1. Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee.
2. Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee.
3. Duke Human Vaccine Institute, Duke University School of Medicine, Duke University Medical Center, Durham, North Carolina.
4. Department of Medicine, Duke University School of Medicine, Duke University Medical Center, Durham, North Carolina.