Survival of Macroencapsulated Allogeneic Parathyroid Tissue One Year after Transplantation in Nonimmunosuppressed Humans

Electrocatalytic on-site oxygenation for transplanted cell-based-therapies

Implantable cell therapies and tissue transplants require sufficient oxygen supply to function and are limited by a delay or lack of vascularization from the transplant host. Previous exogenous oxygenation strategies have been bulky and had limited oxygen production or regulation. Here, we show an electrocatalytic approach that enables bioelectronic control of oxygen generation in complex cellular environments to sustain engineered cell viability and therapy under hypoxic stress and at high cell densities. We find that nanostructured sputtered iridium oxide serves as an ideal catalyst for oxygen evolution reaction at neutral pH. We demonstrate that this approach exhibits a lower oxygenation onset and selective oxygen production without evolution of toxic byproducts. We show that this electrocatalytic on site oxygenator can sustain high cell loadings (>60k cells/mm3) in hypoxic conditions in vitro and in vivo. Our results showcase that exogenous oxygen production devices can be readily integrated into bioelectronic platforms, enabling high cell loadings in smaller devices with broad applicability.

Recent advances in endocrine organoids for therapeutic application

The endocrine system, consisting of the hypothalamus, pituitary, endocrine glands, and hormones, plays a critical role in hormone metabolic interactions. The complexity of the endocrine system is a significant obstacle to understanding and treating endocrine disorders. Notably, advances in endocrine organoid generation allow a deeper understanding of the endocrine system by providing better comprehension of molecular mechanisms of pathogenesis. Here, we highlight recent advances in endocrine organoids for a wide range of therapeutic applications, from cell transplantation therapy to drug toxicity screening, combined with development in stem cell differentiation and gene editing technologies. In particular, we provide insights into the transplantation of endocrine organoids to reverse endocrine dysfunctions and progress in developing strategies for better engraftments. We also discuss the gap between preclinical and clinical research. Finally, we provide future perspectives for research on endocrine organoids for the development of more effective treatments for endocrine disorders.

Cell delivery systems: Toward the next generation of cell therapies for type 1 diabetes

Immunoprotection and oxygen supply are vital in implementing a cell therapy for type 1 diabetes (T1D). Without these features, the transplanted islet cell clusters will be rejected by the host immune system, and necrosis will occur due to hypoxia. The use of anti-rejection drugs can help protect the transplanted cells from the immune system; yet, they also may have severe side effects. Cell delivery systems (CDS) have been developed for islet transplantation to avoid using immunosuppressants. CDS provide physical barriers to reduce the immune response and chemical coatings to reduce host fibrotic reaction. In some CDS, there is architecture to support vascularization, which enhances oxygen exchange. In this review, we discuss the current clinical and preclinical studies using CDS without immunosuppression as a cell therapy for T1D. We find that though CDS have been demonstrated for their ability to support immunoisolation of the grafted cells, their functionality has not been fully optimized. Current advanced methods in clinical trials demonstrate the systems are partly functional, physically complicated to implement or inefficient. However, modifications are being made to overcome these issues.

Parathyroid Allotransplantation: A Systematic Review

Background: To date, there is no satisfactory treatment for patients with calcium and vitamin D supplementation refractive hypoparathyroidism. Parathyroid allotransplantation by design is a one-time cure through its restoration of the parathyroid function and, therefore, could be the solution. A systematic literature review is conducted in the present paper, with the aim of outlining the possibilities of parathyroid allotransplantation and to calculate its efficacy. Additionally, various transplantation characteristics are linked to success. Methods: This review is carried out according to the PRISMA statement and checklist. Relevant articles were searched for in medical databases with the most recent literature search performed on 9 December 2021. Results: In total, 24 articles involving 22 unique patient cohorts were identified with 203 transplantations performed on 148 patients. Numerous types of (exploratory) interventions were carried out with virtually no protocols that were alike: there was the use of (non-) cryopreserved parathyroid tissue combined with direct transplantation or pretreatment using in vitro techniques, such as culturing cells and macro-/microencapsulation. The variability increased further when considering immunosuppression, graft histology, and donor–recipient compatibility, but this was found to be reported in its entirety by exception. As a result of the large heterogeneity among studies, we constructed our own criterium for transplantation success. With only the studies eligible for our assessment, the pooled success rate for parathyroid allotransplantation emerged to be 46% (13/28 transplantations) with a median follow-up duration of 12 months (Q1–Q3: 8–24 months). Conclusions: Manifold possibilities have been explored around parathyroid allotransplantation but are presented as a double-edged sword due to high clinical diverseness, low expertise in carrying out the procedure, and unsatisfactory study quality. Transplantations carried out with permanent immunosuppression seem to be the most promising, but, in its current state, little could be said about the treatment efficacy with a high quality of evidence. Of foremost importance in pursuing the answer whether parathyroid allotransplantation is a suitable treatment for hypoparathyroidism, a standardized definition of transplantation success must be established with a high-quality trial.

Parathyroid allotransplantation for the treatment of permanent hypoparathyroidism: A systematic review

BACKGROUND

Hypoparathyroidism is the most common complication of bilateral operations in the central neck. No formal guidelines exist for the management of permanent hypoparathyroidism. Current treatment involving medical supplementation increases resource utilization and patient morbidity while decreasing quality of life. Parathyroid allotransplant (PA) offers a promising therapy; however, the optimal technique and role of immunosuppression (IS) in PA remain unclear.

