1. Vaccine Research and Development Group; AIDS Research Center, National Institute of Infectious Diseases; Shinjuku-ku Tokyo 162-8640 Japan
2. Japan Science and Technology Corporation; Kawaguchi Saitama 332-0012, Japan
3. Department of Blood Transfusion; Nagoya University Hospital; Aichi Nagoya 466-8560 Japan
4. Department of Microbiology and Immunology; Nippon Medical School; Bunkyo-ku Tokyo 113-8602 Japan
5. Department of Blood Transfusion Service and Second Department of Internal Medicine; Nara Medical University; Kashihara Nara 634-8522 Japan
6. Institute of Medical Sciences; St. Marianna University of Medicine; Kawasaki Kanagawa 216-8511 Japan