oACh) to repair osteochondral defects in sheep.

Design

oBMSC were characterised for surface marker expression using flow cytometry and evaluated for tri-lineage differentiation capacity. oBMSC micro-pellets were manufactured in a microwell platform, and chondrogenesis was compared at 2%, 5%, and 20% O₂. The capacity of cartilage micro-pellets manufactured from oBMSC or oACh to repair osteochondral defects in adult sheep was evaluated in an 8-week pilot study.

Results

Expanded oBMSC were positive for CD44 and CD146 and negative for CD45. The common adipogenic induction ingredient, 3-Isobutyl-1-methylxanthine (IBMX), was toxic to oBMSC, but adipogenesis could be restored by excluding IBMX from the medium. BMSC chondrogenesis was optimal in a 2% O₂ atmosphere. Micro-pellets formed from oBMSC or oACh appeared morphologically similar, but hypertrophic genes were elevated in oBMSC micro-pellets. While oACh micro-pellets formed cartilage-like repair tissue in sheep, oBMSC micro-pellets did not.

Conclusion

The sensitivity of oBMSC, compared to human BMSC, to IBMX in standard adipogenic assays highlights species-associated differences. Micro-pellets manufactured from oACh were more effective than micro-pellets manufactured from oBMSC in the repair of osteochondral defects in sheep. While oBMSC can be driven to form cartilage-like tissue in vitro, the effective use of these cells in cartilage repair will depend on the successful mitigation of hypertrophy and tissue integration.

Supplementary information

The online version contains supplementary material available at 10.1186/s13287-020-02045-3.

Cell Fate and Tissue Remodeling in Canine Urethral Repair Using a Bone Marrow Mesenchymal Stem Cell+Endothelial Progenitor Cell Amniotic Patch

The Editors of Tissue Engineering: Part A retract the article entitled, "Cell Fate and Tissue Remodeling in Canine Urethral Repair Using a Bone Marrow Mesenchymal Stem Cell+Endothelial Progenitor Cell Amniotic Patch," by Wenxin Zhang, Xin Zhang, Yihua Zhang, Xinke Zhang, Tong Zou, Wen Zhao, Yangou Lv, Jinglu Wang, Pengxiu Dai, Hao Cui, Yi Zhang, Dengke Gao, Chenmei Ruan, and Xia Zhang (epub ahead of print September 21, 2020; DOI: http://doi.org/10.1089/ten.tea.2020.0129). After the online publication of the article, the authors have indicated that they "feel that we have not yet studied our work completely and some new great results are discovered. So after carefully thinking, we are going to rearrange this manuscript and try to give more precise model. [sic]" The authors have not explained what those expected results will be, so it remains unclear the direction their work is headed. The authors also indicated that they plan to submit an updated version of the paper to Tissue Engineering in the future. Upon submission the new manuscript will undergo rigorous peer review, and there is no guarantee of acceptance.

Therapeutic Mesenchymal Stromal Cells for Immunotherapy and for Gene and Drug Delivery

Mesenchymal stromal cells (MSCs) possess several fairly unique properties that, when combined, make them ideally suited for cellular-based immunotherapy and as vehicles for gene and drug delivery for a wide range of diseases and disorders. Key among these are: (1) their relative ease of isolation from a variety of tissues; (2) the ability to be expanded in culture without a loss of functionality, a property that varies to some degree with tissue source; (3) they are relatively immune-inert, perhaps obviating the need for precise donor/recipient matching; (4) they possess potent immunomodulatory functions that can be tailored by so-called licensing in vitro and in vivo; (5) the efficiency with which they can be modified with viral-based vectors; and (6) their almost uncanny ability to selectively home to damaged tissues, tumors, and metastases following systemic administration. In this review, we summarize the latest research in the immunological properties of MSCs, their use as immunomodulatory/anti-inflammatory agents, methods for licensing MSCs to customize their immunological profile, and their use as vehicles for transferring both therapeutic genes in genetic disease and drugs and genes designed to destroy tumor cells.

Cellular behaviours of bone marrow-derived mesenchymal stem cells towards pristine graphene oxide nanosheets

OBJECTIVES

Graphene oxide (GO), the derivative of graphene with unique properties, has attracted much attention for applications in dental implants. The aim of this study was, by two biomimetic cell culture methods, to investigate the quantitative relationship between the concentration of pristine GO nanosheets and their cellular behaviours towards bone marrow-derived mesenchymal stem cells (BMSCs).

MATERIALS AND METHODS

The cells were firstly characterized according to their morphology, self-renewal capabilities and multipotency. Subsequently, adhesion density, proliferation, alkaline phosphatase activity and mineralization of BMSCs treated with various concentrations of GO were analysed. In addition, osteogenic-related proteins were measured for further verification of the GO-induced osteogenic differentiation.

RESULTS

Pristine GO nanosheets inhibited the proliferation of BMSCs at a high concentration of 10 μg/mL during the first 3 days with two seeding methods and facilitated proliferation of BMSCs at a low concentration of 0.1 μg/mL after 5 days with a sequential-seeding method compared to a co-seeding method. Analogously, osteogenic differentiation was promoted when BMSCs were treated with 0.1 μg/mL of GO. Both the proliferation and differentiation showed concentration-dependent behaviour. Interestingly, Wnt/β-catenin signalling pathway appeared to be involved in osteogenic differentiation induced by pristine GO nanosheets.

CONCLUSIONS

Pristine GO nanosheets at a concentration of 0.1 μg/mL provide benefits to promote BMSCs proliferation and osteogenesis under a sequential-seeding method, contributing to the use of GO for dental implantation.

Concentration-dependent behaviors of bone marrow derived mesenchymal stem cells and infectious bacteria toward magnesium oxide nanoparticles

This article reports the quantitative relationship between the concentration of magnesium oxide (MgO) nanoparticles and its distinct biological activities towards mammalian cells and infectious bacteria for the first time. The effects of MgO nanoparticles on the viability of bone marrow derived mesenchymal stem cells (BMSCs) and infectious bacteria (both gram-negative Escherichia coli and gram-positive Staphylococcus epidermidis) showed a concentration-dependent behavior in vitro. The critical concentrations of MgO nanoparticles identified in this study provided valuable guidelines for biomaterial design toward potential clinical translation. BMSCs density increased significantly when cultured in 200μg/mL of MgO in comparison to the Cells Only control without MgO. The density of BMSCs decreased significantly after culture in the media with 500μg/mL or more of MgO. Concentrations at or above 1000μg/mL of MgO resulted in complete BMSCs death. Quantification of colony forming units (CFU) revealed that the minimum bactericidal concentration (MBC) of MgO for E. coli and S. epidermidis was 1200μg/mL. The addition of MgO nanoparticles into the cultures increased the pH and Mg(2+) ion concentration in the respective culture media, which might have played a role in the observed cell responses but not the main factors. E. coli and S. epidermidis still proliferated significantly at alkaline pH up to 10 or with supplemental Mg(2+) dosages up to 50mM, indicating bactericidal properties of MgO are beyond the effects of increased media pH and Mg(2+) ion concentrations. MgO nanoparticles at a concentration of 200μg/mL provided dual benefits of promoting BMSC proliferation while reducing bacterial adhesion, which should be further studied for potential medical implant applications. The use of free MgO nanoparticles yielded detrimental effects to BMSCs in concentrations above 300μg/mL. We recommend further study into MgO nanoparticle as a coating material or as a part of a composite.

STATEMENT OF SIGNIFICANCE

This article reports the quantitative relationship between the concentration of magnesium oxide (MgO) nanoparticles and its distinct biological activities towards mammalian cells and infectious bacteria for the first time. The effects of MgO nanoparticles on the viability of bone marrow derived mesenchymal stem cells (BMSCs) and infectious bacteria (both gram-negative Escherichia coli and gram-positive Staphylococcus epidermidis) showed a concentration-dependent behavior in vitro. The critical concentrations of MgO nanoparticles identified in this study provided valuable guidelines for biomaterial design toward potential clinical translation.

Fundamentals and application of magnetic particles in cell isolation and enrichment: a review

Magnetic sorting using magnetic beads has become a routine methodology for the separation of key cell populations from biological suspensions. Due to the inherent ability of magnets to provide forces at a distance, magnetic cell manipulation is now a standardized process step in numerous processes in tissue engineering, medicine, and in fundamental biological research. Herein we review the current status of magnetic particles to enable isolation and separation of cells, with a strong focus on the fundamental governing physical phenomena, properties and syntheses of magnetic particles and on current applications of magnet-based cell separation in laboratory and clinical settings. We highlight the contribution of cell separation to biomedical research and medicine and detail modern cell-separation methods (both magnetic and non-magnetic). In addition to a review of the current state-of-the-art in magnet-based cell sorting, we discuss current challenges and available opportunities for further research, development and commercialization of magnetic particle-based cell-separation systems.

Hemophilia A: an ideal disease to correct in utero

Hemophilia A (HA) is the most frequent inheritable defect of the coagulation proteins. The current standard of care for patients with HA is prophylactic factor infusion, which is comprised of regular (2-3 times per week) intravenous infusions of recombinant or plasma-derived FVIII to maintain hemostasis. While this treatment has greatly increased the quality of life and lengthened the life expectancy for many HA patients, its high cost, the need for lifelong infusions, and the fact that it is unavailable to roughly 75% of the world's HA patients make this type of treatment far from ideal. In addition, this lifesaving therapy suffers from a high risk of treatment failure due to immune response to the infused FVIII. There is thus a need for novel treatments, such as those using stem cells and/or gene therapy, which have the potential to mediate long-term correction or permanent cure following a single intervention. In the present review, we discuss the clinical feasibility and unique advantages that an in utero approach to treating HA could offer, placing special emphasis on a new sheep model of HA we have developed and on the use of mesenchymal stromal cells (MSC) as cellular vehicles for delivering the FVIII gene.

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure.

De novo hem- and lymphangiogenesis by endothelial progenitor and mesenchymal stem cells in immunocompetent mice

Cellular pro-angiogenic therapies may be applicable for the treatment of peripheral vascular diseases. Interactions between mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) may provide such a treatment option. With the exception of some studies in man, experiments have only been performed in immunodeficient mice and rats. We studied an immunocompetent syngeneic mouse model. We isolated MSCs from bone marrow and EPCs from the lung of adult C57/Bl.6 mice and co-injected them in Matrigel subcutaneously in adult C57/Bl.6 mice. We demonstrate development of both blood vessels and lymphatics. Grafted EPCs integrated into the lining of the two vessel types, whereas MSCs usually did not incorporate into the vessel wall. Injections of each separate cell type did not, or hardly, reveal de novo angiogenesis. The release of VEGF-A by MSCs has been shown before, but its inhibitors, e.g., soluble VEGF receptors, have not been studied. We performed qualitative and quantitative studies of the proteins released by EPCs, MSCs, and cocultures of the cells. Despite the secretion of VEGF inhibitors (sVEGFR-1, sVEGFR-2) by EPCs, VEGF-A was secreted by MSCs at bioavailable amounts (350 pg/ml). We confirm the secretion of PlGF, FGF-1, MCP-1, and PDGFs by EPCs/MSCs and suggest functions for VEGF-B, amphiregulin, fractalkine, CXCL10, and CXCL16 during MSC-induced hem- and lymphangiogenesis. We assume that lymphangiogenesis is induced indirectly by growth factors from immigrating leukocytes, which we found in close association with the lymphatic networks. Inflammatory responses to the cellular markers GFP and cell-tracker red (CMPTX) used for tracing of EPCs or MSCs were not observed. Our studies demonstrate the feasibility of pro-angiogenic/lymphangiogenic therapies in immunocompetent animals and indicate new MSC/EPC-derived angiogenic factors.

New technologies for surgery of the congenital cardiac defect

The surgical repair of complex congenital heart defects frequently requires additional tissue in various forms, such as patches, conduits, and valves. These devices often require replacement over a patient's lifetime because of degeneration, calcification, or lack of growth. The main new technologies in congenital cardiac surgery aim at, on the one hand, avoiding such reoperations and, on the other hand, improving long-term outcomes of devices used to repair or replace diseased structural malformations. These technologies are: 1) new patches: CorMatrix® patches made of decellularized porcine small intestinal submucosa extracellular matrix; 2) new devices: the Melody® valve (for percutaneous pulmonary valve implantation) and tissue-engineered valved conduits (either decellularized scaffolds or polymeric scaffolds); and 3) new emerging fields, such as antenatal corrective cardiac surgery or robotically assisted congenital cardiac surgical procedures. These new technologies for structural malformation surgery are still in their infancy but certainly present great promise for the future. But the translation of these emerging technologies to routine health care and public health policy will also largely depend on economic considerations, value judgments, and political factors.

Update: Innovation in cardiology (IV). Cardiac tissue engineering and the bioartificial heart

Heart failure is the end-stage of many cardiovascular diseases-such as acute myocardial infarction-and remains one of the most appealing challenges for regenerative medicine because of its high incidence and prevalence. Over the last 20 years, cardiomyoplasty, based on the isolated administration of cells with regenerative capacity, has been the focal point of most studies aimed at regenerating the heart. Although this therapy has proved feasible in the clinical setting, the degree of infarcted myocardium regenerated and of improved cardiac function are at best modest. Hence, tissue engineering has emerged as a novel technology using cells with regenerative capacity, biological and/or synthetic materials, growth, proangiogenic and differentiation factors, and online registry systems, to induce the regeneration of whole organs or locally damaged tissue. The next step, seen recently in pioneering animal studies, is de novo generation of bioartificial hearts by decellularization and preservation of supporting structures for their subsequent repopulation with new contractile, vascular muscle tissue. Ultimately, this new approach would entail transplantation of the "rebuilt" heart, reestablishing cardiac function in the recipient.

Treatment of Hemophilia A in Utero and Postnatally using Sheep as a Model for Cell and Gene Delivery

Hemophilia A represents the most common inheritable deficiency of the coagulation proteins. Current state-of- the-art treatment consists of frequent prophylactic infusions of plasma-derived or recombinant FVIII protein to maintain hemostasis, and has greatly increased life expectancy and quality of life for many hemophilia A patients. This treatment approach is, however, far from ideal, due to the need for lifelong intravenous infusions, the high treatment cost, and the fact that it is unavailable to a large percentage of the world's hemophiliacs. There is thus a need for novel treatments that can promise long-term or permanent correction. In contrast to existing protein based therapeutics, gene therapy offers to provide a permanent cure following few, or even a single, treatment. In the present paper, we review ongoing work towards this end, focusing on studies we have performed in a large animal model. Some of the key topics covered in this review include the unique opportunities sheep offer as a model system, the re-establishment and clinical and molecular characterization of a line of sheep with severe hemophilia A, the advantages and feasibility of treating a disease like hemophilia A in utero, and the use of Mesenchymal Stem Cells (MSC) as cellular delivery vehicles for the FVIII gene. The review finishes with a brief discussion of our recent success correcting ovine hemophilia A with a postnatal transplant with gene-modified MSC, and the limitations of this approach that remain to be overcome.

Gene regulation of extracellular matrix remodeling in human bone marrow stem cell-seeded tissue-engineered grafts

Tissue-engineered heart valves are prone to early structural deterioration. We hypothesize that cell-scaffold interaction and mechanical deformation results in upregulation of genes related to osteogenic/chondrogenic differentiation and thus changes extracellular matrix (ECM) composition in human bone marrow mesenchymal stem cell (hBMSC)-derived tissue-engineered grafts. hBMSC were expanded and seeded onto poly-glycolic acid/poly-lactic acid scaffold for 14 days. Seeded tissue-engineered constructs (TEC) were subjected to cyclic flexure for 24 h, whereas control TEC was maintained in roller bottles for the same duration. hBMSC, TEC, and mechanically deformed TEC were subjected to gene-array and histological analysis. Expression levels of RNA and/or protein markers related to chondrogenesis (Sox9, MGP, RunX2, Col II, Col X, and Col XI) and osteogenesis (ALPL, BMP2, EDN1, RunX1, and Col I) were increased in TEC compared to unseeded hBMSC. Histological sections of TEC stained positive for Saffranin O, alkaline phosphatase activity, and calcium deposits. The expression levels of the above gene and protein markers further increased in deformed TEC compared to static TEC. Cell-scaffold interactions and mechanical stress results in gene expression suggestive of endochondral-ossification that impact upon ECM composition and may predispose them to eventual calcification.

Substrates for cardiovascular tissue engineering

Cardiovascular tissue engineering aims to find solutions for the suboptimal regeneration of heart valves, arteries and myocardium by creating 'living' tissue replacements outside (in vitro) or inside (in situ) the human body. A combination of cells, biomaterials and environmental cues of tissue development is employed to obtain tissues with targeted structure and functional properties that can survive and develop within the harsh hemodynamic environment of the cardiovascular system. This paper reviews the up-to-date status of cardiovascular tissue engineering with special emphasis on the development and use of biomaterial substrates. Key requirements and properties of these substrates, as well as methods and readout parameters to test their efficacy in the human body, are described in detail and discussed in the light of current trends toward designing biologically inspired microenviroments for in situ tissue engineering purposes.

