Diabetic rats and mice are resistant to porcine and human insulin: flawed experimental models for testing islet xenografts

Enhanced Insulin Production From Porcine Islets: More Insulin, Less Islets

Clinical pancreatic islet xenotransplantation will most probably rely on genetically modified pigs as donors. Several lines of transgenic pigs carrying one and more often, multiple modifications already exist. The vast majority of these modifications aim to mitigate the host immune response by suppressing major xeno-antigens, or expressing immunomodulatory molecules that act locally at the graft site. While these modifications are essential and have proven beneficial in preclinical trials, ensuring good intrinsic islet secretory function is equally important to achieve normoglycemia in recipients. Neonatal and even adult porcine islets are known for their low secretory response to physiological stimulation, a shortcoming that is often overcome by implanting extremely large numbers of such islets to compensate for insulin requirement incompatibilities between donor pigs and rodent, non-human primate or human recipients. Recent studies have revealed the existence of secretory amplifying pathways in porcine beta-cells previously identified in murine and human cells. Building upon these findings, a new line of transgenic pigs where these pathways are activated specifically in beta-cells has been created. Compared to their wild-type counterparts, islets from these transgenic pigs have proven to be better insulin secretors in their native pancreas environment, in vitro after isolation and most importantly in vivo after transplantation to diabetic mice.

Double transgenic neonatal porcine islets as an alternative source for beta cell replacement therapy

To be clinically efficient, beta cell replacement therapies such as pig islet xenotransplantation must ensure sufficient insulin secretion from grafted islets. While protection from host immune reaction is essential for islet engraftment and their subsequent functioning, intrinsic physiological properties of used cells are also a key factor. We have previously shown that islets with adenoviral-mediated expression of a dipeptidyl peptidase-resistant form of glucagon-like-peptide-1 (GLP-1) and a constitutively activated form of type 3 muscarinic receptor (M3R) in their beta cells have greatly improved insulin secretory response to glucose stimulation that is otherwise 4 to 10 times lower than human islets. Here, we describe in vitro characterization of the secretory function of pancreatic islets, derived from transgenic pigs expressing the GLP-1M3R cassette under the porcine insulin promoter (InsGLP-1M3R), and their usage to treat insulin-dependent diabetes in an immunodeficient mouse model. Our results show that InsGLP-1M3R islets isolated from neonatal and adult pigs secrete up to 15-fold more insulin in response to glucose stimulation compared to wild-type (WT) islets. They also proved to be more efficient in treating diabetes in a preclinical model as shown by a significantly higher percentage of normoglycemic recipients and higher porcine C-peptide levels up to 9 mo post implantation.

Inflammation-induced subcutaneous neovascularization for the long-term survival of encapsulated islets without immunosuppression

Cellular therapies for type-1 diabetes can leverage cell encapsulation to dispense with immunosuppression. However, encapsulated islet cells do not survive long, particularly when implanted in poorly vascularized subcutaneous sites. Here we show that the induction of neovascularization via temporary controlled inflammation through the implantation of a nylon catheter can be used to create a subcutaneous cavity that supports the transplantation and optimal function of a geometrically matching islet-encapsulation device consisting of a twisted nylon surgical thread coated with an islet-seeded alginate hydrogel. The neovascularized cavity led to the sustained reversal of diabetes, as we show in immunocompetent syngeneic, allogeneic and xenogeneic mouse models of diabetes, owing to increased oxygenation, physiological glucose responsiveness and islet survival, as indicated by a computational model of mass transport. The cavity also allowed for the in situ replacement of impaired devices, with prompt return to normoglycemia. Controlled inflammation-induced neovascularization is a scalable approach, as we show with a minipig model, and may facilitate the clinical translation of immunosuppression-free subcutaneous islet transplantation.

Multi-Targeting Intranasal Nanoformulation as a Therapeutic for Alzheimer's Disease

