1. Baltimore VA Medical Center, VA Maryland Health Care System, Baltimore, Maryland, USA
2. Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA
3. Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA
4. Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology, La Jolla, California, USA
5. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Maryland, USA
6. Department of Medicine, Division of Infectious Diseases and Global Public Health, University of California, San Diego (UCSD), La Jolla, California, USA