Challenges facing islet transplantation for the treatment of type 1 diabetes mellitus

Combining cell therapy and nanotechnology

Cell transplantation to treat diseases characterised by tissue and cell dysfunction, ranging from diabetes to spinal cord injury, has made great strides preclinically and towards clinical efficacy. In order to enhance clinical outcomes, research needs to continue in areas including the development of a universal cell source that can be differentiated into specific cellular phenotypes, methods to protect the transplanted allogeneic or xenogeneic cells from rejection by the host immune system, techniques to enhance cellular integration of the transplant within the host tissue, strategies for in vivo detection and monitoring of the cellular implants, and new techniques to deliver genes to cells without eliciting a host immune response. Overcoming these obstacles will be of considerable benefit, as it allows understanding, visualising and controlling cellular interactions at a submicron level. Nanotechnology is a multidisciplinary field that allows us to manipulate materials, tissues, cells and DNA at the level of and within the individual cell. As such, nanotechnology may be well suited to optimise the generally encouraging results already achieved in cell transplantation. This review presents some of the ways that nanotechnology can directly contribute to cell transplantation.

Assessment of islet function following islet and pancreas transplantation

Pancreas and islet transplant recipients are monitored using various metabolic and imaging methods. The inaccessibility of the transplanted whole pancreas and of the isolated islets poses specific problems (eg, all assessment techniques are indirect). Although successful pancreas transplantation typically restores normal glucose homeostasis, islet transplantation into the liver does not completely normalize islet hormone secretion and glucose metabolism. Development of better testing strategies, such as direct islet imaging, will significantly advance the field.

Is facilitating pancreatic beta cell regeneration a valid option for clinical therapy?

Type 1 diabetes (T1D) is an autoimmune disease in which the clinical onset most frequently presents in adolescents who are genetically predisposed. There is accumulating evidence that the endocrine pancreas has regenerative properties, that hematopoietic chimerism can abrogate destruction of beta cells in autoimmune diabetes, and that, in this manner, physiologically sufficient endogenous insulin production can be restored in clinically diabetic NOD mice. Recapitulating what also has been seen sporadically in humans, we set out to test reliable and clinically translatable alternatives able to achieve these same goals. Recently, Tian and colleagues demonstrated that T1D can be prevented in genetically susceptible mice by substituting a "diabetes-susceptible" class II MHC beta chain with a "diabetes-resistant" allelic transgene on their hematopoietic stem cells through gene supplantation. The expression of the newly formed diabetes-resistant molecule in the reinfused hematopoietic cells was sufficient to prevent T1D onset even in the presence of the native, diabetogenic molecule. If this approach to obtain autoimmunity abrogation could facilitate a possible recovery of autologous insulin production in diabetic patients, safe induction of an autoimmunity-free status might become a new promising therapy for T1D.

In vivo bioluminescence imaging of transplanted islets and early detection of graft rejection

BACKGROUND

Bioluminescence imaging (BLI) modalities are being developed to monitor islet transplant mass and function in vivo. The aim of this study was to use the BLI system to determine how the change in functional islet mass correlated to metabolic abnormalities during the course of alloimmune rejection in a murine transplant model.

METHODS

Islets obtained from a transgenic mouse strain (FVB/NJ-luc) that constitutively expressed firefly luciferase were transplanted to various implantation sites of syngeneic wild-type FVB/NJ or allogeneic Balb/C streptozotocin-induced diabetic recipients. In vivo graft luminescent signals were repeatedly measured after transplantation using the BLI system and related to blood glucose levels and graft site histologic findings.

RESULTS

The BLI signals were detected in as few as 10 islets implanted in the renal subcapsular space, intrahepatic, intraabdominal, and subcutaneous locations. There was a linear relationship between the number of islets transplanted and luminescence intensity. In isografts, stable luminescence intensity signals occurred within 2 weeks of transplantation and remained consistent on a long-term basis (18 months) after transplantation. In allografts, after normoglycemia was achieved and stable luminescence intensity occurred, graft bioluminescent intensity progressively decreased several days before permanent recurrence of hyperglycemia as a result of histologically proven rejection ensued.

