1. Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, Washington, USA
2. Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
3. Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
4. Howard Hughes Medical Institute and Departments of Microbial Pathogenesis and of Immunobiology, Yale University, New Haven, Connecticut, USA
5. Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, USA