Reversal of diabetes by the creation of neo-islet tissues into a subcutaneous site using islet cell sheets. Transplantation. 2011;92:1231-1236. [PMID: 22124282 DOI: 10.1097/tp.0b013e3182375835]

The underlying causes, treatment options of gut microbiota and food habits in type 2 diabetes mellitus: a narrative review

Type 2 diabetes mellitus is a long-lasting endocrine disorder characterized by persistent hyperglycaemia, which is often triggered by an entire or relative inadequacy of insulin production or insulin resistance. As a result of resistance to insulin (IR) and an overall lack of insulin in the body, type 2 diabetes mellitus (T2DM) is a metabolic illness that is characterized by hyperglycaemia. Notably, the occurrence of vascular complications of diabetes and the advancement of IR in T2DM are accompanied by dysbiosis of the gut microbiota. Due to the difficulties in managing the disease and the dangers of multiple accompanying complications, diabetes is a chronic, progressive immune-mediated condition that plays a significant clinical and health burden on patients. The frequency and incidence of diabetes among young people have been rising worldwide. The relationship between the gut microbiota composition and the physio-pathological characteristics of T2DM proposes a novel way to monitor the condition and enhance the effectiveness of therapies. Our knowledge of the microbiota of the gut and how it affects health and illness has changed over the last 20 years. Species of the genus Eubacterium, which make up a significant portion of the core animal gut microbiome, are some of the recently discovered 'generation' of possibly helpful bacteria. In this article, we have focused on pathogenesis and therapeutic approaches towards T2DM, with a special reference to gut bacteria from ancient times to the present day.

Cell Sheet Technology: An Emerging Approach for Tendon and Ligament Tissue Engineering

Tendon and ligament injuries account for a substantial proportion of disorders in the musculoskeletal system. While non-operative and operative treatment strategies have advanced, the restoration of native tendon and ligament structures after injury is still challenging due to its innate limited regenerative ability. Cell sheet technology is an innovative tool for tissue fabrication and cell transplantation in regenerative medicine. In this review, we first summarize different harvesting procedures and advantages of cell sheet technology, which preserves intact cell-to-cell connections and extracellular matrix. We then describe the recent progress of cell sheet technology from preclinical studies, focusing on the application of stem cell-derived sheets in treating tendon and ligament injuries, as well as highlighting its effects on mitigating inflammation and promoting tendon/graft-bone interface healing. Finally, we discuss several prerequisites for future clinical translation including the selection of appropriate cell source, optimization of preparation process, establishment of suitable animal model, and the fabrication of vascularized complex tissue. We believe this review could potentially provoke new ideas and drive the development of more functional biomimetic tissues using cell sheet technology to meet the needs of clinical patients.

Production of alginate macrocapsule device for long-term normoglycaemia in the treatment of type 1 diabetes mellitus with pancreatic cell sheet engineering

Type 1 diabetes-mellitus (T1DM) is characterized by damage of beta cells in pancreatic islets. Cell-sheet engineering, one of the newest therapeutic approaches, has also been used to create functional islet systems by creating islet/beta cell-sheets and transferring these systems to areas that require minimally invasive intervention, such as extrahepatic areas. Since islets, beta cells, and pancreas transplants are allogeneic, immune problems such as tissue rejection occur after treatment, and patients become insulin dependent again. In this study, we aimed to design the most suitable cell-sheet treatment method and macrocapsule-device that could provide long-term normoglycemia in rats. Firstly, mesenchymal stem cells (MSCs) and beta cells were co-cultured in a temperature-responsive culture dish to obtain a cell-sheet and then the cell-sheets macroencapsulated using different concentrations of alginate. The mechanical properties and pore sizes of the macrocapsule-device were characterized. The viability and activity of cell-sheets in the macrocapsule were evaluatedin vitroandin vivo. Fasting blood glucose levels, body weight, and serum insulin & C-peptide levels were evaluated after transplantation in diabetic-rats. After the transplantation, the blood glucose level at 225 mg dl-1on the 10th day dropped to 168 mg dl-1on the 15th day, and remained at the normoglycemic level for 210 days. In this study, an alginate macrocapsule-device was successfully developed to protect cell-sheets from immune attacks after transplantation. The results of our study provide the basis for future animal and human studies in which this method can be used to provide long-term cellular therapy in T1DM patients.

The bioengineering of perfusable endocrine tissue with anastomosable blood vessels

Organ transplantation is a definitive treatment for endocrine disorders, but donor shortages limit the use of this technique. The development of regenerative therapies would revolutionize the treatment of endocrine disorders. As is the case for harvested organs, the ideal bioengineered graft would comprise vascularized endocrine tissue, contain blood vessels that could be anastomosed to host vessels, have stable blood flow, and be suitable for transplantation into various sites. Here, we describe a transplantable endocrine tissue graft that was fabricated byex vivoperfusion of tricultured cell sheets (isletβ-cells, vascular endothelial cells (vECs), and mesenchymal stem cells (MSCs)) on a vascularized tissue flap ofin vivoorigin. The present study has three key findings. First, mild hypothermic conditions enhanced the success ofex vivoperfusion culture. Specifically, graft construction failed at 37 °C but succeeded at 32 °C (mild hypothermia), and endocrine tissue fabricated under mild hypothermia contained aggregations of isletβ-cells surrounded by dense vascular networks. Second, the construction of transplantable endocrine tissue byex vivoperfusion culture was better achieved using a vascular flap (VF) than a muscle flap. Third, the endocrine tissue construct generated using a VF could be transplanted into the rat by anastomosis of the graft artery and vein to host blood vessels, and the graft secreted insulin into the host's circulatory system for at least two weeks after transplantation. Endocrine tissues bioengineered using these techniques potentially could be used as novel endocrine therapies.

The preclinical and clinical progress of cell sheet engineering in regenerative medicine

Cell therapy is an accessible method for curing damaged organs or tissues. Yet, this approach is limited by the delivery efficiency of cell suspension injection. Over recent years, biological scaffolds have emerged as carriers of delivering therapeutic cells to the target sites. Although they can be regarded as revolutionary research output and promote the development of tissue engineering, the defect of biological scaffolds in repairing cell-dense tissues is apparent. Cell sheet engineering (CSE) is a novel technique that supports enzyme-free cell detachment in the shape of a sheet-like structure. Compared with the traditional method of enzymatic digestion, products harvested by this technique retain extracellular matrix (ECM) secreted by cells as well as cell-matrix and intercellular junctions established during in vitro culture. Herein, we discussed the current status and recent progress of CSE in basic research and clinical application by reviewing relevant articles that have been published, hoping to provide a reference for the development of CSE in the field of stem cells and regenerative medicine.

