The use of Flt3 ligand as an adjuvant for hepatitis B vaccination of healthy adults

A phase I/II clinical trial was carried out to determine the safety of Flt3 ligand used as a vaccine adjuvant when administered to healthy human volunteers on two different schedules. In the first phase of this study, Flt3 ligand was administered SQ at a dose of 20μg/kg (to a maximum of 1500μg) every day (N=10) or every other day (N=10) for 1 week. The Flt3 ligand injection series was followed 1 day later by the first of three vaccinations with the licensed hepatitis B vaccine. In the second phase of the trial, 30 volunteers received either Flt3 ligand or placebo on the alternate day schedule in a randomized, double-blind design. The Flt3 ligand injections were safe and very well-tolerated. The number of lineage negative, HLA-DRhi, CD11c+, CD123− dendritic cells (DCs) increased 23-fold, and the lineage negative, HLA-DRhi, CD11c−, CD123bright pre-DCs increased 6-fold. There was an associated increase in monocytes and WBCs in the Flt3 ligand recipients. Despite the marked increase in peripheral circulating dendritic cells, no increase was observed in the hepatitis B antibody titers induced after vaccination.