Human islet cell implants in a nude rat model of diabetes survive better in omentum than in liver with a positive influence of beta cell number and purity

Non-invasive quantification of stem cell-derived islet graft size and composition

AIMS/HYPOTHESIS

Stem cell-derived islets (SC-islets) are being used as cell replacement therapy for insulin-dependent diabetes. Non-invasive long-term monitoring methods for SC-islet grafts, which are needed to detect misguided differentiation in vivo and to optimise their therapeutic effectiveness, are lacking. Positron emission tomography (PET) has been used to monitor transplanted primary islets. We therefore aimed to apply PET as a non-invasive monitoring method for SC-islet grafts.

METHODS

We implanted different doses of human SC-islets, SC-islets derived using an older protocol or a state-of-the-art protocol and SC-islets genetically rendered hyper- or hypoactive into mouse calf muscle to yield different kinds of grafts. We followed the grafts with PET using two tracers, glucagon-like peptide 1 receptor-binding [18F]F-dibenzocyclooctyne-exendin-4 ([18F]exendin) and the dopamine precursor 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine ([18F]FDOPA), for 5 months, followed by histological assessment of graft size and composition. Additionally, we implanted a kidney subcapsular cohort with different SC-islet doses to assess the connection between C-peptide and stem cell-derived beta cell (SC-beta cell) mass.

RESULTS

Small but pure and large but impure grafts were derived from SC-islets. PET imaging allowed detection of SC-islet grafts even <1 mm3 in size, [18F]exendin having a better detection rate than [18F]FDOPA (69% vs 44%, <1 mm3; 96% vs 85%, >1 mm3). Graft volume quantified with [18F]exendin (r2=0.91) and [18F]FDOPA (r2=0.86) strongly correlated with actual graft volume. [18F]exendin PET delineated large cystic structures and its uptake correlated with graft SC-beta cell proportion (r2=0.68). The performance of neither tracer was affected by SC-islet graft hyper- or hypoactivity. C-peptide measurements under fasted or glucose-stimulated conditions did not correlate with SC-islet graft volume or SC-beta cell mass, with C-peptide under hypoglycaemia having a weak correlation with SC-beta cell mass (r2=0.52).

CONCLUSIONS/INTERPRETATION

[18F]exendin and [18F]FDOPA PET enable non-invasive assessment of SC-islet graft size and aspects of graft composition. These methods could be leveraged for optimising SC-islet cell replacement therapy in diabetes.

Comparison of Omentum and Subcutis as Implant Sites for Device-Encapsulated Human iPSC-Derived Pancreatic Endoderm in Nude Rats

Subcutaneous implants of device-encapsulated stem cell-derived pancreatic endoderm (PE) can establish a functional beta cell mass (FBM) with metabolic control in immune-compromised mice. In a study with human-induced pluripotent stem cell-PE, this outcome was favored by a preformed pouch which allowed lesion-free insertion of devices in a pre-vascularized site. This was not reproduced in nude rats, known to exhibit a higher innate reactivity than mice and therefore relevant as preclinical model: a dense fibrotic capsule formed around subcutis (SC) implants with virtually no FBM formation. Placement in omentum (OM) of nude rats provided a less fibrous, better vascularized environment than SC. It resulted in less donor cell loss (56% recovery at post-transplant-PT week 3 versus 16% in SC) allowing FBM-formation. At PT week 30, 6/13 OM-recipients exhibited glucose-induced plasma hu-C-peptide to 0.1-0.4 ng/ml, versus 0/8 in SC-recipients. These levels are more than 10-fold lower than in a state of metabolic control. This shortcoming is not caused by inadequate glucose responsiveness of the beta cells but by their insufficient number. The size of the formed beta cell mass (0.4 ± 0.2 µl) was lower than that reported in mice receiving the same cell product subcutaneously; the difference is attributed to a lower expansion of pancreatic progenitor cells and to their lower degree of differentiation to beta cells. This study in the nude rat model demonstrates that OM provides a better environment for formation of beta cells in device-encapsulated PE-implants than SC. It also identified targets for increasing their dose-efficacy.

Function and composition of pancreatic islet cell implants in omentum of type 1 diabetes patients

Intraportal (IP) islet cell transplants can restore metabolic control in type 1 diabetes patients, but limitations raise the need for establishing a functional beta cell mass (FBM) in a confined extrahepatic site. This study reports on function and composition of omental (OM) implants after placement of islet cell grafts with similar beta cell mass as in our IP-protocol (2-5.10⁶ beta cells/kg body weight) on a scaffold. Four of seven C-peptide-negative recipients achieved low beta cell function (hyperglycemic clamp [HGC] 2-8 percent of controls) until laparoscopy, 2-6 months later, for OM-biopsy and concomitant IP-transplant with similar beta cell dose. This IP-transplant increased HGC-values to 15-40 percent. OM-biopsies reflected the composition of initial grafts, exhibiting varying proportions of endocrine-cell-enriched clusters with more beta than alpha cells and leucocyte pole, non-endocrine cytokeratin-positive clusters surrounded by leucocytes, and scaffold remnants with foreign body reaction. OM-implants on a polyglactin-thrombin-fibrinogen-scaffold presented larger endocrine clusters with infiltrating endothelial cells and corresponded to the higher HGC-values. No activation of cellular immunity to GAD/IA2 was measured post-OM-transplant. Establishment of a metabolically adequate FBM in omentum may require a higher beta cell number in grafts but also elimination of their immunogenic non-endocrine components as well as local conditioning that favors endocrine cell engraftment and function.