METHODS

We performed a systematic search of the Embase, MEDLINE, and Cochrane Library databases to identify studies investigating PA for treatment of hypoparathyroidism.

RESULTS

A total of 24 studies including 186 individual allograft transplants in 146 patients were identified. Pooled graft survival for allotransplants in transplant-naïve vs prior transplant recipients was 29.9% and 80%, respectively.

CONCLUSIONS

PA using normocellular, fresh parathyroid donor tissue that is ABO-compatible, with induction and, at minimum, short-term maintenance IS presents a potentially safe and effective therapeutic option for permanent hypoparathyroidism in patients tolerating IS.

Sustained subcutaneous delivery of secretome of human cardiac stem cells promotes cardiac repair following myocardial infarction

AIMS

To establish pre-clinical proof of concept that sustained subcutaneous delivery of the secretome of human cardiac stem cells (CSCs) can be achieved in vivo to produce significant cardioreparative outcomes in the setting of myocardial infarction.

METHODS AND RESULTS

Rats were subjected to permanent ligation of left anterior descending coronary artery and randomized to receive subcutaneous implantation of TheraCyte devices containing either culture media as control or 1 × 106 human W8B2+ CSCs, immediately following myocardial ischaemia. At 4 weeks following myocardial infarction, rats treated with W8B2+ CSCs encapsulated within the TheraCyte device showed preserved left ventricular ejection fraction. The preservation of cardiac function was accompanied by reduced fibrotic scar tissue, interstitial fibrosis, cardiomyocyte hypertrophy, as well as increased myocardial vascular density. Histological analysis of the TheraCyte devices harvested at 4 weeks post-implantation demonstrated survival of human W8B2+ CSCs within the devices, and the outer membrane was highly vascularized by host blood vessels. Using CSCs expressing plasma membrane reporters, extracellular vesicles of W8B2+ CSCs were found to be transferred to the heart and other organs at 4 weeks post-implantation. Furthermore, mass spectrometry-based proteomic profiling of extracellular vesicles of W8B2+ CSCs identified proteins implicated in inflammation, immunoregulation, cell survival, angiogenesis, as well as tissue remodelling and fibrosis that could mediate the cardioreparative effects of secretome of human W8B2+ CSCs.

CONCLUSIONS

Subcutaneous implantation of TheraCyte devices encapsulating human W8B2+ CSCs attenuated adverse cardiac remodelling and preserved cardiac function following myocardial infarction. The TheraCyte device can be employed to deliver stem cells in a minimally invasive manner for effective secretome-based cardiac therapy.

Tissue-engineered parathyroid gland and its regulatory secretion of parathyroid hormone

Parathyroid glands (PTGs) are important endocrine organs being mainly responsible for the secretion of parathyroid hormone (PTH) to regulate the balance of calcium (Ca) /phosphorus (P) ions in the body. Once PTGs get injured or removed, their resulting defect or loss of PTH secretion should disturb the level of Ca/P in blood, thus damaging other related organs (bone, kidney, etc.) and even causing death. Recently, tissue-engineered PTGs (TE-PTGs) have attracted lots of attention as a potential treatment for the related diseases of PTGs caused by hypoparathyroidism and hyperparathyroidism, including tetany, muscle cramp, nephrolithiasis, nephrocalcinosis, and osteoporosis. Although great progress has been made in the establishment of TE-PTGs with an effective strategy to integrate the key factors of cells and biomaterials, its regulatory secretion of PTH to mimic its natural rhythms in the body remains a huge challenge. This review comprehensively describes an overview of PTGs from physiology and pathology to cytobiology and tissue engineering. The state of the arts in TE-PTGs and the feasible strategies to regulate PTH secretion behaviors are highlighted to provide an important foundation for further investigation.

The effectiveness of parathyroid gland autotransplantation in preserving parathyroid function during thyroid surgery for thyroid neoplasms: A meta-analysis

Objective

We conducted this meta-analysis to assess the effectiveness of parathyroid gland autotransplantation in preserving parathyroid function during thyroid surgery for thyroid neoplasms.

Methods

We conducted a search by using PubMed, Embase, and the Cochrane Library electronic databases for studies that were published up to January 2019. The reference lists of the retrieved articles were also reviewed. Two authors independently assessed the methodological quality and extracted the data. A random-effects model was used to calculate the overall combined risk estimates. Publication bias was evaluated with a funnel plot using Egger’s and Begg’s tests.

