ISG15 and cancer: Western blot results demonstrated a various amount of ISG15 in the conditioned media, which corresponded to the expression levels of ISG15 in the four ovarian cancer cell lines (Supplementary Figure S2A), suggesting that ISG15 is being actively secreted by the ovarian cancer cells into the extracellular space, cancer cell-derived ISG15 can engage in autocrine and paracrine signaling with different cell types in the ovarian tumor microenvironment.