Lentivirus-Mediated Transduction of Islet Grafts with Interleukin 4 Results in Sustained Gene Expression and Protection from Insulitis

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Abstract
Autoimmune destruction of islets in the pancreas leads to the development of insulin-dependent diabetes mellitus (IDDM). Replacement of insulin-producing tissue by transplantation of islets provides a cure to disease but requires immunosuppression or a means of controlling anti-graft immune responses. To promote islet survival we have utilized a local approach by expressing immunoregulatory molecules in islet grafts. The results presented here show that the human immunodeficiency virus (HIV)-based lentiviral vector is capable of stably transducing whole islets. Foreign reporter gene expression was observed both in vitro and in vivo 30 days after transplantation. Grafts containing insulin-positive β-islet cells expressing foreign protein indicate that transduction does not interfere with glucose regulation. The absence of inflammatory infiltrates in grafts suggests that transduction does not activate the immune system. When islets transduced with an HIV vector expressing IL-4 were transplanted into diabetes-prone mice, animals were protected from autoimmune insulitis and islet destruction. As demonstrated by proliferative and cytokine analysis, protection was consistent with a switching of islet-antigen-specific T cell responses toward a Th2 phenotype. These results suggest that HIV-based lentivirus vectors can efficiently transduce islet cells with genes encoding potentially therapeutic molecules, for possibly managing diabetes. Islet transplantation in conjunction with immunosuppressive therapy has proven to be a successful and curative approach to treating diabetes. To improve transplantation therapies and avoid the problems associated with systemic immunosuppression, a localized approach to regulating anti-graft immune responses may prove beneficial. The transfer of genes encoding immune regulatory molecules into islets prior to transplantation may fulfill this requirement. For such transfers to be stable and efficient, a vector must be capable of transducing nondividing islet cells and maintaining gene expression in vivo. While retroviral vectors inefficiently transduce islets, adenovirus vectors activate the immune system limiting gene expression. In this article, we demonstrate that lentivirus-based vectors efficiently and stably transduce whole islets. When an immune regulatory molecule was incorporated into this vector, transduced islet transplants as well as pancreatic islets were safeguarded from autoimmune attack. By examining T cell responses to islet antigens it was evident that protection was associated with the development of a repertoire of T cells displaying a nonpathogenic phenotype. These observations establish lentivirus-based vectors as transducing vehicles for use in transplantation therapies aimed at deviating autoimmune and anti-graft immune responses.