PRF1 and neoplasm: In the presence of TIPE2, tumor growth was not affected significantly by conditional knockout of perforin in NK cells (Prf1ΔNK/ΔNK mice) (Figure 4E), possibly due to the minimal contribution to overall tumor control by perforin‐dependent antitumor effector functions of the exhausted tumor‐infiltrating NK cells, which was diminished by TIPE2.