Hyaluronic acid biodegradable material for reconstruction of vascular wall: a preliminary study in rats

The objective of this preliminary study was to develop a reabsorbable vascular patch that did not require in vitro cell or biochemical preconditioning for vascular wall repair. Patches were composed only of hyaluronic acid (HA). Twenty male Wistar rats weighing 250-350 g were used. The abdominal aorta was exposed and isolated. A rectangular breach (1 mm × 5 mm) was made on vessel wall and arterial defect was repaired with HA made patch. Performance was assessed at 1, 2, 4, 8, and 16 weeks after surgery by histology and immunohistochemistry. Extracellular matrix components were evaluated by molecular biological methods. After 16 weeks, the biomaterial was almost completely degraded and replaced by a neoartery wall composed of endothelial cells, smooth muscle cells, collagen, and elastin fibers organized in layers. In conclusion, HA patches provide a provisional three-dimensional support to interact with cells for the control of their function, guiding the spatially and temporally multicellular processes of artery regeneration.

Acellular cardiac extracellular matrix as a scaffold for tissue engineering: in vitro cell support, remodeling, and biocompatibility

We have developed an efficient decellularization process for the isolation of extracellular matrix (ECM) from native cardiac tissue. The isolated ECM exhibited desirable mechanical properties in terms of elasticity, strength and durability-properties required from scaffolds used for cardiac tissue repair. This study further investigates the potential use of this scaffold for cardiac tissue engineering in terms of interactions with seeded cells and biocompatibility. We used the commonly studied fibroblasts, cardiomyocytes, and mesenchymal stem cells, which were isolated and seeded onto the scaffold. Cell density and distribution were followed by 3,3'-dioctadecyloxacarbocyanine perchlorate staining, and their proliferation and viability were assessed by AlamarBlue assay and fluorecein-diacetate/propidium iodide staining. Fibroblast-seeded scaffolds shrank to 1-2 mm(3) spheroids, and their glycosaminoglycans significantly increased by 23%. The expression of ECM remodeling-related mRNAs of collagens I and III, matrix metalloproteinase 2, and type 1 tissue inhibitor of metalloproteinases was quantified by real-time polymerase chain reaction, and was found significantly elevated in fibroblast-seeded scaffold, compared with the control cells on plates. Fibroblast-seeded scaffolds lost some flexibility, yet gained strength compared with the acellular scaffolds, as shown by mechanical testing. Scaffold seeded with cardiomyocyte began to beat in concert few days after seeding, and the myocytes expressed typical functional cardiac markers such as alpha-actinin, troponin I, and connexin43. The cells revealed aligned elongated morphology, as presented by immunofluorescent staining and scanning electron microscopy. Mesenchymal stem cell-seeded scaffolds maintained viability over 24 days in culture. These findings further strengthen the potential use of acellular cardiac ECM as a biomaterial for heart regeneration.

Mesenchymal stem cells as therapeutics and vehicles for gene and drug delivery

Mesenchymal stem cells (MSCs) possess a set of several fairly unique properties which make them ideally suited both for cellular therapies/regenerative medicine, and as vehicles for gene and drug delivery. These include: 1) relative ease of isolation; 2) the ability to differentiate into a wide variety of seemingly functional cell types of both mesenchymal and non-mesenchymal origin; 3) the ability to be extensively expanded in culture without a loss of differentiative capacity; 4) they are not only hypoimmunogenic, but they produce immunosuppression upon transplantation; 5) their pronounced anti-inflammatory properties; and 6) their ability to home to damaged tissues, tumors, and metastases following in vivo administration. In this review, we summarize the latest research in the use of mesenchymal stem cells in regenerative medicine, as immunomodulatory/anti-inflammatory agents, and as vehicles for transferring both therapeutic genes in genetic disease and genes designed to destroy malignant cells.

Minimally-invasive implantation of living tissue engineered heart valves: a comprehensive approach from autologous vascular cells to stem cells

OBJECTIVES

The aim of this study was to demonstrate the feasibility of combining the novel heart valve replacement technologies of: 1) tissue engineering; and 2) minimally-invasive implantation based on autologous cells and composite self-expandable biodegradable biomaterials.

BACKGROUND

Minimally-invasive valve replacement procedures are rapidly evolving as alternative treatment option for patients with valvular heart disease. However, currently used valve substitutes are bioprosthetic and as such have limited durability. To overcome this limitation, tissue engineering technologies provide living autologous valve replacements with regeneration and growth potential.