Results

A total of 25 independent studies involving 10,531 participants were included in the meta-analysis. Compared with patients who did not undergo parathyroid gland autotransplantation, the overall pooled relative risks for patients who underwent parathyroid gland autotransplantation were 1.75 (95% CI: 1.51–2.02, p<0.001) for postoperative hypoparathyroidism, 1.72 (95% CI: 1.45–2.05, p<0.001) for protracted hypoparathyroidism, 1.06 (95% CI: 0.44–2.58, p = 0.894) and 0.71 (95% CI: 0.22–2.29, p = 0.561) for biochemical hypoparathyroidism and biochemical hypocalcemia at 6 months postoperatively, respectively, and 1.89 (95% CI: 1.33–2.69, p<0.001) and 0.22 (95% CI: 0.09–0.52, p = 0.001) for biochemical hypoparathyroidism and biochemical hypocalcemia at 12 months postoperatively, respectively. The pooled relative risks for patients who underwent one parathyroid gland autotransplantation and patients who underwent two or more parathyroid gland autotransplantations were 1.71 (95% CI: 1.25–2.35, p = 0.001) and 2.22 (95% CI: 1.43–3.45, p<0.001) for postoperative hypoparathyroidism, 1.09 (95% CI: 0.59–2.01, p = 0.781) and 0.55 (95% CI: 0.16–1.87, p = 0.341) for hypoparathyroidism at 6 months postoperatively compared with those of patients who did not undergo parathyroid gland autotransplantation.

Conclusions

Parathyroid gland autotransplantation is significantly associated with increased risk of postoperative and protracted hypoparathyroidism, and the number of autoplastic parathyroid glands is positively correlated with the incidence of postoperative hypoparathyroidism.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Transplantation of macroencapsulated human islets within the bioartificial pancreas βAir to patients with type 1 diabetes mellitus

Macroencapsulation devices provide the dual possibility of immunoprotecting transplanted cells while also being retrievable, the latter bearing importance for safety in future trials with stem cell-derived cells. However, macroencapsulation entails a problem with oxygen supply to the encapsulated cells. The βAir device solves this with an incorporated refillable oxygen tank. This phase 1 study evaluated the safety and efficacy of implanting the βAir device containing allogeneic human pancreatic islets into patients with type 1 diabetes. Four patients were transplanted with 1-2 βAir devices, each containing 155 000-180 000 islet equivalents (ie, 1800-4600 islet equivalents per kg body weight), and monitored for 3-6 months, followed by the recovery of devices. Implantation of the βAir device was safe and successfully prevented immunization and rejection of the transplanted tissue. However, although beta cells survived in the device, only minute levels of circulating C-peptide were observed with no impact on metabolic control. Fibrotic tissue with immune cells was formed in capsule surroundings. Recovered devices displayed a blunted glucose-stimulated insulin response, and amyloid formation in the endocrine tissue. We conclude that the βAir device is safe and can support survival of allogeneic islets for several months, although the function of the transplanted cells was limited (Clinicaltrials.gov: NCT02064309).

Current advanced therapy cell-based medicinal products for type-1-diabetes treatment

In the XXI century diabetes mellitus has become one of the main threats to human health with higher incidence in regions such as Europe and North America. Type 1 diabetes mellitus (T1DM) occurs as a consequence of the immune-mediated destruction of insulin producing β-cells located in the endocrine part of the pancreas, the islets of Langerhans. The administration of exogenous insulin through daily injections is the most prominent treatment for T1DM but its administration is frequently associated to failure in glucose metabolism control, finally leading to hyperglycemia episodes. Other approaches have been developed in the past decades, such as whole pancreas and islet allotransplantation, but they are restricted to patients who exhibit frequent episodes of hypoglycemia or renal failure because the lack of donors and islet survival. Moreover, patients transplanted with either whole pancreas or islets require of immune suppression to avoid the rejection of the transplant. Currently, advanced therapy medicinal products (ATMP), such as implantable devices, have been developed in order to reduce immune rejection response while increasing cell survival. To overcome these issues, ATMPs must promote vascularization, guaranteeing the nutritional contribution, while providing O₂ until vasculature can surround the device. Moreover, it should help in the immune-protection to avoid acute and chronic rejection. The transplanted cells or islets should be embedded within biomaterials with tunable properties like injectability, stiffness and porosity mimicking natural ECM structural characteristics. And finally, an infinitive cell source that solves the donor scarcity should be found such as insulin producing cells derived from mesenchymal stem cells (MSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Several companies have registered their ATMPs and future studies envision new prototypes. In this review, we will discuss the mechanisms and etiology of diabetes, comparing the clinical trials in the last decades in order to define the main characteristics for future ATMPs.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

[Allogeneic parathyroid: 2-year follow-up]

BACKGROUND

Hypoparathyroidism is one of the most frequent complications of neck surgery. The treatment is currently medical; however this involves several complications secondary to high doses of calcium and vitamin D, thus making parathyroid allotransplantation a good management option.

MATERIAL AND METHODS

Patients with hypoparathyroidism were selected in the April-December period of 2011 in the general surgical clinic. They were between 16 and 65 years, and ingested high doses of calcium. The donors were patients with primary and secondary hyperparathyroidism, and the transplants were performed in relation to blood group and human leucocyte antigen.

RESULTS

Five parathyroid allografts were performed. All the patients had iatrogenic hypoparathyroidism, all women with a mean age of 49.8 years. The graft was implanted under local anaesthesia in the non-dominant forearm. Four of the patients are so far considered functional due to the increase in paratohormone, and demonstrating its function by scintigraphy with sestamibi. One of the patients showed no increase in paratohormone or imaging studies that demonstrate its functionality. After a two year follow up the graft remains functional but with with oral calcium intake at a lower dose than before transplantation. None of the patients had immunosuppression side effects.

