EX-VIVO ADENOVIRUS-MEDIATED GENE DELIVERY LEADS TO LONG-TERM EXPRESSION IN PANCREATIC-ISLET TRANSPLANTS

Background. Replication-deficient adenovirus, one of the most efficien t vectors in gene therapy, has been limited by transient transgene exp ression due to its episomal location and loss during cell division, as well as a host immune response against viral proteins. Methods. Murin e pancreatic islets were infected ex vivo with ad5-cytomegalovirus (CM V)-beta-galactosidase and transplanted into diabetic recipients with n ormalization of glucose metabolism. Results. High levels of beta-galac tosidase activity were detectable histologically for at least 20 weeks after transplant, and beta-galactosidase and viral mRNA were also pre sent that long. Sera from transplanted animals did not significantly i nhibit ad5-CMV-interleukin-2-Ig infection of HeLa cells in vitro, wher eas sera from intravenously delivered ad5-CMV-beta-galactosidase drast ically diminished HeLa cell infection, suggesting the presence of redu ced levels of antibodies in transplanted animals as compared with intr avenously infected animals. Immunofluorescent staining of islet isogra fts infected with ad5-CMV-beta-galactosidase revealed the presence of CD8(+) and CD4(+) T lymphocytes at all time points, however, no islet destruction was seen. Conclusions. Treatment of islet isografts ex viv o with ad5-CMV-beta-galactosidase results in prolonged transgene expre ssion, possibly due to an attenuated immune response against adenoviru s.