CONCLUSIONS

Bioluminescence imaging is a sensitive method for tracking the fate of islets after transplantation and is a useful method to detect early loss of functional islet mass caused by host immune responses even before overt metabolic dysfunction is evident. Bioluminescence imaging holds promise for use in designing and testing interventions to prolong islet graft survival.

Pancreatic islet transplantation for treating diabetes

Pancreatic islet transplantation is one of the options for treating diabetes and has been shown to improve the quality of life of severe diabetic patients. Since the Edmonton protocol was announced, islet transplantation have advanced considerably, including islet after kidney transplantation, utilisation of non-heart-beating donors, single-donor islet transplantation and living-donor islet transplantation. These advances were based on revised immunosuppression protocols, improved pancreas procurement and islet isolation methods, and enhanced islet engraftment. Further improvements are necessary to make islet transplantation a routine clinical treatment. To synergise efforts towards a cure for type 1 diabetes, a Diabetes Research Institute (DRI) Federation is currently being established to include leading diabetes research centres worldwide, including DRIs in Miami, Edmonton and Kyoto among others.

Cystic cholangiomas after transplantation of pancreatic islets into the livers of diabetic rats

Islet transplantation is increasingly used as a therapy for human type 1 diabetes mellitus. In our study, we investigated the effect of the transplantation of a low number (n = 350) of pancreatic islets into the right liver part on the neighboring portal bile ducts. Male streptozotocin- diabetic Lewis or autoimmune-diabetic BB/Pfd rats (n = 1065) were subdivided into 11 experimental groups. A few days after low-number islet transplantation, cholangiocytes adjacent to the grafts showed an increase in proliferative activity. During the next 12-24 months, many peri-insular ductules progressed via tumor-like cystic lesions to large cystic cholangiomas, accompanied by a translocation of the insulin receptor into the cytoplasm and an increase in expression of insulin-related signaling proteins (Insulin-receptor-substrate-1, Raf-1, Mek-1). After 24 months, 53% of rats with low-number transplantation exhibited at least one cholangioma >10 mm, significantly outnumbering tumor development in the transplant-free left liver part and in any control group. No cholangiocarcinomas emerged. A graft cell origin of the tumors was excluded by Y chromosome in situ hybridization in cross-gender transplantations. Conclusively, low-number intrahepatic islet transplantation, most likely acting by permanent local hyperinsulinism, leads to prolonged cholangiocellular proliferation in streptozotocin- and in autoimmune-diabetic rats, resulting in the development of benign cystic cholangiomas.

Magnetic resonance imaging of intrahepatically transplanted islets using paramagnetic beads

Superparamagnetic agents can be reliably used for magnetic resonance imaging (MRI) of pancreatic islets located in the liver sinusoids. However, the main disadvantages seemed to be the rather long culture time necessary for islet labeling and the low specificity of these agents. In the present study we investigated a more specific approach with a shorter labeling time using immunomagnetic particles. Isolated rat islets were cultivated with immunomagnetic beads coated with antibody against rat MHC class I antigen. Labeled islets were transplanted into the livers of syngeneic rats. The animals were examined weekly by MRI or livers explanted 10 minutes after islet transplantation for in vitro experiments. In both in vitro and in vivo studies, labeled transplanted islets were imaged as hypointensive spots, diffusely distributed throughout the liver. This experiment represents an alternative way of islet imaging by magnetic resonance, which is as effective as the use of known superparamagnetic contrast agents and more specific owing to targeting to specific donor antigens.

Gene therapy for diabetes: reinventing the islet

A cure for type 1 (insulin dependent) diabetes might be found in generating surrogate insulin-producing cells to replace beta cells. A gene therapy strategy using constructs designed to allow glucose-regulated insulin transcription when delivered to non-pancreatic tissues has not fully recreated the stringent control of blood glucose provided by the beta cell. A more promising gene therapy approach has been to express pancreatic endocrine developmental factors, such as PDX-1, NeuroD/BETA2 and Neurogenin 3, to promote differentiation of non-endocrine cells towards a beta cell or islet phenotype, enabling these cells to synthesize and secrete insulin in a glucose-regulated manner. Further research is necessary, however, to better define the most effective pro-endocrine factors and the most amenable cell types to achieve transdifferentiation for beta cell replacement.

