ISG15 and ovarian cancer: We further used both in vitro and in vivo models to determine the functional roles of one of the CD8+ lymphocyte density associated genes, ISG15 (Interferon-stimulated gene 15), which demonstrates significant differential expression between normal and malignant serous epithelia and is up-regulated by α and β interferons (IFNs) and has been shown to be associated with progression of ovarian cancer [12,13] and longer overall survival of ovarian cancer patients [14].