Immunity to islet grafts transduced with adenovirus vectors does not inhibit long-term islet function

Adenoviral gene transfer is a potential ex vivo gene therapy for islet transplantation. However, the immunogenicity of adenoviral vectors can potentially impair vector efficacy in transplants where long-term gene expression is required. We investigated the effect of this antiviral immunity on vector expression and islet graft function. Syngeneic murine islets transduced with adenovirus encoding β-galactosidase (AdCMVnt-βgal) were transplanted under the renal capsule. At different time points after transplant, blood glucose and glucose tolerance, intragraft cellular infiltration and IgG, IgM productions, and expression of transgene, cytokines and chemokines/receptors were assessed. Splenocytes and sera were analyzed to evaluate the systemic anti-adenoviral immune response. Diabetes was reversed in 1 day in recipients of a marginal amount (200) of untransduced islets, while AdCMVnt-βgal-transduced islets failed to reverse diabetes until 10 days post-transplant (p ≤ 0.048). A profound and progressive infiltration with CD4+, CD8+ cells, natural killer cells, and macrophages was identified in adenovirus transduced grafts, which paralleled a decline in β-gal expression. However, this did not extinguish transgene and insulin expression, which persisted for over 3 months. Glucose tolerance was impaired in transduced grafts at 25 days compared with non-transduced grafts (p = 0.008), but was equivalent at 3 months (p = 0.275) post-transplant. Intragraft interferon (IFN)-γ and RANTES mRNA expression was not different between transduced and untransduced islet grafts, despite an increased expression of CC chemokine receptor 5 (CCR5). No significant splenocyte IFN-γ and interleukin (IL)-4 production or serum anti-adenoviral antibodies were discovered albeit IgM antibody was detected in transduced grafts. Transduction of islets with adenoviral vectors results in overt local inflammation of islet grafts and inhibits early graft function. However, long-term graft function is preserved, and transgene expression persists. Thus, antivector immunity leads to neither loss of islet graft nor eradication of vector.