PRF1 and neoplasm: We then measured the capacity for sgNT or sgNkg7 OT-I T cells to kill MC38-OVA or MC38-OVA-Tnfrsf1a-/- tumor cells in 4 hours (when tumor cell death is mediated by the perforin-granzyme pathway) or 18 hours (when tumor cell death is mediated by both the perforin-granzyme and TNF pathways) (27).