1. From the Section of Genetic Engineering, Research Center for Genetic Engineering and Cell Transplantation, and Department of Immunology, Tokai University School of Medicine, Isehara 259-1193, Japan; the Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan; the Department of Immunology, Juntendo University School of Medicine, Tokyo 113-0033, J