Myeloid-derived-suppression cells (MDSC) are functionally defined to suppress T-cells in their primary means of immune evasion mechanism in cancer. However, we have discovered that MDSC can have direct, T-cell independent pro-carcinogenic effect on tumor cells. Sorted monocytic CD14+/CD11b+/HLA-DRlow MDSCs from head and neck squamous cell carcinoma (HNSCC) patients were found to increase the proliferation index of HNSCC cells. This induction of tumor proliferation was not dependent on MDSC-tumor cell contact. Exome analysis showed that these human MDSC from cancer patients expressed high levels of inflammasome complex, and supernatant from the MDSCs were found to secrete IL-1b and IL-18. When we probed the functional significance of these inflammasome complex, we found that MDSC's promotion of tumor proliferative index of the tumor was found to be Caspase-1 dependent. To test this in vivo, T-cell depleted caspase-1 null mice showed significant decrease in tumor growth rate. To confirm the importance of myeloid inflammasome signaling in carcinogenesis, we suppressed MyD88 gene in tumor cell line Cal27 and found that the ability of MDSC to promoting tumor proliferation is diminished. Taken together, our findings demonstrate that tumor infiltrating MDSCs may play a prominent role in chronic inflammation associated carcinogenesis.

Citation Format: Qi Zeng, Jesse R. Qualliotine, Lee Blosser, Drew Pardoll, Young J. Kim. Caspase-1 from MDSC promote MyD88 dependent carcinogenesis that is T-cell independent. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3250.