Utility of Islet Cell Preparations From Donor Pancreases After Euthanasia

Patients fulfilling criteria for euthanasia can choose to donate their organs after circulatory death [donors after euthanasia (DCD V)]. This study assesses the outcome of islet cell isolation from DCD V pancreases. A procedure for DCD V procurement provided 13 pancreases preserved in Institut Georges Lopez-1 preservation solution and following acirculatory warm ischemia time under 10 minutes. Islet cell isolation outcomes are compared with those from reference donors after brain death (DBD, n = 234) and a cohort of donors after controlled circulatory death (DCD III, n = 29) procured under the same conditions. Islet cell isolation from DCD V organs resulted in better in vitro outcome than for selected DCD III or reference DBD organs. A 50% higher average beta cell number before and after culture and a higher average beta cell purity (35% vs 24% and 25%) was observed, which led to more frequent selection for our clinical protocol (77% of isolates vs 50%). The functional capacity of a DCD V islet cell preparation was illustrated by its in vivo effect following intraportal transplantation in a type 1 diabetes patient: injection of 2 million beta cells/kg body weight (1,900 IEQ/kg body weight) at 39% insulin purity resulted in an implant with functional beta cell mass that represented 30% of that in non-diabetic controls. In conclusion, this study describes procurement and preservation conditions for donor organs after euthanasia, which allow preparation of cultured islet cells, that more frequently meet criteria for clinical use than those from DBD or DCD III organs.

Bioluminescence Imaging In Vivo Confirms the Viability of Pancreatic Islets Transplanted into the Greater Omentum

PURPOSE

The liver is the most widely used site for pancreatic islet transplantation. However, several site-specific limitations impair functional success, with instant blood-mediated inflammatory reaction being the most important. The aim of this study was to develop a preclinical model for placement of the islet graft into a highly vascularized omental flap using a fibrin gel. For this purpose, we tested islet viability by bioluminescence imaging (BLI).

PROCEDURES

Pancreatic islets were isolated from luciferase-positive and luciferase-negative rats, mixed at a 1:1 ratio, placed into a plasma-thrombin bioscaffold, and transplanted in standard (10 pancreatic islets/g wt; n = 10) and marginal (4 pancreatic islets/g wt; n = 7) numbers into the omentums of syngeneic diabetic animals. For the control, 4 pancreatic islets/g were transplanted into the liver using the standard procedure (n = 7). Graft viability was tested by bioluminescence at days 14, 30, 60, and 90 post transplant. Glucose levels, intravenous glucose tolerance, and serum C-peptide were assessed regularly.

RESULTS

Nonfasting glucose levels < 10 mmol/l were restored in all animals. While islet viability in the omentum was clearly detected by stable luminescence signals throughout the whole study period, no signals were detected from islets transplanted into the liver. The bioluminescence signals were highly correlated with stimulated C-peptide levels detected at 80 days post transplant. Glucose tolerance did not differ among the 3 groups.

CONCLUSIONS

We successfully tested a preclinical model of islet transplantation into the greater omentum using a biocompatible scaffold made from autologous plasma and human thrombin. Both standard and marginal pancreatic islet numbers in a gel-form bioscaffold placed in the omentum restored glucose homeostasis in recipients with diabetes. Bioluminescence was shown promising as a direct proof of islet viability.

Use of Culture to Reach Metabolically Adequate Beta-cell Dose by Combining Donor Islet Cell Isolates for Transplantation in Type 1 Diabetes Patients

BACKGROUND

Clinical islet transplantation is generally conducted within 72 hours after isolating sufficient beta-cell mass. A preparation that does not meet the sufficient dose can be cultured until this is reached after combination with subsequent ones. This retrospective study examines whether metabolic outcome is influenced by culture duration.

METHODS

Forty type 1 diabetes recipients of intraportal islet cell grafts under antithymocyte globulin induction and mycophenolate mofetil-tacrolimus maintenance immunosuppression were analyzed. One subgroup (n = 10) was transplanted with preparations cultured for ≥96 hours; in the other subgroup (n = 30) grafts contained similar beta-cell numbers but included isolates that were cultured for a shorter duration. Both subgroups were compared by numbers with plasma C-peptide ≥0.5 ng/mL, low glycemic variability associated with C-peptide ≥1.0 ng/mL, and with insulin independence.

RESULTS

The subgroup with all cells cultured ≥96 hours exhibited longer C-peptide ≥0.5 ng/mL (103 versus 48 mo; P = 0.006), and more patients with low glycemic variability and C-peptide ≥1.0 ng/mL, at month 12 (9/10 versus 12/30; P = 0.005) and 24 (7/10 versus 6/30; P = 0.007). In addition, 9/10 became insulin-independent versus 15/30 (P = 0.03). Grafts with all cells cultured ≥96 hours did not contain more beta cells but a higher endocrine purity (49% versus 36%; P = 0.03). In multivariate analysis, longer culture duration and older recipient age were independently associated with longer graft function.

