1. National AIDS Center, Istituto Superiore di Sanità, Rome, Italy.
2. Present address: Department of Cellular and Molecular Medicine, St. George's University of London, London, United Kingdom.
3. Department of Infectious, Parasitic, and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
4. Department of Drug Research and Evaluation, Istituto Superiore di Sanità, Rome, Italy.
5. National AIDS Center, Istituto Superiore di Sanitá, Rome, Italy.