Supporting Survival of Transplanted Stem-Cell-Derived Insulin-Producing Cells in an Encapsulation Device Augmented with Controlled Release of Amino Acids

A composite capsule strategy to support longevity of microencapsulated pancreatic β cells

Pancreatic islet microencapsulation allows transplantation of insulin producing cells in absence of systemic immunosuppression, but graft survival is still limited. In vivo studies have demonstrated that many islet-cells die in the immediate period after transplantation. Here we test whether intracapsular inclusion of ECM components (collagen IV and RGD) with necrostatin-1 (Nec-1), as well as amino acids (AA) have protective effects on islet survival. Also, the inclusion of pectin was tested as it enhances the mitochondrial health of β-cells. To enhance the longevity of encapsulated islets, we studied the impact of the incorporation of the mentioned components into the alginate-based microcapsules in vitro. The efficacy of the different composite microcapsules on MIN6 β-cell or human islet-cell survival and function, as well as suppression of DAMP-induced immune activation, were determined. Finally, we examined the mitochondrial dynamic genes. This was done in the absence and presence of a cytokine cocktail. Here, we found that composite microcapsules of APENAA improved insulin secretion and enhanced the mitochondrial activity of β-cells. Under cytokine exposure, they prevented the cytokine-induced decrease of mitochondrial activity as well as viability till day 5. The rescuing effects of the composite capsules were accompanied by alleviated mitochondrial dynamic gene expression. The composite capsule strategy of APENAA might support the longevity of microencapsulated β-cells by lowering susceptibility to inflammatory stress. Our data demonstrate that combining strategies to support β-cells by changing the intracapsular microenvironment might be an effective way to preserve islet graft longevity in the immediate period after transplantation.

Solid implantable devices for sustained drug delivery

Implantable drug delivery systems (IDDS) are an attractive alternative to conventional drug administration routes. Oral and injectable drug administration are the most common routes for drug delivery providing peaks of drug concentrations in blood after administration followed by concentration decay after a few hours. Therefore, constant drug administration is required to keep drug levels within the therapeutic window of the drug. Moreover, oral drug delivery presents alternative challenges due to drug degradation within the gastrointestinal tract or first pass metabolism. IDDS can be used to provide sustained drug delivery for prolonged periods of time. The use of this type of systems is especially interesting for the treatment of chronic conditions where patient adherence to conventional treatments can be challenging. These systems are normally used for systemic drug delivery. However, IDDS can be used for localised administration to maximise the amount of drug delivered within the active site while reducing systemic exposure. This review will cover current applications of IDDS focusing on the materials used to prepare this type of systems and the main therapeutic areas of application.

Replenishable prevascularized cell encapsulation devices increase graft survival and function in the subcutaneous space

Beta cell replacement therapy (BCRT) for patients with type 1 diabetes (T1D) improves blood glucose regulation by replenishing the endogenous beta cells destroyed by autoimmune attack. Several limitations, including immune isolation, prevent this therapy from reaching its full potential. Cell encapsulation devices used for BCRT provide a protective physical barrier for insulin-producing beta cells, thereby protecting transplanted cells from immune attack. However, poor device engraftment posttransplantation leads to nutrient deprivation and hypoxia, causing metabolic strain on transplanted beta cells. Prevascularization of encapsulation devices at the transplantation site can help establish a host vascular network around the implant, increasing solute transport to the encapsulated cells. Here, we present a replenishable prevascularized implantation methodology (RPVIM) that allows for the vascular integration of replenishable encapsulation devices in the subcutaneous space. Empty encapsulation devices were vascularized for 14 days, after which insulin-producing cells were inserted without disrupting the surrounding vasculature. The RPVIM devices were compared with nonprevascularized devices (Standard Implantation Methodology [SIM]) and previously established prevascularized devices (Standard Prevascularization Implantation Methodology [SPVIM]). Results show that over 75% of RPVIM devices containing stem cell-derived insulin-producing beta cell clusters showed a signal after 28 days of implantation in subcutaneous space. Notably, not only was the percent of RPVIM devices showing signal significantly greater than SIM and SPVIM devices, but the intraperitoneal glucose tolerance tests and histological analyses showed that encapsulated stem-cell derived insulin-producing beta cell clusters retained their function in the RPVIM devices, which is crucial for the successful management of T1D.

