A substance being studied in the treatment of brain tumors. Transferrin-CRM107 is made by linking a diphtheria toxin to transferrin, a protein that binds to fast growing cells, such as tumor cells. The diphtheria toxin then kills the tumor cells. Transferrin-CRM107 is a type of immunotoxin. OR A synthetic targeted protein toxin which consists of human transferrin (Tf) conjugated to a diphtheria toxin that contains a point mutation (CRM107). After binding to the transferrin receptor expressed on the tumor cell surface, transferrin-CRM107 is internalized, where the diphtheria toxin moiety exerts its cytotoxic effect intracellularly by inhibiting protein synthesis through ADP-ribosylation of elongation factor. Check for active clinical trialsusing this agent.