Xeno-free culture and proliferation of hPSCs on 2D biomaterials

Human pluripotent stem cells (human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs)) have unlimited proliferative potential, whereas adult stem cells such as bone marrow-derived stem cells and adipose-derived stem cells have problems with aging. When hPSCs are intended to be cultured on feeder-free or xeno-free conditions without utilizing mouse embryonic fibroblasts or human fibroblasts, they cannot be cultured on conventional tissue culture polystyrene dishes, as adult stem cells can be cultured but should be cultivated on material surfaces grafted or coated with (a) natural or recombinant extracellular matrix (ECM) proteins, (b) ECM protein-derived peptides and specific synthetic polymer surfaces in xeno-free and/or chemically defined conditions. This review describes current developing cell culture biomaterials for the proliferation of hPSCs while maintaining the pluripotency and differentiation potential of the cells into 3 germ layers. Biomaterials for the cultivation of hPSCs without utilizing a feeder layer are essential to decrease the risk of xenogenic molecules, which contributes to the potential clinical usage of hPSCs. ECM proteins such as human recombinant vitronectin, laminin-511 and laminin-521 have been utilized instead of Matrigel for the feeder-free cultivation of hPSCs. The following biomaterials are also discussed for hPSC cultivation: (a) decellularized ECM, (b) peptide-grafted biomaterials derived from ECM proteins, (c) recombinant E-cadherin-coated surface, (d) polysaccharide-immobilized surface, (e) synthetic polymer surfaces with and without bioactive sites, (f) thermoresponsive polymer surfaces with and without bioactive sites, and (g) synthetic microfibrous scaffolds.

Tricultured Cell Sheets Develop into Functional Pancreatic Islet Tissue with a Vascular Network

Methods to induce islet β-cells from induced pluripotent stem cells or embryonic stem cells have been established. However, islet β-cells are susceptible to apoptosis under hypoxic conditions, so the technique used to transplant β-cells must maintain the viability of cells in vivo. This study describes the development of a tricultured cell sheet, which was made by coculturing islet β-cells, vascular endothelial cells, and mesenchymal stem cells for 1 day. The islet β-cells in the tricultured cell sheet self-organized into islet-like structures surrounded by a dense vascular network in vitro. Triple-layered tricultured cell sheets engrafted well after transplantation in vivo and developed into insulin-secreting tissue with abundant blood vessels and a high density of islet β-cells. We anticipate that the tricultured cell sheet could be used as an in vitro pseudo-islet model for pharmaceutical testing and may have potential for development into transplantable grafts for use in regenerative medicine.

The Potential of Cell Sheet Technology for Beta Cell Replacement Therapy

Purpose of Review

Here, we review the use of cell sheet technology using different cell types and its potential for restoring the extracellular matrix microenvironment, perfusion, and immunomodulatory action on islets and beta cells.

Recent Findings

Cell sheets can be produced with different fabrication techniques ranging from the widely used temperature responsive system to the magnetic system. A variety of cells have been used to produce cell sheets including skin fibroblasts, smooth muscle cells, human umbilical vein endothelial cells, and mesenchymal stem cells.

Summary

CST would allow to recreate the ECM of islets which would provide cues to support islet survival and improvement of islet function. Depending on the used cell type, different additional supporting properties like immunoprotection or cues for better revascularization could be provided. Furthermore, CST offers the possibility to use other implantation sites than inside the liver. Further research should focus on cell sheet thickness and size to generate a potential translational therapy.

Bioabsorption of Subcutaneous Nanofibrous Scaffolds Influences the Engraftment and Function of Neonatal Porcine Islets

The subcutaneous space is currently being pursued as an alternative transplant site for ß-cell replacement therapies due to its retrievability, minimally invasive procedure and potential for graft imaging. However, implantation of ß-cells into an unmodified subcutaneous niche fails to reverse diabetes due to a lack of adequate blood supply. Herein, poly (ε-caprolactone) (PCL) and poly (lactic-co-glycolic acid) (PLGA) polymers were used to make scaffolds and were functionalized with peptides (RGD (Arginine-glycine-aspartate), VEGF (Vascular endothelial growth factor), laminin) or gelatin to augment engraftment. PCL, PCL + RGD + VEGF (PCL + R + V), PCL + RGD + Laminin (PCL + R + L), PLGA and PLGA + Gelatin (PLGA + G) scaffolds were implanted into the subcutaneous space of immunodeficient Rag mice. After four weeks, neonatal porcine islets (NPIs) were transplanted within the lumen of the scaffolds or under the kidney capsule (KC). Graft function was evaluated by blood glucose, serum porcine insulin, glucose tolerance tests, graft cellular insulin content and histologically. PLGA and PLGA + G scaffold recipients achieved significantly superior euglycemia rates (86% and 100%, respectively) compared to PCL scaffold recipients (0% euglycemic) (* p < 0.05, ** p < 0.01, respectively). PLGA scaffolds exhibited superior glucose tolerance (* p < 0.05) and serum porcine insulin secretion (* p < 0.05) compared to PCL scaffolds. Functionalized PLGA + G scaffold recipients exhibited higher total cellular insulin contents compared to PLGA-only recipients (* p < 0.05). This study demonstrates that the bioabsorption of PLGA-based fibrous scaffolds is a key factor that facilitates the function of NPIs transplanted subcutaneously in diabetic mice.

Emerging Treatment Strategies for Diabetes Mellitus and Associated Complications: An Update

The occurrence of diabetes mellitus (DM) is increasing rapidly at an accelerating rate worldwide. The status of diabetes has changed over the last three generations; whereas before it was deemed a minor disease of older people but currently it is now one of the leading causes of morbidity and mortality among middle-aged and young people. High blood glucose-mediated functional loss, insulin sensitivity, and insulin deficiency lead to chronic disorders such as Type 1 and Type 2 DM. Traditional treatments of DM, such as insulin sensitization and insulin secretion cause undesirable side effects, leading to patient incompliance and lack of treatment. Nanotechnology in diabetes studies has encouraged the development of new modalities for measuring glucose and supplying insulin that hold the potential to improve the quality of life of diabetics. Other therapies, such as β-cells regeneration and gene therapy, in addition to insulin and oral hypoglycemic drugs, are currently used to control diabetes. The present review highlights the nanocarrier-based drug delivery systems and emerging treatment strategies of DM.

Tissue Engineering Strategies for Improving Beta Cell Transplantation Outcome

Purpose of Review

Beta cell replacement therapy as a form of islet transplantation is a promising alternative therapy with the possibility to make selected patients with type 1 diabetes (T1D) insulin independent. However, this technique faces challenges such as extensive activation of the host immune system post-transplantation, lifelong need for immunosuppression, and the scarcity of islet donor pancreas. Advancement in tissue engineering strategies can improve these challenges and allow for a more widespread application of this therapy. This review will discuss the recent development and clinical translation of tissue engineering strategies in beta cell replacement therapy.

