DEATH OF SOLID TUMOR-CELLS INDUCED BY FAS LIGAND EXPRESSING PRIMARY MYOBLASTS

Anticancer therapy for solid tumors suffers from inadequate methods fo r the localized administration of cytotoxic agents. Fas ligand (FasL) has been reported to be cytotoxic to a variety of cells, including cer tain tumor cell lines. We therefore postulated that myoblasts could se rve as non-transformed gene therapy vehicles for the continuous locali zed delivery of cytotoxic anticancer agents such as FasL. However, con trary to previous reports, fluorescence activated cell sorting (FACS) analyses revealed that both primary mouse and human myoblasts express Fas, the receptor for FasL. To avoid self-destruction and test the cyt otoxic potential of myoblasts, the cells were isolated from mice defic ient in Fas (lpr/lpr), the mouse counterpart of human autoimmune lymph oproliferative syndrome (ALPS). These primary mouse myoblasts were tra nsduced with a retroviral vector encoding mouse FasL and expression of a biologically active and soluble form of the molecule was confirmed by the apoptotic demise of cocultured Fas-expressing Jurkat cells, the standard in the field To test whether the lpr myoblasts expressing Fa sL could be used in anticancer therapy, human rhabdomyosarcoma derived cell lines were assayed for Fas and then tested in the apoptosis cocu lture assay. The majority of Fas-expressing muscle tumor cells were ra pidly killed. Moreover, FasL expressing myoblasts were remarkably pote nt; indeed well characterized cytotoxic antibodies to Fas were only 20 % as efficient at killing rhabdomyosarcoma cells as FasL expressing my oblasts. These findings together with previous findings suggest that p rimary myoblasts, defective in Fas but genetically engineered to expre ss FasL, could function as potent anticancer agents for use in the loc alized destruction of solid tumors in vivo by three synergist ic mecha nisms: (1) directly via Fas/FasL mediated apoptosis, (2) indirectly vi a neutrophil infiltration and immunodestruction, and (3) as allogeneic inducers of a bystander effect via B and T cells.