CD46 and neoplasm: On the other hand, TpeL-knob fusion toxin was highly specific for tumor cells, because primary Normal Human Dermal Fibroblasts (NHDF) of the foreskin, which reportedly express no or very low amounts of CD46 [30] were not affected by the fusion toxin, while wild-type TpeL readily modified Ras of these cells (Supplementary Figure 3).