CT-guided fine-needle approach for intrathymic islet transplantation in a diabetic patient

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.

Revascularization of transplanted pancreatic islets and role of the transplantation site

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

Transplantation of pancreatic islets to adrenal gland is promoted by agonists of growth-hormone-releasing hormone

Here, we evaluate an alternative approach of preconditioning pancreatic islets before transplantation using a potent agonist of growth-hormone-releasing hormone (GHRH) to promote islet viability and function, and we explore the adrenal gland as an alternative transplantation site for islet engraftment. The endocrine microenvironment of the adrenal represents a promising niche with the unique advantages of exceptional high oxygen tension and local anti-inflammatory and immunosuppressive properties. GHRH agonists have been shown to promote islet graft survival and function, which may help to reduce the islet mass necessary to reverse diabetes. In the present study, the most potent GHRH agonist MR403 was tested on insulinoma cells, isolated rat islets, and adrenal β-cell cocultures in vitro. GHRH receptor is expressed on both adrenal cells and islets. MR403 caused a significant increase in cell viability and proliferation and revealed an antiapoptotic effect on insulinoma cells. Viability of rat islets was increased after treatment with the agonist and in coculture with adrenal cells. Rat islets were transplanted into diabetic mice to the intraadrenal transplant site and compared with the classical transplants underneath the kidney capsule. Graft function and integration were tested by metabolic follow-up and immunohistochemical staining of intraadrenal grafts. A rapid decrease occurred in blood glucose levels in both models, and all animals reached normoglycemia within the first days after transplantation. Our studies demonstrated that the adrenal may be an attractive site for islet transplantation and that GHRH analogs might allow reduction of the islet mass needed to reverse a diabetic status.

Optimal implantation site for pancreatic islet transplantation

BACKGROUND

Since the first report of successful pancreatic islet transplantation to reverse hyperglycaemia in diabetic rodents, there has been great interest in determining the optimal site for implantation. Although the portal vein remains the most frequently used site clinically, it is not ideal. About half of the islets introduced into the liver die during or shortly after transplantation. Although many patients achieve insulin independence after portal vein infusion of islets, in the long term most resume insulin injections.

METHODS

This review considers possible sites and techniques of islet transplantation in small and large animal models, and in humans. Metabolic, immunological and technical aspects are discussed.

RESULTS AND CONCLUSION

Many groups have sought an alternative site that might offer improved engraftment and long-term survival, together with reduced procedure-related complications. The spleen, pancreas, kidney capsule, peritoneum and omental pouch have been explored. The advantages and disadvantages of various sites are discussed in order to define the most suitable for clinical use and to direct future research.

Radiologic aspects of islet cell transplantation

Percutaneous transhepatic intraportal pancreatic islet transplantation is an experimental treatment for patients with type 1 diabetes. The radiologic aspects of pancreatic islet transplantation are described, including a review of interventional radiology, ultrasound, and fluoroscopy image-guided, minimally invasive techniques and procedure-related complications and their avoidance.

Clinical islet transplant: current and future directions towards tolerance

The ultimate goal of islet transplantation is to completely correct the diabetic state from an unlimited donor source, without the need for chronic immunosuppressive drug therapy. Although islet transplantation provides an opportunity to develop innovative strategies for tolerance in the clinic, both alloimmune and autoimmune barriers must be controlled, if stable graft function is to be maintained long-term. After islet extraction from the pancreas, the cellular graft may be stored in tissue culture or cryopreserved for banking, providing an opportunity not only to optimally condition the recipient but also to allow in vitro immunologic manipulation of the graft before transplantation, unlike solid organ grafts. As such, islets may be considered a "special case." Remarkable progress has occurred in the last three years, with dramatic improvements in outcomes after clinical islet transplantation. The introduction of a steroid-free, sirolimus-based, anti-rejection protocol and islets prepared from two (or rarely three) donors led to high rates of insulin independence. The "Edmonton Protocol" has been successfully replicated by other centers in an international multicenter trial. A number of key refinements in pancreas transportation, processing, purification on non-ficoll-based media, storage of islets in culture for two days and newer immunological conditioning and induction therapies have led to continued advancement through extensive collaboration between key centers. This review outlines the historical development of islet transplantation over the past 30 years, provides an update on current clinical outcomes, and summarizes a series of unique opportunities for development and early testing of tolerance protocols in patients.

