1. Surgical Research Laboratory, San Francisco General Hospital
2. Departments of Surgery, Medicine, and Physiology, University of California at San Francisco, San Francisco, California 94143
3. Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
4. Dana-Farber Cancer Institute
5. Harvard Medical School
6. Howard Hughes Medical Institute, Boston, Massachusetts 02115