1. Institute of Clinical Physiology, National Research Council, 54100 Massa, Italy
2. Virology Unit, Pisa University Hospital, 56124 Pisa, Italy
3. Retrovirus Center, Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, 56124 Pisa, Italy
4. Institute of Biophysics, National Research Council, 56124 Pisa, Italy