About the Authors
Division of Virology, Department of Pathology, University of Cambridge, Addenbrookes Hospital, Cambridge, United Kingdom
The authors have declared that no competing interests exist.
Conceived and designed the experiments: PGS BF RM. Performed the experiments: PGS BF RM JSM LG. Analyzed the data: PGS BF RM JSM LG. Wrote the paper: PGS.