1. Department of Gastroenterology and Hepatology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
2. Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan.
3. Japan Science and Technology Agency, PRESTO, Kyoto 606-8507, Japan.
4. Japan Science and Technology Agency, CREST, Kyoto 606-8507, Japan.