TF and glioblastoma: Experimental trials for treatment of GBM with immunotoxins have been directed at other therapeutic targets, such as transferrin receptor (TfR) taking advantage of the TfR endocytic pathway [26], fused human transferrin to a mutated diphtheria toxin (CRM107) by a stable and non-reducible thioether bond (Tf-CRM107); IL-13 receptor (Cintredekin besudotox) composed of human IL-13 and a truncated form of Pseudomonas exotoxin A [27]; IL-4 receptor as a chimeric immunotoxin constructed by fusion of mutein cpIL-4(13D) to a modified version of Pseudomonas exotoxin A (PE38KDEL) [28]; and EGFR.