1. National Institute of Allergy and Infectious Diseases, National Institutes of Health, 31 Center Drive, Bethesda, MD 20892, USA.
2. Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037, USA.
3. Division of Infectious Diseases, Columbia University Medical Center, New York, NY 10032, USA.
4. Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
5. Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.