1. Department of Infectious Parasitic and Immune-mediated Diseases; Istituto Superiore di Sanità; viale Regina Elena, 299 Rome Italy
2. Regina Elena National Cancer Institute; Laboratory of Virology and HPV-Unit; via delle Messi d'Oro 156 Rome Italy
3. Department of Science; University Roma Tre; Viale G. Marconi 446 Rome Italy
4. Department of Biology; University of Rome Tor Vergata; Via della Ricerca Scientifica 1 Rome Italy