Complete Protection of Islets Against Allorejection and Autoimmunity by a Simple Barium-Alginate Membrane

Abstract

We describe a new technique for microencapsulation with high-mannuronic acid (high-M) alginate crosslinked with BaCl 2 without a traditional permselective component, which allows the production of biocompatible capsules that allow prolonged survival of syngeneic and allogeneic transplanted islets in diabetic BALB/c and NOD mice for >350 days. The normalization of the glycemia in the transplanted mice was associated with normal glucose profiles in response to intravenous glucose tolerance tests. After explantation of the capsules, all mice became hyperglycemic, demonstrating the efficacy of the encapsulated islets. The retrieved capsules were free of cellular overgrowth and islets responded to glucose stimulation with a 5-to 10-fold increase of insulin secretion. Transfer of splenocytes isolated from transplanted NOD mice to NOD/SCID mice adoptively transferred diabetes, indicating that NOD recipients maintained islet-specific autoimmunity. In conclusion, we have developed a simple technique for microencapsulation that prolongs islet survival without immunosuppression, providing complete protection against allorejection and the recurrence of autoimmune diabetes. Diabetes 50: 1698 -1705, 2001 I slet transplantation represents an important alternative for the treatment of type 1 diabetes but still requires immunosuppressive agents with their serious side effects (1). One approach to avoid such treatment is to protect islets from the host's immune system with a semipermeable, biocompatible membrane (2,3). Transplantation of islets contained in alginate-poly-L-lysine (PLL) capsules was first described by Lim and Sun (4). Numerous studies have shown successful reversal of diabetes by transplantation of islets enclosed in alginate-PLL capsules in streptozotocin-induced animals (5-9). However, limited success has been reported in spontaneously diabetic NOD mice, a model of autoimmune diabetes (10 -13). Various factors have been implicated in the failure of encapsulated islets. A cellular reaction surrounding the capsules has often been observed, which could lead to depletion of oxygen and nutrients (14) or production of toxic cytokines (15). This accumulation of cells could be due to an immune response to the contained islets or to bioincompatibility of the capsular materials (16,17). Failure might also be attributed to problems with ␤-cell viability in the capsules (18).Protection of porcine islets remains a goal of encapsulation, but xenografts might be more difficult to protect than allografts, as suggested by studies performed with permeable polymer membranes (19,20). This concept is important because of the improved prospects for obtaining an abundant supply of human ␤-cells from precursor cells (21,22). The goal of this study was to determine whether stable biocompatible alginate microcapsules without a permselective component, such as PLL or polyethylene-glycol, would be able to protect mouse islets against allorejection and autoimmunity. RESEARCH DESIGN AND METHODSIslet isolation. Islets were isolated from ma...

Improved survival of microencapsulated islets during in vitro culture and enhanced metabolic function following transplantation

“…Nonetheless, an open pore alginate capsule is not so much an immune barrier as a support matrix to enhance islet viability, which is a critical essential step before a perm-selective membrane is placed on the islet. The ability of these capsules to so successfully restore glucose responsiveness may largely be a result of the high purity and low endotoxin content of the alginate [6,32]. Therefore, microencapsulating islets with an alginate of excellent biocompatibility can provide an environment that supports long-term islet graft survival and function, ultimately reducing beta cell loss and dysfunction in the immediate post-transplant period.…”

“…Since islets placed under the kidney capsule tend to fuse together forming large clumps, these grafts may be exposed to more hypoxic conditions resulting in necrosis and/or apoptosis [31]. Furthermore, encapsulation of islets, while not providing a perfect immune barrier, certainly may prolong graft survival [6,32]. While the exclusion of poly-L-lysine from our alginate capsule increases the porosity of the capsule [33], the capsule retains the ability to prevent contact of host cells such as macrophages with the islets, ultimately extending graft survival [34].…”

“…Furthermore, while the addition of poly-L-lysine has been used to reduce capsule porosity [19], its addition has resulted in an increased fibrotic response [15]. Recently, it has been shown that a simple alginate capsule devoid of poly-L-lysine retains the ability to prolong graft survival and protect the graft [6].…”

“…Unfortunately, long-term islet culture often results in a significant loss of islet mass and viability. Biocompatible matrixes such as sodium alginate have been used as a means of reducing the detrimental effects of long-term culture [4,5,6].…”

Microparticles for cell encapsulation and colonic delivery produced by membrane emulsification

“…The immobilization of cells in particles is widely discussed in tissue engineering; the possibility to encapsulate non-human cells reduces the host's immune system response, facilitating transplantation as an alternative to the limited donor tissues available [1]. The technique of cell encapsulation is being used for the production of "Bio artificial Pancreas" [2], immunobarrier for islet cells transplantation [2][3][4], and the encapsulation of stem cells [5,6]. Encapsulation of living cells was also suggested for the production of chemicals such as alcohol, organic acids, steroids, antibiotics, vaccines [7].…”