Melatonin, insulin, and Δ9-tetrahydrocannabinol (THC) have been shown to reverse cognitive deficits and attenuate neuropathologies in transgenic mouse models of Alzheimer's disease (AD) when used individually. Here, we evaluated the therapeutic properties of long-term intranasal treatment with a novel nanoformulation containing melatonin, insulin, and THC in aged APPswe/PS1ΔE9 (APP/PS1) mice, a transgenic model of AD. Transgenic mice at the age of 12 months were intranasally administered with a new nanoformulation containing melatonin, insulin, and THC at doses of 0.04, 0.008, and 0.02 mg/kg, respectively, once daily for 3 months. The spatial memory of the mice was assessed using the radial arm water maze (RAWM) test before and after drug treatment. Brain tissues were collected at the end of the treatment period for the assessment of Aβ load, tauopathy state, and markers of mitochondrial function. The RAWM test revealed that the treatment with the melatonin-insulin-THC (MIT) nasal spray improved the spatial learning memory of APP/PS1 mice significantly. Results of protein analyses of brain homogenates indicated that MIT treatment significantly decreased the tau phosphorylation implicated in tau toxicity (p < 0.05) and the expression of CKMT1 associated with mitochondrial dysfunction. Moreover, MIT significantly decreased the expression of two mitochondrial fusion-related proteins, Mfn2 and Opa1 (p < 0.01 for both), while increasing the expression of a mitophagy regulator, Parkin, suggesting a compensatory enhancement of mitophagy due to MIT-promoted mitochondrial fusion. In conclusion, this study was the first to demonstrate the ability of an MIT nanoformulation to improve spatial memory in AD mice through its multi-targeting effects on Aβ production, tau phosphorylation, and mitochondrial dynamics. Thus, MIT may be a safe and effective therapeutic for AD.

Immunoregulatory Sertoli Cell Allografts Engineered to Express Human Insulin Survive Humoral-Mediated Rejection

An effective treatment and possible cure for type 1 diabetes is transplantation of pancreatic islets. Unfortunately, transplanted islets are rejected by the immune system with humoral-mediated responses being an important part of rejection. Sertoli cells (SC), an immune regulatory cell shown to survive as allografts long-term without immunosuppressants, have the potential to be used as a cell-based gene therapy vehicle to deliver endogenous insulin-a possible alternative to islets. Previously, we transduced a mouse SC line to produce human insulin. After transplantation into diabetic mice, these cells consistently produced low levels of insulin with graft survival of 75% at 50 days post-transplantation. The object of this study was to assess humoral immune regulation by these engineered SC. Both nontransduced and transduced SC survived exposure to human serum with complement in vitro. Analysis of allografts in vivo at 20 and 50 days post-transplantation revealed that despite IgG antibody detection, complement factor deposition was low and grafts survived through 50 days post-transplantation. Furthermore, the transduced SC secreted elevated levels of the complement inhibitor C1q binding protein. Overall, this suggests SC genetically engineered to express insulin maintain their ability to prevent complement-mediated killing. Since inhibiting complement-mediated rejection is important for graft survival, further studies of how SC modifies the immune response could be utilized to advance the use of genetically engineered SC or to prolong islet allograft survival to improve the treatment of diabetes.

Islet allografts expressing a PD-L1 and IDO fusion protein evade immune rejection and reverse preexisting diabetes in immunocompetent mice without systemic immunosuppression

Allogeneic islet transplantation is a promising experimental therapy for poorly controlled diabetes. Despite pharmacological immunosuppression, long-term islet engraftment remains elusive. Here, we designed a synthetic fusion transgene coupling PD-L1 and indoleamine dioxygenase [hereafter PIDO] whose constitutive expression prevents immune destruction of genetically engineered islet allograft transplanted in immunocompetent mice. PIDO expressing murine islets maintain robust dynamic insulin secretion in vitro and when transplanted in allogeneic hyperglycemic murine recipients reverse pre-existing streptozotocin-induced and autoimmune diabetes in the absence of pharmacological immunosuppression for more than 50 and 8 weeks, respectively, and is dependent on host CD4 competence. Additionally, PIDO expression in allografts preserves endocrine functional viability of islets and promotes a localized tolerogenic milieu characterized by the suppression of host CD8 T cell and phagocyte recruitment and accumulation of FOXP3⁺ Tregs. Furthermore, in the canine model of xenogeneic islet transplantation, muscle implanted PIDO-expressing porcine islets displayed physiological glucose-responsive insulin secretion competency in euglycemic recipient for up to 20 weeks. In conclusion, the PIDO transgenic technology enables host CD4⁺ T cell-modulated immune evasiveness and long-term functional viability of islet allo- and xenografts in immune-competent recipients without the need for pharmacological immune suppression and would allow for improved outcomes for tissue transplantation.

