Local co-delivery of pancreatic islets and liposomal clodronate using injectable hydrogel to prevent acute immune reactions in a type 1 diabetes

Development of finely tuned liposome nanoplatform for macrophage depletion

BACKGROUND

Immunotherapy with clodronate-encapsulated liposomes, which induce macrophage depletion, has been studied extensively. However, previously reported liposomal formulation-based drugs (Clodrosome® and m-Clodrosome®) are limited by their inconsistent size and therapeutic efficacy. Thus, we aimed to achieve consistent therapeutic effects by effectively depleting macrophages with uniform-sized liposomes.

RESULTS

We developed four types of click chemistry-based liposome nanoplatforms that were uniformly sized and encapsulated with clodronate, for effective macrophage depletion, followed by conjugation with Man-N3 and radiolabeling. Functionalization with Man-N3 improves the specific targeting of M2 macrophages, and radioisotope labeling enables in vivo imaging of the liposome nanoplatforms. The functionalized liposome nanoplatforms are stable under physiological conditions. The difference in the biodistribution of the four liposome nanoplatforms in vivo were recorded using positron emission tomography imaging. Among the four platforms, the clodronate-encapsulated mannosylated liposome effectively depleted M2 macrophages in the normal liver and tumor microenvironment ex vivo compared to that by Clodrosome® and m-Clodrosome®.

CONCLUSION

The newly-developed liposome nanoplatform, with finely tuned size control, high in vivo stability, and excellent ex vivo M2 macrophage targeting and depletion effects, is a promising macrophage-depleting agent.

Emerging strategies to bypass transplant rejection via biomaterial-assisted immunoengineering: Insights from islets and beyond

Novel transplantation techniques are currently under development to preserve the function of impaired tissues or organs. While current technologies can enhance the survival of recipients, they have remained elusive to date due to graft rejection by undesired in vivo immune responses despite systemic prescription of immunosuppressants. The need for life-long immunomodulation and serious adverse effects of current medicines, the development of novel biomaterial-based immunoengineering strategies has attracted much attention lately. Immunomodulatory 3D platforms can alter immune responses locally and/or prevent transplant rejection through the protection of the graft from the attack of immune system. These new approaches aim to overcome the complexity of the long-term administration of systemic immunosuppressants, including the risks of infection, cancer incidence, and systemic toxicity. In addition, they can decrease the effective dose of the delivered drugs via direct delivery at the transplantation site. In this review, we comprehensively address the immune rejection mechanisms, followed by recent developments in biomaterial-based immunoengineering strategies to prolong transplant survival. We also compare the efficacy and safety of these new platforms with conventional agents. Finally, challenges and barriers for the clinical translation of the biomaterial-based immunoengineering transplants and prospects are discussed.

Polymeric Based Hydrogel Membranes for Biomedical Applications

The development of biomedical applications is a transdisciplinary field that in recent years has involved researchers from chemistry, pharmacy, medicine, biology, biophysics, and biomechanical engineering. The fabrication of biomedical devices requires the use of biocompatible materials that do not damage living tissues and have some biomechanical characteristics. The use of polymeric membranes, as materials meeting the above-mentioned requirements, has become increasingly popular in recent years, with outstanding results in tissue engineering, for regeneration and replenishment of tissues constituting internal organs, in wound healing dressings, and in the realization of systems for diagnosis and therapy, through the controlled release of active substances. The biomedical application of hydrogel membranes has had little uptake in the past due to the toxicity of cross-linking agents and to the existing limitations regarding gelation under physiological conditions, but now it is proving to be a very promising field This review presents the important technological innovations that the use of membrane hydrogels has promoted, enabling the resolution of recurrent clinical problems, such as post-transplant rejection crises, haemorrhagic crises due to the adhesion of proteins, bacteria, and platelets on biomedical devices in contact with blood, and poor compliance of patients undergoing long-term drug therapies.