CONCLUSIONS

In this study, allogeneic unrelated living parathyroid transplant with an immunosuppressive regimen of six months has proven to be a safe alternative treatment to improve quality of life by decreasing the excessive calcium intake and improving physical activity with adequate graft survival at 24 months follow up.

Treating diet-induced diabetes and obesity with human embryonic stem cell-derived pancreatic progenitor cells and antidiabetic drugs

Human embryonic stem cell (hESC)-derived pancreatic progenitor cells effectively reverse hyperglycemia in rodent models of type 1 diabetes, but their capacity to treat type 2 diabetes has not been reported. An immunodeficient model of type 2 diabetes was generated by high-fat diet (HFD) feeding in SCID-beige mice. Exposure to HFDs did not impact the maturation of macroencapsulated pancreatic progenitor cells into glucose-responsive insulin-secreting cells following transplantation, and the cell therapy improved glucose tolerance in HFD-fed transplant recipients after 24 weeks. However, since diet-induced hyperglycemia and obesity were not fully ameliorated by transplantation alone, a second cohort of HFD-fed mice was treated with pancreatic progenitor cells combined with one of three antidiabetic drugs. All combination therapies rapidly improved body weight and co-treatment with either sitagliptin or metformin improved hyperglycemia after only 12 weeks. Therefore, a stem cell-based therapy may be effective for treating type 2 diabetes, particularly in combination with antidiabetic drugs.

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High-fat diets (HFDs) caused rapid metabolic dysfunction in immunodeficient mice

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HFDs and/or antidiabetic drugs did not affect function of hESC-derived beta cells

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hESC-derived beta cells improved glucose tolerance in HFD-fed mice

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Cell therapy combined with an antidiabetic drug was the most effective treatment

Oxygen supply to encapsulated therapeutic cells

Therapeutic cells encapsulated in immunobarrier devices have promise for treatment of a variety of human diseases without immunosuppression. The absence of sufficient oxygen supply to maintain viability and function of encapsulated tissue has been the most critical impediment to progress. Within the framework of oxygen supply limitations, we review the major issues related to development of these devices, primarily in the context of encapsulated islets of Langerhans for treating diabetes, including device designs and materials, supply of tissue, protection from immune rejection, and maintenance of cell viability and function. We describe various defensive measures investigated to enhance survival of transplanted tissue, and we review the diverse approaches to enhancement of oxygen transport to encapsulated tissue, including manipulation of diffusion distances and oxygen permeability of materials, induction of neovascularization with angiogenic factors and vascularizing membranes, and methods for increasing the oxygen concentration adjacent to encapsulated tissue so as to exceed that in the microvasculature. Recent developments, particularly in this latter area, suggest that the field is ready for clinical trials of encapsulated therapeutic cells to treat diabetes.

Human embryonic stem cell derived islet progenitors mature inside an encapsulation device without evidence of increased biomass or cell escape

There are several challenges to successful implementation of a cell therapy for insulin dependent diabetes derived from human embryonic stem cells (hESC). Among these are development of functional insulin producing cells, a clinical delivery method that eliminates the need for chronic immunosuppression, and assurance that hESC derived tumors do not form in the patient. We and others have shown that encapsulation of cells in a bilaminar device (TheraCyte) provides immunoprotection in rodents and primates. Here we monitored human insulin secretion and employed bioluminescent imaging (BLI) to evaluate the maturation, growth, and containment of encapsulated islet progenitors derived from CyT49 hESC, transplanted into mice. Human insulin was detectable by 7 weeks post-transplant and increased 17-fold over the course of 8 weeks, yet during this period the biomass of encapsulated cells remained constant. Remarkably, by 20 weeks post-transplant encapsulated cells secreted sufficient levels of human insulin to ameliorate alloxan induced diabetes. Further, bioluminescent imaging revealed for the first time that hESCs remained fully contained in encapsulation devices for up to 150 days, the longest period tested. Collectively, the data suggest that encapsulated hESC derived islet progenitors hold great promise as an effective and safe cell replacement therapy for insulin dependent diabetes.

Bioengineered sites for islet cell transplantation

Although islet transplantation has demonstrated its potential use in treating type 1 diabetes, this remains limited by the need for daily immunosuppression. Islet encapsulation was then proposed with a view to avoiding any immunosuppressive regimen and related side effects. In order to obtain a standard clinical procedure in terms of safety and reproducibility, two important factors have to be taken into account: the encapsulation design (which determines the graft volume) and the implantation site. Indeed, the implantation site should meet certain requirements: (1) its space must be large enough for the volume of transplanted tissues; (2) there must be proximity to abundant vascularization with a good oxygen supply; (3) there must be real-time access to physiologically representative blood glucose levels; (4) there must be easy access for implantation and the reversibility of the procedure (for safety); and finally, (5) the site should have minimal early inflammatory reaction and promote long-term survival. The aim of this article is to review possible preclinical/clinical implantation sites (in comparison with free islets) for encapsulated islet transplantation as a function of the encapsulation design: macro/microcapsules and conformal coating.