Necrostatin-1 Supplementation to Islet Tissue Culture Enhances the In-Vitro Development and Graft Function of Young Porcine Islets

Pre-weaned porcine islets (PPIs) represent an unlimited source for islet transplantation but are functionally immature. We previously showed that necrostatin-1 (Nec-1) immediately after islet isolation enhanced the in vitro development of PPIs. Here, we examined the impact of Nec-1 on the in vivo function of PPIs after transplantation in diabetic mice. PPIs were isolated from pancreata of 8-15-day-old, pre-weaned pigs and cultured in media alone, or supplemented with Nec-1 (100 µM) on day 0 or on day 3 of culture (n = 5 for each group). On day 7, islet recovery, viability, oxygen consumption rate, insulin content, cellular composition, insulin secretion capacity, and transplant outcomes were evaluated. While islet viability and oxygen consumption rate remained high throughout 7-day tissue culture, Nec-1 supplementation on day 3 significantly improved islet recovery, insulin content, endocrine composition, GLUT2 expression, differentiation potential, proliferation capacity of endocrine cells, and insulin secretion. Adding Nec-1 on day 3 of tissue culture enhanced the islet recovery, proportion of delta cells, beta-cell differentiation and proliferation, and stimulation index. In vivo, this leads to shorter times to normoglycemia, better glycemic control, and higher circulating insulin. Our findings identify the novel time-dependent effects of Nec-1 supplementation on porcine islet quantity and quality prior to transplantation.

Insulin inhibits inflammation-induced cone death in retinal detachment

BACKGROUND

Rhegmatogenous retinal detachment (RD) involving the macula is a major cause of visual impairment despite high surgical success rate, mainly because of cone death. RD causes the infiltration of activated immune cells, but it is not clear whether and how infiltrating inflammatory cells contribute to cone cell loss.

METHODS

Vitreous samples from patients with RD and from control patients with macular hole were analyzed to characterize the inflammatory response to RD. A mouse model of RD and retinal explants culture were then used to explore the mechanisms leading to cone death.

RESULTS

Analysis of vitreous samples confirms that RD induces a marked inflammatory response with increased cytokine and chemokine expression in humans, which is closely mimicked by experimental murine RD. In this model, we corroborate that myeloid cells and T-lymphocytes contribute to cone loss, as the inhibition of their accumulation by Thrombospondin 1 (TSP1) increased cone survival. Using monocyte/retinal co-cultures and TSP1 treatment in RD, we demonstrate that immune cell infiltration downregulates rod-derived cone viability factor (RdCVF), which physiologically regulates glucose uptake in cones. Insulin and the insulin sensitizers rosiglitazone and metformin prevent in part the RD-induced cone loss in vivo, despite the persistence of inflammation CONCLUSION: Our results describe a new mechanism by which inflammation induces cone death in RD, likely through cone starvation due to the downregulation of RdCVF that could be reversed by insulin. Therapeutic inhibition of inflammation and stimulation of glucose availability in cones by insulin signaling might prevent RD-associated cone death until the RD can be surgically repaired and improve visual outcome after RD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03318588.

A model for determining an effective in vivo dose of transplanted islets based on in vitro insulin secretion

BACKGROUND

Allogeneic islet transplantation for the treatment of type 1 diabetes often requires multiple implant procedures, from as many as several human pancreas donors, to achieve lasting clinical benefit. Given the limited availability of human pancreases for islet isolation, porcine islets have long been considered a potential option for clinical use. Agarose-encapsulated porcine islets (macrobeads) permit long-term culture and thus a thorough evaluation of microbiological safety and daily insulin secretory capacity, prior to implantation. The goal of this study was the development of a method for determining an effective dose of encapsulated islets based on their measured in vitro insulin secretion in a preclinical model of type 1 diabetes.

METHODS

Spontaneously diabetic BioBreeding diabetes-prone rats were implanted with osmotic insulin pumps in combination with continuous glucose monitoring to establish the daily insulin dose required to achieve continuous euglycaemia in individual animals. Rats were then implanted with a 1×, 2× or 3× dose (defined as the ratio of macrobead in vitro insulin secretion per 24 hours to the recipient animal's total daily insulin requirement) of porcine islet macrobeads, in the absence of immunosuppression. In vivo macrobead function was assessed by recipient non-fasted morning blood glucose values, continuous glucose monitoring and the presence of peritoneal porcine C-peptide. At the end of the study, the implanted macrobeads were removed and returned to in vitro culture for the evaluation of insulin secretion.

