1. Department of Internal Medicine, Division of Infectious Diseases, The University of Texas Southwestern Medical Center, Dallas, Texas 753901;
2. Vaccine and Gene Therapy Institute, Oregon Health Sciences University, Portland, Oregon 97201-30982;
3. Merck Research Laboratories, West Point, Pennsylvania 194863; and
4. Institute for Medical Immunology, Charité, Humboldt Universität zu Berlin, 10098 Berlin, Germany4