The potential for stem cell therapy in diabetes

Both type 1 and type 2 diabetes are characterized by a marked deficit in beta-cell mass causing insufficient insulin secretion. Beta-cell replacement strategies may eventually provide a cure for diabetes. Current therapeutic approaches include pancreas and islet transplantation, but the chronic shortage of donor organs restricts this treatment option to a small proportion of affected patients. Moreover, recent evidence shows a progressive decline in beta-cell function after islet transplantation so that most patients have to revert to insulin treatment within a few years. In this article recent progress in the generation, culture and targeted differentiation of human embryonic stem (ES) cells is reviewed, and some of the issues surrounding their use as a source of beta-cells are discussed.

Hepatocellular neoplasms induced by low-number pancreatic islet transplants in autoimmune diabetic BB/Pfd rats

It has been shown that combined high local hyperinsulinism and hyperglycemia after low-number islet transplantation into the livers of streptozotocin-diabetic rats lead to the development of hepatocellular neoplasms but a substantial cocarcinogenic effect of genotoxic streptozotocin could not be ruled out completely. Thus, we herein investigated this model in BB/Pfd rats (n = 805; nine experimental groups), which develop spontaneous autoimmune diabetes similar to human type 1 diabetes. After low-number islet transplantation (n = 450), the liver acini downstream of the islets show insulin-induced alterations: massive glycogen and/or fat accumulation, translocation of the insulin receptor, decrease in glucose-6-phosphatase activity, increase in expression of insulin-like growth factor (IGF)-I, IGF-II/mannose-6-phosphate receptor, insulin receptor substrate-1, Raf-1, and Mek-1, corresponding to clear cell preneoplastic foci of altered hepatocytes known from chemical hepatocarcinogenesis and identical to that in streptozotocin-diabetic Lewis rats. After 6 months, many altered liver acini progressed to other types of preneoplasias often accompanied by an overexpression of the glutathione-S transferase (placental form), IGF-I receptor, and transforming growth factor (TGF)-alpha. After 12 to 15 and 15 to 18 months, 52% and 100% of the animals showed one or multiple hepatocellular adenomas or hepatocellular carcinomas (HCCs), respectively. Conclusively, this study identifies combined hyperinsulinism and hyperglycemia as a carcinogenic mechanism for the development of HCCs in diabetic rats. Hepatocarcinogenesis is independent from additional genotoxic compounds (i.e., streptozotocin), but is primarily triggered by increased intracellular insulin signaling via pathways associated with cell growth and proliferation, such as the Ras-Raf-mitogen-activated protein kinase pathway and the IGF system, and secondarily involves other growth factors, such as TGF-alpha.

Effective islet isolation method with extremely high islet yields from adult pigs

Achieving good islet isolation is one of the most important factors for successful islet transplantation. Porcine pancreas is suitable for islet isolation research due to its anatomical and physiological similarities to human pancreas. In this study, we evaluated a new porcine islet isolation method designed to maximize islet yield and compared it with our previous open pan method and the standard method using a Ricordi chamber (Ricordi method). We performed 15 porcine islet isolations, five each with the new method, the open pan method, and the Ricordi method. The new method features several important improvements. Pancreata remain uncut and are kept intact during collagenase intraductal injection, a large filtration chamber to handle whole pancreata, low concentration of collagenase (Liberase HI) for digestion, and large plastic containers for large-scale islet purification. All isolated islets were assessed for yield, purity, viability and in vitro function. Islets isolated with this new method were transplanted under the kidney capsules of SCID mice with chemically induced diabetes for in vivo functional assessment (n = 8). With the new method, we obtained on average more than 1,000,000 islet equivalents (IE) (1,236,266 +/- 213,486 IE) (mean +/- SE) before purification and 800,000 IE (879,815 +/- 222,729 IE) after purification from one adult pig. Islet yield per pancreas was significantly higher compared with our previous open pan method (30,666 +/- 11,532 IE, p < 0.01) and the Ricordi method (317,073 +/- 86,093 IE, p < 0.05). All mice, transplanted with 1000 islets from the new method, returned to normoglycemia within 4 days after transplantation. Our new method makes it possible to obtain extremely high porcine islet yield with good function. It should produce useful information for human islet isolation and transplantation, and might be applied to single donor clinical xenogeneic transplantation.

