1. Department of Obstetrics and Gynecology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-8655, Japan
2. Department of Obstetrics and Gynecology, Nihon University School of Medicine, Itabashi-ku, Tokyo 173-8610, Japan
3. Division of Virology, National Cancer Center Research Institute, Chuo-ku, Tokyo 104-0045, Japan