The TheraCyte™ device protects against islet allograft rejection in immunized hosts

Clinically, many candidates for islet transplantation are already immunized, which increases their risk of graft rejection. Encapsulation of pancreatic islets using the TheraCyte™ device has been shown to protect against allograft rejection in nonimmunized recipients. However, the capacity of the TheraCyte™ device to prevent rejection in immunized recipients has not yet been studied. In this study, the protective capacity of the TheraCyte™ device was evaluated in an allogeneic rat model. Lewis rats were used as islet donors, and nonimmunized (control) and alloimmunized, diabetic Wistar-Furth (WF) rats were used as recipients. Graft survival was shorter in immunized recipients than in nonimmunized recipients (mean survival, 5.3 ± 2.7 and 9.3 ± 1.6 days, respectively, p < 0.01) when nonencapsulated islets were transplanted under the kidney capsule. When islets were transplanted into the TheraCyte™ device, graft function was maintained during the 6-month study period in both immunized and nonimmunized rats. In oral glucose tolerance tests performed at 1 month after transplantation, both groups had similar insulin and blood glucose levels indicating similar metabolic functions. Volume densities and absolute volumes of tissue inside the devices 6 months after transplantation were also comparable between the two groups, indicating that both groups maintained similar amounts of endocrine tissue. A higher number of IFN-γ-producing CD8+ T-cells were detected in immunized WF rats compared to control WF rats transplanted with encapsulated islets. This suggests that donor-specific alloreactivity in recipient rats was sustained throughout the study period. This study suggests that the TheraCyte™ device protects islet allografts also in immunized recipients. Our results further highlight the potential for using macroencapsulation to avoid immunosuppressive therapy in clinical islet transplantation.

Concise review: pancreas regeneration: recent advances and perspectives

The replacement of functional pancreatic β-cells is seen as an attractive potential therapy for diabetes, because diabetes results from an inadequate β-cell mass. Inducing replication of the remaining β-cells and new islet formation from progenitors within the pancreas (neogenesis) are the most direct ways to increase the β-cell mass. Stimulation of both replication and neogenesis have been reported in rodents, but their clinical significance must still be shown. Because human islet transplantation is limited by the scarcity of donors and graft failure within a few years, efforts have recently concentrated on the use of stem cells to replace the deficient β-cells. Currently, embryonic stem cells and induced pluripotent stem cells achieve high levels of β-cell differentiation, but their clinical use is still hampered by ethical issues and/or the risk of developing tumors after transplantation. Pancreatic epithelial cells (duct, acinar, or α-cells) represent an appealing alternative to stem cells because they demonstrate β-cell differentiation capacities. Yet translation of such capacity to human cells after significant in vitro expansion has yet to be achieved. Besides providing new β-cells, cell therapy also has to address the question on how to protect the transplanted cells from destruction by the immune system via either allo- or autoimmunity. Encouraging developments have been made in encapsulation and immunomodulation techniques, but many challenges still remain. Herein, we discuss recent advances in the search for β-cell replacement therapies, current strategies for circumventing the immune system, and mandatory steps for new techniques to be translated from bench to clinics.

Synthesis of magnetic resonance-, X-ray- and ultrasound-visible alginate microcapsules for immunoisolation and noninvasive imaging of cellular therapeutics

Cell therapy has the potential to treat or cure a wide variety of diseases. Non-invasive cell tracking techniques are, however, necessary to translate this approach to the clinical setting. This protocol details methods to create microcapsules that are visible by X-ray, ultrasound (US) or magnetic resonance (MR) for the encapsulation and immunoisolation of cellular therapeutics. Three steps are generally used to encapsulate cellular therapeutics in an alginate matrix: (i) droplets of cell-containing liquid alginate are extruded, using an electrostatic generator, through a needle tip into a solution containing a dissolved divalent cation salt to form a solid gel; (ii) the resulting gelled spheres are coated with polycations as a cross-linker; and (iii) these complexes are then incubated in a second solution of alginate to form a semipermeable membrane composed of an inner and an outer layer of alginate. The microcapsules can be rendered visible during the first step by adding contrast agents to the primary alginate layer. Such contrast agents include superparamagnetic iron oxide for detection by (1)H MR imaging (MRI); the radiopaque agents barium or bismuth sulfate for detection by X-ray modalities; or perfluorocarbon emulsions for multimodal detection by (19)F MRI, X-ray and US imaging. The entire synthesis can be completed within 2 h.

Induction of tolerance to parental parathyroid grafts using allogeneic thymus tissue in patients with DiGeorge anomaly

DiGeorge anomaly can affect both thymic and parathyroid function. Although athymia is corrected by allogeneic thymus transplantation, treatment options for hypoparathyroidism have been unsatisfactory. Parathyroid transplantation offers the potential for definitive cure but remains challenging because of graft rejection. Some allogeneic parathyroid grafts have functioned in adult recipients in the context of immunosuppression for renal transplantation. Other efforts have attempted to reduce the allogenicity of the parathyroid grafts through manipulation of the parathyroid tissues before transplantation (by using encapsulation or special culture techniques). Recently, we demonstrated the efficacy of parental parathyroid transplantation when combined with allogeneic thymus transplantation in an infant with complete DiGeorge anomaly. The recipient developed tolerance toward the parathyroid donor. The parathyroid graft has functioned for 5 years after transplantation without the need for continued immunosuppression or calcium supplementation. We observed that matching of the allogeneic thymus graft to the parathyroid donor HLA class II alleles that are unshared with the recipient appears to be associated with the induction of tolerance toward the parathyroid graft. Further work is needed to determine the optimal means for using combined allogeneic thymus and parental parathyroid transplantation to correct hypoparathyroidism in patients with both complete and partial DiGeorge anomaly.

