What protects killer immune cells from harming themselves?

White blood cells, which release a toxic potion of proteins to kill cancerous and virus-infected cells, are protected from any harm by the physical properties of their cell envelopes, find scientists. Until now, it has been a mystery to scientists how these white blood cells — called cytotoxic lymphocytes — avoid being killed by their own actions and the discovery could help explain why some tumors are more resistant than others to recently developed cancer immunotherapies.