Non-Cleavable Mutant Fas Ligand Transfection of Donor Cornea Abrogates Ocular Immune Privilege

Abstract

The expression of Fas ligand (FasL) in donor corneal tissue has been thought to contribute to the prolonged survival of orthotopic corneal allografts. However, in solid organ transplantation, FasL gene-transfected tissues have been reported to lead to graft destruction through neutrophil recruitment. We wished to examine whether transfection of mutant FasL cDNA, which produces only membrane-binding forms of FasL because of its cleavage site, prolonged corneal allograft survival in mice. Donor corneal tissues were transduced with two adenovirus vectors containing human mutant FasL cDNA (AxCALNmFasL) and Cre recombinase (AxCANCre). Donor corneal tissues were then transplanted orthotopically onto recipient mice, and graft clarity was examined by slit lamp microscopy. We found that donor corneal grafts transfected with mutant FasL were intensely opaque for 1–2 weeks after grafting, when grafts without transfection remained clear. Histological examination revealed polymorphonuclear cell infiltration in the transfected grafted tissue. Moreover, mutant FasL transduced to donor tissues was found to exert its effects by binding to host, rather than donor Fas molecules, since corneal grafts with mutant FasL survived as long as those without transfection only when host animals, but not donor animals, lacked Fas molecules. Our results indicate that membrane-binding FasL over expression in donor cornea does not prolong corneal allograft survival; indeed, it causes rapid graft destruction.