1. Department of Medicine, Section of Rheumatology, University of Chicago, Chicago, IL 60637
2. Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute
3. Department of Pediatric Oncology, Dana-Farber Cancer Institute
4. Center for Blood Research, Harvard Medical School, Boston, MA 02115
5. Howard Hughes Medical Institute, Dana-Farber Cancer Institute
6. Department of Immunology, University of Toronto, Sunnybrook and Women's College Health Sciences Center, Toronto M4N 3M5, Canada
7. Department of Experimental Medicine and Pathology, University La Sapienza, 00185 Rome, Italy