METHODS

Trileaflet heart valves fabricated from biodegradable synthetic scaffolds, integrated in self-expanding stents and seeded with autologous vascular or stem cells (bone marrow and peripheral blood), were generated in vitro using dynamic bioreactors. Subsequently, the tissue engineered heart valves (TEHV) were minimally-invasively implanted as pulmonary valve replacements in sheep. In vivo functionality was assessed by echocardiography and angiography up to 8 weeks. The tissue composition of explanted TEHV and corresponding control valves was analyzed.

RESULTS

The transapical implantations were successful in all animals. The TEHV demonstrated in vivo functionality with mobile but thickened leaflets. Histology revealed layered neotissues with endothelialized surfaces. Quantitative extracellular matrix analysis at 8 weeks showed higher values for deoxyribonucleic acid, collagen, and glycosaminoglycans compared to native valves. Mechanical profiles demonstrated sufficient tissue strength, but less pliability independent of the cell source.

CONCLUSIONS

This study demonstrates the principal feasibility of merging tissue engineering and minimally-invasive valve replacement technologies. Using adult stem cells is successful, enabling minimally-invasive cell harvest. Thus, this new technology may enable a valid alternative to current bioprosthetic devices.

Developing cell therapy techniques for respiratory disease: intratracheal delivery of genetically engineered stem cells in a murine model of airway injury

Interest has increased in the use of exogenous stem cells to optimize lung repair and serve as carriers of a therapeutic gene for genetic airway diseases such as cystic fibrosis. We investigated the survival and engraftment of exogenous stem cells after intratracheal injection, in a murine model of acute epithelial airway injury already used in gene therapy experiments on cystic fibrosis. Embryonic stem cells and mesenchymal stem cells were intratracheally injected 24 hr after 2% polidocanol administration, when epithelial airway injury was maximal. Stem cells were transfected with reporter genes immediately before administration. Reporter gene expression was analyzed in trachea-lungs and bronchoalveolar lavage, using nonfluorescence, quantitative, and sensitive methods. Enzyme-linked immunosorbent assay quantitative results showed that 0.4 to 5.5% of stem cells survived in the injured airway. Importantly, no stem cells survived in healthy airway or in the epithelial lining fluid. Using 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining, transduced mesenchymal stem cells were detected in injured trachea and bronchi lumen. When the epithelium was spontaneously regenerated, the in vivo amount of engrafted mesenchymal stem cells from cell lines decreased dramatically. No stem cells from primary culture were located within the lungs at 7 days. This study demonstrated the feasibility of intratracheal cell delivery for airway diseases with acute epithelial injury.

Factors Affecting Residence Time of Mesenchymal Stromal Cells (MSC) Injected into the Myocardium

The therapeutic mechanism of mesenchymal stromal/stem cells (MSC) for the treatment of acute myocardial infarction is not well understood. Our goal was to get insights into this mechanism by analyzing the survival kinetics of allogeneic and syngeneic cell transplants under different tissue conditions. Two MSC cell banks, stably and equally expressing the luciferase reporter construct, were developed for these studies and injected directly to the myocardium of Lewis rat recipients under syngeneic or allogeneic transplantation conditions. Cell survival was monitored by real-time fashion for up to 2 weeks, using optical imaging device (IVIS, Xenogen Corp.). We found that both syngeneic and allogeneic grafts reduced significantly in size during the first week of transplantation, either in the normal or in the late infarcted heart (5 days after MI) and allotransplants became always smaller than syngeneic grafts during this period. Low dose of cyclosporine A treatment had a benefit on both allo- and syngeneic graft sizes, suggesting that multiple mechanisms play a role in early graft reduction. The MSC characteristic factors IL-6, IL-8, MCP-1, and VEGF were well above the control level in the heart tissue at 4 days after cell injection, suggesting that the peak therapeutic effect of MSC can be expected during the first week of the administration. Although allogeneic cells induced immunoglobulin production, their biological effects (cell survival, factor productions) are very similar to the syngeneic transplants and therefore they could deliver the same therapeutic effect as the syngeneic cells. Finally, freshly infarcted tissue (30 min) supported better the survival of MSC than late postischemic tissue (5 days) but only “off the shelf” allogeneic cell transplants fits with this treatment strategy.