CONCLUSIONS

Human islet isolates with insufficient beta-cell mass for implantation within 72 hours can be cultured for 96 hours and longer to combine multiple preparations in order to reach the desired beta-cell dose and therefore result in a better metabolic benefit.

Safety and function of a new pre-vascularized bioartificial pancreas in an allogeneic rat model

Cell encapsulation could overcome limitations of free islets transplantation but is currently limited by inefficient cells immune protection and hypoxia. As a response to these challenges, we tested in vitro and in vivo the safety and efficacy of a new macroencapsulation device named MailPan^®. Membranes of MailPan^® device were tested in vitro in static conditions. Its bio-integration and level of oxygenation was assessed after implantation in non-diabetic rats. Immune protection properties were also assessed in rat with injection in the device of allogeneic islets with incompatible Major Histocompatibility Complex. Finally, function was assessed in diabetic rats with a Beta cell line injected in MailPan^®. In vitro, membranes of the device showed high permeability to glucose, insulin, and rejected IgG. In rat, the device displayed good bio-integration, efficient vascularization, and satisfactory oxygenation (>5%), while positron emission tomography (PET)-scan and angiography also highlighted rapid exchanges between blood circulation and the MailPan^®. The device showed its immune protection properties by preventing formation, by the rat recipient, of antibodies against encapsulated allogenic islets. Injection of a rat beta cell line into the device normalized fasting glycemia of diabetic rat with retrieval of viable cell clusters after 2 months. These data suggest that MailPan^® constitutes a promising encapsulation device for widespread use of cell therapy for type 1 diabetes.

Considerations for an Alternative Site of Islet Cell Transplantation

Islet cell transplantation has been limited most by poor graft survival. Optimizing the site of transplantation could improve clinical outcomes by minimizing required donor cells, increasing graft integration, and simplifying the transplantation and monitoring process. In this article, we review the history and significant human and animal data for clinically relevant sites, including the liver, spleen, and kidney subcapsule, and identify promising new sites for further research. While the liver was the first studied site and has been used the most in clinical practice, the majority of transplanted islets become necrotic. We review the potential causes for graft death, including the instant blood-mediated inflammatory reaction, exposure to immunosuppressive agents, and low oxygen tension. Significant research exists on alternative sites for islet cell transplantation, suggesting a promising future for patients undergoing pancreatectomy.

Function and Gene Expression of Islets Experimentally Transplanted to Muscle and Omentum

Islet transplantation to the liver is a potential curative treatment for patients with type 1 diabetes. Muscle and the greater omentum are two alternative implantation sites, which can provide excellent engraftment and hold potential as future sites for stem-cell-derived beta-cell replacement. We evaluated the functional outcome after islet transplantation to muscle and omentum and found that alloxan-diabetic animals were cured with a low number of islets (200) at both sites. The cured animals had a normal area under the curve blood glucose response to intravenous glucose, albeit animals with intramuscular islet grafts had increased 120-min blood glucose levels. They also demonstrated an exaggerated counter regulatory response to hypoglycemia. The expression of genes important for beta-cell function was, at both implantation sites, comparable to that in native pancreatic islets. The gene expression of insulin (INS1 and INS2) and glucose transporter-2 was even increased, and the expression of lactate dehydrogenase decreased, at both sites when compared to native islets. We conclude that muscle and omentum provide excellent conditions for engraftment of transplanted islets. When compared to control, 200 islets implanted to the omentum displayed a restored glucose tolerance, whereas animals with intramuscular islet grafts of similar size displayed mild glucose intolerance.

Tissue-engineering approaches in pancreatic islet transplantation

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

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

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

A Synthetic-Biology-Inspired Therapeutic Strategy for Targeting and Treating Hepatogenous Diabetes

Hepatogenous diabetes is a complex disease that is typified by the simultaneous presence of type 2 diabetes and many forms of liver disease. The chief pathogenic determinant in this pathophysiological network is insulin resistance (IR), an asymptomatic disease state in which impaired insulin signaling in target tissues initiates a variety of organ dysfunctions. However, pharmacotherapies targeting IR remain limited and are generally inapplicable for liver disease patients. Oleanolic acid (OA) is a plant-derived triterpenoid that is frequently used in Chinese medicine as a safe but slow-acting treatment in many liver disorders. Here, we utilized the congruent pharmacological activities of OA and glucagon-like-peptide 1 (GLP-1) in relieving IR and improving liver and pancreas functions and used a synthetic-biology-inspired design principle to engineer a therapeutic gene circuit that enables a concerted action of both drugs. In particular, OA-triggered short human GLP-1 (shGLP-1) expression in hepatogenous diabetic mice rapidly and simultaneously attenuated many disease-specific metabolic failures, whereas OA or shGLP-1 monotherapy failed to achieve corresponding therapeutic effects. Collectively, this work shows that rationally engineered synthetic gene circuits are capable of treating multifactorial diseases in a synergistic manner by multiplexing the targeting efficacies of single therapeutics.

