1. Departments of Immunology and Molecular Biology, The Scripps Research Institute, La Jolla, California 920371;
2. Tulane Regional Primate Research Center and School of Public Health and Tropical Medicine, Tulane University Health Sciences Center, Covington, Louisiana 704332;
3. Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York 100163; and
4. Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 100214