Improving islet transplantation: a road map for a widespread application for the cure of persons with type I diabetes

PURPOSE OF REVIEW

The widespread application of replacement therapies for type I diabetes is at present limited by the side-effects of systemic immunosuppression. Results obtained in several animal models show that islet encapsulation can control the rejection process without systemic side-effects. However, results have, in general, been disappointing when transferred to large animal models or to humans.

RECENT FINDINGS

Growing insights into how cells respond to mechanical forces and surrounding extracellular matrixes indicate that differences in the Young's modulus (the resistance to deformation) between the implanted biomaterial and surrounding tissues induce inflammation and fibrosis. A valid approach would be to select for implantation a tissue having a higher value of the Young's modulus, for example, bone, allowing direct contact with the highly vascularized bone marrow providing nutrient and oxygen support as well as a rapid distribution of released insulin to the systemic circulation.

SUMMARY

Development of a biochamber with bone-integrating properties will allow initiation of clinical trials with allogeneic human islets, xenogeneic pig islets or insulin-producing cells generated from human embryonic stem cell (hESC)/inducible pluripotent stem cell (iPSC).

Cell microencapsulation

In the past several decades, many attempts have been made to prevent the rejection of transplanted cells by the immune system. Cell encapsulation is primary machinery for cell transplantation and new materials and approaches were developed to encapsulate various types of cells to treat a wide range of diseases. This technology involves placing the transplanted cells within a biocompatible membrane in attempt to isolate the cells from the host immune attack and enhance or prolong their function in vivo. In this chapter, we will review the situation of cell microencapsulation field and discuss its potentials and challenges for cell therapy and regeneration of tissue function.

Human beta-cell precursors mature into functional insulin-producing cells in an immunoisolation device: implications for diabetes cell therapies

BACKGROUND

Islet transplantation is limited by the need for chronic immunosuppression and the paucity of donor tissue. As new sources of human beta-cells are developed (e.g., stem cell-derived tissue), transplanting them in a durable device could obviate the need for immunosuppression, while also protecting the patient from any risk of tumorigenicity. Here, we studied (1) the survival and function of encapsulated human beta-cells and their progenitors and (2) the engraftment of encapsulated murine beta-cells in allo- and autoimmune settings.

METHODS

Human islets and human fetal pancreatic islet-like cell clusters were encapsulated in polytetrafluorethylene devices (TheraCyte) and transplanted into immunodeficient mice. Graft survival and function was measured by immunohistochemistry, circulating human C-peptide levels, and blood glucose levels. Bioluminescent imaging was used to monitor encapsulated neonatal murine islets.

RESULTS

Encapsulated human islet-like cell clusters survived, replicated, and acquired a level of glucose responsive insulin secretion sufficient to ameliorate hyperglycemia in diabetic mice. Bioluminescent imaging of encapsulated murine neonatal islets revealed a dynamic process of cell death followed by regrowth, resulting in robust long-term allograft survival. Further, in the non-obese diabetic (NOD) mouse model of type I diabetes, encapsulated primary beta-cells ameliorated diabetes without stimulating a detectable T-cell response.

CONCLUSIONS

We demonstrate for the first time that human beta-cells function is compatible with encapsulation in a durable, immunoprotective device. Moreover, our study suggests that encapsulation of beta-cells before terminal differentiation will be a successful approach for new cell-based therapies for diabetes, such as those derived from stem cells.

Preimplantation of an immunoprotective device can lower the curative dose of islets to that of free islet transplantation: studies in a rodent model

Islet graft survival inside macroencapsulation devices is suboptimal. We hypothesized that induction of neovascularization by preimplantation of devices would improve the physiological conditions, thereby lowering the number of islets required for cure. Several rat islets were transplanted to TheraCyte immunoprotective devices implanted subcutaneously in diabetic athymic mice. Cure rates in the groups with preimplanted devices were significantly better than in those with freshly implanted devices (375 islets: 8/8 vs. 1/6, P=0.003; 125 islets: 6/6 vs. 0/7, P=0.001). Morphometric evaluations of the 125 islet groups showed higher fractional and absolute volumes of endocrine tissue in the group with preimplanted devices (P<0.001 and P=0.035, respectively). In the following dose titration study, using preimplanted devices, as low as 50 islets cured diabetic mice (100% cure, n=6). We conclude that preimplantation significantly lowers the curative dose of macroencapsulated islets to levels resembling those of free islets transplanted under the renal capsule.