Human islet xenotransplantation in rodents: A literature review of experimental model trends

Among the innovations for the treatment of type 1 diabetes, islet transplantation is a less invasive method of treatment, although it is still in development. One of the greatest barriers to this technique is the low number of pancreas donors and the low number of pancreases that are available for transplantation. Rodent models have been chosen in most studies of islet rejection and type 1 diabetes prevention to evaluate the quality and function of isolated human islets and to identify alternative solutions to the problem of islet scarcity. The purpose of this study is to conduct a review of islet xenotransplantation experiments from humans to rodents, to organize and analyze the parameters of these experiments, to describe trends in experimental modeling and to assess the viability of this procedure. In this study, we reviewed recently published research regarding islet xenotransplantation from humans to rodents, and we summarized the findings and organized the relevant data. The included studies were recent reports that involved xenotransplantation using human islets in a rodent model. We excluded the studies that related to isotransplantation, autotransplantation and allotransplantation. A total of 34 studies that related to xenotransplantation were selected for review based on their relevance and current data. Advances in the use of different graft sites may overcome autoimmunity and rejection after transplantation, which may solve the problem of the scarcity of islet donors in patients with type 1 diabetes.

Rapid Restoration of Vascularity and Oxygenation in Mouse and Human Islets Transplanted to Omentum May Contribute to Their Superior Function Compared to Intraportally Transplanted Islets

Transplantation of islets into the liver confers several site-specific challenges, including a delayed vascularization and prevailing hypoxia. The greater omentum has in several experimental studies been suggested as an alternative implantation site for clinical use, but there has been no direct functional comparison to the liver. In this experimental study in mice, we characterized the engraftment of mouse and human islets in the omentum and compared engraftment and functional outcome with those in the intraportal site. The vascularization and innervation of the islets transplanted into the omentum were restored within the first month by paralleled ingrowth of capillaries and nerves. The hypoxic conditions in the islets early posttransplantation were transient and restricted to the first days. Newly formed blood vessels were fully functional, and the blood perfusion and oxygenation of the islets became similar to that of endogenous islets. Furthermore, islet grafts in the omentum showed at 1 month posttransplantation functional superiority to intraportally transplanted grafts. We conclude that in contrast to the liver the omentum provides excellent engraftment conditions for transplanted islets. Future studies in humans will be of great interest to investigate the capability of this site to also harbor larger grafts without interfering with islet functionality.

Quantification of β-Cell Mass in Intramuscular Islet Grafts Using Radiolabeled Exendin-4

Background

There is an increasing interest in alternative implantation sites to the liver for islet transplantation. Intramuscular implantation has even been tested clinically. Possibilities to monitor β-cell mass would be of huge importance not only for the understanding of islet engraftment but also for the decision of changing the immunosuppressive regime. We have therefore evaluated the feasibility of quantifying intramuscular β-cell mass using the radiolabeled glucagon like peptide-1 receptor agonist DO3A-VS-Cys⁴⁰-Exendin-4.

Methods

One hundred to 400 islets were transplanted to the abdominal muscle of nondiabetic mice. After 3 to 4 weeks, 0.2 to 0.5 MBq [¹⁷⁷Lu]DO3A-VS-Cys⁴⁰-Exendin-4 was administered intravenously. Sixty minutes postinjection abdominal organs and graft bearing muscle were retrieved, and the radioactive uptake measured in a well counter within 10 minutes. The specific uptake in native and transplanted islets was assessed by autoradiography. The total insulin-positive area of the islet grafts was determined by immunohistochemistry.

Results

Intramuscular islet grafts could easily be visualized by this tracer, and the background uptake was very low. There was a linear correlation between the radioactivity uptake and the number of transplanted islets, both for standardized uptake values and the total radiotracer uptake in each graft (percentage of injected dose). The quantified total insulin area of surviving β cells showed an even stronger correlation to both standardized uptake values (R = 0.96, P = 0.0002) and percentage of injected dose (R = 0.88, P = 0.0095). There was no correlation to estimated α cell mass.

Conclusions

[¹⁷⁷Lu]DO3A-VS-Cys⁴⁰-Exendin-4 could be used to quantify β-cell mass after experimental intramuscular islet transplantation. This technique may well be transferred to the clinical setting by exchanging Lutetium-177 radionuclide to a positron emitting Gallium-68.

