ARTICLE ABSTRACT
The PD-1:PD-L1 immune signaling axis mediates suppression of T-cell–dependent tumor immunity. PD-1 expression was recently found to be upregulated on tumor-infiltrating murine (CD11c+CD11b+CD8−CD209a+) and human (CD1c+CD19−) myeloid dendritic cells (TIDC), an innate immune cell type also implicated in immune escape. However, there is little knowledge concerning how PD-1 regulates innate immune cells. In this study, we examined the role of PD-1 in TIDCs derived from mice bearing ovarian tumors. Similar to lymphocytes, TIDC expression of PD-1 was associated with expression of the adapter protein SHP-2, which signals to NF-κB; however, in contrast to its role in lymphocytes, we found that expression of PD-1 in TIDC tonically paralyzed NF-κB activation. Further mechanistic investigations showed that PD-1 blocked NF-κB–dependent cytokine release in a SHP-2–dependent manner. Conversely, inhibition of NF-κB–mediated antigen presentation by PD-1 occurred independently of SHP-2. Collectively, our findings revealed that PD-1 acts in a distinct manner in innate immune cells compared with adaptive immune cells, prompting further investigations of the signaling pathways controlled by this central mediator of immune escape in cancer. Cancer Res; 76(2); 239–50. ©2015 AACR.
