PRF1 and leukemia: They showed that rat basophilic leukemia (RBL)cells, which do not normally express perforin, acquired cytotoxicfunction if they expressed wild-type mouse perforin.60 This approach has subsequently been modified to definethe molecular and cellular bases of the loss of function of variousinherited human perforin mutations22,61 and to characterizethe various functional domains of perforin.15,18