Treatment of diabetic rats with encapsulated islets

Immunoprotection of islets using bioisolator systems permits introduction of allogeneic cells to diabetic patients without the need for immunosuppression. Using TheraCyte™ immunoisolation devices, we investigated two rat models of type 1 diabetes mellitus (T1DM), BB rats and rats made diabetic by streptozotocin (STZ) treatment. We chose to implant islets after the onset of diabetes to mimic the probable treatment of children with T1DM as they are usually diagnosed after disease onset. We encapsulated 1000 rat islets and implanted them subcutaneously (SQ) into diabetic biobreeding (BB) rats and STZ-induced diabetic rats, defined as two or more consecutive days of blood glucose >350 mg/dl. Rats were monitored for weight and blood glucose. Untreated BB rats rapidly lost weight and were euthanized at >20% weight loss that occurred between 4 and 10 days from implantation. For period of 30–40 days following islet implantation weights of treated rats remained steady or increased. Rapid weight loss occurred after surgical removal of devices that contained insulin positive islets. STZ-treated rats that received encapsulated islets showed steady weight gain for up to 130 days, whereas untreated control rats showed steady weight loss that achieved >20% at around 55 days. Although islet implants did not normalize blood glucose, treated rats were apparently healthy and groomed normally. Autologous or allogeneic islets were equally effective in providing treatment. TheraCyte™ devices can sustain islets, protect allogeneic cells from immune attack and provide treatment for diabetic-mediated weight loss in both BB rats and STZ-induced diabetic rats.

Challenges and emerging technologies in the immunoisolation of cells and tissues

Protection of transplanted cells from the host immune system using immunoisolation technology will be important in realizing the full potential of cell-based therapeutics. Microencapsulation of cells and cell aggregates has been the most widely explored immunoisolation strategy, but widespread clinical application of this technology has been limited, in part, by inadequate transport of nutrients, deleterious innate inflammatory responses, and immune recognition of encapsulated cells via indirect antigen presentation pathways. To reduce mass transport limitations and decrease void volume, recent efforts have focused on developing conformal coatings of micron and submicron scale on individual cells or cell aggregates. Additionally, anti-inflammatory and immunomodulatory capabilities are being integrated into immunoisolation devices to generate bioactive barriers that locally modulate host responses to encapsulated cells. Continued exploration of emerging paradigms governed by the inherent challenges associated with immunoisolation will be critical to actualizing the clinical potential of cell-based therapeutics.

Allotransplantation of Cultured Parathyroid Progenitor Cells Without Immunosuppression: Clinical Results

BACKGROUND

Hypoparathyroidism is a well-known consequence of extensive thyroid and parathyroid surgery. Allotransplantation of cultured parathyroid cells can be considered as an alternative to vitamin D3 and calcium supplementation in treatment of hypoparathyroidism. We present the long-term allotransplant activity in 85 patients who had undergone cellular allotransplantation for surgical hypoparathyroidism. Also, a modified technique to prepare parathyroid explants is described for obtaining a new nonimmunogenic cell population.

METHODS

From March 1990 to December 2004, 85 patients underwent 116 allotransplantations of cultured parathyroid cells. Mean recipient age was 46.2+/-11.1 years. Donors were selected from patients undergoing parathyroidectomy for secondary and tertiary hyperparathyroidism.

RESULTS

After 6 weeks of cultivation and freezing, the parathyroid cells decreased their normal human leukocyte antigen (HLA) class I ABC expression and were free of HLA class II positive cells. The viability of cultured cells was 95.15+/-2.94%. Eighty-five patients underwent primary allotransplantation. Of these, 25 patients subsequently underwent a repeat procedure. In six cases, the parathyroid cells were obtained from the same donor and in 19 cases from a different donor. For all patients, the mean cellular allograft survival was 6.35+/-13.08 months. In 64 patients (55.1%), the allografts retained their endocrine function for more than 2 months.

CONCLUSIONS

The present study has shown that in some patients parathyroid cell allotransplantation may be considered a method of treatment for permanent hypoparathyroidism after thyroid surgery. Graft function and/or survival did not depend on the baseline viability or secretory activity of cultured cells used for transplantation.

Macroencapsulation protects against sensitization after allogeneic islet transplantation in rats

BACKGROUND

The aim of this study was to evaluate the risks of sensitization by islet grafts encapsulated in a bilaminar immunoprotective membrane.

METHODS

We studied five groups of Lewis rats: one control group (no islets), two groups that received free islets (200 or 1000 s.c.), and two groups that received encapsulated ones (200 or 1000 s.c.) from Dark Agouti (DA) rats. Four weeks later, abdominal heterotopic DA-heart transplantation was performed on the same recipients. The time-to-heart graft rejection was assessed by the cessation of heart contractions. Rejection was confirmed by histological examinations. Antidonor antibodies were determined by fluorescence activated cell sorter (FACS) analysis.

RESULTS

The control animals had a mean heart graft survival of 6.4 days. The free islet groups had significantly shorter heart graft survivals-i.e., 4.8 days (200 islets) and 1.0 day (1000 islets) (P < 0.001)-while those of the encapsulated islet groups were about the same as that of the control group-i.e., 6.4 days (200 islets) and 6.0 days (1000 islets). In the free islet groups, anti-DA antibodies developed in 7/10 (200 islets) and 8/8 (1000 islets) animals after the islet transplantation. In the encapsulated groups, 1/10 (200 islets) and 3/8 (1000 islets) animals developed anti-DA antibodies after these transplantations. All animals had anti-DA antibodies at the time of heart graft rejection. On histological examination all grafts showed various features of rejection.

CONCLUSIONS

The bilaminar membrane protects against sensitization and prevents accelerated rejection of a subsequent vascularized graft, at least during the first month after the islet transplantation.

