1. Departments of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
2. Departments of Virology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
3. Departments of Pathology, Nagoya University Graduate School of Medicine, Showa-ku, Nagoya 466-8550, Japan
4. Center of Stem Cell and Regenerative Medicine, Tokyo Medical and Dental University, Chiyoda-ku, Tokyo 101-0062, Japan