Synthesis of Immunoisolation Barriers That Provide Localized Immunosuppression for Encapsulated Pancreatic Islets

Abstract

Pancreatic islet encapsulation into synthetic, passive material matrixes can provide protection for transplanted islets from destruction via cell-contacted mediated interactions with autoreactive immune cells for treatment of Type I diabetes mellitus. However, one of the fundamental deficiencies with current encapsulation technology is that passive material barriers cannot protect islets from exposure to cytokines and other small, diffusible cytotoxic molecules produced by activated immune cells, subsequently leading to beta-cell destruction. Preparation of material matrixes that can actively provide localized immunosuppression of autoreactive immune cells may prolong the viability, and hence function, of encapsulated islet grafts. We have demonstrated the ability to conjugate apoptosis-inducing anti-Fas monoclonal antibodies (MAbs) to the surfaces of poly(ethylene glycol)-modified hydrogels, providing a surface that actively attempts to locally down-regulate the autoimmune response by destroying autoreactive T cells against pancreatic islet cells. We have conjugated anti-Fas MAbs to a high degree to the surface of these hydrogels, with retention of anti-Fas recognition of the Fas antigen as shown by ELISA testing. Apoptosis induction of Fas-sensitive Jurkat T cells was enhanced in the presence of anti-Fas conjugated hydrogels. In addition, this apoptosis induction was specific to anti-Fas MAbs, with no apoptosis induction with control antibodies or with Fas-insensitive T cells. These experiments promote the concept that surface-conjugated hydrogel constructs can provide localized immunosuppression for encapsulated grafted tissue.