1. Department of Immunology, The Weizmann Institute of Science, Rehovot, 76100 Israel
2. Department of Tumor Immunology, University Hospital Nijmegen, Nijmegen 6525 EX, The Netherlands
3. Unite d'Immunologie Virale, Institute Pasteur, 75724 Paris, France
4. Biogen, Incorporated, Cambridge, Massachusetts 02142