Immunotoxins are proteins containing a cell-targeting element linked to a toxin that are under investigation for next-generation cancer treatment. These agents, however, are difficult to synthesize, chemically heterogeneous, expensive and show toxicity towards healthy cells. In this work, we describe the synthesis and characterization of a new kind of immunotoxins that showed exquisite selectivity towards targeted cells. In our construct, targeting molecules were covalently attached or genetically fused to oligomeric pore-forming toxins. The activity of the immunotoxin was then caged by fusing a soluble protein to the transmembrane domain and activated via cleavage with furin, a protease overexpressed in many cancer cells. During the several coupling steps, directed evolution allowed to efficiently synthesize the molecules in E. coli cells, and to select for further specificity towards targeted cells. The final construct showed no off-target activity, while acquiring an additional degree of specificity towards the targeted cells upon activation. The pore-forming toxins described here do not require internalization to operate; while the many protomeric subunits can be individually modified to refine target specificity.