Enhancing longevity of immunoisolated pancreatic islet grafts by modifying both the intracapsular and extracapsular environment

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease characterized by autoimmune destruction of pancreatic β cells. Transplantation of immunoisolated pancreatic islets might treat T1DM in the absence of chronic immunosuppression. Important advances have been made in the past decade as capsules can be produced that provoke minimal to no foreign body response after implantation. However, graft survival is still limited as islet dysfunction may occur due to chronic damage to islets during islet isolation, immune responses induced by inflammatory cells, and nutritional issues for encapsulated cells. This review summarizes the current challenges for promoting longevity of grafts. Possible strategies for improving islet graft longevity are also discussed, including supplementation of the intracapsular milieu with essential survival factors, promotion of vascularization and oxygenation near capsules, modulation of biomaterials, and co-transplantation of accessory cells. Current insight is that both the intracapsular as well as the extracapsular properties should be improved to achieve long-term survival of islet-tissue. Some of these approaches reproducibly induce normoglycemia for more than a year in rodents. Further development of the technology requires collective research efforts in material science, immunology, and endocrinology. STATEMENT OF SIGNIFICANCE: Islet immunoisolation allows for transplantation of insulin producing cells in absence of immunosuppression and might facilitate the use of xenogeneic cell sources or grafting of cells obtained from replenishable cell sources. However, a major challenge to date is to create a microenvironment that supports long-term graft survival. This review provides a comprehensive overview of the currently identified factors that have been demonstrated to be involved in either stimulating or reducing islet graft survival in immunoisolating devices and discussed current strategies to enhance the longevity of encapsulated islet grafts as treatment for type 1 diabetes. Although significant challenges remain, interdisciplinary collaboration across fields may overcome obstacles and facilitate the translation of encapsulated cell therapy from the laboratory to clinical application.

Instructional materials that control cellular activity through synthetic Notch receptors

The field of regenerative engineering relies primarily on the dual technical platforms of cell selection/conditioning and biomaterial fabrication to support directed cell differentiation. As the field has matured, an appreciation for the influence of biomaterials on cell behaviors has resulted in engineered matrices that meet biomechanical and biochemical demands of target pathologies. Yet, despite advances in methods to produce designer matrices, regenerative engineers remain unable to reliably orchestrate behaviors of therapeutic cells in situ. Here, we present a platform named MATRIX whereby cellular responses to biomaterials can be custom defined by combining engineered materials with cells expressing cognate synthetic biology control modules. Such privileged channels of material-to-cell communication can activate synthetic Notch receptors and govern activities as diverse as transcriptome engineering, inflammation attenuation, and pluripotent stem cell differentiation, all in response to materials decorated with otherwise bioinert ligands. Further, we show that engineered cellular behaviors are confined to programmed biomaterial surfaces, highlighting the potential to use this platform to spatially organize cellular responses to bulk, soluble factors. This integrated approach of co-engineering cells and biomaterials for orthogonal interactions opens new avenues for reproducible control of cell-based therapies and tissue replacements.

Role of nanotechnology in the prolonged release of drugs by the subcutaneous route

INTRODUCTION

Subcutaneous physiology is distinct from other parenteral routes that benefit the administration of prolonged-release formulations. A prolonged-release effect is particularly convenient for treating chronic diseases because it is associated with complex and often prolonged posologies. Therefore, drug-delivery systems focused on nanotechnology are proposed as alternatives that can overcome the limitations of current therapeutic regimens and improve therapeutic efficacy.

AREAS COVERED

This review presents an updated systematization of nanosystems, focusing on their applications in highly prevalent chronic diseases. Subcutaneous-delivered nanosystem-based therapies comprehensively summarize nanosystems, drugs, and diseases and their advantages, limitations, and strategies to increase their translation into clinical applications. An outline of the potential contribution of quality-by-design (QbD) and artificial intelligence (AI) to the pharmaceutical development of nanosystems is presented.

EXPERT OPINION

Although recent academic research and development (R&D) advances in the subcutaneous delivery of nanosystems have exhibited promising results, pharmaceutical industries and regulatory agencies need to catch up. The lack of standardized methodologies for analyzing in vitro data from nanosystems for subcutaneous administration and subsequent in vivo correlation limits their access to clinical trials. There is an urgent need for regulatory agencies to develop methods that faithfully mimic subcutaneous administration and specific guidelines for evaluating nanosystems.

Successful Islet Transplantation Into a Subcutaneous Polycaprolactone Scaffold in Mice and Pigs

Islet transplantation is a promising treatment for type 1 diabetes. It has the potential to improve glycemic control, particularly in patients suffering from hypoglycemic unawareness and glycemic instability. As most islet grafts do not function permanently, efforts are needed to create an accessible and replaceable site, for islet grafts or for insulin-producing cells obtained from replenishable sources. To this end, we designed and tested an artificial, polymeric subcutaneous transplantation site that allows repeated transplantation of islets.

Methods

In this study, we developed and compared scaffolds made of poly(D,L,-lactide-co-ε-caprolactone) (PDLLCL) and polycaprolactone (PCL). Efficacy was first tested in mice' and then, as a proof of principle for application in a large animal model, the scaffolds were tested in pigs, as their skin structure is similar to that of humans.

Results

In mice, islet transplantation in a PCL scaffold expedited return to normoglycemia in comparison to PDLLCL (7.7 ± 3.7 versus 16.8 ± 6.5 d), but it took longer than the kidney capsule control group. PCL also supported porcine functional islet survival in vitro. Subcutaneous implantation of PDLLCL and PCL scaffolds in pigs revealed that PCL scaffolds were more stable and was associated with less infiltration by immune cells than PDLLCL scaffolds. Prevascularized PCL scaffolds were therefore used to demonstrate the functional survival of allogenic islets under the skin of pigs.