Localization of drug biodistribution in a 3D-bioengineered subcutaneous neovascularized microenvironment

Local immunomodulation has shown the potential to control the immune response in a site-specific manner for wound healing, cancer, allergy, and cell transplantation, thus abrogating adverse effects associated with systemic administration of immunotherapeutics. Localized immunomodulation requires confining the biodistribution of immunotherapeutics on-site for maximal immune control and minimal systemic drug exposure. To this end, we developed a 3D-printed subcutaneous implant termed 'NICHE', consisting of a bioengineered vascularized microenvironment enabled by sustained drug delivery on-site. The NICHE was designed as a platform technology for investigating local immunomodulation in the context of cell therapeutics and cancer vaccines. Here we studied the ability of the NICHE to localize the PK and biodistribution of different model immunomodulatory agents in vivo. For this, we first performed a mechanistic evaluation of the microenvironment generated within and surrounding the NICHE, with emphasis on the parameters related to molecular transport. Second, we longitudinally studied the biodistribution of ovalbumin, cytotoxic T lymphocyte-associated antigen-4-Ig (CTLA4Ig), and IgG delivered locally via NICHE over 30 days. Third, we used our findings to develop a physiologically-based pharmacokinetic (PBPK) model. Despite dense and mature vascularization within and surrounding the NICHE, we showed sustained orders of magnitude higher molecular drug concentrations within its microenvironment as compared to systemic circulation and major organs. Further, the PBPK model was able to recapitulate the biodistribution of the 3 molecules with high accuracy (r ​> ​0.98). Overall, the NICHE and the PBPK model represent an adaptable platform for the investigation of local immunomodulation strategies for a wide range of biomedical applications.

Emerging local immunomodulatory strategies to circumvent systemic immunosuppression in cell transplantation

INTRODUCTION

Cell transplantation is a promising curative therapeutic strategy whereby impaired organ functions can be restored without the need for whole organ transplantation. A key challenge in allotransplantation is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with serious adverse effects such as increased risk of opportunistic infections and the development of neoplasms. This challenge underscores the urgent need for novel strategies to prevent graft rejection while abrogating toxicity-associated adverse events.

AREAS COVERED

We review recent advances in immunoengineering strategies for localized immunomodulation that aim to support allograft function and provide immune tolerance in a safe and effective manner.

EXPERT OPINION

Immunoengineering strategies are tailored approaches for achieving immunomodulation of the transplant microenvironment. Biomaterials can be adapted for localized and controlled release of immunomodulatory agents, decreasing the effective dose threshold and frequency of administration. The future of transplant rejection management lies in the shift from systemic to local immunomodulation with suppression of effector and activation of regulatory T cells, to promote immune tolerance.

Engineering β Cell Replacement Therapies for Type 1 Diabetes: Biomaterial Advances and Considerations for Macroscale Constructs

While significant progress has been made in treatments for type 1 diabetes (T1D) based on exogenous insulin, transplantation of insulin-producing cells (islets or stem cell-derived β cells) remains a promising curative strategy. The current paradigm for T1D cell therapy is clinical islet transplantation (CIT)-the infusion of islets into the liver-although this therapeutic modality comes with its own limitations that deteriorate islet health. Biomaterials can be leveraged to actively address the limitations of CIT, including undesired host inflammatory and immune responses, lack of vascularization, hypoxia, and the absence of native islet extracellular matrix cues. Moreover, in efforts toward a clinically translatable T1D cell therapy, much research now focuses on developing biomaterial platforms at the macroscale, at which implanted platforms can be easily retrieved and monitored. In this review, we discuss how biomaterials have recently been harnessed for macroscale T1D β cell replacement therapies.

Local delivery strategies to restore immune homeostasis in the context of inflammation

Immune homeostasis is maintained by a precise balance between effector immune cells and regulatory immune cells. Chronic deviations from immune homeostasis, driven by a greater ratio of effector to regulatory cues, can promote the development and propagation of inflammatory diseases/conditions (i.e., autoimmune diseases, transplant rejection, etc.). Current methods to treat chronic inflammation rely upon systemic administration of non-specific small molecules, resulting in broad immunosuppression with unwanted side effects. Consequently, recent studies have developed more localized and specific immunomodulatory approaches to treat inflammation through the use of local biomaterial-based delivery systems. In particular, this review focuses on (1) local biomaterial-based delivery systems, (2) common materials used for polymeric-delivery systems and (3) emerging immunomodulatory trends used to treat inflammation with increased specificity.

