1. R. De Maria, F. Malisan, B. Tomassini, A. Zeuner, M. R. Rippo, R. Testi, Department of Experimental Medicine and Biochemical Sciences, University of Rome “Tor Vergata,” 00133 Rome, Italy.
2. L. Lenti and F. d'Agostino, Department of Experimental Medicine and Pathology, University of Rome “La Sapienza,” 00161 Rome, Italy.