PRF1 and neoplasm: The essential role of perforin in granule exocytosis and hence NKCC has been confirmed by studies in perforin-deficient mice, showing an increased susceptibility towards tumours (van den Broek et al. 1996) and inefficient control of viral challenges (van Dommelen et al. 2006) in these mice due to impairments in NKCC (Kagi et al. 1994).