Advances in Encapsulation and Delivery Strategies for Islet Transplantation

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease caused by the destruction of pancreatic β-cells in response to autoimmune reactions. Shapiro et al. conducted novel islet transplantation with a glucocorticoid-free immunosuppressive agent in 2000 and achieved great success; since then, islet transplantation has been increasingly regarded as a promising strategy for the curative treatment of T1DM. However, many unavoidable challenges, such as a lack of donors, poor revascularization, blood-mediated inflammatory reactions, hypoxia, and side effects caused by immunosuppression have severely hindered the widespread application of islet transplantation in clinics. Biomaterial-based encapsulation and delivery strategies are proposed for overcoming these obstacles, and have demonstrated remarkable improvements in islet transplantation outcomes. Herein, the major problems faced by islet transplantation are summarized and updated biomaterial-based strategies for islet transplantation, including islet encapsulation across different scales, delivery of stem cell-derived beta cells, co-delivery of islets with accessory cells and immunomodulatory molecules are highlighted.

Local Immunomodulatory Strategies to Prevent Allo-Rejection in Transplantation of Insulin-Producing Cells

Islet transplantation has shown promise as a curative therapy for type 1 diabetes (T1D). However, the side effects of systemic immunosuppression and limited long-term viability of engrafted islets, together with the scarcity of donor organs, highlight an urgent need for the development of new, improved, and safer cell-replacement strategies. Induction of local immunotolerance to prevent allo-rejection against islets and stem cell derived β cells has the potential to improve graft function and broaden the applicability of cellular therapy while minimizing adverse effects of systemic immunosuppression. In this mini review, recent developments in non-encapsulation, local immunomodulatory approaches for T1D cell replacement therapies, including islet/β cell modification, immunomodulatory biomaterial platforms, and co-transplantation of immunomodulatory cells are discussed. Key advantages and remaining challenges in translating such technologies to clinical settings are identified. Although many of the studies discussed are preliminary, the growing interest in the field has led to the exploration of new combinatorial strategies involving cellular engineering, immunotherapy, and novel biomaterials. Such interdisciplinary research will undoubtedly accelerate the development of therapies that can benefit the whole T1D population.

An Overview of Engineered Hydrogel-Based Biomaterials for Improved β-Cell Survival and Insulin Secretion

Islet transplantation provides a promising strategy in treating type 1 diabetes as an autoimmune disease, in which damaged β-cells are replaced with new islets in a minimally invasive procedure. Although islet transplantation avoids the complications associated with whole pancreas transplantations, its clinical applications maintain significant drawbacks, including long-term immunosuppression, a lack of compatible donors, and blood-mediated inflammatory responses. Biomaterial-assisted islet transplantation is an emerging technology that embeds desired cells into biomaterials, which are then directly transplanted into the patient, overcoming the aforementioned challenges. Among various biomaterials, hydrogels are the preferred biomaterial of choice in these transplants due to their ECM-like structure and tunable properties. This review aims to present a comprehensive overview of hydrogel-based biomaterials that are engineered for encapsulation of insulin-secreting cells, focusing on new hydrogel design and modification strategies to improve β-cell viability, decrease inflammatory responses, and enhance insulin secretion. We will discuss the current status of clinical studies using therapeutic bioengineering hydrogels in insulin release and prospective approaches.

A Comprehensive Review on the Applications of Exosomes and Liposomes in Regenerative Medicine and Tissue Engineering

Tissue engineering and regenerative medicine are generally concerned with reconstructing cells, tissues, or organs to restore typical biological characteristics. Liposomes are round vesicles with a hydrophilic center and bilayers of amphiphiles which are the most influential family of nanomedicine. Liposomes have extensive research, engineering, and medicine uses, particularly in a drug delivery system, genes, and vaccines for treatments. Exosomes are extracellular vesicles (EVs) that carry various biomolecular cargos such as miRNA, mRNA, DNA, and proteins. As exosomal cargo changes with adjustments in parent cells and position, research of exosomal cargo constituents provides a rare chance for sicknesses prognosis and care. Exosomes have a more substantial degree of bioactivity and immunogenicity than liposomes as they are distinctly chiefly formed by cells, which improves their steadiness in the bloodstream, and enhances their absorption potential and medicinal effectiveness in vitro and in vivo. In this review, the crucial challenges of exosome and liposome science and their functions in disease improvement and therapeutic applications in tissue engineering and regenerative medicine strategies are prominently highlighted.

