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.