The invention proposes a novel therapeutic and diagnostic methodology based on the use of effector cells (for example CTL and NK cells) selected for being able to induce lysis in target cells. In particular, the invention teaches how to select strains of effector cells of the immune system according to their lytic properties. It also teaches how diagnostic procedures for checking the activity of therapeutic vaccines can be improved with respect to what shown. Finally, it shows how cell therapies used at present can be improved by using this approach.