UTILITY OF ADENOVIRAL-MEDIATED FAS LIGAND GENE-TRANSFER TO MODULATE ISLET ALLOGRAFT SURVIVAL

Background. One of the best-defined mechanisms for the induction of ap optosis involves signaling via the cell surface molecule Fas, after bi nding of Fas ligand. Expression of Fas ligand is tightly regulated, be ing expressed primarily by T cells after activation, where it serves a s a self-regulatory mechanism for immune responses. Fas ligand has als o been found to be expressed constitutively at sites of immune privile ge such as the testes and the anterior chamber of the eye. Recently, c o-transplantation of Fas ligand-transfected myoblasts in association w ith islet cell allo grafts was shown to prolong islet allograft surviv al but only rarely led to indefinite graft survival. Graft rejection w as associated with loss of Fas ligand on the myoblasts, suggesting tha t direct expression of the transgene on the islets might be more effec tive. Methods. A replication-defective adenoviral construct containing murine Fas ligand (Ad/MFL) was prepared by homologous recombination. NIH 3T3 cells, rodent splenocytes, and murine islets were infected wit h Ad/MFL and examined in vitro for functional murine Fas ligand expres sion. Survival of Ad/MFL-infected islets was subsequently evaluated in vivo in both syngeneic and allogeneic islet transplantation models. R esults, Cell lines and islet allografts transfected with Ad/MFL expres sed a functional Fas ligand, capable of inducing apoptosis (confirmed by three distinct assays for DNA fragmentation) in Fas' targets, but n ot in Fas(-) controls. Furthermore, Ad/MFL was able to modify allogene ic immune responses in vitro, as addition of this virus, but not a con trol adenovirus, significantly reduced proliferation in a mixed lympho cyte reaction, Surprisingly, however, transplantation of islet allogra fts transfected with Ad/MFL resulted in long-term allograft survival i n only 1 of 30 recipients. Moreover, adenoviral-mediated Fas ligand ge ne transfer was complicated by transient, dose-dependent islet dysfunc tion, perhaps contributing to the lack of longterm engraftment, Conclu sion. These data suggest that adenoviral-mediated Fas ligand expressio n may impair normal islet function in vivo, and indicate that alternat ive strategies for Fas ligand transgene delivery may be required in th is setting.