PROJECT SUMMARY/ABSTRACT High-grade serous ovarian cancer (HGSC) metastasizes preferentially to the omentum, which is a well- vascularized fold of peritoneal tissue covered by mesothelial cells and a major site of intra-abdominal fat accumulation. It was reported that HGSC and stromal cell-derived pro-inflammatory cytokines downregulate omentin (ITLN1), a novel mesothelial cell-derived adipokine to promote the invasive potential and proliferation of cancer cells in the omental microenvironment. Omentin has been shown to suppress ovarian cancer invasive potential and cell growth through suppressing MMP1 expression and cell traction force in cancer cells, and inducing a local rapid metabolic coupling between ovarian cancer cells and neighboring adipocytes. Besides, higher levels of pre-operative serum omentin in patients with HGSC were associated with longer survival times. In addition, mice treated with omentin had marked increase in activated CD8+ T cell density compared to the untreated control. These findings suggested that adipocytes play an important role in mediating the suppressive effect of omentin on the malignant phenotype of ovarian cancer cells, and the immune microenvironment. Therefore, we focus on secretory proteins that can be upregulated by omentin in mature adipocytes. A recent proteomic study demonstrated that an anti-inflammatory protein tumor necrosis factor-inducible gene 6 protein (TSG-6) was the top gene upregulated by omentin in adipocytes. Previous studies demonstrated that TSG-6 inhibits infiltration of immune cells during inflammation. It can also bind to specific chemokines such as CXCL12 and prevent them to bind to glycosaminoglycan (GAG)-rich tumor stroma and endothelial cell surface, suggesting that TSG-6-mediated blockade of these cytokines to suppress tumor growth, angiogenesis, and regulatory T cell trafficking. Based on these findings, we hypothesize that omentin normalizes the pro-inflammatory omental microenvironment in ovarian c