Abstract 179: Identification of a novel crosstalk between MDSC and NKregs in immunotherapy resistant triple negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is one of the most aggressive forms of breast cancer and lacks standard treatment options. Although immunotherapy shows some response in these patients along with chemotherapy, heterogeneity of tumor cells and immune cells results in significant low response to immunotherapy treatment. Based on single cell sequencing which enables identity of heterogenous population at single cell level and functional studies involving preclinical mouse models, our laboratory recently identified distinct CD56brightSOCS3highCD11b−CD27− immature NK cells subpopulations, with diminished cytotoxic granzyme signatures that promote TNBC tumor progression. However, the precise characterization and functionality of these rogue tumor promoting NK cells remains unclear in clinical samples. Here, we aimed to illustrate mechanistic insight of these novel immature NK subpopulation in context of immunotherapy resistant TNBC patient samples. The scRNA seq analysis of TNBC patient samples identified four specific subclusters of NK cells in TNBC. We further found that NK2 and NK3 subclusters are CD56dim Granzymehigh cytotoxic NK cells and the other two subclusters (NK0 and NK1) are CD56bright immature NKs. Interestingly, the NK0 and NK1 subcluster specifically exhibit distinctive characteristics and functions. Notably, CD56bright immature NK1 cells, identified as tissue-resident NK cells, were engaged in direct communication with myeloid-derived suppressor cells (MDSCs). The CD56bright NK0 possesses moderate to low SOCS3 expression and moderate to high granzyme expression with elevated early NK activation markers and inhibitory receptor expressions, suggesting its regulatory property (NKregs). scRNA seq and flow cytometry analysis showed higher NKregs and immunosuppressive MDSC population, specifically with high monocytic-MDSCs (mMDSCs) in non-responder TNBC (to adjuvant combinational treatment of chemo and immunotherapy) patient samples rather than responder patients’ tissue. Based on in silico analysis, we further found a potential crosstalk between these mMDSC Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 179.