[1] Whitehead Inst Biomed Res, 9 Cambridge Ctr, Cambridge, MA 02142 USA
[2] MIT, Dept Biol, Cambridge, MA USA
[3] MIT, Dept Chem, IMES, Cambridge, MA 02139 USA
[4] MIT, Koch Inst Integrat Canc Res, 77 Massachusetts Ave, Cambridge, MA 02139 USA
[5] Univ Calif Davis, Sch Vet Med, Dept Pathol Microbiol & Immunol, Davis, CA 95616 USA