PRF1 and cancer: To discriminate the relative contributions of killing and cytokine production to cancer immunoediting, we performed two independent long-term co-culture experiments with NK cells deficient in perforin (Prf1-/-), which renders them unable to kill their target cell (20), or deficient in IFN-γ production (Ifng-/-) (21) (Figures 4, Supplementary S8 and Supplementary S9).