Ca2+ influx induction was strictly dependent on perforin expression in OT1 cells (Fig. 2b; “perforin events”) and the Ca2+ signal originated at CTL–tumor cell contact region differed in signal intensity and duration from unspecific intracellular Ca2+ fluctuations (Supplementary Fig. 3b1 and b2, c). Here, PRF1 is linked to neoplasm.