Concise Review: Markers for Assessing Human Stem Cell-Derived Implants as β-Cell Replacement in Type 1 Diabetes

: A depleted β-cell mass causes diabetes complications that cannot be avoided by insulin administration. β-Cell replacement can stop their development when restoring insulin's homeostatic role. This requires a sufficient number and an adequate functional state of the β cells, together defined as "functional β-cell mass." Intraportal implants of human pancreatic islet cells correct hyperglycemia in patients with type 1 diabetes, but this effect is transient and often incomplete. Studies to improve outcome are hindered by shortage in donor pancreases. Human pluripotent stem cells are a candidate source for mass production of grafts for β-cell replacement. Their in vitro differentiation to pancreatic endoderm (stage 4) and to β-cell-containing preparations (stage 7) provides grafts that generate β-cell implants in mice. In vivo markers indicated a better outcome of device-encapsulated stage 4 cells and microencapsulated stage 7 cells as compared with nonencapsulated grafts. Encapsulation also offers the advantage of representative implant retrieval for direct analysis by ex vivo markers. Combination of in vitro, in vivo, and ex vivo markers allows comparison of different stem cell-derived grafts and implants, with each other and with clinical islet cell preparations that serve as reference. Data in mice provide insights into the biology of stem cell-generated β-cell implants, in particular their capacity to establish and sustain a functional β-cell mass. They can thus be indicative for translation of a graft to similar studies in patients, where metabolic benefit will be an additional marker of primordial importance.

SIGNIFICANCE

Human stem cell-derived preparations can generate insulin-producing implants in immune-incompetent mice. Steps are undertaken for translation to patients with type 1 diabetes. Their therapeutic significance will depend on their capacity to establish a functional β-cell mass that provides metabolic benefit. This study proposes the combined use of in vitro, in vivo, and ex vivo markers to assess this potential in preclinical models and in clinical studies.

Bioengineering the Endocrine Pancreas: Intraomental Islet Transplantation Within a Biologic Resorbable Scaffold

Transplantation of pancreatic islets is a therapeutic option to preserve or restore β-cell function. Our study was aimed at developing a clinically applicable protocol for extrahepatic transplantation of pancreatic islets. The potency of islets implanted onto the omentum, using an in situ-generated adherent, resorbable plasma-thrombin biologic scaffold, was evaluated in diabetic rat and nonhuman primate (NHP) models. Intraomental islet engraftment in the biologic scaffold was confirmed by achievement of improved metabolic function and preservation of islet cytoarchitecture, with reconstitution of rich intrainsular vascular networks in both species. Long-term nonfasting normoglycemia and adequate glucose clearance (tolerance tests) were achieved in both intrahepatic and intraomental sites in rats. Intraomental graft recipients displayed lower levels of serum biomarkers of islet distress (e.g., acute serum insulin) and inflammation (e.g., leptin and α2-macroglobulin). Importantly, low-purity (30:70% endocrine:exocrine) syngeneic rat islet preparations displayed function equivalent to that of pure (>95% endocrine) preparations after intraomental biologic scaffold implantation. Moreover, the biologic scaffold sustained allogeneic islet engraftment in immunosuppressed recipients. Collectively, our feasibility/efficacy data, along with the simplicity of the procedure and the safety of the biologic scaffold components, represented sufficient preclinical testing to proceed to a pilot phase I/II clinical trial.

Fibrin gels engineered with pro-angiogenic growth factors promote engraftment of pancreatic islets in extrahepatic sites in mice

With a view toward reduction of graft loss, we explored pancreatic islet transplantation within fibrin matrices rendered pro-angiogenic by incorporation of minimal doses of vascular endothelial growth factor-A165 and platelet-derived growth factor-BB presented complexed to a fibrin-bound integrin-binding fibronectin domain. Engineered matrices allowed for extended release of pro-angiogenic factors and for their synergistic signaling with extracellular matrix-binding domains in the post-transplant period. Aprotinin addition delayed matrix degradation and prolonged pro-angiogenic factor availability within the graft. Both subcutaneous (SC) and epididymal fat pad (EFP) sites were evaluated. We show that in the SC site, diabetes reversal in mice transplanted with 1,000 IEQ of syngeneic islets was not observed for islets transplanted alone, while engineered matrices resulted in a diabetes median reversal time (MDRT) of 38 days. In the EFP site, the MDRT with 250 IEQ of syngeneic islets within the engineered matrices was 24 days versus 86 days for islets transplanted alone. Improved function of engineered grafts was associated with enhanced and earlier (by day 7) angiogenesis. Our findings show that by engineering the transplant site to promote prompt re-vascularization, engraftment and long-term function of islet grafts can be improved in relevant extrahepatic sites.

Composition and function of macroencapsulated human embryonic stem cell-derived implants: comparison with clinical human islet cell grafts

β-Cells generated from large-scale sources can overcome current shortages in clinical islet cell grafts provided that they adequately respond to metabolic variations. Pancreatic (non)endocrine cells can develop from human embryonic stem (huES) cells following in vitro derivation to pancreatic endoderm (PE) that is subsequently implanted in immune-incompetent mice for further differentiation. Encapsulation of PE increases the proportion of endocrine cells in subcutaneous implants, with enrichment in β-cells when they are placed in TheraCyte-macrodevices and predominantly α-cells when they are alginate-microencapsulated. At posttransplant (PT) weeks 20-30, macroencapsulated huES implants presented higher glucose-responsive plasma C-peptide levels and a lower proinsulin-over-C-peptide ratio than human islet cell implants under the kidney capsule. Their ex vivo analysis showed the presence of single-hormone-positive α- and β-cells that exhibited rapid secretory responses to increasing and decreasing glucose concentrations, similar to isolated human islet cells. However, their insulin secretory amplitude was lower, which was attributed in part to a lower cellular hormone content; it was associated with a lower glucose-induced insulin biosynthesis, but not with lower glucagon-induced stimulation, which together is compatible with an immature functional state of the huES-derived β-cells at PT weeks 20-30. These data support the therapeutic potential of macroencapsulated huES implants but indicate the need for further functional analysis. Their comparison with clinical-grade human islet cell grafts sets references for future development and clinical translation.

