1. R. Rappuoli is with IRIS, Chiron SpA, Via Fiorentina 1, 53100 Siena, Italy.
2. H. I. Miller is at the Hoover Institution, Stanford University, Stanford, CA 94305, USA.
3. S. Falkow is in the Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.