Adenovirus-Mediated Gene Transfer into Isolated Mouse Adult Pancreatic Islets: Normal β -Cell Function Despite Induction of an Anti-Adenovirus Immune Response

Abstract

The in vitro purification of pancreatic islets offers an opportunity for their modification by ex vivo gene transfer. We investigated the efficiency and functional consequences of adenovirus-mediated gene transfer into adult murine pancreatic islets with a recombinant adenovirus encoding for the β-galactosidase (β-Gal) reporter gene. At 10⁶ pfu/islet, almost all of the islets were transduced, but maximal transduction was obtained at 10⁷ pfu/islet. Histochemical analysis of frozen islet sections showed that transduced cells were only located at the periphery of islets. Transduced islets showed normal insulin secretion in vitro, and were able to normalize in vivo the glycemia of streptozotocin-induced diabetes in syngeneic and allogeneic mice. β-Gal expression in transduced islets was observed for at least 6 weeks in naive normal recipients and in immunodeficient mice, but was shortened in mice preimmunized to adenovirus. Nevertheless, islets maintained normal control of glycemia in all mice. An early leukocyte infiltrate was observed in syngeneic grafts of transduced islets, but no acceleration in rejection of fully MHC-incompatible islet grafts occurred. In summary, adenovirus-mediated gene transfer in adult mouse islets, although sparing most of the β-cells, was highly efficient and did not impair insulin secretion by islets. The immune response to the adenovirus and/or to the transgene might be only partially responsible for the decreased expression over time of the transduced gene. Accordingly, adenovirus-mediated gene transfer might allow efficient expression of vectorized sequences with potential immunosuppressive effects in the islet microenvironment.

Overview summary

Isolated pancreatic islets constitute an ideal target for ex vivo gene transfer, allowing reconstitution of gene defects or vectorization of immunomodulating molecules prior to transplantation. Although various gene transfer methods have already been described, our aim was to characterize better the transfer efficiency of recombinant adenoviral vectors in adult mouse islets. We found that even with high doses of adenovirus only peripheral islet cells were transduced, avoiding most of the insulin-producing cells. Insulin secretion of transduced islets was maintained both in vitro and indefinitively in vivo. Expression of the reporter gene was observed for several weeks in both normal and nude mice, suggesting that mechanisms other than immunogenicity of transduced islets might be involved in persistence of transgene expression. These results suggest that adenoviral vectors might be more efficient at modifying the islet microenvironment during an allogeneic response or recurrence of autoimmune process, than for permanent correction of β-cell dysfunction.