RESULTS

Diabetic rats receiving a 2× macrobead implant exhibited significantly improved blood glucose regulation compared to that of rats receiving a 1× dose during a 30-day pilot study. In a 3-month follow-up study, 2× and 3× macrobead doses initially controlled blood glucose levels equally well, although several animals receiving a 3× dose maintained euglycaemia throughout the study, compared to none of the 2× animals. The presence of porcine C-peptide in rat peritoneal fluid 3 months post-implant and the recurrence of hyperglycaemia following macrobead removal, along with the finding of persistent in vitro insulin secretion from retrieved macrobeads, confirmed long-term graft function.

CONCLUSIONS

Increasing dosages of islet macrobeads transplanted into diabetic rats, based on multiples of in vitro insulin secretion matched to the recipient's exogenous insulin requirements, correlated with improved blood glucose regulation and increased duration of graft function. These results demonstrate the usefulness of a standardized model for the evaluation of the functional effectiveness of islets intended for transplantation, in this case using intraperitoneally implanted agarose macrobeads, in diabetic rats. The results suggest that some features of this islet-dosing methodology may be applicable, and indeed necessary, to clinical allogeneic and xenogeneic islet transplantation.

Sertoli Cells Engineered to Express Insulin to Lower Blood Glucose in Diabetic Mice

Long-term survival of allo- and xenotransplanted immune-privileged Sertoli cells (SCs) is well documented suggesting that SCs can be used to deliver foreign proteins for cell-based gene therapy. The aim of this study was to use a lentivirus carrying proinsulin cDNA to achieve stable expression and lowering of blood glucose levels (BGLs). A SC line transduced with the lentivirus (MSC-LV-mI) maintained stable insulin expression in vitro. These MSC-LV-mI cells were transplanted and grafts were analyzed for cell survival, continued proinsulin mRNA, and insulin protein expression. All grafts contained MSC-LV-mI cells that expressed proinsulin mRNA and insulin protein. Transplantation of MSC-LV-mI cells into diabetic mice significantly lowered BGLs for 4 days after transplantation. Interestingly, in three transplanted SCID mice and one transplanted BALB/c mouse, the BGLs again significantly lowered by day 50 and 70, respectively. This is the first time SC transduced with a lentiviral vector was able to stably express insulin and lower BGLs. In conclusion, a SC line can be modified to stably express therapeutic proteins (e.g., insulin), thus taking us one step further in the use of SCs as an immune-privileged vehicle for cell-based gene therapy.

Insulin-Deficient Mouse β-Cells Do Not Fully Mature but Can Be Remedied Through Insulin Replacement by Islet Transplantation

Insulin receptor (IR) insufficiency in β-cells leads to impaired insulin secretion and reduced β-cell hyperplasia in response to hyperglycemia. Selective IR deficiency in β-cells in later embryological development may lead to compensatory β-cell hyperplasia. Although these findings suggest insulin signaling on the β-cell is important for β-cell function, they are confounded by loss of signaling by the insulinlike growth factors through the IR. To determine whether insulin itself is necessary for β-cell development and maturation, we performed a characterization of pancreatic islets in mice with deletions of both nonallelic insulin genes (Ins1-/-Ins2-/-). We immunostained neonatal Ins1-/-Ins2-/- and Ins1+/+Ins2+/+ pancreata and performed quantitative polymerase chain reaction on isolated neonatal islets. Insulin-deficient islets had reduced expression of factors normally expressed in maturing β-cells, including muscoloaponeurotic fibrosarcoma oncogene homolog A, homeodomain transcription factor 6.1, and glucose transporter 2. Ins1-/-Ins2-/-β-cells expressed progenitor factors associated with stem cells or dedifferentiated β-cells, including v-myc avian myolocytomatosis viral oncogene lung carcinoma derived and homeobox protein NANOG. We replaced insulin by injection or islet transplantation to keep mice alive into adulthood to determine whether insulin replacement was sufficient for the completed maturation of insulin-deficient β-cells. Short-term insulin glargine (Lantus®) injections partially rescued the β-cell phenotype, whereas long-term replacement of insulin by isogenic islet transplantation supported the formation of more mature β-cells. Our findings suggest that tightly regulated glycemia, insulin species, or other islet factors are necessary for β-cell maturation.

Porcine Islet Xenografts: a Clinical Source of ß-Cell Grafts

PURPOSE OF REVIEW

Diabetes is medical and social burden affecting millions around the world. Despite intensive therapy, insulin fails to maintain adequate glucose homeostasis and often results in episodes of hypoglycemic unawareness. Islet transplantation is a propitious replacement therapy, and incremental improvements in islet isolation and immunosuppressive drugs have made this procedure a feasible option. Shortage of donors, graft loss, and toxic immunosuppressive agents are few of many hurdles against making human allogenic islet transplantation a routine procedure.