Recent Findings

Tissue engineering offers innovative solutions for producing unlimited glucose responsive cells and fabrication of appropriate devices/scaffolds for transplantation applications. Generation of pancreatic organoids with supporting cells in biocompatible biomaterials is a powerful technique to improve the function of insulin-producing cell clusters. Fabrication of physical barriers such as encapsulation strategies can protect the cells from the host immune system and allow for graft retrieval, although this strategy still faces major challenges to fully restore physiological glucose regulation.

Summary

The three main components of tissue engineering strategies including the generation of stem cell-derived insulin-producing cells and organoids and the possibilities for therapeutic delivery of cell-seeded devices to extra-hepatic sites need to come together in order to provide safe and functional insulin-producing devices for clinical beta cell replacement therapy.

Feasibility of large experimental animal models in testing novel therapeutic strategies for diabetes

Diabetes is among the top 10 causes of death in adults and caused approximately four million deaths worldwide in 2017. The incidence and prevalence of diabetes is predicted to increase. To alleviate this potentially severe situation, safer and more effective therapeutics are urgently required. Mice have long been the mainstay as preclinical models for basic research on diabetes, although they are not ideally suited for translating basic knowledge into clinical applications. To validate and optimize novel therapeutics for safe application in humans, an appropriate large animal model is needed. Large animals, especially pigs, are well suited for biomedical research and share many similarities with humans, including body size, anatomical features, physiology, and pathophysiology. Moreover, pigs already play an important role in translational studies, including clinical trials for xenotransplantation. Progress in genetic engineering over the past few decades has facilitated the development of transgenic animals, including porcine models of diabetes. This article discusses features that attest to the attractiveness of genetically modified porcine models of diabetes for testing novel treatment strategies using recent technical advances.

Comprehensive analysis of gene expression of isolated pancreatic islets during pretransplant culture

Background:

The aim of this study was to investigate the effect of pretransplant culture on the survival of pancreatic islet grafts, and to determine the biological characteristics of isolated islets during pretransplant culture.

Methods:

The survival of islets from Wistar rats, transplanted to diabetic C57BL/B6 mice, was compared between fresh islets and cultured islets. A comprehensive gene expression analysis was employed to investigate biological processes during pretransplant culture, and in vitro validation studies were performed.

Results:

Survival of cultured xenografts was significantly prolonged as compared to that of fresh islets (fresh: 12.5 ± 1.9 days, 1-day cultured: 16.0 ± 1.3 days (p= 0.017), 3-day cultured: 17.0 ± 2.6 days (p= 0.014)). Comprehensive gene expression analysis identified significant upregulation of annotated functions associated with inflammation in cultured groups. Six proinflammatory genes, including heme oxygenase 1 (HO-1) and IL-6, were significantly upregulated during culture. Validation studies revealed significantly higher levels of IL-6 in the supernatant of cultured islets and HO-1 in the cultured islets when compared with fresh islets.

Conclusion:

Transplantation of cultured islets induced significant but minimal prolongation of graft survival in xenogeneic combinations. Comprehensive analysis of gene expression in cultured islets showed biological processes associated with proinflammation during culture.

Evaluation of Multi-Layered Pancreatic Islets and Adipose-Derived Stem Cell Sheets Transplanted on Various Sites for Diabetes Treatment

Islet cell transplantation is considered an ideal treatment for insulin-deficient diabetes, but implantation sites are limited and show low graft survival. Cell sheet technology and adipose-derived stem cells (ADSCs) can be useful tools for improving islet cell transplantation outcomes since both can increase implantation efficacy and graft survival. Herein, the optimal transplantation site in diabetic mice was investigated using islets and stem cell sheets. We constructed multi-layered cell sheets using rat/human islets and human ADSCs. Cell sheets were fabricated using temperature-responsive culture dishes. Islet/ADSC sheet (AI sheet) group showed higher viability and glucose-stimulated insulin secretion than islet-only group. Compared to islet transplantation alone, subcutaneous AI sheet transplantation showed better blood glucose control and CD31+ vascular traits. Because of the adhesive properties of cell sheets, AI sheets were easily applied on liver and peritoneal surfaces. Liver or peritoneal surface grafts showed better glucose control, weight gain, and intraperitoneal glucose tolerance test (IPGTT) profiles than subcutaneous site grafts using both rat and human islets. Stem cell sheets increased the therapeutic efficacy of islets in vivo because mesenchymal stem cells enhance islet function and induce neovascularization around transplanted islets. The liver and peritoneal surface can be used more effectively than the subcutaneous site in future clinical applications.

Adipose Tissue-Derived Stem Cell Sheet Improves Glucose Metabolism in Obese Mice

Previous studies indicate that the administration of adipose tissue-derived stem cells (ADSCs) through the venous route improves insulin resistance partly through a reduction in the proinflammatory cytokines in diabetic animals. However, the effects of ADSC sheet transplantation for the treatment of diabetes and obesity still remained unknown. In this study, we investigated the effects of ADSC sheet transplantation into the subcutaneous sites on the diabetic state of mice fed high-fat and high-sucrose diet (HF/HSD). ADSCs were isolated and propagated from subcutaneous adipose tissues of non-diabetic intact mice. We used the thermoresponsive designated cell culture dishes to fabricate ADSC cell sheets. ADSC sheet transplantation into the subcutaneous sites significantly improved glucose intolerance induced by HF/HSD in mice. ADSC-conditioned medium (CM) augmented the phosphorylation of Akt with or without insulin in mouse C2C12 myotubes and mouse 3T3-L1 adipocytes. Plasma adiponectin and tumor necrosis factor-α (TNF-α) levels were significantly increased and decreased by ADSC sheet transplantation in mice with or without HF/HSD, respectively. Moreover, ADSC sheet enhanced adiponectin expression in the subcutaneous adipose tissues in HF/HSD-fed mice, whereas it reduced TNF-α expression in the visceral adipose tissues. ADSC-CM enhanced and reduced the protein levels of adiponectin and TNF-α in 3T3-L1 adipocytes, respectively. In conclusion, we first revealed that ADSC sheet transplantation into the subcutaneous sites improves glucose intolerance in mice fed with HF/HSD. Changes of adiponectin and TNF-α production from the host adipose tissues might be involved in the effects of ADSC sheet on glucose metabolism in mice. ADSC sheet transplantation therapy may be a novel clinical application for diabetes.

