1. Z.-S. Zhao, F. Granucci, H. Cantor, Department of Pathology, Harvard Medical School, and Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
2. L. Yeh and P. A. Schaffer, Division of Molecular Genetics, Dana-Farber Cancer Institute, Boston, MA 02115 USA.