Directly auto-transplanted mesenchymal stem cells induce bone formation in a ceramic bone substitute in an ectopic sheep model

Bone tissue engineering approaches increasingly focus on the use of mesenchymal stem cells (MSC). In most animal transplantation models MSC are isolated and expanded before auto cell transplantation which might be critical for clinical application in the future. Hence this study compares the potential of directly auto-transplanted versus in vitro expanded MSC with or without bone morphogenetic protein-2 (BMP-2) to induce bone formation in a large volume ceramic bone substitute in the sheep model. MSC were isolated from bone marrow aspirates and directly auto-transplanted or expanded in vitro and characterized using fluorescence activated cell sorting (FACS) and RT-PCR analysis before subcutaneous implantation in combination with BMP-2 and β-tricalcium phosphate/hydroxyapatite (β-TCP/HA) granules. Constructs were explanted after 1 to 12 weeks followed by histological and RT-PCR evaluation. Sheep MSC were CD29(+), CD44(+) and CD166(+) after selection by Ficoll gradient centrifugation, while directly auto-transplanted MSC-populations expressed CD29 and CD166 at lower levels. Both, directly auto-transplanted and expanded MSC, were constantly proliferating and had a decreasing apoptosis over time in vivo. Directly auto-transplanted MSC led to de novo bone formation in a heterotopic sheep model using a β-TCP/HA matrix comparable to the application of 60 μg/ml BMP-2 only or implantation of expanded MSC. Bone matrix proteins were up-regulated in constructs following direct auto-transplantation and in expanded MSC as well as in BMP-2 constructs. Up-regulation was detected using immunohistology methods and RT-PCR. Dense vascularization was demonstrated by CD31 immunohistology staining in all three groups. Ectopic bone could be generated using directly auto-transplanted or expanded MSC with β-TCP/HA granules alone. Hence BMP-2 stimulation might become dispensable in the future, thus providing an attractive, clinically feasible approach to bone tissue engineering.

Development of microfluidics as endothelial progenitor cell capture technology for cardiovascular tissue engineering and diagnostic medicine

We have developed a unique microfluidic platform capable of capturing circulating endothelial progenitor cells (EPCs) by understanding surface chemistries and adhesion profiles. The surface of a variable-shear-stress microfluidic device was conjugated with 6 different antibodies [anti-CD34, -CD31, -vascular endothelial growth factor receptor-2 (VEGFR-2), -CD146, -CD45, and -von Willebrand factor (vWF)] designed to match the surface antigens on ovine peripheral blood-derived EPCs. Microfluidic analysis showed a shear-stress-dependent decrease in EPC adhesion on attached surface antigens. EPCs exhibited increased adhesion to antibodies against CD34, VEGFR-2, CD31, and CD146 compared to CD45, consistent with their endothelial cell-specific surface profile, when exposed to a minimum shear stress of 1.47 dyn/cm(2). Bone-marrow-derived mesenchymal stem cells and artery-derived endothelial and smooth muscle cells were used to demonstrate the specificity of the EPC microfluidic device. Coated hematopoietic specific-surface (CD45) and granular vWF antibodies, as well as uncoated bare glass and substrate (1% BSA), were utilized as controls. Microfluidic devices have been developed as an EPC capture platform using immobilized antibodies targeted as EPC surface antigens. This EPC chip may provide a new and effective tool for addressing challenges in cardiovascular disease and tissue engineering.

Differential interaction of retroviral vector with target cell: quantitative effect of cellular receptor, soluble proteoglycan, and cell type on gene delivery efficiency

Retroviral vectors are powerful tools for gene therapy and stem cell engineering. To improve efficiency of retroviral gene delivery, quantitative understanding of interactions of a retroviral vector and a cell is crucial. Effects of nonspecific adsorption of retrovirus on a cell via proteoglycans and receptor-mediated binding of retrovirus to a cell on overall transduction efficiency were quantified by combining a mathematical model and experimental data. Results represented by transduction rate constant, a lumped parameter of overall transduction efficiency, delineated that chondroitin sulfate C (CSC) plays dual roles as either enhancer or inhibitor of retroviral transduction, depending on its concentrations in the retroviral supernatant. At the concentration of 20 microg/mL, CSC enhanced the transduction efficiency up to threefold but inhibited more than sevenfold at the concentration of 100 microg/mL. Transduction rate constants for amphotropic retroviral infection of NIH 3T3 cells under phosphate-depleted culture condition showed a proportional relationship between cellular receptor density on a cell and transduction efficiency. It was finally shown that amphotropic retrovirus transduced human fibroblast HT1080 cells more efficiently than NIH 3T3 cells. On the contrary, the transduction efficiency of NIH 3T3 cells by vesicular stomatitis virus G protein pseudotyped retroviruses was eightfold higher than that of HT1080 cells. This study implies usefulness of using quantitative analysis of retroviral transduction in understanding and optimizing retroviral gene delivery systems for therapeutic approaches to tissue engineering.

