Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, 94305, CA, USA.|Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, 94305, CA, USA.|Interdepartmental Program in Computational Biology and Bioinformatics, Department of Computational Biology & Bioinformatics, Yale University, New Haven, 06520, CT, USA.|Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, 94305, CA, USA. mmdavis@stanford.edu.