Clinical Immunosuppressants Inhibit Inflammatory, Proliferative, and Reprogramming Potential, But Not Angiogenesis of Human Pancreatic Duct Cells

The presence of pancreatic duct cells in clinical islet grafts may affect long-term metabolic success. Human pancreatic duct cells express factors that may exert both protective and damaging effects on islet cells in the graft. Here we studied the potential of commonly used immunosuppressive drugs in islet transplantation-sirolimus, tacrolimus, and mycophenolate mofetil (MMF)-to influence the inflammatory and angiogenic capacity of human pancreatic duct cells in addition to their proliferation and reprogramming abilities. Our data show that the expression of specific proinflammatory cytokines by the human pancreatic duct cells was either unaltered or inhibited by the immunosuppressants studied, especially tacrolimus and MMF, whereas expression of chemotactic and angiogenic factors was unaffected. Although none of the immunosuppressants directly led to duct cell death, MMF prevented duct cell proliferation, and sirolimus inhibited neurogenin 3-mediated duct-to-(neuro)endocrine cell reprogramming. Our data indicate that the immunosuppressant tacrolimus was the least aggressive on the angiogenic, proliferative, and reprogramming potential of human pancreatic duct cells, while it was most powerful in inhibiting inflammatory cytokines, which may influence the outcome of islet transplantation.

Long-term function of islets encapsulated in a redesigned alginate microcapsule construct in omentum pouches of immune-competent diabetic rats

OBJECTIVE

Our study aim was to determine encapsulated islet graft viability in an omentum pouch and the effect of fibroblast growth factor 1 (FGF-1) released from our redesigned alginate microcapsules on the function of the graft.

METHODS

Isolated rat islets were encapsulated in an inner core made with 1.5% low-viscosity-high-mannuronic-acid alginate followed by an external layer made with 1.25% low-viscosity high-guluronic acid alginate with or without FGF-1, in microcapsules measuring 300 to 400 µm in diameter. The 2 alginate layers were separated by a perm-selective membrane made with 0.1% poly-L-ornithine, and the inner low-viscosity-high-mannuronic-acid core was partially chelated using 55 mM sodium citrate for 2 minutes.

RESULTS

A marginal mass of encapsulated islet allografts (∼2000 islets/kg) in streptozotocin-diabetic Lewis rats caused significant reduction in blood glucose levels similar to the effect observed with encapsulated islet isografts. Transplantation of alloislets coencapsulated with FGF-1 did not result in better glycemic control, but induced greater body weight maintenance in transplant recipients compared with those that received only alloislets. Histological examination of the retrieved tissue demonstrated morphologically and functionally intact islets in the microcapsules, with no signs of fibrosis.

CONCLUSIONS

We conclude that the omentum is a viable site for encapsulated islet transplantation.

Omentum is better site than kidney capsule for growth, differentiation, and vascularization of immature porcine β-cell implants in immunodeficient rats

BACKGROUND

Rapid revascularization of islet cell implants is important for engraftment and subsequent survival and function. Development of an adequate vascular network is expected to allow adaptive growth of the β-cell mass. The present study compares omentum and kidney capsule as sites for growth and differentiation of immature β-cell grafts.

METHODS

Perinatal porcine islet cell grafts were implanted in omentum or under kidney capsule of nondiabetic nude rats. Implants were compared over 10 weeks for their respective growth, cellular composition, number and size of β cells, their proliferative activity, and implant blood vessel density.

RESULTS

In both sites, the β-cell volume increased fourfold between weeks 1 and 10 reflecting a rise in β-cell number. In the omental implants, however, the cellular insulin reserves and the percent of proliferating cells were twofold higher than in kidney implants. In parallel, the blood vessel density in omental implants increased twofold, reaching a density comparable with islets in adult pig pancreas. A positive correlation was found between the percent bromodeoxyuridine-positive β cells and the vessel density.

CONCLUSIONS

Growth of the β-cell volume proceeds similarly in the omentum and under the kidney capsule. However, the omentum leads to higher insulin reserves and an increased pool of proliferating cells, which might be related to a more extended vascular network. Our observations support the omentum as an alternative site for immature porcine islet cells, with beneficial effects on proliferation and implant revascularization.