Cell sheet tissue engineering for scaffold-free three-dimensional (3D) tissue reconstruction

Three-dimensional (3D) reconstruction of highly functional tissues is of great importance in advancing the clinical benefit of tissue engineering and regenerative medicine. In the last quarter century, many studies have found that by engineering a 3D microenvironment that resembles the in vivo tissue condition, cells exhibit behaviors and functions that reflect those of native tissue. Biomaterial scaffolds are a central technology for providing 3D microenvironments in vitro, and, in conjunction with diverse design and cell seeding advents, have produced highly functional and complex 3D tissues. Here, we describe a new approach to creating 3D cell-dense tissue-like constructs without a biomaterial scaffold. Cell sheet technology with cell sheet layering strategies generates highly cell dense, engineered tissue capable of direct crosstalk with the tissue-engraftment surface, in addition to paracrine-mediated signaling. In this chapter, we will introduce methods of reconstructing 3D tissue using cell sheet technology and the advantages of a scaffold-free design.

Tissue-engineering approaches in pancreatic islet transplantation

Pancreatic islet transplantation is a promising alternative to whole-pancreas transplantation as a treatment of type 1 diabetes mellitus. This technique has been extensively developed during the past few years, with the main purpose of minimizing the complications arising from the standard protocols used in organ transplantation. By using a variety of strategies used in tissue engineering and regenerative medicine, pancreatic islets have been successfully introduced in host patients with different outcomes in terms of islet survival and functionality, as well as the desired normoglycemic control. Here, we describe and discuss those strategies to transplant islets together with different scaffolds, in combination with various cell types and diffusible factors, and always with the aim of reducing host immune response and achieving islet survival, regardless of the site of transplantation.

The liver surface as a favorable site for islet cell sheet transplantation in type 1 diabetes model mice

INTRODUCTION

Islet transplantation is one of the most promising therapeutic approaches for patients with severe type 1 diabetes mellitus (T1DM). Transplantation of engineered islet cell sheets holds great potential for treating T1DM as it enables the creation of stable neo-islet tissues. However, a large mass of islet cell sheets is required for the subcutaneous transplantation to reverse hyperglycemia in diabetic mice. Here, we investigated whether the liver surface could serve as an alternative site for islet cell sheet transplantation.

METHODS

Dispersed rat islet cells (0.8 × 106 cells) were cultured on laminin-332-coated thermoresponsive culture dishes. After 2 days of cultivation, we harvested the islet cell sheets by lowering the culture temperature using a support membrane with a gelatin gel. We transplanted two recovered islet cell sheets into the subcutaneous space or onto the liver surface of severe combined immunodeficiency (SCID) mice with streptozocin-induced diabetes.

RESULTS

In the liver surface group, the non-fasting blood glucose level decreased rapidly within several days after transplantation. In marked contrast, the hyperglycemia state was maintained in the subcutaneous space transplantation group. The levels of rat C-peptide and insulin in the liver surface group were significantly higher than those in the subcutaneous space group. An immunohistological analysis confirmed that most of the islet cells engrafted on the liver surface were insulin-positive. The CD31-positive endothelial cells formed vascular networks within the neo-islets and in the surrounding tissues. In contrast, viable islet cells were not found in the subcutaneous space group.

CONCLUSIONS

Compared with the subcutaneous space, a relatively small mass of islet cell sheets was enough to achieve normoglycemia in diabetic mice when the liver surface was selected as the transplantation site. Our results demonstrate that the optimization of the transplantation site for islet cell sheets leads to significant improvements in the therapeutic efficiency for T1DM.

Ex vivo Pretreatment of Islets with Mitomycin C: Reduction in Immunogenic Potential of Islets by Suppressing Secretion of Multiple Chemotactic Factors

Strategies to reduce the immunogenicity of pancreatic islets and to prevent the activation of proinflammatory events are essential for successful islet engraftment. Pretransplant islet culture presents an opportunity for preconditioning to improve outcomes of islet transplantation. We previously demonstrated that ex vivo mitomycin C (MMC) pretreatment and subsequent culture significantly prolonged graft survival. Fully understanding the biological process of pretreatment could result in the development of a protocol to improve the survival of islet grafts. Microarrays were employed to conduct a comprehensive analysis of genes expressed in untreated or MMC-treated rat islets that were subsequently cultured for 3 d. A bioinformatics software was used to identify biological processes that were most affected by MMC pretreatment, and validation studies, including in vivo and in vitro assay, were performed. The gene expression analysis identified significant downregulation of annotated functions associated with cellular movement and revealed significant downregulation of multiple genes encoding proinflammatory mediators with chemotactic activity. Validation studies revealed significantly decreased levels of interleukin 6 (IL-6), monocyte chemoattractant protein 3 (MCP-3), and matrix metallopeptidase 2 (MMP2) in culture supernatants of MMC-treated islets compared with controls. Moreover, we showed the suppression of leukocyte chemotactic activity of MMC-treated islets in vitro. We also showed that MMC-treated islets secreted lower levels of chemoattractants that synergistically reduced the immunogenic potential of islets. Histological and immunohistochemical analyses of the implant site revealed that infiltration of monocytes, CD3-positive T cells, and B cells was decreased in MMC-treated islets. In conclusion, the ex vivo pretreatment of islets with MMC and subsequent culture can reduce the immunogenic potential and prolong the survival of islet grafts by inducing the suppression of multiple leukocyte chemotactic factors.

Effectiveness of bioengineered islet cell sheets for the treatment of diabetes mellitus

BACKGROUND

The present study aimed to evaluate whether bioengineered mouse islet cell sheets can be used for the treatment of diabetes mellitus.

METHODS

Isolated mouse pancreatic islets were dispersed, and cells were plated on temperature-responsive culture plates coated with iMatrix-551. On day 3 of culture, the sheets were detached from the plates and used for further analysis or transplantation. The following parameters were assessed: (1) morphology, (2) expression of β-cell-specific transcription factors and other islet-related proteins, (3) methylation level of the pancreatic duodenal homeobox-1 (Pdx-1) promoter, as determined by bisulfite sequencing, and (4) levels of serum glucose after transplantation of one or two islet cell sheets into the abdominal cavity of streptozotocin-induced diabetic severe combined immunodeficiency mice.

RESULTS

From each mouse, we recovered approximately 233.3 ± 12.5 islets and 1.4 ± 0.1 × 10⁵ cells after dispersion. We estimate that approximately 68.2% of the cells were lost during dispersion. The viability of recovered single cells was 91.3 ± 0.9%. The engineered islet cell sheets were stable, but the messenger RNA levels of various β-cell-specific transcription factors were significantly lower than those of primary islets, whereas Pdx-1 promoter methylation and the expression of NeuroD, Pdx-1, and glucagon proteins were similar between sheets and islets. Moreover, transplantation of islet cell sheets did not revert serum hyperglycemia in any of the recipient mice.

