EXPRESSION OF CTLA4-IG BY BIOLISTICALLY TRANSFECTED MOUSE ISLETS PROMOTES ISLET ALLOGRAFT SURVIVAL

Background. Localized delivery of immunosuppressive molecules, limited to the graft site, may allow transplantation of tissue in the absence of systemic immunosuppressive agents. We tested whether purified mous e islets that had been engineered to produce human CTLA4-Ig locally at the graft site could survive in allogeneic recipients receiving no sy stemic immunosuppression. Methods. CBA (H2(k)) islets were subjected t o biolistic (gene gun) transfection with a cDNA encoding human CTLA4-I g under control of the human cytomegalovirus immediate early promoter. After 40-48 hr of culture, the transfected islets (500 per recipient) were transplanted beneath the renal capsule of alloxan-induced diabet ic BALB/c (H2(d)) recipients. Results. Control grafts (n=10) consistin g of islets biolistically transfected with the expression plasmid alon e (i.e., no gene inserted) survived for 12.8+/-3.6 (mean +/- SD) days. In contrast, islets transfected with CTLA4-Ig (n=12) survived 66.8+/- 61.5 days (P=0.01), with 50% demonstrating functional survival until f ollow-up was concluded at 50 (n=2), 130 (n=2), or 165 (n=2) days. Immu nohistochemistry on grafts that survived long term showed well-granula ted, insulin-positive islets lying adjacent to, but not infiltrated by , dense aggregates of mononuclear cells. Conclusions. Transfection of allogeneic mouse islets with human CTLA4-Ig results in prolonged allog raft survival. Although on histology mononuclear cells are present in the area of the transfected graft, they do not appear to infiltrate or destroy the islet graft.