Bioactivities of Fas ligand-expressing retroviral particles

Culture supernatants from retroviral packaging cells carrying the human Fas ligand (FasL) gene killed both human (Jurkat) and mouse (LB27.4) targets w ithin 5 h of incubation. Cytotoxicity was found both in a fraction greater than or equal to 500 kDa and a fraction between 50 and 500 kDa, Following u ltracentrifugation, the activity in the greater than or equal to 500-kDa fr action was concentrated in the pellet (FasL vector preparation (VP)), which was also infective when added to NIH-3T3 cells. Both Polybrene and poly-L- lysine significantly enhanced the cytotoxicity of Fast VP but not anti-Fas mAb, soluble Fast (sFasL), and cell-associated Fast. In the presence of Pol ybrene, Fast VP killed targets that are resistant to anti-Fas mAb and sFasL , The infectivity but not Fast cytotoxicity of Fast VP was sensitive to irr adiation and heat shock. By contrast, cytotoxicity of Fast VP could be enha nced or inhibited depending on the doses of anti-Fast mAb, Interestingly, t he infectivity of Fast VP was specifically enhanced by anti-Fast mAb, sugge sting that a nonviral gene product could be used to regulate the behavior o f the retroviral vector. Thus, in addition to expressing potent Fast cytoto xicity, the Fast VP exhibits unique properties heretofore not attributed to anti-Fas mAb, sFasL, and cell-associated Fast. Our study raises the possib ility of using the retroviral gene-packaging technology to make powerful, v ersatile, and regulatable bioactive vesicles expressing a predetermined fun ction of the protein encoded by the target gene.