CONCLUSIONS

Engineering effective islet cell sheets require further research efforts, as the currently produced sheets remain functionally inferior compared with primary islets.

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

Pancreatic islet transplantation has been validated as a valuable therapy for type 1 diabetes mellitus patients with exhausted insulin treatment. However, this therapy remains limited by the shortage of donor and the requirement of lifelong immunosuppression. Islet encapsulation, as an available bioartificial pancreas (BAP), represents a promising approach to enable protecting islet grafts without or with minimal immunosuppression and possibly expanding the donor pool. To develop a clinically implantable BAP, some key aspects need to be taken into account: encapsulation material, capsule design, and implant site. Among them, the implant site exerts an important influence on the engraftment, stability, and biocompatibility of implanted BAP. Currently, an optimal site for encapsulated islet transplantation may include sufficient capacity to host large graft volumes, portal drainage, ease of access using safe and reproducible procedure, adequate blood/oxygen supply, minimal immune/inflammatory reaction, pliable for noninvasive imaging and biopsy, and potential of local microenvironment manipulation or bioengineering. Varying degrees of success have been confirmed with the utilization of liver or extrahepatic sites in an experimental or preclinical setting. However, the ideal implant site remains to be further engineered or selected for the widespread application of encapsulated islet transplantation.

Design of Temperature-Responsive Cell Culture Surfaces for Cell Sheet-Based Regenerative Therapy and 3D Tissue Fabrication

This chapter describes the concept of "cell sheet engineering" for the creation of transplantable cellular tissues and organs. In contrast to scaffold-based tissue engineering, cell sheet engineering facilitates the reconstruction of scaffold-free, cell-dense tissues. Cell sheets were harvested by changing the temperature of thermoresponsive cell culture surfaces modified with poly(N-isopropylacrylamide) (PIPAAm) with a thickness on the nanometer scale. The transplantation of 2D cell sheet tissues has been used in clinical settings. Although 3D tissues were formed simply by layering 2D cell sheets, issues related to vascularization within 3D tissues and the large-scale production of cells must be addressed to create thick and large 3D tissues and organs.

Hepatocyte Transplantation: Cell Sheet Technology for Liver Cell Transplantation

Purpose of Review

We will review the recent developments of cell sheet technology as a feasible tissue engineering approach. Specifically, we will focus on the technological advancement for engineering functional liver tissue using cell sheet technology, and the associated therapeutic effect of cell sheets for liver diseases, highlighting hemophilia.

Recent Findings

Cell-based therapies using hepatocytes have recently been explored as a new therapeutic modality for patients with many forms of liver disease. We have developed a cell sheet technology, which allows cells to be harvested in a monolithic layer format. We have succeeded in fabricating functional liver tissues in mice by stacking the cell sheets composed of primary hepatocytes. As a curative measure for hemophilia, we have also succeeded in treating hemophilia mice by transplanting of cells sheets composed of genetically modified autologous cells.

Summary

Tissue engineering using cell sheet technology provides the opportunity to create new therapeutic options for patients with various types of liver diseases.

Stimulation of vascularization of a subcutaneous scaffold applicable for pancreatic islet-transplantation enhances immediate post-transplant islet graft function but not long-term normoglycemia

The liver as transplantation site for pancreatic islets is associated with significant loss of islets, which can be prevented by grafting in a prevascularized, subcutaneous scaffold. Supporting vascularization of a scaffold to limit the period of ischemia is challenging and was developed here by applying liposomes for controlled release of angiogenic factors. The angiogenic capacity of platelet-derived growth factor, vascular endothelial growth factor, acidic fibroblast growth factor (aFGF), and basic FGF were compared in a tube formation assay. Furthermore, the release kinetics of different liposome compositions were tested. aFGF and L-α-phosphatidylcholine/cholesterol liposomes were selected to support vascularization. Two dosages of aFGF-liposomes (0.5 and 1.0 μg aFGF per injection) were administered weekly for a month after which islets were transplanted. We observed enhanced efficacy in the immediate post-transplant period compared to the untreated scaffolds. However, on the long-term, glucose levels of the aFGF treated animals started to increase to diabetic levels. These results suggest that injections with aFGF liposomes do improve vascularization and the immediate restoration of blood glucose levels but does not facilitate the long-term survival of islets. Our data emphasize the need for long-term studies to evaluate potential beneficial and adverse effects of vascularization protocols of scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2533-2542, 2017.

The Efficacy of a Prevascularized, Retrievable Poly(D,L,-lactide-co-ε-caprolactone) Subcutaneous Scaffold as Transplantation Site for Pancreatic Islets

BACKGROUND

The liver as transplantation site for human pancreatic islets is a harsh microenvironment for islets and it lacks the ability to retrieve the graft. A retrievable, extrahepatic transplantation site that mimics the pancreatic environment is desired. Ideally, this transplantation site should be located subdermal for easy surgical-access but this never resulted in normoglycemia. Here, we describe the design and efficacy of a novel prevascularized, subcutaneously implanted, retrievable poly (D,L-lactide-co-ε-caprolactone) scaffold.

METHOD

Three dosages of rat islets, that is, 400, 800, and 1200, were implanted in immune compromised mice to test the efficacy (n = 5). Islet transplantation under the kidney capsule served as control (n = 5). The efficacy was determined by nonfasting blood glucose measurements and glucose tolerance tests.

RESULTS

Transplantation of 800 (n = 5) and 1200 islets (n = 5) into the scaffold reversed diabetes in respectively 80 and 100% of the mice within 6.8 to 18.5 days posttransplant. The marginal dose of 400 islets (n = 5) induced normoglycemia in 20%. The glucose tolerance test showed major improvement of the glucose clearance in the scaffold groups compared to diabetic controls. However, the kidney capsule was slightly more efficacious because all 800 (n = 5) and 1200 islets (n = 5) recipients and 40% of the 400 islets (n = 5) recipients became normoglycemic within 8 days. Removal of the scaffolds or kidney grafts resulted in immediate return to hyperglycemia. Normoglycemia was not achieved with 1200 islets in the unmodified skin group.

CONCLUSIONS

Our findings demonstrate that the prevascularized poly (D,L-lactide-co-ε-caprolactone) scaffold maintains viability and function of islets in the subcutaneous site.

