1. M. Osawa and H. Nakauchi, Department of Immunology, Institute of Basic Medical Sciences and Center for Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba Science-City, Ibaraki 305, Japan.
2. K.-i. Hanada and H. Hamada, Department of Molecular Biotherapy, Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo 170, Japan.