In vitro and in vivo performance of porcine islets encapsulated in interfacially photopolymerized poly(ethylene glycol) diacrylate membranes.

The usefulness of interfacial photopolymerization of poly(ethylene glycol) (PEG) diacrylate at a variety of concentrations and molecular weights to form hydrogel membranes for encapsulating porcine islets of Langerhans was investigated. The results from this study show in vitro and in vivo function of PEG-encapsulated porcine islets and the ability of PEG membranes to prevent immune rejection in a discordant xenograft model. Encapsulated islets demonstrated an average viability of 85% during the first week after encapsulation, slightly but significantly lower than unencapsulated controls.

A sensitivity study of the key parameters in the interfacial photopolymerization of poly(ethylene glycol) diacrylate upon porcine islets.

A method has been defined to interfacially photopolymerize poly(ethylene glycol) diacrylates (PEG diacrylates) to form a crosslinked hydrogel membrane upon the surfaces of porcine islets of Langerhans to serve as an immune barrier for allo- and xenotransplantation. A sensitivity study of six key parameters in the interfacial photopolymerization process was performed to aid in determination of the optimal encapsulation conditions, leading to the most uniform hydrogel membranes and viable islets. The key parameters included the concentrations of the components of the initiation scheme, namely eosin Y, triethanolamine, and 1-vinyl 2-pyrrolidinone.

Immunoisolation of adult porcine islets for the treatment of diabetes mellitus. The use of photopolymerizable polyethylene glycol in the conformal coating of mass-isolated porcine islets.

Functional porcine islets, free of known pathogens, can serve as a source of insulin producing cells for the treatment of experimentally induced insulin dependent Diabetes Mellitus. Porcine islets can be conformally coated (microencapsulated) with a covalently linked, stable permselective membrane while maintaining islet viability and function. The PEG conformal coating is immunoprotective in a discordant xenograft animal model (porcine islets to rat).

Clonal insulinoma cell line that stably maintains correct glucose responsiveness.

A number of pancreatic beta-tumor cell (beta TC) lines have been derived from insulinomas arising in transgenic mice expressing the SV40 T antigen gene under control of the insulin promoter. Some of these lines secrete insulin in response to physiological glucose concentrations. However, this phenotype is unstable.

Protection of encapsulated human islets implanted without immunosuppression in patients with type I or type II diabetes and in nondiabetic control subjects.

Human islets were macroencapsulated in permselective hollow fiber membrane devices and successfully allotransplanted subcutaneously with > 90% viability after 2 weeks in situ. Recipients were patients with type I or type II diabetes and normal control subjects; none was immunosuppressed. Between 150 and 200 islet equivalents were implanted in each of the nine patients.

Long-term survival and strain-specific tolerance induction in rat-to-mouse neonatal islet xenografts.

These studies were designed to determine (1) if culture-isolated, neonatal rat islets are capable of inducing xenogeneic tolerance in mice and (2) whether this tolerance is species- or strain-specific. We attempted to induce xenogeneic tolerance by transplanting culture-isolated neonatal FSH islets to 26 diabetic C57B1/6 recipients. These animals received one injection of ALS at the time of transplant.

Dendritic cell/lymphocyte clustering: morphologic analysis by transmission electron microscopy and distribution of gold-labeled MHC class II antigens by high-resolution scanning electron microscopy.

Dendritic cells (DCs) are potent antigen-presenting cells for a variety of immune responses; however, their mechanism of action has not been established. It is known that DCs can cluster with one another and with other cell types during in vitro immune responses, and clustering may be essential for the activation of resting lymphocytes. In this study, ultrastructural examination of clusters that form during extended culture of enriched rat splenic DCs (approximately 70% DCs) is reported.

Growth of neonatal islet transplants in the spontaneously diabetic BB/Wor rat.

We have previously shown that culture-isolated neonatal islets are able to survive both rejection and the recurrence of autoimmunity in the spontaneously diabetic BB/Wor rat. In trials designed to demonstrate the MHC restriction of the autoimmune response in this model, we discovered that neonatal islet grafts from diabetic BB rats appeared larger than grafts from nondiabetic controls. This study was undertaken to quantify the mass difference seen in this original study and to determine the characteristics of graft growth in more highly controlled trials.

Increased islet allograft survival after extended culture by a mechanism other than depletion of donor APCs. Lack of correlation between the elimination of donor MHC class II-positive accessory cells and increased transplantability.