Comparison of the Effects of Liraglutide on Islet Graft Survival Between Local and Systemic Delivery

Islet transplantation has emerged as a promising treatment for type 1 diabetes mellitus. Liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, protects beta cells after islet transplantation by improving glycemic control through several mechanisms. In this study, we compared the effects of local pretreatment and systemic treatment with liraglutide on islet transplantation in a diabetic mouse model. Streptozotocin (STZ)-induced diabetic C57BL/6 mice were transplanted with syngeneic islets under the kidney capsule. Isolated islets were either locally treated with liraglutide before transplantation or mice were treated systemically by intraperitoneal injection after islet transplantation. Local pretreatment of islets with liraglutide was more effective in increasing body weight, decreasing hemoglobin A1c levels, and lowering blood glucose levels in STZ-diabetic mice transplanted with islets. Local pretreatment was also more effective in increasing insulin secretion and islet survival in STZ-diabetic mice. Histological analysis of the transplantation site revealed fewer apoptotic cells following local pretreatment compared with systemic injection of liraglutide. These findings indicate that liraglutide administered once locally before transplantation might have superior effects on islet preservation than systemic administration.

Particulate-Based Single-Dose Local Immunosuppressive Regimen for Inducing Tolerogenic Dendritic Cells in Xenogeneic Islet Transplantation

Recent studies emphasize on developing immune tolerance by an interim administration of various immunosuppressive drugs. In this study, a robust protocol is reported for local immunomodulation using a single-dose of FK506 microspheres and clodronate liposomes (mFK+CLO) in a xenogeneic model of islet transplantation. Surprisingly, the single-dose treatment with mFK+CLO induce tolerance to the islet xenograft. The recipient mice display tolerogenic dendritic cells (tDCs) with decreased antigen presenting ability and T cell activation capacity. Furthermore, a reduced percentage of CD4⁺ and CD8⁺ T cells and an impaired differentiation of naïve CD4⁺ T cells into interferon-γ producing Th1 and interleukin-17 producing Th17 cells are observed. In addition, the immunosuppressive protocol leads to the generation of Foxp3⁺ regulatory T cells (Tregs) which are required for the long-term graft survival. The enhanced generation of tDCs and Tregs by the single treatment of mFK+CLO cause xenograft tolerance, suggesting a possible clinical strategy which may pave the way towards improving therapeutic outcomes of clinical islet transplantation.

Extra-skeletal effects of bisphosphonates

Bisphosphonates (BPs) are pyrophosphate analogues widely used in diseases related to bone loss and increased bone turnover. Their high affinity for bone hydroxyapatite makes them ideal agents for bone diseases, while preventing them from reaching other cells and tissues. Data of the last decade, however, have demonstrated extra-skeletal tissue deposition and a variety of non-skeletal effects have been recently recognized. As such, BPs have been shown to exert anti-tumor, immunomodulatory, anti-inflammatory and anti-diabetic effects. In addition, new delivery systems (liposomes, nanoparticles, hydrogels) are being developed in an effort to expand BPs clinical application to extra-skeletal tissues and enhance their overall therapeutic spectrum and effectiveness. In the present review, we outline current data on extra-skeletal actions of bisphosphonates and attempt to unravel the underlying pathophysiological mechanisms.

Hydrogel materials for the application of islet transplantation

Type 1 diabetes mellitus is a serious disease comprising approximately 10% of all diabetes cases, and the global incidence of type 1 diabetes mellitus is steadily rising without any promise of a cure in the near future. Although islet transplantation has proven to be an effective means of treating type 1 diabetes mellitus and promoting insulin independence in patients, its widespread implementation has been severely constrained by instances of post-transplantation islet cell death, rejection, and severe adverse immune responses. Islet encapsulation is an active area of research aimed at shielding implanted islets from immunological rejection and inflammation while still allowing for effective insulin and nutrient exchange with donor cells. Given their promising physical and chemical properties, hydrogels have been a major subject of focus in the field of islet transplantation and encapsulation technology, offering promising advances towards immunologically privileged islet implants. The present review therefore summarizes the current state of research regarding the use of hydrogels in the context of islet transplantation, including both natural molecular hydrogels and artificial polymer hydrogels, with the goal of understanding the current strengths and weaknesses of this treatment strategy.

