1Amgen Institute, Ontario Cancer Institute, and the Departments of Medical Biophysics and Immunology, University of Toronto, 620 University Avenue, Toronto, Ontario M5G 2C1, Canada
2Department of Pathology, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California 91320-1789, USA
3Department of Cell Biology, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California 91320-1789, USA