Response of human monocyte-derived dendritic cells to immunostimulatory DNA

Activated dendritic cells (DC) are of key importance for the initiation of primary immune responses and represent promising tools for immunotherapies in humans. Since DNA containing CpG motifs have been described as potent im munostimulatory (IS) adjuvants for murine DC, we here studied maturation an d stimulation of functional activity in human monocyte-derived DC (MODC) in response to several immunostimulatory oligodeoxynucleotides (IS-ODN) and p lasmid DNA (IS-PL). We show that exposure of MODC to IS-FL, but not IS-ODN, induced a dose-dependent strong up-regulation of HLA class II and cc-stimu latory molecules (CD80, CD86), similar to that observed after treatment wit h TNF-alpha. Functional activity was assessed by the detection of increased secretions of IL-6 and IL-12(p75) following treatment with IS-FL. In addit ion, IS-PL-stimulated MODC acquired a high T cell-stimulatory capacity. T c ells stimulated by tetanus toroid-pulsed, IS-PL-matured MODC were significa ntly more frequently IFN-gamma positive (25.2+/-2.7%) as compared to TNF-al pha -treated MODC (15.4+/-1.4 %), indicating a strong activation of Th1 lym phocytes. In conclusion, we demonstrate that human MODC are activated by IS -FL but not IS-ODN previously used as adjuvants in animal models. The Th1-l ike immune response observed after stimulation with IS-PL-treated DC sugges ts that preincubation of human MODC with IS-PL or coimmunization with IS-FL may represent an useful approach to generate strongly activated human MODC for several therapeutic applications such as DC-based tumor immunotherapy.