1. Laboratory of Molecular Virology and Epidemiology, AIDS Research Center, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan
2. Department of Medicine, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
3. Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom
4. Key Laboratory of AIDS Immunology, Ministry of Health, The First Affiliated Hospital, China Medical University, Shenyang, Liaoning 110001, The People's Republic of China