Quantitative assessment of neuronal differentiation in three-dimensional collagen gels using enhanced green fluorescence protein expressing PC12 pheochromocytoma cells

There is a paucity of quantitative methods for evaluating the morphological differentiation of neuronal cells in a three-dimensional (3-D) system to assist in quality control of neural tissue engineering constructs for use in reparative medicine. Neuronal cells tend to aggregate in the 3-D scaffolds, hindering the application of two-dimensional (2-D) morphological methods to quantitate neuronal differentiation. To address this problem, we developed a stable transfectant green fluorescence protein (GFP)-PC12 neuronal cell model, in which the differentiation process in 3-D can be monitored with high sensitivity by fluorescence microscopy. Under 2-D conditions, the green cells showed collagen adherence, round morphology, proliferation properties, expression of the nerve growth factor (NGF) receptors TrkA and p75(NTR), stimulation of extracellular signal-regulated kinase phosphorylation by NGF and were able to differentiate in a dose-dependent manner upon NGF treatment, like wild-type (wt)-PC12 cells. When grown within 3-D collagen gels, upon NGF treatment, the GFP-PC12 cells differentiated, expressing long neurite outgrowths. We describe here a new validated method to measure NGF-induced differentiation in 3-D. Having properties similar to those of wt-PC12 and an ability to grow and differentiate in 3-D structures, these highly visualized GFP-expressing PC12 cells may serve as an ideal model for investigating various aspects of differentiation to serve in neural engineering.

The development of tissue-engineered grafts for reconstructive cardiothoracic surgical applications

Surgical correction of congenital heart defects often requires the use of valves, patches, or conduits to establish anatomic continuity. Homografts, xenografts, or mechanical prosthetic devices are frequently implanted during these surgical procedures. These grafts however lack growth potential, are associated with increased risk of thrombosis and infection and have limited durability, thus increasing the morbidity and mortality of their application in pediatric cardiac surgery. These limitations are being addressed through the development of living, biologic tissue-engineered valves, patches, and conduits. Pilot studies and phase 1 clinical trials are currently underway to evaluate their feasibility, safety, and efficacy. The optimal scaffold, cell source, and conditioning parameters, however, still remain to be determined and are areas of active research.

Healing and remodeling of bioengineered pulmonary artery patches implanted in sheep

PURPOSE

We hypothesized that cell-seeded patches implanted into sheep pulmonary artery would undergo progressive and complete healing into a viable structure well integrated with the arterial wall.

METHODS

Autologous ovine blood-derived endothelial progenitor cells (EPCs) and bone marrow-derived mesenchymal stem cells (MSCs) were isolated and cultured in vitro. MSCs and EPCs were seeded onto poly-4-hydroxybutyrate (P4HB)-coated polyglycolic acid (PGA) nonwoven biodegradable mesh scaffolds (10x20 mm) and cultured for 5 days in a laminar fluid flow system. Seeded patches were implanted into the wall of sheep pulmonary artery for 1-2 weeks (n=4) or 4-6 weeks (n=3). Preimplant and postexplant specimens were analyzed by histology and immunohistochemistry.

RESULTS

Unimplanted constructs contained alpha-smooth muscle actin (SMA)-positive cells and early extracellular matrix formation (primarily glycosaminoglycans). One week after implantation, seeded patches had surface thrombus formation and macrophage infiltration. Seeded patches implanted for 2 weeks showed granulation tissue, early pannus formation, macrophages, foreign body giant cells around disintegrating polymer, and early angiogenesis (microvessel formation). After 4 weeks in vivo, seeded patches contained glycosaminoglycans, collagen, and coverage of the luminal surface by host artery-derived pannus containing alpha-SMA-positive cells and laminated elastin; polymer scaffold degradation was almost complete with replacement by fibrous tissue containing viable cells.

CONCLUSIONS

This study shows that cell-seeded patches implanted in sheep pulmonary artery remodel to layered and viable tissue well integrated into the native arterial wall. The key remodeling processes included (1) intimal overgrowth at the luminal surface (pannus formation; neointima) and (2) granulation tissue formation and fibrosis with foreign body reaction.