Inhibition of growth of melanoma cells by CD95 (Fas/APO-1) gene transfer in vivo

Interaction of CD95 ligand with its cognate receptor CD95 induces apoptotic cell death. Alterations in this pathway within tumor cells can result in e scape from apoptosis and from immune surveillance. Melanoma cells recently were found to escape an immune attack via high expression of CD95 ligand, t hereby inducing apoptosis of activated T lymphocytes, When screening four h uman melanoma cell lines for expression of CD95 and CD95 ligand, respective ly, an inverse correlation was found, i.e., cells expressing high levels fo r CD95 ligand (CD95L(high)) were almost negative for CD95 and vice versa, S ince coexpression of CD95 and CD95 ligand may lead to apoptosis by autocrin e suicide or fratricide, it was tested whether overexpression of CD95 in CD 95L(high) melanoma cells results in apoptotic cell death. Upon transfection with a cytomegalovirus-promoter-driven expression vector encoding the CD95 gene, CD95L(high) melanoma cells underwent apoptosis at a much higher leve l than CD95L(low) melanoma cells. Apoptosis appeared to be due to the activ ation of CD95 as cell death was inhibited by cotransfection with a dominant negative mutant for the CD95 signaling protein, pas-associated protein wit h death domain. Tumor progression of CD95L(high) melanoma cells transplante d into nude mice was significantly reduced when recipient animals were inje cted with liposomes containing the CD95 expression vector. As demonstrated by immunohistochemistry and TUNEL staining, in vivo transfected tumor cells expressed CD95 and underwent apoptotic cell death. Hence, this study indic ates that delivery of the CD95 gene inhibits tumor growth in vivo and thus might be a therapeutic strategy to treat tumor cells that express high leve ls of CD95 ligand.