In Situ Protection Against Islet Allograft Rejection by CTLA4Ig Transduction

Background. Immunosuppression focused at or near the graft site would reduce the need for systemic immunosuppression thus educing fewer side effects. We investigated whether locally produced CTLA4Ig, mediated by adenovirus ( Adv) transduction of mouse islets, would protect allografts and whether such immunosuppression would remain localized. Methods. Adv-CTLA4Ig- or Adv-control-transduced islets were grafted under the kidney capsule of fully allogeneic diabetic mice. CTLA4Ig secreted from the grafted islets was detected by enzyme immunoassay of blood or immunohistochemistry of graft sections. Graft survival was monitored by blood glucose measurement. Histologic scores of graft sections stained with Gomori aldehyde fuchsin to detect insulin granules or hematoxylin-eosin to detect inflammation were used to compare grafts placed at different sites within the same mouse. Results. Adv-CTLA4Ig-transduced islet grafts secreted CTLA4Ig that was detected transiently in the circulation but persistently at the graft site. Survival of these grafts was significantly enhanced compared with control Adv-transduced and untransduced grafts. The kidney graft site availed elucidation of the site of action of CTLA4Ig. Histologic scores indicated that CTLA4Ig-producing grafts were protected by comparison with control grafts on the contralateral kidney. Hence, graft protection was not attributable to general systemic immunosuppression. Indeed, survival of CTLA4Ig-producing grafts was enhanced over control grafts placed at the opposite pole of the same kidney, indicating that graft protection was not solely due to inhibition of priming in the common draining lymph nodes. Conclusions. Islet allografts are protected by locally produced CTLA4Ig-disrupting immune interactions at the effector site.