Vascularized tissue-engineered chambers promote survival and function of transplanted islets and improve glycemic control

We have developed a chamber model of islet engraftment that optimizes islet survival by rapidly restoring islet-extracellular matrix relationships and vascularization. Our aim was to assess the ability of syngeneic adult islets seeded into blood vessel-containing chambers to correct streptozotocin-induced diabetes in mice. Approximately 350 syngeneic islets suspended in Matrigel extracellular matrix were inserted into chambers based on either the splenic or groin (epigastric) vascular beds, or, in the standard approach, injected under the renal capsule. Blood glucose was monitored weekly for 7 weeks, and an intraperitoneal glucose tolerance test performed at 6 weeks in the presence of the islet grafts. Relative to untreated diabetic animals, glycemic control significantly improved in all islet transplant groups, strongly correlating with islet counts in the graft (P<0.01), and with best results in the splenic chamber group. Glycemic control deteriorated after chambers were surgically removed at week 8. Immunohistochemistry revealed islets with abundant insulin content in grafts from all groups, but with significantly more islets in splenic chamber grafts than the other treatment groups (P<0.05). It is concluded that hyperglycemia in experimental type 1 diabetes can be effectively treated by islets seeded into a vascularized chamber functioning as a "pancreatic organoid."

Streptozotocin-induced diabetes in large animals (pigs/primates): role of GLUT2 transporter and beta-cell plasticity

BACKGROUND

To induce irreversible diabetes in large animals, the efficiency of streptozotocin (STZ) was evaluated in pigs, primates and compared to the gold standard model in rats.

METHODS

Low (50 mg/kg) and high (150 mg/kg) doses of STZ were tested. Hepatic/renal function, glucose metabolism (intravenous glucose tolerance tests, fasting blood glucose) and histomorphometry were evaluated prior to, 1, and 4 weeks after STZ treatment.

RESULTS

In rats and primates, expressing a high level of GLUT2 expression on beta cells, a dose of 50 mg/kg STZ induced irreversible diabetes (due to the 97% destruction of beta cell mass) without provoking liver or renal failure. In pigs, despite the use of high STZ dose, partial correction of hyperglycaemia was observed four weeks after STZ injection (decreased fasting blood glucose and intravenous glucose tolerance tests; increased insulin production). The correction of hyperglycaemia was associated with significant hypertrophy of immature pig beta-cell clusters (+30%, P<0.05), whereas no hypertrophy was observed in rats/primates.

CONCLUSION

These results demonstrated that STZ might be used to induce irreversible diabetes in rats and primates. In contrast, the low STZ sensitivity in pigs related to a low expression of GLUT2, higher number of immature beta cells and compensatory beta-cell hypertrophy, renders STZ-induced diabetes inappropriate for studying islet allografts in swine.

Inhibition of apoptosis by survivin improves transplantation of pancreatic islets for treatment of diabetes in mice

Survivin is a cancer gene implicated in inhibition of apoptosis and regulation of mitosis, but its function in normal cells has remained elusive. Here, we show that transgenic mice expressing survivin in pancreatic islet beta-cells show no changes in cell proliferation, as determined by islet size or islet number. Transplantation of survivin transgenic islets in diabetic recipient mice affords long-term engraftment and stable correction of hyperglycaemia. This involves intrinsic inhibition of beta-cell apoptosis, in vivo, and global transcriptional changes in pancreatic islets with upregulation of stress response genes, antagonists of cytokine signalling and promoters of angiogenesis. These broad cytoprotective functions of survivin in vivo might be beneficial for gene therapy of diabetes.

