Recombinant fowlpox virus for in vitro gene delivery to pancreatic islet tissue

The feasibility of using avipox virus as a vector for gene delivery to islet tissue (adult islets and fetal proislets) was examined using a recombinant fowlpox virus (FPV) engineered to express the reporter gene LacZ (FPV-LacZ). The efficiency of in vitro transduction was dose-dependent and influenced by the donor species and maturation status of the islet tissue. Reporter gene expression in FPV-LacZ-transduced islet grafts was transient (3-7 days) in immunoincompetent nude mice and was not prolonged by in vivo treatment with anti-IFN-γ mAb. In contrast, FPV-LacZ-transduced NIT-1 cells (a mouse islet beta cell line) expressed the LacZ gene beyond 18 days in vitro. Silencing of transgene expression therefore appeared to occur in vivo and was T cell- and IFN-γ-independent. Isografts of FPV-LacZ-transduced islets in immunocompetent mice underwent immunological destruction by 7 days, suggesting that either FPV proteins or the reporter protein β-galactosidase induced an adaptive immune response. Co-delivery of the rat bioactive immunoregulatory cytokine gene TGF-β to islets using FPV-TGF-β led to enhanced expression of TGF-β mRNA in isografts but no long-term protection. Nevertheless, compared to control islet isografts at 5 days, FPV-transduced islets remained embedded in the clotted blood used to facilitate implantation. This phenomenon was TGF-β transgene-independent, correlated with lack of cellular infiltration, and suggested that the FPV vector transformed the blood clot into a temporary immunological barrier.