IRF1 and neoplasm: These results are consistent with previous observations demonstrating that the transcription factors STAT1 and IRF1, which are activated in response to IFNγ signaling, bind to the promoter region of IDO1 and regulate gene expression.33 Taken together, our results indicate that anti-CD40-therapy induces activation of T-cells in the tumor microenvironment, and that IFNγ secreted by activated T-cells induces up-regulation of IDO1 in tumor endothelial cells (schematically illustrated in Figure 4f).