1. Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
2. Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
3. Stanford Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
4. Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
5. Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305, USA.
6. Center for Health Sciences, SRI International, Menlo Park, CA 94025, USA.