Many toxin-based therapies are under clinical trials, but Moxetumomab pasudotox, composed of an anti-CD22 antibody fused to a 38 kDa portion of the Pseudomonas exotoxin A, is one of the few approved immunotoxins by the FDA, in this case for the treatment of hairy-cell leukemia (Kreitman et al., 2012). This evidence concerns the gene CD22 and hairy cell leukemia.