1. National AIDS Center, Istituto Superiore di Sanità, Rome, Italy.
2. Department of Drugs and Evaluation, Istituto Superiore di Sanità, Rome, Italy.
3. Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
4. Department of Histology, Microbiology and Medical Biotechnologies, University of Padova, Padova, Italy.