RECENT FINDINGS

Xenografts-especially pig islets-offer a logical alternative source for islets. Current preclinical studies have revealed problems such as optimal islet source, zoonosis, and immune rejection. These issues are slowing clinical application. Genetically modified pigs, encapsulation devices, and new immune-suppressive regimens can confer graft protection. In addition, extrahepatic transplant sites are showing promising results. Notwithstanding few approved clinical human trials, and available data from non-human primates, recent reports indicate that porcine islets are closer to be the promising solution to cure diabetes.

Xeno-Transplantation of macro-encapsulated islets and Pluripotent Stem Cell-Derived Pancreatic Progenitors without Immunosuppression

Islet transplantation effectively treats diabetes but relies on immune suppression and is practically limited by the number of cadaveric islets available. An alternative cellular source is insulin-producing cells derived from pluripotent cell sources. Three animal cohorts were used in the current study to evaluate whether an oxygen-providing macro-encapsulation device, 'βAIR', could function in conjunction with human embryonic stem cells (hESCs) and their derivatives. The first cohort received macro-encapsulated undifferentiated hESCs, a second cohort received hESCs differentiated to a pancreatic progenitor state with limited endocrine differentiation. A reference cohort received human islets. Macro-encapsulation devices were implanted subcutaneously and monitored for up to 4 months. Undifferentiated pluripotent stem cells did not form teratoma but underwent cell death following implantation. Human C-peptide (hC- peptide) was detectable in host serum one week after implantation for both other cohorts. hC-peptide levels decreasing over time but remained detectable up to the end of the study. Key factors associated with mature endocrine cells were observed in grafts recovered from cohorts containing islets and hESC-derivatives including C-peptide, insulin, glucagon and urocortin 3. We conclude that the 'βAIR' macroencapsulation device is compatible with both human islets and pluripotent derivatives, but has a limited capability of sustaining undifferentiated pluripotent cells.

Replacing and safeguarding pancreatic β cells for diabetes

Pluripotent stem cells are a scalable source of pancreatic cells for transplantation into patients with diabetes. Here, we describe how the field is gaining momentum toward a β cell replacement therapy.

Lung-Derived Microscaffolds Facilitate Diabetes Reversal after Mouse and Human Intraperitoneal Islet Transplantation

There is a need to develop three-dimensional structures that mimic the natural islet tissue microenvironment. Endocrine micro-pancreata (EMPs) made up of acellular organ-derived micro-scaffolds seeded with human islets have been shown to express high levels of key beta-cell specific genes and secrete quantities of insulin per cell similar to freshly isolated human islets in a glucose-regulated manner for more than three months in vitro. The aim of this study was to investigate the capacity of EMPs to restore euglycemia in vivo after transplantation of mouse or human islets in chemically diabetic mice. We proposed that the organ-derived EMPs would restore the extracellular components of the islet microenvironment, generating favorable conditions for islet function and survival. EMPs seeded with 500 mouse islets were implanted intraperitoneally into streptozotocin-induced diabetic mice and reverted diabetes in 67% of mice compared to 13% of controls (p = 0.018, n = 9 per group). Histological analysis of the explanted grafts 60 days post-transplantation stained positive for insulin and exhibited increased vascular density in a collagen-rich background. EMPs were also seeded with human islets and transplanted into the peritoneal cavity of immune-deficient diabetic mice at 250 islet equivalents (IEQ), 500 IEQ and 1000 IEQ. Escalating islet dose increased rates of normoglycemia (50% of the 500 IEQ group and 75% of the 1000 IEQ group, n = 3 per group). Human c-peptide levels were detected 90 days post-transplantation in a dose-response relationship. Herein, we report reversal of diabetes in mice by intraperitoneal transplantation of human islet seeded on EMPs with a human islet dose as low as 500 IEQ.

Clinical Islet Isolation

The overarching success of islet transplantation relies on the success in the laboratory to isolate the islets. This chapter focuses on the processes of human islet cell isolation and the ways to optimally provide islet cells for transplantation. The major improvements in regards to the choice of enzyme type, way the digested pancreas tissue is handled to best separate islets from the acinar and surrounding tissues, the various methods of purification of the islets, their subsequent culture and quality assurance to improve outcomes to culminate in safe and effective islet transplantation will be discussed. After decades of improvements, islet cell isolation and transplantation now clearly offer a safe, effective and feasible therapeutic treatment option for an increasing number of patients suffering from type 1 diabetes specifically for those with severe hypoglycaemic unawareness.

