1. Center for Vaccine Development and Department of Microbiology and Immunology
2. Department of Pediatrics, Division of Infectious Disease, Johns Hopkins University, Baltimore, Maryland 21205
3. Division of Infectious Disease, Department of Medicine and Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201
4. Department of Medicine, Section of Digestive and Liver Diseases, University of Illinois, and West Side Veterans Affairs Medical Center, Chicago, Illinois 60612