1. Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N., Seattle, WA 98109, USA
2. Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N., Seattle, WA 98109, USA
3. Virology Division, Department of Laboratory Medicine, University of Washington, 1616 Eastlake Ave. E, Seattle WA 98102, USA