Effects of Transplanted Islets Nano-Encapsulated with Hyperbranched Polyethylene Glycol and Heparin on Microenvironment Reconstruction and Glucose Control

The microenvironment of pancreatic islets gets disrupted during enzyme digestion and causes islets to remain in a vulnerable state, leading to poor outcome in the initial days of transplantation. To avoid immune invasion while allowing the reconstruction of the microenvironment of the transplanted site, we propose immunoisolation polymers, which can nanoencapsulate islets quickly without cytotoxicity. Here, nonhuman primate (NHP) islets were nanoencapsulated with hyperbranched polyethylene glycol (hb-PEG) and heparin by layer-by-layer technology and transplanted into the kidney subcapsular space of diabetic C57BL/6 mice. An immunosuppressive drug protocol was applied to increase the survival time until the animals were sacrificed. The recipients of NHP islets exhibited high nonfasting blood glucose level (BGL) for 2-3 weeks, which was normalized afterward. Immunohistochemical (IHC) analysis revealed an immature vascular basement membrane and cell surface integrins directly associated with poor initial insulin production. The transplanted grafts regained their own microenvironment within a month without any outside stimuli. No lymphocyte infiltration was observed in the grafts at any time. Humoral and cell-mediated immune responses were prominently diminished by the hb-PEG/Heparin nanoencapsulated islets. Immunoisolation accompanied by an immunosuppressive drug protocol protects islets by helping them avoid immunogenesis while at the same time allowing them to reconstruct their microenvironment.

Single synchronous delivery of FK506-loaded polymeric microspheres with pancreatic islets for the successful treatment of streptozocin-induced diabetes in mice

Immune rejection after transplantation is common, which leads to prompt failure of the graft. Therefore, to prolong the survival time of the graft, immunosuppressive therapy is the norm. Here, we report a robust immune protection protocol using FK506-loaded microspheres (FK506M) in injectable hydrogel. Pancreatic islets were codelivered with the FK506M into the subcutaneous space of streptozocin-induced diabetic mice. The islets codelivered with 10 mg/kg FK506M maintained normal blood glucose levels during the study period (survival rate: 60%). However, transplantation of islets and FK506M at different sites hardly controlled the blood glucose level (survival rate: 20%). Immunohistochemical analysis revealed an intact morphology of the islets transplanted with FK506M. In addition, minimal number of immune cells invaded inside the gel of the islet-FK506M group. The single injection of FK506M into the local microenvironment effectively inhibited immune rejection and prolonged the survival time of transplanted islets in a xenograft model.

Hybrid Congregation of Islet Single Cells and Curcumin-Loaded Polymeric Microspheres as an Interventional Strategy to Overcome Apoptosis Associated with Pancreatic Islets Transplantation

Hypoxic or near-anoxic conditions that occur in the core of transplanted islets induce necrosis and apoptosis during the early stages after transplantation, primarily due to loss of vascularization during the isolation process. Moreover, secretion of various cytokines from pancreatic islets is detrimental to the viability of islet cells in vitro. In this study, we aimed to protect pancreatic islet cells against apoptosis by establishing a method for in situ delivery of curcumin to the pancreatic islets. Self-assembled heterospheroids composed of pancreatic islet cells and curcumin-loaded polymeric microspheres were prepared by the three-dimensional cell culture technique. Release of curcumin in the microenvironment of pancreatic islets promoted survival of the islets. In hypoxic culture conditions, which mimic the in vivo conditions after transplantation, viability of the islets was significantly improved, as indicated by a decreased expression of pro-apoptotic protein and an increased expression of anti-apoptotic protein. Additionally, oxidative stress-induced cell death was suppressed. Thus, unlike co-transplantation of pancreatic islets and free microspheres, which provided a wide distribution of microspheres throughout the transplanted area, the heterospheroid transplantation resulted in colocalization of pancreatic islet cells and microspheres, thereby exerting beneficial effects on the cells.

