She started her career with the United States Department of Defense as a clinician in immunology, focusing on HIV/AIDS vaccine research.[7] She then served in the Department of Allergy and Clinical Immunology at the Walter Reed Army Medical Center from 1985 to 1989, authoring an article on the defective regulation of Epstein–Barr virus infection in patients with HIV/AIDS and related disorders that The New England Journal of Medicine published in 1986 and that Robert R. Redfield of the Walter Reed Army Institute of Research (presently the director of the Centers for Disease Control and Prevention (CDC)) co-authored.[8] In 1996, she became the Director of the United States Military HIV Research Program at the Walter Reed Army Institute of Research, a role she held until 2005.[7]