Early Clinical Studies of IL-2 Fusion Toxin in Patients with Severe Rheumatoid Arthritis, Recent-Onset Insulin-Dependent Diabetes Mellitus, and Psoriasis

Figure 1 Schematic drawings of diphtheria toxin, DAB4s6IL·2 and DAB3g9IL-2 showing the regions of enzymatic activity (ADP-ribosyltransferase), membrane associating domains, receptor-binding domains and, in the case of DAB4s6IL-2 and DAB3s9IL-2, the

fu•ioo joootioo. Di•ulfido booill; "' fil.u iodio'1od [: J . DAB4s6IL-2 (67 Kd) was the first fusion toxin to be evaluated clinically; DAB3s9IL-2 (58 Kd) is approximately 10-fold more potent compared to DAB4s61L-2 with an enhanced therapeutic index in animal disease models. Potency is measured according to the ICso corresponding to 50% inhibition of protein synthesis in a standardized bioassay in which I 0 U/ml is approximately 10-10 M. Specific activity is expressed in kU/mg.