Immunotoxins (ITs), monoclonal antibodies conjugated to plant or bacterial toxins, have been
extensively investigated for their possible use as anti-tumor agents although not in
carcinoma patients with minimal residual disease. Various ITs have been tested in early
clinical trials and recent studies demonstrate anti-tumor activity of IT treatment in
patients with glioblastoma and different solid tumors. Systemic treatment with immunotoxins
directed against carefully selected epithelial cell surface molecules may have a potential
for eradicating also dormant metastatic tumor cells, as their action is independent of cell
proliferation. The effector moieties of the IT used here, the Pseudomonas exotoxin A (PE),
inhibits protein synthesis in eukaryotic cells by catalytic inactivation (ribosylation) of
elongation factor 2 in the ribosome complex.