1. Divisions of Experimental Medicine and Hematology-Oncology, Brigham & Women's Hospital, Department of Medicine, Harvard Medical School, Boston, MA 02115.
2. Department of Hematology-Oncology, Children's Hospital, Pediatric Oncology Division, Dana- Farber Cancer Institute, Boston, MA 02115.
3. Department of Pathology, Massachusetts General Hospital, Boston, MA 02114.