Focuses on a study regarding the self-protection of cytotoxic cells from the damaging contents of their granules. Significance of granule-derived cathepsin B for the self-protection cytotoxic lymphocytes; Effect of anti-CD3 antibodies with cathepsin inhibitors on cytotoxic T lymphocytes (CTL); Occurrence of cathepsin-mediated protection of degranulating CTL against perforin attack.