Human T lymphocyte priming in vitro by haptenated autologous dendritic cells

Dendritic cells (DC), generated from adherent peripheral blood mononuclear cells (PBMC) by culturing with granulocyte-macrophage colony- stimulating factor (GM-CSF) and IL-4, were used to study in vitro sensitization of naive, hapten-specific T cells and to analyse cross- reactivities to related compounds. DC were hapten-derivatized with nickel sulphate (Ni) or 2-hydroxyethyl-methacrylate (HEMA), followed by tumour necrosis factor-alpha (TNF-α)-induced maturation, before autologous T cells and a cytokine cocktail of IL-1β, IL-2 and IL-7 were added. After T cell priming for 7 days, wells were split and challenged for another 7 days with Ni or HEMA, and potentially cross-reactive haptens. Hapten-specificity of in vitro priming was demonstrated by proliferative responses to the haptens used for priming but not to the unrelated haptens. Highest priming efficiencies were obtained when both IL-4 and IL-12 were added to the cytokine supplement. Marked interferon-gamma (IFN-γ) release (up to 4 ng/ml) was found when IL- 12 was included in the cultures, whereas IL-5 release (up to 500 pg/ml) was observed after addition of IL-4 alone, or in combination with IL-12. Nickel- primed T cells showed frequent cross-reactivities with other metals closely positioned in the periodic table, i.e. palladium and copper, whereas HEMA- primed T cells showed distinct cross-reactivities with selected methacrylate congeners. Similar cross-reactivities are known to occur in allergic patients. Thus, in vitro T cell priming provides a promising tool for studying factors regulating cytokine synthesis, and cross-reactivity patterns of hapten-specific T cells.