Neonatal rat islets derived by nonenzymic (in vitro) isolation procedures from the Fischer-344 (F-344, Rt1lv1) strain have been shown to be freely transplantable across complete MHC barriers without the use of any form of immunosuppression. However, islets obtained by in vitro isolation from some donor strains, such as the ACI, retain a degree of immunogenicity upon transplantation. This study examined the immunogenic nature of these neonatal ACI islets, and correlated this with the presence of a residual population of MHC class II-positive antigen presenting cells within the islets.

Maintenance of normoglycemia in diabetic mice by subcutaneous xenografts of encapsulated islets.

The goal of islet transplantation in human diabetes is to maintain the islet grafts in the recipients without the use of immunosuppression. One approach is to encapsulate the donor islets in permselective membranes. Hollow fibers fabricated from an acrylic copolymer were used to encapsulate small numbers of rat islets that were immobilized in an alginate hydrogel for transplantation in diabetic mice.

Comparative analysis of potency of splenic dendritic and adherent cells (macrophages) as alloantigen presenters in vivo.

Dendritic cells and macrophages have been attributed with stimulatory capacity for in vivo and in vitro immune responses. However, the relative contribution of each of these cell types has long been in dispute. Therefore, the differential ability of dendritic cells and macrophages (splenic adherent cells [SACs]) to stimulate pancreatic islet allograft rejection in reversed alloxan-induced diabetic rats was examined.

Growth of neonatal islet graft following transplantation to the BB/Wor rat.

Culture-derived neonatal Fischer-344 (Rtllvl) rat islets have reduced immunogenicity and have been shown to be fully transplantable into Wistar Furth (Rtlu) recipients. In studies designed to test the MHC-restriction of the autoimmune disease process in the BB/Wor rat, MHC-matched (Wistar Furth) and MHC-mismatched (Fischer-344) neonatal islets were isolated by a nonenzymatic tissue culture procedure and transplanted to the renal subcapsular site of BB/Wor rats before the onset of disease. All MHC-mismatched and most MHC-matched grafts survived intact.

Cultured neonatal islet transplants in alloxan-treated and spontaneously diabetic rats.

Neonatal Fischer-344 (FSH) islets isolated by a nonenzymatic method have been shown to survive indefinitely in Wistar/Furth (WF) recipients. We have applied this islet isolation method to six different donor strains and transplanted the resulting islets across 20 different strain combinations. We report the variable results obtained, with FSH being the most consistently successful donor strain and ACI being the best recipient strain.

Effect of prolactin versus growth hormone on islet function and the importance of using homologous mammosomatotropic hormones.

The purpose of this study was to determine the effects of homologous rat PRL (rPRL) and rat GH (rGH) on islet B-cell function in neonatal and adult rat islets in vitro. In neonatal rat islets, exposure to rPRL for more than 24 h was necessary for a stimulatory effect on insulin secretion. By day 4, insulin secretion was 3.

Islet transplantation in spontaneously diabetic BB/Wor rats.

We investigated the effectiveness of islet transplantation as therapy in an animal model of spontaneous type I (insulin-dependent) diabetes mellitus. Grafting MHC-matched and -mismatched islets with the spontaneously diabetic BB rat as a model has been previously reported to result in recurrence of the disease in the grafted tissue. When transplanted with nonimmunogenic islets isolated by nonenzymatic culture, we found that MHC-matched grafts proved to be susceptible to disease recurrence when allowed to remain in situ until ketosis developed in the host.

Allotransplantation of culture-isolated neonatal rat islet tissue. Absence of MHC class II positive antigen-presenting cells in nonimmunogenic islets.

When highly purified neonatal rat islet tissue, derived after 10 days in vitro, was allografted, it was found to be nonimmunogenic or weakly immunogenic. In contrast, nonislet pancreatic components, derived from the same culture system, transplanted with highly purified islet tissue resulted in rejection in 88% of cases. Extension of the culture period did not result in reduced immunogenicity of the nonislet material.

Decreased immunogenicity of fetal kidneys: the role of passenger leukocytes.

Early in gestation, fetal rat kidneys are less immunogenic than in later fetal stages, and also less immunogenic than early-gestation fetal hepatic tissue. The purpose of this study was to test this observation in an allogeneic model, and to explore the basis of the decreased immunogenicity of early-gestation fetal kidneys. Kidneys were harvested from Fischer (FSH) fetal rats on the 15th, 17th, 18th, and 19th gestational day (GD), and then grafted under the kidney capsule of incompatible Wistar/Furth (W/F) adult male rats.