PVR and cervical carcinoma: In vitro studies have demonstrated that factors released by cervical cancer cell lines significantly reduce NKG2D expression on NK cells and their cytotoxic activity (Jimenez-Perez et al., 2012) and that ovarian and cervical cancer cell lines expressing CD155 can downregulate the expression of the DNAX accessary molecule 1 DNAM-1 on NK cells (Carlsten et al., 2009).