CTSB and neoplasm: To see if a similar protease processing of virions occurs within Raji cured tumours, which results in their susceptibility to killing by reovirions in vivo, we used the specific cysteine protease inhibitor E64, which has been shown to block the conversion of reovirions to ISVPs (Baer and Dermody, 1997; Chandran and Nibert, 1998).