Anti-GAD antibody targeted non-viral gene delivery to islet beta cells

Abstract

Type I diabetes results from the destruction of the insulinproducing beta-cells of the pancreatic islets. Since the destructive process is mainly mediated by immune response, immune intervention using gene therapy has been thought as one of the possible approaches to treat the autoimmune disease. Furthermore, the slow progressive nature of immune destruction makes it even feasible to prevent the autoimmune disease at a pre-clinical stage. Non-viral gene delivery systems having specificity toward islet beta cells could be an attractive approach for a systemic treatment of type I diabetes. An islet cell targeting polymeric gene carrier was synthesized by conjugating Fab` fragment to PEI via PEG linker (PEI-PEG-Fab`). The Fab` fragment was prepared from monoclonal antibody against glutamic acid decarboxylase (GAD), which is identified as one of the major autoantigens expressed in islet cells, and used as a targeting moiety for islet cell targeting. The migration of plasmid DNA/PEIPEG-Fab` complexes was completely retarded above the N/P ratio of 2. The complexes demonstrated a size of 100 - 250 nm with an almost neutral surface charge. Confocal microscopy revealed that the PEI-PEG-Fab` complexes showed much higher cellular binding and uptake efficiency compared to PEI-PEG complexes. The PEIPEG-Fab` showed about 10-fold higher transfection efficiency than PEI-PEG in GAD expressing cells (MIN6), however the transfection efficiency of PEI-PEG-Fab` reduced to that of PEI-PEG either in GAD negative cells (293) or in the presence of competitive free Fab`. Considering neutral surface charge of its complexes with DNA, selectivity toward the islet cells expressing a specific antigen, and lower cytotoxicity, the PEI-PEG-Fab` conjugate could be thought as a potential candidate of the systemic gene therapy for the treatment of type I diabetes.