Inducing Tolerance to a Soluble Foreign Antigen by Encapsulated Cell Transplants

The immune response to soluble antigens constitutes a current clinical problem impeding the development of protein therapeutics. We have developed an encapsulated-cell delivery system, which, transiently combined with an anti-CD154 antibody treatment, allows for the suppression of this immune response and the establishment of long-term secretion of a foreign antigen, human erythropoietin (huEPO). The chronic presence of antigen appears to be required to maintain this tolerance, as a 21-day gap in the exposure to huEPO is sufficient to restore the ability of mice to mount an antibody response. In contrast, chronic huEPO expression maintains tolerance even in the absence of further anti-CD154 treatment. These results suggest that a soluble antigenic protein can be continuously released, without inducing an antibody response, using encapsulated allogeneic cells. The temporary anti-CD154 treatment induces immune unresponsiveness to the delivered antigen, while the immunoprotected cell implant allows for chronic antigen release, favoring the establishment of tolerance.

Cell-based gene therapy experiments in murine experimental autoimmune encephalomyelitis

With the ultimate goal of developing a novel treatment for multiple sclerosis (MS), we have developed a cell-based gene therapy protocol for the treatment of murine experimental autoimmune encephalomyelitis (EAE), a powerful animal model for MS. We have determined that transduced fibroblasts secreting encephalogenic epitopes, when injected into mice with EAE, cause a striking abrogation of disease. Both myelin basic protein (MBP) and proteolipid protein mini-gene constructs expressed in syngeneic fibroblast cells were capable of ameliorating ongoing EAE induced by MBP protein. These experiments are crucial since they suggest that not all encephalogenic epitopes need be secreted for the control of disease. We also demonstrate the success of this protocol when transduced syngeneic, and most importantly, allogeneic cells are sequestered within an implantable chamber. Furthermore, we find that through modifying antigen expression by changing the signal sequence of the mini-gene construct, we were able to significantly reduce the dose of cells required for treatment. These improvements to the mini-gene delivery system are critical for the eventual translation of our protocol to the clinic.

Neovascularization of the amniotic membrane as a biological immune barrier

The clinical application of islet transplantation is limited due to the limited source and the morbidity of systemic immunosuppression to prevent rejection. The two problems can be solved by using encapsulated islets. We have used amniotic membranes as biocompatible natural immune barriers. The objective of this study was to assess the revascularization of the membrane, which is necessary to ensure islet viability when the membrane is used for islet encapsulation. The amniotic membranes, obtained from full-term pregnant female dogs, were molded to form macrocapsules, which were implanted in the peritoneal cavity. The capsules were removed after 3, 10, 15, and 30 days and examined histopathologically using hematoxylin and eosin and by immunohistochemistry for neovascularization using factor VIII to detect angiogenesis. Upon histopathological examination, all specimens showed localized, moderate inflammation and congested blood vessels with no thrombosis or rejection. There was a mild degree of fibroblast proliferation starting from day 10 to day 30. Immunohistochemical staining revealed that the number of blood vessels was 7, 11, 13, 10 per high-power microscopic field on days 3, 10, 15, and 30, respectively. We concluded from this study that implanted amniotic sac capsules were vascularized within the omental tissue from day 10 on with significant blood vessel formation starting on day 3 by immunohistochemical study.

Improved survival of macroencapsulated islets of Langerhans by preimplantation of the immunoisolating device: a morphometric study

Encapsulation of cells in a semipermeable membrane may in the future provide an opportunity to treat a variety of endocrine and neurological disorders, without the need for lifelong immunosuppression. The physiological conditions in the device are crucial factors for graft survival. Previously, we have shown that the exchange across the immunoisolating membrane and the microcirculation around the TheraCyte device increase around 3 months after implantation. The aim of this study was to determine whether preimplantation of the TheraCyte device would improve the survival of a later transplanted islet graft. A TheraCyte device was implanted SC on one side of the back of a nondiabetic SD rat. After 3 months, 1500 islets isolated from SD rats were transplanted via the device port. At the same time, another device, loaded with the same number of islets, was implanted on the other side of the back. Both devices were explanted 2 weeks after islet transplantation (i.e., 3.5 months and 0.5 month after device implantation, respectively). Six pairs of devices were evaluated by morphometery. The volume densities of viable islets were 0.22 +/- 0.04 in the preimplanted device vs. 0.06 +/- 0.03 in the nonpreimplanted one (p < 0.05). The corresponding volume densities of fibrosis and necrosis were 0.64 +/- 0.13 vs. 0.85 +/- 0.08 (p < 0.05) and 0.11 +/- 0.14 vs. 0.09 +/- 0.07 (ns), respectively. When the absolute volumes (mm3) were calculated, preimplanted devices contained 1.1 +/- 0.7 endocrine cells while nonpreimplanted ones contained 0.4 +/- 0.2 (p < 0.05). The percentages of insulin- positive beta-cells in the preimplanted versus nonpreimplanted device were 80 +/- 5% and 67 +/- 6%, respectively (p < 0.01). The corresponding volumes of fibrotic tissue were 3.0 +/- 1.8 vs. 5.2 +/- 1.2 (p < 0.05), while the amount of necrotic tissue did not differ significantly (0.42 +/- 0.5 vs. 0.50 +/- 0.3). Preimplantation of the TheraCyte device seems to improve the survival of an encapsulated islet graft and reduce fibroblast outgrowth in the device.