1. Department of Surgery, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
2. Department of Immunology, Institute of Basic Medical Sciences, University of Tsukuba, and CREST (Japan Science and Technology Corporation), Tsukuba, Ibaraki 305-8575, Japan
3. Laboratory of Stem Cell Therapy, Center for Experimental Medicine, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan