Early exposure of interferon‐γ inhibits signal transducer and activator of transcription‐6 signalling and nuclear factor κB activation in a short‐term monocyte‐derived dendritic cell culture promoting ‘FAST’ regulatory dendritic cells

Summary Interferon (IFN)‐γ is a cytokine with immunomodulatory properties, which has been shown previously to enhance the generation of tolerogenic dendritic cells (DC) when administered early ex vivo in 7‐day monocyte‐derived DC culture. To generate tolerogenic DC rapidly within 48 h, human monocytes were cultured for 24 h with interleukin (IL)‐4 and granulocyte–macrophage colony‐stimulating factor (GM‐CSF) in the presence (IFN‐γ‐DC) or absence of IFN‐γ (500 U/ml) (UT‐DC). DC were matured for 24 h with TNF‐α and prostaglandin E 2 (PGE 2 ). DC phenotype, signal transducer and activator of transcription‐6 (STAT‐6) phosphorylation and promotion of CD4 + CD25 + CD127 neg/low forkhead box P3 (FoxP3) hi T cells were analysed by flow cytometry. DC nuclear factor (NF)‐κB transcription factor reticuloendotheliosis viral oncogene homologue B (RELB) and IL‐12p70 protein expression were also determined. Phenotypically, IFN‐γ‐DC displayed reduced DC maturation marker CD83 by 62% and co‐stimulation molecules CD80 (26%) and CD86 (8%). IFN‐γ treatment of monocytes inhibited intracellular STAT6, RELB nuclear translocation and IL‐12p70 production. IFN‐γ‐DC increased the proportion of CD4 + CD25 + CD127 neg/low foxp3 hi T cells compared to UT‐DC from 12 to 23%. IFN‐γ‐DC primed T cells inhibited antigen‐specific, autologous naive T cell proliferation by 70% at a 1:1 naive T cells to IFN‐γ‐DC primed T cell ratio in suppression assays. In addition, we examined the reported paradoxical proinflammatory effects of IFN‐γ and confirmed in this system that late IFN‐γ exposure does not inhibit DC maturation marker expression. Early IFN‐γ exposure is critical in promoting the generation of regulatory DC. Early IFN‐γ modulated DC generated in 48 h are maturation arrested and promote the generation of antigen‐specific regulatory T cells, which may be clinically applicable as a novel cellular therapy for allograft rejection.