1. Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
2. Rakai Health Sciences Program, Entebbe, Uganda.
3. Division of Infectious Diseases, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland.
4. Laboratory of Immunoregulation, Division of Intramural Research, National Institute for Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland.