1. Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), Bethesda, MD 20892, USA.
2. Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Department of Pathology, Division of AIDS, Harvard Medical School, Boston, MA 02115, USA.
3. Laboratory of Molecular Immunology and Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10065, USA.
4. Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, USA.
5. Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.