1. Laboratory of Tumor Cell Biology, National Cancer Institute, Bethesda, Maryland 20205
2. Laboratory of Central Nervous System Studies, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, Maryland 20205
3. Departments of Neurology and Pathology, Cornell University Medical College, New York 10021
4. Departments of Pathology and Medicine, New England Deaconess Hospital, Boston, Massachusetts 02215
5. Departments of Pathology and Pediatrics, University of Medicine and Dentistry of New Jersey, Newark 07103