Evaluation of a collagen-chitosan hydrogel for potential use as a pro-angiogenic site for islet transplantation

Islet transplantation to treat type 1 diabetes (T1D) has shown varied long-term success, due in part to insufficient blood supply to maintain the islets. In the current study, collagen and collagen:chitosan (10:1) hydrogels, +/- circulating angiogenic cells (CACs), were compared for their ability to produce a pro-angiogenic environment in a streptozotocin-induced mouse model of T1D. Initial characterization showed that collagen-chitosan gels were mechanically stronger than the collagen gels (0.7 kPa vs. 0.4 kPa elastic modulus, respectively), had more cross-links (9.2 vs. 7.4/µm(2)), and were degraded more slowly by collagenase. After gelation with CACs, live/dead staining showed greater CAC viability in the collagen-chitosan gels after 18 h compared to collagen (79% vs. 69%). In vivo, collagen-chitosan gels, subcutaneously implanted for up to 6 weeks in a T1D mouse, showed increased levels of pro-angiogenic cytokines over time. By 6 weeks, anti-islet cytokine levels were decreased in all matrix formulations ± CACs. The 6-week implants demonstrated increased expression of VCAM-1 in collagen-chitosan implants. Despite this, infiltrating vWF(+) and CXCR4(+) angiogenic cell numbers were not different between the implant types, which may be due to a delayed and reduced cytokine response in a T1D versus non-diabetic setting. The mechanical, degradation and cytokine data all suggest that the collagen-chitosan gel may be a suitable candidate for use as a pro-angiogenic ectopic islet transplant site.

The use of stem cells for pancreatic regeneration in diabetes mellitus

The endocrine pancreas represents an interesting arena for regenerative medicine and cell therapeutics. One of the major pancreatic diseases, diabetes mellitus is a metabolic disorder caused by having an insufficient number of insulin-producing β cells. Replenishment of β cells by cell transplantation can restore normal metabolic control. The shortage in donor pancreata has meant that the demand for transplantable β cells has outstripped the supply, which could be met by using alternative sources of stem cells. This situation has opened up new areas of research, such as cellular reprogramming and in vivo β-cell regeneration. Pluripotent stem cells seem to be the best option for clinical applications of β-cell regeneration in the near future, as these cells have been demonstrated to represent an unlimited source of functional β cells. Although compelling evidence shows that the adult pancreas retains regenerative capacity, it remains unclear whether this organ contains stem cells. Alternatively, specialized cell types within or outside the pancreas retain plasticity in proliferation and differentiation. Cellular reprogramming or transdifferentiation of exocrine cells or other types of endocrine cells in the pancreas could provide a long-term solution.

Mouse muscle as an ectopic permissive site for human pancreatic development

While sporadic human genetic studies have permitted some comparisons between rodent and human pancreatic development, the lack of a robust experimental system has not permitted detailed examination of human pancreatic development. We previously developed a xenograft model of immature human fetal pancreas grafted under the kidney capsule of immune-incompetent mice, which allowed the development of human pancreatic β-cells. Here, we compared the development of human and murine fetal pancreatic grafts either under skeletal muscle epimysium or under the renal capsule. We demonstrated that human pancreatic β-cell development occurs more slowly (weeks) than murine pancreas (days) both by differentiation of pancreatic progenitors and by proliferation of developing β-cells. The superficial location of the skeletal muscle graft and its easier access permitted in vivo lentivirus-mediated gene transfer with a green fluorescent protein-labeled construct under control of the insulin or elastase gene promoter, which targeted β-cells and nonendocrine cells, respectively. This model of engraftment under the skeletal muscle epimysium is a new approach for longitudinal studies, which allows localized manipulation to determine the regulation of human pancreatic development.

Predictive factors of allosensitization after immunosuppressant withdrawal in recipients of long-term cultured islet cell grafts

BACKGROUND

Islet transplantation has been reported to induce allosensitization in the majority of type 1 diabetic recipients of fresh or shortly incubated islet grafts prepared from one to three donors.

METHODS

We examined the appearance of human leukocyte antigen (HLA) antibodies after withdrawal of immunosuppressants in 35 type 1 diabetic recipients of islet cell grafts prepared from a median of 6 donors (range, 2-11), cultured for longer periods, and characterized for their cellular composition. Immunosuppression consisted of antithymocyte globulin induction followed by mycophenolate mofetil plus calcineurin inhibitors (n=28, with 7 also receiving steroids) or sirolimus with (n=3) or without calcineurin inhibitors (n=4). Both the complement-dependent cytotoxicity (CDC) assay (class I) and the solid-phase flow-based Luminex method (class I and II) were used to identify HLA antibodies.

RESULTS

Immunosuppressant withdrawal resulted in CDC positivity for class I antibodies in only 6% of patients. However, the majority became positive for class I antibodies (72%) or class II antibodies (72%) in the Luminex assay; positivity was not correlated to a higher number of donors or HLA mismatches, but with a lower β-cell purity; use of steroids reduced de novo positivity for Luminex class I antibodies.

CONCLUSION

Allosensitization to cultured human islet cell grafts was low when assessed by CDC assay but high in Luminex. No correlation was found with the number of donors but risk was higher for grafts with lower β-cell purity.