Facilitating physiologic self-regeneration: a step beyond islet cell replacement

Type 1 diabetes (T1D) is an autoimmune disease, the clinical onset of which most frequently presents in children and adolescents who are genetically predisposed. T1D is characterized by specific insulin-producing beta cell destruction. The well-differentiated and specialized islet beta cells seem to physiologically retain the ability to compensate for the cells lost by reproducing themselves, whereas undifferentiated cell sources may help in generating new ones, even while the autoimmune process takes place. Diabetes clinical onset, i.e., establishment of a detectable, chronic hyperglycemia, occurs at a critical stage when autoimmunity, having acted for a while, supersedes the regenerative effort and reduces the number of beta cells below the physiologic threshold at which the produced insulin becomes insufficient for the body's needs. Clinical solutions aimed at avoiding cumbersome daily insulin administrations by the reestablishment of physiologic insulin production, like whole pancreas or pancreatic islet allotransplantation, are limited by the scarcity of pancreas donors and by the toxic effects of the immunosuppressive drugs administered to prevent rejection. However, new accumulating evidence suggests that, once autoimmunity is abrogated, the endocrine pancreas properties may be sufficient to allow the physiological regenerative process to restore endogenous insulin production, even after the disease has become clinically manifest. Knowledge of these properties of the endocrine pancreas suggests the testing of reliable and clinically translatable protocols for obliterating autoimmunity, thus allowing the regeneration of the patient's own endocrine cells. The safe induction of an autoimmunity-free status might become a new promising therapy for T1D.

Pancreatic islet cell transplantation using non-heart-beating donors (NHBDs)

Recent dramatic improvements in clinical islet cell transplantation demonstrated by the Edmonton group have increased the demand for this treatment, and donor shortage could become a major problem. Utilization of marginal donors could alleviate the donor shortage, and non-heart-beating donors (NHBDs) might be good resources. The University of Pennsylvania group demonstrated that it was possible to isolate islets from NHBDs, and the group actually transplanted islets from NHBDs, for the first time. The patient became insulin-independent; however, there had been no more cases using NHBDs until our group initiated islet transplantations from NHBDs in Japan. In order to utilize NHBDs effectively, we modified the standard islet isolation method. These modifications included minimizing the warm ischemic time, the use of trypsin inhibition during isolation, carrying out density measurement before purification and the use of a less toxic islet purification solution. With these modifications we were able to transplant nine of ten islet preparations from ten NHBDs (90%), into five type-1 diabetic patients. The first transplantation was performed on April 7, 2004 (the first time in Japan), and this patient became insulin-independent after the second islet transplantation (first time in Japan). All patients showed improved glycemic control and reduced insulin requirements, without hypoglycemic events. We also performed living-donor islet transplantation, with our modified islet isolation protocol, on January 19, 2005. The improved islet isolation protocol enabled us to perform effective islet transplantations from NHBDs, and it also enabled us to perform the living-donor islet transplantation.

Glucose-stimulated DNA synthesis through mammalian target of rapamycin (mTOR) is regulated by KATP channels: effects on cell cycle progression in rodent islets

The aim of this study was to define metabolic signaling pathways that mediate DNA synthesis and cell cycle progression in adult rodent islets to devise strategies to enhance survival, growth, and proliferation. Since previous studies indicated that glucose-stimulated activation of mammalian target of rapamycin (mTOR) leads to [3H]thymidine incorporation and that mTOR activation is mediated, in part, through the K(ATP) channel and changes in cytosolic Ca2+, we determined whether glyburide, an inhibitor of K(ATP) channels that stimulates Ca2+ influx, modulates [3H]thymidine incorporation. Glyburide (10-100 nm) at basal glucose stimulated [3H]thymidine incorporation to the same magnitude as elevated glucose and further enhanced the ability of elevated glucose to increase [3H]thymidine incorporation. Diazoxide (250 microm), an activator of KATP channels, paradoxically potentiated glucose-stimulated [3H]thymidine incorporation 2-4-fold above elevated glucose alone. Cell cycle analysis demonstrated that chronic exposure of islets to basal glucose resulted in a typical cell cycle progression pattern that is consistent with a low level of proliferation. In contrast, chronic exposure to elevated glucose or glyburide resulted in progression from G0/G1 to an accumulation in S phase and a reduction in G2/M phase. Rapamycin (100 nm) resulted in an approximately 62% reduction of S phase accumulation. The enhanced [3H]thymidine incorporation with chronic elevated glucose or glyburide therefore appears to be associated with S phase accumulation. Since diazoxide significantly enhanced [3H]thymidine incorporation without altering S phase accumulation under chronic elevated glucose, this increase in DNA synthesis also appears to be primarily related to an arrest in S phase and not cell proliferation.

