1. Department of Cancer Biology, Harvard University School of Public Health, Boston, Massachusetts 02115
2. Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20205
3. Laboratory of Biochemical Pharmacology, Dana-Farber Cancer Center, Department of Pathology, Harvard Medical School, Boston 02115
4. Laboratory of Tumor Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20205