The effects of a CRISPR/Cas9 IL-6 knockout in 4T1 mammary carcinoma cells on myeloid-derived suppressor cells (MDSCs) and Th17/Th22 cells

Abstract The 4T1 mouse mammary carcinoma cell line is syngeneic to Balb/c mice and is an effective tumor model to study the interactions between the immune system and metastatic breast cancer. The pro-tumor effects that myeloid-derived suppressor cell (MDSC) populations have on CD8+ T cells and Tregs are well known, but comparably less attention has been directed at the relationship between MDSCs and Type III immune Th17/Th22 cells in breast cancer. MDSCs and Th17/Th22 cells have been linked in other inflammatory settings, so in this study, we investigated MDSC, Th17 and Th22 cell interactions in 4T1 tumors, and the role of tumor-derived IL-6 in these interactions. IL-6 plays a key role in the induction of MDSCs under pathological conditions, as well as fate determining in Th maturation. Thus, the removal of IL-6 from 4T1 tumors allowed us to better characterize the source of these interactions. Populations of Monocytic (M)-MDSCs (CD11b+Ly-6G−Ly-6Chi), Polymorphonuclear (PMN)-MDSCs (CD11b+Ly-6G+Ly-6Clow), Th17 (CD3+CD4+RORγt+IFN-γ−IL-17A+IL-22−) and Th22 (CD3+CD4+IFN-γ−RORγt−IL-17A−IL-22+) cells were identified in peripheral blood, spleen, tumor and bone marrow (BM) of mice bearing wild-type and IL-6 knockout 4T1 tumors. Finally, we isolated 4T1 induced MDSCs (CD11b+Gr-1+)and cocultured them with healthy donors to investigate Th17 and Th22 population expansion. Our findings provide further insight into the interactions among MDSCs, Th17 and Th22 cells in a murine cancer model, which may inform immunotherapy efficacy and outcomes in human breast cancer.