Multifaceted therapeutic approaches for a multigenic disease

Diabetes is a severe chronic disease that affects approximately 200 million individuals worldwide, with extremely debilitating effects and considerably high health care costs. The two major classes of diabetes, known as type 1 (previously known as insulin-dependent or juvenile-onset diabetes) and type 2 (non-insulin-dependent diabetes), share common symptoms such as hyperglycemia and the development of long-term complications, but they differ in many aspects, including their etiopathogenesis. New insights suggest that overlapping factors, formerly considered typical hallmarks of each specific type, can coexist in the same diabetic patient, making it difficult to support a sharp distinction between the two classes and, more importantly, to adopt appropriate therapeutic solutions. In type 1 and type 2 diabetic subjects, but even more in patients with combined types, multiple genetic factors play a role in determining susceptibility or resistance to the disease, and perhaps also the time of onset, the severity of the symptoms, the possibility of developing complications and, ultimately, the response to therapy. In this review, the therapeutic treatments currently under investigation, as well as the curative strategies envisioned for future applications, are reanalyzed considering the multifaceted and complex aspects of a continuum that can be just defined as "diabetes."

Natural history of beta-cell function in type 1 diabetes

Despite extensive and ongoing investigations of the immune mechanisms of autoimmune diabetes in humans and animal models, there is much less information about the natural history of insulin secretion before and after the clinical presentation of type 1 diabetes and the factors that may affect its course. Studies of insulin production previously published and from the Diabetes Prevention Trial (DPT)-1 suggest that there is progressive impairment in insulin secretory responses but the reserve in response to physiological stimuli may be significant at the time of diagnosis, although maximal responses are more significantly impaired. Other factors, including insulin resistance, may play a role in the timing of clinical presentation along this continuum. The factors that predict the occurrence and rapidity of decline in beta-cell function are still largely unknown, but most studies have identified islet cell autoantibodies as predictors of future decline and age as a determinant of residual insulin production at diagnosis. Historical as well as recent clinical experience has emphasized the importance of residual insulin production for glycemic control and prevention of end-organ complications. Understanding the modifiers and predictors of beta-cell function would allow targeting immunological approaches to those individuals most likely to benefit from therapy.

Would blockage of cytokines improve the outcome of pancreatic islet transplantation?

It has been estimated that up to 60% of pancreatic islet tissue undergoes apoptosis within the first several days post-transplantation. This strongly suggests the involvement of an inflammatory event other than alloantigen-specific immune reaction following islet transplantation which contributes to partial destruction of grafts. Inflammatory cytokines including IL-1beta, TNF-alpha and IFN-gamma are implicated in the pancreatic islet beta-cell death and functional loss during autoimmune diabetes and also seem to be involved in early loss of islet mass in islet transplantation. Inflammatory cytokines and free oxygen radicals released in situ could cause apoptosis and the functional impairment of islets after islet transplantation and graft failure. It can be hypothesized that preventing destruction of transplanted islets using cytokine blockade could be helpful in improving islet transplantation outcome. Several approaches have been made based on this hypothesis to examine the effect of inflammatory blockade on the islets survival and functional islet mass. Further investigations are required to identify most efficient way for block of cytokine-induced damage in pancreatic islets transplantation.

Harmful delayed effects of exogenous isolation enzymes on isolated human islets: relevance to clinical transplantation

The isolation process exposes human pancreatic islets to exogenous isolation enzymes. Exposure to these enzymes, as a result of intraductal injection in the pancreas or simple contact of islets with enzyme components, causes internalization into the islet cells of enzymes and their by-products. Human islets exposed to Liberase-HI exhibit a decreased insulin secretory ability that correlates with the time of exposure. This phenomenon is paralleled by increased expression of adhesion molecules (CD106 and CD62p) and activation of apoptotic pathways (Bax and Bcl-2) in islet cells. Increased functional impairment is also observed after islet transplantation in diabetic immunodeficient mice. Experimental exposure of islet grafts to exogenous isolation enzymes causes intense inflammation (CD11b positive cells) at the transplant site and it was associated with sickness behavior and eventually death of mouse recipients. The extent of these adverse effects likely deceives the standard qualitative protocols currently in use to assess islet quality in vitro. Reducing the secondary effects of exogenous isolation enzymes on isolated human islets may be crucial to enhance the quality of islets as tissue grafts.

