Subject matter of the invention are antibody-cytokine fusion proteins having proapoptotic and immune modulating properties, but wherein the cytokine moiety a priori has a bioactivity which is very low or restricted to certain receptor subtypes. These reagent exert their full biological activity via the corresponding cytokine receptor(s) only after antibody-mediated binding of the fusion protein to a specific cell membrane-expressed target molecule. By suitable choice of the antibody specificity, the cytokine activity is directed to the tissue, e.g. tumour tissue, to be treated, and a therapeutic agent can be produced being specifically designed/optimised for the respective indication/tumour entity.