Immunotoxins

Immunotoxins are protein molecules composed of a cell surface-directed ligand covalently linked to a peptide cytotoxin. This definition excludes a number of important therapeutic compounds with distinct pharmacologic properties which react with intracellular targets. Such molecules would be unlikely to find and react with their intracellular targets due to the permeability barrier of the plasma membrane. Thus, the ligands must bind cell surface receptors or antigens. Ligands which have been used include monoclonal antibodies and antibody fragments, adhesion molecules, growth factors, and cytok-ines.