Invariant natural killer T (iNKT) cells express T-cell receptor, which recognizes α-galactosylceramide (α-GalCer) presented on CD1d, and they also play an essential role in antitumor immunity. We previously developed NKT cell immunotherapy, which adoptively transfers α-GalCer pulsed dendritic cells (DCs) to activate iNKT cells followed by the activation of other immune cells for treating lung cancer patients. Since some patients responded to the treatment and showed an increased IFN-γ production with a prolonged survival whereas others did not, it is important to understand the mechanism by which NKT cells are activated by DCs in order to improve the current therapy. Aryl hydrocarbon receptor (AhR) is a transcription factor that translocates from the cytoplasm to the nucleus upon ligand binding. AhR signaling is known to modulate multiple immune cell functions and differentiation. However, whether or not AhR signaling plays any role in NKT cell immunotherapy still remains unclear. We therefore sought to determine whether AhR signaling affects the NKT cell responses in antitumor immunity. We found that monocyte derived DCs (moDCs) treated with the AhR ligand FICZ had the ability to induce greater cytokine production, including IFN-γ and TNF-α, by iNKT cells in vitro. Furthermore, the expression of the immune checkpoint molecules PD-L1 and PD-L2 was downregulated on these moDCs. These data suggest that the AhR ligand may be potentially useful for next-generation NKT cell immunotherapy. We are currently investigating the mechanism underlying PD-L downregulation by AhR signaling.