Suppression of epithelial-to-mesenchymal transitioning enhances ex vivo reprogramming of human exocrine pancreatic tissue toward functional insulin-producing β-like cells

Because of the lack of tissue available for islet transplantation, new sources of β-cells have been sought for the treatment of type 1 diabetes. The aim of this study was to determine whether the human exocrine-enriched fraction from the islet isolation procedure could be reprogrammed to provide additional islet tissue for transplantation. The exocrine-enriched cells rapidly dedifferentiated in culture and grew as a mesenchymal monolayer. Genetic lineage tracing confirmed that these mesenchymal cells arose, in part, through a process of epithelial-to-mesenchymal transitioning (EMT). A protocol was developed whereby transduction of these mesenchymal cells with adenoviruses containing Pdx1, Ngn3, MafA, and Pax4 generated a population of cells that were enriched in glucagon-secreting α-like cells. Transdifferentiation or reprogramming toward insulin-secreting β-cells was enhanced, however, when using unpassaged cells in combination with inhibition of EMT by inclusion of Rho-associated kinase (ROCK) and transforming growth factor-β1 inhibitors. Resultant cells were able to secrete insulin in response to glucose and on transplantation were able to normalize blood glucose levels in streptozotocin diabetic NOD/SCID mice. In conclusion, reprogramming of human exocrine-enriched tissue can be best achieved using fresh material under conditions whereby EMT is inhibited, rather than allowing the culture to expand as a mesenchymal monolayer.

Sustained function of alginate-encapsulated human islet cell implants in the peritoneal cavity of mice leading to a pilot study in a type 1 diabetic patient

AIMS/HYPOTHESIS

Alginate-encapsulated human islet cell grafts have not been able to correct diabetes in humans, whereas free grafts have. This study examined in immunodeficient mice whether alginate-encapsulated graft function was inferior to that of free grafts of the same size and composition.

METHODS

Cultured human islet cells were equally distributed over free and alginate-encapsulated grafts before implantation in, respectively, the kidney capsule and the peritoneal cavity of non-obese diabetic mice with severe combined immunodeficiency and alloxan-induced diabetes. Implants were followed for in vivo function and retrieved for analysis of cellular composition (all) and insulin secretory responsiveness (capsules).

RESULTS

Free implants with low beta cell purity (19 ± 1%) were non-functional and underwent 90% beta cell loss. At medium purity (50 ± 1%), they were functional at post-transplant week 1, evolving to normoglycaemia (4/8) or to C-peptide negativity (4/8) depending on the degree of beta cell-specific losses. Encapsulated implants immediately and sustainably corrected diabetes, irrespective of beta cell purity (16/16). Most capsules were retrievable as single units, enriched in endocrine cells that exhibited rapid secretory responses to glucose and glucagon. Single capsules with similar properties were also retrieved from a type 1 diabetic recipient at post-transplant month 3. However, the vast majority were clustered and contained debris, explaining the poor rise in plasma C-peptide.

CONCLUSIONS/INTERPRETATION

In immunodeficient mice, i.p. implanted alginate-encapsulated human islet cells exhibited a better outcome than free implants under the kidney capsule. They did not show primary non-function at low beta cell purity and avoided beta cell-specific losses by rapidly establishing normoglycaemia. Retrieved capsules presented secretory responses to glucose, which was also observed in a type 1 diabetic recipient.

Sensitive and specific time-resolved fluorescence immunoassay of rat C-peptide for measuring hormone secretory and storage capacity of β-cells in vivo and in vitro

The limitations of current rat C-peptide assays led us to develop a time-resolved fluorescence immunoassay for measurements in plasma, incubation media, and tissue/cell extracts. The assay uses 2 monoclonal antibodies, binding to different parts of the C-peptide molecule, and allowing, respectively, capture of the peptide and its detection by europium-labeled streptavidin. It is performed on 25-μL samples for a dynamic range from 66pM up to 3900pM C-peptide and displays over 95% recovery of added peptide in the range of 111pM to 2786pM. Its inter- and intra-assay coefficients of variations are, respectively, lower than 7.6% and 4.8%. Cross-reactivities by rat insulin and by human and porcine C-peptide are negligible, and cross-reactivity by mouse C-peptide is 6% ± 2%. The assay has been validated for in vivo and in vitro measurements of C-peptide release and cellular content. Release patterns were similar to those for insulin and occurred in equimolar concentrations for both peptides. The molar C-peptide contents in purified β-cells and isolated islets were similar to the corresponding insulin contents. This was also the case for pancreatic extracts containing protease inhibitors.

Striated muscle as implantation site for transplanted pancreatic islets

Islet transplantation is an attractive treatment for selected patients with brittle type 1 diabetes. In the clinical setting, intraportal transplantation predominates. However, due to extensive early islet cell death, the quantity of islets needed to restore glucose homeostasis requires in general a minimum of two donors. Moreover, the deterioration of islet function over time results in few insulin-independent patients after five-year followup. Specific obstacles to the success of islet transplantation include site-specific concerns for the liver such as the instant blood mediated inflammatory reaction, islet lipotoxicity, low oxygen tension, and poor revascularization, impediments that have led to the developing interest for alternative implantation sites over recent years. Within preclinical settings, several alternative sites have now been investigated and proven favorable in various aspects. Muscle is considered a very promising site and has physiologically properties and technical advantages that could make it optimal for islet transplantation.