We compared and contrasted three systemic delivery strategies involving i.v. infusion of either free (“naked”) virus, or else ex vivo loading of virus onto two different populations of carrier leukocytes, namely autologous BM leukocytes or autologous peripheral blood mononuclear cells (PBMCs), to administer TNF-armed MYXV after the osteosarcoma has been seeded into lungs. The gene discussed is TNF; the disease is osteosarcoma.