Finally, we evaluated the efficacy of CY in IFN-γ/perforin double knock-out mice and found that combined deficiency of IFN-γ and perforin completely abrogated the CY-induced anti-tumor effects (9/9 mice, two experiments), consistent with the results from the IFN-γ-knock-out mice and highlighting the key role of this effector molecule (Figure 5C). This evidence concerns the gene PRF1 and neoplasm.