Accelerated Maturation of Human Stem Cell-Derived Pancreatic Progenitor Cells into Insulin-Secreting Cells in Immunodeficient Rats Relative to Mice

Pluripotent human embryonic stem cells (hESCs) are a potential source of transplantable cells for treating patients with diabetes. To investigate the impact of the host recipient on hESC-derived pancreatic progenitor cell maturation, cells were transplanted into immunodeficient SCID-beige mice or nude rats. Following the transplant, basal human C-peptide levels were consistently higher in mice compared with rats, but only rats showed robust meal- and glucose-responsive human C-peptide secretion by 19-21 weeks. Grafts from rats contained a higher proportion of insulin:glucagon immunoreactivity, fewer exocrine cells, and improved expression of mature β cell markers compared with mice. Moreover, ECM-related genes were enriched, the collagen network was denser, and blood vessels were more intricately integrated into the engrafted endocrine tissue in rats relative to mice. Overall, hESC-derived pancreatic progenitor cells matured faster in nude rats compared with SCID-beige mice, indicating that the host recipient can greatly influence the fate of immature pancreatic progenitor cells post-transplantation.

Therapeutic effects of a non-β cell bioartificial pancreas in diabetic mice

BACKGROUND

Cell-based insulin therapies can potentially improve glycemic regulation in insulin-dependent diabetic patients. Enteroendocrine cells engineered to secrete recombinant insulin have exhibited glycemic efficacy, but have been primarily studied as uncontrollable growth systems in immune incompetent mice. Furthermore, reports suggest that suboptimal insulin secretion remains a barrier to expanded application.

METHODS

Genetic and tissue engineering strategies were applied to improve recombinant insulin secretion from intestinal L-cells on both a per-cell and per-graft basis. Transduction of insulin-expressing GLUTag L-cells with lentivirus carrying an additional human insulin gene-enhanced secretion twofold. We infected cells with lentivirus expressing a luciferase reporter gene to track cell survival in vivo. To provide a growth-controlled and immune protective environment without affecting secretory capacity, cells were microencapsulated in barium alginate. Approximately 9×10(7) microencapsulated cells were injected intraperitoneally in immune competent streptozotocin-induced diabetic mice for therapeutic efficacy evaluation.

RESULTS

Graft insulin secretion was increased to 16 to 24 mU insulin per day. Transient normoglycemia was achieved in treated mice two days after transplantation, and endogenous insulin was sufficient to sustain body weights of treated mice receiving minimal supplementation.

CONCLUSION

Glycemic efficacy of a bioartificial pancreas based on insulin-secreting enteroendocrine cells is insufficient as a standalone therapy, despite enhancement of graft insulin secretion capacity. Supplemental strategies to alleviate secretion limitations should be pursued.

In Vitro Assessment of Human Islet Vulnerability to Instant Blood-Mediated Inflammatory Reaction (IBMIR) and Its Use to Demonstrate a Beneficial Effect of Tissue Culture

Culture of human pancreatic islets is now routinely carried out prior to clinical islet allotransplantation, using conditions that have been developed empirically. One of the major causes of early islet destruction after transplantation is the process termed instant blood-mediated inflammatory reaction (IBMIR). The aim of this study was to develop in vitro methods to investigate IBMIR and apply them to the culture conditions used routinely in our human islet isolation laboratory. Freshly isolated or precultured (24 h, 48 h) human islets were incubated in either ABO-compatible allogeneic human blood or Hank's buffered salt solution (HBSS) for 1 h at 37°C. Tissue factor (TF) expression and leukocyte migration were assessed by light microscopy. TF was also quantified by ELISA. To assess β-cell function, glucose-stimulated insulin secretion (GSIS) assay was carried out. The extent of islet β-cell damage was quantified using a proinsulin assay. Islets cultured for 24 h had higher GSIS when compared to freshly isolated or 48-h precultured islets. Freshly isolated islets had significantly higher TF content than 24-h and 48-h precultured islets. Incubation of freshly isolated human islets in allogeneic human blood released 6.5-fold higher level of proinsulin in comparison to freshly isolated human islets in HBSS. The high level of proinsulin released was significantly attenuated when precultured islets (24 h or 48 h) were exposed to fresh blood. Histological examination of fresh islets in blood clot showed that some islets were fragmented, showing signs of extraislet insulin leakage and extensive neutrophil infiltration and necrosis. These features were markedly reduced when the islets were cultured for 24 h. These results suggest that our standard 24-h islet culture is markedly beneficial in attenuating IBMIR, as evidenced by increased GSIS, lower content of TF, decrease islet fragmentation, and proinsulin release.

Survival of free and encapsulated human and rat islet xenografts transplanted into the mouse bone marrow

Bone marrow was recently proposed as an alternative and potentially immune-privileged site for pancreatic islet transplantation. The aim of the present study was to assess the survival and rejection mechanisms of free and encapsulated xenogeneic islets transplanted into the medullary cavity of the femur, or under the kidney capsule of streptozotocin-induced diabetic C57BL/6 mice. The median survival of free rat islets transplanted into the bone marrow or under the kidney capsule was 9 and 14 days, respectively, whereas that of free human islets was shorter, 7 days (bone marrow) and 10 days (kidney capsule). Infiltrating CD8⁺ T cells and redistributed CD4⁺ T cells, and macrophages were detected around the transplanted islets in bone sections. Recipient mouse splenocytes proliferated in response to donor rat stimulator cells. One month after transplantation under both kidney capsule or into bone marrow, encapsulated rat islets had induced a similar degree of fibrotic reaction and still contained insulin positive cells. In conclusion, we successfully established a small animal model for xenogeneic islet transplantation into the bone marrow. The rejection of xenogeneic islets was associated with local and systemic T cell responses and macrophage recruitment. Although there was no evidence for immune-privilege, the bone marrow may represent a feasible site for encapsulated xenogeneic islet transplantation.

Maturation and function of human embryonic stem cell-derived pancreatic progenitors in macroencapsulation devices following transplant into mice

AIMS/HYPOTHESIS

Islet transplantation is a promising cell therapy for patients with diabetes, but it is currently limited by the reliance upon cadaveric donor tissue. We previously demonstrated that human embryonic stem cell (hESC)-derived pancreatic progenitor cells matured under the kidney capsule in a mouse model of diabetes into glucose-responsive insulin-secreting cells capable of reversing diabetes. However, the formation of cells resembling bone and cartilage was a major limitation of that study. Therefore, we developed an improved differentiation protocol that aimed to prevent the formation of off-target mesoderm tissue following transplantation. We also examined how variation within the complex host environment influenced the development of pancreatic progenitors in vivo.

METHODS

The hESCs were differentiated for 14 days into pancreatic progenitor cells and transplanted either under the kidney capsule or within Theracyte (TheraCyte, Laguna Hills, CA, USA) devices into diabetic mice.

RESULTS

Our revised differentiation protocol successfully eliminated the formation of non-endodermal cell populations in 99% of transplanted mice and generated grafts containing >80% endocrine cells. Progenitor cells developed efficiently into pancreatic endocrine tissue within macroencapsulation devices, despite lacking direct contact with the host environment, and reversed diabetes within 3 months. The preparation of cell aggregates pre-transplant was critical for the formation of insulin-producing cells in vivo and endocrine cell development was accelerated within a diabetic host environment compared with healthy mice. Neither insulin nor exendin-4 therapy post-transplant affected the maturation of macroencapsulated cells.

CONCLUSIONS/INTERPRETATION

Efficient differentiation of hESC-derived pancreatic endocrine cells can occur in a macroencapsulation device, yielding glucose-responsive insulin-producing cells capable of reversing diabetes.

The islet size to oxygen consumption ratio reliably predicts reversal of diabetes posttransplant

β-Cell replacement therapy by either whole-organ pancreas or islets of Langerhans transplantation can restore carbohydrate control to diabetic patients and reduces complications associated with the disease. One of the variables inherent in islet transplantation is the isolation of functional islets from donor pancreata. Islet isolations fail to consistently produce good-quality functional islets. A rapid pretransplant assay to determine posttransplant function of islets would be an invaluable tool. We have tested the novel hypothesis that modified oxygen consumption rates (OCR), standardized to DNA quantity (nmol/min-mg DNA), would serve as a pretransplant assessment of the metabolic potency of the islets postisolation. This study compares the ability of current in vitro assays to predict in vivo restoration of normoglycemia in a diabetic nude mouse posttransplantation of adult pig islets. There is known to be a diversity of islet sizes within each preparation. This parameter has not heretofore been effectively considered a critical factor in islet engraftment. Our results suggest a surprising finding that islet size influences the probability of restoring carbohydrate control. Based on this observation, we thus developed a novel predictor of islet graft function that combines the effects of both islet OCR and size. When OCR was divided by the islet index (size), a highly significant predictor of graft function was established (p = 0.0002, n = 75). Furthermore, when OCR/islet index values exceeded 70.0 nmol/min-mg DNA/islet index, an effective threshold of diabetes reversal was observed. This assay can be performed with as few as 1,000 islet equivalents (IEQ) and conducted in less than 60 min. Our data suggest that, using this novel method to assess islet cell function prior to transplantation, OCR/islet index thresholds provide a valuable tool in identifying which islet preparations are most likely to restore glycemic control posttransplant.