Chitosan-clodronate nanoparticles loaded in poloxamer gel for intra-articular administration

This work was based on the study of an intra-articular delivery system constituted by a poloxamer gel vehiculating clodronate in chitosan nanoparticles. This system has been conceived to obtain a specific and controlled release of clodronate in the joints to reduce the arthritis rheumatoid degenerative effect. Clodronate (CLO) is a first-generation bisphosphonate with anti-inflammatory properties, inhibiting the cytokine and NO secretion from macrophages, therefore causing apoptosis in these cells. This is related to its ability to be metabolized by cells and converted into a cytotoxic intermediate as a non-hydrolysable analogue of ATP. Chitosan (CHI) was used to develop nanosystems, by ionotropic gelation induced by clodronate itself. A fractional factorial experimental design allowed us to obtain nanoparticles, the diameter of which ranged from 200 to 300nm. Glutaraldehyde was used to increase nanoparticle stability and modify the drug release profile. The zeta potential value of crosslinked nanopaparticles was 21.0mV±1.3, while drug loading was 31.0%±5.4 w/w; nanoparticle yield was 18.2%±1.8 w/w, the encapsulation efficiency was 48.8%±9.9 w/w. Nanoparticles were homogenously loaded in a poloxamer sol, and the drug delivery system is produced in-situ after local administration, when sol become gel at physiological temperature. The properties of poloxamer gels containing CHI-CLO nanoparticles, such as viscosity, gelation temperature and drug release properties, were evaluated. In vitro studies were conducted to evaluate the effects of these nanoparticles on a human monocytic cell line (THP1). The results showed that this drug delivery system is more efficient, with respect to the free drug, to counteract the inflammatory process characteristic of several degenerative diseases.

Combination strategy of multi-layered surface camouflage using hyperbranched polyethylene glycol and immunosuppressive drugs for the prevention of immune reactions against transplanted porcine islets

This study suggests a novel method of stabilizing fragile porcine islets to prevent the dissociation after isolation and reducing immune cell invasion in a combination therapy of 'surface camouflaging' and immunosuppressive drugs (FK506, Rapamycin, MR-1, anti-CD19 mAb, and Clodrosome(®)) to effectively alleviate overall immune reactions against xenotransplanted porcine islets. The surface camouflage of pancreatic islets using biocompatible materials improved stabilization of pancreatic islet and prevented the infiltration of immune cells. Firstly, the surface of porcine islets was camouflaged by SH-6-arm-PEG-lipid and gelatin-catechol (artificial extracellular matrix) in order to stabilize the fragile isolated islets. Secondly, three different PEG layers (6-arm-PEG-SH, 6-arm-PEG-catechol, and linear PEG-SH) were chemically conjugated onto the surface of the stabilized porcine islets. Both artificial extracellular matrix (artificial ECM) and PEGylation effectively covered the surface of porcine islets without increasing the size of the whole islet. In addition, the viability and functionality of the islets were not affected by this multi-layer surface modification. The multi-layer modification significantly reduced the attachment of human serum albumin, fibronectin, and immunoglobulin G in comparison to the control collagen surface. The combination effect of multi-layer PEGylation and cocktailed immunosuppressive drugs on the survival time of the transplanted islets was assessed in a xenogeneic porcine-to-mouse model. The median survival time (MST) of 'artificial ECM + PEGylation' group was 4-fold increased compared to that of control group. In addition, the MST of 'artificial ECM + PEGylation + drug' group was 2.16-fold increased, compared to the 'control + drug' group. In conclusion, we proposed a novel porcine islet transplantation protocol using surface multi-layer modification and cocktailed immunosuppressive drugs, for stabilization and immunoprotection against xenogeneic immune reactions.

Using a peptide segment to covalently conjugate doxorubicin and taxol for the study of drug combination effect

Doxorubicin (Dox) and Taxol can be covalently bonded to the same peptide segment via proper structural modification.