1. Institute for Research in Biomedicine, Università della Svizzera italiana, 6500 Bellinzona, Switzerland;
2. Radcliffe Department of Medicine, University of Oxford, Oxford OX3 9DU, United Kingdom
3. Current affiliation: National Institute of Allergy and Infectious Diseases, Rockville, Maryland 20852, USA
4. VIR Biotechnology, San Francisco, California 94158, USA