Stem cell-derived cell-sheets for connective tissue engineering

Cell-sheet technology involves the recovery of cells with its secreted ECM and cell-cell junctions intact, and thereby harvesting them in a single contiguous layer. Temperature changes coupled with a thermoresponsive polymer grafted culture plate surface are typically used to induce detachment of this cell-matrix layer by controlling the hydrophobicity and hydrophilicity properties of the culture surface. This review article details the genesis and development of this technique as a critical tissue-engineering tool, with a comprehensive discussion on connective tissue applications. This includes applications in the myocardial, vascular, cartilage, bone, tendon/ligament, and periodontal areas among others discussed. In particular, further focus will be given to the use of stem cells-derived cell-sheets, such as those involving bone marrow-derived and adipose tissue-derived mesenchymal stem cells. In addition, some of the associated challenges faced by approaches using stem cells-derived cell-sheets will also be discussed. Finally, recent advances pertaining to technologies forming, detaching, and manipulating cell-sheets will be covered in view of the potential impact they will have on shaping the way cell-sheet technology will be utilized in the future as a tissue-engineering technique.

Size effect of engineered islets prepared using microfabricated wells on islet cell function and arrangement

Pancreatic islets are heterogeneous clusters mainly composed of α and β cells, and these clusters range in diameter from 50 to several hundred micrometers. Native small islets are known to have a higher insulin secretion ability in vitro and to provide better transplantation outcomes when compared with large islets. In this study, we prepared microengineered pseudo-islets from dispersed rat islet cells using precisely-fabricated agarose gel-based microwells with different diameters (100, 300, or 500 μm) to investigate the function and survival of islet cell aggregates with well-controlled sizes. We observed that dead cells were rarely present in the small pseudo-islets with an average diameter of ∼60 μm prepared using 100 μm microwells. In contrast, we observed more dead cells in the larger pseudo-islets prepared using 300 and 500 μm microwells. The relative amount of hypoxic cells was significantly low in the small pseudo-islets whereas a hypoxic condition was present in the core region of the larger pseudo-islets. In addition, we found that the small-sized pseudo-islets reconstituted the in vivo-tissue like arrangement of the α and β cells, and restored the high insulin secretory capacity in response to high glucose. These results clearly suggest that precise size control of pseudo-islets is essential for maintaining islet cell function and survival in vitro. The small-sized pseudo-islets may be advantageous for providing a better therapeutic approach for treating type 1 diabetes mellitus via islet reorganization and transplantation.

Engineering pancreatic tissues from stem cells towards therapy

Pancreatic islet transplantation is performed as a potential treatment for type 1 diabetes mellitus. However, this approach is significantly limited due to the critical shortage of islet sources. Recently, a number of publications have developed protocols for directed β-cell differentiation of pluripotent cells, such as embryonic stem (ES) or induced pluripotent stem (iPS) cells. Decades of studies have led to the development of modified protocols that recapitulate molecular developmental cues by combining various growth factors and small molecules with improved efficiency. However, the later step of pancreatic differentiation into functional β-cells has yet to be satisfactory in vitro, highlighting alternative approach by recapitulating spatiotemporal multicellular interaction in three-dimensional (3D) culture. Here, we summarize recent progress in the directed differentiation into pancreatic β-cells with a focus on both two-dimensional (2D) and 3D differentiation settings. We also discuss the potential transplantation strategies in combination with current bioengineering approaches towards diabetes therapy.

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Transplantation of stem cell derived pancreatic progenitors is a possible approach for generating mature β-cell in vivo.

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Promise of 3-D (or 4-D) culture has started to be explored by reconstituting pancreatic tissue structures.

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Self-condensation culture is a basic technique of integrating multiple heterotypic lineages including vasculatures.

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Bioengineering approach has been combined for developing effective transplant strategies.

Human Fibroblast Sheet Promotes Human Pancreatic Islet Survival and Function In Vitro

In previous work, we engineered functional cell sheets using bone marrow-derived mesenchymal stem cells (BM-MSCs) to promote islet graft survival. In the present study, we hypothesized that a cell sheet using dermal fibroblasts could be an alternative to MSCs, and then we aimed to evaluate the effects of this cell sheet on the functional viability of human islets. Fibroblast sheets were fabricated using temperature-responsive culture dishes. Human islets were seeded onto fibroblast sheets. The efficacy of the fibroblast sheets was evaluated by dividing islets into three groups: the islets-alone group, the coculture with fibroblasts group, and the islet culture on fibroblast sheet group. The ultrastructure of the islets cultured on each fibroblast sheet was examined by electron microscopy. The fibroblast sheet expression of fibronectin (as a component of the extracellular matrix) was quantified by Western blotting. After 3 days of culture, islet viabilities were 70.2 ± 9.8%, 87.4 ± 5.8%, and 88.6 ± 4.5%, and survival rates were 60.3 ± 6.8%, 65.3 ± 3.0%, and 75.8 ± 5.6%, respectively. Insulin secretions in response to high-glucose stimulation were 5.1 ± 1.6, 9.4 ± 3.8, and 23.5 ± 12.4 µIU/islet, and interleukin-6 (IL-6) secretions were 3.0 ± 0.7, 5.1 ± 1.2, and 7.3 ± 1.0 ng/day, respectively. Islets were found to incorporate into the fibroblast sheets while maintaining a three-dimensional structure and well-preserved extracellular matrix. The fibroblast sheets exhibited a higher expression of fibronectin compared to fibroblasts alone. In conclusion, human dermal fibroblast sheets fabricated by tissue-engineering techniques could provide an optimal substrate for human islets, as a source of cytokines and extracellular matrix.

Efficient Gene Transduction of Dispersed Islet Cells in Culture Using Fiber-Modified Adenoviral Vectors

To establish novel islet-based therapies, our group has recently developed technologies for creating functional neo-islet tissues in the subcutaneous space by transplanting monolithic sheets of dispersed islet cells (islet cell sheets). Improving cellular function and viability are the next important challenges for enhancing the therapeutic effects. This article describes the adenoviral vector-mediated gene transduction of dispersed islet cells under culture conditions. Purified pancreatic islets were obtained from Lewis rats and dissociated into single islet cells. Cells were plated onto laminin-5-coated temperature-responsive polymer poly(N-isopropylacrylamide)-immobilized plastic dishes. At 0 h, islet cells were infected for 1 h with either conventional type 5 adenoviral vector (Ad-CA-GFP) or fiber-modified adenoviral vector (AdK7-CA-GFP) harboring a polylysine (K7) peptide in the C terminus of the fiber knob. We investigated gene transduction efficiency at 48 h after infection and found that AdK7-CA-GFP yielded higher transduction efficiencies than Ad-CA-GFP at a multiplicity of infection (MOI) of 5 and 10. For AdK7-CA-GFP at MOI = 10, 84.4 ± 1.5% of islet cells were found to be genetically transduced without marked vector infection-related cellular damage as determined by viable cell number and lactate dehydrogenase (LDH) release assay. After AdK7-CA-GFP infection at MOI = 10, cells remained attached and expanded to nearly full confluency, showing that this adenoviral infection protocol is a feasible approach for creating islet cell sheets. We have shown that dispersed and cultured islet cells can be genetically modified efficiently using fiber-modified adenoviral vectors. Therefore, this gene therapy technique could be used for cellular modification or biological assessment of dispersed islet cells.

