CSF2 and fibrosarcoma: We choose an in-house plasmid encoding the cytokine GM-CSF and the costimulatory molecule human B71, which we previously demonstrated an effective recruitment of cytotoxic anti-tumor response and the permanent elimination of a poorly immunogenic fibrosarcoma tumor.15 B71 is usually expressed on the membrane of antigen-presenting cells, whereas tumor cells usually lack its expression and without this costimulatory signal, T cells may become clonally anergic when the T-cell receptor signal is delivered.