Vol. 4, No. 4, 2004 • The Journal of Applied Research 536 had greater TT-specific DTH reactivity. In contrast, FL did not augment periph- eral blood mononuclear cell prolifera- tive responses or antibody responses to TT. FL resulted in inconsistent TT-spe- cific T cell responses as measured by interferon-gamma ELISPOT and cytokine flow cytometry.We conclude that while FL mobilization of DC may enhance in vivo immune responses to a known immunogenic recall antigen, there are inconsistent effects on immune response detected by in vitro assays. Further study will be required to determine which individuals might experience augmentation of the immune response with FL. INTRODUCTION The specific and nonspecific compart- ments of the immune system function in concert to generate effectors and responses against peptides and proteins identified as “foreign.” It is now recog- nized that dendritic cells (DC) function Flt3-ligand as a Vaccine Adjuvant: Results in a Study of Flt3-ligand Plus Tetanus Toxoid Immunization Stephen Chui, MD * Timothy M. Clay, PhD † Paul J. Mosca, MD, PhD † Amy C. Hobeika † Takuya Osada, MD † Laurent Galibert, PhD ‡ Dania Caron, MD ‡ H. Kim Lyerly, MD †§ Michael A. Morse, MD * *Department of Medicine, † Department of Surgery, Duke University Medical Center, Durham, North Carolina ‡ Amgen Corporation, Seattle, Washington § Departments of Immunology and Pathology, Duke University Medical Center, Durham, North Carolina KEY WORDS: Flt3-ligand, tetanus toxoid, vaccination, T cell, interferon gamma ABSTRACT Dendritic cells (DC) efficiently process and present antigens to the effector arm of the immune system, thereby stimulat- ing immunity against antigens of both foreign and self origin. Administration of Flt3-ligand (FL) has been reported to increase dendritic cell (DC) numbers in mice and humans. As a result, FL has attracted interest as an adjuvant for vac- cine immunotherapy.To investigate whether FL might increase the immune response to a model recall antigen, we administered FL 25μg/kg/d subcuta- neously to six healthy volunteers fol- lowed by a standard injection of intramuscular tetanus toxoid (TT). A control cohort of six healthy volunteers received tetanus toxoid alone. Compared to subjects who received only TT, subjects who received Flt3L and TT