Combination therapy with epidermal growth factor and gastrin increases beta-cell mass and reverses hyperglycemia in diabetic NOD mice

Combination therapy with epidermal growth factor (EGF) and gastrin induces beta-cell regeneration in rodents with chemically induced diabetes. We investigated whether EGF plus gastrin could correct hyperglycemia in NOD mice with autoimmune diabetes. Combined treatment with EGF (1 mug/kg) and gastrin (3 mug/kg) for 2 weeks restored normoglycemia after diabetes onset in NOD mice, whereas EGF or gastrin alone did not. Fasting blood glucose remained normal (3.5-6.5 mmol/l) or mildly elevated (<11 mmol/l) in five of six mice (83%) for 10 weeks after EGF plus gastrin treatment was stopped, whereas all mice treated with vehicle or EGF or gastrin alone became severely hyperglycemic (12-35 mmol/l). Pancreatic beta-cell mass was increased threefold and insulin content was increased eightfold in mice treated with EGF plus gastrin compared with pretreatment values. The correction of hyperglycemia correlated significantly with increases in pancreatic beta-cell mass and insulin content. In addition, splenic cells from mice treated with EGF plus gastrin delayed diabetes induction by adoptive transfer of diabetogenic cells into immunodeficient NOD-scid mice, suggesting the induction of immunoregulatory cells in NOD mice treated with EGF plus gastrin. We conclude that a short course of combined EGF and gastrin therapy increases pancreatic beta-cell mass and reverses hyperglycemia in acutely diabetic NOD mice; the impact of this combined therapy may result from the effects of EGF and gastrin on beta-cells, immune cells, or both.

Growth factors and beta cell replication

Recent studies have demonstrated that human islet allograft transplantation can be a successful therapeutic option in the treatment of patients with Type I diabetes. However, this impressive recent advance is accompanied by a very important constraint. There is a critical paucity of pancreatic islets or pancreatic beta cells for islet transplantation to become a large-scale therapeutic option in patients with diabetes. This has prompted many laboratories around the world to invigorate their efforts in finding ways for increasing the availability of beta cells or beta cell surrogates that potentially could be transplanted into patients with diabetes. The number of studies analyzing the mechanisms that govern beta cell proliferation and growth in physiological and pathological conditions has increased exponentially during the last decade. These studies exploring the role of growth factors, intracellular signaling molecules and cell cycle regulators constitute the substrate for future strategies aimed at expanding human beta cells in vitro and/or in vivo after transplantation. In this review, we describe the current knowledge on the effects of several beta cell growth factors that have been shown to increase beta cell proliferation and expand beta cell mass in vitro and/or in vivo and that they could be potentially deployed in an effort to increase the number of patients transplanted with islets. Furthermore, we also analyze in this review recent studies deciphering the relevance of these specific islet growth factors as physiological and pathophysiological regulators of beta cell proliferation and islet growth.

Islet transplantation: current status and future directions

Pancreatic islet transplantation has gone a long way to finally enter the armamentarium of today's clinicians for the battle against diabetes. The proof of principle has been made and current clinical islet transplant trials need to further refine this attractive treatment modality. We review the post-Edmonton era, the selection of islet transplant recipients, the production of islet grafts, and the need for immunosuppression and procedure-related risks. The success of islet transplantation and expansion of clinical trials with islet networks are also discussed.

Cocarcinogenic Effects of Islet Hormones and N-Nitrosomorpholine in Hepatocarcinogenesis after Intrahepatic Transplantation of Pancreatic Islets in Streptozotocin-Diabetic Rats

