[1] Univ Tokyo, Inst Med Sci, Dept Cell Proc, Tokyo 108, Japan
[2] Univ Tokyo, Inst Med Sci, Dept Clin Immunol, Tokyo 108, Japan
[3] Univ Tokyo, Inst Med Sci, Ctr AIDS Res, Tokyo 108, Japan
[4] Japanese Red Cross Cent Blood Ctr, Tokyo, Japan
[5] Yamanouchi Pharmaceut Co Ltd, Inst Drug Discovery Res, Tsukuba, Ibaraki, Japan