Mechanisms of tolerance induction after intrathymic islet injection: determination of the fate of alloreactive thymocytes

BACKGROUND

Intrathymic (IT) administration of antigen when combined with peripheral T-cell depletion has been shown to induce operational tolerance in a wide range of experimental protocols. IT injection of pancreatic islets has been demonstrated not only to induce tolerance to alloantigen but also to prevent the development of autoimmune beta-cell destruction in models of type I diabetes. However, little is known about the mechanisms involved in tolerance induction after IT islet injection.

METHODS AND RESULTS

A protocol for the induction of tolerance to fully allogeneic (C57BL/10; H2b) peripheral islet allografts was developed in CBA/Ca (H2k) recipients by the IT injection of allogeneic islets combined with depletion of peripheral CD4+ T cells. This protocol was based upon our own data and those of others showing that CD4+ T cells play a critical role in islet allograft rejection. Using this regimen, donor-type peripheral islet allografts survived indefinitely whereas third-party grafts were rejected. To determine the fate of alloreactive thymocytes that recognize donor major histocompatibility complex antigens via the direct pathway, T-cell receptor transgenic mice specific for the major histocompatibility complex class I molecule Kb (BM3 and DES) were used as recipients. IT injection of islets expressing the specific alloantigen Kb resulted in clonal deletion of alloreactive thymocytes in T-cell receptor transgenic recipients. No evidence of clonal inactivation in the residual peripheral alloreactive population was observed in this system.

CONCLUSIONS

IT injection of allogeneic islets and concomitant CD4+ T-cell depletion is able to induce donor-specific unresponsiveness. One mechanism responsible for this unresponsiveness is the clonal deletion of thymocytes that recognize alloantigen via the direct pathway.

Prevention of experimental autoimmune uveoretinitis by intrathymic S-antigen injection

The objective of this paper was to determine whether intrathymic injection of retinal S-antigen (S-Ag) can prevent experimental autoimmune uveoretinitis (EAU) in Lewis rats. Lewis rats were injected intrathymically with 25-100 micrograms of S-Ag in 100 microliters split between thymic lobes. Controls received vehicle alone (PBS) or 100 micrograms of BSA. Animals were immunized two weeks later with 100 micrograms of S-Ag in CFA with or without pertussis toxin (0.5 micrograms/rat). Clinical ocular disease was confirmed by histopathology. Splenocytes and lymph node cells were assayed, in vitro, for their ability to proliferate in response to various concentrations of S-Ag. Furthermore, attempts were made to adoptively transfer protection to naive rats using spleen cells from intrathymically injected animals and to adoptively transfer EAU to protected rats using Con A activated cells from affected animals. Intrathymic injection of S-Ag reduced the incidence of EAU in animals subsequently immunized with S-Ag and pertussis, and prevented it entirely in rats immunized in the absence of pertussis. Splenic and lymph node cells from intrathymically injected animals showed reduced reactivity to S-Ag compared to controls, suggesting that intrathymic S-Ag injection may have rendered them tolerant to this antigen. We were unable to adoptively transfer protection to naive rats, nor were intrathymically injected rats protected from EAU induced by the adoptive transfer of primed lymph node cells. These data demonstrate that intrathymic S-Ag injection can be an effective method for protection from EAU, apparently through the induction of immunological tolerance and not active suppression. The tolerance was not absolute and could be overcome by increasing the intensity of the antigenic challenge.