In contrast to high local insulin levels obtained after low-number transplantation (n = 350) of islets of Langerhans into the livers of diabetic rats, low insulin levels after high-number transplantation (n = 1,000) do not suffice to induce hepatocarcinogenesis. Herein, we investigated the possible cocarcinogenic potential of high and, in particular, low insulin levels, combining this in vivo model with a chemical model of hepatocarcinogenesis after administration of N-nitrosomorpholine (NNM). In three main experiments, different schemes of single or continuous NNM administration were combined with different transplantation procedures in diabetic or nondiabetic animals, i.e., low-number and high-number islet transplantation, transplantation of polystyrene particles, and sham transplantation. Animals were sacrificed between 3 and 53 weeks after transplantation procedures. Evidence for the cocarcinogenic effects of NNM and insulin was provided in each main experiment. NNM treatment after low-number islet transplantation resulted in an increase in the number of preneoplastic hepatocellular foci, and a significant increase in the number and an earlier appearance of hepatocellular adenomas and carcinomas compared with controls. Most intriguing was the increase in preneoplastic foci after combined NNM treatment and high-number islet transplantation, proving that insulin, even in lower doses, has at least cocarcinogenic effects on the downstream hepatocytes and thus promotes an otherwise initiated hepatocarcinogenic process. Conclusively, intrahepatic transplantation of pancreatic islets acts as a strong cocarcinogenic factor together with NNM in streptozotocin-diabetic rats.

Strategic opportunities in clinical islet transplantation

More than 471 patients with type 1 diabetes have received islet transplants at 43 institutions worldwide in the past 5 years. High rates of insulin independence have been observed at 1 year in the leading islet transplant centers, and an international multicenter trial has demonstrated reproducible success of the approach. Loss of insulin independence by 5 years in the majority of recipients remains of concern, and immunosuppressant drug side effects necessitate stringent inclusion criteria for islet-alone candidates that have the most severe, unstable glycemic control despite optimal insulin therapy. The advent of new immunosuppressive drugs with superior side-effect profiles (e.g., LEA29Y and FTY720) may open up opportunities for more "islet-friendly" approaches. Future opportunities to expand the donor pool using living donor islet transplantation are within reach, and will be enhanced considerably with both donor and recipient adjunctive treatment using islet-specific growth-factors.

Treatment of severe autoimmune disease by stem-cell transplantation

Transplantation of haematopoietic stem cells--cells capable of self renewing and reconstituting all types of blood cell--can treat numerous lethal diseases, including leukaemias and lymphomas. It may now be applicable for the treatment of severe autoimmune diseases, such as therapy-resistant rheumatoid arthritis and multiple sclerosis. Studies in animal models show that the transfer of haematopoietic stem cells can reverse autoimmunity, and several mechanistic pathways may explain this phenomenon. The outcome of ongoing clinical trials, as well as of studies in patients and animal models, will help to determine the role that stem-cell transplantation can play in the treatment of autoimmune diseases.

Closed-loop insulin delivery – what lies between where we are and where we are going?

Closed-loop insulin delivery in individuals with diabetes can potentially lead to near-normal glucose profiles. To this end, existing subcutaneous glucose sensors and external insulin pumps can be linked with an insulin delivery algorithm to create a completely automated closed-loop system. This paper reviews current research into the development of such a system, with particular emphasis on creating a system emulating the physiological properties of the beta-cell. Issues related to using subcutaneous interstitial fluid for glucose sensing and insulin delivery are reviewed. Criteria for optimising the system are discussed using historical data. Existing strategies for open-loop pump therapy are presented with the objective of defining a path to advance from the existing physician/patient determined insulin therapy to a completely automated system.

ADA Outstanding Scientific Achievement Lecture 2004. Thirty years of investigating the autoimmune basis for type 1 diabetes: why can't we prevent or reverse this disease?

Thirty years ago, a convergence of investigational observations lead to the now widely accepted notion that type 1 diabetes results from an autoimmune destruction of insulin-producing beta-cells in subjects genetically predisposed to the disease. Improvements in understanding of the natural history of type 1 diabetes, the biochemical identification of autoantigens, the discovery of spontaneous animal models for the disease, the availability of immune-modulating agents, and other important facets, including disease prediction, drove an early sense of optimism that the prevention of type 1 diabetes was possible and, in some research circles, that ability was thought to be within a not-to-distant reach. Unfortunately, those early expectations proved overly optimistic, and despite the aforementioned knowledge gains, the generation of improved investigational tools, the identification of methods to prevent the disease in animal models, and the formation of very large disease prevention trials, a means to prevent type 1 diabetes in humans continues to remain elusive. Believing in the concept of "informative failures" (a.k.a., wise people learn from their mistakes), this lecture reviews the knowledge base collected over this time period and, when combined with an analysis of those research experiences, sets forth a proposal for future investigations that will, hopefully, turn discoveries into a means for the prevention or reversal of type 1 diabetes.