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82 | Chapter 3 Discussion Cervical cancer is the fourth most common malignancy in women worldwide. Survival is severely reduced in case of lymph node metastasis, with no curative treatment options available. In cervical cancer, ACT involving T cell or NK cell based therapies have not yet been widely explored, but they have been successfully applied in the treatment of various other cancer types 40-42 . In one clinical trial adoptive transfer of tumor infiltrating T-cells in metastatic cervical cancer resulted in tumor responses in 3/9 patients with complete remission in 2/9 patients 43 . These findings suggest that ACT could be a viable treatment option for some patients with cervical cancer. However, most cervical tumors have HLA class I alterations and will therefore not respond completely to T-cell-based therapies 13,14,44 . NK cell-based therapies present a viable alternative in that case, but in advanced cervical cancer these effector cells are often impaired in their functionality 24,25 . In this study, we therefore explored the possible therapeutic efficacy of allogeneic NK cells. Clinically applicable NK cells may be derived from two sources, i.e. NK cells derived from peripheral blood and NK cells cultured and expanded from umbilical cord blood stem cells. We tested their cytotoxic efficacy (with and without CET for PBNK) on ten cervical cancer cell lines representing different histological subtypes, HPV types, and expressing differential levels of NK activating and inhibitory ligands. Initially, we investigated the effect of PBNK alone and a combination of PBNK with CET on the cervical cancer cell lines. From literature it is known that cervical tumors often present with variable levels of EGFR 6,8 . In colorectal cancers, mutant KRAS is associated with resistance to CET 45 . Although most of the cervical cancer cell lines were EGFR-positive and all were RAS wt , their EGFR expression levels were relatively low, and, in keeping with clinical observations for cervical cancer, they did not respond to CET as a single agent 9,10,46 . Our observation of increased PBNK cytotoxicity upon combination with CET is in line with a report by Meira and colleagues who showed that one of the antitumor effector mechanisms upon combined CET and chemoradiation actually was ADCC 47 . Next, we compared the functionality of PBNK with that of ex vivo generated UCB-NK derived from cord blood stem cells, and showed that UCB-NK were significantly more cytotoxic than PBNK (Figure 2). NK cytotoxicity and NK degranulation levels were equivalent for UCB-NK and PBNK + CET. Further study of the NK killing mechanism, revealed that the cytotoxic activity of both PBNK and UCB-NK was at least in part dependent on DNAM-1 and NKG2D receptors, as also previously reported for an NK cell line (NKL) and cytotoxicity it induced in the CaSki and SiHa cell lines 19 . This was in keeping with high expression levels of both NKG2D and DNAM-1 observed on both PBNK and UCB-NK. As complete abrogation of tumor cell killing was not achieved by combined blocking of DNAM-1 and NKG2D on activated PBNK and UCB-NK, other NK killing mechanisms such as NKp44/NKp44L, TRAIL