Optical coherence microscopy of living cells and bioengineered tissue dynamics in high-resolution cross-section

Optical coherence tomography (OCT) is a valuable tool in the cross-sectional observation/analysis of three-dimensional (3-D) biological tissues, and that histological observation is important clinically. However, the resolution of the technology is approximately 10-20 μm. In this study, optical coherence microscopy (OCM), a tomographic system combining OCT technology with a microscopic technique, was constructed for observing cells individually with a resolution at the submicrometer level. Cells and 3-D tissues fabricated by cell sheet technology were observed by OCM. Importantly, the cell nuclei and cytoplasm could be clearly distinguished, and the time-dependent dynamics of cell-sheet tissues could be observed in detail. Additionally, the 3-D migration of cells in the bioengineered tissue was also detected using OCM and metal-labeled cells. Bovine aortic endothelial cells, but not NIH3T3 murine embryonic skin fibroblasts, actively migrated within the 3-D tissues. This study showed that the OCM system would be a valuable tool in the fields of cell biology, tissue engineering, and regenerative medicine. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 481-488, 2017.

Enhanced angiogenesis in ischemic skeletal muscle after transplantation of cell sheets from baculovirus-transduced adipose-derived stromal cells expressing VEGF165

Introduction

Cell therapy using adipose-derived stromal cells (ADSC) is an intensively developing approach to promote angiogenesis and regeneration. Administration technique is crucial and among others minimal constructs - cell sheets (CS) have certain advantages. Delivery of CS allows transplantation of cells along with matrix proteins to facilitate engraftment. Cells’ therapeutic potential can be also increased by expression of proangiogenic factors by viral transduction. In this work we report on therapeutic efficacy of CS from mouse ADSC transduced to express human vascular endothelial growth factor 165 a/a isoform (VEGF165), which showed potency to restore perfusion and protect tissue in a model of limb ischemia.

Methods

Mouse ADSC (mADSC) isolated from C57 male mice were expanded for CS formation (10⁶cells per CS). Constructs were transduced to express human VEGF165 by baculoviral (BV) system. CS were transplanted subcutaneously to mice with surgically induced limb ischemia and followed by laser Doppler perfusion measurements. At endpoint animals were sacrificed and skeletal muscle was evaluated for necrosis and vessel density; CS with underlying muscle was stained for apoptosis, proliferation, monocytes and blood vessels.

Results

Using BV system and sodium butyrate treatment we expressed human VEGF165 in mADSC (production of VEGF165 reached ≈ 25-27 ng/ml/10⁵ cells) and optimized conditions to ensure cells’ viability after transduction. Implantation of mock-transduced CS resulted in significant improvement of limb perfusion, increased capillary density and necrosis reduction at 2 weeks post-surgery compared to untreated animals. Additional improvement of blood flow and angiogenesis was observed after transplantation of VEGF165-expressing CS indicating enhanced therapeutic potential of genetically modified constructs. Moreover, we found delivery of mADSC as CS to be superior to equivalent dose of suspended cells in terms of perfusion and angiogenesis. Histology analysis of extracted CS detected limited proliferation and approximately 10 % prevalence of apoptosis in transplanted mADSC. Significant vascularization of CS and infiltration by monocytes were found in both – BV-transduced and control CS indicating graft and host interaction after transplantation.

Conclusions

Delivery of ADSC by subcutaneous transplantation of CS is effective for stimulation of angiogenesis and tissue protection in limb ischemia with a potential for efficacy improvement by BV transduction to express VEGF165.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0199-6) contains supplementary material, which is available to authorized users.

Osteogenic Ability of Canine Adipose-Derived Mesenchymal Stromal Cell Sheets in Relation to Culture Time

Cell sheets could be used for bone regeneration without requiring a scaffold and can be easily produced from autologous mesenchymal stromal cells (MSCs). We compared the osteogenic potential of MSC-derived cell sheets in relation to culture time. Undifferentiated cell sheets (U-CS) and osteogenic differentiated cell sheets (O-CS) were generated using canine adipose-derived MSCs. Undifferentiated cells (UCs) were used as the control. Osteogenic differentiation was assessed by assaying alkaline phosphatase (ALP) activity. Expression of osteogenesis-related genes was evaluated by reverse transcription-polymerase chain reaction at 4, 7, 14, and 21 days after initiation of culture. The calcium content in cells was measured, and the cells were stained with Alizarin red S (ARS). The mRNA expression of transforming growth factor-β in U-CS and O-CS at day 4 was higher than that in UCs (p < 0.05). The level of bone morphogenetic protein 7 mRNA in O-CS increased significantly at day 4 and was significantly higher than that of U-CS at day 7. The mRNA level of runt-related transcription factor-2 in both sheet types increased significantly at 7 days of culture. The mRNA level of ALP in O-CS and U-CS increased significantly at day 7, and ALP activity was highest at days 7 and 14, respectively (p < 0.05). The mRNA level of osteocalcin in U-CS and O-CS increased significantly at day 21. O-CS and U-CS showed negative ARS staining but their calcium contents increased marginally at day 21. The O-CS cells started to aggregate at days 10-12, and only a partial sheet remained at day 21. The upregulation of expression of genes related to osteogenic differentiation, peak in ALP activity, and morphological changes in cell sheets suggest that the optimal time for application of O-CS and U-CS is between 7 and 10 days and after 14 days of culture, respectively.

