1. Department of Microbiology, Molecular Biology Institute and the Howard Hughes Medical Institute, UCLA, Los Angeles, CA 90024.
2. The Lautenberg Center for General and Tumor Immunology, The Hebrew University Hadassah Medical School, Jerusalem, Israel.
3. Department of Hematology/Oncology, St. Jude Children's Research Hospital, and Department of Pediatrics, University of Tennessee, Memphis, College of Medicine, Memphis, TN 38101.
4. The Wistar Institute, Philadelphia, PA 19104.
5. Department of Pediatrics, Children's Hospital at Stanford, Palo Alto, CA 94304.