A Dominant-Negative Approach That Prevents Diphthamide Formation Confers Resistance to Pseudomonas Exotoxin A and Diphtheria Toxin

Diphtheria toxin (DT), Pseudomonas aeruginosa Exotoxin A (ETA) and cholix toxin from Vibrio cholerae share the same mechanism of toxicity; these enzymes ADP-rybosylate elongation factor-2 (EF-2) on a modified histidine residue called diphthamide, leading to a block in protein synthesis. Mutant Chinese hamster ovary cells that are defective in the formation of diphthamide have no distinct phenotype except their resistance to DT and ETA. These observations led us to predict that a strategy that prevents the formation of diphthamide to confer DT and ETA resistance is likely to be safe. It is well documented that Dph1 and Dph2 are involved in the first biochemical step of diphthamide formation and that these two proteins interact with each other. We hypothesized that we could block diphthamide formation with a dominant negative mutant of either Dph1 or Dph2. We report in this study the first cellular-targeted strategy that protects against DT and ETA toxicity. We have generated Dph2(C-), a dominant-negative mutant of Dph2, that could block very efficiently the formation of diphthamide. Cells expressing Dph2(C-) were 1000-fold more resistant to DT than parental cells, and a similar protection against Pseudomonas exotoxin A was also obtained. The targeting of a cellular component with this approach should have a reduced risk of generating resistance as it is commonly seen with antibiotic treatments

Cutaneous Crohn disease in a child

Cutaneous Crohn disease refers to granulomatous skin manifestations not contiguous with gastrointestinal affected areas. It is a very rare condition, especially in children, and is easily misdiagnosed when characteristic gastrointestinal symptoms are absent. We report a 10-year-old Caucasian girl with a 6-month history of erythematous, firm tumescence of the left labium majus pudendi and moist vegetations circumscribing the anal ostium. Histologic analysis of skin biopsy specimens from both types of lesions showed a characteristic granulomatous noncaseating infiltrate throughout the dermis. Endoscopic examination and a colon biopsy specimen showed chronic granulomatous inflammation consistent with Crohn disease. Treatment with prednisolone 20 mg daily, metronidazole 250 mg three times daily, topical corticosteroids, and mupirocin ointment produced marked improvement of the vulvar edema, whereas the perianal lesion had a relapsing course. Early recognition of extra-intestinal manifestations of Crohn disease, which are extremely rare in children, may be difficult. Coexistence of contiguous and noncontiguous lesions, representing the very first signs of the disease, are further peculiarities in our patient