1. From the Department of Medicine, Division of Hematology, Peter Bent Brigham Hospital, the Center for Cancer Research and the Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, the Division of Hematology-Oncology, Children's Hospital Medical Center and Sidney Farber Cancer Institute, and the Department of Medicine and of Pediatrics, Harvard Medical School (address reprint requests to Dr. Marks at the Division of Hematology, Peter Bent Brigham Hospital, 721 Huntington Ave., Boston...