Human Laminin Isotype Coating for Creating Islet Cell Sheets

Our experimental approach toward the development of new islet-based treatment for diabetes mellitus has been the creation of a monolayered islet cell construct (islet cell sheet), followed by its transplantation into a subcutaneous pocket. Previous studies describe rat laminin-5 (chain composition: α3, β3, γ2) as a suitable extracellular matrix (ECM) for surfaces comprised of a coated temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). To progress toward the clinical application of this approach, the present study attempted to identify an optimal human ECM as a coating material on PIPAAm surfaces, which allowed islet cells to attach on the surfaces and subsequently to be harvested as a monolithic cell sheet. Dispersed rat islet cells were seeded onto PIPAAm dishes coated with various human laminin isotypes: human laminin (HL)-211, HL-332, HL-411, HL-511, and HL-placenta. Plating efficiency at day 1, the confluency at day 3, and glucose-stimulated insulin secretion test at day 3 were performed. The highest value of plating efficiency was found in the HL-332-PIPAAm group (83.1 ± 0.7%). The HL-332-PIPAAm group also showed the highest cellular confluency (98.6 ± 0.5%). Islet cells cultured on the HL-332-PIPAAm surfaces showed a positive response in the glucose-stimulated insulin secretion test. By reducing culture temperature from 37°C to 20°C in the HL-332-PIPAAm group, cells were able to be harvested as a monolithic islet sheet. The present study showed that HL-332 was an optimal human-derived ECM on a PIPAAm coating for preparing islet cell sheets.

A Method for Performing Islet Transplantation Using Tissue-Engineered Sheets of Islets and Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are known to have a protective effect on islet cells. Cell sheets developed using tissue engineering help maintain the function of the cells themselves. This study describes a tissue engineering approach using islets with MSC sheets to improve the therapeutic effect of islet transplantation. MSCs were obtained from Fischer 344 rats and engineered into cell sheets using temperature-responsive culture dishes. The islets obtained from Fischer 344 rats were seeded onto MSC sheets, and the islets with MSC sheets were harvested by low-temperature treatment after coculture. The functional activity of the islets with MSC sheets was confirmed by a histological examination, insulin secretion assay, and quantification of the levels of cytokines. The therapeutic effects of the islets with MSC sheets were investigated by transplanting the sheets at subcutaneous sites in severe combined immunodeficiency (SCID) mice with streptozotocin-induced diabetes. Improvement of islet function and viability was shown in situ on the MSC sheet, and the histological examination showed that the MSC sheet maintained adhesion factor on the surface. In the recipient mice, normoglycemia was maintained for at least 84 days after transplantation, and neovascularization was observed. These results demonstrated that islet transplantation in a subcutaneous site would be possible by using the MSC sheet as a scaffold for islets.

A prevascularized subcutaneous device-less site for islet and cellular transplantation

Transplantation of donor-derived islets into the liver is a successful cellular replacement therapy for individuals with diabetes. However, the hepatic vasculature is not an optimal transplant site for several reasons, including graft attrition and the inability to retrieve or image the islets. Here we describe islet transplantation into a prevascularized, subcutaneous site created by temporary placement of a medically approved vascular access catheter. In mice with streptozotocin (STZ)-induced diabetes, transplantation of ∼500 syngeneic islets into the resulting 'device-less' space reversed diabetes in 91% of mice and maintained normoglycemia for >100 days. The approach was also effective in mice with pre-existing diabetes, in another mouse strain that mounts a more vigorous inflammatory response, and across an allogeneic barrier. These results demonstrate that transient priming of a subcutaneous site supports diabetes-reversing islet transplantation in mouse models without the need for a permanent cell-encapsulation device.

Mesenchymal Stem Cells: Rising Concerns over Their Application in Treatment of Type One Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder that leads to beta cell destruction and lowered insulin production. In recent years, stem cell therapies have opened up new horizons to treatment of diabetes mellitus. Among all kinds of stem cells, mesenchymal stem cells (MSCs) have been shown to be an interesting therapeutic option based on their immunomodulatory properties and differentiation potentials confirmed in various experimental and clinical trial studies. In this review, we discuss MSCs differential potentials in differentiation into insulin-producing cells (IPCs) from various sources and also have an overview on currently understood mechanisms through which MSCs exhibit their immunomodulatory effects. Other important issues that are provided in this review, due to their importance in the field of cell therapy, are genetic manipulations (as a new biotechnological method), routes of transplantation, combination of MSCs with other cell types, frequency of transplantation, and special considerations regarding diabetic patients' autologous MSCs transplantation. At the end, utilization of biomaterials either as encapsulation tools or as scaffolds to prevent immune rejection, preparation of tridimensional vascularized microenvironment, and completed or ongoing clinical trials using MSCs are discussed. Despite all unresolved concerns about clinical applications of MSCs, this group of stem cells still remains a promising therapeutic modality for treatment of diabetes.

Topographical arrangement of α- and β-cells within neo-islet tissues engineered by islet cell sheet transplantation in mice

BACKGROUND

We established a procedure to engineer therapeutic neo-islets in subcutaneous spaces in mice by transplanting contiguous layers of islet cell sheets. In this study, we investigated the cellular arrangements of α and β within these engineered neo-islets in vivo as a function of time after sheet transplantation.

METHODS AND RESULTS

Temperature-responsive culture dishes optimized for dispersed islet cell culture were prepared by covalently immobilizing a temperature-responsive polymer poly(N-isopropylacrylamide) (PIPAAm) on plastic dishes followed by laminin-5 coating. Dispersed islet cells obtained from Lewis rats were plated onto the PIPAAm dishes. After reaching confluence at day 2, islet cells were harvested as uniformly spread islet cell sheets by lowering the culture temperature from 37°C to 20°C for 20 minutes. Islet sheet transplantation was performed to creat neo-islet tissues in the subcutaneous spaces of SCID mice with streptozotocin-induced diabetes. This neo-islet engineering approach successfully lowered mouse blood glucose levels, achieving euglycemia at day 5 and thereafter. Histologic analyses of samples obtained at day 4 revealed that neo-islet tissues in the subcutaneous spaces showed heterogeneous cellular alignment of α and β cells. In contrast, analyses of samples at days 14 and 60 revealed α and β cells predominantly located at the peripheral and central parts of the engineered tissues, respectively.

CONCLUSIONS

Reassembly of α and β cells occurred in neo-islet tissues engineered by sheet transplantation. The unique cellular arrangements in neo-islet tissues, which were similar to those in naïve pancreatic islets, may contribute to their longevity and long-term function.

Strategy for clinical setting in intramuscular and subcutaneous islet transplantation

Intraportal islet transplantation has a long history as a procedure for clinical islet transplantation. However, many recent studies revealed that the intraportal procedure has some disadvantages in transplant efficiency and safety. Many candidates as an optimal transplant site for islets have been assessed, but further studies and clinical trials are still necessary. Intramuscular and subcutaneous spaces are important candidates, because the transplant and biopsy procedures are simple approaches with minimal invasion and few complications. Although they are sites with hypovascularity and hypoxia, which contribute to the poor transplant efficiency, many experimental trials for improving the outcome in intramuscular and subcutaneous islet transplantations have been performed, focusing on early angiogenesis and scaffolds for engrafting transplanted islets. We review current progress in intramuscular and subcutaneous islet transplantations and discuss ways to develop them as optimal transplant sites for islets.