Characterization of human umbilical cord lining-derived epithelial cells and transplantation potential

In this study we describe the derivation and immunological characterization of a primary epithelial cell type from the human umbilical cord membrane. These cord lining epithelial cells (CLECs) expressed and/or secreted isoforms of the nonclassical human leukocyte antigen class I (HLA-1b) glycoproteins, HLA-G and E. Conditioned media from CLECs inhibited mitogen-stimulated T-lymphocyte responses, and in a mixed leukocyte reaction (MLR) assay, cocultured CLECs inhibited allogeneic responses with a concomitant reduction in proinflammatory cytokines. Using a transwell coculture system, it was demonstrated that these immunoregulatory effects were mediated by soluble factors secreted by CLECs, in a dose-dependent manner. Functional studies using HLA-G blocking antibody showed that the effects of CLEC-secreted products could be inhibited, thus demonstrating a significant and important role for soluble HLA-G. In vivo, we show that transplanted CLECs could be maintained for extended periods in immunocompetent mice where xenorejection rapidly destroyed primary keratinocytes, a control human epithelial cell type. Additionally, CLECs delayed the rejection of keratinocytes and extended their survival when cotransplanted, indicating an ability to protect adjacent human cell types that would otherwise be rejected if transplanted alone. We also show that CLECs transduced with a modified human proinsulin gene were transplanted intraperitoneally into streptozotocin (STZ)-induced diabetic mice, resulting in significantly lower levels of serum glucose compared to control mice. This study has characterized the immunological properties of CLECs and tested a potential therapeutic application in the treatment of a type 1 diabetes mouse model.

Signalling pathways and the host-parasite relationship: putative targets for control interventions against schistosomiasis: signalling pathways and future anti-schistosome therapies

A better understanding of how schistosomes exploit host nutrients, neuro-endocrine hormones and signalling pathways for growth, development and maturation may provide new insights for improved interventions in the control of schistosomiasis. This paper describes recent advances in the identification and characterisation of schistosome tyrosine kinase and signalling pathways. It discusses the potential intervention value of insulin signalling, which may play an important role in glucose uptake and carbohydrate metabolism in schistosomes, providing the nutrients essential for parasite growth, development and, notably, female fecundity. Significant progress has also been made in the characterisation of other schistosome growth factor receptors, such as transforming growth factor beta receptor and epidermal growth factor receptor, and in our understanding of their roles in the host-parasite molecular dialogue and parasite development. The use of parasite signal transduction components as novel vaccine or drug targets may prove invaluable in prevention, treatment and control strategies to combat schistosomiasis.

Delivery of a therapeutic protein by immune-privileged Sertoli cells

Immune-privileged Sertoli cells survive long term after allogeneic or xenogeneic transplantation without the use of immunosuppressive drugs, suggesting they could be used as a vehicle to deliver therapeutic proteins. As a model to test this, we engineered Sertoli cells to transiently produce basal levels of insulin and then examined their ability to lower blood glucose levels after transplantation into diabetic SCID mice. Mouse and porcine Sertoli cells transduced with a recombinant adenoviral vector containing furin-modified human proinsulin cDNA expressed insulin mRNA and secreted insulin protein. Transplantation of 5-20 million insulin-expressing porcine Sertoli cells into diabetic SCID mice significantly decreased blood glucose levels in a dose-dependent manner, with 20 million Sertoli cells decreasing blood glucose levels to 9.8 ± 2.7 mM. Similar results were obtained when 20 million insulin-positive, BALB/c mouse Sertoli cells were transplanted; blood glucose levels dropped to 6.3 ± 2.4 mM and remained significantly lower for 5 days. To our knowledge, this is the first study to demonstrate Sertoli cells can be engineered to produce and secrete a clinically relevant factor that has a therapeutic effect, thus supporting the concept of using immune-privileged Sertoli cells as a potential vehicle for gene therapy.