1. Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109, United States
2. Department of Laboratory Medicine, University of Washington, 1959 NE Pacific Street, Seattle, Washington 98195, United States
3. Department of Microbiology, University of Washington, 1959 NE Pacific Street, Seattle, Washington 98195, United States