Conclusions

To conclude, a novel PCL scaffold shows efficacy as a readily accessible and replaceable, subcutaneous transplantation site for islets in mice and demonstrated islet survival after a month in pigs.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Mechanobiological Strategies to Enhance Stem Cell Functionality for Regenerative Medicine and Tissue Engineering

Stem cells have been extensively used in regenerative medicine and tissue engineering; however, they often lose their functionality because of the inflammatory microenvironment. This leads to their poor survival, retention, and engraftment at transplantation sites. Considering the rapid loss of transplanted cells due to poor cell-cell and cell-extracellular matrix (ECM) interactions during transplantation, it has been reasoned that stem cells mainly mediate reparative responses via paracrine mechanisms, including the secretion of extracellular vesicles (EVs). Ameliorating poor cell-cell and cell-ECM interactions may obviate the limitations associated with the poor retention and engraftment of transplanted cells and enable them to mediate tissue repair through the sustained and localized presentation of secreted bioactive cues. Biomaterial-mediated strategies may be leveraged to confer stem cells enhanced immunomodulatory properties, as well as better engraftment and retention at the target site. In these approaches, biomaterials have been exploited to spatiotemporally present bioactive cues to stem cell-laden platforms (e.g., aggregates, microtissues, and tissue-engineered constructs). An array of biomaterials, such as nanoparticles, hydrogels, and scaffolds, has been exploited to facilitate stem cells function at the target site. Additionally, biomaterials can be harnessed to suppress the inflammatory microenvironment to induce enhanced tissue repair. In this review, we summarize biomaterial-based platforms that impact stem cell function for better tissue repair that may have broader implications for the treatment of various diseases as well as tissue regeneration.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Applying Immunomodulation to Promote Longevity of Immunoisolated Pancreatic Islet Grafts

Islet transplantation is a promising therapy for insulin-dependent diabetes, but large-scale application is hampered by the lack of a consistent source of insulin-producing cells and need for lifelong administration of immunosuppressive drugs, which are associated with severe side effects. To avoid chronic immunosuppression, islet grafts can be enveloped in immunoisolating polymeric membranes. These immunoisolating polymeric membranes protect islet grafts from cell-mediated rejection while allowing diffusion of oxygen, nutrients, and insulin. Although clinical trials have shown the safety and feasibility of encapsulated islets to control glucose homeostasis, the strategy does up till now not support long-term graft survival. This partly can be explained by a significant loss of insulin-producing cells in the immediate period after implantation. The loss can be prevented by combining immunoisolation with immunomodulation, such as combined administration of immunomodulating cytokines or coencapsulation of immunomodulating cell types such as regulatory T cells, mesenchymal stem cells, or Sertoli cells. Also, administration of specific antibodies or apoptotic donor leucocytes is considered to create a tolerant microenvironment around immunoisolated grafts. In this review, we describe the outcomes and limitations of these approaches, as well as the recent progress in immunoisolating devices. Impact statement Immunoisolation by enveloping islets in semipermeable membranes allows for successful transplantation of islet grafts in the absence of chronic immunosuppression, but the duration of graft survival is still not permanent. The reasons for long-term final graft failure is not fully understood, but combining immunoisolation with immunomodulation of tissues or host immune system has been proposed to enhance the longevity of grafts. This article reviews the recent progress and challenges of immunoisolation, as well as the benefits and feasibility of combining encapsulation approaches with immunomodulation to promote longevity of encapsulated grafts.

In Vivo Differentiation of Stem Cell-derived Human Pancreatic Progenitors to Treat Type 1 Diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease that results from the loss of the pancreatic β-cells. The autoimmune destruction of the β-cells causes the loss of insulin production from the islets of the pancreas, resulting in the loss of blood glucose regulation. This loss of regulation, if not treated, can lead to a plethora of long-term complications in patients. Subsequently, T1DM patients rely on the administration of exogenous insulin sources to maintain their blood glucose levels. In this review, we summarize the history of T1DM therapy and current treatment options. Although treatments for T1DM have progressed substantially, none of the available treatment options allow the patient to live autonomously. Therefore, the challenge to develop a therapy that will fully reverse the disease still remains. A promising field of T1DM therapies is cell replacement therapies derived from human pluripotent stem cells. Here, we specifically review studies that employ stem-cell derived pancreatic progenitors transplanted for in vivo differentiation/maturation and discuss, in detail, the complications that arise post transplantation, including heterogeneity, graft immaturity, and host foreign bodyresponse. We also discuss efforts to induce human stem cell-derived mature β-cells in vitro and compare strategies regarding transplantation of pancreatic progenitors versus mature β-cells cells. Finally, we review key approaches that address critical limitations of in vivo progenitor differentiation including vascularization, oxygenation, and transplant location. The field of islet replacement therapy has made tremendous progress in the last two decades. If the strengths and limitations of the field continue to be identified and addressed, future studies will lead to an ideal treatment for T1DM. Graphical abstract.